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[vsnet-grb-info 42392] GRB 260411A: SVOM/GRM observation
by GCN Circulars 11 Apr '26

11 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44270 SUBJECT: GRB 260411A: SVOM/GRM observation DATE: 26/04/11 17:35:00 GMT FROM: xueyuan zao <zaoxueyuan(a)gmail.com> SVOM/GRM team: Xue-Yuan Zao, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Daigne (IAP) Report on behalf of the SVOM team: SVOM/GRM detected the burst GRB 260411A at 2026-04-11T06:36:28.200 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44261). With the event-by-event data downloaded through the X-band ground station, we conducted the standard analysis pipeline of GRB 260411A. The GRM light curve shows that this burst consists of multiple pulses with a T90 of 2.0 +3.2/-1.6 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here： https://www.bursthub.cn//admin/static/svgrb260411A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 153.6, DEC=12.0, GCN#44261), is located at about 69.8 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. 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/GRM point of contact for this burst is: Xue-Yuan Zao (IHEP) (zaoxy(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44270. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42391] GRB 260407B: SVOM/GRM detection of a possible magnetar X-ray burst
by GCN Circulars 11 Apr '26

11 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44269 SUBJECT: GRB 260407B: SVOM/GRM detection of a possible magnetar X-ray burst DATE: 26/04/11 16:25:49 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Tais Maiolino (LUPM) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a bright short burst GRB 260407B (SVOM trigger reference: sb26040702) at 2026-04-07T10:58:55.900 UTC (T0). ECLAIRs was not collecting data at the time of this burst. With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a narrow spike with a T90 of 0.11 +0.06/-0.03 s in the 15-5000 keV band. All the signal is detected lower than 100 keV. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260407B.png We note that both the soft spectrum and the short duration suggest a magnetar X-ray burst. 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: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44269. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42390] GRB 260411B: SVOM/GRM observation of a long burst
by GCN Circulars 11 Apr '26

11 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44268 SUBJECT: GRB 260411B: SVOM/GRM observation of a long burst DATE: 26/04/11 16:24:34 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Chao Zheng, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Daigne (IAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight GRB 260411B (SVOM trigger reference: sb26041103) at 2026-04-11T08:04:37.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN#44262). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of two emission episodes with a T90 of 16.2 +2.1/-1.4 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260411B.png In addition, the position of this burst, as determined by GOTO (RA= 85.567893 deg, DEC= 1.984983 deg, GCN#44265), is located at about 81 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-2.5 to T0+16.4 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.81 +0.09/-0.09 and the cutoff energy, parameterized as Epeak, is 385 +44/-37 keV. The event fluence (10-1000 keV) in this time interval is (2.37 +0.09/-0.09)E-05 erg/cm^2. The 1s peak spectrum, measured from T0+6.7 to T0+7.7 s, is also best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.41 +0.09/-0.09 and the cutoff energy, parameterized as Epeak, is 331 +20/-17 keV. The flux (10-1000 keV) in this time interval is (6.34 +0.20/-0.20)E-06 erg/cm^2/s. The localization of GRB 260411B in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260411B_amati.png And the localization in the 'Yonetoku' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260411B_yonetoku.png With the brightness of the prompt emission, the predicted soft X-ray afterglow [1] is shown at: https://www.bursthub.cn//admin/static/svgrb260411B_xag_pre.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: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) [1] Chen-Wei Wang et al. ApJ 997 353 https://doi.org/10.3847/1538-4357/ae2eae View this GCN Circular online at https://gcn.nasa.gov/circulars/44268. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42389] GRB 260409A: Insight-HXMT/HE detection
by GCN Circulars 11 Apr '26

11 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44267 SUBJECT: GRB 260409A: Insight-HXMT/HE detection DATE: 26/04/11 15:14:51 GMT FROM: zhangjinpeng(a)ihep.ac.cn Jin-Peng Zhang, Chen-Wei Wang, Chao Zheng, and Shao-Lin Xiong (IHEP) report on behalf of the Insight-HXMT team: At 2026-04-09T17:32:46.000 (T0), Insight-HXMT/HE detected GRB 260409A, which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44249). The Insight-HXMT/HE light curve mainly consists of several pulses with a T90 of 43 +6/-3 s. The 1 s peak rate, measured from T0+8.5 s, is 919 cnts/sec. Insight-HXMT/HE detected a total of 11547 counts from this burst. The Insight-HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb260409A.png All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the low gain mode with the energy range of about 300-3000 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/44267. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42388] GRB 260411B: Fermi GBM Detection
by GCN Circulars 11 Apr '26

11 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44266 SUBJECT: GRB 260411B: Fermi GBM Detection DATE: 26/04/11 13:46:30 GMT FROM: Utkarsh Pathak at IIT Bombay <utkarshpathak.07(a)gmail.com> U. Pathak (IITB) and R. Sonawane (IISER TVM) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 08:04:35.31 UT on 11 April 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260411B (trigger 797587480/260411337). The Fermi GBM final real-time Localization is reported in GCN 44262. An optical counterpart is also detected by GOTO (O'Neill et al. 2026 GCN 44265). The angle from the Fermi LAT boresight is 60 degrees. The GBM light curve consists of two spikes in a single emission episode, with a duration (T90) of about 33 s (50-300 keV). The time-averaged spectrum from T0-2.9 to T0+29.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.62 +/- 0.02 and the cutoff energy, parameterized as Epeak, is 348 +/- 4 keV. The event fluence (10-1000 keV) in this time interval is (2.31 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+8.3 s in the 10-1000 keV band is 21.8 +/- 0.4 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 293 +/- 3 keV, alpha = -0.54 +/- 0.05 and beta = -2.3 +/- 0.1. 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/44266. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42387] GRB 260411B: GOTO optical counterpart candidate
by GCN Circulars 11 Apr '26

