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[vsnet-grb-info 42596] GRB 260504C: SVOM/GRM observation of short GRB
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44471 SUBJECT: GRB 260504C: SVOM/GRM observation of short GRB DATE: 26/05/05 12:42:20 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: Frédéric Piron (LUPM) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a short burst GRB 260504C (SVOM trigger reference: sb26050401) at 2026-05-04T07:10:06.60 UTC (T0). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple spikes with a T90 of 0.26 +0.06/-0.08 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260504C.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) View this GCN Circular online at https://gcn.nasa.gov/circulars/44471. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42597] GRB 260504B: SVOM/GRM spectral analysis
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44470 SUBJECT: GRB 260504B: SVOM/GRM spectral analysis DATE: 26/05/05 12:31:40 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: Stéphane Schanne (CEA) Report on behalf of the SVOM team: With the event-by-event data downloaded through the X-band ground station, we conducted the standard analysis pipeline of GRB 260504B. With the localization of ECLAIRs (RA= 351.2451 deg, DEC= -80.3291 deg, GCN#44454), the time-averaged spectrum from T0-0.10 to T0+0.34 s can be fitted by a power law function with an exponential high-energy cutoff adequately. The power law index is -0.72 +0.11/-0.10 and the cutoff energy, parameterized as Epeak, is 1340 +590/-380 keV. The event fluence (10-1000 keV) in this time interval is (1.46 +0.10/-0.09)E-06 erg/cm^2. Thus GRB 260504B is consistent with Type I GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/svgrb260504B_amati.png The SVOM/GRM light curve was updated using the X-band data： https://www.bursthub.cn//admin/static/svgrb260504B.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/GRM 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/44470. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42595] GRB 260430B: AstroSat CZTI detection of a long burst
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44469 SUBJECT: GRB 260430B: AstroSat CZTI detection of a long burst DATE: 26/05/05 11:53:54 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> Harsha K. H. (IUCAA), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), A. Goyal (IITB), A. Arya (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 GRB 260430B. The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-04-30 16:04:26.34 UTC. The measured peak count rate associated with the burst is 100 (+32, -10) counts/s above the background in the combined data of three quadrants (out of four), with a total of 1436 (+290, -227) counts. The local mean background count rate was 219 (+1, -2) counts/s. Using cumulative rates, we measure a T90 of 47 (+2, -4) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-04-30 16:04:22.5 UTC. The measured peak count rate associated with the burst is 417 (+77, -26) counts/s above the background in the combined data of all quadrants, with a total of 6007 (+912, -928) counts. The local mean background count rate was 1271 (+6, -6) counts/s. We measure a T90 of 40 (+11, -6) 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 data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/515261050.0/S515261050.0_detai… 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/44469. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42594] GRB 260504B: SVOM/MXT refined analysis and potential detection
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44468 SUBJECT: GRB 260504B: SVOM/MXT refined analysis and potential detection DATE: 26/05/05 09:32:52 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> P. Maggi (ObAS), D. Götz (CEA), H. Goto (RIKEN/CEA), M. Moita (CEA), C. Plasse (UHK), F. Robinet (IJCLab), C. Van Hove (IJCLab) report of behalf of the SVOM/MXT Team: GRB 260504B (Saccardi et al. GCN 44454) was observed by SVOM/MXT after an automatic SVOM slew, starting at T_MXT = 2026-05-04T09:33:16, 117 s after trigger time T0. MXT observed for the remainder of the orbit for 730s and the subsequent 5 orbits. Using the full X-band dataset, an uncatalogued X-ray source is only detected significantly at the very start of the MXT observation. Restricting the analysis until T_MXT+60s, the position of the MXT candidate afterglow is refined to: R.A. (J2000) = 23h24m10.8s Dec (J2000) = -80d17m01s with a 90% C.L. radius of 113” (including 25 arcseconds systematic error added in quadrature). This position is compatible with the SVOM/ECLAIRS position, but not with the SVOM/MXT position using the onboard processed data, initially reported. This position supersedes the one published in the GCN 44454. The light curve exhibits a fast decay with temporal index alpha < -6 (with count rate proportional to t^alpha). At t >T_MXT + 60s the source is no longer detected by MXT. The source is below the MXT detection limit in subsequent orbits. We analysed the spectrum extracted from the first 60s of observation, modelled with an absorbed power-law. The absorbing column was fixed to the Galactic NH of 7x1e20 /cm². A photon index Gamma = 1.3 +/- 0.4 is measured. We measure a 0.3-8 keV flux of 2.6 (-1.6/ +2.28) x 1e-10 erg/s/cm² (all uncertainties at 90% C. L.; these preliminary results may be improved) The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE. The Burst Advocate (BA) on shift for this alert is Yun Wang: wangyun(a)pmo.