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

[vsnet-grb-info 38634] GRB 250530A: VLT/HAWK-I NIR counterpart fading
by GCN Circulars 01 Jun '25

01 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40598 SUBJECT: GRB 250530A: VLT/HAWK-I NIR counterpart fading DATE: 25/06/01 19:26:39 GMT FROM: Ben Rayson at University of Leicester <br155(a)leicester.ac.uk> B. C. Rayson (Leicester), B. Schneider (LAM), P. D'Avanzo (INAF-OAB), A. Saccardi (CEA/Irfu), G. Corcoran (UCD), B. P. Gompertz (U. Birmingham), N. Habeeb (Leicester), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), G. Pugliese (API), N. R. Tanvir (Leicester) report on behalf of the Stargate collaboration: We observed the near-infrared source reported by D'Avanzo et al. (GCN 40588), a candidate afterglow of GRB 250530A detected by SVOM/ECLAIRs (Wang et al., GCN 40576). We used the ESO VLT UT4 (Yepun) equipped with the HAWK-I near-infrared camera. We obtained a 20 min exposure in the J band, starting at 23:17:32 UT on 2025-05-31, i.e. 1.7 days after the SVOM trigger. The near-infrared source is well detected in our image and we measured J = 21.65 +/- 0.10 mag (Vega), calibrated against the 2MASS catalogue. Compared with the value reported by D'Avanzo et al. (GCN 40588), our measurement indicates fading of the counterpart with a power-law decay index of ~0.6. This confirms the source as the NIR afterglow of GRB 250530A. As noted by D'Avanzo et al. (GCN 40588), this source is consistent with a catalogued source reported in the Legacy Survey. This is the likely GRB host, therefore, the red colors and the optical faintness (Li et al., GCN 40582) are likely due to dust extinction rather than high redshift - as also confirmed by the large column density measured in the X-ray spectrum (Evans et al., GCN 40579; see also: https://www.swift.ac.uk/SVOM/SVOM_FIELD00017/Source1.php). We acknowledge excellent support from the ESO observing staff in Paranal, in particular Thallis Pessi, Israel Blanchard, Miguel Lopez & Aaron Labdon View this GCN Circular online at https://gcn.nasa.gov/circulars/40598. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38633] GRB 250521C/AT2025mgj: FTW optical and NIR observations
by GCN Circulars 01 Jun '25

01 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40597 SUBJECT: GRB 250521C/AT2025mgj: FTW optical and NIR observations DATE: 25/06/01 18:58:47 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU), and Antonella Palmese (Carnegie Mellon U.) report: We observed the candidate counterpart AT2025mgj (Andreoni et al., GCN 40566; Martin-Carrillo et al., GCN 40584; Becerra et al., GCN 40590) of GRB 250521C (Fermi GBM team, GCN 40515) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 10 x 180 s starting at 2025-05-30T20:31:19 UT (9.3 days after the GRB trigger). We detect the source at r = (19.28 +/- 0.01) mag i = (19.45 +/- 0.02) mag J = (20.03 +/- 0.07) mag. We note that the blue color is inconsistent with an afterglow origin, despite the similar power law temporal decay (Martin-Carrillo et al., GCN 40584; Becerra et al., GCN 40590). The source is therefore unlikely to be associated to GRB 250521C. The most likely origin in a Cataclysmic Variable (CV) as noted by Andreoni et al. (GCN 40566). However, given the coincidence with GRB 250521C, we encourage additional observations to conclusively determine the nature of this transient. The r and i band magnitudes are calibrated against the PS1 catalog and the J band is calibrated with the 2MASS Catalog. All magnitudes are provided in the AB system and are not corrected for Galactic extinction. We thank Michael Schmidt from the Wendelstein Observatory staff for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40597. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38632] GRB 250601A: Fermi GBM Final Real-time Localization
by GCN Circulars 01 Jun '25

01 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40596 SUBJECT: GRB 250601A: Fermi GBM Final Real-time Localization DATE: 25/06/01 17:40:08 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 17:29:35 UT on 1 Jun 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250601A (trigger 770491780.538054 / 250601729). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 86.5, Dec = -55.7 (J2000 degrees, equivalent to J2000 05h 46m, -55d 42'), with a statistical uncertainty of 4.5 degrees. The angle from the Fermi LAT boresight is 23.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250601729/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250601729/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250601729/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40596. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38631] EP#01709177494: SVOM/VT optical observations
by GCN Circulars 01 Jun '25

01 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40595 SUBJECT: EP#01709177494: SVOM/VT optical observations DATE: 25/06/01 00:30:31 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, J. Wang, Y. Liu report on behalf of the SVOM and EP mission teams: SVOM performed a Target of Opportunity observation of he EP-WXT trigger Einstein Probe/WXT-detected source EP#01709177494 (Wu et al., ATEL #17212). SVOM/VT began observing the field at 2025-05-31T02:37:05 UTC, 50.7 min after the trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The exposure time for each frame is 70 seconds. A cataloged source was identified during the outburst in VT_B and VT_R band images during our 2 orbit observations, compared to the DSS catalog. The position is RA=257.37661 deg, DEC=-26.65560 deg, corresponding to RA(J2000) = 17:09:30.39 DEC(J2000) = -26:39:20.15 Error = 0.5 arcseconds, The position is consistent with the location of XRT Source 1 (SWIFT J170930.3-263917) (Evens et al., GCN 40592). Preliminary analysis shows that the brightness of the source was VT_B=19.44+/-0.05 and VT_R=18.81+/-0.05, respectively. 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/40595. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38630] Fermi GRB 250531A: Global MASTER-Net observations report
by GCN Circulars 31 May '25

31 May '25

TITLE: GCN CIRCULAR NUMBER: 40594 SUBJECT: Fermi GRB 250531A: Global MASTER-Net observations report DATE: 25/05/31 19:31:27 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 250531A ( Fermi GBM team, GCN 40593) errorbox 1696 sec after notice time and 1758 sec after trigger time at 2025-05-31 18:31:43 UT, with upper limit up to 19.5 mag. The observations began at zenith distance = 40 deg. The sun altitude is -35.3 deg. The galactic latitude b = 60 deg., longitude l = 256 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2887934 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 1789 | 2025-05-31 18:31:43 | MASTER-SAAO | (11h 22m 12.13s , +04d 56m 45.8s) | C | 60 | 19.5 | 1789 | 2025-05-31 18:31:43 | MASTER- | (11h 20m 21.93s , +05d 14m 38.0s) | C | 60 | 18.2 | 2577 | 2025-05-31 18:44:51 | MASTER-SAAO | (11h 30m 08.86s , +04d 56m 11.0s) | C | 60 | 19.3 | 2577 | 2025-05-31 18:44:51 | MASTER- | (11h 28m 19.20s , +05d 14m 00.4s) | C | 60 | 18.0 | 3202 | 2025-05-31 18:55:16 | MASTER-SAAO | (11h 22m 07.05s , +04d 58m 37.2s) | C | 60 | 19.5 | 3202 | 2025-05-31 18:55:16 | MASTER- | (11h 20m 17.21s , +05d 16m 27.2s) | C | 60 | 18.1 | 3797 | 2025-05-31 19:05:11 | MASTER-SAAO | (11h 30m 09.65s , +04d 57m 47.3s) | C | 60 | 19.3 | 3797 | 2025-05-31 19:05:11 | MASTER- | (11h 28m 19.98s , +05d 15m 38.0s) | C | 60 | 18.1 | 4208 | 2025-05-31 19:12:03 | MASTER-SAAO | (11h 22m 12.67s , +04d 57m 20.7s) | C | 60 | 19.4 | 4208 | 2025-05-31 19:12:03 | MASTER- | (11h 20m 22.82s , +05d 15m 08.3s) | C | 60 | 18.1 | 4404 | 2025-05-31 19:15:18 | MASTER-SAAO | (11h 30m 12.61s , +04d 57m 31.8s) | C | 60 | 19.3 | 4404 | 2025-05-31 19:15:18 | MASTER- | (11h 28m 22.60s , +05d 15m 21.9s) | C | 60 | 18.1 | 4501 | 2025-05-31 19:16:55 | MASTER-SAAO | (11h 20m 30.68s , +03d 04m 26.2s) | C | 60 | 19.4 | 4501 | 2025-05-31 19:16:55 | MASTER- | (11h 18m 41.05s , +03d 22m 16.5s) | C | 60 | 18.2 | 4594 | 2025-05-31 19:18:28 | MASTER-SAAO | (11h 28m 31.94s , +03d 05m 15.3s) | C | 60 | 19.4 | 4594 | 2025-05-31 19:18:28 | MASTER- | (11h 26m 42.18s , +03d 23m 06.9s) | C | 60 | 18.2 | 4688 | 2025-05-31 19:20:02 | MASTER-SAAO | (11h 24m 27.91s , +06d 51m 33.1s) | C | 60 | 19.4 | 4688 | 2025-05-31 19:20:02 | MASTER- | (11h 22m 37.83s , +07d 09m 23.1s) | C | 60 | 17.9 | 4783 | 2025-05-31 19:21:37 | MASTER-SAAO | (11h 32m 38.83s , +06d 51m 42.0s) | C | 60 | 19.2 | 4783 | 2025-05-31 19:21:37 | MASTER- | (11h 30m 48.71s , +07d 09m 32.8s) | C | 60 | 17.9 | 4877 | 2025-05-31 19:23:11 | MASTER-SAAO | (11h 22m 08.08s , +04d 59m 13.6s) | C | 60 | 19.5 | 4877 | 2025-05-31 19:23:11 | MASTER- | (11h 20m 18.35s , +05d 17m 04.3s) | C | 60 | 18.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40594. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38629] GRB 250531A: Fermi GBM Final Real-time Localization
by GCN Circulars 31 May '25

31 May '25

TITLE: GCN CIRCULAR NUMBER: 40593 SUBJECT: GRB 250531A: Fermi GBM Final Real-time Localization DATE: 25/05/31 18:12:52 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 18:02:24 UT on 31 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250531A (trigger 770407349.523472 / 250531752). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 170.8, Dec = 5.4 (J2000 degrees, equivalent to J2000 11h 23m, 5d 24'), with a statistical uncertainty of 6.4 degrees. The angle from the Fermi LAT boresight is 37.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250531752/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250531752/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250531752/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40593. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38628] EP#01709177494: Swift-XRT counterpart detection of known source
by GCN Circulars 31 May '25

31 May '25

TITLE: GCN CIRCULAR NUMBER: 40592 SUBJECT: EP#01709177494: Swift-XRT counterpart detection of known source DATE: 25/05/31 17:47:34 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-IASFPA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected source EP#01709177494, collecting 2.0 ks of Photon Counting (PC) mode data between T0+388 s and T0+6.2 ks after the trigger. A candidate counterpart has been found. The details of this source are: Source 1 (SWIFT J170930.3-263917): ================================== RA (J2000.0): 257.3766 = 17h 09m 30.38s Dec (J2000.0): -26.6548 = -26d 39' 17.3" Error: 3.5 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 20 arcsec from the Einstein Probe/WXT position. Mean rate: 11.35 +/- 0.22 ct s^-1 Mean flux: (4.665 +/- 0.088)e-10 erg cm^-2 s^-1 Peak rate: 18.7 +/- 3.1 ct s^-1 Peak flux: (7.7 +/- 1.3)e-10 erg cm^-2 s^-1 ECF: 4.11e-11 erg cm^-2 ct^-1, assuming NH=4.40e+21 cm^-2, gamma=1.98; determined from a spectral fit. This matches a catalogued X-ray source LSXPS J170930.1-263918 in the LSXPS catalogue. Details: Separation: 3.2" from the XRT source Cat Rate: 1.2e+00 +/- 9.0e-03 ct s^-1 Cat Flux: 4.7e-11 +/- 3.7e-13 erg cm^-2 s^-1 (0.3-10 keV) so the source is 5.7-sigma above the catalogued flux. There is no evidence for fading. A SIMBAD object `RX J1709.5-2639' is 8.3" away. There is 1 2MASS object within the source's 3-sigma error radius. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/EP. This circular is an officicial product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40592. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38627] EP#01709177494: Swift-XRT counterpart detection of known source
by GCN Circulars 31 May '25