11 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44265 SUBJECT: GRB 260411B: GOTO optical counterpart candidate DATE: 26/04/11 10:56:59 GMT FROM: d.s.oneill(a)bham.ac.uk D. O'Neill, R. Starling, G. Ramsay, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Gompertz, B. Godson, T. Killestein, A. Kumar, M. Pursiainen, on behalf of GOTO collaboration We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the Fermi/GBM alert GRB 260411B (Fermi GBM team, GCN #44262). Observations covering the localisation area began at 2026-04-11 08:57:53 UT (t0 +0.89h). 8 images consisting of 4 x 90s exposures were taken in the L band (400-700 nm), covering 38.5 sq deg within the 90% localisation contour. ~32.3% of the total 2D localisation probability was covered, with an average 5-sigma depth of 20.4 mag. Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks. A new optical source GOTO26dam is identified within the GBM 90% localisation region (22% contour) with co-ordinates: RA,DEC (J2000) = 85.567893, 1.984983, 05:42:16.29, +01:59:05.94 The source was detected with L = 17.55 ± 0.02 AB mag (+0.89h) and is rapidly fading with a decay index alpha ~ -2.1±0.4. We find no evidence of the source prior to the GRB trigger time in previous ATLAS observations at 2026-04-07 17:36:17.597 (t0 -86.47h) down to c > 19.37 mag using the forced photometry server (Shingles et al. 2021). GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/44265. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42386] EP260409a: Gemini/FLAMINGOS2 J-band counterpart
by GCN Circulars 11 Apr '26

11 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44264 SUBJECT: EP260409a: Gemini/FLAMINGOS2 J-band counterpart DATE: 26/04/11 09:24:03 GMT FROM: P.G. Jonker at Radboud University <p.jonker(a)astro.ru.nl> J. Quirola-Vasquez (Radboud), J. Sanchez-Sierras (Radboud), A. J. Levan (Radboud & Warwick), P. G. Jonker (Radboud), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), R. A. J. Eyles-Ferris (Leicester), F. E. Bauer (SSI and UTA), J. Chácon (PUC), B. Lemaux (Gemini) report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP260409a (Jiang et al. 2026, GCN 44242) using the FLAMINGOS2 instrument mounted on the Gemini-South telescope. Two J-band observations were obtained, one on 2026-04-09 06:52:40 (~0.27 d after the EP trigger, T0, 8x40 s exposures) and one on 2026-04-11 02:13:36 UT (i.e., ~2.08 d after T0, 16x40 s exposures). In our first epoch stacked images, we detect a candidate counterpart at coordinates (J2000): RA: 11:31:37.985 DEC: -9:20:43.00 Photometry yields J = 21.06 +/- 0.10 (Vega) calibrated against nearby stars from the 2MASS catalog (not corrected for Galactic extinction). During the second epoch, the target is no longer detected, with a 3sigma limit of J>22.65 (Vega), implying it faded significantly. No source is detected at this location in the Legacy Survey in any band, nor in archival J-, H-, and K-band images from the VISTA Hemisphere Survey. Given the lack of optical detection (Globus et al., GCN 44243; Li et al., GCN 44244) and from our Las Cumbres observations we report a 3 sigma limit of r>23.5 and z>21.5 AB mag (obtained at ~1.37 and 3.26 hours, respectively, after T0 with an exposure time of 6x300 s), this candidate counterpart is significantly red, implying EP260409a could be a high-redshift or high extinction Fast X-ray Transient. We thank the Gemini-South staff, for their rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44264. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42385] GRB 260411B: BALROG localization (Fermi Trigger 797587480 / GRB 260411337)
by GCN Circulars 11 Apr '26

11 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44263 SUBJECT: GRB 260411B: BALROG localization (Fermi Trigger 797587480 / GRB 260411337) DATE: 26/04/11 08:50:14 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 797587480 at 08:04:35 on 11 April 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) = 85.7 deg Decl.(2000.0) = 3.1 deg The 1 sigma statistical error radius is 2.5 deg. We estimate an additional systematic error of 2 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260411337/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260411337/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260411337/json View this GCN Circular online at https://gcn.nasa.gov/circulars/44263. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42384] GRB 260411B: Fermi GBM Final Real-time Localization
by GCN Circulars 11 Apr '26

11 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44262 SUBJECT: GRB 260411B: Fermi GBM Final Real-time Localization DATE: 26/04/11 08:15:05 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 08:04:35 UT on 11 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260411B (trigger 797587480.306254 / 260411337). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 83.2, Dec = 2.8 (J2000 degrees, equivalent to J2000 05h 32m, 2d 47'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 60.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260411337/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260411337/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260411337/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44262. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42383] GRB 260411A: Fermi GBM Final Real-time Localization
by GCN Circulars 11 Apr '26

11 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44261 SUBJECT: GRB 260411A: Fermi GBM Final Real-time Localization DATE: 26/04/11 06:46:58 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 SHORT GRB At 06:36:28 UT on 11 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260411A (trigger 797582193.127706 / 260411275). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 153.6, Dec = 12.0 (J2000 degrees, equivalent to J2000 10h 14m, 12d 00'), with a statistical uncertainty of 9.6 degrees. The angle from the Fermi LAT boresight is 32.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260411275/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260411275/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260411275/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44261. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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