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[vsnet-grb-info 42180] GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44059 SUBJECT: GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening DATE: 26/03/20 20:08:08 GMT FROM: Rosa L. Becerra at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Rosa L. Becerra (UNAM), Camila Angulo (UNAM), Sarah Antier (IJCLAB), Noémie Globus (UNAM), Enrique Moreno Méndez (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Antonio de Ugarte Postigo (LAM), and Benjamin Schneider (LAM) report: We reimaged the field of AT 2026fgk, first reported by Hinds et al. (AstroNote 2026-65) and followed-up by a large number of facilities across multiple wavelengths (GCNs Circ. 43951, 43954, 43958, 43974, 43975, 43977, 43978, 43979, 43980, 43981, 43984, 43986, 43990, 43991, 43993, 43994, 43996, 44000, 44001, 44002, 44003, 44004, 44005, 44006, 44020, 44021, 44022, 44043, 44044, 44045, 44051, 44053, 44057, 44058), as a possible counterpart to 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 several epochs from 2026-03-20 03:35 to 11:21 UTC (from 9.94 to 10.27 days after the GRB trigger) 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. Compared with the photometry acquired on 2026-03-19, we observe a rebrightening in all three filters throughout the night, with a temporal index of alpha > 1.5. We encourage extended follow-up observations. 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/44059. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42179] GRB 260310A/AT2026fgk: LBT near-infrared observations
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44058 SUBJECT: GRB 260310A/AT2026fgk: LBT near-infrared observations DATE: 26/03/20 17:40:46 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva(a)uniroma1.it> Niccolo’ Passaleva, Yu-Han Yang, Narges Shahamt, Eleonora Troja (U Rome) report on behalf of the ERC BHianca team: Following the detection of GRB 260310A by Fermi/GBM and AstroSat CZTI (Fermi GBM team, GCN 43951,43975; AstroSat CZTI collaboration, GCN 43958), we observed the likely counterpart AT2026fgk (discovered by GOTO; O’Neill et al. 2026, TNS Discovery Report 294132) in J and K filters with the LUCI near-infrared imager mounted on the Large Binocular Telescope (LBT). Observations started at 2026-03-16T08:07:32 (~ 6.2 d after the GBM trigger) with an average airmass of 1.3. We detect the source with a preliminary magnitude of J~18.03 AB mag, calibrated using nearby stars from the 2MASS catalog (Skrutskie et al. 2006), uncorrected for Galactic extinction. Compared with previous near-infrared observations (Li et al., GCN 43993; Stein et al., GCN 43996; Brivio et al., GCN 44004), our measurement is consistent with a fading slope of 0.7. We acknowledge excellent support from the LBTO and LBT-INAF staff. View this GCN Circular online at https://gcn.nasa.gov/circulars/44058. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42178] NOEMA Detection of GRB 260310A
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44057 SUBJECT: NOEMA Detection of GRB 260310A DATE: 26/03/20 14:52:58 GMT FROM: Anna Y Q Ho at Cornell University <ayh24(a)cornell.edu> Anna Y. Q. Ho (Cornell), Michael Bremer (IRAM), Genevieve Schroeder (Cornell) report on behalf of a larger collaboration: On UT 2026 March 20 the NOrthern Extended Millimeter Array (NOEMA) observed the position of GRB 260310A / AT2026fgk (GCN 43951, 43958, 43974), a nearby (z=0.153; GCN 43977) gamma-ray burst with bright radio emission at cm wavelengths (GCN 44005, 44045). Observations were obtained in the new dual-band mode (100+230 GHz) as well as in Band 2 (150 GHz). With self-calibration, we measure a preliminary flux density of 17 mJy at 100 GHz, corresponding to a luminosity of 10^42 erg/s, typical for GRB afterglows at this epoch. Further observations are planned. We thank the NOEMA staff for rapidly approving and scheduling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44057. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42177] EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44056 SUBJECT: EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7 DATE: 26/03/20 10:46:01 GMT FROM: I. Perez-Garcia at Instituto de Astrofísica de Andalucía <ipg(a)iaa.es> I. Perez-Garcia, S.