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44468. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42593] GRB 260504B: EP-FXT upper limit
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44467 SUBJECT: GRB 260504B: EP-FXT upper limit DATE: 26/05/05 04:30:12 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H. Zhou (PMO, CAS), Y.Q. Zhao (PRIC, USTC), T.Y. Liu, Y. Liu (NAOC, CAS) on behalf of the Einstein Probe (EP) team: The Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission observed GRB 260504B (Saccardi, GCN 44454) autonomously at 2026-05-04 11:46:16 (UTC, ~ 2.25 hours after the burst). The exposure time of this observation is 1472s. On-ground analysis of the FXT data did not found any significant source within the error circle (90% C.L. radius of 167 arcsec) of GRB 260504B. The 5-sigma upper limit of EP-FXT observation is 4.8 x 10^-13 erg/s/cm^2 in the 0.5-10 keV band. 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/44467. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42592] GRB 260502A: SVOM/GRM observation of a short GRB
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44466 SUBJECT: GRB 260502A: SVOM/GRM observation of a short GRB DATE: 26/05/05 03:09:45 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> SVOM/GRM team: Xing-Hao Luo, 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 on-ground by GRB 260502A at 2026-05-02T05:01:00.300 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44447). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 0.61 +0.28/-0.15 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260502A.png In addition, the position of this burst, as determined by Fermi/GBM (RA=283.76 , DEC=57.62, with a statistical uncertainty of 13.77 degrees, Fermi GBM team, GCN #44447), is located at about 82 degrees form the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-0.04 to T0+0.01 s is best fitted by a power law function. The power law index is -1.12 +/-0.10. The event fluence (10-1000keV) in this time interval is (2.3 +0.37/-0.33)E-07 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: Xing-Hao Luo (luoxh(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44466. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42591] GRB 260503A: SVOM/GRM observation of a GRB
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44465 SUBJECT: GRB 260503A: SVOM/GRM observation of a GRB DATE: 26/05/05 03:08:00 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> SVOM/GRM team: Xing-Hao Luo, Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Marius Brunet (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 260503A (SVOM trigger reference: sb26050309) at 2026-05-03T20:40:20.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44451). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 21 +7/-3 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260503A.png In addition, the position of this burst, as determined by Fermi/GBM (RA=287.1 , DEC=-2.0, with a statistical uncertainty of 2.6 degrees, Fermi GBM team, GCN #44451), is located at about 87 degrees form the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-3 to T0+17 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.12 +0.17/-0.16 and the cutoff energy, parameterized as Epeak, is 128 +21/-15 keV. The event fluence (10-1000keV) in this time interval is (6.65 +0.53/-0.46)E-06 erg/cm^2. The localization of GRB 260503A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260503A_amati.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: Xing-Hao Luo (luoxh(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44465. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42590] IceCube-260504A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44464 SUBJECT: IceCube-260504A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 26/05/05 01:46:29 GMT FROM: jliao(a)icecube.wisc.edu The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 26-05-04 at 21:11:20.90 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_BRONZE alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of None events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/142545_58544625.