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[vsnet-grb-info 42275] EP260329a: COLIBRÍ optical upper limit
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44154 SUBJECT: EP260329a: COLIBRÍ optical upper limit DATE: 26/03/30 07:26:18 GMT FROM: Camila Angulo Valdez at UNAM <camiangulo(a)astro.unam.mx> Camila Angulo (UNAM), Stéphane Basa (UAR Pytheas), Rosa L. Becerra (UNAM), William H. Lee (UNAM), Alan M. Watson (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), 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), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP260329a (Yang et al., GCN Circ. 44141) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-29 11:41:47 to 12:23:53 UTC (from 8.19 to 8.89 hours after the trigger, starting 1.3 hours after the notice) and obtained 29 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded 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 image, we do not detect any new source at the position of the two EP/FXT sources (assuming a 10″ error) reported by Yang et al. (GCN Circ. 44153), as well as at the position of the optical counterpart reported by NOT (He et al., GCN Circ. 44152), down to the following 3-sigma limit: r > 22.45 z > 21.06 Our non-detection, together with the FXT observation, is consistent with the candidate reported by NOT (He et al., GCN Circ. 44152) being a plausible optical counterpart of EP260329A. 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/44154. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42274] EP260329a: EP-FXT follow up observation
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44153 SUBJECT: EP260329a: EP-FXT follow up observation DATE: 26/03/30 06:40:23 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Guojiong Yang (NAO, CAS), F.-F. Song (YNAO, CAS), Wei Chen, Yuan Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260329a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Yang et al., GCN 44141). Early optical follow-up observations reported only upper limits (Sankar et al., GCN 44145). A possible uncatalogued optical counterpart was reported by later optical observations (He et al., GCN 44152). EP-FXT performed a follow-up observation starting at 2026-03-29T14:47:27 UTC, approximately 11.3 hours after the WXT trigger, with a total exposure time of 5934 s. Two uncataloged sources are detected within the WXT error circle. Preliminary analysis on these sources is automatically conducted, and the details are listed as follows. EPF_J002151.2+822924 RA (J2000): 5.4918, Dec (J2000): 82.4881 Flux: 4.9e-14 erg/s/cm^2 (observed, 0.5-10 keV) Flux_err: 1.3e-14 erg/s/cm^2 (1 sigma) EPF_J002212.3+823200 RA (J2000): 5.5758 Dec (J2000): 82.5335 Flux: 5.3e-14 erg/s/cm^2 (observed, 0.5-10 keV) Flux_err: 1.5e-14 erg/s/cm^2 (1 sigma) We note that the position of EPF_J002151.2+822924 is consistent with the optical uncatalogued counterpart reported by GCN 44152 (He et al.) 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/44153. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42273] EP260329a: NOT optical counterpart candidate
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44152 SUBJECT: EP260329a: NOT optical counterpart candidate DATE: 26/03/30 06:09:01 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He, S.Q. Jiang, Z.P. Zhu, J. An, X. Liu, D. Xu (NAOC), S.Y. Fu (HUST), J. P. U. Fynbo (DAWN/NBI), K. Valeckas (NOT) report: We observed the field of EP260329a detected by Einstein Probe (EP), using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. We obtained 3 x 300 s frames in the Sloan r-band. An uncatalogued optical source is detected within the EP-WXT error circle (Yang et al., GCN 44141) at coordinates R.A. (J2000) = 5.4770 (deg) Dec. (J2000) = 82.4894 (deg) with an uncertainty of ~ 0.5 arcsec. The source has r ~ 21.6 mag (AB) at a median time of 45 mins after the EP trigger, calibrated with nearby PanSTARRS1-dr2 catalog and not corrected for Galactic extinction. No source is present at the above position in PanSTARRS down to a 5-sigma limit of r ~22.3 mag. No NEO object would be at the above position at the NOT observational time by checking MPC. We thus think the source could be the optical counterpart of EP260329a. View this GCN Circular online at https://gcn.nasa.gov/circulars/44152. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42272] GRB 260330A: Fermi GBM Final Real-time Localization
by GCN Circulars 30 Mar '26

30 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44151 SUBJECT: GRB 260330A: Fermi GBM Final Real-time Localization DATE: 26/03/30 03:48:27 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 03:40:19 UT on 30 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260330A (trigger 796534824.63566 / 260330153). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 93.6, Dec = -44.6 (J2000 degrees, equivalent to J2000 06h 14m, -44d 36'), with a statistical uncertainty of 2.8 degrees. The angle from the Fermi LAT boresight is 63.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260330153/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260330153/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260330153/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44151. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42271] EP260329b: Global MASTER-Net observations report
