May 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 38540] GRB 250521A: Fermi GBM Final Real-time Localization
by GCN Circulars 21 May '25

21 May '25

TITLE: GCN CIRCULAR NUMBER: 40508 SUBJECT: GRB 250521A: Fermi GBM Final Real-time Localization DATE: 25/05/21 04:37:01 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 04:27:02 UT on 21 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250521A (trigger 769494427.113864 / 250521185). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 213.0, Dec = 30.1 (J2000 degrees, equivalent to J2000 14h 11m, 30d 06'), with a statistical uncertainty of 4.6 degrees. The angle from the Fermi LAT boresight is 74.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250521185/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250521185/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250521185/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40508. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38539] Konus-Wind detection of GRB 250516B
by GCN Circulars 20 May '25

20 May '25

TITLE: GCN CIRCULAR NUMBER: 40507 SUBJECT: Konus-Wind detection of GRB 250516B DATE: 25/05/20 21:30:43 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline on behalf of the Konus-Wind team, report: The bright, long-duration GRB 250516B (GECAM-B detection: Wang et al., GCN 40469; NuSTAR-ACS detection: Grefenstette et al., GCN 40484; Insight-HXMT-HE detection: Wang et al., GCN 40489; GRBAlpha detection: Dafcikova et al., GCN 40496; IPN triangulation: Svinkin et al., GCN 40506) triggered Konus-Wind at T0=23492.766 s UT (06:31:32.766). The burst light curve shows multi-peaked structure which starts at ~T0-0.5 s and has a total duration of ~56 s. The emission is seen up to ~10 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250516_T23492/ As observed by Konus-Wind, the burst had a fluence of 3.00(-0.07,+0.07)x10^-4 erg/cm2, and a 64-ms peak flux, measured from T0+19.232 s, of 2.16(-0.19,+0.19)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+60.416 s) is best fit in the 20 keV - 15 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.80(-0.03,+0.03), the high energy photon index beta = -2.52(-0.07,+0.06), the peak energy Ep = 356(-10,+11) keV (chi2 = 124/97 dof). The spectrum near the maximum count rate (measured from T0+18.688 to T0+19.712 s) is best fit in the 20 keV - 15 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.82(-0.07,+0.07), the high energy photon index beta = -2.92(-0.50,+0.26), the peak energy Ep = 482(-37,+41) keV (chi2 = 46/53 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/40507. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38538] IPN triangulation of GRB 250516B
by GCN Circulars 20 May '25

20 May '25

TITLE: GCN CIRCULAR NUMBER: 40506 SUBJECT: IPN triangulation of GRB 250516B DATE: 25/05/20 21:24:50 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, E. Burns on behalf of the IPN, S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, and A. Tohuvavohu on behalf of the Swift-BAT team, C. Wang, S. Xiong, S. Zheng and Y. Zhang, on behalf of the Insight-HXMT and GECAM team, and M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), F. Munz (Masaryk U.), on behalf of the GRBAlpha team, report: The bright, long-duration GRB 250516B (GECAM-B detection: Wang et al., GCN 40469; NuSTAR-ACS detection: Grefenstette et al., GCN 40484; Insight-HXMT-HE detection: Wang et al., GCN 40489; GRBAlpha detection: Dafcikova et al., GCN 40496) was detected by GECAM-B, GECAM-A, Konus-Wind, NuSTAR (ACS), Insight-HXMT (HE), Swift (BAT), and GRBAlpha at about 23492 s UT (06:31:32). The burst was outside the coded field of view of the BAT. We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: ------------------------------- RA(2000), deg Dec(2000), deg ------------------------------- Center: 143.08 21.29 Corners: 144.27 24.01 143.64 24.28 141.81 18.37 142.40 18.15 ------------------------------- The error box area is 4.2 sq. deg, and its maximum dimension is 6.3 deg (the minimum one is 41 arcmin). The Sun distance was 82 deg. This localization may be improved. A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB250516_T23492/IPN The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/40506. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38537] GRB 250520A: J-band observations with WINTER
by GCN Circulars 20 May '25