31 May '25

TITLE: GCN CIRCULAR NUMBER: 40592 SUBJECT: EP#01709177494: Swift-XRT counterpart detection of known source DATE: 25/05/31 17:47:34 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-IASFPA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected source EP#01709177494, collecting 2.0 ks of Photon Counting (PC) mode data between T0+388 s and T0+6.2 ks after the trigger. A candidate counterpart has been found. The details of this source are: Source 1 (SWIFT J170930.3-263917): ================================== RA (J2000.0): 257.3766 = 17h 09m 30.38s Dec (J2000.0): -26.6548 = -26d 39' 17.3" Error: 3.5 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 20 arcsec from the Einstein Probe/WXT position. Mean rate: 11.35 +/- 0.22 ct s^-1 Mean flux: (4.665 +/- 0.088)e-10 erg cm^-2 s^-1 Peak rate: 18.7 +/- 3.1 ct s^-1 Peak flux: (7.7 +/- 1.3)e-10 erg cm^-2 s^-1 ECF: 4.11e-11 erg cm^-2 ct^-1, assuming NH=4.40e+21 cm^-2, gamma=1.98; determined from a spectral fit. This matches a catalogued X-ray source LSXPS J170930.1-263918 in the LSXPS catalogue. Details: Separation: 3.2" from the XRT source Cat Rate: 1.2e+00 +/- 9.0e-03 ct s^-1 Cat Flux: 4.7e-11 +/- 3.7e-13 erg cm^-2 s^-1 (0.3-10 keV) so the source is 5.7-sigma above the catalogued flux. There is no evidence for fading. A SIMBAD object `RX J1709.5-2639' is 8.3" away. There is 1 2MASS object within the source's 3-sigma error radius. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/EP. This circular is an officicial product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40592. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38626] GRB 250530C: BOOTES-7 optical upper limit
by GCN Circulars 31 May '25

31 May '25

TITLE: GCN CIRCULAR NUMBER: 40591 SUBJECT: GRB 250530C: BOOTES-7 optical upper limit DATE: 25/05/31 17:31:45 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Perez-Garcia, E. Fernandez-Garcia, S.-Y. Wu, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar (Univ. of Malaga), L. Hernandez-Garcia (Univ. of Valparaiso), M. Gritsevich (Univ. of Helsinki), Y.-D. Hu (GXU), B.-B. Zhang (Nanjing Univ.), and A. Maury (Space Obs., San Pedro de Atacama), on behalf of a larger collaboration, report: Following the detection of GRB 250530C by Swift (Osborne et al., GCNC [40586](https://gcn.nasa.gov/circulars/40586)), the 0.6m BOOTES-7 robotic telescope at Space Observatory (San Pedro de Atacama, Chile) automatically responded to this high-energy event starting on May 21, 09:42:59 UT (i.e., 14.73 hour after detection), observing at low elevation (airmass ≈ 5). No optical transient is detected down to 16.4 mag (clear filter). On a coadd (11) of images at 09:51:43 UT (mid exposure time; i.e. 14.88 post burst), nothing is detected down to 18.2 mag. We would like to thank the staff at San Pedro de Atacama Space Observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/40591. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38625] GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
by GCN Circulars 31 May '25

31 May '25

TITLE: GCN CIRCULAR NUMBER: 40590 SUBJECT: GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations DATE: 25/05/31 15:39:50 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Francis Fortin (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Fredd Alvarez (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), 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), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of ZTF25aarhkyn/AT2025mgj (Andreoni et al., GCN Circ. 40566) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-05-31 03:33 to 04:32 UTC, after 9.6 days after the trigger of GRB 250521C (Fermi GBM team, GCN 40515) and obtained 16 minutes of exposure in each of the g, r and i filters. The data were reduced and stacked using the COLIBRÍ 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. We detected the candidate ZTF25aarhkyn/AT2025mgj (Andreoni et al., GCN Circ. 40566), at preliminary magnitudes of: g = 19.34 +/- 0.03 r = 19.46 +/- 0.03 i = 19.50 +/- 0.05 Compared with the NOT observations reported by Martin-Carrillo et al. (GCN Circ. 40584), we estimate a steeper temporal decay index of ~1.5. The measured colours are consistent with those typically observed in GRBs, suggesting a similar nature. Additionally, the temporal evolution may indicate that AT2025mgj is a possible off-axis GRB; however, the absence of a nearby galaxy makes this scenario unlikely. Further observations are planned in order to unravel the nature of this object. 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/40590. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38624] GRB 250530C: Swift-XRT refined Analysis
by GCN Circulars 31 May '25

31 May '25

TITLE: GCN CIRCULAR NUMBER: 40589 SUBJECT: GRB 250530C: Swift-XRT refined Analysis DATE: 25/05/31 11:31:46 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> M.A. Williams (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S. Dichiara (PSU), J.A. Kennea (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 7.7 ks of XRT data for GRB 250530C, from 90 s to 52.0 ks after the trigger. The data comprise 9 s in Windowed Timing (WT) mode (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=0.80 (+/-0.04). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.55 (+0.20, -0.19). The best-fitting absorption column is 2.8 (+1.1, -0.9) x 10^21 cm^-2, in excess of the Galactic value of 1.7 x 10^20 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 (6.1 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.8 (+1.1, -0.9) x 10^21 cm^-2 Galactic foreground: 1.7 x 10^20 cm^-2 Excess significance: 4.7 sigma Photon index: 1.55 (+0.20, -0.19) If the light curve continues to decay with a power-law decay index of 0.80, the count rate at T+24 hours will be 0.012 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.0 x 10^-13 (7.3 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01319125. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40589. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38623] GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
by GCN Circulars 31 May '25

31 May '25

TITLE: GCN CIRCULAR NUMBER: 40588 SUBJECT: GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle DATE: 25/05/31 09:10:56 GMT FROM: Paolo D'Avanzo at INAF - OAB <paolo.davanzo(a)inaf.it> P. D'Avanzo, (INAF-OAB), A. Melandri (INAF-OAR), L. Izzo (INAF - OACn), M. G. Bernardini (INAF-OAB & LUPM), R. Brivio, M. Ferro (INAF-OAB), M. Pedani (INAF-TNG) on behalf of the CIBO collaboration report: We observed the field of the GRB 250530A detected by SVOM (Wang et al., GCN Circ. 40576) with the Italian 3.6m TNG telescope, located in Canary Islands (Spain), equipped with the near-infrared camera NICS in imaging mode. A series of images were obtained with the J filters starting on 2025-05-30T20:57:35 UT (i.e. 14.4 hours post T0). Within the refined Swift/XRT error circle (Evans et al., GCN Circ. 40579; see also: https://www.swift.ac.uk/SVOM/SVOM_FIELD00017/Source1.php) a faint object is detected in the co-added image at the following coordinates: RA (J2000) = 12:26:50.53 Dec (J2000) = -02:34:32.0 +/- 0.3" We note that these coordinates are consistent (within 0.4") with those of a catalogue source reported in the DESI Legacy Imaging Survey (Duncan et al., 2022, MNRAS, 512, 366). From preliminary photometry, we estimate for this source J ~ 21.0 mag (Vega; calibrated against the 2MASS catalogue). This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France (DOI : 10.26093/cds/vizier). The original description of the VizieR service was published in 2000, A&AS 143, 23. View this GCN Circular online at https://gcn.nasa.gov/circulars/40588. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38622] Swift GRB 250530C: Global MASTER-Net observations report
by GCN Circulars 31 May '25

31 May '25

TITLE: GCN CIRCULAR NUMBER: 40587 SUBJECT: Swift GRB 250530C: Global MASTER-Net observations report DATE: 25/05/31 04:17:20 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 250530C ( R. Caputo et al., GCN 40585) errorbox 31007 sec after notice time and 31055 sec after trigger time at 2025-05-31 03:36:18 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 79 deg. The sun altitude is -23.6 deg. The galactic latitude b = -51 deg., longitude l = 216 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2887090 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 31086 | MASTER-SAAO | C | 60 | 18.6 | 31086 | MASTER- | C | 60 | 13.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40587. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38621] GRB 250530C: Enhanced Swift-XRT position
by GCN Circulars 31 May '25

31 May '25

TITLE: GCN CIRCULAR NUMBER: 40586 SUBJECT: GRB 250530C: Enhanced Swift-XRT position DATE: 25/05/31 00:38:35 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 2203 s of XRT Photon Counting mode data and 5 UVOT images for GRB 250530C, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 55.17085, -22.44801 which is equivalent to: RA (J2000): 03h 40m 41.00s Dec (J2000): -22d 26' 52.8" with an uncertainty of 2.0 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40586. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38620] GRB 250530C: Swift detection of a burst
by GCN Circulars 30 May '25

30 May '25

TITLE: GCN CIRCULAR NUMBER: 40585 SUBJECT: GRB 250530C: Swift detection of a burst DATE: 25/05/30 19:23:04 GMT FROM: Boris Sbarufatti at INAF-OAB <boris.sbarufatti(a)inaf.it> R. Caputo (GSFC), R. Caputo (NASA/GSFC), R. Gupta (NASA GSFC), J. A. Kennea (PSU), M. J. Moss (GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), T. M. Parsotan (GSFC), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB) and B. Sbarufatti (INAF-OAB) report on behalf of the Neil Gehrels Swift Observatory Team: At 18:58:42 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250530C (trigger=1319125). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 55.143, -22.459 which is RA(J2000) = 3h 40m 34s Dec(J2000) = -22d 27' 32" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Due to a telemetry gap, the immediately-available BAT light curve does not start until T+8s. This shows possible activity out to T+40 s. The count rate was ~200 counts/sec (15-350 keV), at the start of available light curve. A more complete description of the emission, including the trigger time, will require the full downlinked data from the next ground pass. The XRT began observing the field at 19:00:29.8 UT, 106.9 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 55.17029, -22.44825 which is equivalent to: RA(J2000) = 03h 40m 40.87s Dec(J2000) = -22d 26' 53.7" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 98 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (1.70 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.6 (+2.00/-1.76) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 111 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.025. Burst Advocate for this burst is R. Caputo (regina.caputo AT nasa.gov). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/40585. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38619] GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
by GCN Circulars 30 May '25

30 May '25

TITLE: GCN CIRCULAR NUMBER: 40584 SUBJECT: GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate DATE: 25/05/30 16:12:30 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> A. Martin-Carrillo (UCD), A. de Ugarte Postigo (LAM), G. Corcoran (UCD), B. Schneider (LAM), D. B. Malesani (DAWN/NBI and Radboud), A. Acebron Munoz (UNICAN), report on behalf of a larger collaboration. We observed the position of AT2025mgj (Andreoni et al., GCN 40566), a candidate optical counterpart to GRB 250521C (Fermi GBM team, GCN 40515), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained exposures in the SDSS r band (3x300 s) and SDSS z band (5x200 s) starting at 21:06 UT on 2025-05-29 (8.32 days after the Fermi trigger). The proposed candidate is well detected in both bands with an AB magnitudes of r = 19.22 +/- 0.06 z = 19.67 +/- 0.08. The photometric calibration was performed using nearby stars from the Pan-STARRS catalog and the magnitudes are not corrected for Galactic extinction. Assuming the explosion time of GRB 250521C, when compared to the last magnitude reported by Andreoni et al., (GCN 40566), our observation shows a power-law decay index of ~1.3, consistent with those typically seen in GRB afterglows. However, it should be noted that the object is much brighter than a typical GRB afterglow at T0+8 days. Further observations are planned (and encouraged) to establish the nature of this object and its association to GRB 250521C. View this GCN Circular online at https://gcn.nasa.gov/circulars/40584. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38618] GRB 250530A: EP-FXT counterpart detection
by GCN Circulars 30 May '25

30 May '25

TITLE: GCN CIRCULAR NUMBER: 40583 SUBJECT: GRB 250530A: EP-FXT counterpart detection DATE: 25/05/30 15:06:14 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> D.Y. Li (NAO, CAS), Z. H. Yang, Q. C. Zhao (IHEP, CAS), J. Yang (NJU), H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 250530A (SVOM/sb25053002, Wang et al. GCN #40576) at 2025-05-30T07:26:04 (UTC), about 1 hour after the SVOM/ECLAIRs trigger, with an exposure time of 2970s. Three uncatalogued sources are detected within the ECLAIRs error circle, among which Source 1 is spatially consistent with the candidate counterpart detected by Swift/XRT (Evans et al. GCN #40579). Preliminary analysis on these source are automatically conducted, and details are listed as follows. Source 1: EPF_J122650.7-023433 RA (J2000): 186.7114 Dec (J2000): -2.5759 Flux: 4.54 x 10^-12 erg/s/cm2 (observed, 0.5-10 kev) Flux_err: 4.89 x 10^-13 erg/s/cm2 (1 sigma) Note: This source is spatially consistent with the candidate counterpart detected by Swift/XRT, whose flux is (4.86 +/- 0.27) x 10^-11 erg/s/cm2 (0.3-10 keV). Source 2: EPF_J122627.9-023807 RA (J2000): 186.6163 Dec (J2000): -2.6354 Flux: 6.31 x 10^-14 erg/s/cm2 (observed, 0.5-10 kev) Flux_err: 1.94 x 10^-14 erg/s/cm2 (1 sigma) Source 3: EPF_J122655.8-023705 RA (J2000): 186.7326 Dec (J2000): -2.5759 Flux: 1.33 x 10^-13 erg/s/cm2 (observed, 0.5-10 kev) Flux_err: 2.74 x 10^-14 erg/s/cm2 (1 sigma) The position uncertainty of the sources are about 10 arcsec in radius (90% C.L. statistical and systematic). 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/40583. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38617] GRB 2500530A: SVOM/VT optical upper limit
by GCN Circulars 30 May '25