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44150 SUBJECT: EP260329b: Global MASTER-Net observations report DATE: 26/03/29 23:45:30 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-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP260329b ( EP Team et al., GCN 44142) errorbox 41172 sec after notice time and 46747 sec after trigger time at 2026-03-29 23:35:07 UT, with upper limit up to 17.2 mag. Observations started at twilight. The observations began at zenith distance = 75 deg. The sun altitude is -13.8 deg. The galactic latitude b = 65 deg., longitude l = 277 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3219325 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 46777 | 2026-03-29 23:35:07 | MASTER-OAFA | (12h 05m 25.47s , +04d 20m 43.8s) | C | 60 | 16.4 | 46837 | 2026-03-29 23:35:07 | MASTER-OAFA | (12h 05m 25.47s , +04d 20m 43.7s) | C | 180 | 17.2 | Coadd 46852 | 2026-03-29 23:36:21 | MASTER-OAFA | (12h 05m 25.71s , +04d 21m 49.7s) | C | 60 | 16.6 | 46927 | 2026-03-29 23:37:36 | MASTER-OAFA | (12h 05m 33.10s , +04d 20m 55.0s) | C | 60 | 16.7 | 47124 | 2026-03-29 23:40:54 | MASTER-OAFA | (12h 05m 30.36s , +04d 21m 51.8s) | C | 60 | 16.9 | 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/44150. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42270] Fermi trigger No 796485221: Global MASTER-Net observations report
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44149 SUBJECT: Fermi trigger No 796485221: Global MASTER-Net observations report DATE: 26/03/29 23:31:14 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-SAAO robotic telescope [1] located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB260329.58 (trigger No 796485221,19h 47m 48.00s , -55d 55m 12.0s, R=7.59) errorbox 33703 sec after notice time and 33736 sec after trigger time at 2026-03-29 23:15:52 UT, with upper limit up to 18.9 mag. The observations began at zenith distance = 69 deg. The sun altitude is -60.5 deg. The galactic latitude b = -30 deg., longitude l = 342 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3219478 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 33796 | 2026-03-29 23:15:52 | MASTER-SAAO | (19h 42m 30.66s , -55d 55m 47.3s) | C | 120 | 18.7 | 33796 | 2026-03-29 23:15:52 | MASTER-SAAO | (19h 45m 45.76s , -56d 11m 20.9s) | C | 120 | 18.7 | 33948 | 2026-03-29 23:18:24 | MASTER-SAAO | (19h 42m 36.60s , -55d 56m 48.4s) | C | 120 | 18.8 | 33948 | 2026-03-29 23:18:24 | MASTER-SAAO | (19h 45m 51.90s , -56d 12m 19.9s) | C | 120 | 18.8 | 34100 | 2026-03-29 23:20:56 | MASTER-SAAO | (19h 17m 26.52s , -55d 57m 25.2s) | C | 120 | 18.6 | 34100 | 2026-03-29 23:20:56 | MASTER-SAAO | (19h 20m 42.35s , -56d 12m 54.8s) | C | 120 | 18.9 | 34252 | 2026-03-29 23:23:28 | MASTER-SAAO | (19h 17m 32.63s , -55d 57m 06.4s) | C | 120 | 18.6 | 34252 | 2026-03-29 23:23:28 | MASTER-SAAO | (19h 20m 48.48s , -56d 12m 34.7s) | C | 120 | 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/44149. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42269] GRB 260327A: Insight-HXMT/HE detection
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44148 SUBJECT: GRB 260327A: Insight-HXMT/HE detection DATE: 26/03/29 15:18:30 GMT FROM: xueyuan zao <zaoxueyuan(a)gmail.com> Xue-Yuan Zao, Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng (IHEP) report on behalf of the Insight-HXMT team: At 2026-03-27T02:28:50.350 (T0), Insight-HXMT/HE detected a long burst, GRB 260327A, which is also detected by AstroSat CZTI (A. Arya et. al., GCN #44130) and Konus-Wind (IPN notice). The Insight-HXMT/HE light curve mainly consists of two emission episodes with a total duration (T90) of 98 +14/-6 s. The 1s peak rate, measured from T0-1 s, is 2435 cnts/sec. Insight-HXMT/HE detected a total of 22378 counts from this burst. The Insight-HXMT /HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb260327A.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/44148. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42268] EP260329b: Optical follow-up with Kinder observations
