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[vsnet-grb-info 42142] GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44021 SUBJECT: GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations DATE: 26/03/15 16:12:58 GMT FROM: A. Brosio at ABObservatory Rosarno <antonino.brosio(a)gmail.com> A. Brosio (ABObservatory Rosarno), M. A. Tripodi (ABObservatory Rosarno), S. Savaglio (Università della Calabria), S. Benatti, M. G. Guarcello (INAF - Osservatorio Astronomico di Palermo), M. Basilicata, L. Cabona, M. Rainer, F. M. Zerbi (INAF - Osservatorio Astronomico di Brera), G. Bracco, P. Cianfarra, L. Sangaletti, S. Tosi, S. Zappatore (Università di Genova), A. Di Dato (INAF - Osservatorio Astronomico di Capodimonte), D. Liguori (Osservatorio "G. Galilei", Liceo Scientifico Cariati), S. Masiero, A. Nastasi (GAL Hassin, Isnello), R. Nesci (Associazione Astronomica Antares APS di Foligno), L. Betti, E. Pace, R. Stanga (Università di Firenze), D. Ricci (INAF - Osservatorio Astronomico di Padova) for the NOCTIS team report We observed the transient AT 2026fgk, proposed as the likely optical counterpart of GRB 260310A (Konno et al., GCN 43974; Hamburg & Meegan,GCN 43975). Observations were carried out on 2026-03-14.80913 UT with the 0.30-m f/4 telescope at ABObservatory in clear band The obtained photometry is: 2026-03-14.80913 UT JD 2461114.30913 m_CV = 18.50 +/- 0.04 mag The measurement was calibrated against two APASS catalog stars,selected using Aladin. The reported magnitude is in the CV system. This measurement confirms that the optical counterpart is still clearly detected about 4.6 days after the GRB trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/44021. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42141] GRB 260310A / AT 2026fgk: iTelescope optical observations
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44020 SUBJECT: GRB 260310A / AT 2026fgk: iTelescope optical observations DATE: 26/03/15 15:06:06 GMT FROM: Filipp Dmitrievich Romanov at Amateur astronomer <filipp.romanov.27.04.1997(a)gmail.com> I observed the field of GRB 260310A = AT 2026fgk (Fermi GBM Team, GCN Circ. #43951) remotely using iTelescope.Net T21 (0.43-m f/6.8 reflector + CCD + f/4.5 focal reducer) in Utah Desert Remote Observatory at Great Basin Desert, Beryl Junction, Utah, USA. Six images with exposures of 300 sec. and Rc filter were obtained on 2026-03-15 from 08:56:17 UT (5.166 d. after the trigger) to 09:32:41 UT (5.191 d. after the trigger). I detected the optical afterglow and measured its magnitude (compared to Rc magnitudes of nearby stars from the ATLAS star catalog: Tonry et al., 2018) in the stacked image = 18.0 +/- 0.1 Rc. Magnitude is not corrected for Galactic extinction. The magnitude may be affected by contamination from the host galaxy. Stacked image: https://www.flickr.com/photos/filipp-romanov/55149149955/ F. D. Romanov (AAVSO). View this GCN Circular online at https://gcn.nasa.gov/circulars/44020. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42140] EP260314a: COLIBRÍ optical upper limit
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44019 SUBJECT: EP260314a: COLIBRÍ optical upper limit DATE: 26/03/15 12:33:39 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu(a)gmail.com> Francis Fortin (IRAP), Edilberto Aguilar-Ruiz (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Missimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of EP260314a (Zhao et al., GCN Circ. 44010, Wu et al., GCN Circ. 44016) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-15 04:49:56 to 11:14:09 UTC (from 9.1 to 12.4 hours after the trigger) and obtained 144 minutes of simultaneous exposure in the i and z filters. The data were reduced and coadded with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect the SVOM/VT optical counterpart candidate reported by Li et al., GCN Circ. 44013 down to the following 3-sigma limit: i > 24.08 z > 23.17 While a direct comparison of magnitudes between the i, z filters and the VT filters is not possible, we suggest that our limits may be consistent with a fading of the VT optical candidate, which would strengthen the hypothesis that it is the true counterpart of EP260314A. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/44019. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42139] GRID detection of GRB 260312B
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44018 SUBJECT: GRID detection of GRB 260312B DATE: 26/03/15 11:40:03 GMT FROM: GRID Student Team at Tsinghua University <grid(a)tsinghua.edu.cn> Fanqing Zhou, Longhao Li, Chenyu Wang report on behalf of the GRID Collaboration: GRID-11B reports the detection of the long-duration GRB 260312B, which was also detected by Fermi GBM (GCN Circular 43969), MASTER-Kislovodsk (GCN Circular 43973), BALROG (GCN Circular 43970), Glowbug (GCN Circular 43976), AstroSat CZTI (GCN Circular 43989). The event was triggered with GRID on 2026-03-12 at 09:46:46 UTC. The measured burst duration (T90) in the 30-2000 keV range is approximately 11.8+/-2.3 seconds. The GRID light curve of this event can be found at https://mirrors.tuna.tsinghua.edu.cn/GRID/data/GRID-GCN/GRB260312B/GRID_260…. GRID is a student-led project to monitor the transient gamma-ray sky with multiple detectors onboard different nanosatellites in the era of multi-messenger astronomy. For more information about GRID, please refer to the following references: https://doi.org/10.1007/s10686-019-09636-w and https://doi.org/10.1007/s10686-021-09819-4. View this GCN Circular online at https://gcn.nasa.gov/circulars/44018. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42138] IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44017 SUBJECT: IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 26/03/15 11:21:27 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 26-03-15 at 02:19:06.60 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_BRONZE alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 3.3512 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/142272_46886533.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 26-03-15 Time: 02:19:06.60 UT RA: 175.69 (+0.49/-0.46 deg 90% PSF containment) J2000 Dec: -1.90 (+0.53/-0.51 deg 90% PSF containment) J2000 As announced in GCN Circular 43419 (https://gcn.nasa.gov/circulars/43419) IceCube alert notices for high-energy track alerts are now also streamed via Kafka. IceCube Gold/Bronze track alerts are available on the Kafka topic 'gcn.notices.icecube.gold_bronze_track_alerts'. The probability distribution of the true neutrino direction, allowing the extraction of precise 90% containment regions around the best-fit direction, is now available for revised reconstruction of high-energy track alerts. The corresponding sky map is distributed as a FITS file and follows the explicit naming convention IceCube-YYMMDDX, where YYMMDD indicates the date of the event and X is a letter distinguishing multiple alerts on the same day. The download link is provided through the GCN schema distributed via Kafka. Detailed documentation describing the alert distribution, schemas, and probability maps is available at: https://gcn.nasa.gov/missions/icecube. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of this event. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/44017. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42137] EP260314a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44016 SUBJECT: EP260314a: refined analysis of the EP-WXT and EP-FXT observations DATE: 26/03/15 09:29:55 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Yue Wu (NJU), Rui-Zhi Li (YNAO, CAS), Yaqi Zhao (USTC, PRIC) and Hai-Wu Pan (NAOC) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260314a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhao et al., GCN 44010). The transient was detected immediately when WXT observation started at T0=2026-03-14T22:51:20. The WXT observation lasted for approximately 16 seconds, and was interrupted due to the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a hydrogen column density of 0.54（-0.27/+0.32）×10^22 cm^-2 and a photon index of 1.81(-0.75/+0.83). The derived average unabsorbed 0.5-4 keV flux is 2.14 (-0.55/+1.13) × 10^(-8) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2026-03-14T22:54:51 (UTC, T0+211 s). The exposure time of this observation is 2.9ks. On-ground analysis of the FXT data found an uncatalogued source at R.A., Dec. = 211.8426, -23.4577 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 0.22 (-0.07/+0.07) × 10^22 cm^-2 and a photon index of 2.21 (-0.27/+0.28). The derived average unabsorbed 0.5-10 keV flux is 5.11 (+0.46/-0.41) × 10^(-12) erg/s/cm^2. A follow-up observation with the EP/FXT was planned, and further information will be updated when the telemetry data is received. The optical follow-up observations were performed by Li et al. (GCN 44009), Li et al. (GCN 44013), Lipunov et al. (GCN 44014) and Pérez-García et al. (GCN 44015). We note that the SVOM/VT candidate (Li et al., GCN 44013) is located within the 10 arcsec error circle of EP/FXT. Further multi-band follow-up observations are encouraged to explore the nature of EP260314a. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44016. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42136] EP260314a: BOOTES-6/DPR optical upper limits at early times
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44015 SUBJECT: EP260314a: BOOTES-6/DPR optical upper limits at early times DATE: 26/03/15 09:27:12 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Pérez-García, E. Fernández-García, M.D. Caballero-García, M. Gritsevich, S. Guziy, R. Sánchez-Ramírez, S.-Y. Wu, and A. J. Castro-Tirado (IAA-CSIC, Granada), P. J. Meintjes and H. J. van Heerden (UFS, South Africa), A. Martín-Carrillo and L. Hanlon (UCD, Ireland), Y.-D. Hu (GXU), D. R. Xiong (Yunnan Observatories of CAS) and C. J. Pérez del Pulgar (UMA, Malaga), on behalf of a larger collaboration, report: Following the detection of EP260314a by Einstein Probe (Zhao et al., GCNC 44010), the BOOTES-6/DPRT 0.6m robotic telescope at Boyden Observatory in Maselspoort (South Africa) responded to this event starting on Mar 14, 23:00:01 UT (~ 8.5 min after trigger) with a 10s clear filter image. No new source is detected at the position of the proposed optical counterpart by SVOM/VT (Li et al., GCNC 44013) up to magnitude 16.3 using Gaia DR3 Gmag magnitude as reference on our first image. Further images were gathered and using ATLAS REFCAT2 as reference (Tonry et al. 2018) we get upper limits of: 18.5 (60s clear, at 23:03 UT), 20.9 (300s clear, at 23:06 UT) and 21.7 (600s clear, at 23:18 UT), in agreement with the upper limit reported by LCO (Li et al. GCNC 44009). We thank the staff at Boyden Observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/44015. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42135] EP260314a: Global MASTER-Net observations report
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44014 SUBJECT: EP260314a: Global MASTER-Net observations report DATE: 26/03/15 09:18:43 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP260314a ( EP Team et al., GCN 44010) errorbox 18771 sec after notice time and 31448 sec after trigger time at 2026-03-15 07:35:44 UT, with upper limit up to 20.4 mag. The observations began at zenith distance = 10 deg. The sun altitude is -37.3 deg. The galactic latitude b = 36 deg., longitude l = 325 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3187114 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 31478 | 2026-03-15 07:35:44 | MASTER-OAFA | (14h 03m 09.70s , -23d 05m 06.7s) | C | 60 | 20.1 | 31538 | 2026-03-15 07:35:44 | MASTER-OAFA | (14h 03m 09.70s , -23d 05m 06.8s) | C | 180 | 20.4 | Coadd 31555 | 2026-03-15 07:37:01 | MASTER-OAFA | (14h 11m 52.28s , -23d 06m 44.8s) | C | 60 | 20.0 | 31615 | 2026-03-15 07:37:01 | MASTER-OAFA | (14h 11m 52.28s , -23d 06m 44.8s) | C | 180 | 20.4 | Coadd 31632 | 2026-03-15 07:38:17 | MASTER-OAFA | (14h 03m 12.03s , -23d 05m 00.4s) | C | 60 | 20.0 | 31707 | 2026-03-15 07:39:33 | MASTER-OAFA | (14h 11m 49.57s , -23d 06m 01.9s) | C | 60 | 20.0 | 31784 | 2026-03-15 07:40:49 | MASTER-OAFA | (14h 03m 07.51s , -23d 04m 36.7s) | C | 60 | 20.0 | 33575 | 2026-03-15 08:10:40 | MASTER-OAFA | (14h 11m 51.09s , -23d 04m 19.3s) | C | 60 | 20.0 | 33650 | 2026-03-15 08:11:56 | MASTER-OAFA | (14h 11m 57.93s , -23d 05m 18.8s) | C | 60 | 19.9 | 33710 | 2026-03-15 08:11:56 | MASTER-OAFA | (14h 11m 57.94s , -23d 05m 18.8s) | C | 180 | 20.4 | Coadd 33726 | 2026-03-15 08:13:11 | MASTER-OAFA | (14h 11m 51.16s , -23d 06m 17.7s) | C | 60 | 19.8 | 33806 | 2026-03-15 08:14:32 | MASTER-OAFA | (14h 03m 15.81s , -23d 05m 54.0s) | C | 60 | 20.0 | 33866 | 2026-03-15 08:14:32 | MASTER-OAFA | (14h 03m 15.81s , -23d 05m 54.1s) | C | 180 | 20.4 | Coadd 33886 | 2026-03-15 08:15:52 | MASTER-OAFA | (14h 03m 12.24s , -23d 04m 20.5s) | C | 60 | 20.1 | 33966 | 2026-03-15 08:17:12 | MASTER-OAFA | (14h 03m 12.30s , -23d 05m 42.2s) | C | 60 | 20.1 | 35185 | 2026-03-15 08:36:30 | MASTER- | (14h 07m 08.18s , -23d 27m 00.1s) | C | 180 | 19.3 | 35185 | 2026-03-15 08:36:30 | MASTER- | (14h 08m 27.19s , -24d 01m 06.3s) | C | 180 | 19.5 | 35377 | 2026-03-15 08:39:42 | MASTER- | (14h 07m 13.49s , -23d 28m 05.1s) | C | 180 | 19.6 | 35377 | 2026-03-15 08:39:42 | MASTER- | (14h 08m 32.57s , -24d 02m 10.3s) | C | 180 | 19.6 | 35568 | 2026-03-15 08:42:54 | MASTER- | (14h 07m 08.52s , -23d 29m 07.4s) | C | 180 | 19.5 | 35568 | 2026-03-15 08:42:54 | MASTER- | (14h 08m 27.64s , -24d 03m 12.2s) | C | 180 | 19.8 | 35534 | 2026-03-15 08:43:20 | MASTER-OAFA | (14h 11m 56.24s , -23d 04m 00.8s) | C | 60 | 19.9 | 35610 | 2026-03-15 08:44:36 | MASTER-OAFA | (14h 11m 56.27s , -23d 05m 30.6s) | C | 60 | 19.9 | 35760 | 2026-03-15 08:46:05 | MASTER- | (14h 07m 13.91s , -23d 28m 54.9s) | C | 180 | 19.3 | 35760 | 2026-03-15 08:46:05 | MASTER- | (14h 08m 33.15s , -24d 02m 59.4s) | C | 180 | 19.8 | 35891 | 2026-03-15 08:49:17 | MASTER-OAFA | (14h 03m 17.80s , -23d 04m 26.7s) | C | 60 | 20.0 | 35951 | 2026-03-15 08:49:17 | MASTER- | (14h 07m 10.42s , -23d 27m 22.5s) | C | 180 | 19.4 | 35951 | 2026-03-15 08:49:17 | MASTER- | (14h 08m 29.74s , -24d 01m 26.6s) | C | 180 | 19.9 | 36142 | 2026-03-15 08:52:28 | MASTER- | (14h 07m 10.07s , -23d 29m 05.4s) | C | 180 | 19.6 | 36142 | 2026-03-15 08:52:28 | MASTER- | (14h 08m 29.52s , -24d 03m 08.8s) | C | 180 | 19.8 | 36335 | 2026-03-15 08:55:40 | MASTER- | (14h 07m 12.33s , -23d 27m 15.8s) | C | 180 | 19.7 | 36335 | 2026-03-15 08:55:40 | MASTER- | (14h 08m 31.87s , -24d 01m 18.8s) | C | 180 | 19.9 | 36526 | 2026-03-15 08:58:52 | MASTER- | (14h 07m 05.49s , -23d 28m 09.4s) | C | 180 | 19.8 | 36526 | 2026-03-15 08:58:52 | MASTER- | (14h 08m 25.17s , -24d 02m 11.9s) | C | 180 | 19.8 | 36723 | 2026-03-15 09:02:09 | MASTER- | (14h 07m 05.49s , -23d 27m 09.1s) | C | 180 | 19.8 | 36723 | 2026-03-15 09:02:09 | MASTER- | (14h 08m 25.25s , -24d 01m 11.3s) | C | 180 | 19.8 | 36914 | 2026-03-15 09:05:20 | MASTER- | (14h 07m 12.73s , -23d 28m 09.7s) | C | 180 | 19.7 | 36914 | 2026-03-15 09:05:20 | MASTER- | (14h 08m 32.56s , -24d 02m 11.3s) | C | 180 | 19.8 | 37105 | 2026-03-15 09:08:31 | MASTER- | (14h 07m 05.16s , -23d 29m 09.4s) | C | 180 | 19.7 | 37105 | 2026-03-15 09:08:31 | MASTER- | (14h 08m 25.09s , -24d 03m 10.6s) | C | 180 | 19.6 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44014. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42134] EP260314a: SVOM/VT optical candidate