30 May '25

TITLE: GCN CIRCULAR NUMBER: 40582 SUBJECT: GRB 2500530A: SVOM/VT optical upper limit DATE: 25/05/30 14:07:06 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, Y. N. Ma (NAOC) and J. Palmerio (CEA), Y. Wang (PMO, CAS), R.-Z. Li (YNAO, CAS), J. X. Cao, D. F. Kong (GXU), report on behalf of the SVOM mission team. SVOM performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Wang et al., GCN 40576). SVOM/VT began observing the field at 2025-05-30T06:34:57 UTC, about 183 seconds after Tb, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. No credible candidate was detected in our single or stacked images within the error box of SVOM/Eclalirs (Wang et al., GCN 40576) or Swift/XRT (Source 1, Evans et al., GCN 40579), after excluding more than 9 minor planets found in our images. The 3 sigma limits are: | mid-time | exposure time (s) | band | upper limit (AB) | | ------------ | ------------ | ------------ | ------------ | | 868 sec | 29*50 | VT_B | 23.1 | | 868 sec | 29*50 | VT_R | 23.1 | The results are consistent with the SVOM/COLIBRÍ reports (de Ugarte Postigo et al., GCN 40578). A bright source Gaia DR3 3693833129108758912 is near at the location of XRT Source 1 with a distance of about 6.0 arcseconds. The photometry shows that the brightness of the source is stable at the level of 1% of uncertainties in both channels in VT images during our observations. This result does not favor the possiblity that the event is a stellar flare. Given the detection of the bright X-ray candidate and the optical upper limit at the early phase, this event is likey a high-redshift or heavy extinctied GRB. Deeper or redder follow-ups are encouraged to investigate the nature of the burst. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre 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. The SVOM/VT point of contact for this burst is: Rui-Zhi Li (liruizhi AT ynao.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/40582. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38616] Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB
by GCN Circulars 30 May '25

30 May '25

TITLE: GCN CIRCULAR NUMBER: 40581 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB DATE: 25/05/30 14:00:40 GMT FROM: Peter Veres at University of Alabama in Huntsville <veresp(a)gmail.com> "The Fermi Gamma-ray Burst Monitor (GBM) trigger 770296643/250530470 at 11:17:18.008 UT on 30 May 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due a particle event." View this GCN Circular online at https://gcn.nasa.gov/circulars/40581. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38615] GRB 250530B: Fermi GBM Final Real-time Localization
by GCN Circulars 30 May '25

30 May '25

TITLE: GCN CIRCULAR NUMBER: 40580 SUBJECT: GRB 250530B: Fermi GBM Final Real-time Localization DATE: 25/05/30 11:27:57 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 11:17:18 UT on 30 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250530B (trigger 770296643.008128 / 250530470). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 324.9, Dec = 11.3 (J2000 degrees, equivalent to J2000 21h 39m, 11d 18'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 0.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250530470/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250530470/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250530470/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40580. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38614] GRB 250530A: Swift-XRT counterpart detection
by GCN Circulars 30 May '25

30 May '25

TITLE: GCN CIRCULAR NUMBER: 40579 SUBJECT: GRB 250530A: Swift-XRT counterpart detection DATE: 25/05/30 10:31:16 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-IASFPA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source GRB 250530A (sb25053002), collecting 1.7 ks of Photon Counting (PC) mode data between T0+994 s and T0+2.8 ks after the trigger. We have detected a total of 2 sources. These have been automatically classified as follows: * 0 likely counterparts * 1 candidate counterpart (Source 1) * 1 uncatalogued X-ray source * 0 known X-ray sources A candidate counterpart has been found. The details of this source are: Source 1 (SWIFT J122650.6-023432): ================================== RA (J2000.0): 186.7111 = 12h 26m 50.66s Dec (J2000.0): -2.5758 = -02d 34' 32.9" Error: 3.5 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 4.1 arcmin from the SVOM/ECLAIRs position. Mean rate: 0.761 +/- 0.043 ct s^-1 Mean flux: (4.86 +/- 0.27)e-11 erg cm^-2 s^-1 Peak rate: 3.73 +/- 0.84 ct s^-1 Peak flux: (2.38 +/- 0.53)e-10 erg cm^-2 s^-1 ECF: 6.39e-11 erg cm^-2 ct^-1, assuming NH=2.47e+22 cm^-2, gamma=2.04; determined from a spectral fit. XMM UL: 1.8e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 4.4-sigma above this 3-sigma upper limit. The source IS FADING at the 4.3-sigma level. There is 1 2MASS object within the source's 3-sigma error radius. Details of the other uncatalogued X-ray source: Source 2 (SWIFT J122602.0-023341): ================================== RA (J2000.0): 186.5087 = 12h 26m 02.09s Dec (J2000.0): -2.5614 = -02d 33' 41.0" Error: 6.3 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 8.1 arcmin from the SVOM/ECLAIRs position. Mean rate: (8.4 [+3.1, -2.5])e-3 ct s^-1 Mean flux: (1.34 [+0.50, -0.40])e-12 erg cm^-2 s^-1 Peak rate: (8.4 [+3.1, -2.5])e-3 ct s^-1 Peak flux: (1.34 [+0.50, -0.40])e-12 erg cm^-2 s^-1 ECF: 1.58e-10 erg cm^-2 ct^-1, assuming NH=1.47e+22 cm^-2, gamma=0.98; determined from a spectral fit. XMM UL: 2.9e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 3.4-sigma above this 3-sigma upper limit. There is no evidence for fading. There is 1 2MASS object within the source's 3-sigma error radius. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/SVOM. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40579. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38613] GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
by GCN Circulars 30 May '25

30 May '25

TITLE: GCN CIRCULAR NUMBER: 40578 SUBJECT: GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit DATE: 25/05/30 09:26:33 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Enrique Moreno Méndez (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), Camila Angulo (UNAM), Dalya Akl (AUS), 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), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), and Y. Wang (PMO, CAS): Further analysis of the data observed by COLIBRÍ (de Ugarte Postigo et al. GCN Circ. 40577) reveals that the source that we had identified was a known minor planet (2001 VE24). Further analysis of the field, including a stack of 32x60 s images obtained in the i-band between 2025-05-30 06:40:04 to 07:10:38 UTC do not show any credible counterpart down to a 5-sigma limit of i > 22.0 mag (AB). We apologize for the confusion generated by our previous GCN. 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/40578. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38612] GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
by GCN Circulars 30 May '25

30 May '25

TITLE: GCN CIRCULAR NUMBER: 40577 SUBJECT: GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate DATE: 25/05/30 08:26:50 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Enrique Moreno Méndez (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), Camila Angulo (UNAM), Dalya Akl (AUS), 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), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), and Y. Wang (PMO, CAS): We imaged the field of the SVOM GRB 250530A (Wang et al., GCN Circ. 40576) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-05-30 06:40:04 to 06:41:59 UTC (from 489 s after the burst onset) and obtained 3x30 s of exposure in the i-band in our first stack of images. 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. We detect an uncatalogued source (after the image subtraction using Legacy Survey/PanSTARRS as template and) consistent with the ECLAIRs error circle (Wang et al., GCN Circ. 40576) at: RA(J2000) = 12:26:56.38 = 186.7349 degrees Dec(J2000) = -2:41:56.900 = -2.6991 degrees with an uncertainty of 0.5 arcsec. The preliminary magnitude derived for that source is: i = 19.49 +/- 0.07 mag Compared with subsequents stacks, we observe the fading of the brightness in this candidate, suggesting that this is indeed the afterglow of the GRB. Further analysis and observations 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/40577. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38611] GRB 250530A: SVOM detection of a burst
by GCN Circulars 30 May '25

30 May '25

TITLE: GCN CIRCULAR NUMBER: 40576 SUBJECT: GRB 250530A: SVOM detection of a burst DATE: 25/05/30 07:10:37 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y. Wang (PMO, CAS), J.X Cao (GXU), D. Turpin (CEA), M. G. Bernardini (INAF-OAB, LUPM), D. Götz (CEA), C. Plasse (CEA), L. Zhang (IHEP) on behalf of the SVOM mission team. SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250530A (SVOM burst-id sb25053002) starting at 2025-05-30T06:31:54.99 UTC (Tb). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected by both the Count Rate Trigger (CRT) and the Image Trigger (IMT). A sequence of 11 alerts was produced. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 9.50 in the 8-50 keV energy band over a time window of 20.40 seconds starting at Tb. The localization of the best alert is R.A., Dec. 186.71, -2.5648 degrees: R.A. (J2000) = 12h26m50.37s Dec. (J2000) = -02d33m53.38s with a 90% confidence level (C.L.) radius of 8.35 arcmin (including systematic error of 2 arcmin added in quadrature). The ECLAIRs light curve showed a multiple peak structure with a T90 duration of about 7.57 (-4.98 +2.48). The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250530A.png SVOM slewed to the burst. MXT began observing the field after the slew. The onboard software did not detect any x-ray source in the ECLAIRs error region. Further analysis of MXT data will be published in a future circular. VT began observing the field after the slew. The analysis of the recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments. The Space-based multi-band astronomical 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. The Burst Advocate (BA) on shift for this burst is Y. Wang: wangyun(a)pmo.ac.cn. Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/40576. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38610] GRB 250527D: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 30 May '25