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44147 SUBJECT: EP260329b: Optical follow-up with Kinder observations DATE: 26/03/29 14:47:29 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> A. Aryan, A. Sankar.K, T.-W. Chen, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), S. J. Smartt, J. Gillanders (both Oxford), M. Nicholl (QUB), M.-H. Lee, A. Dutta, Y.-H. Lee, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, H.-C. Lin, W.-J. Hou, H.-Y. Hsiao, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), Y. J. Yang (NYUAD), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Fulton, K. W. Smith, C. Angus, A. Aamer (all QUB), T. Moore (STScI), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP260329b (Song et al., GCN 44142) 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 r-band started at 12:01 UTC on 29th of March 2026 (MJD 61128.501), 1.42 hr after the EP-WXT detection. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. Our images were strongly affected by moonlight, and are therefore relatively shallow. In the stacked r-band image at t_mid - t_0 =1.80 hr, we did detect a very faint source (SNR 3.4) at the reported position of the optical counterpart candidate (Wenxiong et al., GCN 44139; Zhu et al., GCN 44140; and Eyles-Ferris et al., GCN 44144). Moreover, we further used AutoPhOT to perform PSF photometry. The details of the observations and measured photometry/the 3-sigma upper limit (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | Med. Airmass LOT | r | 61128.501 | 1.42 | 300 * 8 | 20.19+/-0.14 |1".71 | 1.54 LOT | g | 61128.536 | 2.26 | 300 * 7 | >19.9 |1".50 | 1.34 Our observations confirm the rapidly fading nature of the optical counterpart candidate. The presented magnitudes are calibrated using the field stars from ATLAS-RefCat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105). The reported magnitudes are not corrected for an expected galactic extinction of A_g = 0.06 mag and A_r = 0.04, in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission 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/44147. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42267] EP 260329b: COLIBRÍ optical observations
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44146 SUBJECT: EP 260329b: COLIBRÍ optical observations DATE: 26/03/29 14:45:02 GMT FROM: Francesco at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work(a)gmail.com> Francesco Magnani (CPPM), Noémie Globus (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), 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), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), 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 EP 260329b (Song et al., GCN Circ. 44142) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-29 11:21 to 11:41 UTC (from 45.7 to 65.0 minutes after the trigger) and obtained 16 minutes of exposure in the r and z filters, respectively. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). 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 detected the optical counterpart reported by LCO (Li et al., GCN Circ. 44139, Eyles-Ferris et al., GCN Circ. 44144) and TRT (Zhu et al., GCN Circ 44140), at preliminary magnitudes of: r = 18.85 +/- 0.08 z = 18.53 +/- 0.13 Further observations are planned. 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/44146. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42266] EP260329a: Optical upper limit with Kinder observations
by GCN Circulars 29 Mar '26

29 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44145 SUBJECT: EP260329a: Optical upper limit with Kinder observations DATE: 26/03/29 14:40:17 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> A. Sankar.K, A. Aryan, T.-W. Chen, C.-S. Lin (all NCU), S. Yang (HNAS), A. K. H. Kong (NTHU), S. J. Smartt, J. Gillanders (both Oxford), M. Nicholl (QUB), M.-H. Lee, A. Dutta, Y.-H. Lee, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, H.-C. Lin, W.-J. Hou, H.-Y. Hsiao, J.-K. Guo (all NCU), Y. J. Yang (NYUAD), Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz M. Huber, K. Chambers (all IfA, Hawaii) report: We observed the field of the EP260329a (Yang et al., GCN 44141) using the 40cm SLT 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 SLT epoch of observations in g-band started at 11:03 UTC on 29th of March 2026 (MJD 61128.460), 7.54 hr after the EP-WXT detection. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We used the Python-based AutoPhOT package (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction of the Pan-STARRS1 3Pi archive image (Chambers et al., 2016, arXiv:1612.05560) using the 'SFFT' (Hu et al., 2022, ApJ, 936, 157) algorithm. Neither in the stacked nor in the difference image did we detect any signature of a new or uncatalogued source within the EP-WXT localization circle (3.2'). Moreover, we further used AutoPhOT to perform PSF photometry. The details of the observations and the 3-sigma upper limit (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude| avg. Seeing | Med. Airmass SLT | r | 61128.460 | 7.54 | 300 * 9 | >21.1 | 2".36 | 3.02 The presented magnitudes are calibrated using the field stars from the PanSTARRS catalog. The reported upper limit is not corrected for an expected galactic extinction of A_r = 0.44 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission 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/44145. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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