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44013 SUBJECT: EP260314a: SVOM/VT optical candidate DATE: 26/03/15 03:58:26 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. N. Ma, C. Wu, Z. H. Yao, Y. L. Qiu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observation of the field of EP260314a detected by Einstein Probe (Zhao et al., GCN 44010). The observation started at 2026-03-14T23:03:04 UTC, i.e., about 11.5 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. An uncatalogued optical source was detected in VT_R stacked image within the error box of FXT (Zhao et al., GCN 44010). The position is at R.A., Dec. = 211.842259, -23.457728 degrees, equivalent to: R.A. (J2000) = +14:07:22.14 Dec. (J2000) = -23:27:27.82 with an uncertainty of 0.5 arcsec. The measurements in AB magnitudes are given below: Mid_time Band Exposure Time Magnitude (AB) 1.07 hour VT_R 29*50 sec 22.70+/-0.26 mag 1.07 hour VT_B 29*50 sec > 23.0 mag With the available data, we could not confirm the fading of the candidate. Our photometry was not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/44013. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42133] Fermi trigger No 795185313: Global MASTER-Net observations report
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44012 SUBJECT: Fermi trigger No 795185313: Global MASTER-Net observations report DATE: 26/03/15 03:30:44 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB260314.53 (trigger No 795185313,14h 23m 00.00s , -11d 19m 58.8s, R=50) errorbox 48826 sec after notice time and 48862 sec after trigger time at 2026-03-15 02:22:50 UT, with upper limit up to 20.4 mag. The observations began at zenith distance = 45 deg. The sun altitude is -42.8 deg. The galactic latitude b = 45 deg., longitude l = 337 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3186061 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 48883 | 2026-03-15 02:22:50 | MASTER-OAFA | (11h 42m 55.30s , -01d 47m 48.0s) | C | 40 | 19.7 | 48943 | 2026-03-15 02:22:50 | MASTER-OAFA | (11h 42m 55.30s , -01d 47m 48.0s) | C | 160 | 20.4 | Coadd 48934 | 2026-03-15 02:23:36 | MASTER-OAFA | (11h 42m 55.23s , -01d 47m 46.9s) | C | 50 | 19.8 | 48999 | 2026-03-15 02:24:32 | MASTER-OAFA | (11h 42m 55.19s , -01d 47m 45.7s) | C | 70 | 19.9 | 49081 | 2026-03-15 02:25:48 | MASTER-OAFA | (11h 42m 55.10s , -01d 47m 45.0s) | C | 80 | 19.9 | 49191 | 2026-03-15 02:25:48 | MASTER-OAFA | (11h 42m 55.10s , -01d 47m 45.0s) | C | 300 | 20.0 | Coadd 49177 | 2026-03-15 02:27:15 | MASTER-OAFA | (11h 42m 54.96s , -01d 47m 43.8s) | C | 100 | 20.0 | 49293 | 2026-03-15 02:29:01 | MASTER-OAFA | (11h 42m 54.80s , -01d 47m 42.7s) | C | 120 | 20.1 | 49429 | 2026-03-15 02:31:07 | MASTER-OAFA | (11h 42m 54.61s , -01d 47m 41.6s) | C | 140 | 20.2 | 49544 | 2026-03-15 02:31:07 | MASTER-OAFA | (11h 42m 54.61s , -01d 47m 41.6s) | C | 370 | 20.0 | Coadd 49590 | 2026-03-15 02:33:33 | MASTER-OAFA | (11h 42m 54.38s , -01d 47m 40.7s) | C | 170 | 20.3 | 49711 | 2026-03-15 02:36:29 | MASTER-OAFA | (11h 42m 54.21s , -01d 47m 40.3s) | C | 60 | 19.8 | 49777 | 2026-03-15 02:37:35 | MASTER-OAFA | (11h 42m 54.10s , -01d 47m 40.2s) | C | 60 | 19.9 | 49837 | 2026-03-15 02:37:35 | MASTER-OAFA | (11h 42m 54.10s , -01d 47m 40.1s) | C | 180 | 20.4 | Coadd 49843 | 2026-03-15 02:38:40 | MASTER-OAFA | (11h 42m 54.00s , -01d 47m 39.9s) | C | 60 | 19.9 | 49909 | 2026-03-15 02:39:47 | MASTER-OAFA | (11h 42m 53.89s , -01d 47m 39.7s) | C | 60 | 19.9 | 49974 | 2026-03-15 02:40:52 | MASTER-OAFA | (11h 42m 53.81s , -01d 47m 39.7s) | C | 60 | 19.9 | 50034 | 2026-03-15 02:40:52 | MASTER-OAFA | (11h 42m 53.81s , -01d 47m 39.7s) | C | 180 | 20.4 | Coadd 50040 | 2026-03-15 02:41:57 | MASTER-OAFA | (11h 42m 53.70s , -01d 47m 39.5s) | C | 60 | 19.8 | 50106 | 2026-03-15 02:43:04 | MASTER-OAFA | (11h 42m 53.59s , -01d 47m 39.7s) | C | 60 | 19.9 | 50172 | 2026-03-15 02:44:10 | MASTER-OAFA | (11h 42m 53.49s , -01d 47m 39.9s) | C | 60 | 19.9 | 50232 | 2026-03-15 02:44:10 | MASTER-OAFA | (11h 42m 53.49s , -01d 47m 39.9s) | C | 180 | 20.4 | Coadd 50237 | 2026-03-15 02:45:15 | MASTER-OAFA | (11h 42m 53.37s , -01d 47m 40.1s) | C | 60 | 19.9 | 50304 | 2026-03-15 02:46:21 | MASTER-OAFA | (11h 42m 53.26s , -01d 47m 40.2s) | C | 60 | 19.8 | 50369 | 2026-03-15 02:47:27 | MASTER-OAFA | (11h 42m 53.14s , -01d 47m 40.1s) | C | 60 | 19.9 | 50429 | 2026-03-15 02:47:27 | MASTER-OAFA | (11h 42m 53.14s , -01d 47m 40.1s) | C | 180 | 20.0 | Coadd 50434 | 2026-03-15 02:48:32 | MASTER-OAFA | (11h 42m 53.02s , -01d 47m 40.5s) | C | 60 | 19.9 | 50500 | 2026-03-15 02:49:38 | MASTER-OAFA | (11h 42m 52.89s , -01d 47m 40.4s) | C | 60 | 19.9 | 50566 | 2026-03-15 02:50:44 | MASTER-OAFA | (11h 42m 52.77s , -01d 47m 40.4s) | C | 60 | 19.9 | 50626 | 2026-03-15 02:50:44 | MASTER-OAFA | (11h 42m 52.77s , -01d 47m 40.4s) | C | 180 | 20.4 | Coadd 50632 | 2026-03-15 02:51:49 | MASTER-OAFA | (11h 42m 52.64s , -01d 47m 40.6s) | C | 60 | 19.9 | 50698 | 2026-03-15 02:52:56 | MASTER-OAFA | (11h 42m 52.47s , -01d 47m 40.8s) | C | 60 | 19.9 | 50764 | 2026-03-15 02:54:02 | MASTER-OAFA | (11h 42m 52.36s , -01d 47m 41.4s) | C | 60 | 19.9 | 50824 | 2026-03-15 02:54:02 | MASTER-OAFA | (11h 42m 52.36s , -01d 47m 41.4s) | C | 180 | 20.0 | Coadd 50829 | 2026-03-15 02:55:07 | MASTER-OAFA | (11h 42m 52.22s , -01d 47m 41.7s) | C | 60 | 19.9 | 50896 | 2026-03-15 02:56:13 | MASTER-OAFA | (11h 42m 52.09s , -01d 47m 42.1s) | C | 60 | 19.9 | 50961 | 2026-03-15 02:57:19 | MASTER-OAFA | (11h 42m 51.92s , -01d 47m 42.9s) | C | 60 | 19.9 | 51021 | 2026-03-15 02:57:19 | MASTER-OAFA | (11h 42m 51.92s , -01d 47m 42.9s) | C | 180 | 20.0 | Coadd 51027 | 2026-03-15 02:58:24 | MASTER-OAFA | (11h 42m 51.79s , -01d 47m 43.3s) | C | 60 | 19.9 | 51093 | 2026-03-15 02:59:31 | MASTER-OAFA | (11h 42m 51.62s , -01d 47m 43.7s) | C | 60 | 19.9 | 51159 | 2026-03-15 03:00:36 | MASTER-OAFA | (11h 42m 51.50s , -01d 47m 44.1s) | C | 60 | 19.9 | 51219 | 2026-03-15 03:00:36 | MASTER-OAFA | (11h 42m 51.50s , -01d 47m 44.0s) | C | 180 | 20.0 | Coadd 51224 | 2026-03-15 03:01:42 | MASTER-OAFA | (11h 42m 51.36s , -01d 47m 44.9s) | C | 60 | 19.9 | 51291 | 2026-03-15 03:02:48 | MASTER-OAFA | (11h 42m 51.20s , -01d 47m 45.9s) | C | 60 | 19.9 | 51356 | 2026-03-15 03:03:54 | MASTER-OAFA | (11h 42m 51.07s , -01d 47m 46.3s) | C | 60 | 19.9 | 51416 | 2026-03-15 03:03:54 | MASTER-OAFA | (11h 42m 51.07s , -01d 47m 46.3s) | C | 180 | 20.0 | Coadd 51421 | 2026-03-15 03:04:59 | MASTER-OAFA | (11h 42m 50.89s , -01d 47m 46.6s) | C | 60 | 20.0 | 51488 | 2026-03-15 03:06:06 | MASTER-OAFA | (11h 42m 50.76s , -01d 47m 47.3s) | C | 60 | 19.9 | 51553 | 2026-03-15 03:07:11 | MASTER-OAFA | (11h 42m 50.58s , -01d 47m 48.2s) | C | 60 | 19.9 | 51613 | 2026-03-15 03:07:11 | MASTER-OAFA | (11h 42m 50.58s , -01d 47m 48.2s) | C | 180 | 20.0 | Coadd 51619 | 2026-03-15 03:08:17 | MASTER-OAFA | (11h 42m 50.44s , -01d 47m 49.1s) | C | 60 | 19.9 | 51686 | 2026-03-15 03:09:24 | MASTER-OAFA | (11h 42m 50.31s , -01d 47m 49.8s) | C | 60 | 19.9 | 51751 | 2026-03-15 03:10:29 | MASTER-OAFA | (11h 42m 50.15s , -01d 47m 50.8s) | C | 60 | 19.9 | 51811 | 2026-03-15 03:10:29 | MASTER-OAFA | (11h 42m 50.15s , -01d 47m 50.8s) | C | 180 | 20.0 | Coadd 51816 | 2026-03-15 03:11:34 | MASTER-OAFA | (11h 42m 50.01s , -01d 47m 51.7s) | C | 60 | 19.9 | 51883 | 2026-03-15 03:12:40 | MASTER-OAFA | (11h 42m 49.85s , -01d 47m 53.2s) | C | 60 | 19.9 | 51948 | 2026-03-15 03:13:46 | MASTER-OAFA | (11h 42m 49.69s , -01d 47m 53.9s) | C | 60 | 19.9 | 52008 | 2026-03-15 03:13:46 | MASTER-OAFA | (11h 42m 49.69s , -01d 47m 53.9s) | C | 180 | 20.0 | Coadd 52014 | 2026-03-15 03:14:51 | MASTER-OAFA | (11h 42m 49.52s , -01d 47m 54.8s) | C | 60 | 19.9 | 52080 | 2026-03-15 03:15:58 | MASTER-OAFA | (11h 42m 49.36s , -01d 47m 55.6s) | C | 60 | 19.9 | 52146 | 2026-03-15 03:17:03 | MASTER-OAFA | (11h 42m 49.19s , -01d 47m 56.2s) | C | 60 | 19.9 | 52206 | 2026-03-15 03:17:03 | MASTER-OAFA | (11h 42m 49.19s , -01d 47m 56.2s) | C | 180 | 20.0 | Coadd 52211 | 2026-03-15 03:18:09 | MASTER-OAFA | (11h 42m 49.02s , -01d 47m 57.7s) | C | 60 | 19.9 | 52277 | 2026-03-15 03:19:14 | MASTER-OAFA | (11h 42m 48.86s , -01d 47m 58.8s) | C | 60 | 19.9 | 52342 | 2026-03-15 03:20:20 | MASTER-OAFA | (11h 42m 48.71s , -01d 48m 00.4s) | C | 60 | 19.9 | 52408 | 2026-03-15 03:21:26 | MASTER-OAFA | (11h 42m 48.52s , -01d 48m 01.7s) | C | 60 | 19.9 | 52474 | 2026-03-15 03:22:32 | MASTER-OAFA | (11h 42m 48.36s , -01d 48m 02.8s) | C | 60 | 19.9 | 52540 | 2026-03-15 03:23:37 | MASTER-OAFA | (11h 42m 48.20s , -01d 48m 04.0s) | C | 60 | 19.9 | 52605 | 2026-03-15 03:24:43 | MASTER-OAFA | (11h 42m 48.01s , -01d 48m 05.0s) | C | 60 | 19.9 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44012. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42132] IceCube Alert 260315A: Global MASTER-Net observations report
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44011 SUBJECT: IceCube Alert 260315A: Global MASTER-Net observations report DATE: 26/03/15 02:40:16 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) was pointed to the IceCube Alert 260315A (trigger No 46886533,11h 42m 40.32s , -01d 53m 06.0s, R=0.71) errorbox 105 sec after notice time and 224 sec after trigger time at 2026-03-15 02:22:50 UT, with upper limit up to 20.4 mag. The observations began at zenith distance = 45 deg. The sun altitude is -42.8 deg. The galactic latitude b = 57 deg., longitude l = 272 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3187113 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 244 | 2026-03-15 02:22:50 | MASTER-OAFA | (11h 42m 55.30s , -01d 47m 48.0s) | C | 40 | 19.7 | 304 | 2026-03-15 02:22:50 | MASTER-OAFA | (11h 42m 55.30s , -01d 47m 48.0s) | C | 160 | 20.4 | Coadd 295 | 2026-03-15 02:23:36 | MASTER-OAFA | (11h 42m 55.23s , -01d 47m 46.9s) | C | 50 | 19.8 | 361 | 2026-03-15 02:24:32 | MASTER-OAFA | (11h 42m 55.19s , -01d 47m 45.7s) | C | 70 | 19.9 | 442 | 2026-03-15 02:25:48 | MASTER-OAFA | (11h 42m 55.10s , -01d 47m 45.0s) | C | 80 | 19.9 | 552 | 2026-03-15 02:25:48 | MASTER-OAFA | (11h 42m 55.10s , -01d 47m 45.0s) | C | 300 | 20.0 | Coadd 539 | 2026-03-15 02:27:15 | MASTER-OAFA | (11h 42m 54.96s , -01d 47m 43.8s) | C | 100 | 20.0 | 655 | 2026-03-15 02:29:01 | MASTER-OAFA | (11h 42m 54.80s , -01d 47m 42.7s) | C | 120 | 20.1 | 790 | 2026-03-15 02:31:07 | MASTER-OAFA | (11h 42m 54.61s , -01d 47m 41.6s) | C | 140 | 20.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44011. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42131] EP260314a: Einstein Probe detection of an X-ray transient
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44010 SUBJECT: EP260314a: Einstein Probe detection of an X-ray transient DATE: 26/03/15 02:16:51 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Yaqi Zhao (USTC, PRIC), Yue Wu (NJU), Rui-Zhi Li (YNAO, CAS) and Hai-Wu Pan (NAOC) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260314a. The transient triggered EP-WXT (ID: 01709258851) at 2026-03-14T22:51:36 (UTC). The WXT position of the source is R.A. = 211.845 deg, DEC = -23.445 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 211.8437 deg, DEC = -23.4601 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44010. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42130] The EP-WXT trigger 01709258851: Las Cumbres upper limit
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44009 SUBJECT: The EP-WXT trigger 01709258851: Las Cumbres upper limit DATE: 26/03/15 01:07:35 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> Wenxiong Li, Runduo Liang (NAOC), Iair Arcavi, Ido Keinan (TAU), David Sand (U of Arizona) We observed the position of the EP-WXT trigger 01709258851 with a Las Cumbres 1m telescope at Sutherland Observatory, South Africa, 50 mins after the Einstein Probe WXT trigger. We took 4x300s exposures in the broad optical w band. We didn’t detect any uncataloged source within the EP-WXT error circle down to a limiting r-band mag of 21.5 mag. View this GCN Circular online at https://gcn.nasa.gov/circulars/44009. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42129] GRB 260314A: GECAM-B observation of a burst
by GCN Circulars 15 Mar '26