30 May '25

TITLE: GCN CIRCULAR NUMBER: 40575 SUBJECT: GRB 250527D: CALET Gamma-Ray Burst Monitor detection DATE: 25/05/30 03:02:08 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> Y. Akaike (Waseda U), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, K. Kobayashi (Waseda U), Y. Shimizu, 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 250527D (Swift/BAT-GUANO localization skymap: DeLaunay et al., GCN Circ. 40573) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 23:38:44.85 UTC on 27 May 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1432424119). The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure that starts at T+2.1 sec, peaks at T+5.1 sec, and ends at T+5.6 sec. The T90 and T50 durations measured by the SGM data are 3.1 +/- 0.2 sec and 1.7 +/- 0.2 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1432424119 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/40575. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38609] GRB 250527C: Swift/UVOT Upper Limits
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40574 SUBJECT: GRB 250527C: Swift/UVOT Upper Limits DATE: 25/05/29 21:29:30 GMT FROM: noelklin(a)umbc.edu N. Klingler (UMBC / NASA-GSFC / CRESST II) reports on behalf of the Swift/UVOT team: Swift/UVOT has performed observations of GRB 250527C centered on the BAT position, RA, Dec = 21h 18m 31.92s, +52d 44' 13.2" (= 319.633, 52.737 deg; 90% uncertainty of 5 arcmin) (DeLaunay et al.; GCN 40563). UVOT collected 4536 s of data between 96 ks and 113 ks post-trigger, using the White filter. No uncatalogued/transient sources are detected, with an approximate 3 sigma upper limit > 22.56 (AB) in the 90% BAT localization region. For the X-ray sources detected by XRT (https://www.swift.ac.uk/ToO_GRBs/00021843/): sources 3, 4, and 6 fall outside the UVOT field of view. XRT source 2 is not detected. XRT source 1 is a star: TYC 3953-1190-2. XRT 5 has an optical counterpart (AB mag 17.99 +/- 0.07), but it is seen in archival DSS images and thus does not appear to be a transient. No correction has been made for the expected Galactic extinction due to the reddening of E(B-V) = 3.43 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40574. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38608] GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40573 SUBJECT: GRB 250527D: Swift/BAT-GUANO localization skymap of a burst DATE: 25/05/29 13:56:28 GMT FROM: Jimmy DeLaunay at Penn State <delauj2(a)gmail.com> James DeLaunay (PSU), Samuele Ronchini (PSU), Aaron Tohuvavohu (Caltech), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (PSU) report: Swift/BAT did not localize GRB 250527D onboard (T0: 2025-05-27T23:38:44.84 UTC, CALET trig 1432424119) The CALET notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 90 seconds of BAT event-mode data from [-45,+45] seconds around the time of the burst. All the requested event mode data was delivered to the ground. The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 20.4 in a 2.048 s analysis time bin, starting at T0 + 3.584 s. Using the NITRATES analysis, parameter estimation was performed to obtain the localization of this burst in the form of a HEALPIX Multi-Order Coverage (MOC) skymap. This localization accounts for both statistical and systematic errors. More details in the creation and calibration of these maps will soon be published (DeLaunay et al. 2025. in prep) The 90% credible area is 4,958 deg2 and the 50% credible area is 912 deg2. The integrated probability inside the coded field of view is <1%. A plot of the probability skymap can be viewed here: [skymap_plot](https://guano.swift.psu.edu/trigger_report?id=770081960/#:~:te… The probability skymap file can be downloaded from the link here [skymap_fits_file](https://guano.swift.psu.edu/files/770081960/0_n_PROBMAP) Instructions on how to read and manipulate this map can be found here: https://guano.swift.psu.edu/documentation More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=770081960 GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/ View this GCN Circular online at https://gcn.nasa.gov/circulars/40573. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38607] EP J1350.0-8622: EP-FXT follow-up observation
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40572 SUBJECT: EP J1350.0-8622: EP-FXT follow-up observation DATE: 25/05/29 13:35:43 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> D. H. Zhao, M. J. Liu (NAO, CAS), Y. Wang (PMO, CAS),W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: After the EP-WXT detection of the X-ray transient candidate EP J1350.0-8622 (Liu et al., GCN 40548, I. Perez-Garcia et al., GCN 40549), a follow-up observation was performed by EP-FXT at 2025-05-26T23:17:23 (UTC), about 24 hours after the detection, with an exposure time of 1.85 ks. An X-ray source is detected at R.A., Dec. = 207.5779, -86.3934 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% confidence level, including both statistical and systematic errors), which is likely associated with the 1eRASS J135031.1-862323. The unabsorbed 0.5-10 keV flux is estimated to be 1.9 (+1.2, -0.9) x 10^-13 erg/cm^2/s, derived using an absorbed power law model with the hydrogen column density fixed to the Galactic value of 8.2 x 10^20 cm^-2 and the photon index fixed at 2.0, due to the limited photon statistics. All uncertainties quoted above are at the 90% confidence level. 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/40572. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38606] GRB 250529B: Fermi GBM Final Real-time Localization
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40571 SUBJECT: GRB 250529B: Fermi GBM Final Real-time Localization DATE: 25/05/29 11:08:59 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 10:58:24 UT on 29 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250529B (trigger 770209109.316756 / 250529457). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 149.1, Dec = 71.6 (J2000 degrees, equivalent to J2000 09h 56m, 71d 35'), with a statistical uncertainty of 2.9 degrees. The angle from the Fermi LAT boresight is 121.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250529457/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250529457/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250529457/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40571. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38605] GRB 250527B: Swift-XRT observations
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40570 SUBJECT: GRB 250527B: Swift-XRT observations DATE: 25/05/29 09:30:00 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.A. Kennea (PSU), D.N. Burrows (PSU), M.A. Williams (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the MAXI-detected burst GRB 250527B in a series of observations tiled on the sky. The total exposure time is 3.5 ks, distributed over 12 tiles; the maximum exposure at a single sky location in the tiling was 620 s. The data were collected between T0+57.5 ks and T0+65.2 ks, and are entirely in Photon Counting (PC) mode. No X-ray sources have been detected. The 3-sigma upper limit in the field (not including the regions where the tiles overlap) ranges from ~0.02 to ~0.05 ct s^-1, corresponding to a 0.3-10 keV observed flux of 9.2e-13 to 2.0e-12 erg cm^-2 s^-1 (assuming a typical GRB spectrum). The results of the XRT-team automatic analysis of the tiled XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00136. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40570. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38604] EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40569 SUBJECT: EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6 DATE: 25/05/29 04:32:53 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Perez-Garcia, S.-Y. Wu, E. Fernandez-Garcia, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, G. Garcia-Segura and A. J. Castro-Tirado (IAA-CSIC, Granada), P. J. Meintjes and H. J. van Heerden (UFS, South Africa), A. Martin-Carrillo and L. Hanlon (UCD, Ireland), M. Gritsevich (Univ. of Helsinki) and C. J. Perez del Pulgar (UMA, Malaga), on behalf of a larger collaboration, report: Following the detection of trigger 01709177124 by EP-WXT (Hu et al. GCNC [40568](https://gcn.nasa.gov/circulars/40568)), the BOOTES-6/DPRT 0.6m robotic telescope at Boyden Observatory in Maselspoort (South Africa) responded to the alert on May. 28, 17:17 UT (i.e. 2 min after detection and 32 min after notification). Within the reported EP-FXT error circle we find the star Gaia DR3 5778356748440163840 decreasing in brightness from 14.0 to 16.0 mag in clear filter and using Gaia DR3 Gmag magnitude as reference, during a ~3 hour time interval, confirming as due to a stellar flare. We thank the staff at Boyden Observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/40569. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38603] The EP-WXT trigger 01709177124 is likely a flaring star
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40568 SUBJECT: The EP-WXT trigger 01709177124 is likely a flaring star DATE: 25/05/29 04:00:07 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> D. F. Hu (PMO, CAS), S. Q. Jiang, W. X. Wang, Y. J. Song, C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709177124 at the time of 2025-05-28T16:45:02, is likely a stellar flare associated with Gaia DR3 5778356748440163840. The estimated flux of the flare is around 1.4 x 10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 2.5 x 10^(31) 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/40568. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38602] GRB 250529A: Fermi GBM Final Real-time Localization
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40567 SUBJECT: GRB 250529A: Fermi GBM Final Real-time Localization DATE: 25/05/29 03:56:55 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 03:46:16 UT on 29 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250529A (trigger 770183181.316048 / 250529157). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 7.1, Dec = 54.7 (J2000 degrees, equivalent to J2000 00h 28m, 54d 42'), with a statistical uncertainty of 4.2 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/2025/bn250529157/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250529157/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250529157/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40567. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38601] GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40566 SUBJECT: GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart DATE: 25/05/29 02:45:22 GMT FROM: Igor Andreoni at JSI/UMD/NASA <igor.andreoni(a)gmail.com> Igor Andreoni (UNC), Anna Ho (Cornell), Vishwajeet Swain (IITB), Michael Coughlin (UMN), on behalf of the ZTF Collaboration The optical transient ZTF25aarhkyn / AT2025mgj was first detected by the Zwicky Transient Facility (ZTF, Bellm et al. 2019, Graham et al. 2019) on 2025-05-23 03:42 UT at a magnitude r = 17.61 +- 0.07 (AB) during the regular survey. The previous non-detection at the transient location was on 2025-05-09 05:23. AT2025mgj was identified as a rapidly evolving transient by the ''ZTF Realtime Search and Triggering'' project (ZTFReST; Andreoni & Coughlin et al., 2021) and by a custom filter for fast transient discovery (Ho et al., 2022) within the ZTF Collaboration. A fading rate of ~0.4 mag/day was observed in r-band in the first two days after the initial detection. This was followed by a slower evolution. The latest photometric data point, r~18.7 mag, was taken on 2025-05-27 04:07 UT. Only r-band data points are available, so we do not have color information. The rapidly fading transient AT2025mgj is spatially and temporally consistent with the “likely short” gamma-ray burst GRB 250521C detected by the Fermi GBM instrument on 2025-05-21 13:31:01.20 UT (Fermi GBM team, GCN Circular 40515). The GRB location was reported with a statistical uncertainty of 16.05 deg, the angular separation between AT2025mgj and the center of the GBM localization is 11.05 deg. Archival ZTF and Legacy Survey images do not reveal high S/N detections. A faint (r=24.21 mag) source may be present near the transient location in Legacy Survey DR10, which is classified as a likely galaxy according to Tractor modeling, although classification is challenging at such faint magnitudes. We caution that, with the data in hand, we cannot exclude that AT2025mgj is a Galactic source. The transient was found at a relatively low Galactic latitude (l, b = 161.329994, 21.4 deg) and the light curve behavior may resemble a CV. Follow-up observations are strongly encouraged to determine the nature of this optical transient and its possible association with GRB 250521C. Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan, and OKC, University of Stockholm, Sweden. Operations are conducted by Caltech's Optical Observatory (COO), Caltech/IPAC, and the University of Washington at Seattle, USA. View this GCN Circular online at https://gcn.nasa.gov/circulars/40566. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38600] GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40566 SUBJECT: GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart DATE: 25/05/29 02:45:22 GMT FROM: Igor Andreoni at JSI/UMD/NASA <igor.andreoni(a)gmail.com> Igor Andreoni (UNC), Anna Ho (Cornell), Vishwajeet Swain (IITB), Michael Coughlin (UMN), on behalf of the ZTF Collaboration The optical transient ZTF25aarhkyn / AT2025mgj was first detected by the Zwicky Transient Facility (ZTF, Bellm et al. 2019, Graham et al. 2019) on 2025-05-23 03:42 UT at a magnitude r = 17.61 +- 0.07 (AB) during the regular survey. The previous non-detection at the transient location was on 2025-05-09 05:23. AT2025mgj was identified as a rapidly evolving transient by the ''ZTF Realtime Search and Triggering'' project (ZTFReST; Andreoni & Coughlin et al., 2021) and by a custom filter for fast transient discovery (Ho et al., 2022) within the ZTF Collaboration. A fading rate of ~0.4 mag/day was observed in r-band in the first two days after the initial detection. This was followed by a slower evolution. The latest photometric data point, r~18.7 mag, was taken on 2025-05-27 04:07 UT. Only r-band data points are available, so we do not have color information. The rapidly fading transient AT2025mgj is spatially and temporally consistent with the “likely short” gamma-ray burst GRB 250521C detected by the Fermi GBM instrument on 2025-05-21 13:31:01.20 UT (Fermi GBM team, GCN Circular 40515). The GRB location was reported with a statistical uncertainty of 16.05 deg, the angular separation between AT2025mgj and the center of the GBM localization is 11.05 deg. Archival ZTF and Legacy Survey images do not reveal high S/N detections. A faint (r=24.21 mag) source may be present near the transient location in Legacy Survey DR10, which is classified as a likely galaxy according to Tractor modeling, although classification is challenging at such faint magnitudes. We caution that, with the data in hand, we cannot exclude that AT2025mgj is a Galactic source. The transient was found at a relatively low Galactic latitude (l, b = 161.329994, 21.4 deg) and the light curve behavior may resemble a CV. Follow-up observations are strongly encouraged to determine the nature of this optical transient and its possible association with GRB 250521C. Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan, and OKC, University of Stockholm, Sweden. Operations are conducted by Caltech's Optical Observatory (COO), Caltech/IPAC, and the University of Washington at Seattle, USA. View this GCN Circular online at https://gcn.nasa.gov/circulars/40566. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38599] GRB 250520A: Swift-BAT refined analysis
by GCN Circulars 28 May '25

28 May '25

TITLE: GCN CIRCULAR NUMBER: 40565 SUBJECT: GRB 250520A: Swift-BAT refined analysis DATE: 25/05/28 20:11:35 GMT FROM: Rahul Gupta at NASA GSFC <rahul.gupta(a)nasa.gov> R. Gupta (GSFC), S. D. Barthelmy (GSFC), R. A. J. Eyles-Ferris (U Leicester), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+200 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250520A (trigger #1315630) (Eyles-Ferris, et al., GCN Circ. 40491). The BAT ground-calculated position is RA, Dec = 282.265, -11.852 deg which is RA(J2000) = 18h 49m 03.6s Dec(J2000) = -11d 51' 08.6" with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment). The partial coding was 68%. The mask-weighted BAT light curve exhibits a single pulsed emission. T90 (15-350 keV) is 0.46 +- 0.15 sec (estimated error including systematics). The time-averaged spectrum from T-0.33 to T+0.23 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 0.55 +- 0.23. The fluence in the 15-150 keV band is 1.8 +- 0.2 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T-0.54 sec in the 15-150 keV band is 1.9 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1315630 View this GCN Circular online at https://gcn.nasa.gov/circulars/40565. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38598] GRB 250527C: Swift ToO observations
by GCN Circulars 28 May '25

