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[vsnet-grb-info 42321] GRB 260402B: GECAM-B observation
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44200 SUBJECT: GRB 260402B: GECAM-B observation DATE: 26/04/03 08:53:36 GMT FROM: zhangjinpeng(a)ihep.ac.cn Jin-Peng Zhang, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B ground search was triggered by GRB 260402B, at 2026-04-02T22:57:17.100 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44193). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of one pulse, with a duration (T90) of 2.0 +0.5/-1.0 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260402B.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/44200. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42320] EP260402a/GRB 260402A: Jinshan near-infrared upper limit
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44199 SUBJECT: EP260402a/GRB 260402A: Jinshan near-infrared upper limit DATE: 26/04/03 08:06:20 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L. B. He, X. Liu (NAOC), S.Y. Fu, A.D. Zhu, L. Lei, H.Z. Wu, W.H. Lei, Y.C. Zou (HUST), J. An, S.Q. Jiang, Z.P. Zhu, D. Xu (NAOC), J.Z. Liu (XAO), Z.N. Dong, B. Ma (SYU) report: We observed the field of EP260402a/GRB 260402A detected by EP (Zhao et al., GCN 44186) and SVOM (Tan et al., GCN 44181; Gotz et al., GCN 44182), using the JinShan 100C telescope located at Altay, Xinjiang, China. Observation started at 2026-04-02 14:51:48 UT, i.e., 4.36 hrs post-burst, and a series of J-band frames were obtained. No new source is detected in the stacked image within the EP/FXT error circle, down to a 5-sigma limiting magnitude of J ~ 17.3 (Vega), calibrated with 2MASS stars in the field. This upper limit is consistent with that reported at WINTER (Schneider et al., GCN 44192). We acknowledge the excellent support from T.Q. Chen and J.F. Zhang for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44199. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42319] GRB 260402C: NuSTAR detection of prompt emission
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44198 SUBJECT: GRB 260402C: NuSTAR detection of prompt emission DATE: 26/04/03 07:28:44 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 260402C in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm, triggered at 2026-04-02 13:13:00 UTC, shows a detection of GRB 260402C, consistent with AstroSat/CZTI (Tembhurnikar et al., GCN Circ. 44197). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a ~10-s burst consistent with the first bright peak in the AstroSat/CZTI light curve, with marginal evidence of a second peak consistent with the CZTI light curve. The peak count rate is ~2000-cps with a baseline rate of ~1000-cps during this time period. We do see marginal evidence in the signal above 100 keV in the CZT detectors. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260402C/ Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/44198. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42318] GRB 260402C: AstroSat CZTI detection of a long burst
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44197 SUBJECT: GRB 260402C: AstroSat CZTI detection of a long burst DATE: 26/04/03 07:19:42 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (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-duration GRB 260402C. The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-04-02 13:13:05.78 UTC. The measured peak count rate associated with the burst is 254 (+34, -26) counts/s above the background in the combined data of three quadrants (out of four), with a total of 1786 (+230, -307) counts. The local mean background count rate was 210 (+2, -3) counts/s. Using cumulative rates, we measure a T90 of 27 (+4, -3) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-04-02 13:13:05.08 UTC. The measured peak count rate associated with the burst is 570 (+82, -42) counts/s above the background in the combined data of all quadrants, with a total of 3647 (+569, -635) counts. The local mean background count rate was 1405 (+6, -7) counts/s. We measure a T90 of 25 (+4, -1) s from the cumulative Veto light curve. 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/44197. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42317] EP260324A / AT 2026hir: COLIBRÍ optical observations
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44196 SUBJECT: EP260324A / AT 2026hir: COLIBRÍ optical observations DATE: 26/04/03 05:33:45 GMT FROM: globus(a)astro.unam.mx Noémie Globus (UNAM), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), 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), 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 observed AT2026hir/ZTF26aapviim, the optical counterpart (Anumarlapudi et al., GCN Circ. 44120, Stein et al., GCN Circ. 44194) associated to EP260324a (Wu et al., Atel #17728) with the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-03 03:09:08 to 03:26:20 UTC (from 9.95 to 9.96 days after the discovery time reported in the TNS entry and from 9.84 to 9.85 days after the EP trigger) and obtained 5 minutes of exposure in the g, r, i filters, and 15 minutes of simultaneous exposure in the z filter. In the stacked image, we detect the optical counterpart. 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. The preliminary PSF magnitudes revealed after performing image subtraction using PanSTARRS DR1 as template are: r = 17.73 +/- 0.01, z = 18.26 +/- 0.02. 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/44196. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42316] GRB 260403A: Fermi GBM Final Real-time Localization
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44195 SUBJECT: GRB 260403A: Fermi GBM Final Real-time Localization DATE: 26/04/03 02:41:58 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 02:31:27 UT on 3 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260403A (trigger 796876292.704364 / 260403105). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 236.2, Dec = -31.0 (J2000 degrees, equivalent to J2000 15h 44m, -31d 00'), with a statistical uncertainty of 5.0 degrees. The angle from the Fermi LAT boresight is 86.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260403105/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260403105/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260403105/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44195. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42315] EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