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 26-05-04 Time: 21:11:20.90 UT RA: 246.99 (+0.86/-0.80 deg 90% PSF containment) J2000 Dec: 54.87 (+0.46/-0.47 deg 90% PSF containment) J2000 One gamma-ray source from the Fermi 4FGL-DR4 catalog is located within the 90% uncertainty region of this event: 4FGL J1626.0+5436 , at RA = 246.51° and Dec = 54.61° (J2000), with an angular separation of 0.38° from the best-fit event position. As announced in GCN Circular 43419 (https://gcn.nasa.gov/circulars/43419) IceCube alert notices for high-energy track alerts are now also streamed via Kafka. IceCube Gold/Bronze track alerts are available on the Kafka topic 'gcn.notices.icecube.gold_bronze_track_alerts'. The probability distribution of the true neutrino direction, allowing the extraction of precise 90% containment regions around the best-fit direction, is now available for revised reconstruction of high-energy track alerts. The corresponding sky map is distributed as a FITS file and follows the explicit naming convention IceCube-YYMMDDX, where YYMMDD indicates the date of the event and X is a letter distinguishing multiple alerts on the same day. The download link is provided through the GCN schema distributed via Kafka. Detailed documentation describing the alert distribution, schemas, and probability maps is available at: https://gcn.nasa.gov/missions/icecube. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/44464. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42589] Konus-Wind detection of GRB 260415C
by GCN Circulars 04 May '26

04 May '26

TITLE: GCN CIRCULAR NUMBER: 44463 SUBJECT: Konus-Wind detection of GRB 260415C DATE: 26/05/04 20:18:18 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260415C triggered Konus-Wind at T0=27659.163 s UT (07:40:59.163). The burst light curve shows a single pulse which starts at ~T0-2.5 s and has a total duration of ~11.3 s. The emission is seen up to 2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260415_T27659/ As observed by Konus-Wind, the burst had the total fluence of 3.64(-0.42,+0.54)x10^-6 erg/cm2, and the 64-ms peak flux, measured from T0-0.446 s, of 1.56(-0.41,+0.45)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.06(-0.45,+0.60), the high energy photon index beta = -2.91(-0.94,+0.36), the peak energy Ep = 105(-11,+12) keV (chi2 = 92/77 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/44463. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42588] GCN Announcement: New BOOM Notices and Schema v7.0.0
by GCN Announcements 04 May '26

04 May '26

The GCN Team is pleased to announce a new Notice Type and a schema release. BOOM Cross-Correlated Optical Transient Notices The Burst & Outburst Observations Monitor (BOOM)/Babamul Team (https://www.ztf.caltech.edu/ztf-boom-babamul.html) and the GCN Team are pleased to announce the availability of a new notice type via the new GCN in JSON format. BOOM provides real-time brokering, archival context, and coordination tools that enable rapid identification, vetting, and follow-up of astrophysical transients. BOOM is the software stack operating to enable a multi-survey alert broker and data archive (Babamul) that ingests and combines alerts from the Zwicky Transient Facility (ZTF) and the Vera C. Rubin Observatory alert stream. BOOM is contributing a GCN Notices stream, where cross-matches from the BOOM fast transient stream (which analyzes ZTF and LSST alert streams) are checked for (i) gravitational-wave alert candidates consistent with a binary neutron star merger or neutron star-black hole merger and (ii) gamma-ray bursts detected by Fermi, SVOM, and Swift. This enables rapid cross-identification of events across experiments and observatories, enhancing situational awareness and time-critical response for the broader transient astronomy community. Alert includes localization, photometry, cross-matches with other GCN Notices, and classification scores from machine-learning models. BOOM notices are published on the GCN Kafka topic gcn.notices.boom.alert. See the BOOM mission page (https://gcn.nasa.gov/missions/boom) for a more extensive description of the information provided in these new notices. Schema v7.0.0 GCN Schema v7.0.0 is available with recent changes including new Notice types and a modified and generalized Spectral core schema (Release Notes; https://github.com/nasa-gcn/gcn-schema/releases/tag/v7.0.0) For more details on this new feature and an archive of GCN news and announcements, see https://gcn.nasa.gov/news. For questions, issues, or bug reports, please contact us via: - Contact form: https://gcn.nasa.gov/contact - GitHub issue tracker: https://github.com/nasa-gcn/gcn.nasa.gov/issues --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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