28 May '25

TITLE: GCN CIRCULAR NUMBER: 40564 SUBJECT: GRB 250527C: Swift ToO observations DATE: 25/05/28 16:37:51 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a ToO observation of the Swift/BAT-detected event GRB 250527C. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021843 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Swift/BAT event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration. Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40564. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38597] GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
by GCN Circulars 28 May '25

28 May '25

TITLE: GCN CIRCULAR NUMBER: 40563 SUBJECT: GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst DATE: 25/05/28 15:52:17 GMT FROM: Jimmy DeLaunay at Penn State <delauj2(a)gmail.com> James DeLaunay (PSU), Aaron Tohuvavohu (Caltech), Samuele Ronchini (PSU), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report: Swift/BAT did not localize GRB 250527C onboard (T0: 2025-05-27T13:58:32.41 UTC, Fermi Trig 770047117). The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground. The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), detects the burst in a 8.192 s analysis time bin starting at T0 - 4.096 s with a sqrt(TS) of 11.6. An arcminute localization is found with DeltaLLHOut of 29.5 and a DeltaLLHPeak of 17.4. See Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut. The BAT position is RA, Dec = 319.633, 52.737 deg which is RA(J2000) = 21h 18m 31.92s Dec(J2000) = 52d 44’ 13.2″ with an estimated uncertainty of 5 arcmin radius. More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=770047148 XRT and UVOT follow-up has been requested. Results of follow-up observations will be reported in future circulars. GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/ View this GCN Circular online at https://gcn.nasa.gov/circulars/40563. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38596] EP250526a: SVOM/VT optical upper limit
by GCN Circulars 28 May '25

28 May '25

TITLE: GCN CIRCULAR NUMBER: 40562 SUBJECT: EP250526a: SVOM/VT optical upper limit DATE: 25/05/28 12:59:03 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, J. Wang, D. Y. Li (NAO, CAS), B.-T. Wang (YNAO, CAS), W. F. Wen (SZTU), J. H. Wu (GZHU), Y. Liu (NAO, CAS) report on behalf of the SVOM and EP mission team SVOM/VT conducted ToO follow-up observations of the EP250526a (Li et al., GCN 40550, Wu et al., GCN 40554). The observation started on 2025-05-27T04:04:19 UT (i.e. 7.66 hour after trigger time) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. No uncatalogued source was detected, compared to the Legacy survey, within errorbox of EP-FXT (Li et al., GCN 40550), down to 3 sigma upper limit of VT_R~23.0 mag (AB) in 16*70 sec stacked images at the mid time of 7.81 hour. The upper limit is consistent with the reports(Lipunov et al., GCN 40551, Angulo et al., GCN 40552). 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/40562. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38595] GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
by GCN Circulars 28 May '25

28 May '25

TITLE: GCN CIRCULAR NUMBER: 40561 SUBJECT: GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst DATE: 25/05/28 10:15:39 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Wang-Chen Xue, Wen-Jun Tan, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Marius Brunet (IRAP), Frédéric Piron (LUPM) report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a long burst GRB 250521D at 2025-05-21T22:21:56.3 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #40516). The real-time alert data and light curves of SVOM/GRM were downlinked to the ground through the VHF system with low latency. The GRM light curve shows that this burst consists of multiple episodes, including a possible precursor, a main emission followed by an possible extended emission, with a T90 of 12.1 +1.7/-5.4 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250521D.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 281.6, Dec= 21.3, GCN #40516), is located at about 80 degrees from the SVOM optical axis. With this localization, the time-averaged spectrum from T0–2 s to T0+15 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.9 +/-0.1 and the cutoff energy, parameterized as Epeak, is 890 +302/-194 keV. The event fluence (10-1000 keV) in this time interval is (2.95 +0.76/-0.62)E-07 erg/cm^2. Thus GRB 250521D is consistent with Type I GRBs in the 'Amati' relation diagram although the duration is much longer than 2 seconds, as shown at: https://www.bursthub.cn//admin/static/grb250521D_amati.png Since the special location of this GRB in 'Amati' relation diagram, as well as the “Type IL” pattern of lightcurve, which is similar with other “long” duration type I GRBs (i.e. GRB 211211A and GRB 230307A), a possible merger origin is suggested [1,2]. Further follow-up observations are strongly 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. 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 979 73 https://doi.org/10.3847/1538-4357/ad98ec [2] Wen-Jun Tan et al. arXiv:2504.06616 [astro-ph.HE] https://doi.org/10.48550/arXiv.2504.06616 View this GCN Circular online at https://gcn.nasa.gov/circulars/40561. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38594] GRB 250527B: Tiled Swift observations
by GCN Circulars 28 May '25

28 May '25

TITLE: GCN CIRCULAR NUMBER: 40560 SUBJECT: GRB 250527B: Tiled Swift observations DATE: 25/05/28 09:36:49 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a series of observations, tiled on the sky, of the MAXI GRB 250527B. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/xrt_products/TILED_GRB00136 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. The probability of finding serendipitous sources, unrelated to the MAXI event is high: any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration. Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40560. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38593] GRB 250520A: Gemini-South optical afterglow detection
by GCN Circulars 28 May '25

28 May '25

TITLE: GCN CIRCULAR NUMBER: 40559 SUBJECT: GRB 250520A: Gemini-South optical afterglow detection DATE: 25/05/28 04:33:41 GMT FROM: Wen-fai Fong at Northwestern University <wfong(a)northwestern.edu> Jillian Rastinejad, Wen-fai Fong (Northwestern), and Genevieve Schroeder (Cornell) report on behalf of a larger collaboration: We re-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 20x120-sec imaging in i-band starting at 2025-05-24 04:50:10.7 UT (4.1 days post-burst), at a median airmass of 1.3 and seeing of 0.6". Calibrated to Pan-STARRS DR2 (Flewelling et al., 2020, ApJS, 251, 7), we measure a 3-sigma limiting magnitude of 24.9 AB mag for the image. We perform image subtraction between our GMOS i-band images observed at 1.06 hours (Rastinejad et al., GCN 40504) and at 4.1 days post-burst. We detect a clear residual coincident within the X-ray position (Goad et al., GCN 40494) and coincident with the radio afterglow position (Schroeder et al., GCNs 40518, 40545) at: R.A. = 18:49:08.58 (J2000) Decl. = -11:52:07.9 (J2000) with an uncertainty of ~0.3". We do not detect any other significant residuals within or around the XRT localization. Given its rapid fading and spatial coincidence with the X-ray and radio afterglows, we consider this source to be the optical afterglow of the short GRB 250520A. We note that this source is distinct from the optical candidate reported previously (e.g., Xin et al., GCN 40500). Calibrated to Pan-STARRS DR2, we measure a magnitude for the optical afterglow of i = 23.9 +/- 0.2 AB mag, uncorrected for high Galactic extinction (Schlafly and Finkbeiner 2011, ApJ, 737, 103), at 1.06 hours post-burst. 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/40559. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38592] Fermi trigger No 770058372: Global MASTER-Net observations report
by GCN Circulars 28 May '25

28 May '25

TITLE: GCN CIRCULAR NUMBER: 40558 SUBJECT: Fermi trigger No 770058372: Global MASTER-Net observations report DATE: 25/05/28 04:02:49 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB250527.71 (trigger No 770058372,02h 02m 09.60s , +15d 01m 48.0s, R=9.71) errorbox 35536 sec after notice time and 35573 sec after trigger time at 2025-05-28 02:59:01 UT, with upper limit up to 18.2 mag. The observations began at zenith distance = 78 deg. The sun altitude is -31.1 deg. The galactic latitude b = -44 deg., longitude l = 148 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2884026 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 35604 | 2025-05-28 02:59:01 | MASTER-SAAO | (01h 24m 28.47s , +08d 41m 03.5s) | C | 60 | 17.7 | 35767 | 2025-05-28 03:01:44 | MASTER-SAAO | (01h 18m 04.52s , +12d 26m 58.9s) | C | 60 | 17.8 | 36322 | 2025-05-28 03:10:59 | MASTER-SAAO | (01h 24m 29.70s , +08d 40m 12.3s) | C | 60 | 17.9 | 36402 | 2025-05-28 03:12:19 | MASTER-SAAO | (01h 32m 29.52s , +08d 39m 17.3s) | C | 60 | 18.1 | 36560 | 2025-05-28 03:14:57 | MASTER-SAAO | (01h 18m 08.20s , +12d 28m 59.1s) | C | 60 | 18.0 | 37115 | 2025-05-28 03:24:12 | MASTER-SAAO | (01h 24m 28.68s , +08d 39m 13.6s) | C | 60 | 18.0 | 37195 | 2025-05-28 03:25:31 | MASTER-SAAO | (01h 32m 31.95s , +08d 41m 10.7s) | C | 60 | 18.1 | 37354 | 2025-05-28 03:28:11 | MASTER-SAAO | (01h 18m 12.02s , +12d 29m 02.7s) | C | 60 | 18.0 | 37909 | 2025-05-28 03:37:26 | MASTER-SAAO | (01h 24m 25.89s , +08d 39m 37.4s) | C | 60 | 17.9 | 37988 | 2025-05-28 03:38:45 | MASTER-SAAO | (01h 32m 34.75s , +08d 40m 49.6s) | C | 60 | 18.2 | 38147 | 2025-05-28 03:41:24 | MASTER-SAAO | (01h 18m 05.24s , +12d 29m 04.8s) | C | 60 | 18.1 | 38544 | 2025-05-28 03:48:01 | MASTER-SAAO | (01h 24m 25.46s , +08d 39m 20.1s) | C | 60 | 18.0 | 38623 | 2025-05-28 03:49:20 | MASTER-SAAO | (01h 32m 33.84s , +08d 41m 14.9s) | C | 60 | 18.3 | 38782 | 2025-05-28 03:51:59 | MASTER-SAAO | (01h 18m 04.65s , +12d 29m 03.5s) | C | 60 | 18.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40558. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38591] Fermi trigger No 770047117: Global MASTER-Net observations report
by GCN Circulars 27 May '25

27 May '25

TITLE: GCN CIRCULAR NUMBER: 40557 SUBJECT: Fermi trigger No 770047117: Global MASTER-Net observations report DATE: 25/05/27 23:16:25 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB250527.58 (trigger No 770047117,21h 07m 14.40s , +54d 07m 48.0s, R=11.19) errorbox 30074 sec after notice time and 30346 sec after trigger time at 2025-05-27 22:24:18 UT, with upper limit up to 18.9 mag. The observations began at zenith distance = 35 deg. The sun altitude is -23.2 deg. The galactic latitude b = 4 deg., longitude l = 94 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2884392 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 30376 | 2025-05-27 22:24:18 | MASTER-Kislovodsk | (21h 00m 42.39s , +58d 25m 20.9s) | C | 60 | 18.5 | 30543 | 2025-05-27 22:27:05 | MASTER-Kislovodsk | (21h 15m 57.58s , +58d 23m 21.4s) | C | 60 | 18.4 | 31835 | 2025-05-27 22:48:37 | MASTER-Kislovodsk | (21h 00m 35.18s , +58d 25m 57.2s) | C | 60 | 18.5 | 32002 | 2025-05-27 22:51:24 | MASTER-Kislovodsk | (21h 15m 52.21s , +58d 25m 43.7s) | C | 60 | 18.3 | 32090 | 2025-05-27 22:52:52 | MASTER-Kislovodsk | (20h 24m 18.82s , +56d 33m 52.5s) | C | 60 | 18.8 | 32422 | 2025-05-27 22:58:24 | MASTER-Kislovodsk | (20h 38m 49.19s , +56d 33m 27.5s) | C | 60 | 18.6 | 32836 | 2025-05-27 23:05:18 | MASTER-Kislovodsk | (21h 00m 33.74s , +58d 25m 58.8s) | C | 60 | 18.5 | 33000 | 2025-05-27 23:08:02 | MASTER-Kislovodsk | (21h 15m 47.16s , +58d 24m 43.3s) | C | 60 | 18.3 | 33082 | 2025-05-27 23:09:24 | MASTER-Kislovodsk | (20h 24m 17.09s , +56d 34m 05.8s) | C | 60 | 18.9 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40557. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38590] GRB 250527B / MAXI J1450-527 : MAXI/GSC detection
by GCN Circulars 27 May '25