by GCN Circulars 03 Apr '26

03 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44194 SUBJECT: EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph DATE: 26/04/03 00:03:49 GMT FROM: Robert David Stein at JSI <rdstein(a)umd.edu> Robert Stein (UMD/JSI/NASA GSFC), Kaustav Das (Caltech), Christoffer Fremling (Caltech), Tomas Ahumada (NOIRLab), Akash Anumarlapudi (UNC CH), Ryan Chornock (UC Berkeley),Michael C. Davis (UMN), K-Ryan Hinds (Caltech), Mansi Kasliwal (Caltech), Jillian Rastinejad (UMD), Gokul Srinivasaragavan (UMD) and Yuhan Yao (UC Berkeley) report, on behalf of the ZTF collaboration: We observed AT2026hir/ZTF26aapviim, the optical counterpart (Anumarlapudi et al, GCN #44120) to EP260324A (Wu et al., ATEL #17728), with the Next Generation Palomar Spectrograph (NGPS; AstroNote 2024-340) on the Palomar 5.1m Hale Telescope (P200). Our observations began on 2026-03-27T03:51:37 (~3 days after the EP trigger), and data were reduced using the standard NGPS pipeline. The spectrum was extremely blue, as also noted by Zhu et al. (Astronote #2026-87). From our spectrum, in addition to the continuum, we see an excess that would be consistent with broad He II with a velocity of ~15000 km / s. However, we have not performed host galaxy subtraction, and we caution that the SNR is insufficient to be certain whether this broad feature is real. In any case, given the nuclear location (GCN #44120) and blue spectrum which is either featureless or has broad He, our observations would be consistent with a TDE-F or TDE-He classification for this source. However, we plan for and encourage additional multi-wavelength observations to secure the classification. The transient is bright (mg=17.3 in the latest ZTF data), so remains accessible to a wide variety of ground-based telescopes. View this GCN Circular online at https://gcn.nasa.gov/circulars/44194. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42314] GRB 260402B: Fermi GBM Final Real-time Localization
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44193 SUBJECT: GRB 260402B: Fermi GBM Final Real-time Localization DATE: 26/04/02 23:07:38 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 22:57:17 UT on 2 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260402B (trigger 796863442.54282 / 260402956). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 238.4, Dec = 0.2 (J2000 degrees, equivalent to J2000 15h 53m, 0d 12'), with a statistical uncertainty of 11.4 degrees. The angle from the Fermi LAT boresight is 72.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260402956/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260402956/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260402956/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44193. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42313] GRB 260402A: WINTER J-band upper limit
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44192 SUBJECT: GRB 260402A: WINTER J-band upper limit DATE: 26/04/02 18:08:21 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Benjamin Schneider (LAM), Geoffrey Mo (Caltech/Carnegie), Robert Stein (UMD), Viraj Karambelkar (Columbia), Tomas Ahumada (NOIRLab), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 260402A detected by SVOM/ECLAIRs (Tan et al., GCN 44181) and EP/WXT (Zhao et al., GCN Circ. 44186) in the near-infrared with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations started on 2026-04-02 at 10:58:52 UT (28.58 min after the trigger) and consisted of 30 exposures of 120 s in the J-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) The photometric calibration was performed using nearby stars from the 2MASS catalog. The magnitude 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 FXT position (Zhao et al., GCN Circ. 44186) or MXT position (Gotz et al., GCN Circ. 44182) and derive the following 5-sigma upper limit: J > 18.9 Our upper limit is consistent with previously reported optical upper limits from Antier et al. (GCN Circ. 44183), Carrasco et al. (GCN Circ. 44184), Freeberg et al. (GCN Circ. 44185), Wu et al. (GCN Circ. 44189), Li et al. (GCN Circ. 44190), and Vijaykumar et al. (GCN Circ. 44191). 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/44192. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42312] GRB260402A: GROWTH-India Telescope optical upper limit
by GCN Circulars 02 Apr '26

02 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44191 SUBJECT: GRB260402A: GROWTH-India Telescope optical upper limit DATE: 26/04/02 17:45:27 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> V. Vijaykumar, A. Khade, R. Arya, V. Swain, S. Patil, A.P. Saikia, T. Mohan, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and R. Norbu (IAO) report on behalf of the GIT team: We observed the field of GRB260402A detected by SVOM/ECLAIRs (SVOM, GCN 44181), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-04-02 14:10:35 (UTC), i.e., 3.65 hours after the trigger, and obtained multiple exposures in the r' filter. We do not detect any transient in our image within the uncertainty region of source position reported by ECLAIRs and MXT (Tan et al., GCN Circ. 44181, Gotz et al., GCN Circ.44182). The photometric upper limit is as follows: | MJD (mid) | Filter | tmid-t0 (hours) | Exposure Time (sec) | Magnitude (AB) | | ------------ | ------ | -------------- | ------------------- | -------------- | | 61132.590| r' | 3.92 | 5x360 | 20.5 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our magnitude for the optical counterpart is consistent with other optical observations (GCN 44190 Li et al.; GCN 44189 Wu et al.; GCN 44185 Freeberg et al.; GCN 44184 Carrasco et al.; GCN 44183 Antier et al.) 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/44191. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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