- vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[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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