15 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44008 SUBJECT: GRB 260314A: GECAM-B observation of a burst DATE: 26/03/15 01:04:49 GMT FROM: xueyuan zao <zaoxueyuan(a)gmail.com> Xue-Yuan Zao, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 260314A, at 2026-03-14T00:58:53.100 UTC, which is also detected by Fermi/GBM (Fermi GBM team, GCN #43997). The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260314A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/44008. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42128] Fermi Gamma-ray Burst Monitor trigger 795185313/260314534 is not a GRB
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44007 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 795185313/260314534 is not a GRB DATE: 26/03/14 18:19:35 GMT FROM: Bagrat Mailyan at Florida Tech <mbagrat(a)gmail.com> B. Mailyan (Florida Tech) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 795185313/260314534 at 12:48:28.23 UT on 14 March 2026, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely accidental." View this GCN Circular online at https://gcn.nasa.gov/circulars/44007. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42127] GRB 260310A / AT2026fgk: SAO RAS optical observations
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44006 SUBJECT: GRB 260310A / AT2026fgk: SAO RAS optical observations DATE: 26/03/14 15:46:52 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), O. Spiridonova (SAO RAS), A. Pozanenko (IKI), N. Pankov (IKI), A. Volnova (IKI), report on behalf of GRB follow-up team and IKI-GRB-FuN. We observed the field of the AT2026fgk, potential counterpart of the GRB 260310A (Fermi GBM team, GCN 43951; Hamburg and Meegan, GCN 43975; Salunke et al., GCN 43958) with the Zeiss-1000 1m telescope of the SAO RAS equipped with the CCD photometer. We obtained series of 300 sec images in B, V, Rc, Ic filters on March 12/13 and 13/14. The observations carried out under a good weather conditions and typical seeing of 1".5--2".5. The candidate discovered by GOTO (O'Neill et al. 2026, TNS Discovery Report 294132) and observed by numerous observatories (Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979; Moren Méndez et al., GCN 43980; de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Pursiainen et al., GCN 43990; Becerra et al., GCN 43991; Li et al., GCN 43993; Jayaraman et al., GCN 43994; Stein et al., GCN 43996; Martin-Carrillo et al., GCN 44000; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo, GCN 44003; Brivio et al., GCN 44004; Rhodes et al., GCN 44005) is clearly detected in our images with the following brightness. Date UT_start t_mid - T0, filter exp, mag +/- err days s 2026.03.12T23:27:00 2.80565 B 5*300 18.77 +/- 0.01 2026.03.12T23:09:50 2.79577 Rc 6*300 18.00 +/- 0.01 2026.03.13T23:56:42 3.82450 B 5*300 18.92 +/- 0.01 2026.03.13T23:45:30 3.81664 Rc 4*300 18.14 +/- 0.01 This preliminary photometry is based on the nearby stars from PanSTARRS catalogue. Magnitudes of standards converted to B, Rc with the Lupton 2005 equations. The magnitudes of the AT2026fgk are not corrected for Galactic and host extinction and may be contaminated by the host galaxy. We can not trace any colour evolution between the two epochs (2.8 and 3.8 days after GRB trigger). View this GCN Circular online at https://gcn.nasa.gov/circulars/44006. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42126] GRB 260310A/AT 2026fgk: radio detection at 15GHz
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44005 SUBJECT: GRB 260310A/AT 2026fgk: radio detection at 15GHz DATE: 26/03/14 15:23:56 GMT FROM: Lauren Rhodes at McGill <lauren.rhodes(a)mcgill.ca> Lauren Rhodes (McGill), Andrew Hughes, Rob Fender (Oxford), Joe Bright (Oxford/Breakthrough Listen), Dave Green, Dave Titterington (Cambridge) report: We observed the position of GRB 260310A/AT 2026fgk (Fermi GBM Team, GCN 43951; Konno et al., GCN 43974; Hinds et al., AstroNote 2026-65; O’Neill et al. 2026, TNS Discovery Report 294132) with the Arcminute Microkelvin Imager Large-Array (AMI-LA) at 15.2 GHz beginning at 2026 March 13 23:20:06 for a total of 8 hours. The flux standard 3c286 was used to calibrate the bandpass response and flux scale of the AMI-LA and J1435+7605 was used as an interleaved complex gain calibrator. We detect an unresolved source with coordinates consistent with those of GRB 260310A/AT 2026fgk. We measure a peak flux density of 9.8 +/- 0.5 mJy/beam. Given the high flux density of the source, we cross checked with the VLASS survey and find no preexisting radio emission at the afterglow coordinates down to a 3sigma upper limit of around 0.5mJy/beam. We thank the staff at the Mullard Radio Astronomy Observatory for carrying out these observations and operating the AMI-LA. View this GCN Circular online at https://gcn.nasa.gov/circulars/44005. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42125] GRB 260310A / AT2026fgk: TNG NIR detection
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44004 SUBJECT: GRB 260310A / AT2026fgk: TNG NIR detection DATE: 26/03/14 14:48:10 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio (INAF-OAB), D. Malesani (DAWN/NBI and Radboud), L. Izzo (INAF-OACn and DARK/NBI), P. D’Avanzo (INAF-OAB), V. D’Elia (ASI-SSDC), A. Melandri (INAF-OAR), A. Rossi (INAF-OAS), M. de Pasquale (Univ. Messina), Aldo Fiorenzano (INAF-TNG), Carmen Padilla (INAF-TNG) report on behalf of the CIBO collaboration: We observed the likely counterpart of GRB 260310A, detected by Fermi/GBM (Fermi GBM team, GCN 43951; Hamburg & Meagan, GCNC 43975) and AstroSat CZTI (Salunke et al., GCN 43958) with the Italian 3.6m TNG telescope equipped with the near-infrared camera NICS. A series of images was obtained with the J and H filters starting on 2026 March 14 at 05:11:46 UT (i.e. 96.2 hours after the burst), and lasted 40 minutes for each filter. The optical/NIR counterpart, also reported as AT2026fgk (Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979; Moreno Méndez et al., GCN 43980; de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Pursiainen et al., GCN 43990; Becerra et al., GCN 43991; Li et al., GCN 43993; Stein et al, GCN 43996; Martin-Carrillo et al., GCN 44000; Watson et al., GCN 44001; Lai et al., GCN 44002; L. Izzo, GCN 44003) is detected in the co-added images with the following magnitudes: J = 17.0 +/- 0.1 (Vega, calibrated against the 2MASS catalogue), at a mid-time of 96.5 hr after the trigger; H = 15.9 +/- 0.1 (Vega, calibrated against the 2MASS catalogue), at a mid-time of 97.1 hr after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/44004. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42124] GRB 260310A / AT2026fgk: OASDG optical observations
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44003 SUBJECT: GRB 260310A / AT2026fgk: OASDG optical observations DATE: 26/03/14 09:12:46 GMT FROM: luca.izzo(a)inaf.it L. Izzo (INAF-OACn and DARK/NBI) reports: We observed the likely counterpart of GRB 261013A (Fermi GBM team, GCN #43951; Hamburg et al., GCN #43975) using the 0.5-m T1 telescope of the Osservatorio Astronomico S. Di Giacomo, located in Agerola, Italy. Our observations started on 2026 March 14 at 00:04 UT, 3.797 days after the GRB trigger. We acquired a series of 8 × 300 s images in the Rc and Ic filters. The optical counterpart, also reported as AT2026fgk (Konno et al., GCN #43974; Hinds et al., GCN #43977; Lipunov et al., GCN #43978; Martin-Carrillo et al., GCN #43979; Moreno Méndez et al., GCN #43980; de Ugarte Postigo et al., GCN #43984; Hsu et al., GCN #43986; Pursiainen et al., GCN #43990; Becerra et al., GCN #43991; Martin-Carrillo et al., GCN #44000; Watson et al., GCN #44001; Lai et al., GCN #44002) is clearly detected in the individual frames. In the Rc-band stacked image, we measure a preliminary magnitude of Rc = 18.21 +/- 0.07 mag (AB), calibrated against nearby stars from the Pan-STARRS catalog and appropriately transformed to Rc magnitudes. The measured magnitude may still be affected by contamination from the bright host galaxy, but further analysis is ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/44003. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42123] GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44002 SUBJECT: GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations DATE: 26/03/14 08:19:29 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> C.-H. Lai, A. Aryan, Y.-H. Lee, C.-S. Lin, T.-W. Chen (all NCU), A. K. H. Kong (NTHU), J. H. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), A. Sankar.K, M.-H. Lee, Y.-C. Pan, C.-C. Ngeow, W.-J. Hou, H.-Y. Hsiao, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz, and M. Huber (both IfA, Hawaii) report: We performed multiband optical observations of the field of the GRB 260310A (Fermi GBM team, GCN 43951, Hamburg et al., GCN 43975) using the 1m LOT at the Lulin observatory, as part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations in g-band started at 13:45 UTC on 13th of March 2026 (MJD 61092.577), 3.37 days after the Fermi GBM detection. The reported optical counterpart, AT 2026fgk (Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979; Moreno Méndez et al., GCN 43980; Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Pursiainen et al., GCN 43990; Becerra et al., GCN 43991; Martin-Carrillo et al., GCN 44000; Watson et al., GCN 44001), is clearly visible in each individual frame. The GRB also had X-ray (Salunke et al., GCN 43958; Jayaraman et al., GCN 43994) and NIR (Li et al., GCN 43993; Stein et al., GCN 43996) detections. We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtractions with the Pan-STARRS1 3Pi archive images (Chambers et al. 2016 arXiv:1612.05560) using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. Moreover, we further used AutoPhOT to perform PSF photometry. The details of the observations and the measured photometry (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (d) | Exposure (s) | Magnitude | avg.Seeing | Airmass LOT | g | 61112.573 | 3.367 | 300 * 1 | 18.72 +/- 0.02 | 1".94 | 2.35 LOT | r | 61112.576 | 3.371 | 300 * 1 | 18.42 +/- 0.02 | 1".70 | 2.32 LOT | i | 61112.581 | 3.374 | 300 * 1 | 18.26 +/- 0.02 | 1".77 | 2.28 LOT | z | 61112.584 | 3.378 | 300 * 1 | 17.96 +/- 0.05 | 1".90 | 2.25 In multiband photometry, the optical counterpart appears red. The presented magnitudes are calibrated using the field stars from the ATLAS-refcat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105). In the direction of the transient, these magnitudes are not corrected for the expected Galactic foreground extinctions of 0.09, 0.06, 0.04, and 0.03 mags (Schlafly & Finkbeiner 2011) for the g, r, i, and z bands, respectively. The details on the Lulin observatory telescopes and the follow-up methodology for such transients are presented in Aryan et al. (2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69). View this GCN Circular online at https://gcn.nasa.gov/circulars/44002. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42122] GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44001 SUBJECT: GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations DATE: 26/03/14 06:20:02 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Alan M. Watson (UNAM), Damien Dornic (CPPM), Rosa L. Becerra (UNAM), Antonio de Ugarte Postigo (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Camila Angulo (UNAM), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Benjamin Schneider (LAM) report: We again imaged the field of AT 2026fgk (Lipunov et al., GCN Circ. 43954; Konno et al., GCN Circ. 43975; Hinds et al., GCN Circ. 43977; Lipunov et al., GCN Circ. 43978, Martin-Carrillo et al., GCN Circ. 43079; Moren Méndez et al., GCN Circ 43980; de Ugarte Postiga et al., GCN Circ. 43984; Hsu et al., GCN Circ. 43986; Pursiainen et al., GCN Circ. 43990; Becerra et al., GCN Circ 43991; Li et al., GCn Circ. 43993; Stein et al., GCN Circ 43996; Martin-Carrillo et al., GCn Circ. 44000), a possible counterpart of the Fermi GBM GRB 260310A (Fermi GBM Team, GCN Circ. 43951; Humburg & Meegan, GCN Circ. 43975) and also detected by AstroSat CZTI (Salunke et al., GCN Circ. 43958), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-14 02:46 to 05:07 UTC (from 93.82 to 96.17 hours after the GRB trigger) and obtained 15, 14, and 28 minutes, respectively, of exposure in the g, r, and z filters. The data were reduced, coadded, calibrated, and analysed with the ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked images, we continue to detect AT 2026fgk with a preliminary PSF magnitude of: r = 18.47 +/- 0.01 Compared to the magnitudes in our first epoch reported in Moreno Méndez et al. (GCN Circ. 43980), we estimate a temporal decay index of about -1.2, consistent with the normal decay observed in GRBs. Moreover, from the optical/IR magnitudes from our first epoch and the photometry reported with WINTER (Stein et al., GCN Circ. 43996) between T+71.5 and T+72.5 hours, we estimate a spectral index beta of about -1.1 also supporting a synchrotron spectrum and a likely origin in a GRB afterglow. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/44001. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42121] GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44000 SUBJECT: GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay DATE: 26/03/14 04:43:17 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> A. Martin-Carrillo, E. Aasen, L. Brown, D. Colfer, M. Collins, J. Costello, C. Harris, R. Odunuga, H. O'Leary Jeffers, C. O'Malley, J. Parimkayala, J. Roca Garcia-Valino, R. Roddy, D. Scott, A. Valdivia y Alvarado Carvajal (UCD), A. Fernandez-Martin (CAHA), J. F. Agui Fernandez (CAHA), report on behalf of a larger collaboration: We observed the position of AT2026fgk, the likely counterpart to GRB 260310A (Fermi GBM team, GCN 43951; Salunke et al., GCN 43958; Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979; Méndez et al., GCN 43980; de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Malesani et al., GCN 43990; Becerra et al., GCN 43991, Li et al., GCN 43993; Stein et al., GCN 43996; discovered by GOTO; O'Neill et al. 2026, TNS Discovery Report 294132) using the CAHA 1.23m telescope equipped with the DLR-MkIII CCD camera. A series of 3 x 150s exposures were taken in the BVRI bands starting at 2026-03-13T23:59:00 (~3.793 days after the Fermi trigger). The candidate is still well detected in the individual images with a preliminary AB magnitude of R = 18.3 +/- 0.1. Our photometry was calibrated using nearby stars from the Pan-STARRS catalogue and is neither corrected for Galactic extinction nor the host galaxy contribution. Comparing this new epoch with our previously reported R-band magnitude (Martin-Carrillo et al., GCN 43979) we infer a shallow decay with a power-law index of ~0.3, significantly shallower than the decay observed (~0.7) since the initial report by Konno et al., GCN 43974. These observations were made during the UCD Academy observing run at Calar Alto Observatory (Almeria, Spain) as part of the final year undergraduate projects of the University College Dublin BSc (Hons) in Physics with Astronomy and Space Science. View this GCN Circular online at https://gcn.nasa.gov/circulars/44000. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42120] Fermi GRB 260314A: Global MASTER-Net observations report
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43999 SUBJECT: Fermi GRB 260314A: Global MASTER-Net observations report DATE: 26/03/14 01:18:37 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260314A ( Fermi GBM team, GCN 43997) errorbox 83 sec after trigger time at 2026-03-14 01:00:13 UT, with upper limit up to 18.8 mag. The observations began at zenith distance = 28 deg. The sun altitude is -26.8 deg. The galactic latitude b = 34 deg., longitude l = 92 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3185241 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 93 | 2026-03-14 01:00:13 | MASTER-Kislovodsk | (17h 29m 20.27s , +62d 52m 60.0s) | C | 20 | 17.8 | 134 | 2026-03-14 01:00:54 | MASTER-Kislovodsk | (17h 29m 20.09s , +62d 53m 03.0s) | C | 20 | 17.8 | 179 | 2026-03-14 01:01:34 | MASTER-Kislovodsk | (17h 29m 19.85s , +62d 53m 05.9s) | C | 30 | 18.1 | 234 | 2026-03-14 01:02:24 | MASTER-Kislovodsk | (17h 29m 19.53s , +62d 53m 09.3s) | C | 40 | 18.4 | 300 | 2026-03-14 01:03:25 | MASTER-Kislovodsk | (17h 29m 19.14s , +62d 53m 12.2s) | C | 50 | 18.5 | 380 | 2026-03-14 01:04:35 | MASTER-Kislovodsk | (17h 29m 18.64s , +62d 53m 15.1s) | C | 70 | 18.8 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43999. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42119] Fermi GRB 260313A: Global MASTER-Net observations report
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43998 SUBJECT: Fermi GRB 260313A: Global MASTER-Net observations report DATE: 26/03/14 01:16:55 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260313A ( Fermi GBM team, GCN 43987) errorbox 31381 sec after notice time and 31405 sec after trigger time at 2026-03-13 20:43:54 UT, with upper limit up to 18.7 mag. The observations began at zenith distance = 76 deg. The sun altitude is -49.0 deg. The galactic latitude b = 39 deg., longitude l = 17 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3184597 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 91 | 2026-03-13 12:01:49 | MASTER- | (16h 26m 25.94s , +10d 37m 52.9s) | C | 20 | 19.1 | 91 | 2026-03-13 12:01:49 | MASTER- | (16h 27m 45.04s , +10d 04m 45.6s) | C | 20 | 19.3 | 121 | 2026-03-13 12:02:19 | MASTER- | (16h 26m 25.91s , +10d 36m 25.9s) | C | 20 | 19.0 | 121 | 2026-03-13 12:02:19 | MASTER- | (16h 27m 45.05s , +10d 03m 19.4s) | C | 20 | 19.2 | 156 | 2026-03-13 12:02:49 | MASTER- | (16h 26m 28.86s , +10d 38m 02.1s) | C | 30 | 19.3 | 156 | 2026-03-13 12:02:49 | MASTER- | (16h 27m 48.04s , +10d 04m 55.7s) | C | 30 | 19.6 | 201 | 2026-03-13 12:03:29 | MASTER- | (16h 26m 23.44s , +10d 37m 13.5s) | C | 40 | 19.6 | 201 | 2026-03-13 12:03:29 | MASTER- | (16h 27m 42.65s , +10d 04m 07.8s) | C | 40 | 19.7 | 256 | 2026-03-13 12:04:19 | MASTER- | (16h 26m 22.44s , +10d 38m 13.7s) | C | 50 | 19.7 | 256 | 2026-03-13 12:04:19 | MASTER- | (16h 27m 41.66s , +10d 05m 08.4s) | C | 50 | 19.8 | 321 | 2026-03-13 12:05:19 | MASTER- | (16h 26m 30.02s , +10d 37m 13.3s) | C | 60 | 19.8 | 321 | 2026-03-13 12:05:19 | MASTER- | (16h 27m 49.26s , +10d 04m 08.7s) | C | 60 | 19.9 | 397 | 2026-03-13 12:06:30 | MASTER- | (16h 26m 22.89s , +10d 36m 13.8s) | C | 70 | 19.9 | 397 | 2026-03-13 12:06:30 | MASTER- | (16h 27m 42.12s , +10d 03m 09.8s) | C | 70 | 19.9 | 914 | 2026-03-13 12:15:13 | MASTER- | (16h 27m 20.26s , +10d 02m 33.4s) | C | 60 | 19.9 | 914 | 2026-03-13 12:15:13 | MASTER- | (16h 26m 01.06s , +10d 35m 40.9s) | C | 60 | 19.7 | 1058 | 2026-03-13 12:17:36 | MASTER- | (16h 21m 46.15s , +08d 09m 04.5s) | C | 60 | 19.8 | 1058 | 2026-03-13 12:17:36 | MASTER- | (16h 20m 27.41s , +08d 42m 10.1s) | C | 60 | 19.7 | 1131 | 2026-03-13 12:18:49 | MASTER- | (16h 29m 54.57s , +08d 10m 15.0s) | C | 60 | 19.9 | 1131 | 2026-03-13 12:18:49 | MASTER- | (16h 28m 35.81s , +08d 43m 20.6s) | C | 60 | 19.7 | 1644 | 2026-03-13 12:27:23 | MASTER- | (16h 27m 24.44s , +10d 02m 47.0s) | C | 60 | 19.9 | 1644 | 2026-03-13 12:27:23 | MASTER- | (16h 26m 05.20s , +10d 35m 52.9s) | C | 60 | 19.7 | 1787 | 2026-03-13 12:29:45 | MASTER- | (16h 21m 44.33s , +08d 09m 55.3s) | C | 60 | 19.8 | 1787 | 2026-03-13 12:29:45 | MASTER- | (16h 20m 25.58s , +08d 42m 59.8s) | C | 60 | 19.7 | 1859 | 2026-03-13 12:30:57 | MASTER- | (16h 29m 49.96s , +08d 10m 36.5s) | C | 60 | 19.8 | 1859 | 2026-03-13 12:30:57 | MASTER- | (16h 28m 31.19s , +08d 43m 41.1s) | C | 60 | 19.7 | 2387 | 2026-03-13 12:39:45 | MASTER- | (16h 26m 07.46s , +10d 36m 46.3s) | C | 60 | 19.4 | 2387 | 2026-03-13 12:39:45 | MASTER- | (16h 24m 53.49s , +11d 09m 55.3s) | C | 60 | 19.5 | 2530 | 2026-03-13 12:42:08 | MASTER- | (16h 19m 23.33s , +09d 16m 12.3s) | C | 60 | 19.2 | 2530 | 2026-03-13 12:42:08 | MASTER- | (16h 20m 36.37s , +08d 43m 04.5s) | C | 60 | 19.1 | 2601 | 2026-03-13 12:43:19 | MASTER- | (16h 27m 22.55s , +09d 14m 45.8s) | C | 60 | 19.3 | 2601 | 2026-03-13 12:43:19 | MASTER- | (16h 28m 35.59s , +08d 41m 38.2s) | C | 60 | 19.0 | 3152 | 2026-03-13 12:52:30 | MASTER- | (16h 26m 13.15s , +10d 36m 57.7s) | C | 60 | 18.0 | 3152 | 2026-03-13 12:52:30 | MASTER- | (16h 24m 59.66s , +11d 10m 07.2s) | C | 60 | 18.2 | 3298 | 2026-03-13 12:54:56 | MASTER- | (16h 20m 35.88s , +08d 42m 46.2s) | C | 60 | 17.7 | 3298 | 2026-03-13 12:54:56 | MASTER- | (16h 19m 23.36s , +09d 15m 54.5s) | C | 60 | 17.8 | 3370 | 2026-03-13 12:56:08 | MASTER- | (16h 27m 25.46s , +09d 16m 34.4s) | C | 60 | 17.7 | 3370 | 2026-03-13 12:56:08 | MASTER- | (16h 28m 38.01s , +08d 43m 26.8s) | C | 60 | 17.4 | 31435 | 2026-03-13 20:43:54 | MASTER-Kislovodsk | (15h 57m 41.97s , +04d 46m 40.9s) | C | 60 | 18.1 | 31540 | 2026-03-13 20:45:38 | MASTER-Kislovodsk | (16h 01m 07.45s , +06d 40m 48.5s) | C | 60 | 18.1 | 31645 | 2026-03-13 20:47:24 | MASTER-Kislovodsk | (15h 48m 59.18s , +06d 43m 14.5s) | C | 60 | 18.1 | 31753 | 2026-03-13 20:49:11 | MASTER-Kislovodsk | (15h 55m 31.20s , +02d 53m 04.3s) | C | 60 | 18.2 | 31853 | 2026-03-13 20:50:52 | MASTER-Kislovodsk | (15h 53m 31.18s , +08d 36m 59.4s) | C | 60 | 18.3 | 31960 | 2026-03-13 20:52:39 | MASTER-Kislovodsk | (15h 54m 36.75s , +08d 36m 58.4s) | C | 60 | 12.5 | 41297 | 2026-03-13 23:28:15 | MASTER-Kislovodsk | (16h 09m 55.10s , +04d 56m 04.0s) | C | 60 | 17.9 | 41401 | 2026-03-13 23:29:59 | MASTER-Kislovodsk | (16h 05m 46.45s , +08d 42m 26.9s) | C | 60 | 18.5 | 41506 | 2026-03-13 23:31:44 | MASTER-Kislovodsk | (16h 07m 41.96s , +03d 01m 52.5s) | C | 60 | 18.3 | 41604 | 2026-03-13 23:33:22 | MASTER-Kislovodsk | (16h 13m 25.35s , +06d 48m 48.5s) | C | 60 | 18.4 | 41707 | 2026-03-13 23:35:05 | MASTER-Kislovodsk | (15h 59m 05.81s , +10d 38m 10.3s) | C | 60 | 18.7 | 41820 | 2026-03-13 23:36:58 | MASTER-Kislovodsk | (15h 43m 40.10s , +03d 02m 39.4s) | C | 60 | 18.1 | 42252 | 2026-03-13 23:44:10 | MASTER-Kislovodsk | (15h 54m 29.49s , +01d 08m 26.1s) | C | 60 | 18.5 | 42360 | 2026-03-13 23:45:58 | MASTER-Kislovodsk | (15h 41m 30.91s , +08d 43m 08.7s) | C | 60 | 18.6 | 42478 | 2026-03-13 23:47:56 | MASTER-Kislovodsk | (15h 37m 05.30s , +06d 50m 16.8s) | C | 60 | 18.6 | 42581 | 2026-03-13 23:49:39 | MASTER-Kislovodsk | (15h 46m 50.58s , +10d 36m 59.0s) | C | 60 | 18.6 | 42681 | 2026-03-13 23:51:19 | MASTER-Kislovodsk | (16h 06m 25.20s , +01d 06m 49.4s) | C | 60 | 18.4 | 42802 | 2026-03-13 23:53:20 | MASTER-Kislovodsk | (16h 11m 16.05s , +10d 36m 20.0s) | C | 60 | 18.4 | 42914 | 2026-03-13 23:55:12 | MASTER-Kislovodsk | (16h 12m 12.42s , +10d 36m 20.3s) | C | 60 | 13.0 | 43021 | 2026-03-13 23:56:59 | MASTER-Kislovodsk | (16h 13m 46.32s , +10d 36m 17.0s) | C | 60 | 12.9 | 43195 | 2026-03-13 23:59:53 | MASTER-Kislovodsk | (16h 19m 39.08s , +03d 02m 31.4s) | C | 60 | 18.3 | 43305 | 2026-03-14 00:01:43 | MASTER-Kislovodsk | (15h 33m 51.88s , +04d 55m 55.3s) | C | 60 | 18.1 | 43425 | 2026-03-14 00:03:43 | MASTER-Kislovodsk | (15h 42m 27.14s , +01d 09m 22.2s) | C | 60 | 18.2 | 43540 | 2026-03-14 00:05:39 | MASTER-Kislovodsk | (15h 53m 26.55s , +12d 31m 34.8s) | C | 60 | 18.3 | 43643 | 2026-03-14 00:07:21 | MASTER-Kislovodsk | (16h 25m 31.18s , +06d 50m 11.1s) | C | 60 | 17.6 | 43748 | 2026-03-14 00:09:06 | MASTER-Kislovodsk | (16h 05m 42.64s , +12d 31m 14.8s) | C | 60 | 18.1 | 43962 | 2026-03-14 00:12:40 | MASTER-Kislovodsk | (15h 54m 17.96s , -00d 44m 27.8s) | C | 60 | 12.1 | 46601 | 2026-03-14 00:56:39 | MASTER-Kislovodsk | (16h 06m 19.90s , -00d 45m 06.5s) | C | 60 | 17.9 | 46699 | 2026-03-14 00:58:17 | MASTER-Kislovodsk | (16h 18m 28.04s , +01d 10m 17.3s) | C | 60 | 18.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43998. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42118] GRB 260314A: Fermi GBM Final Real-time Localization
by GCN Circulars 14 Mar '26