20 May '25

TITLE: GCN CIRCULAR NUMBER: 40505 SUBJECT: GRB 250520A: J-band observations with WINTER DATE: 25/05/20 18:00:54 GMT FROM: Geoffrey Mo at MIT <gmo(a)mit.edu> Geoffrey Mo (MIT), Tomas Ahumada (Caltech), Benjamin Schneider (LAM), Viraj Karambelkar (Caltech), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 250520A (Eyles-Ferris et al., GCN 40491; SVOM/GRM Team, GCN 40495; Tembhurnikar et al., GCN 40497) in the near-infrared J-band with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations were triggered automatically and began at 2025-05-20T07:26:08 UTC (4.7 hours after the GRB), consisting of 15 x 120 s exposures. 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) We do not detect any uncataloged sources at the SVOM/VT optical candidate location (Xin et al., GCN 40500) or in the Swift/XRT localization (Evans et al., GCN 40492; Goad et al., GCN 40494; Perri et al., GCN 40503), after visual comparison to archival VISTA Hemisphere Survey J-band imaging (McMahon et al. 2013). This is consistent with observations by Lipunov et al., GCN 40490; Eyles-Ferris et al., GCN 40491; Kumar et al., GCN 40493; Becerra et al, GCN 40498; Pereyra et al, GCN 40499; Brivio et al., GCN 40502; and Rastinejad et al., GCN 40504. We obtain the following 5-sigma upper limit: J ~ 18.5 mag (AB). 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/40505. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38536] GRB 250520A: Gemini-South optical observations
by GCN Circulars 20 May '25

20 May '25

TITLE: GCN CIRCULAR NUMBER: 40504 SUBJECT: GRB 250520A: Gemini-South optical observations DATE: 25/05/20 16:07:09 GMT FROM: Jillian Rastinejad at Northwestern Univ. <jillianrastinejad2024(a)u.northwestern.edu> Jillian Rastinejad, Wen-fai Fong, and Charlie Kilpatrick (Northwestern) report on behalf of a larger collaboration: We observed the location of the short-duration GRB 250520A (Eyles-Ferris et al., GCN 40491) with the Gemini Multi-Object Spectrograph (GMOS) mounted on Gemini-South under Program GS-2025A-Q-112 (PI: Fong). We obtained 15x120-sec imaging in i-band starting at 2025-05-20 03:45:39.2 UT (1.06 hrs post-burst), at a median airmass of 1.8 and seeing of 0.7''. We detect a clear source coincident with the candidate optical counterpart discovered by SVOM (Xin et al., GCN 40500) that is within the enhanced XRT localization (Goad et al., GCN 40494). Calibrated to Pan-STARRS DR2 (Flewelling et al., 2020, ApJS, 251, 7), we measure a magnitude for this source of i = 22.4 +/- 0.2 AB mag. This value does not include a correction for Galactic extinction, which is significant (A_V = 2.1 mag; Schlafly and Finkbeiner 2011, ApJ, 737, 103). The brightness of this source is consistent with reported upper limits (Brivio et al. GCN 40502, Pereyra et al., GCN 40499, Becerra et al. GCN 40498, Kumar et al. GCN 40493). Correcting our measurement and the value reported by SVOM at 2.14 hours post-burst (VT_R = 23.2 +/- 0.2 mag; Xin et al., GCN 40500) for Galactic extinction, we find no clear evidence for fading within the uncertainties. At or very close to the position of the SVOM and Gemini source, there appears to be a faint source in i- and z-band archival PS1 imaging (Flewelling et al., 2020, ApJS, 251, 7), though more precise astrometry is needed to determine their relative positions. However, forced photometry near the position of the SVOM source (Xin et al., GCN 40500) in the PS1 images yields 3-sigma upper limits on underlying emission of i > 22.2 and z > 21.7 AB mag, uncorrected for extinction. Given that the PS1 i-band limit is shallower than our source magnitude, it is difficult to tell whether the faint source was pre-existing or is the afterglow of GRB 250520A. Further observations are planned to assess the variability of the source and others in the field. We thank the Gemini staff for the rapid scheduling and execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40504. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38535] GRB 250520A: Swift-XRT refined Analysis
by GCN Circulars 20 May '25

20 May '25

TITLE: GCN CIRCULAR NUMBER: 40503 SUBJECT: GRB 250520A: Swift-XRT refined Analysis DATE: 25/05/20 14:29:54 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), M.A. Williams (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), B. Sbarufatti (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.7 ks of XRT data for GRB 250520A, from 127 s to 34.5 ks after the trigger. The data comprise 16 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=2.35 (+0.23, -0.22). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.1 (+/-0.4). The best-fitting absorption column is 1.3 (+0.5, -0.4) x 10^22 cm^-2, in excess of the Galactic value of 3.7 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 5.0 x 10^-11 (1.1 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.3 (+0.5, -0.4) x 10^22 cm^-2 Galactic foreground: 3.7 x 10^21 cm^-2 Excess significance: 3.6 sigma Photon index: 2.1 (+/-0.4) If the light curve continues to decay with a power-law decay index of 2.35, the count rate at T+24 hours will be 10.0 x 10^-7 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.0 x 10^-17 (1.1 x 10^-16) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01315630. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40503. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38534] GRB 250520A: REM optical/NIR early observations
by GCN Circulars 20 May '25