-Y. Wu, A. J. Castro-Tirado, E. J. Fernandez-Garcia, M.D. Caballero-Garcia, S. Guziy, G. Garcia-Segura, R. Sanchez-Ramirez (IAA-CSIC), Y.-D. Hu (INAF-OAB), C. Perez del Pulgar, A. Castellon, I. Carrasco (Univ. de Malaga), L. Hernandez-Garcia (Univ. de Valparaiso), M. Gritsevich (Univ. of Helsinki), D.-R. Xiong (Yunnan Observatories of CAS), B.-B. Zhang (Nanjing Univ.) and A. Maury (Space, San Pedro de Atacama), on behalf of a larger collaboration, report: Following the detection of EP-WXT trigger 01709258989 (Zhou et al. GCN 44054), the 0.6m BOOTES-7 robotic telescope at San Pedro de Atacama (Chile) responded to the alert on Mar. 20, 02:39 UT (i.e. 6-min after trigger, 1 min after notification). Within the reported EP-FXT error circle we find the star 1RXS J073101.9+460030 decreasing 0.9, 0.5 and 0.4 mag in g, r and i filters during a 20 min time interval, confirming EP-WXT trigger 01709258989 as due to a stellar flare. We thank the staff at San Pedro de Atacama Celestial Observations for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/44056. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42176] GRB 260318A: SVOM/GRM observation
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44055 SUBJECT: GRB 260318A: SVOM/GRM observation DATE: 26/03/20 06:30:30 GMT FROM: yzh807926(a)163.com SVOM/GRM team: Zheng-Hang Yu, Chao Zheng, Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Hui Yang (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 260318A (SVOM trigger reference: sb26031805) at 2026-03-18T22:36:00.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44049). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a precursor followed by a main episode with two peaks a T90 of 28.5 +7.0/-8.0 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260318A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 303.6, DEC= 57.0 GCN#44049), is located at about 164 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-16 to T0+10 s is best fitted by a power law function. The power law index is -2.55 +0.17/-0.16. The event fluence (10-1000 keV) in this time interval is (6.72 +1.45/-1.02)E-05 erg/cm^2. 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: Zheng-Hang Yu(IHEP)(zhyu(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44055. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42175] The EP-WXT trigger 01709258989 is likely a flaring star
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44054 SUBJECT: The EP-WXT trigger 01709258989 is likely a flaring star DATE: 26/03/20 03:33:53 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H. Zhou, Y. Wang, Q. J. Huang (PMO, CAS), J. P. Chen (SYSU), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709258989 at the time of 2026-03-20T02:33:39 UTC, EP-FXT performed an automatic follow-up observation, and detected a source at RA: 112.7520 deg, Dec: 46.0075 deg, is likely a stellar flare associated with 1RXS J073101.9+460030. The estimated flux of the flare is around 1.0 x 10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 3.6 x 10^31 erg/s. 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/44054. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42174] GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
by GCN Circulars 20 Mar '26

20 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44053 SUBJECT: GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90 DATE: 26/03/20 01:38:39 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> P. Minaev (IKI) , A. Pozanenko (IKI) on behalf of GRB follow-up team We analyzed GRB 260310A (Hamburg et al., GCN 43975; Salunke et al., GCN 43958; Atteia et al., GCN 43981) using publicly available data of GBM/Fermi. The burst consists of several emission episodes with a total duration of T_90 = 86 s. Time integrated energy spectrum, constructed in the time interval (-4, 70) s since GBM trigger, is best described by Band model with E_p = 175 keV and fluence F = 1.74e-5 erg cm^-2 in 1 keV - 10 MeV range. Using z = 0.153 (Hinds et al., GCN 43977; de Ugarte Postigo et al., GCN 43984) we obtain E_iso = 9.8e50 erg. GRB 260310A is placed above the correlation fit for type II (long) bursts on Ep,i – Eiso diagram, as mentioned in (Atteia et al., GCN 43981), but it is inside 2 sigma correlation regions for both type I (short) and type II (long) bursts, therefore we cannot consider it as a clear outlier. Indeed, at the EH – T_90,i diagram (see [1-2] for details) GRB 260310A is well classified as type II (long) burst. The Ep,i – Eiso and EH - T90,i diagrams can be found at https://heaiki.ru/lvc/GRB260310A/ [1] - Minaev et al., MNRAS, 492, 1919, 2020 [2] - Minaev et al., Astronomy Letters, 46, 9, 573, 2020 View this GCN Circular online at https://gcn.nasa.gov/circulars/44053. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42173] GRB 260318A: GECAM-B observation