14 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43997 SUBJECT: GRB 260314A: Fermi GBM Final Real-time Localization DATE: 26/03/14 01:09:31 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 00:58:50 UT on 14 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260314A (trigger 795142735.353478 / 260314041). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 260.2, Dec = 62.9 (J2000 degrees, equivalent to J2000 17h 20m, 62d 53'), with a statistical uncertainty of 8.2 degrees. The angle from the Fermi LAT boresight is 59.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260314041/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260314041/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260314041/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43997. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42117] GRB 260310A/AT 2026fgk: WINTER NIR Detections
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43996 SUBJECT: GRB 260310A/AT 2026fgk: WINTER NIR Detections DATE: 26/03/13 21:05:01 GMT FROM: Robert David Stein at JSI <rdstein(a)umd.edu> Robert Stein (UMD), Geoffrey Mo (Caltech/Carnegie), Viraj Karambelkar (Columbia), Xander J. Hall (CMU), Tomas Ahumada (NOIRLab), Danielle Frostig (CfA), Mansi Kasliwal (Caltech), Nathan Lourie (MIT), Benjamin Schneider (LAM), Robert Simcoe (MIT), and report: We observed AT 2026fgk (Konno et al., GCN 43974; Hinds et al., AstroNote 2026-65; O’Neill et al. 2026, TNS Discovery Report 294132), identified as the likely counterpart to GRB 260310A (Fermi GBM Team, GCN 43951). We used the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began at 2026-03-12T09:57:09.115 UTC (~53 hours after the GRB trigger), and continued over several expochs in both J-band and Hs-band. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) We clearly detect a source in all of our stacked images, with times given relative to burst time (2026-03-10T04:57:11): | t - t0 (hr) | filter | mag(AB) | magerr | limiting mag | |-------------|--------|---------|--------|--------------| | 53.00 | J | 17.16 | 0.09 | 19.28 | | 53.58 | J | 17.28 | 0.09 | 19.18 | | 54.13 | Hs | 17.10 | 0.21 | 17.91 | | 71.87 | J | 17.34 | 0.12 | 19.03 | | 72.17 | Hs | 16.97 | 0.20 | 17.77 | We do not perform image subtraction due to a lack of suitable reference images, so there might be some contamination from the host galaxy. However, given the large offset and relatively faint host, we do not expect this to substantially alter our measurements. We do not measure significant evolution over our ~20 hour baseline, after accounting for the uncertainty in each measurement. A slow fading would be consistent with these observations, and with expectations for a power-law decay of an afterglow at this relatively late (>2 days) phase. Our observations are consistent with values reported by Li et al (GCN 43993), who quote a value of J=16.7 +/- 0.1 mag in the Vega system (~17.6 mag AB) at a later phase of +81 hours. Further observations of this transient are planned. WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/43996. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42116] GRB 260313A: A Correction to the Fermi GBM Final Localization
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43995 SUBJECT: GRB 260313A: A Correction to the Fermi GBM Final Localization DATE: 26/03/13 18:31:37 GMT FROM: oliver.roberts(a)universityofgalway.ie O.J. Roberts (Uni. of Galway, Ireland) reports on behalf of the Fermi Gamma-ray Burst Monitor Team. "At 12:00:28.58 UT on 13 March 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260313A (trigger 795096033/260312500). An on-ground calculated location, using the Fermi GBM trigger data, was initially reported in GCN 43987 by the GBM Team. Further analysis found the location of the short GRB to be inaccurate. We report the updated/refined location to be RA = 241.16, Dec = 5.80 (J2000 degrees, equivalent to J2000 16h 05m, 05d 48'), with a statistical uncertainty of 5.8 degrees. The angle from the Fermi LAT boresight with this new position is 15 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260312500/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260312500/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260312500q…" View this GCN Circular online at https://gcn.nasa.gov/circulars/43995. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42115] GRB 260310A: Einstein Probe Follow-up X-ray Telescope (FXT) Detection
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43994 SUBJECT: GRB 260310A: Einstein Probe Follow-up X-ray Telescope (FXT) Detection DATE: 26/03/13 17:39:34 GMT FROM: Rahul Jayaraman at Cornell University <rj438(a)cornell.edu> Rahul Jayaraman (Cornell), Anna Y. Q. Ho (Cornell), K-Ryan Hinds (Caltech), S. Y. Fu (HUST), R. D. Liang, M. J. Liu, Z. X. Ling, Hui Sun, Weimin Yuan (NAO, CAS), Genevieve Schroeder (Cornell), Xander J. Hall (CMU), Michael Coughlin (UMN) report: The Follow-up X-ray Telescope on board the Einstein Probe observed the position of AT2026fgk, the likely counterpart to GRB 260310A (Fermi GBM team, GCN 43951; Arya et al., GCN 43958; Konno et al., GCN 43974; Martin-Carrillo et al., GCN 43979; Méndez et al., GCN 43980; Becerra et al., GCN 43991), beginning at 2026-03-12T17:22:58 UTC. The exposure time of this observation was 1498 s. An uncatalogued X-ray source was detected at RA = 219.3158, DEC = 71.8417, with an uncertainty of 10 arcsec (radius, 90% CL statistical and systematic); this X-ray source is consistent with the optical position initially reported by Hinds et al., AstroNote 2026-65. We performed a preliminary analysis of the FXT spectrum in the 0.5-10 keV energy range from both the A and B modules. We fit an absorbed power-law with a line-of-sight hydrogen column density of 2.65 x 10^20 cm^-2. We find a photon index of 1.55 ± 0.09, with an unabsorbed flux of (5.51 ± 0.22) x 10^-12 erg/s/cm^2. At the redshift of z = 0.153 from Ugarte Postigo et al. (GCN 43984), this would correspond to an X-ray luminosity of (3.74 ± 0.15) x 10^44 erg/s. Parameter uncertainties are reported at the 90% C.L. We consider this source the likely X-ray afterglow to GRB 260310A, and encourage further follow-up. The Einstein Probe is a space mission supported by the Strategic Priority Program on Space Sciénce of the Chinese Academy of Sciences, in collaboration with the European Space Agency, the Max-Planck-Institute for Extraterrestrial Physics (Germany), and the Centre National d'études Spatiales (France). View this GCN Circular online at https://gcn.nasa.gov/circulars/43994. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42114] GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43993 SUBJECT: GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope DATE: 26/03/13 17:35:21 GMT FROM: lijj328(a)mail2.sysu.edu.cn Jin-Ji Li, Chun Chen, Duo-Le Cao, Zhong-Nan Dong, Wei-Sen Huang, Jia-Qi Lin, Pu Lin, Yun Shi, Hao-Nan Yang, Yan Yu, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm infrared telescope team: We observed the field of GRB 260310A (Fermi GBM Team, GCN 43951; Salunke et al., GCN 43958), using the Sun Yat-sen University (SYSU) 80 cm infrared telescope. Our observations were carried out on 2026 Mar 13, 13:58 UT, 81.0 hours after the GRB trigger, using stacked images in the J band. We clearly detect an infrared counterpart at the position of the optical afterglow candidate AT 2026fgk (Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979; Moreno Méndez et al., GCN 43980; Atteia et al., GCN 43981; de Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; Malesani et al., GCN 43990; Becerra et al., GCN 43991; discovered by GOTO; O'Neill et al. 2026, TNS Discovery Report 294132), and we measure J = 16.7±0.1 Vega mag. The photometry was calibrated against nearby stars from the 2MASS catalog and is reported in the Vega system, without correction for Galactic extinction. The SYSU 80 cm infrared telescope is operated and managed by the Department of Astronomy, Sun Yat-sen University. View this GCN Circular online at https://gcn.nasa.gov/circulars/43993. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42113] GRB 260310B: Insight-HXMT/HE detection
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43992 SUBJECT: GRB 260310B: Insight-HXMT/HE detection DATE: 26/03/13 15:05:40 GMT FROM: renyz16607(a)163.com Yang-Zhao Ren, Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng (IHEP) report on behalf of the Insight-HXMT team: At 2026-03-10T21:41:23.850 (T0), Insight-HXMT/HE detected a long burst, GRB 260310B, which is also detected by Fermi/GBM (Fermi GBM team, GCN #43955), and GECAM-B (Ren et al., GCN #43967). The Insight-HXMT/HE light curve mainly consists of multi-pulses with T90 of 43.5 +5.5/-7.5 s. The 1s peak rate, measured from T0+0.25 s, is 1147 cnts/sec. Insight-HXMT/HE detected a total of 11204 counts from this burst. The Insight-HXMT /HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb260310B.png All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://hxmten.ihep.ac.cn/ View this GCN Circular online at https://gcn.nasa.gov/circulars/43992. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42112] GRB 260310A/AT 2026fgk: DDOTI Optical Detection
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43991 SUBJECT: GRB 260310A/AT 2026fgk: DDOTI Optical Detection DATE: 26/03/13 14:38:23 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observe the field of the Fermi/GBM GRB 260310A (Fermi GBM Team, GCN 43951) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the nights of 2026-03-10 and 2026-03-11 UTC. DDOTI observed from 05:11 UTC to 9:34 on 2026-03-10 (from T+0.2 hours to T+4.6 hours after the trigger) with a total exposure time of 2.1 hours and from 03:32 UTC to 12:20 on 2026-03-11 (from T+22.6 hours to T+31.4 hours after the trigger), with a total exposure time of 3.1 hours. On both nights we detect the source AT2026fgk (discovered by GOTO; O’Neill et al. 2026, TNS Discovery Report 294132), proposed as the optical counterpart (Konno et al.; GCN Circ. 43974), with preliminary AB magnitudes of: w ≈ 16.6 (in our first epoch); w = 17.52 +/- 0.01 (in our second epoch). The photometry of the second night is consistent with a temporal decay of alpha≈-0.6 between the magnitudes reported by the LAST collaboration (Konno et al.; GCN Circ. 43974) and COLIBRÍ (Moreno Méndez et al.; GCN Circ. 43980). Due to technical problems during the first night, the photometry from that epoch should be considered tentative. These values are not corrected for the Galactic extinction. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/43991. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42111] GRB 260310A: NOT optical polarimetry
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43990 SUBJECT: GRB 260310A: NOT optical polarimetry DATE: 26/03/13 14:33:29 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> M. Pursiainen (Warwick), D. B. Malesani (DAWN/NBI and Radboud), G. Leloudas (DTU Space), Dimple (Birmingham), A. Martin-Carrillo (UCD), B. P. Gompertz (Birmingham), D. A. Perley (LJMU), N. Pyykkinen (NOT and UTU), report on behalf of a larger collaboration: We observed the likely optical counterpart AT 2026fgk (Konno et al., GCN 43974; Hinds et al., AstroNote 2026-65; O’Neill et al. 2026, TNS Discovery Report 294132) of GRB 260310A (Hamburg & Meegan, GCN 43975; Salunke et al., GCN 43958), using the Nordic Optical Telescope (NOT) equipped with ALFOSC, carrying out imaging polarimetry. In an image taken on 2026 Mar 13.09 UT (2.89 days after trigger), the transient had an AB magnitude of r = 18.12 +- 0.02 (calibrated against Pan-STARRS sources, not corrected for Galactic extinction). Unfortunately the seeing conditions were poor (~2.8" FWHM). A sequence of 4x900 s exposures was secured in linear imaging polarimetry (mean epoch Mar 13.09 UT), employing four different retarder plate angles and an SDSS r filter. The data were reduced with a custom-built reduction pipeline (Pursiainen et al. 2025, doi:10.1093/mnras/staf232) based on the photutils python library (Bradley et al. 2024, doi:10.5281/zenodo.13989456), with reduction steps detailed in Pursiainen et al. (2023, doi:10.1051/0004-6361/202345945). No significant polarization is found for the transient, down to a 3-sigma upper limit of P < 1.5%. No correction for Galactic interstellar polarization has been applied, though we note that the line of sight to GRB 260310A only suffers from very modest extinction (A_V = 0.05 mag). View this GCN Circular online at https://gcn.nasa.gov/circulars/43990. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42110] GRB 260312B: AstroSat CZTI detection
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43989 SUBJECT: GRB 260312B: AstroSat CZTI detection DATE: 26/03/13 13:07:30 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Goyal (IITB), A. Arya (IITB), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long GRB 260312B which was also detected by Fermi GBM (Fermi GBM Team , GCN Circ. 43969), and Glowbug (Cheung et. al., GCN Circ. 43976). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-03-12 09:46:53.50 UTC. The measured peak count rate associated with the burst is 131 (+29, -30) counts/s above the background in the combined data of three quadrants (out of four), with a total of 605 (+164, -182) counts. The local mean background count rate was 186 (+3, -4) counts/s. Using cumulative rates, we measure a T90 of 14 (+1, -6) s. The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/43989. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42109] Swift BAT trigger 1500295: A solar flare
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43988 SUBJECT: Swift BAT trigger 1500295: A solar flare DATE: 26/03/13 12:49:55 GMT FROM: Amy <yarleen(a)gmail.com> C. Gronwall (PSU), R. Gupta (NASA GSFC) and A. Y. Lien (U Tampa) report on behalf of the Neil Gehrels Swift Observatory Team: BAT trigger 1500295 is not a GRB, but was caused by a solar flare. Swift's automatic slews are currently disabled, so there will be no XRT or UVOT data for this trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/43988. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42108] GRB 260313A: Fermi GBM Final Real-time Localization
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43987 SUBJECT: GRB 260313A: Fermi GBM Final Real-time Localization DATE: 26/03/13 12:11:03 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 12:00:28 UT on 13 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260313A (trigger 795096033.584074 / 260313500). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 53.4, Dec = 33.3 (J2000 degrees, equivalent to J2000 03h 33m, 33d 17'), with a statistical uncertainty of 14.1 degrees. The angle from the Fermi LAT boresight is 152.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260313500/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260313500/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260313500/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43987. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42107] GRB 260310A/AT 2026fgk: Bok spectroscopic observation
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43986 SUBJECT: GRB 260310A/AT 2026fgk: Bok spectroscopic observation DATE: 26/03/13 11:30:56 GMT FROM: Brian Hsu at University of Arizona <bhsu(a)arizona.edu> B. Hsu (U of Arizona), M. Shrestha (Monash U), Jennifer Andrews (Gemini-N/NOIRLab), D. J. Sand (U of Arizona), N. Franz (U of Arizona), J. Pearson (U of Arizona), C. Christy (U of Arizona), C. L. Ransome (U of Arizona), Bhagya Subrayan (U of Arizona), K. Bostroem (U of Arizona), G. Hosseinzadeh (UCSD), N. Smith (U of Arizona) We observed the possible optical counterpart to GRB 20260310A/AT2026fgk (Konno et al., GCN 43974; Lipunov et al., GCN 43978, discovered by GOTO; O'Neill et al. 2026, TNS Discovery Report 294132) on UT 2025-03-13T06:02:23.850 using the B&C spectrograph on the 90-inch Bok telescope. The optical counterpart is clearly visible. The optical spectrum shows a featureless red continuum, although there is a strong, narrow emission line at 5571 Angstroms that we attribute to H-beta from the candidate host galaxy at z = 0.146, which is in agreement with the redshift obtained by Hinds et al., GCN 43977. Additional follow-up observations are encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/43986. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42106] Swift BAT trigger 1500287: A solar flare
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43985 SUBJECT: Swift BAT trigger 1500287: A solar flare DATE: 26/03/13 11:28:17 GMT FROM: Amy <yarleen(a)gmail.com> P. A. Evans (U Leicester), C. Gronwall (PSU), R. Gupta (NASA GSFC) and A. Y. Lien (U Tampa) report on behalf of the Neil Gehrels Swift Observatory Team: BAT trigger 1500287 is not a GRB, but was caused by a solar flare. Swift's automatic slews are currently disabled, so there will be no XRT or UVOT data for this trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/43985. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42105] GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43984 SUBJECT: GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153 DATE: 26/03/13 11:16:28 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> A. de Ugarte Postigo (LAM), L. Izzo (INAF/OACN and DARK/NBI), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), S. Geier (GTC), C. C. Thoene (AbAO), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), G. Lombardi (GTC), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), D. A. Perley (LJMU), F. M. Pérez Toledo (GTC), D. Pérez Valladares (GTC) report: We observed AT2026fgk (a.k.a. GOTO26buh, O’Neill et al. 2026, TNS Discovery Report 294132; Hinds et al., AstroNote 2026-65), proposed as the optical counterpart (Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979; Moreno Méndez et al., GCN 43979) of GRB 260310A (Hamburg & Meegan, GCN 43975; Salunke et al., GCN 43958) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument. The seeing conditions were very poor (3.5" measured in the acquisition image). In the 30-s acquisition image (beginning on 2026-03-13 at 04:23:43 UT, that is 2.98 days after trigger), the optical afterglow is well detected with a magnitude r = 18.05 + 0.05 (AB), calibrated against nearby Pan-STARRS objects, and not corrected for Galactic extinction. We warn that, given the poor seeing, some contamination from the nearby galaxy cannot be excluded. A total of 3x600 s spectra were secured in each of grism R1000B (3600-7800 AA) and R1000R (5100-10000 AA), with mean epoch 2026-03-13 at 04:58:13 UT (3.00 days after trigger). The slit covers both the optical transient and the core of the nearby galaxy. Continuum is visible over the entire range 3600-10000 AA. We detect a number of emission features that extend from the galaxy core to the location of the transient, with a typical drift due to galaxy rotation. These features include [O II], [O III], H-beta, H-alpha, [N II] and [SII] at a redshift of z = 0.153, confirming, and consolidating, the measurement by Hinds et al. (GCN 43977). No absorption features are detected either at the emission redshift (no Ca II, Ca I or Na I) nor in any other part of the spectrum. The lack of Mg II detection (typically the strongest feature in GRB afterglow spectra) in our spectral range would discard a redshift larger than 0.3 for a long GRB sight line with typical line strengths (using as reference the sample of de Ugarte Postigo et al. 2012, doi:10.1051/0004-6361/201219894). In particular at a redshift of 0.3, where the SNR would be worse, Mg II would have to be fainter than 95% of the GRB sight lines. At z = 0.7, this line of sight would need to be weaker than any in the sample. Furthermore, the chance probability of a transient appearing within 5" from the galaxy without being related is just ~1% (Moreno Méndez et al., GCN 43979). All of this indicates that the transient is indeed at the redshift of z = 0.153. The GRB afterglow is located in the outskirts of a galaxy, at a projected distance of ~13.5 kpc from the galaxy core. This offset is very large for a GRB from a collapsar origin and more in line with the expectations for mergers (e.g. Fong et al. 2022, doi: 10.3847/1538-4357/ac91d0), although not unprecedented even for collapsars (see e.g. Thoene et al. 2024, doi:10.1051/0004-6361/202348141). Together with the location in the merger region of the Epeak - Eiso diagram (Atteia et al., GCN 43981), this opens the possibility that GRB 260310A had a merger progenitor. Further monitoring to constrain the emergence of an associated SN will clarify the nature of the source and is strongly encouraged. This work has used the GRBspec database at http://grbspec.eu (de Ugarte Postigo et al. 2014, doi:10.1117/12.2055774). View this GCN Circular online at https://gcn.nasa.gov/circulars/43984. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42104] GRB 260308A: Insight-HXMT/HE detection
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43983 SUBJECT: GRB 260308A: Insight-HXMT/HE detection DATE: 26/03/13 11:02:02 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> Xing-Hao Luo, Chen-Wei Wang, Chao Zheng, Hao-Xuan Guo, Xiao-Bo Li and Shao-Lin Xiong (IHEP) report on behalf of the Insight-HXMT team: At 2026-03-08T20:05:53.000 (T0), Insight-HXMT/HE detected the burst GRB 260308A, which is also detected by Fermi/GBM (Fermi GBM Team, GCN #43949) and SVOM/GRM (Xing-Hao Luo et.al., GCN#43960). The Insight-HXMT/HE light curve mainly consists of a single pulse with a T90 of 0.3 +0.2/-0.1 s. The 1s peak rate, measured from T0-0.65 s, is 625 cnts/sec. Insight-HXMT/HE detected a total of 512 counts form this burst. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb260308A.png All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://hxmten.ihep.ac.cn/ View this GCN Circular online at https://gcn.nasa.gov/circulars/43983. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42103] GRB 260307A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43982 SUBJECT: GRB 260307A: CALET Gamma-Ray Burst Monitor detection DATE: 26/03/13 10:45:12 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> Y. Shimizu (Kanagawa U), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena) and the CALET collaboration: The long GRB 260307A (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN Circ. 43939; Glowbug gamma-ray detection: Cheung et al., GCN Circ. 43950; GECAM-B observation: Zao et al., GCN Circ. 43961) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 11:27:56.49 UTC on 7 March 2026 (https://cgbm.calet.jp/cgbm_trigger/flight/1456918069/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure that starts at T+2.8 sec, peaks at T+5.2 sec, and ends at T+8.0 sec. The T90 and T50 durations measured by the SGM data are 4.6 +/- 0.5 sec and 2.0 +/- 0.2 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1456918069/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/43982. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42102] GRB 260310A / AT 2026fgk: Location in the Epeak - Eiso diagram
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43981 SUBJECT: GRB 260310A / AT 2026fgk: Location in the Epeak - Eiso diagram DATE: 26/03/13 08:04:42 GMT FROM: Jean-Luc Atteia at IRAP <jean-luc.atteia(a)irap.omp.eu> Jean-Luc Atteia (IRAP), Enrique Moreno Méndez (UNAM), Massimiliano Lincetto (CPPM), Damien Dornic (CPPM), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Camila Angulo (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report: we computed the isotropic equivalent energy of GRB 260310A (Fermi GBM Team, GCN Circ. 43951) , using the spectral information on the prompt emission measured by Fermi GBM (Hamburg & Meegan, GCN Circ. 43975), in order to locate the GRB in the Amati diagram. At z = 0.153 (Hinds et al. GCN 43977), Ep,i = 198 keV, Eiso = 3.5e50 erg and GRB 260310A clearly lies in the Type I (mergers) region of the Amati plot, which is unusual for a long GRB. In order to locate GRB 260310A in the Type II (collapsars) region of the Amati plot, it has to be at z ≥ 0.7, and not associated with the bright galaxy noticed by the LAST team (Konno et al., GCN Circ. 43974). View this GCN Circular online at https://gcn.nasa.gov/circulars/43981. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42101] GRB 260310A / AT 2026fgk: COLIBRÍ optical observations
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43980 SUBJECT: GRB 260310A / AT 2026fgk: COLIBRÍ optical observations DATE: 26/03/13 04:01:22 GMT FROM: enriquemm(a)astro.unam.mx Enrique Moreno Méndez (UNAM), Massimiliano Lincetto (CPPM), Damien Dornic (CPPM), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Camila Angulo (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM),, and Antonio de Ugarte Postigo (LAM) report: We imaged the field of AT 2026fgk (Lipunov et al., GCN Circ. 43954; Konno et al., GCN Circ. 43975; Hinds et al., GCN Circ. 43977; Lipunov et al., GCN Circ. 43978, Martin-Carrillo et al., GCN Circ. 43079), a possible counterpart of the Fermi GBM GRB 260310A (Fermi GBM Team, GCN Circ. 43951; Humburg & Meegan, GCN Circ. 43975) and also detected by AstroSat CZTI (Salunke et al., GCN Circ. 43958), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-13 02:37 to 03:06 UTC (from 69.67 to 70.15 hours after the GRB trigger) and obtained 8, 8, 8, 8, and 16 minutes, respectively, of exposure in the g, r, i, z, and y filters. The data were reduced, coadded, calibrated, and analysed with the ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked images, we detect AT 2026fgk with preliminary PSF magnitudes of: g = 18.53 +/- 0.01 r = 18.15 +/- 0.01 i = 17.95 +/- 0.01 z = 17.74 +/- 0.01 y = 17.63 +/- 0.02 Our photometry is consistent with the reported by Martin-Carrillo (GCN Circ. 43979) and with the colours expected for a low-redshift GRB, supporting its association with GRB 260310A (Fermi GBM Team, GCN Circ. 43951). As was firstly noticed by the LAST team (Konno et al.; GCN Circ. 43974), this source is projected separation of 11.3 kpc from the center of a nearby galaxy with photo-z ≈ 0.11 (Legacy Survey DR10, Dey et al. 2019) and likely spectroscopic redshift z = 0.153 (Hinds et al., GCN Circ. 43977). This source has a probability of chance alignment with the nearby galaxy of <1%, strongly suggesting an association. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/43980. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42100] GRB 260310A / AT2026fgk: CAHA 1.23m telescope optical observations
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43979 SUBJECT: GRB 260310A / AT2026fgk: CAHA 1.23m telescope optical observations DATE: 26/03/13 02:28:03 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> A. Martin-Carrillo, J. Roca Garcia-Valino, E. Aasen, L. Brown, D. Colfer, M. Collins, J. Costello, C. Harris, R. Odunuga, H. O'Leary Jeffers, C. O'Malley, J. Parimkayala, R. Roddy, D. Scott, A. Valdivia y Alvarado Carvajal (UCD), J. F. Agui Fernandez (CAHA), A. Fernandez-Martin (CAHA) report on behalf of a larger collaboration: We observed the optical counterpart candidate (Konno et al., GCN 43974; Lipunov et al. GCN 43978, discovered by GOTO; O'Neill et al. 2026, TNS Discovery Report 294132) of GRB 260310A (Fermi GBM Team, GCN 43951; Salunke et al. 2026, GCN 43958) using the CAHA 1.23m telescope equipped with the DLR-MkIII CCD camera. A series of 3 x 150s exposures were taken in the BVR bands starting at 2026-03-12T22:57:09 (~2.75 days after the Fermi trigger). The candidate is well detected in the individual images with a preliminary AB magnitude of R = 18.2 +/- 0.1. Our photometry was calibrated using nearby stars from the Pan-STARRS catalogue and is not corrected for Galactic extinction. It should be noted that it is likely that this value has some contribution from the nearby likely host galaxy. These observations were made during the UCD Academy observing run at Calar Alto Observatory (Almeria, Spain) as part of the final year undergraduate projects of the University College Dublin BSc (Hons) in Physics with Astronomy and Space Science. View this GCN Circular online at https://gcn.nasa.gov/circulars/43979. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42099] GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43978 SUBJECT: GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations DATE: 26/03/13 02:18:22 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov (Lomonosov MSU), N.Budnev, O.Gress (ISU), A.Kuznetsov, I.Panchenko, P.Balanutsa, G.Antipov, E.Gorbovskoy, N.Tiurina, Ya.Kechin, V.Senik, A.Chasovnikov, M.Shilova,V.Topolev, D.Vlasenko, A.Sankovich, Yu.Tselik (Lomonosov MSU), D.Svinkin (Ioffe Institute), M.J. Segura, C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,A.R.Corella, J.Tanori, L. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) MASTER Global Robotic Net [1-4] started Fermi GRB 260310A observations (Fermi team GCN 43951) at MASTER-Tunka robotic telescope at 2026-03-10 16:01:36 UT (Lipunov et al. GCN 43954) Optical transient AT2026fgk, discovered by GOTO at 2026-03-10 05:14:30.624 (TNSC 1001, https://www.wis-tns.org/object/2026fgk ) was detected as MASTER OT J143716.19+715031.2 at our images at 2026-03-12 13:46:11UT with m_unfiltered~18.3. This OT was observed at 400 images with rebrigtening detection to 17.2 at 2026-03-12 21:02:59 UT. Observation and reduction will continue. [1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L [2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271 [3] Lipunov et a. 2019, ARep, vol.63, 293 [4] Lipunov et al. 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp. http://www.pereplet.ru/lipunov/625.html#625 View this GCN Circular online at https://gcn.nasa.gov/circulars/43978. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42098] GRB260310A / AT2026fgk: P200 Spectroscopy
by GCN Circulars 13 Mar '26

