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[vsnet-grb-info 42575] GRB 260503A: Fermi GBM Final Real-time Localization
by GCN Circulars 03 May '26

03 May '26

TITLE: GCN CIRCULAR NUMBER: 44451 SUBJECT: GRB 260503A: Fermi GBM Final Real-time Localization DATE: 26/05/03 20:50:53 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 20:40:17 UT on 3 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260503A (trigger 799533622.581348 / 260503861). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 287.1, Dec = -2.0 (J2000 degrees, equivalent to J2000 19h 08m, -2d 00'), with a statistical uncertainty of 2.6 degrees. The angle from the Fermi LAT boresight is 30.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260503861/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260503861/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260503861/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44451. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42574] SVOM/GRM observation of a bright burst from SGR 1E1841-045
by GCN Circulars 03 May '26

03 May '26

TITLE: GCN CIRCULAR NUMBER: 44450 SUBJECT: SVOM/GRM observation of a bright burst from SGR 1E1841-045 DATE: 26/05/03 16:26:46 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: Hui Yang, Sebastien Guillot (IRAP) Report on behalf of the SVOM team: SVOM/GRM detected a bright burst from SGR 1E1841-045 at 2026-05-02T05:39:51.950 UTC (T0), which is also detected by Konus-Wind (A. Ridnaia el at., GCN#44448). 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 0.08 +0.08/-0.02 s in the 15-5000 keV band. All the signal is detected below 100 keV. The SVOM/GRM light curve can be found here： https://www.bursthub.cn//admin/static/svsgr_260502_053951.png In addition, the localization of SGR 1E1841-045 is located at about 94 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. The time-averaged spectrum from T0-0.04 to T0+0.07 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.49 +0.28/-0.27 and the cutoff energy, parameterized as Epeak, is 37.08 +1.88/-2.12 keV. The event fluence (10-1000 keV) in this time interval is (7.29 +0.32/-0.31) 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/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/44450. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42573] GRB 260502A: GECAM-B observation of a short burst
by GCN Circulars 03 May '26

03 May '26

TITLE: GCN CIRCULAR NUMBER: 44449 SUBJECT: GRB 260502A: GECAM-B observation of a short burst DATE: 26/05/03 15:58:17 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> Xing-Hao Luo, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 260502A, at 2026-05-02T05:01:00.300 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44447). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a single pulse pulses with a duration (T90) of 0.40 +0.14/-0.08 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260502A.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/44449. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42572] IPN triangulation of a bright burst from SGR 1E1841-045
by GCN Circulars 03 May '26

03 May '26

TITLE: GCN CIRCULAR NUMBER: 44448 SUBJECT: IPN triangulation of a bright burst from SGR 1E1841-045 DATE: 26/05/03 15:05:53 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, and T. Cline on behalf of the Konus-Wind team, C. Wang (IHEP), S. Xiong (IHEP), S. Zhang (IHEP), J. Wei (NAOC), B. Cordier (CEA) on behalf of the SVOM-GRM team, and E. Burns on behalf of the IPN, report: A bright, short-duration, soft burst was detected by Konus-Wind and SVOM (GRM) at about 20396 s UT (05:39:56) on May 2. We have triangulated it to a Konus-GRM annulus centered at RA(2000)=243.691 deg (16h 14m 46s) Dec(2000)=-21.870 deg (-21d 52' 12"), whose radius is 39.329 +/- 0.068 deg (3 sigma). Among known SGRs, only the position of SGR 1E1841-045 is inside the annulus. Given the positional coincidence of this burst with SGR 1E1841-045, its time history, and softness of its spectrum (as observed by Konus-Wind), we conclude this burst likely originated from SGR 1E1841-045. A triangulation map is posted at http://www.ioffe.ru/LEA/SGRs/260502_T20396/IPN/ The time history and spectrum will be given in forthcoming GCN circulars. View this GCN Circular online at https://gcn.nasa.gov/circulars/44448. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42571] GRB 260502A: Fermi GBM Final Localization
by GCN Circulars 03 May '26