by GCN Circulars 19 Mar '26

19 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44052 SUBJECT: GRB 260318A: GECAM-B observation DATE: 26/03/19 15:47:49 GMT FROM: yzh807926(a)163.com Zheng-Hang Yu, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 260318A, at 2026-03-18T22:35:52.600 UTC (denoted as T0), which is also detected by Fermi/GBM ((Fermi GBM team, GCN #44049). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 19.5 +3.0/-2.5 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260318A.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/44052. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42172] GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
by GCN Circulars 19 Mar '26

19 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44051 SUBJECT: GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT DATE: 26/03/19 14:57:05 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180(a)gmail.com> Anshika Gupta, Kumar Pranshu, Dhruv Jain, Debalina Kar, Pankaj Pawar, and Kuntal Misra (ARIES) report: We observed the field of GRB260310A/AT2026fgk detected by Fermi/GBM (Fermi GBM team, GCN 43951) and AstroSat(Salunke et al., GCN 43958) 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 2026-03-17 at 20:33:36.00 UT, i.e., ~ 7.65 days after the Fermi/GBM trigger. We have taken multiple frames with an exposure time of 300s in the I filter. We stacked the images after the alignment. We detect an optical afterglow in our stacked image. We obtain the following preliminary magnitude in the stacked image: Date Start_UT T_start-T0 (days) Filter Exp time (s) Magnitude ================================================================ 2026-03-17 20:33:36.00 ~7.65 I 300s*3 18.01 +/-0.02 The optical detection of the burst is consistent with Lipunov et al., GCN 43954; Konno et al., GCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979, 44000; Moreno Méndez et al., GCN 43980; Becerra et al., GCN 43991; Li et al., GCN 43993; Stein et al., GCN 43996; Watson et al., GCN 44001; Lai et al., GCN 44002; Izzo et al., GCN 44003; Brivio et al., GCN 44004; Moskvitin et al., GCN 44006; Romanov, GCN 44020; Brosio et al., GCN 44021; Pawar et al., GCN 44022; Belkin et al., GCN 44043; Li et al., GCN 44044. The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the USNO-B1.0 catalogue. View this GCN Circular online at https://gcn.nasa.gov/circulars/44051. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42171] Fermi GRB 260318A: Global MASTER-Net observations report
by GCN Circulars 18 Mar '26

18 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44050 SUBJECT: Fermi GRB 260318A: Global MASTER-Net observations report DATE: 26/03/18 23:00:55 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 260318A ( Fermi GBM team, GCN 44049) errorbox 572 sec after notice time and 596 sec after trigger time at 2026-03-18 22:45:44 UT, with upper limit up to 18.1 mag. The observations began at zenith distance = 62 deg. The sun altitude is -43.5 deg. The galactic latitude b = 12 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=3194853 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 657 | 2026-03-18 22:45:44 | MASTER-Kislovodsk | (20h 14m 11.39s , +56d 41m 32.7s) | P| | 120 | 17.6 | 797 | 2026-03-18 22:48:04 | MASTER-Kislovodsk | (20h 14m 11.18s , +56d 41m 32.8s) | P| | 120 | 17.4 | 938 | 2026-03-18 22:50:25 | MASTER-Kislovodsk | (20h 14m 11.08s , +56d 41m 36.1s) | P| | 120 | 18.1 | 1078 | 2026-03-18 22:52:45 | MASTER-Kislovodsk | (20h 14m 11.06s , +56d 41m 40.9s) | P| | 120 | 18.0 | 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/44050. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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