13 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43977 SUBJECT: GRB260310A / AT2026fgk: P200 Spectroscopy DATE: 26/03/13 00:27:51 GMT FROM: khinds(a)caltech.edu K-Ryan Hinds (Caltech), Daniel A. Perley (LJMU), Anna Y. Q. Ho (Cornell), Sam Rose (Caltech), Jillian Rastinejad (UMd), Robert Stein (UMd), Geoffrey Mo (Caltech), Mansi Kasliwal (Caltech), Jesper Sollerman (OKC), Xander J. Hall (CMU), Jacob Wise (LJMU), Rahul Jayaraman (Cornell), Aleksandra Bochenek (LJMU) We previously reported the optical transient AT 2026fgk (ID 294132) as an afterglow candidate based on its fast evolution, red color, and high implied luminosity (Hinds et al., AstroNote 2026-65). Konno et al. (GCN 43974) reported additional detections of AT 2026fgk using the Large Array Survey Telescope (LAST) whilst tiling the probability region for GRB 260310A (Fermi GBM Team, GCN 43951; Salunke et al., GCN 43958), and noted the temporal and spatial coincidence that identifies AT 2026fgk as the likely optical counterpart of this GRB. We observed GRB 260310A starting at 2026-03-12 10:23:42 UTC (~2.2 d after the Fermi GBM trigger time) with the Next Generation Palomar Spectrograph (NGPS; AstroNote 2024-340) on the Palomar 5.1m Hale Telescope (P200). The optical spectrum shows a featureless red continuum, although there is a strong, narrow emission line at 7566 Angstroms that we attribute to H-alpha from the candidate host galaxy at z = 0.153. If this is the redshift of the GRB, it would be among the closest long-duration bursts to date. For GRB 260310A, using a fluence of 5.8e-6 erg/cm^2 (10-1000 keV) reported by Hamburg et al. (GCN 43795) and assuming the redshift above, we find the gamma-ray E_iso is ~3.69e50 erg, characteristic of low-luminosity long-GRBs. The peak observed optical luminosity (from ATLAS forced photometry) is M_o ~ -22.7 mag at 7.2 hours post-trigger, more luminous than the equivalent value seen in most other nearby LLGRBs. An associated supernova similar to SN 1998bw would peak at an apparent magnitude of r = 19.7 at this redshift in the absence of host extinction. Further observations are encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/43977. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42097] GRB 260312B: Glowbug gamma-ray detection
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43976 SUBJECT: GRB 260312B: Glowbug gamma-ray detection DATE: 26/03/12 23:50:31 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260312B, which was also detected by Fermi/GBM (GCN 43969, 43970). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-03-12 09:46:45.000 with a duration of 12.3 s and a total significance of about 43 sigma. The light curve comprises a faint peak at ~T0+1s and a primary peak at ~T0+7s. Note that data from ~T0+4.0s to +6.0s and ~T0+10.0s to +11.5s suffered from deadtime in various detectors. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/43976. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42096] GRB 260310A: Fermi GBM Observation
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43975 SUBJECT: GRB 260310A: Fermi GBM Observation DATE: 26/03/12 22:19:13 GMT FROM: rhamburg(a)usra.edu R. Hamburg (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 04:57:10.81 UT on 10 March 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260310A (trigger 794811435/260310206), which was also detected by AstroSat (Salunke et al. 2026, GCN 43958). This GRB has been reported to have a potential optical counterpart, AT2026fgk, which was discovered by GOTO (O'Neill et al. 2026, TNS Discovery Report 294132) and LAST (Konno et al. 2026, GCN 43974). AT2026fgk has a photometric redshift measurement of z = 0.11 (Hinds et al. 2026, AstroNote 2026-65). The angle from the Fermi LAT boresight is 124 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 60 s (50-300 keV). The time-averaged spectrum from T0-9.6 to T0+61.6 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.15 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 172 +/- 5 keV. The event fluence (10-1000 keV) in this time interval is (5.8 +/- 0.4)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+9.8 s in the 10-1000 keV band is 2.3 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/43975. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42095] GRB 260310A: potential optical counterpart
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43974 SUBJECT: GRB 260310A: potential optical counterpart DATE: 26/03/12 19:11:47 GMT FROM: Ruslan Konno at Weizmann Institute of Science <ruslankonno(a)gmail.com> R. Konno (WIS), S. Garrappa (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), S. Fainer (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), and S. Spitzer (WIS) report on behalf of the LAST Collaboration. We report observations of GRB 260310A, detected by Fermi/GBM (Fermi GBM Team, GCN 43951), as well as by AstroSat/CZTI (Salunke et al., GCN 43958). Observations were conducted with the Large Array Survey Telescope (LAST; Ofek et al. 2023, PASP 135, 5001; Ben-Ami et al. 2023, PASP 135, 5002). Observations of GRB 260310A were taken over several tiling epochs starting at 2026-03-10 16:37:45 UTC (T-T0 = 11.67 h), in clear band (similar to the Gaia Bp band) with 24 telescopes. Each epoch consists of 20x20s exposures per telescope. The follow-up covers an integrated localization probability of 97% as given within the HEALPix FITS file glg_healpix_all_bn260310206.fit (Fermi GBM Team, GCN 43951). Initially, we do not detect a credible counterpart within our automated pipeline due to incomplete reference coverage of the field. However, we note AT 2026fgk (discovered by GOTO; O'Neill et al. 2026, TNS Discovery Report 294132) as a potential counterpart. The transient was first detected at T-T0 = 1040 s, has an angular separation of about 7 deg from the best-fit Fermi/GBM position, and is shown to be highly variable (Hinds et al., AstroNote 2026-65). This transient is clearly detected within the LAST data and shows an initial rise and a subsequent steady decay, consistent with Hinds et al., AstroNote 2026-65. The LAST photometry is as follows | Tmid-T0 (h) | Mag (AB) | | ------------ | ------------ | | 14.05 | 17.18 +/- 0.04 | | 14.17 | 17.17 +/- 0.04 | | 14.30 | 17.09 +/- 0.04 | | 14.41 | 17.16 +/- 0.04 | | 14.54 | 17.10 +/- 0.04 | | 14.66 | 17.11 +/- 0.04 | | 17.97 | 17.23 +/- 0.04 | | 19.01 | 17.25 +/- 0.04 | | 20.05 | 17.19 +/- 0.04 | | 21.09 | 17.30 +/- 0.04 | | 22.02 | 17.32 +/- 0.04 | Furthermore, serendipitous LAST observations of the field prior to the GRB event time, up to 2026-03-10 02:51:01 UTC (T-T0 = -2.15 h), shows no detection up to a 5-sigma limiting magnitude of 20.74 (AB). We thus note this transient as a potential optical counterpart, and encourage further follow-up observations. LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/) View this GCN Circular online at https://gcn.nasa.gov/circulars/43974. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42094] Fermi GRB 260312B: Global MASTER-Net observations report
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43973 SUBJECT: Fermi GRB 260312B: Global MASTER-Net observations report DATE: 26/03/12 16:45:30 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260312B ( Fermi GBM team, GCN 43969) errorbox 24262 sec after notice time and 24340 sec after trigger time at 2026-03-12 16:32:26 UT, with upper limit up to 16.8 mag. Observations started at twilight. The observations began at zenith distance = 80 deg. The sun altitude is -15.4 deg. The galactic latitude b = -63 deg., longitude l = 154 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3182510 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 24370 | 2026-03-12 16:32:26 | MASTER-Kislovodsk | (01h 43m 41.60s , -02d 12m 39.7s) | C | 60 | 16.1 | 24472 | 2026-03-12 16:34:07 | MASTER-Kislovodsk | (01h 43m 29.55s , -00d 19m 40.6s) | C | 60 | 16.5 | 24577 | 2026-03-12 16:35:53 | MASTER-Kislovodsk | (01h 55m 57.24s , -04d 08m 01.4s) | C | 60 | 16.8 | 24677 | 2026-03-12 16:37:33 | MASTER-Kislovodsk | (01h 55m 42.13s , -02d 14m 03.2s) | C | 60 | 16.6 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43973. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42093] Fermi GRB 260311B: Global MASTER-Net observations report
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43972 SUBJECT: Fermi GRB 260311B: Global MASTER-Net observations report DATE: 26/03/12 12:32:31 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260311B ( Fermi GBM team, GCN 43964) errorbox 24516 sec after notice time and 24692 sec after trigger time at 2026-03-12 01:49:28 UT, with upper limit up to 15.6 mag. The observations began at zenith distance = 57 deg. The sun altitude is -18.9 deg. The galactic latitude b = 4 deg., longitude l = 32 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3181495 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 24723 | 2026-03-12 01:49:28 | MASTER-Kislovodsk | (19h 10m 01.93s , +04d 53m 01.1s) | C | 60 | 15.6 | 59805 | 2026-03-12 11:34:10 | MASTER- | (18h 18m 16.48s , +06d 44m 41.9s) | C | 60 | 17.4 | 59805 | 2026-03-12 11:34:10 | MASTER- | (18h 19m 31.23s , +06d 11m 34.9s) | C | 60 | 17.5 | 59876 | 2026-03-12 11:35:21 | MASTER- | (18h 26m 26.82s , +06d 44m 33.6s) | C | 60 | 17.2 | 59876 | 2026-03-12 11:35:21 | MASTER- | (18h 27m 41.28s , +06d 11m 25.0s) | C | 60 | 17.3 | 60391 | 2026-03-12 11:43:55 | MASTER- | (18h 18m 23.46s , +06d 44m 43.7s) | C | 60 | 17.2 | 60391 | 2026-03-12 11:43:55 | MASTER- | (18h 19m 38.47s , +06d 11m 36.0s) | C | 60 | 17.2 | 60478 | 2026-03-12 11:45:23 | MASTER- | (18h 26m 21.18s , +06d 44m 18.1s) | C | 60 | 17.3 | 60478 | 2026-03-12 11:45:23 | MASTER- | (18h 27m 36.03s , +06d 11m 09.5s) | C | 60 | 17.4 | 61508 | 2026-03-12 12:02:33 | MASTER- | (18h 18m 19.70s , +06d 44m 43.2s) | C | 60 | 17.5 | 61508 | 2026-03-12 12:02:33 | MASTER- | (18h 19m 35.99s , +06d 11m 38.1s) | C | 60 | 17.6 | 61579 | 2026-03-12 12:03:44 | MASTER- | (18h 26m 26.43s , +06d 45m 59.2s) | C | 60 | 17.5 | 61579 | 2026-03-12 12:03:44 | MASTER- | (18h 27m 42.44s , +06d 12m 52.6s) | C | 60 | 17.6 | 61657 | 2026-03-12 12:05:02 | MASTER- | (18h 02m 57.54s , +06d 46m 34.6s) | C | 60 | 17.4 | 61657 | 2026-03-12 12:05:02 | MASTER- | (18h 04m 14.17s , +06d 13m 30.5s) | C | 60 | 17.6 | 61729 | 2026-03-12 12:06:14 | MASTER- | (18h 12m 23.49s , +06d 12m 17.2s) | C | 60 | 17.5 | 61729 | 2026-03-12 12:06:14 | MASTER- | (18h 11m 06.96s , +06d 45m 21.9s) | C | 60 | 17.4 | 61810 | 2026-03-12 12:07:35 | MASTER- | (18h 23m 25.76s , +08d 38m 13.5s) | C | 60 | 17.5 | 61810 | 2026-03-12 12:07:35 | MASTER- | (18h 24m 42.43s , +08d 05m 07.3s) | C | 60 | 17.5 | 61890 | 2026-03-12 12:08:55 | MASTER- | (18h 31m 28.03s , +08d 39m 36.9s) | C | 60 | 16.7 | 61890 | 2026-03-12 12:08:55 | MASTER- | (18h 32m 44.52s , +08d 06m 30.1s) | C | 60 | 16.7 | 61964 | 2026-03-12 12:10:09 | MASTER- | (18h 08m 02.64s , +08d 40m 18.8s) | C | 60 | 17.5 | 61964 | 2026-03-12 12:10:09 | MASTER- | (18h 09m 19.69s , +08d 07m 14.2s) | C | 60 | 17.5 | 62053 | 2026-03-12 12:11:38 | MASTER- | (18h 16m 02.67s , +08d 39m 09.5s) | C | 60 | 17.8 | 62053 | 2026-03-12 12:11:38 | MASTER- | (18h 17m 19.59s , +08d 06m 04.4s) | C | 60 | 17.9 | 62137 | 2026-03-12 12:13:02 | MASTER- | (18h 19m 34.48s , +06d 13m 00.2s) | C | 60 | 17.5 | 62137 | 2026-03-12 12:13:02 | MASTER- | (18h 18m 17.96s , +06d 46m 05.6s) | C | 60 | 17.5 | 62213 | 2026-03-12 12:14:18 | MASTER- | (18h 27m 43.41s , +06d 11m 45.8s) | C | 60 | 17.6 | 62213 | 2026-03-12 12:14:18 | MASTER- | (18h 26m 27.07s , +06d 44m 51.9s) | C | 60 | 17.5 | 62289 | 2026-03-12 12:15:34 | MASTER- | (18h 04m 15.28s , +06d 11m 22.4s) | C | 60 | 17.8 | 62289 | 2026-03-12 12:15:34 | MASTER- | (18h 02m 58.43s , +06d 44m 26.1s) | C | 60 | 17.7 | 62361 | 2026-03-12 12:16:46 | MASTER- | (18h 11m 08.08s , +06d 44m 34.3s) | C | 60 | 17.5 | 62361 | 2026-03-12 12:16:46 | MASTER- | (18h 12m 24.83s , +06d 11m 29.9s) | C | 60 | 17.5 | 62435 | 2026-03-12 12:18:00 | MASTER- | (18h 24m 39.81s , +08d 06m 36.2s) | C | 60 | 17.6 | 62435 | 2026-03-12 12:18:00 | MASTER- | (18h 23m 22.92s , +08d 39m 41.6s) | C | 60 | 17.6 | 62534 | 2026-03-12 12:19:39 | MASTER- | (18h 31m 28.26s , +08d 38m 04.6s) | C | 60 | 16.7 | 62534 | 2026-03-12 12:19:39 | MASTER- | (18h 32m 45.03s , +08d 04m 58.7s) | C | 60 | 16.7 | 62607 | 2026-03-12 12:20:52 | MASTER- | (18h 09m 21.12s , +08d 06m 49.7s) | C | 60 | 17.5 | 62607 | 2026-03-12 12:20:52 | MASTER- | (18h 08m 03.80s , +08d 39m 53.7s) | C | 60 | 17.4 | 62679 | 2026-03-12 12:22:04 | MASTER- | (18h 17m 19.94s , +08d 05m 57.7s) | C | 60 | 18.0 | 62679 | 2026-03-12 12:22:04 | MASTER- | (18h 16m 02.75s , +08d 39m 01.9s) | C | 60 | 17.9 | 62750 | 2026-03-12 12:23:15 | MASTER- | (18h 19m 35.12s , +06d 12m 53.1s) | C | 60 | 17.8 | 62750 | 2026-03-12 12:23:15 | MASTER- | (18h 18m 18.36s , +06d 45m 57.6s) | C | 60 | 17.8 | 62825 | 2026-03-12 12:24:30 | MASTER- | (18h 27m 42.53s , +06d 11m 38.8s) | C | 60 | 17.7 | 62825 | 2026-03-12 12:24:30 | MASTER- | (18h 26m 25.94s , +06d 44m 44.0s) | C | 60 | 17.6 | 62898 | 2026-03-12 12:25:43 | MASTER- | (18h 04m 17.41s , +06d 11m 17.9s) | C | 60 | 17.9 | 62898 | 2026-03-12 12:25:43 | MASTER- | (18h 03m 00.33s , +06d 44m 20.9s) | C | 60 | 17.8 | 62970 | 2026-03-12 12:26:55 | MASTER- | (18h 12m 26.18s , +06d 11m 27.7s) | C | 60 | 17.6 | 62970 | 2026-03-12 12:26:55 | MASTER- | (18h 11m 09.22s , +06d 44m 31.3s) | C | 60 | 17.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43972. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42092] Swift BAT trigger 1500148: A solar flare
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43971 SUBJECT: Swift BAT trigger 1500148: A solar flare DATE: 26/03/12 10:45:18 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> P. A. Evans (U Leicester), C. Gronwall (PSU), R. Gupta (NASA GSFC), A. Y. Lien (U Tampa) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team: BAT trigger 1500148 is not a GRB, but was caused by a solar flare. Swift's automatic slews are currently disabled, so there will be no XRT or UVOT data for this trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/43971. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42091] GRB 260312B: BALROG localization (Fermi Trigger 795001611 / GRB 260312407)
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43970 SUBJECT: GRB 260312B: BALROG localization (Fermi Trigger 795001611 / GRB 260312407) DATE: 26/03/12 10:16:35 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 795001611 at 09:46:46 on 12 March 2026 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 26.3 deg Decl.(2000.0) = -8.3 deg The 1 sigma statistical error radius is 2.2 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260312407/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260312407/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260312407/json View this GCN Circular online at https://gcn.nasa.gov/circulars/43970. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42090] GRB 260312B: Fermi GBM Final Real-time Localization
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43969 SUBJECT: GRB 260312B: Fermi GBM Final Real-time Localization DATE: 26/03/12 09:57:18 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 09:46:46 UT on 12 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260312B (trigger 795001611.054834 / 260312407). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 25.9, Dec = -3.9 (J2000 degrees, equivalent to J2000 01h 43m, -3d 53'), with a statistical uncertainty of 1.9 degrees. The angle from the Fermi LAT boresight is 67.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260312407/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260312407/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260312407/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43969. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42089] The EP-WXT trigger 01709258843 is not a real source
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43968 SUBJECT: The EP-WXT trigger 01709258843 is not a real source DATE: 26/03/12 08:26:04 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R. D. Liang, M. J. Liu (NAOC), S. Y. Fu (HUST), Z. X. Ling (NAOC) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709258843 at the time of 2026-03-12T07:55:13, is not a real source. View this GCN Circular online at https://gcn.nasa.gov/circulars/43968. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42088] GRB 260310B: GECAM-B observation of a burst
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43967 SUBJECT: GRB 260310B: GECAM-B observation of a burst DATE: 26/03/12 05:08:05 GMT FROM: renyz16607(a)163.com Yang-Zhao Ren, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 260310B, at 2026-03-10T21:41:26.000 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43955). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 46 +6/-7 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260310B.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/43967. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42087] Retraction of GCN 43965: GRB is actually solar flare
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43966 SUBJECT: Retraction of GCN 43965: GRB is actually solar flare DATE: 26/03/12 03:36:34 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team: The claimed GRB 260312A, reported in GCN Circular 43965, is found to be consistent with the location of the Sun and is due to a solar flare. View this GCN Circular online at https://gcn.nasa.gov/circulars/43966. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42086] GRB 260312A: Swift detection of a burst
by GCN Circulars 12 Mar '26