27 May '25

TITLE: GCN CIRCULAR NUMBER: 40556 SUBJECT: GRB 250527B / MAXI J1450-527 : MAXI/GSC detection DATE: 25/05/27 22:44:00 GMT FROM: taiki.kawamuro(a)riken.jp T. Kawamuro (Osaka U.), M. Nakajima (Nihon U.), M. Serino (AGU), W. Iwakiri (Chiba U.), H. Negoro, K. Takagi, H. Takahashi, K. Tatano, H. Nishio (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, Y. Kawakubo, H. Hiramatsu, Y. Kondo, A. Yoshida (AGU), Y. Tsuboi, H. Sugai, N. Nagashima (Chuo U.), M. Shidatsu, Y. Niida, C. Kang, T. Nakamoto (Ehime U.), I. Takahashi, M. Niwano, N. Higuchi, Y. Yatsu (Tokyo Tech), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), S. Yamada (Tohoku U.) The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 2025-05-27 17:38:05 UT. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (222.622 deg, -52.704 deg) = (14 50 29, -52 42 14) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.12 deg and 0.11 deg, respectively. The roll angle of long axis from the north direction is 90.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 350 +- 36 mCrab (4.0-10.0keV, 1 sigma error). Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners: (222.154, -51.832) deg = (14 48 36, -51 49 55) (J2000) (221.831, -51.930) deg = (14 47 19, -51 55 48) (J2000) (222.883, -53.207) deg = (14 51 31, -53 12 25) (J2000) (223.212, -53.106) deg = (14 52 50, -53 06 21) (J2000) There was no significant excess flux in the previous transit at 17:17 UT and in the next transit at 18:50 UT with an upper limit of 20 mCrab for each. View this GCN Circular online at https://gcn.nasa.gov/circulars/40556. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38589] GCN Announcement: Browse Circulars by Event, Advanced Search, Sample Codes, Schema Release
by GCN Announcements 27 May '25

27 May '25

The GCN Team is pleased to announce new features, documentation, and a schema release on https://gcn.nasa.gov. Browse Circulars by Event By popular demand, you can now view Circulars grouped by astronomical event. In the Circulars archive (https://gcn.nasa.gov/circulars), you can now toggle between two view modes: Circulars View - View Circulars sorted inversely by Circular ID. - Use the search bar to search for text strings (e.g. https://gcn.nasa.gov/circulars/?view=index&query=250101A&startDate=&endDate=), Circulars numbers (e.g. 12345; https://gcn.nasa.gov/circulars?view=index&query=12345), or use Advanced Search (see below). Events View - View a list of astronomical events (e.g. GRB 250101A; https://gcn.nasa.gov/circulars?view=group&query=GRB+250101A), LIGO/Virgo/KAGRA S250331o (https://gcn.nasa.gov/circulars?view=group&query=LIGO%2FVirgo%2FKAGRA+S25033…), EP250101a (https://gcn.nasa.gov/circulars?view=group&query=EP250101a), expand to show all Circulars associated with that event, or tap the event name to see all related Circulars in sequence (similar to the GCN Classic Circulars archive). - Use the search bar to search by event name (e.g. GRB 250404A). - The GCN Team manually associates events with multiple names (e.g. GRB 250404A, EP250404a; https://gcn.nasa.gov/circulars/events/grb-250404a) into event groups. You can view all Circulars associated with any member of an event group by selecting that event in the event view. You can also search for an event by any event name that group. If you would like to suggest additional event names that should be in the same event group, please contact the GCN Team (https://gcn.nasa.gov/support). See additional documentation (https://gcn.nasa.gov/docs/circulars/archive) on event view, event names, and event groups. Circulars Advanced Search The Circulars archive (https://gcn.nasa.gov/circulars) now allows users to search for keywords by Subject, Body, and Submitter. Select "Advanced Search" to view and copy example syntax. See documentation (https://gcn.nasa.gov/docs/circulars/archive#advanced-search) for more details, examples, and compound query logic. Mission Notices Table The Missions page (https://gcn.nasa.gov/missions) now contains a table listing the status of all current, past, and upcoming Notices producers. You can learn about the formats and distribution mechanisms that are available for every Notice type, including the transitions to GCN Kafka. The table provides mission-specific links to signup for Notices over email and the Kafka start streaming guide. Notices Sample Code Sample code (https://gcn.nasa.gov/docs/sample) serves as a starting point for consumers of GCN Notices for functions including consuming Kafka messages, parsing plain text, VOEvent XML, and JSON format notices, and interacting with HEALPix maps. We have also included producer sample code for encoding embedded data (e.g. HEALPix maps). The GCN Team welcomes contributions of additional sample code that might be of use to our community. Apache Spark Kafka client We added Kafka client sample code for Apache Spark (https://gcn.nasa.gov/docs/client#pyspark). Apache Spark (https://spark.apache.org) is a multi-language engine for executing data engineering, data science, and machine learning on single-node machines or clusters. Schema v4.4.1 GCN Schema v4.4.1 is available with recent changes including the generic high-energy neutrino and fast radio burst schema (Release Notes; https://github.com/nasa-gcn/gcn-schema/releases/tag/v4.4.1). 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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[vsnet-grb-info 38588] GRB 250527A: Fermi GBM Final Localization
by GCN Circulars 27 May '25

27 May '25

TITLE: GCN CIRCULAR NUMBER: 40555 SUBJECT: GRB 250527A: Fermi GBM Final Localization DATE: 25/05/27 19:44:11 GMT FROM: eliza.neights(a)gmail.com The Fermi GBM team reports the detection of a likely LONG GRB "At 17:06:07.26 UT on 27 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250527A (trigger 770058372/250527713). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 30.5, Dec = 15.0 (J2000 degrees, equivalent to J2000 2h 2m, 15d 2'), with a statistical uncertainty of 9.7 degrees. The angle from the Fermi LAT boresight is 58.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250527713/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250527713/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250527713/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/40555. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38587] EP250526a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 27 May '25

27 May '25

TITLE: GCN CIRCULAR NUMBER: 40554 SUBJECT: EP250526a: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/05/27 12:44:31 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Jiahua Wu (GZHU), D. Y. Li (NAO, CAS), B.-T. Wang (YNAO, CAS), W. F. Wen (SZTU) and Y. Liu (NAO, CAS) report on behalf of the Einstein Probe team: The X-ray transient EP250526a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Li et al., GCN 40550), and followed up by several optical telescopes (Lipunov et al, GCN 40551, Angulo et al., GCN 40552), while no optical counterpart has been detected yet. Refined analysis of the WXT data shows that the event started at T0=2025-05-26T19:24:55 (UTC) and lasted for about 175 s (T90). The peak flux (0.5-4 keV) is estimated to be 4 x 10^-9 erg/s/cm^2 (T0+39 s). The averaged 0.5-4 keV spectrum of T90 can be fitted with an absorbed power-law with a Galactic hydrogen column density of 7 x 10^20 cm^-2 and a photon index of 1.31 (-/+0.42). The derived average unabsorbed 0.5-4 keV flux is 1.75 (-0.37, +0.51) x 10^-9 erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2025-05-26T19:31:10, about 375 seconds after T0, with an exposure time of 2270 seconds. The averaged 0.5-10 keV spectrum can be fitted with an absorbed power-law with a photon index of 2.59 (-0.43, +0.44). The derived unabsorbed 0.5-10 keV flux is 7.0 (-1.4, +2.0) x 10^-13 erg/s/cm^2. Another FXT observation was conducted at 2025-05-27T04:18:56, about 9 hours after T0. The X-ray spectrum can be fitted with an absorbed power-law with a photon index of 2.37 (-0.93, +0.91), and the derived unabsorbed 0.5-10 keV flux is 1.2 (-0.5, +1.2) x 10^-13 erg/s/cm^2. The absorption was fixed at the Galactic value during the spectral fitting. The uncertainties are at the 90% confidence level for the above parameters. 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). The contact TA of this source is Jiahua Wu, please contact him via the email jhwu(a)e.gzhu.edu.cn if needed. View this GCN Circular online at https://gcn.nasa.gov/circulars/40554. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38586] GRB 250314A: CIDER NB1008 upper limit
by GCN Circulars 27 May '25

27 May '25

TITLE: GCN CIRCULAR NUMBER: 40553 SUBJECT: GRB 250314A: CIDER NB1008 upper limit DATE: 25/05/27 12:41:08 GMT FROM: Zhen-Ya Zheng at Shanghai Astronomical Observatory, CAS <zhengzy(a)shao.ac.cn> Z.-Y. Zheng (SHAO), S.R. Zhu (SHAO), J. X. Wang (USTC), J. E. Rhoads (NASA/GSFC), S. Malhotra (NASA/GSFC), I. G. B. Wold (NASA/GSFC), F. Barrientos (PUC), L. Infante (LCO), W. Hu (TAMU), C. Jiang (SHAO), D. Xu (NAOC), and F. Valdes (NOIRLab) report on behalf of the CIDER collaboration: We observed the near-infrared NB1008 narrowband counterpart (Malesani et al., GCN 39727; see also Kennea et al., GCN 39734; Turpin et al., GCN 39739) of the SVOM/ECLAIRs GRB 250314A (Wang et al., GCN 39719), using the Blanco 4m Telescope equipped with the Dark Energy Camera and a small fraction of the CIDER project’s observing time. A sequence of 19 exposures of 540 s each and 4 exposures of 180s each (3.1 hrs in total) was secured in the NB1008 band, with mid time 2025 April 3 (on Apr. 2-4, about 20 days after the GRB). In a preliminary reduction, no source is detected at the GRB position down to a 1-sigma upper limiting magnitude NB1008 ~ 23.5 (AB), calibrated with the communication pipeline for DES. We also took a 0.35 hrs exposure in the i-band with DECam and no source is detected down to a 1-sigma upper limiting magnitude of i ~ 26.7 (AB), consistent with the high redshift of this GRB. If the redshift 7.27 is correct from the previous spectroscopic and photometric confirmation (z ~ 7.27; Malesani et al., GCN 39732; Rakotondrainibe et al., GCN 39743), the NB1008 filter would cover the pure Lya flux of the GRB host galaxy. The NB1008 band‘s 1-sigma upper limit of 23.5 (AB) can be converted to a Lya flux of < 4.2e-17 erg/cm^2/s, and a Lya luminosity of < 3.1e+43 erg/s at z=7.27. Based on the line emission ratio of Lya to Ha in Case B recombination (Osterbrock et al. 1989) and the relation between SFR and the Ha luminosity (Kennicutt 1998), the derived SFR of the GRB host galaxy is < 28 M_sun/yr (1-sigma upper limit). View this GCN Circular online at https://gcn.nasa.gov/circulars/40553. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38585] EP250526a: COLIBRÍ optical upper limits
by GCN Circulars 27 May '25

27 May '25

TITLE: GCN CIRCULAR NUMBER: 40552 SUBJECT: EP250526a: COLIBRÍ optical upper limits DATE: 25/05/27 08:15:01 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Camila Angulo (UNAM), Benjamin Schneider (LAM), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (AUS), 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), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the EP250526a (Li et al., GCN Circ. 40550) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-05-27 03:30 to 5:35 UTC (from 8.0 to 10.1 hours after the trigger and 58 minutes after the notice) and obtained 32 minutes of exposure in g, r and i filters (each one). 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 SkyMapper catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked images, we do not detect any new source at the FXT position (Li et al., GCN Circ. 40550) down to the following 3-sigma limit: g > 23.6 r > 23.4 i > 23.0 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/40552. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38584] EP250526a: COLIBRÍ optical upper limits
by GCN Circulars 27 May '25

27 May '25

TITLE: GCN CIRCULAR NUMBER: 40552 SUBJECT: EP250526a: COLIBRÍ optical upper limits DATE: 25/05/27 08:15:01 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Camila Angulo (UNAM), Benjamin Schneider (LAM), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (AUS), 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), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the EP250526a (Li et al., GCN Circ. 40550) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-05-27 03:30 to 5:35 UTC (from 8.0 to 10.1 hours after the trigger and 58 minutes after the notice) and obtained 32 minutes of exposure in g, r and i filters (each one). 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 SkyMapper catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked images, we do not detect any new source at the FXT position (Li et al., GCN Circ. 40550) down to the following 3-sigma limit: g > 23.6 r > 23.4 i > 23.0 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/40552. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38583] EP250526a: Global MASTER-Net observations report
by GCN Circulars 27 May '25

27 May '25

TITLE: GCN CIRCULAR NUMBER: 40551 SUBJECT: EP250526a: Global MASTER-Net observations report DATE: 25/05/27 07:36:46 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP250526a ( EP Team et al., GCN 40550) errorbox 15422 sec after notice time and 42778 sec after trigger time at 2025-05-27 07:21:21 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 57 deg. The sun altitude is -51.0 deg. The galactic latitude b = 24 deg., longitude l = 325 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2883070 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 42809 | 2025-05-27 07:21:21 | MASTER-OAFA | (14h 28m 05.95s , -34d 00m 45.3s) | C | 60 | 18.6 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40551. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38582] EP250526a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 27 May '25