03 May '26

TITLE: GCN CIRCULAR NUMBER: 44447 SUBJECT: GRB 260502A: Fermi GBM Final Localization DATE: 26/05/03 05:20:13 GMT FROM: Rushikesh Sonawane at IISER TVM <rushikesh23(a)iisertvm.ac.in> The Fermi GBM team reports the detection of a likely SHORT GRB "At 05:01:00.25 UT on 05 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260502A (trigger 799390865/260502209). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 283.76, Dec = 57.62 (J2000 degrees, equivalent to J2000 18h 55m, +57d 37′), with a statistical uncertainty of 13.77 degrees. The angle from the Fermi LAT boresight is 23 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260502209/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260502209/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260502209/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44447. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42570] The EP-WXT trigger 01709261576 is likely a flaring star
by GCN Circulars 02 May '26

02 May '26

TITLE: GCN CIRCULAR NUMBER: 44446 SUBJECT: The EP-WXT trigger 01709261576 is likely a flaring star DATE: 26/05/02 19:25:21 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> X. Mao (NAO, CAS; OAPa, INAF), H. Zhou (PMO), Z. C. Zou (NJU), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709261576 at the time of 2026-05-02T18:35:45, is likely a stellar flare associated with Sz 30. The estimated flux of the flare is around 1.8e-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 7.3e32 erg/s. 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/44446. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42569] GRB 260429B / EP260429a: EP-FXT follow-up observation
by GCN Circulars 02 May '26

02 May '26

TITLE: GCN CIRCULAR NUMBER: 44445 SUBJECT: GRB 260429B / EP260429a: EP-FXT follow-up observation DATE: 26/05/02 16:46:33 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wang (PMO, CAS; UCB), Y. L. Wang (NAO, CAS; ICE, CSIC), G. J. Yang, C.C Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed two follow-up observations of the EP-WXT detected transient GRB 260429B / EP260429a (Wang et al., GCN), also triggered by AstroSat CZTI (Arya et al., GCN 44443). The observations started at 2026-04-30T07:26:44 UTC and 2026-05-01T21:53:58 UTC, corresponding to approximately 16.8 and 55.2 hours after the EP-WXT trigger, with total exposure times of 9064 s and 5262 s, respectively. Two X-ray sources were detected by FXT within the WXT error region: EPF_J160221.2-093607 RA (J2000): 240.5884 deg Dec (J2000): -9.6018 deg with an uncertainty of 10 arcsec (radius, 90% C.L., statistical and systematic). EPF_J160226.1-093337 RA (J2000): 240.6088 deg Dec (J2000): -9.5602 deg with an uncertainty of 10 arcsec (radius, 90% C.L., statistical and systematic). The 0.5-10 keV flux of EPF_J160221.2-093607 decreased from 2.1e-12 to 5.8e-13 erg cm^-2 s^-1 between the two observations. In contrast, the flux of EPF_J160226.1-093337 remained nearly constant at about 6.6e-13 erg cm^-2 s^-1 in the same energy band. In addition, the position of EPF_J160226.1-093337 is 1.264 arcsec from Gaia DR3 4346772233753744896, suggesting that this Gaia source may be its counterpart. Therefore, EPF_J160221.2-093607 is the more likely X-ray afterglow of GRB 260429B / EP260429a. We note that follow-up observations were carried out by Eyles-Ferris et al. (GCN 44433), Fortin et al. (GCN 44434) and Lipunov et al. (GCN 44437), but no optical counterpart was detected in these observations. Further follow-up observations are encouraged. 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/44445. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42568] EP260502a: BOOTES-7 observations of a fading catalogued source close to the X-ray position
by GCN Circulars 02 May '26