12 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43965 SUBJECT: GRB 260312A: Swift detection of a burst DATE: 26/03/12 03:17:24 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> N. J. Klingler (GSFC/UMBC/CRESSTII), C. Gronwall (PSU), R. Gupta (NASA GSFC), A. Y. Lien (U Tampa), M. J. Moss (GSFC), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 02:57:00 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 260312A (trigger=1500106). Swift did not slew. The BAT on-board calculated location is RA, Dec 351.609, -3.533 which is RA(J2000) = 23h 26m 26s Dec(J2000) = -03d 31' 59" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 30 sec. The peak count rate was ~500 counts/sec (15-350 keV), at ~0 sec after the trigger. Swift automatic follow-up slews are currently disabled. Thus there will be no XRT or UVOT data for this trigger, which is also Sun constrained. Although Swift could not slew to confirm the GRB with an X-ray afterglow, the high significance in the BAT image (9.4 sigma) gives us confidence that this is an astrophysical source. Burst Advocate for this burst is N. J. Klingler (noelklin AT umbc.edu) Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/43965. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42085] GRB 260311B: Fermi GBM Final Real-time Localization
by GCN Circulars 11 Mar '26

11 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43964 SUBJECT: GRB 260311B: Fermi GBM Final Real-time Localization DATE: 26/03/11 19:08:31 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 18:57:55 UT on 11 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260311B (trigger 794948280.422386 / 260311790). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 278.5, Dec = 0.4 (J2000 degrees, equivalent to J2000 18h 33m, 0d 24'), with a statistical uncertainty of 11.7 degrees. The angle from the Fermi LAT boresight is 54.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260311790/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260311790/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260311790/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43964. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42084] GRB 260131A/B: radio detection with the VLA
by GCN Circulars 11 Mar '26

11 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43963 SUBJECT: GRB 260131A/B: radio detection with the VLA DATE: 26/03/11 16:32:24 GMT FROM: Stefano Giarratana at INAF-OAB <s.giarratana(a)ira.inaf.it> S. Giarratana (INAF-OAB), M. Giroletti (INAF-IRA), G. Ghirlanda (INAF-OAB), N. Di Lalla (Stanford Univ.), N. Omodei (Stanford Univ.), O. S. Salafia (INAF-OAB), L. Nava (INAF-OAB) At 00:39:44 UT on 2026 February 5 (T_mid = 4.78 days post-burst) the Karl G. Jansky VLA observed the field of GRB 260131A/B (Fermi GBM team, GCN 43579, 43585; Sugai et al., GCN 43580; Konus-Wind team, GCN 43590; Insight-HXMT team, GCN 43591; GRID Collaboration, GCN 43605) in three bands, with central frequencies of 6, 10 and 15 GHz. The standard 3C48 was used as bandpass, flux density and phase calibrator. From a preliminary analysis, an unresolved radio source is detected at a position (J2000): RA: 01:38:51.308 +- 0.001 Dec: +34:19:40.84 +- 0.01 consistent with the X-ray (Sugai et al., GCN 43580; Jiang et al., GCN 43600;), optical (GOTO collaboration, GCN 43586; Lee et al., GCN 43587; García García, GCN 43599; Jayaraman et al., GCN 43606; Zhu et al., GCN 43607; KAIT GRB team, GCN 43609; MISTRAL GRB collaboration, GCN 43610; Volnova et al., GCN 43632, 43670; Gupta et al., GCN 43708) and infrared (Shi et al., GCN 43601) position of the transient. The preliminary analysis yields the following results: ================================================================ T_mid Freq Peak r.m.s. Beam PA [days] [GHz] [uJy/b] [uJy/b] [arcsec^2] [deg] ================================================================ 4.78 6 669 6 0.94x0.34 74 4.78 10 1018 6 0.60x0.21 70 4.78 15 1671 9 0.49x0.15 68 ================================================================ No source is detected with a >3sigma confidence level at the aforementioned position in the VLASS. We would like to thank the staff of the VLA for approving, executing, and processing the observations. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. These observations were carried out as part of project SF181027, approved in the framework of the Fermi - NRAO joint program agreement. View this GCN Circular online at https://gcn.nasa.gov/circulars/43963. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42083] EP260302a: MeerKAT radio counterpart
by GCN Circulars 11 Mar '26

11 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43962 SUBJECT: EP260302a: MeerKAT radio counterpart DATE: 26/03/11 15:56:12 GMT FROM: Francesco Carotenuto at INAF/OAR <francesco.carotenuto(a)inaf.it> F. Carotenuto (INAF-OAR), J. Bright (Oxford), P. G. Jonker (Radboud), on behalf of a larger collaboration We observed the field of EP260302a detected by the Einstein Probe (GCN 43899, 43906, 43932) with the MeerKAT radio telescope on 2026-03-10, from 18:00 UTC to 18:46 UTC (with a total time on source of 44 minutes) using the S-band receiver at a central frequency of 3.06 GHz. Analysing the SARAO Science Data Processor output continuum image we detect a source at the position of EP260302a (RA 08:51:53.7, DEC -65:59:01) with a flux density of around 170 uJy/beam, and with a typical image noise of around 8 uJy/beam. Further observations are planned. We thank the SARAO staff for rapidly scheduling these observations. The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation. This work has made use of the "MPIfR S-band receiver system" designed, constructed and maintained by funding of the MPI für Radioastronomie and the Max-Planck-Society. View this GCN Circular online at https://gcn.nasa.gov/circulars/43962. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42082] GRB260307A: GECAM-B observation of a burst
by GCN Circulars 11 Mar '26

11 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43961 SUBJECT: GRB260307A: GECAM-B observation of a burst DATE: 26/03/11 14:52:31 GMT FROM: xueyuan zao <zaoxueyuan(a)gmail.com> Xue-Yuan Zao, Chen-Wei Wang, Chao Zheng, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 260307A, at 2026-03-07T11:27:59.350 UTC, which is also detected by Fermi/GBM (Fermi GBM team, GCN #43939). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses, with a duration (T90) of 4.5 +1.0/-0.5 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260307A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/43961. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42081] GRB 260308A: SVOM/GRM observation of a short GRB
by GCN Circulars 11 Mar '26

11 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43960 SUBJECT: GRB 260308A: SVOM/GRM observation of a short GRB DATE: 26/03/11 14:33:12 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> SVOM/GRM team: Xing-Hao Luo, Chen-Wei Wang, Zheng-Hang Yu, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Olivier GODET (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 260308A (SVOM trigger reference: sb26030801) at 2026-03-08T20:05:53.100 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43949). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 1.50 +/-0.4 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260308A.png In addition, the position of this burst, as determined by Fermi/GBM (RA=250.2 , DEC=-32.6, Fermi GBM team, GCN #43949), is located at about 62 degrees form the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-0.8 to T0+0.4 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.86 +0.18/-0.16 and the cutoff energy, parameterized as Epeak, is 643 +346/-180 keV. The localization of GRB 260308A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260308A_amati.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Xing-Hao Luo (luoxh(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/43960. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42080] EP260306a: Mondy optical upper limit
by GCN Circulars 11 Mar '26

11 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43959 SUBJECT: EP260306a: Mondy optical upper limit DATE: 26/03/11 10:31:25 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), E. Klunko (ISTP), N. Pankov (IKI), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We observed the field of the fast X-ray transient EP260306a (Huang et al., GCNs 43930, 43937) using the AZT-33IK 1.5m telescope of the Mondy observatory on March 7, 8, and 9 taking several 120-seconds frames in the R band. In the stacked frame of the three epochs we do not detect the optical counterpart reported previously (Li et al., GCN 43929; Globus et al., GCN 43931; Ma et al., GCN 43933; Levan et al., GCN 43934). Preliminary photometry of the galaxy and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2026-03-07 15:44:24 1.61672 33*120 R n/d n/d 22.8 Mondy/AZT-33IK 2026-03-08 14:30:42 2.57040 40*120 R n/d n/d 22.1 Mondy/AZT-33IK 2026-03-09 16:24:33 3.64947 40*120 R n/d n/d 23.2 Mondy/AZT-33IK The photometry is based on nearby USNO-B1.0 stars (R2-magnitudes) and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43959. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42079] GRB 260310A: AstroSat CZTI detection of a long burst
by GCN Circulars 11 Mar '26

11 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43958 SUBJECT: GRB 260310A: AstroSat CZTI detection of a long burst DATE: 26/03/11 07:19:18 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> S. Salunke (IUCAA), Harsha K. H. (IUCAA), M. Tembhurnikar (IUCAA), A. Arya (IITB), A. Goyal (IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long GRB 260310A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 43951). The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-03-10 04:57:12.05 UTC. The measured peak count rate associated with the burst is 273 (+67, -57) counts/s above the background in the combined data of all quadrants, with a total of 2709 (+573, -589) counts. The local mean background count rate was 1494 (+6, -6) counts/s. We measure a T90 of 30 (+2, -8) s from the cumulative Veto light curve. The source was also clearly detected in the 20-200 keV energy range. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/43958. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42078] GRB 260311A: Fermi GBM Final Real-time Localization
by GCN Circulars 11 Mar '26

11 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43957 SUBJECT: GRB 260311A: Fermi GBM Final Real-time Localization DATE: 26/03/11 03:46:15 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely SHORT GRB At 03:35:40 UT on 11 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260311A (trigger 794892945.615954 / 260311150). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 291.3, Dec = -43.5 (J2000 degrees, equivalent to J2000 19h 25m, -43d 30'), with a statistical uncertainty of 10.8 degrees. The angle from the Fermi LAT boresight is 111.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260311150/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260311150/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260311150/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43957. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42077] Fermi GRB 260310B: Global MASTER-Net observations report
by GCN Circulars 10 Mar '26

10 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43956 SUBJECT: Fermi GRB 260310B: Global MASTER-Net observations report DATE: 26/03/10 22:30:30 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260310B ( Fermi GBM team, GCN 43955) errorbox 542 sec after notice time and 552 sec after trigger time at 2026-03-10 21:50:36 UT, with upper limit up to 16.9 mag. The observations began at zenith distance = 59 deg. The sun altitude is -50.4 deg. The galactic latitude b = 21 deg., longitude l = 209 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3179876 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 582 | 2026-03-10 21:50:36 | MASTER-Kislovodsk | (07h 54m 35.80s , +13d 00m 23.6s) | C | 60 | 16.6 | 687 | 2026-03-10 21:52:21 | MASTER-Kislovodsk | (07h 58m 19.92s , +14d 56m 29.1s) | C | 60 | 16.9 | 790 | 2026-03-10 21:54:03 | MASTER-Kislovodsk | (07h 46m 02.42s , +14d 53m 53.7s) | C | 60 | 16.8 | 892 | 2026-03-10 21:55:45 | MASTER-Kislovodsk | (07h 51m 26.76s , +11d 07m 39.5s) | C | 60 | 16.5 | 1118 | 2026-03-10 21:59:32 | MASTER-Kislovodsk | (08h 03m 35.41s , +11d 08m 23.4s) | C | 60 | 16.6 | 1219 | 2026-03-10 22:01:12 | MASTER-Kislovodsk | (07h 50m 14.85s , +16d 47m 46.5s) | C | 60 | 16.5 | 1322 | 2026-03-10 22:02:55 | MASTER-Kislovodsk | (08h 02m 41.51s , +16d 48m 06.7s) | C | 60 | 16.7 | 1426 | 2026-03-10 22:04:39 | MASTER-Kislovodsk | (08h 10m 41.96s , +14d 55m 27.7s) | C | 60 | 16.8 | 1527 | 2026-03-10 22:06:20 | MASTER-Kislovodsk | (07h 39m 13.82s , +11d 06m 33.0s) | C | 60 | 16.6 | 1631 | 2026-03-10 22:08:04 | MASTER-Kislovodsk | (07h 48m 50.33s , +09d 12m 03.5s) | C | 60 | 16.5 | 1742 | 2026-03-10 22:09:56 | MASTER-Kislovodsk | (08h 00m 58.87s , +09d 12m 38.7s) | C | 60 | 16.7 | 1849 | 2026-03-10 22:11:42 | MASTER-Kislovodsk | (07h 37m 42.68s , +16d 48m 11.2s) | C | 60 | 16.7 | 1955 | 2026-03-10 22:13:28 | MASTER-Kislovodsk | (07h 33m 33.75s , +14d 52m 48.8s) | C | 60 | 16.5 | 2299 | 2026-03-10 22:19:12 | MASTER-Kislovodsk | (07h 30m 05.05s , +12d 59m 15.0s) | C | 60 | 16.2 | 2407 | 2026-03-10 22:21:00 | MASTER-Kislovodsk | (08h 15m 46.83s , +11d 07m 53.6s) | C | 60 | 16.6 | 2515 | 2026-03-10 22:22:48 | MASTER-Kislovodsk | (08h 15m 18.68s , +16d 48m 43.7s) | C | 60 | 16.4 | 2623 | 2026-03-10 22:24:36 | MASTER-Kislovodsk | (08h 19m 09.07s , +12d 59m 50.9s) | C | 60 | 16.8 | 2720 | 2026-03-10 22:26:13 | MASTER-Kislovodsk | (08h 07m 48.22s , +18d 41m 27.6s) | C | 60 | 16.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43956. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42076] GRB 260310B: Fermi GBM Final Real-time Localization
by GCN Circulars 10 Mar '26

10 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43955 SUBJECT: GRB 260310B: Fermi GBM Final Real-time Localization DATE: 26/03/10 21:49:02 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 21:41:23 UT on 10 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260310B (trigger 794871688.893658 / 260310904). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 119.6, Dec = 12.9 (J2000 degrees, equivalent to J2000 07h 58m, 12d 54'), with a statistical uncertainty of 6.7 degrees. The angle from the Fermi LAT boresight is 68.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260310904/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260310904/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260310904/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43955. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42075] Fermi GRB 260310A: Global MASTER-Net observations report
by GCN Circulars 10 Mar '26

10 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43954 SUBJECT: Fermi GRB 260310A: Global MASTER-Net observations report DATE: 26/03/10 16:32:56 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Tunka robotic telescope [1] located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB 260310A ( Fermi GBM team, GCN 43951) errorbox 39832 sec after notice time and 39865 sec after trigger time at 2026-03-10 16:01:36 UT, with upper limit up to 20.0 mag. The observations began at zenith distance = 36 deg. The sun altitude is -40.5 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260310A errorbox 40477 sec after notice time and 40510 sec after trigger time at 2026-03-10 16:12:21 UT, with upper limit up to 18.3 mag. Observations started at twilight. The observations began at zenith distance = 51 deg. The sun altitude is -12.2 deg. The galactic latitude b = 38 deg., longitude l = 118 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3178578 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 39895 | 2026-03-10 16:01:36 | MASTER-Tunka | (14h 43m 00.89s , +78d 55m 32.9s) | C | 60 | 19.9 | 39895 | 2026-03-10 16:01:36 | MASTER-Tunka | (14h 45m 33.78s , +78d 47m 59.9s) | C | 60 | 20.0 | 40197 | 2026-03-10 16:06:37 | MASTER-Tunka | (14h 33m 24.43s , +80d 47m 57.5s) | C | 60 | 19.1 | 40197 | 2026-03-10 16:06:37 | MASTER-Tunka | (14h 36m 13.25s , +80d 42m 38.1s) | C | 60 | 19.2 | 40540 | 2026-03-10 16:12:21 | MASTER-Kislovodsk | (13h 26m 03.01s , +78d 44m 12.4s) | C | 60 | 17.9 | 40643 | 2026-03-10 16:14:03 | MASTER-Kislovodsk | (14h 10m 06.46s , +76d 46m 16.8s) | C | 60 | 17.8 | 40749 | 2026-03-10 16:15:49 | MASTER-Kislovodsk | (14h 29m 09.94s , +78d 40m 44.7s) | C | 60 | 18.1 | 40850 | 2026-03-10 16:17:31 | MASTER-Kislovodsk | (13h 41m 13.66s , +80d 36m 24.9s) | C | 60 | 18.3 | 40941 | 2026-03-10 16:19:01 | MASTER-Kislovodsk | (13h 56m 38.66s , +74d 54m 16.8s) | C | 60 | 18.0 | 41046 | 2026-03-10 16:20:47 | MASTER-Kislovodsk | (14h 57m 06.59s , +80d 32m 41.8s) | C | 60 | 18.3 | 41150 | 2026-03-10 16:22:30 | MASTER-Kislovodsk | (15h 03m 52.45s , +76d 43m 39.0s) | C | 60 | 17.9 | 41357 | 2026-03-10 16:25:57 | MASTER-Kislovodsk | (14h 46m 01.37s , +74d 52m 17.5s) | C | 60 | 14.0 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43954. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42074] GRB 260307B: SVOM/ECLAIRs refined analysis
by GCN Circulars 10 Mar '26

10 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43953 SUBJECT: GRB 260307B: SVOM/ECLAIRs refined analysis DATE: 26/03/10 16:09:19 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, L. Bouchet (IRAP), F. Magnani, A. Foisseau (CPPM), report on behalf of the SVOM/ECLAIRs team. Using the event-by-event data downloaded through the X-band ground station, we report further analysis of SVOM/ECLAIRs observations of GRB 260307B (SVOM burst-id sb26030704 – GCN 43940, trigger time T0 = 2026-03-07T13:45:26 UTC), which was also detected by Fermi/GBM (GCN 43948). The burst that triggered ECLAIRs shows a single peak lightcurve lasting for around 41 s prior to the slew, followed by a featureless emission after the slew. The burst duration is estimated to be around 580 s in the 4-120 keV energy band through imaging. The time-averaged spectrum before the slew (from T0-24 s to T0+17 s) in the energy range 5-120 keV is best fitted by a powerlaw model with a photon index of -1.29 +/-0.10. With this model, the 4-120 keV fluence is (9.4 +0.5/-1.4)e-7 erg/cm^2 and the 4-120 keV photon flux is 0.54 +0.02/-0.06 ph/cm^2/s. The time-averaged spectrum after the slew (from T0+151 s to T0+560 s) in the energy range 5-120 keV is best fitted by a powerlaw model with an exponential cutoff. The photon index is -0.96 +0.37/-0.33 and the peak energy is 36 +38/-14 keV. With this model, the 4-120 keV fluence is (1.4 +0.1/-0.7)e-6 erg/cm^2 and the 4-120 keV photon flux is 0.12 +0.01/-0.06 ph/cm^2/s. Using the best fit parameter from the spectrum before the slew to fit the spectrum after the slew does not give a good fit (chi²/dof: 21.1/12), which implies the presence of a spectral evolution with time. All the quoted errors are at the 68% confidence level. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/43953. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42073] GRB 260208A: radio detection with the VLA
by GCN Circulars 10 Mar '26

10 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43952 SUBJECT: GRB 260208A: radio detection with the VLA DATE: 26/03/10 09:40:09 GMT FROM: Stefano Giarratana at INAF-OAB <s.giarratana(a)ira.inaf.it> S. Giarratana (INAF-OAB), M. Giroletti (INAF-IRA), G. Ghirlanda (INAF-OAB), N. Di Lalla (Stanford Univ.), N. Omodei (Stanford Univ.), O. S. Salafia (INAF-OAB), L. Nava (INAF-OAB) At 05:24:16 UT on 2026 February 10 (T_mid = 2.04 days post-burst) the Karl G. Jansky VLA observed the field of GRB 260208A (Fermi GBM team, GCN 43635, 43673; Fermi-LAT team, GCN 43645; GECAM team, GCN 43658; Waratkar et al., GCN 43674; Cheung et al., GCN 43675; Kirschner et al., GCN 43896) in three bands, with central frequencies of 6, 10 and 15 GHz. The standard 3C286 was used as bandpass, flux density and phase calibrator. From a preliminary analysis, an unresolved radio source is detected at a position (J2000): RA: 13:38:55.595 +- 0.001 Dec: +33:48:06.12 +- 0.01 consistent with the X-ray (Swift-XRT team, GCN 43652) and optical (Podesta et al., GCN 43640; GOTO collaboration, GCN 43641; SVOM/VT team, GCN 43655; ZTF collaboration, GCN 43657; Dimple et al., GCN 43661; Magnani et al., GCN 43664; Gupta et al., GCN 43665; Volnova et al., GCN 43666, 43770, 43771; Bochenek et al., GCN 43676; Pérez-Fournon et al., GCN 43694; Swift/UVOT team, GCN 43702) position of the transient. The preliminary analysis yields the following results: ================================================================ T_mid Freq Peak r.m.s. Beam PA [days] [GHz] [uJy/b] [uJy/b] [arcsec^2] [deg] ================================================================ 2.04 6 59 7 1.57x0.31 -60 2.04 10 90 8 1.27x0.18 -57 2.04 15 125 10 1.02x0.14 -55 ================================================================ No source is detected with a >3sigma confidence level at the aforementioned position in the VLASS. However, the r.m.s. noise level of the survey at the GRB location is approximately 130 uJy/b. We would like to thank the staff of the VLA for approving, executing, and processing the observations. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. These observations were carried out as part of project SF181027, approved in the framework of the Fermi - NRAO joint program agreement. View this GCN Circular online at https://gcn.nasa.gov/circulars/43952. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42072] GRB 260310A: Fermi GBM Final Real-time Localization
by GCN Circulars 10 Mar '26