27 May '25

TITLE: GCN CIRCULAR NUMBER: 40550 SUBJECT: EP250526a: Einstein Probe detection of a fast X-ray transient DATE: 25/05/27 03:02:34 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> D. Y. Li (NAO, CAS), B.-T. Wang (YNAO, CAS), W. F. Wen (SZTU), J. H. Wu (GZHU), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250526a. The transient triggered EP-WXT (ID: 01709176979) at 2025-05-26 19:28:23 (UTC). The WXT position of the source is R.A. = 217.049 deg, DEC = -34.355 deg (J2000) with an uncertainty of 2.9 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 217.0509 deg, DEC = -34.3293 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. 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/40550. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38581] EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
by GCN Circulars 26 May '25

26 May '25

TITLE: GCN CIRCULAR NUMBER: 40549 SUBJECT: EP J1350.0-8622: BOOTES-6/DPRT optical upper limit DATE: 25/05/26 21:51:45 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Perez-Garcia, E. Fernandez-Garcia, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, S.-Y. Wu, G. Garcia-Segura and A. J. Castro-Tirado (IAA-CSIC, Granada), P. J. Meintjes and H. J. van Heerden (UFS, South Africa), A. Martin-Carrillo and L. Hanlon (UCD, Ireland), M. Gritsevich (Univ. of Helsinki) and C. J. Perez del Pulgar (UMA, Malaga), on behalf of a larger collaboration, report: Following the detection of X-ray transient candidate EP J1350.0-8622 by Einstein Probe (Liu et al., GCNC [40548](https://gcn.nasa.gov/circulars/40548)), the BOOTES-6/DPRT 0.6m robotic telescope at Boyden Observatory in Maselspoort (South Africa) responded to this event starting on May 26, 16:59 UT (~ 17.7 h after trigger). No new source is detected in the WXT region up to magnitude 20.3 using the clear filter and Gaia DR3 Gmag magnitude as reference. We thank the staff at Boyden Observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/40549. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38580] EP J1350.0-8622: Einstein Probe detection of an X-ray transient candidate
by GCN Circulars 26 May '25

26 May '25

TITLE: GCN CIRCULAR NUMBER: 40548 SUBJECT: EP J1350.0-8622: Einstein Probe detection of an X-ray transient candidate DATE: 25/05/26 15:19:07 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M. J. Liu, D. H. Zhao (NAO, CAS), Y. Wang(PMO, CAS), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient candidate at 2025-05-25T23:18:23 (UTC) by the Wide-field X-ray Telescope (WXT) on board Einstein Probe (EP), which we designated EP J1350.0-8622. This source was discovered through on-ground analysis of WXT telemetry data. The WXT position of the source is R.A. = 207.494 deg, DEC = -86.373 deg (J2000) with an uncertainty of 2.6 arcmin in radius (90% C.L. statistical and systematic). The derived unabsorbed 0.5-4 keV flux by an absorbed power-law model is 6.8(+9.6/-6.8) x 10^-12 erg/cm^2/s with the column density fixed at the Galactic value of 8.2 x 10^20 cm^-2 and photon index fixed at 2. Within the WXT error circle, an X-ray source 1eRASS J135031.1-862323 was detected by eROSITA with a flux of 4.9 x 10^-14 erg/cm2/s (0.6-2.3 keV). A Gaia source Gaia DR3 5766213157904565376, likely a quasar, is 8.155 arcsec away from the eROSITA source. 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/40548. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38579] EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
by GCN Circulars 24 May '25

24 May '25

TITLE: GCN CIRCULAR NUMBER: 40547 SUBJECT: EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation DATE: 25/05/24 07:03:12 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Chao WU (NAOC), Zhe Kang (CHO), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao (NAOC), Yulei, Qiu(NAOC), Jing Wang (NAOC), Jinsong Deng (NAOC), Lei Huang (NAOC), Jianyan Wei (NAOC) report on behalf of the SVOM/C-GFT team: We observed the field of the X-ray transient WXT trigger 01709176712 from the Einstein Probe (Yang et al., GCN 40537) with LATIOS on SVOM/C-GFT. Observations started at 2025-05-23T12:52:03, ~7.54 mins after the trigger. A series of g, r, and i-band images were obtained over ~2.58 hr. Preliminary analysis shows that the flare star reported by Yang et al. (GCN 40537) and Neill et al. (GCN 40542) exhibited a g-band magnitude decline from 11.36 mag to 12.95 mag, with a color variation (g−i) of~ 0.73 mag (from −0.24 to +0.49) between 11 and 162 minutes post trigger. Magnitudes were calibrated with nearby Pan-STARRS1 stars and were not corrected for dust extinction. We thank the observation assistants Bowen Li and Shuai Liu at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec ×21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k×4k CMOS camera at the prime focus with a 1.28 deg × 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/40547. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38578] GRB 250520A: 3 GHz MeerKAT Detection
by GCN Circulars 24 May '25

24 May '25

TITLE: GCN CIRCULAR NUMBER: 40546 SUBJECT: GRB 250520A: 3 GHz MeerKAT Detection DATE: 25/05/24 00:23:36 GMT FROM: Genevieve Schroeder at Cornell University <genevieveschroeder(a)u.northwestern.edu> G. Schroeder (Cornell), L. Rhodes (TSI/McGill), W. Fong (Northwestern), A. J. Levan (Radboud and Warwick) report: We observed the location of the short-duration GRB 250520A (Eyles-Ferris et al., GCN 40491; SVOM/GRM Team, GCN 40495; Tembhurnikar et al., GCN 40497; Frederiks et al., GCN 40512; Asaoka et al., GCN 40519; Dafcikova et al., GCN 40540) with the MeerKAT radio telescope at 3.1 GHz for a total of 2 hours at a mid time of 2025 May 23 at 03:50 UT (3.05 days post burst). In preliminary analysis, we detect a ~3.4-sigma radio source with a flux density of ~18 microJy consistent with the position of the 10 GHz radio afterglow (Schroeder et al., GCN 40518; GCN 40545) and also with the X-ray afterglow (Goad et al., GCN 40494). Further observations are planned. We thank the staff at the South African Radio Astronomy Observatory for scheduling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40546. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38577] GRB 250520A: 10 GHz VLA Afterglow Confirmation
by GCN Circulars 24 May '25

24 May '25

TITLE: GCN CIRCULAR NUMBER: 40545 SUBJECT: GRB 250520A: 10 GHz VLA Afterglow Confirmation DATE: 25/05/24 00:21:19 GMT FROM: Genevieve Schroeder at Cornell University <genevieveschroeder(a)u.northwestern.edu> G. Schroeder (Cornell), W. Fong (Northwestern), T. Laskar (Utah) report: We re-observed the location of the short-duration GRB 250520A (Eyles-Ferris et al., GCN 40491; SVOM/GRM Team, GCN 40495; Tembhurnikar et al., GCN 40497; Frederiks et al., GCN 40512; Asaoka et al., GCN 40519; Dafcikova et al., GCN 40540) with the Karl G. Jansky Very Large Array (VLA) in C configuration under program 25A-063 (PI Schroeder) at a mid time of 2025 May 21 at 11:24 UT (3.36 days post-burst) for a total of 2.25 hours at a mean frequencies of 6 and 10 GHz. The radio source detected in the previous 10 GHz VLA observation at 1.28 days (Schroeder et al., GCN 40518) is no longer detected at 3.36 days, to a 3 sigma limit of 10 microJy. Given the fading of this source, and its positional coincidence with the XRT afterglow (Goad et al., GCN 40494), we consider it to be the radio afterglow of GRB 250520A. We thank the VLA staff for quickly approving and executing these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40545. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38576] Fermi GRB 250523A: Global MASTER-Net observations report
by GCN Circulars 23 May '25

23 May '25

TITLE: GCN CIRCULAR NUMBER: 40544 SUBJECT: Fermi GRB 250523A: Global MASTER-Net observations report DATE: 25/05/23 20:31:57 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 250523A ( Fermi GBM team, GCN 40538) errorbox 21017 sec after notice time and 21056 sec after trigger time at 2025-05-23 20:17:20 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 81 deg. The sun altitude is -25.3 deg. The galactic latitude b = -0 deg., longitude l = 145 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2879253 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 21087 | 2025-05-23 20:17:20 | MASTER-Kislovodsk | (03h 30m 46.09s , +56d 01m 35.6s) | C | 60 | 17.1 | 21175 | 2025-05-23 20:18:48 | MASTER-Kislovodsk | (03h 45m 14.18s , +56d 02m 05.0s) | C | 60 | 17.0 | 21462 | 2025-05-23 20:23:35 | MASTER-Kislovodsk | (03h 02m 54.34s , +56d 12m 15.7s) | C | 60 | 17.1 | 21545 | 2025-05-23 20:24:58 | MASTER-Kislovodsk | (03h 17m 09.58s , +56d 11m 13.2s) | C | 60 | 17.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40544. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38575] Fermi trigger No 769611916: Global MASTER-Net observations report
by GCN Circulars 23 May '25

23 May '25

TITLE: GCN CIRCULAR NUMBER: 40543 SUBJECT: Fermi trigger No 769611916: Global MASTER-Net observations report DATE: 25/05/23 20:31:00 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB250522.55 (trigger No 769611916,00h 11m 31.92s , +62d 43m 01.2s, R=22.13) errorbox 14609 sec after notice time and 14646 sec after trigger time at 2025-05-22 17:09:17 UT, with upper limit up to 17.3 mag. The observations began at zenith distance = 76 deg. The sun altitude is -18.5 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB250522.55 errorbox 38205 sec after notice time and 38241 sec after trigger time at 2025-05-22 23:42:32 UT, with upper limit up to 19.4 mag. The observations began at zenith distance = 64 deg. The sun altitude is -17.1 deg. The galactic latitude b = 0 deg., longitude l = 119 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2878290 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 14649 | 2025-05-22 17:09:17 | MASTER-Tunka | (02h 05m 46.41s , +50d 25m 27.7s) | C | 6 | 15.6 | 14728 | 2025-05-22 17:10:35 | MASTER-Tunka | (00h 05m 25.37s , +43d 01m 08.1s) | C | 6 | 13.3 | 15462 | 2025-05-22 17:22:50 | MASTER-Tunka | (00h 13m 45.70s , +53d 52m 42.5s) | C | 6 | 16.3 | 16126 | 2025-05-22 17:33:54 | MASTER-Tunka | (00h 42m 26.97s , +70d 56m 56.4s) | C | 6 | 16.9 | 16151 | 2025-05-22 17:34:18 | MASTER-Tunka | (23h 20m 09.37s , +62d 13m 49.0s) | C | 6 | 16.7 | 16175 | 2025-05-22 17:34:42 | MASTER-Tunka | (22h 25m 24.81s , +52d 48m 43.4s) | C | 6 | 16.2 | 16669 | 2025-05-22 17:42:57 | MASTER-Tunka | (22h 55m 39.92s , +83d 36m 50.1s) | C | 6 | 17.2 | 16693 | 2025-05-22 17:43:21 | MASTER-Tunka | (22h 02m 28.60s , +71d 56m 01.9s) | C | 6 | 17.3 | 16718 | 2025-05-22 17:43:46 | MASTER-Tunka | (21h 26m 18.01s , +60d 32m 24.2s) | C | 6 | 17.3 | 21581 | 2025-05-22 19:04:06 | MASTER-Tunka | (00h 42m 07.07s , +41d 08m 07.5s) | C | 90 | 14.5 | 21581 | 2025-05-22 19:04:06 | MASTER- | (00h 41m 41.55s , +41d 04m 52.5s) | C | 90 | 14.4 | 38332 | 2025-05-22 23:42:32 | MASTER-Kislovodsk | (00h 41m 39.16s , +41d 22m 03.8s) | C | 180 | 19.0 | 38512 | 2025-05-22 23:42:32 | MASTER-Kislovodsk | (00h 41m 39.16s , +41d 22m 04.0s) | C | 540 | 19.4 | Coadd 38533 | 2025-05-22 23:45:53 | MASTER-Kislovodsk | (00h 41m 32.32s , +41d 21m 36.5s) | C | 180 | 18.8 | 38735 | 2025-05-22 23:49:16 | MASTER-Kislovodsk | (00h 41m 32.44s , +41d 22m 40.1s) | C | 180 | 18.8 | 112734 | 2025-05-23 20:23:35 | MASTER-Kislovodsk | (03h 02m 54.34s , +56d 12m 15.7s) | C | 60 | 17.1 | 112817 | 2025-05-23 20:24:58 | MASTER-Kislovodsk | (03h 17m 09.58s , +56d 11m 13.2s) | C | 60 | 17.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40543. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38574] EP-WXT trigger 01709176712: GOTO observations confirm stellar counterpart variability
by GCN Circulars 23 May '25