02 May '26

TITLE: GCN CIRCULAR NUMBER: 44444 SUBJECT: EP260502a: BOOTES-7 observations of a fading catalogued source close to the X-ray position DATE: 26/05/02 15:48:54 GMT FROM: I. Perez-Garcia at Instituto de Astrofísica de Andalucía <ipg(a)iaa.es> S.-Y. Wu, I. Perez-Garcia, E. Fernandez-Garcia, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, M. Gritsevich and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar, A. Castellon, A. Reina (Univ. de Malaga),Y.-D. Hu (GXU), L. Hernandez-Garcia (Univ. de Valparaiso), D. R. Xiong (Yunnan Observatories of CAS), B.-B. Zhang (Nanjing Univ.) and A. Maury (Space, San Pedro de Atacama), on behalf of a larger collaboration, report: Further to our previous report on EP260502a (Perez-Garcia et al., GCN 44442), and following a comment by D. B. Malesani, we have inspected the BOOTES-7 images at the position of a bright catalogued source close to the EP/FXT position, located at RA(J2000) = 18:09:07.01 Dec(J2000) = -76:13:26.79. This source is reported as an eROSITA source and lies close to the boundary of the EP/WXT error region. Relative photometry of this source in the BOOTES-7 r'-band images shows a fading trend during the first observing sequence. In the 9 s r'-band exposures, the source faded from r' = 13.8 +/- 0.06 at 2026-05-02 06:24:42 UT to r' = 14.5 +/- 0.08 at 2026-05-02 06:57:36 UT, corresponding to a decline of 0.7 mag over ~30 min. No significant fading trend is observed in the BOOTES-7 i' and Z band images over the same time interval. The final measured value is consistent with the archival SkyMapper magnitude of the source, r = 14.5. We thank D. B. Malesani for pointing out this source. View this GCN Circular online at https://gcn.nasa.gov/circulars/44444. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42567] GRB 260429B / EP260429a: AstroSat CZTI detection
by GCN Circulars 02 May '26

02 May '26

TITLE: GCN CIRCULAR NUMBER: 44443 SUBJECT: GRB 260429B / EP260429a: AstroSat CZTI detection DATE: 26/05/02 12:54:35 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Arya (IITB), A. Goyal (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 260429B which is also detected by Konus-Wind (priv. comm), and is associated with EP260429a (Wang et al., GCN Circ. 44426). The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-04-29 14:42:59.27 UTC. The measured peak count rate associated with the burst is 147 (+31, -33) counts/s above the background in the combined data of all quadrants, with a total of 1802 (+485, -554) counts. The local mean background count rate was 1313 (+3, -3) counts/s. We measure a T90 of 34 (+6, -9) s from the cumulative Veto light curve. The source was also faintly detected in the CZT detectors in the 20-200 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 data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/515169782.27/S515169782.27_det… 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/44443. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42566] GRB EP260502a: BOOTES-7: early optical upper limit
by GCN Circulars 02 May '26

02 May '26

TITLE: GCN CIRCULAR NUMBER: 44442 SUBJECT: GRB EP260502a: BOOTES-7: early optical upper limit DATE: 26/05/02 09:00:37 GMT FROM: I. Perez-Garcia at Instituto de Astrofísica de Andalucía <ipg(a)iaa.es> I. Perez-Garcia, S.-Y. Wu, E. Fernandez-Garcia, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, M. Gritsevich and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar, A. Castellon, A. Reina (Univ. de Malaga),Y.-D. Hu (GXU), L. Hernandez-Garcia (Univ. de Valparaiso), D. R. Xiong (Yunnan Observatories of CAS), B.-B. Zhang (Nanjing Univ.) and A. Maury (Space, San Pedro de Atacama), on behalf of a larger collaboration, report: Following the detection of the fast X-ray transient EP260502a by the Einstein Probe (Liu et al., GCN 44440), the 0.6m BOOTES-7 robotic telescope at San Pedro de Atacama (Chile) observed the fast X-ray transient location starting on May 2, 06:23:31 UT (~14.7 min after trigger) in different optical bands. No new optical source is detected within the EP/WXT 3 arcmin error circle on the initial 10s image or on the first co-added clear-filter images (mid exposure time 2026-05-02 07:34 UT) down to 15.3 mag or 18.3 mag respectively, in agreement with the LCO upper limit (Li et al. GCN 44441). We thank the staff at San Pedro de Atacama Celestial Explorations observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/44442. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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