10 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43951 SUBJECT: GRB 260310A: Fermi GBM Final Real-time Localization DATE: 26/03/10 05:07:50 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 04:57:10 UT on 10 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260310A (trigger 794811435.80987 / 260310206). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 213.6, Dec = 78.7 (J2000 degrees, equivalent to J2000 14h 14m, 78d 42'), with a statistical uncertainty of 4.3 degrees. The angle from the Fermi LAT boresight is 124.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260310206/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260310206/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260310206/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43951. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42071] GRB 260307A: Glowbug gamma-ray detection
by GCN Circulars 09 Mar '26

09 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43950 SUBJECT: GRB 260307A: Glowbug gamma-ray detection DATE: 26/03/09 20:35:59 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, confirms the detection of GRB 260307A, which was detected by Fermi/GBM (GCN 43939) and CALET (Trigger 1456918069). The burst onset is at 2026-03-07 11:27:59.2 with a burst duration of 5.0s. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/43950. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42070] GRB 260308A: Fermi GBM Final Real-time Localization
by GCN Circulars 08 Mar '26

08 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43949 SUBJECT: GRB 260308A: Fermi GBM Final Real-time Localization DATE: 26/03/08 20:16:13 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely SHORT GRB At 20:05:52 UT on 8 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260308A (trigger 794693157.451346 / 260308837). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 250.2, Dec = -32.6 (J2000 degrees, equivalent to J2000 16h 40m, -32d 36'), with a statistical uncertainty of 3.6 degrees. The angle from the Fermi LAT boresight is 108.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260308837/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260308837/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260308837/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43949. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42069] Fermi GBM Sub-Threshold Detection of GRB 260307B
by GCN Circulars 08 Mar '26

08 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43948 SUBJECT: Fermi GBM Sub-Threshold Detection of GRB 260307B DATE: 26/03/08 15:14:09 GMT FROM: Rushikesh Sonawane at IISER, TVM <rushikesh23(a)iisertvm.ac.in> R. Sonawane (IISER TVM), reports on behalf of the Fermi-GBM Team: SVOM/ECLAIRs detected the GRB 260307B on 2026-03-07 at 13:45:26 UTC (Magnani et al. 2026, GCN 43940). There was no Fermi-GBM onboard trigger around this event time. An automated, blind search for gamma-ray bursts below the onboard triggering threshold in Fermi-GBM identified a candidate. The GBM Targeted Search [1], the most sensitive coherent search for GRB-like signals in GBM, identified a transient starting at 2026-03-07T13:45:30.6 (UTC), most significantly on the 32 s timescale, with a false alarm rate of 2.5e-04 Hz. The Fermi-MET of this transient is 794583935.8 s. The Targeted Search localization is found to be spatially consistent with the SVOM/ECLAIRs localization. Additionally, the GBM Targeted Search event was found with the highest significance using a "soft" spectrum (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/43948. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42068] GRB 260307B: Mephisto optical upper limits
by GCN Circulars 08 Mar '26

08 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43947 SUBJECT: GRB 260307B: Mephisto optical upper limits DATE: 26/03/08 13:15:21 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn> Guowang Du, Weikang Lin, Xueling Du, Donglin Gao, Xueteng Zhang, Yu Pan, Xingzhu Zou, Xinlei Chen, Brajesh Kumar, Yuan Fang, Jinghua Zhang, Xufeng Zhu, Tao Wang, Xinzhong Er, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team: The 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at the Lijiang Observatory, was triggered at 2026-03-07T13:48:27 (~181 seconds after the SVOM/ECLAIRs trigger) to observe the field of SVOM GRB 260307B (Magnani et al., GCN 43940). A set of simultaneous multi-band (ugi and vrz) images was collected. In our stacked frames, no optical candidate was detected within the SVOM/ECLAIRs localization and at the position reported by Corcoran et al. (GCN 43946). The upper limits (3 sigma) are listed below, which are consistent with the non-detection previously reported in Kang. et al., GCN 43941, Palmerio. et al., GCN 43942, Vijaykumar et al., GCN 43943 and Ma et al., GCN 43945. ----------------------------------------------------------------------------- Start_Time(UT) | Band | Exp(s) | LimMag (AB) ----------------------------------------------------------------------------- 2026-03-07T13:48:27 | u | 45.0*7,300.0*2 | >21.67 2026-03-07T13:51:28 | v | 45.0*8,300.0*2 | >21.94 2026-03-07T13:48:29 | g | 45.0*6,300.0*2 | >22.23 2026-03-07T13:51:30 | r | 45.0*8,300.0*2 | >22.54 2026-03-07T13:48:29 | i | 45.0*6,300.0*2 | >22.15 2026-03-07T13:51:30 | z | 45.0*8,300.0*2 | >21.31 ----------------------------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. The facility is operated by the South-Western Institute for Astronomy Research (SWIFAR), Yunnan University. It provides real-time, high-quality colors of stellar objects. The Mephisto mosaic cameras were installed in October 2025. The first light was achieved in all three channels on 10 October 2025, and presently, these are under the commissioning phase. All the data have been reduced by the Mephisto data processing pipeline. We note that the current data-processing pipeline is still at a preliminary stage, with flux calibration precision of ~2% in the u and v bands, ~1% in the g and r bands, and better than 1% in the i and z bands. View this GCN Circular online at https://gcn.nasa.gov/circulars/43947. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42067] GRB 260307B: possible NOT optical counterpart
by GCN Circulars 08 Mar '26

08 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43946 SUBJECT: GRB 260307B: possible NOT optical counterpart DATE: 26/03/08 12:01:24 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), S. Bijavara Seshashayana (NOT and Malmo Univ.), report on behalf of a larger collaboration: We observed the field of the SVOM GRB 260307B (Magnani et al., GCN 43940) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC instrument. Observations consisted of 6x200 s in the SDSS-z band and started at 22:29:21 UT on March 7 2026 (about 8.7 hr after the SVOM trigger). The sky conditions were modest, with mediocre and variable seeing (1.6" in our stack), and the imaging sequence had to be interrupted. The mid-time of our combined observation was 9.46 hr after the SVOM trigger. Within the SVOM/MXT localisation region reported by Magnani et al. (GCN 43940), we detect a faint source which visually is brighter than its archival counterpart in the Legacy survey. Its coordinates are: RA (J2000) = 10:22:02.65 Dec (J2000) = -21:00:02.6 with an estimated error of ~0.5". In our stacked images we measure a magnitude (AB) of: z = 22.47 +/- 0.33 This magnitude is calibrated using nearby objects from the Pan-STARRS catalog and is not corrected for Galactic extinction. Photometry of this object on the Legacy survey images yields z = 23.27 +/- 0.22 AB. The source was thus brighter in the NOT images at the 2-sigma level (by 0.8 +/- 0.4 mag). Given the low significance of the detection, we cannot securely claim the counterpart identification, and we invite to double-check the presence of this candidate in other data sets. View this GCN Circular online at https://gcn.nasa.gov/circulars/43946. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42066] GRB 260307B: SVOM/VT upper limit with X band data analysis
by GCN Circulars 08 Mar '26

08 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43945 SUBJECT: GRB 260307B: SVOM/VT upper limit with X band data analysis DATE: 26/03/08 06:53:14 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, H. L. Li, Z. H. Yao, Y. L. Qiu, C. Wu, L. P. Xin, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), F. Magnani, A. Foisseau (CPPM) report on behalf of the SVOM/VT team. SVOM/VT performed an automatic slew on the burst GRB 260307B (sb26030704) triggered by SVOM/ECLAIRs (Magnani et al., GCN 43940). SVOM/VT began observing the field at 2026-03-07T13:50:41 UTC, 315.5 seconds after T0, in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. After quick analyzing the X band data avaliable, the VT-VHF candidate (Palmerio et al., GCN 43942) was not confirmed in either single or stacked X band images. Therefore, we conclude that the VT-VHF candidate is not a real source. Also, no any uncatalogued sources are detected within the error range of MXT (Magnani et al., GCN 43940) down to ~22.5 AB magnitude at the mid time of 10.25 minutes in both VT_B and VT_R. Considering the bright X-ray detection by MXT and non-detection by VT with auto slew, the GRB is an optically dark burst or a high-redshift candidate. Near infrared observations are encouraged. Further data analysis is ongoing. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/43945. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42065] Fermi GRB 260307A: Global MASTER-Net observations report
by GCN Circulars 08 Mar '26

08 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43944 SUBJECT: Fermi GRB 260307A: Global MASTER-Net observations report DATE: 26/03/08 03:00:45 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260307A ( Fermi GBM team, GCN 43939) errorbox 52522 sec after notice time and 52542 sec after trigger time at 2026-03-08 02:03:41 UT, with upper limit up to 17.6 mag. The observations began at zenith distance = 27 deg. The sun altitude is -17.6 deg. The galactic latitude b = 75 deg., longitude l = 43 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3173784 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 52573 | 2026-03-08 02:03:41 | MASTER-Kislovodsk | (13h 56m 48.56s , +30d 11m 50.0s) | C | 60 | 17.5 | 52671 | 2026-03-08 02:05:19 | MASTER-Kislovodsk | (13h 55m 18.49s , +28d 17m 01.2s) | C | 60 | 17.3 | 52762 | 2026-03-08 02:06:51 | MASTER-Kislovodsk | (13h 41m 41.44s , +28d 16m 16.9s) | C | 60 | 17.1 | 52862 | 2026-03-08 02:08:30 | MASTER-Kislovodsk | (13h 42m 54.18s , +30d 11m 08.6s) | C | 60 | 17.4 | 53171 | 2026-03-08 02:13:40 | MASTER-Kislovodsk | (13h 54m 42.32s , +26d 22m 26.2s) | C | 60 | 17.4 | 53271 | 2026-03-08 02:15:20 | MASTER-Kislovodsk | (13h 41m 19.11s , +26d 22m 57.5s) | C | 60 | 17.6 | 53368 | 2026-03-08 02:16:57 | MASTER-Kislovodsk | (14h 08m 52.75s , +28d 17m 54.2s) | C | 60 | 17.2 | 53469 | 2026-03-08 02:18:38 | MASTER-Kislovodsk | (14h 09m 29.84s , +28d 17m 50.9s) | C | 60 | 12.1 | 53580 | 2026-03-08 02:20:28 | MASTER-Kislovodsk | (13h 48m 25.23s , +33d 57m 51.7s) | C | 60 | 17.3 | 54177 | 2026-03-08 02:30:26 | MASTER-Kislovodsk | (14h 08m 06.54s , +26d 23m 27.0s) | C | 60 | 17.3 | 54278 | 2026-03-08 02:32:07 | MASTER-Kislovodsk | (14h 13m 24.07s , +32d 04m 29.5s) | C | 60 | 17.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43944. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42064] GRB260307B: GROWTH-India Telescope optical upper limit
by GCN Circulars 07 Mar '26

07 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43943 SUBJECT: GRB260307B: GROWTH-India Telescope optical upper limit DATE: 26/03/07 17:57:41 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> V. Vijaykumar, A. Khade, V. Swain, S. Patil, A.P. Saikia, T. Mohan, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of GRB260307B detected by SVOM/ECLAIRs (SVOM, GCN 43940), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-03-07 15:51:15 (UTC), i.e., 2.1 hours after the trigger, and obtained 5x300 exposures in the r' filter. We did not detect any transient in our image. The photometric upper limit is as follows: | MJD (mid) | Filter | tmid-t0 (hours) | Exposure Time (sec) | Upper limit (AB) | | ------------ | ------ | --------------- | ------------------- | ---------------- | | 61106.6694 | r' | 2.26 | 5x300 | 20.4 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our magnitude is consistent with other optical observations (Kang. et al., GCN 43941, Palmerio. et al., GCN 43942). The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/43943. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42063] GRB 260307B: SVOM/VT optical candidate
by GCN Circulars 07 Mar '26

07 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43942 SUBJECT: GRB 260307B: SVOM/VT optical candidate DATE: 26/03/07 16:41:03 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> J. T. Palmerio (CEA/Irfu), H. L. Li, L. P. Xin, Y. N. Ma, Y. L. Qiu, C. Wu (NAOC), A. Saccardi (CEA/Irfu), F. Magnani, A. Foisseau (CPPM) on behalf of the SVOM/VT team. After the trigger by SVOM/ECLAIRs at 2026-03-07T13:45:26 UTC (T0), SVOM performed an automatic slew on the burst location (Magnani et al., GCN 43940). SVOM/VT began observing the field at 2026-03-07T13:51:31, 364.31 seconds after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. From a preliminary analysis of the 1-bit subimage and source list downloaded via VHF network, at least one credible candidate is identified, the details of which are presented below. VT_ID 245: This candidate was flagged as an uncatalogued fading source. The position of this candidate is R.A., Dec. 155.5129, -21.0067 degrees, corresponding to: R.A. (J2000) = 10h22m03.1s Dec. (J2000) = -21d00m24.1s with an uncertainty of 0.5 arcsec. This location is within the R90 uncertainty region of the SVOM/MXT onboard localization. The source was detected only in VT_R and faded beyond detection in the third sequence. The candidate's magnitudes are: | date-obs (UTC) | mid-time | exposure | band | mag(AB) | | ------------------- | -------- | -------- | ---- | ---------- | | 2026-03-07T13:51:31 | 6.1 min | 6*50 sec | VT_R | 21.3 ± 0.1 | | 2026-03-07T13:56:31 | 11.1 min | 6*50 sec | VT_R | 21.8 ± 0.1 | Magnitudes were not corrected for Galactic extinction. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/43942. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42062] GRB 260307B: SVOM/C-GFT upper limit
by GCN Circulars 07 Mar '26

07 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43941 SUBJECT: GRB 260307B: SVOM/C-GFT upper limit DATE: 26/03/07 15:46:50 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Z. Kang(CHO), C. Wu (NAOC), L.P. Xin, X.H. Han, P.P. Zhang, X.M. Lu (NAOC), Z.W. Li, Y. Lv (CHO), R.S. Zhang, Y.J. Xiao, Y.L. Qiu, J. Wang, J.S. Deng, L. Huang, J.Y. Wei (NAOC), F. Mag-nani, A. Foisseau (CPPM) report on behalf of the SVOM/C-GFT team: We observed the field of GRB 260307B detected by SVOM/ECLAIRs (Magnani et al. GCN 43940) with LATIOS on SVOM/C-GFT. Observations started at 2026-03-07T13:47:15 UTC, ~109 seconds after the trigger. We obtained i-band follow-up imaging. The target had a very low elevation. After preliminary analysis, no credible candidate was detected within the error box provided by SVOM/MXT (Magnani et al., GCN 43940) in our images. The 5-sigma upper limits are: i > 19.7 mag (AB) (5-sigma, mid-time 7.7 min after the trigger) The photometry was calibrated against the UCAC4 catalogue, and no correction for Galactic dust extinction was applied. Further observations and analyses are ongoing. We thank the observation assistants Chun-Lei Guo and Ying-Huai Hao at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/43941. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42061] GRB 260307B: SVOM detection of a burst
by GCN Circulars 07 Mar '26

07 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43940 SUBJECT: GRB 260307B: SVOM detection of a burst DATE: 26/03/07 14:09:39 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> F. Magnani, A. Foisseau (CPPM), M. Brunet, O. Godet (IRAP), report on behalf of the SVOM mission team: At 2026-03-07T13:45:26 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260307B (SVOM burst-id sb26030704). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 4 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 9.92 in the [8-120] keV energy band over a time window of 40.96 seconds starting at 2026-03-07T13:45:06. The localization of the best alert is R.A., Dec. 155.5760, -21.0620 degrees (J2000) with a 90% confidence level (C.L.) radius of 8.01 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM slewed to the burst. SVOM/MXT began observing the field at 2026-03-07T13:48:16 UTC, 170 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 155.5216, -20.9972 degrees: R.A. (J2000) = 10h22m05.19s Dec. (J2000) = -20d59m49.81s with a 90% C.L. radius of 43.83 arcseconds. This location is 4.94 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. No optical observation could be performed by SVOM/VT for the time being. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Francesco Magnani: magnani(a)cppm.in2p3.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/43940. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42060] GRB 260307A: Fermi GBM Final Localization
by GCN Circulars 07 Mar '26

07 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43939 SUBJECT: GRB 260307A: Fermi GBM Final Localization DATE: 26/03/07 13:08:25 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> The Fermi GBM team reports the detection of a likely LONG GRB "At 11:27:59.32 UT on 07 March 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260307A (trigger 794575684/260307478). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 209.07, Dec = 29.03 (J2000 degrees, equivalent to J2000 13h 56m, 29d 01'), with a statistical uncertainty of 2.88 degrees. The angle from the Fermi LAT boresight is 77 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260307478/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260307478/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260307478/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/43939. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42059] GRB 260211A: late-time NOT i-band observations consistent with archival flux
by GCN Circulars 07 Mar '26

07 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43938 SUBJECT: GRB 260211A: late-time NOT i-band observations consistent with archival flux DATE: 26/03/07 10:55:59 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), S. Bijavara Seshashayana (NOT and Malmo Univ.) report on behalf of a larger collaboration: We observed the optical counterpart (Li et al., GCN 43748) of GRB 260211A (Gotz et al., GCN 43705; Hamburg, GCN 43713) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC instrument. Observations (3x300 s) were conducted in the SDSS i band, in order to reduce the effect of the large Galactic extinction towards this line of sight (A_V = 2.1 mag). Our image quality was unfortunately degraded by poor seeing (2.1"). The optical counterpart is detected in our images (mid time 23.1 days after the SVOM trigger). We measure a magnitude i = 22.5 +/- 0.2 AB, calibrated against nearby objects from the Pan-STARRS catalog, and not corrected for Galactic extinction. The source is also detected in archival imaging from the DELVE survey (Drlica-Wagner et al., 2022, doi:10.3847/1538-4365/ac78eb), for which we find a consistent magnitude to within 0.2 mag. Imagine subtraction between the two data sets yields an upper limit of i > 22.9 for any excess component at the afterglow location. Li et al. (GCN 43923) report a rebrightening of this source between 2.7 and 19.4 days after trigger, possibly suggesting the emergence of a SN. Our data cannot confirm this trend, though the different filters and the large extinction may introduce a systematic difference. View this GCN Circular online at https://gcn.nasa.gov/circulars/43938. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42058] EP260306a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 07 Mar '26

07 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43937 SUBJECT: EP260306a: refined analysis of the EP-WXT and EP-FXT observations DATE: 26/03/07 02:34:23 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> G.L. Huang, Z.X. Li (IHEP), H. Zhou (PMO, CAS) and Z.-X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260306a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Huang et al., GCN 43930). The refined analysis of the WXT data shows that the event started at T0=2026-03-06T 01:28:20(UTC), and lasted for approximately 60 seconds, after which the WXT light curve was interrupted due to the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density (NH) of 3.24×10^20 cm^-2, a photon index of 4.01(-2.04/+3.04) and an additional absorber (z=0) of NH=6.32(-4.37/+6.21)×10^21cm^-2 to represent the comprehensive absorption of the host galaxy (z=4.773, Levan et al., GCN 43934) and the foreground galaxy (z=0.72, Globus et al., GCN 43931). The derived average unabsorbed 0.5-4 keV flux is 3.98×(-2.97/+69.04)×10^(-9) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2026-03-06T01:34:41(UTC, T0+261s). The exposure time of this observation is 4010s. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 145.9497, DEC = 15.6942 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position and position of the optical counterpart (Li et al, GCN 43929; Globus et al., GCN 43931; Ma et al., GCN 43933; Levan et al., GCN 43934). The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 3.24×10^20 cm^-2, a photon index of 2.36(-0.38/+0.41) and an additional absorber of NH=1.53(-1.11/+1.19)×10^21 cm^-2. The derived average unabsorbed 0.5-10 keV flux is 1.37(-0.16/+0.20)×10^(-12) erg/s/cm^2. All uncertainties are reported at the 90% confidence interval. Further FXT follow-up observations have been arranged. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43937. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42057] GRB 260207A: TESS Detection and Possible VLA Counterpart
by GCN Circulars 06 Mar '26