20 May '25

TITLE: GCN CIRCULAR NUMBER: 40502 SUBJECT: GRB 250520A: REM optical/NIR early observations DATE: 25/05/20 11:04:40 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of GRB 250520A detected by Swift/BAT (Eyles-Ferris et al., GCN 40491), SVOM/GRM (SVOM/GRM team, GCN 40495), and AstroSat (Tembhurnikar et al., GCN 40497) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 May 20 at 02:43:22 UT (i.e. 65 sec after the burst), and lasted for about 3 hours. From preliminary inspection, we do not detect any possible counterpart at the position of the optical candidate (Xin et al., GCN 40500), within the Swift/XRT enhanced position (Goad et al., GCN 40494), down to the following 3sigma limits: r > 17.7 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 70 sec after the trigger; H > 15.1 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 113 sec after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40502. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38533] GRB 250520B: Fermi GBM Final Real-time Localization
by GCN Circulars 20 May '25

20 May '25

TITLE: GCN CIRCULAR NUMBER: 40501 SUBJECT: GRB 250520B: Fermi GBM Final Real-time Localization DATE: 25/05/20 10:46:39 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 10:36:02 UT on 20 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250520B (trigger 769430167.408886 / 250520442). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 100.6, Dec = 68.7 (J2000 degrees, equivalent to J2000 06h 42m, 68d 42'), with a statistical uncertainty of 4.3 degrees. The angle from the Fermi LAT boresight is 21.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250520442/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250520442/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250520442/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40501. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38532] GRB 250520A：SVOM/VT optical candidate
by GCN Circulars 20 May '25

20 May '25

TITLE: GCN CIRCULAR NUMBER: 40500 SUBJECT: GRB 250520A：SVOM/VT optical candidate DATE: 25/05/20 10:45:18 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. N. Ma, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC) report on behalf of the SVOM/VT team: SVOM performed a Target of Opportunity observation of GRB 250520A detected by Swift/BAT (Eyles-Ferris et al., GCN 40491), SVOM/GRM (Wang et al., GCN 40495) and AstroSat(Tembhurnikar et al., GCN 40497). SVOM/VT began observing the field at 2025-05-20T03:51:16 UTC, 1.15 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. An uncatalogued faint source, compared to PanStarrs catalogue, is found using VT X-band data, within the error box of Swift/XRT (Goad et al., GCN 40494) at RA=282.28578, Dec=-11.86939 degrees: R.A.(J2000) = 18:49:08.58 Dec.(J2000) = -11:52:09.79 with an uncertainty of 0.5 arcsec. The source is detected in VT_R only. The magnitude is estimated to be 23.2+/-0.1 mag with an effective exposure time of 37*70 seconds at the mid time of 2.14 hours after the burst. The photometry was estimated in AB magnitude and not corrected for Galatic extinction. Give the faintness of the candidate, we cannot determine whether it is fading. More follow-ups are encouraged. 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. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/40500. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38531] GRB 250520A: COLIBRÍ optical upper limit
by GCN Circulars 20 May '25

20 May '25

TITLE: GCN CIRCULAR NUMBER: 40499 SUBJECT: GRB 250520A: COLIBRÍ optical upper limit DATE: 25/05/20 10:34:25 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Margarita Pereyra (UNAM), Stéphane Basa (UAR Pytheas), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the GRB 250520A detected by Swift/BAT (Eyles-Ferris et al., GCN Circ. 40491), SVOM/GRM (SVOM/GRM team, GCN Circ. 40495) and AstroSat/CZTI (Tembhurnikar et al., GCN Circ. 40497) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-05-20 06:42 to 06:45 UTC (from 4.0 to 4.1 hours after the trigger) and obtained 3 minutes of exposure in the i filter. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). 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 image, we do not detect any new source at the XRT enhanced position (Goad et al., GCN Circ. 40494) down to the following 3-sigma limit: i > 21.3 This upper limit is consistent with the non-detection reported by GOTO (Kumar et al., GCN Circ. 40493) and DDOTI (Becerra et al., GCN Circ. 40498). Further observations and analysis are ongoing. 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/40499. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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