06 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43936 SUBJECT: GRB 260207A: TESS Detection and Possible VLA Counterpart DATE: 26/03/06 18:35:15 GMT FROM: Sarah Chastain at Texas Tech University <sarahichastain(a)gmail.com> S. I Chastain (TTU) and M. M. Fausnaugh (TTU) report: Approximately 93% of the Fermi GBM localization of GRB 260207A (Fermi GBM Team, GCN 43628) fell within the field of view of the Transiting Exoplanet Survey Satellite (TESS; Ricker et al. JATIS 1 2015) during observations of sector 100. We identified a counterpart consistent with the counterpart reported by MASTER-OT (C. Francile et al., GCN 43633). At around 14 days post-burst, we carried out VLA observations of this counterpart and identified a faint source within the error region with a flux of 24 +/- 4 microJy/BM at 6 GHz. The position of this source is: RA (J2000): 10:44:11.3314 ± 0.0016 seconds Declination (J2000): -33:09:36.053 ± 0.067 arcseconds This circular includes data collected with the TESS mission, obtained from the MAST data archive at the Space Telescope Science Institute (STScI). Funding for the TESS mission is provided by the NASA Explorer Program. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations were carried out as part of project SF171128, approved in the framework of the Fermi - NRAO joint program agreement. View this GCN Circular online at https://gcn.nasa.gov/circulars/43936. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42056] EP260302a: SVOM/VT optical observation
by GCN Circulars 06 Mar '26

06 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43935 SUBJECT: EP260302a: SVOM/VT optical observation DATE: 26/03/06 15:17:15 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, L. P. Xin, H. L. Li, Z. H. Yao, Y. L. Qiu, C. Wu, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of EP260302a detected by EP/WXT (Zhang et al., GCN 43899; Zhang et al., GCN 43906). SVOM/VT began observing the field at 2026-03-05T07:05:29 UTC, 55.435 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data available, the optical counterpart (Li et al., GCN 43898; Pérez-García et al., GCN 43903; Corcoran et al., GCN 43904; Corcoran et al., GCN 43928; Levan et al., GCN 43932) was detected in both VT_B and VT_R bands. The AB magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) -------------|-------------------|------|------------ 58.03 | 53*50 | VT_B | 21.4+-0.1 58.03 | 50*50 | VT_R | 21.2+-0.1 Our photometry was not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/43935. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42055] EP260306a: Gemini-North redshift z = 4.773
by GCN Circulars 06 Mar '26

06 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43934 SUBJECT: EP260306a: Gemini-North redshift z = 4.773 DATE: 26/03/06 13:36:30 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> A. J. Levan (Radboud), P. G. Jonker (Radboud), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), F. E. Bauer (UTa), J. Chácon (PUC), L. Cotter (UCD), R. A. J. Eyles-Ferris (Leicester), A. Martin-Carrillo (UCD), J. Quirola-Vasquez (Radboud), report on behalf of a larger collaboration: We observed the optical counterpart (Li et al., GCN 43929; Globus et al., GCN 43931; Ma et al., GCN 43933) of the fast X-ray transient EP260306a (Huang et al., GCN 43930) using the Gemini-North telescope equipped with the GMOS-N spectrograph. Four exposures of 600 s each were obtained, using grating R400, a slit width of 1 arcsec, and covering the wavelength range 5200-9900 Å. The observation mid time was 2026 March 6.489 UT (10.2 hr after the EP/WXT trigger). Continuum is significantly detected over the red part of the spectrum, down to ~7020 Å, where a spectral break is apparent. This is due to a combination of the H I damping wing and the onset of the Lyman forest at z ~ 4.77. A number of absorption features, including fine-structure lines, are clearly visible, which we interpret as Si II, Si II*, C II, Si IV, C IV, Fe II, Al II, all at a common redshift z = 4.773, establishing it as the redshift of EP260306a. We note that, given their colors and g-band detection, the two nearby objects noted by Globus et al. (GCN 43931) are both in the foreground of the transient. We acknowledge the excellent support from the Gemini North staff in the execution of this challenging observation. View this GCN Circular online at https://gcn.nasa.gov/circulars/43934. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42054] EP260306a: SVOM/VT optical observation
by GCN Circulars 06 Mar '26

06 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43933 SUBJECT: EP260306a: SVOM/VT optical observation DATE: 26/03/06 10:21:37 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, H. L. Li, Z. H. Yao, Y. L. Qiu, C. Wu, L. P. Xin, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of EP260306a detected by EP/WXT (Huang et al., GCN 43930). SVOM/VT began observing the field at 2026-03-06T03:45:23 UTC, 2.268 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data available, the optical counterpart (Li et al., GCN 43929; Globus et al., GCN 43931) was detected in both VT_B and VT_R bands. The AB magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) -------------|-------------------|------|-------------- 2.608 | 48*50 | VT_B | 23.1+-0.2 2.642 | 53*50 | VT_R | 21.7+-0.1 Our photometry was not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/43933. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42053] EP260302a: Gemini-South redshift z = 1.535
by GCN Circulars 06 Mar '26

06 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43932 SUBJECT: EP260302a: Gemini-South redshift z = 1.535 DATE: 26/03/06 09:26:04 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> A. J. Levan (Radboud), G. Corcoran (UCD), J. Quirola-Vasquez (Radboud), D. B. Malesani (DAWN/NBI and Radboud), P. G. Jonker (Radboud), F. E. Bauer (UTa), J. Chácon (PUC), L. Cotter (UCD), R. A. J. Eyles-Ferris (Leicester), A. Martin-Carrillo (UCD), R. Ruiz (Gemini), V. Firpo (Gemini) report on behalf of a larger collaboration: Taking advantage of its rebrightening (Corcoran et al., GCN 43928), we observed the optical counterpart (Li et al., GCN 43898; Pérez-García et al., GCN 43903; Corcoran et al., GCNs 43904, 43928) of the fast X-ray transient EP260302a (Zhang et al., GCNs 43899, 43906) using Gemini-South equipped with the GMOS spectrograph. In the acquisition image (mid time 3.18 days after trigger) we measure r = 21.30 +- 0.07 AB, suggesting some fading compared with our previous observation (Corcoran et al., GCN 43928). Four exposures of 600 s each were obtained, using grating B480, a slit width of 1 arcsec, and covering the wavelength range 4470-8500 Å. The observation mid time was 2026 March 6.182 UT (3.20 days after the EP/WXT trigger). Continuum is significantly detected over the entire covered wavelength range. From the lack of Hydrogen absorption, we infer a firm upper limit z < 2.67. A number of clear absorption features are also visible, which we interpret as Fe II (2344, 2374, 2383, 2586, 2600 AA) and Mg II (2796, 2803 AA), all at a common redshift z = 1.535. Given the good S/N of the continuum, and the lack of any further unidentified features, we therefore conclude that EP260302a likely lies at this redshift. View this GCN Circular online at https://gcn.nasa.gov/circulars/43932. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42052] EP260306a: COLIBRÍ optical observations of the fading and red counterpart
by GCN Circulars 06 Mar '26

06 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43931 SUBJECT: EP260306a: COLIBRÍ optical observations of the fading and red counterpart DATE: 26/03/06 04:38:09 GMT FROM: globus(a)astro.unam.mx Noémie Globus (UNAM), Benjamin Schneider (LAM), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Camila Angulo (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of EP260306a (Huang et al., GCN Circ. 43930) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-06 02:41 to 03:34 UTC (from 1.20 to 2.10 hours after the trigger) and obtained 23, 12 and 39 minutes of simultaneous exposure in the r, i, and z filters. The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detect the optical counterpart reported by Li et al. (GCN Circ. 43929) at preliminary magnitudes of: r = 23.27 +/- 0.25, z = 21.58 +/- 0.12. Comparing our observations with those reported by Li et al. (GCN Circ. 43929), the transient has faded, and we estimate a temporal decay index alpha ≈ 1. A preliminary fit to the SED suggests a high-z event, with a tentative photometric redshift between z=4 and z=5, but cannot rule out an intrinsically redder source at a lower redshift. We encourage spectroscopy. We notice that at the position of the optical counterpart, there is a faint galaxy with g = 24.91 +/- 0.28, r = 23.90 +/- 0.17, i = 23.54 +/- 0.24, z = 23.30 +/- 0.26, and photo-z = 0.72 +/- 0.27 in the Legacy Survey catalog (Dey et al., 2019). Furthermore, at a distance of 17 arcsec from the source, there is a nearby (photo-z = 0.06 +/- 0.01) bright galaxy with g = 18.04 +/- 0.01, r = 17.34 +/- 0.01, i = 17.02 +/- 0.01, and z = 16.76 +/- 0.01, with a chance coincidence probability Pcc~2%. Both of these galaxies may be unrelated if the event is located at high redshift. Additional observations in g, r, i, z bands and analysis are still ongoing. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/43931. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42051] EP260306a: Einstein Probe detection of an X-ray transient
by GCN Circulars 06 Mar '26

06 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43930 SUBJECT: EP260306a: Einstein Probe detection of an X-ray transient DATE: 26/03/06 02:47:52 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> G.L. Huang, Z.X. Li (IHEP), H. Zhou (PMO, CAS) and Z-.X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260306a. The transient triggered EP-WXT (ID: 01709258759) at 2026-03-06T01:29:20 (UTC). The WXT position of the source is R.A. = 145.955 deg, DEC = 15.685 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 145.9478 deg, DEC = 15.6963 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). The location of the reported optical counterpart (GCN 43929) is consistent with the location of the uncatalogued X-ray source detected by FXT. Further information will be updated when the telemetry data is received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43930. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42050] The EP-WXT trigger 01709258759: Las Cumbres discovery of the optical counterpart
by GCN Circulars 06 Mar '26

06 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43929 SUBJECT: The EP-WXT trigger 01709258759: Las Cumbres discovery of the optical counterpart DATE: 26/03/06 02:31:14 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> Wenxiong Li, Runduo Liang (NAOC), Iair Arcavi, Ido Keinan (TAU), David Sand (U of Arizona) We observed the position of the EP/WXT trigger 01709258759 with a Las Cumbres 1m telescope at McDonald Observatory, Texas, 20 mins after the Einstein Probe WXT trigger. We took 2x300s exposures in the broad optical w band. We find an uncataloged source at RA=145.9490, Dec=15.6937 within the EP/WXT error circle and measure the following preliminary photometry calibrated to the r band: MJD 61105.08 Mag 21.6 View this GCN Circular online at https://gcn.nasa.gov/circulars/43929. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42049] EP260302a: Optical afterglow rebrightening
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43928 SUBJECT: EP260302a: Optical afterglow rebrightening DATE: 26/03/05 23:34:56 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), L. Cotter (UCD), J. Quirola-Vasquez (Radboud), A. Martin-Carrillo (UCD), R. A. J. Eyles-Ferris (Leicester), D. B. Malesani (DAWN/NBI and Radboud), P. G. Jonker (Radboud) report on behalf of a larger collaboration: We observed the optical counterpart (Li et al., GCN 43898; Pérez-García et al., GCN 43903; Corcoran et al., GCN 43904) of the fast X-ray transient EP260302a (Zhang et al., GCN 43899; Zhang et al., GCN 43906) on two epochs. Our first observation was carried out with the Gemini South telescope located in Cerro Pachon (Chile); and the second with the LCO 1m telescope located in Sutherland (South Africa). The exposure times were 1x30 and 9x300 s, respectively, both in the SDSS r band, at mean epochs 2026-03-03 at 07:25:03 UT and 2026-03-05 at 19:05:14 UT (~7.8 and ~67.4 hr after trigger, respectively). The counterpart is clearly detected on both epochs. We measure magnitudes r = 22.06 +- 0.12 (Gemini) and r = 21.07 +/- 0.06 (LCO). Both values are calibrated against nearby stars from the SkyMapper catalog, and are not corrected for Galactic extinction. The observed fluxes imply a rebrightening by ~1 mag, which is uncommon for FXT and GRB afterglows around this epoch, and possibly indicates the emergence of an extra component (for another example, see e.g. van Dalen et al. 2025, doi:10.3847/2041-8213/adbc7e). We encourage further multiwavelength follow up of this unusual source. View this GCN Circular online at https://gcn.nasa.gov/circulars/43928. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42048] GRB 260228A: further EP-FXT observations and X-ray afterglow confirmation
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43927 SUBJECT: GRB 260228A: further EP-FXT observations and X-ray afterglow confirmation DATE: 26/03/05 19:04:24 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), Y. Julakanti (Univ. Leicester), D. Turpin (CEA/Irfu), J.-L. Atteia (IRAP), D. B. Malesani (DAWN/NBI and Radboud), Y. H. Cheng (SWIFAR, YNU), R. A. J. Eyles-Ferris (Univ. Leicester) report on behalf of the SVOM and Einstein Probe teams: We performed a second observation at the location of the SVOM/ECLAIRs GRB 260228A (Julakanti et al., GCN 43882) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started on 2026-03-04 at 19:25:58 UT (3.94 days after the trigger) with a total exposure time of ~6000 s. All six sources detected by EP/FXT during the first visit (Cheng et al., GCN 43900) are detected in the second epoch data set. The brightest of them (EPF_J155124.0+262035; error radius of 10 arcsec) has faded by a factor of ~10, down to a flux of (1.92 +/- 0.47) x 10^-13 erg/s/cm^-2 (0.5-10 keV; 1-sigma uncertainty). The fading behavior of this X-ray source confirms it as the afterglow of GRB 260228A. The early deep optical limits measured by SVOM/VT (Li et al., GCN 43886), compared to the bright X-ray flux (Cheng et al., GCN 43900), suggest that this could be a dark GRB. We encourage multi-wavelength follow-up observation of this source. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43927. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42047] GRB 260228A: further EP-FXT observations and X-ray afterglow confirmation
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43927 SUBJECT: GRB 260228A: further EP-FXT observations and X-ray afterglow confirmation DATE: 26/03/05 19:04:24 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), Y. Julakanti (Univ. Leicester), D. Turpin (CEA/Irfu), J.-L. Atteia (IRAP), D. B. Malesani (DAWN/NBI and Radboud), Y. H. Cheng (SWIFAR, YNU), R. A. J. Eyles-Ferris (Univ. Leicester) report on behalf of the SVOM and Einstein Probe teams: We performed a second observation at the location of the SVOM/ECLAIRs GRB 260228A (Julakanti et al., GCN 43882) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started on 2026-03-04 at 19:25:58 UT (3.94 days after the trigger) with a total exposure time of ~6000 s. All six sources detected by EP/FXT during the first visit (Cheng et al., GCN 43900) are detected in the second epoch data set. The brightest of them (EPF_J155124.0+262035; error radius of 10 arcsec) has faded by a factor of ~10, down to a flux of (1.92 +/- 0.47) x 10^-13 erg/s/cm^-2 (0.5-10 keV; 1-sigma uncertainty). The fading behavior of this X-ray source confirms it as the afterglow of GRB 260228A. The early deep optical limits measured by SVOM/VT (Li et al., GCN 43886), compared to the bright X-ray flux (Cheng et al., GCN 43900), suggest that this could be a dark GRB. We encourage multi-wavelength follow-up observation of this source. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43927. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42046] GRB 260228A: further EP-FXT observations and X-ray afterglow confirmation
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43927 SUBJECT: GRB 260228A: further EP-FXT observations and X-ray afterglow confirmation DATE: 26/03/05 19:04:24 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), Y. Julakanti (Univ. Leicester), D. Turpin (CEA/Irfu), J.-L. Atteia (IRAP), D. B. Malesani (DAWN/NBI and Radboud), Y. H. Cheng (SWIFAR, YNU), R. A. J. Eyles-Ferris (Univ. Leicester) report on behalf of the SVOM and Einstein Probe teams: We performed a second observation at the location of the SVOM/ECLAIRs GRB 260228A (Julakanti et al., GCN 43882) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started on 2026-03-04 at 19:25:58 UT (3.94 days after the trigger) with a total exposure time of ~6000 s. All six sources detected by EP/FXT during the first visit (Cheng et al., GCN 43900) are detected in the second epoch data set. The brightest of them (EPF_J155124.0+262035; error radius of 10 arcsec) has faded by a factor of ~10, down to a flux of (1.92 +/- 0.47) x 10^-13 erg/s/cm^-2 (0.5-10 keV; 1-sigma uncertainty). The fading behavior of this X-ray source confirms it as the afterglow of GRB 260228A. The early deep optical limits measured by SVOM/VT (Li et al., GCN 43886), compared to the bright X-ray flux (Cheng et al., GCN 43900), suggest that this could be a dark GRB. We encourage multi-wavelength follow-up observation of this source. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/43927. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42045] GRB 260303A: 1.3m DFOT optical upper limit
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43926 SUBJECT: GRB 260303A: 1.3m DFOT optical upper limit DATE: 26/03/05 16:36:08 GMT FROM: Debalina Kar at ARIES <kardebalina2000(a)gmail.com> Debalina Kar, Pankaj Pawar, Anshika Gupta, Dhruv Jain and Kuntal Misra (ARIES) report: We observed the field of GRB 260303A triggered by SVOM/ECLAIRs (sb26030303, Wang et al., GCN 43901) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations began on 2026-03-03 at 14:54:29.000 UT, approximately 8.88 hours after the trigger. We obtained multiple exposures of 300 s each in the R filter . A total of 10 frames were aligned and stacked to improve the signal-to-noise ratio. In the stacked frame we do not detect any optical counterpart within the error box of SVOM/ECLAIRs (Brunet et al., GCN 43922, Wang et al., GCN 43901) as well as outside the ECLAIRs error circle as reported by Xin et al. (GCN 43916) and (Schneider et al., GCN 43902). This is consistent with the non-detection in the J band reported by Mo et al. (GCN 43915). We derive the following 3-sigma upper limit from the stacked image: Date (UT) Start Time T_start–T0 (hr) Filter Exposure Magnitude ---------------------------------------------------------------------------------- 2026-03-03 14:54:29 ~8.88 R 300 s × 10 > 20.29 The reported magnitude is not corrected for Galactic extinction. Photometric calibration was performed using standard stars from the USNO-B1.0 catalogue. View this GCN Circular online at https://gcn.nasa.gov/circulars/43926. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42044] GRB 260303A: 1.3m DFOT optical upper limit
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43925 SUBJECT: GRB 260303A: 1.3m DFOT optical upper limit DATE: 26/03/05 16:34:28 GMT FROM: Debalina Kar at ARIES <kardebalina2000(a)gmail.com> Debalina Kar, Pankaj Pawar, Anshika Gupta, Dhruv Jain and Kuntal Misra (ARIES) report: We observed the field of GRB 260303A triggered by SVOM/ECLAIRs (sb26030303, Wang et al., GCN 43901) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations began on 2026-03-03 at 14:54:29.000 UT, approximately 8.88 hours after the trigger. We obtained multiple exposures of 300 s each in the R filter . A total of 10 frames were aligned and stacked to improve the signal-to-noise ratio. In the stacked frame we do not detect any optical counterpart within the error box of SVOM/ECLAIRs (Brunet et al., GCN 43922, Wang et al., GCN 43901) as well as outside the ECLAIRs error circle as reported by Xin et al. (GCN 43916) and (Schneider et al., GCN 43902). This is consistent with the non-detection in the J band reported by Mo et al. (GCN 43915). We derive the following 3-sigma upper limit from the stacked image: Date (UT) Start Time T_start–T0 (hr) Filter Exposure Magnitude ---------------------------------------------------------------------------------- 2026-03-03 14:54:29 ~8.88 R 300 s × 10 > 20.29 The reported magnitude is not corrected for Galactic extinction. Photometric calibration was performed using standard stars from the USNO-B1.0 catalogue. View this GCN Circular online at https://gcn.nasa.gov/circulars/43925. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42043] GRB 260303A: 1.3m DFOT optical upper limit
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43925 SUBJECT: GRB 260303A: 1.3m DFOT optical upper limit DATE: 26/03/05 16:34:28 GMT FROM: Debalina Kar at ARIES <kardebalina2000(a)gmail.com> Debalina Kar, Pankaj Pawar, Anshika Gupta, Dhruv Jain and Kuntal Misra (ARIES) report: We observed the field of GRB 260303A triggered by SVOM/ECLAIRs (sb26030303, Wang et al., GCN 43901) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations began on 2026-03-03 at 14:54:29.000 UT, approximately 8.88 hours after the trigger. We obtained multiple exposures of 300 s each in the R filter . A total of 10 frames were aligned and stacked to improve the signal-to-noise ratio. In the stacked frame we do not detect any optical counterpart within the error box of SVOM/ECLAIRs (Brunet et al., GCN 43922, Wang et al., GCN 43901) as well as outside the ECLAIRs error circle as reported by Xin et al. (GCN 43916) and (Schneider et al., GCN 43902). This is consistent with the non-detection in the J band reported by Mo et al. (GCN 43915). We derive the following 3-sigma upper limit from the stacked image: Date (UT) Start Time T_start–T0 (hr) Filter Exposure Magnitude ---------------------------------------------------------------------------------- 2026-03-03 14:54:29 ~8.88 R 300 s × 10 > 20.29 The reported magnitude is not corrected for Galactic extinction. Photometric calibration was performed using standard stars from the USNO-B1.0 catalogue. View this GCN Circular online at https://gcn.nasa.gov/circulars/43925. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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