23 May '25

TITLE: GCN CIRCULAR NUMBER: 40542 SUBJECT: EP-WXT trigger 01709176712: GOTO observations confirm stellar counterpart variability DATE: 25/05/23 19:51:55 GMT FROM: Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK <amitkundu515(a)gmail.com> D. O'Neill, A. Kumar, K. Ulaczyk, B. P. Gompertz, G. Ramsay, S. Moran, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the 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 EP/WXT alert EP-WXT 01709176712 (Yang et al., GCN 40537). Targeted observations were performed beginning at 2025-05-23 12:56:35 UT (+0.2h post trigger) and continued through to 2025-05-23 15:17:24 UT (+2.55h post trigger). Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. We identify the stellar source reported by Yang et al., GCN 40537. Pre-trigger photometry from the GOTO archive shows the source exhibiting variability in the order of ±0.3 mag over the last 30 days. The latest pre-trigger photometry taken at 2025-05-22 21:44:20 UT (-15.0 h) has L = 15.38 ± 0.01 mag. Post trigger, the star rises to a peak L = 13.09 ± 0.01 mag at 2025-05-23 12:56:35 UT (+0.20 h) before fading to 14.29 ± 0.01 mag at 2025-05-23 15:17:24 UT (+2.55 h). Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. Reported magnitudes are in the AB system. 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 and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/40542. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38573] GRB 250521A: GRBAlpha detection
by GCN Circulars 23 May '25

23 May '25

TITLE: GCN CIRCULAR NUMBER: 40541 SUBJECT: GRB 250521A: GRBAlpha detection DATE: 25/05/23 18:31:11 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> 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), N. Husarikova, F. Munz , M. Topinka, M. Duriskova, M. Kolar, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration. The long-duration GRB 250521A (Fermi/GBM detection: GCN 40508) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract). The detection was confirmed at the peak time 2025-05-21 04:27:02.6 UTC. The T90 duration measured by GRBAlpha is 21 s and the overall significance during T90 reaches 8.6 sigma. The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250521A_GCN.pdf All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/ GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume. View this GCN Circular online at https://gcn.nasa.gov/circulars/40541. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38572] GRB 250520A: GRBAlpha detection
by GCN Circulars 23 May '25

23 May '25

TITLE: GCN CIRCULAR NUMBER: 40540 SUBJECT: GRB 250520A: GRBAlpha detection DATE: 25/05/23 18:30:23 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> 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), N. Husarikova, F. Munz , M. Topinka, M. Duriskova, M. Kolar, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration. The short-duration GRB 250520A (Swift/BAT detection: GCN 40491; SVOM/GRM detection: GCN 40495; AstroSat/CZTI detection: GCN 40497; Wind/Konus detection: GCN 40512, CALET/CGBM detection: GCN 40519) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract). The detection was confirmed at the peak time 2025-05-20 02:42:16.5 UTC. The T90 duration measured by GRBAlpha is 0.5 s and the overall significance during T90 reaches 11 sigma. The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250520A_GCN.pdf All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/ GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume. View this GCN Circular online at https://gcn.nasa.gov/circulars/40540. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38571] GRB 250523A: BALROG localization (Fermi Trigger 769703188 / GRB 250523602)
by GCN Circulars 23 May '25

23 May '25

TITLE: GCN CIRCULAR NUMBER: 40539 SUBJECT: GRB 250523A: BALROG localization (Fermi Trigger 769703188 / GRB 250523602) DATE: 25/05/23 14:53:57 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 769703188 at 14:26:23 on 23 May 2025 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) = 64.4 deg Decl.(2000.0) = 53.7 deg The 1 sigma statistical error radius is 2.9 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB250523602/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB250523602/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB250523602/json View this GCN Circular online at https://gcn.nasa.gov/circulars/40539. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38570] GRB 250523A: Fermi GBM Final Real-time Localization
by GCN Circulars 23 May '25

23 May '25

TITLE: GCN CIRCULAR NUMBER: 40538 SUBJECT: GRB 250523A: Fermi GBM Final Real-time Localization DATE: 25/05/23 14:36:55 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 14:26:23 UT on 23 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250523A (trigger 769703188.305002 / 250523602). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 52.9, Dec = 55.2 (J2000 degrees, equivalent to J2000 03h 31m, 55d 12'), with a statistical uncertainty of 3.0 degrees. The angle from the Fermi LAT boresight is 38.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250523602/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250523602/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250523602/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40538. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38569] The EP-WXT trigger 01709176712 is likely a flaring star
by GCN Circulars 23 May '25

23 May '25

TITLE: GCN CIRCULAR NUMBER: 40537 SUBJECT: The EP-WXT trigger 01709176712 is likely a flaring star DATE: 25/05/23 13:45:17 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J.Yang (NJU), R.-Z. Li (YNAO, CAS), Q.-C. Shui (IHEP, CAS), H.-Q. Cheng and C.-C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709176712 at the time of 2025-05-23T12:44:31, is likely a stellar flare associated with Gaia DR3 6277472183485764992 (R.A., DEC. = 213.94224, -21.58397 deg.). The estimated flux of the flare is around 8e-11 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 2.5e+33 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/40537. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38568] GRB 250521B: SVOM/VT optical upper limit
by GCN Circulars 23 May '25

23 May '25

TITLE: GCN CIRCULAR NUMBER: 40536 SUBJECT: GRB 250521B: SVOM/VT optical upper limit DATE: 25/05/23 12:43:46 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, Y. L. Qiu, L. P. Xin, C. Wu, Z. H. Yao, 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), J. Palmerio (CEA), A. Foisseau (APC) and C. Lachaud (APC) report on behalf of the SVOM/VT team. SVOM/VT conducted ToO follow-up observations of the GRB 250521B (Foisseau et al., GCN 40513). The observation started on 2025-05-21T20:11:45 UT (i.e. 15.87 hour after trigger time) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. No uncatalogued source was detected, compared to the Legacy survey, within errorboxes of the candidates reported by Swift-XRT (Evans et al., GCN 40517) and EP-FXT (Shui et al., GCN 40532), down to 3 sigma upper limit of VT_R~24.0 mag (AB) in 109*100 sec stacked images at the mid time of 19.29 hour. The upper limit is consistent with the report by Angulo et al. (GCN 40521). 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/40536. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38567] The EP-WXT trigger 01709176612: SVOM/VT optical observations
by GCN Circulars 23 May '25

23 May '25

TITLE: GCN CIRCULAR NUMBER: 40535 SUBJECT: The EP-WXT trigger 01709176612: SVOM/VT optical observations DATE: 25/05/23 12:16:31 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, J. Wang, H. Q. Cheng (NAO, CAS), Q. C. Shui (IHEP, CAS), Y. J. Song, Z. X. Ling (NAO, CAS) report on behalf of the SVOM and EP mission teams: SVOM performed a Target of Opportunity observation of he EP-WXT trigger 01709176612 (Song et al., GCN 40523, Chen et al.,, GCN 40534). SVOM/VT began observing the field at 2025-05-22T06:57:11 UTC, 60.32 min after the trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The exposure time for each frame is 70 seconds. The WISEA J122501.45-521614.6 identified as the counterpart of the trigger (Evans et al., GCN 40528, Chen et al., GCN 40534) was saturated in all VT_R band images, but showed a fading for roughly 0.5 mag from saturated to about 13.3 mag (AB) in VT_B band during our 2 orbit observations. The optical variation in VT_B is consistent with the stellar flare (Chen et al., GCN 40534). 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/40535. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38566] The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation
by GCN Circulars 23 May '25

23 May '25

TITLE: GCN CIRCULAR NUMBER: 40534 SUBJECT: The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation DATE: 25/05/23 10:06:35 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H. Q. Cheng (NAO, CAS), Q. C. Shui (IHEP, CAS), Y. J. Song, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: The on-ground analysis of EP-FXT observations shows that the EP-WXT trigger (ID: 01709176612) should be originated from a stellar flare associated with WISEA J122501.45-521614.6, but not Gaia DR3 6077506855610363648. A better localization from the refined analysis is derived as R.A. = 186.2573 deg, Dec = -52.2713 deg (J2000), with an error radius of 10 arcsec (90% C.L.). This is spatially coincident with WISEA J122501.45-521614.6, with a separation of 3.4 arcsec. The result is consistent with the candidate counterpart identified in Swift/XRT observations (Evans et al., GCN #40528). Based on this positional agreement, we suggest that the EP-WXT trigger originates from WISEA J122501.45-521614.6. The previously suggested Young Stellar Object (YSO) candidate, Gaia DR3 6077506855610363648 (Song et al. GCN #40523), has been excluded as the counterpart due to its larger offset of 14.1 arcsec from the FXT error circle. View this GCN Circular online at https://gcn.nasa.gov/circulars/40534. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38565] Fermi GRB 250522B: Global MASTER-Net observations report
by GCN Circulars 23 May '25

23 May '25

TITLE: GCN CIRCULAR NUMBER: 40533 SUBJECT: Fermi GRB 250522B: Global MASTER-Net observations report DATE: 25/05/23 07:31:07 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 250522B ( Fermi GBM team, GCN 40531) errorbox 27574 sec after notice time and 49860 sec after trigger time at 2025-05-23 06:59:53 UT, with upper limit up to 20.3 mag. The observations began at zenith distance = 29 deg. The sun altitude is -55.1 deg. The galactic latitude b = -24 deg., longitude l = 343 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2878662 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 49910 | 2025-05-23 06:59:53 | MASTER-OAFA | (19h 44m 22.76s , -56d 37m 08.7s) | C | 100 | 18.9 | 49920 | 2025-05-23 06:59:53 | MASTER-OAFA | (20h 00m 53.97s , -56d 11m 31.1s) | C | 120 | 20.2 | 50055 | 2025-05-23 07:02:17 | MASTER-OAFA | (19h 44m 22.46s , -56d 38m 27.6s) | C | 100 | 18.9 | 50065 | 2025-05-23 07:02:17 | MASTER-OAFA | (20h 00m 54.27s , -56d 12m 49.5s) | C | 120 | 20.2 | 50193 | 2025-05-23 07:04:35 | MASTER-OAFA | (19h 44m 26.76s , -56d 36m 55.4s) | C | 100 | 19.1 | 50203 | 2025-05-23 07:04:35 | MASTER-OAFA | (20h 00m 57.96s , -56d 11m 17.4s) | C | 120 | 20.3 | 50328 | 2025-05-23 07:06:51 | MASTER-OAFA | (19h 44m 20.88s , -56d 37m 43.4s) | C | 100 | 19.0 | 50339 | 2025-05-23 07:06:51 | MASTER-OAFA | (20h 00m 52.54s , -56d 12m 05.3s) | C | 120 | 20.2 | 50465 | 2025-05-23 07:09:07 | MASTER-OAFA | (19h 44m 22.05s , -56d 36m 37.8s) | C | 100 | 18.9 | 50475 | 2025-05-23 07:09:07 | MASTER-OAFA | (20h 00m 53.32s , -56d 11m 00.0s) | C | 120 | 20.2 | 50601 | 2025-05-23 07:11:23 | MASTER-OAFA | (19h 44m 26.58s , -56d 37m 34.2s) | C | 100 | 18.9 | 50611 | 2025-05-23 07:11:23 | MASTER-OAFA | (20h 00m 58.26s , -56d 11m 55.7s) | C | 120 | 20.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40533. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38564] GRB 250521B: EP-FXT follow-up observation and afterglow candidates
by GCN Circulars 23 May '25

23 May '25

TITLE: GCN CIRCULAR NUMBER: 40532 SUBJECT: GRB 250521B: EP-FXT follow-up observation and afterglow candidates DATE: 25/05/23 07:17:35 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. C. Shui (IHEP, CAS), H. Q. Cheng, Y. J. Song, Z. X. Ling (NAO, CAS), A. Foisseau, C. Lachaud (APC), M. Brunet (IRAP), N. Dagoneau (CEA) report on behalf of the Einstein Probe and SVOM team We performed a follow-up observation of GRB 250521B (detected through offline search of SVOM/ECLAIRs, Foisseau et al, GCN #40513; followed by Swift/XRT, Evans et al. GCN #40517 and SVOM/COLIBRI, Angulo et al. GCN #40521), with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation began at 2025-05-22T02:46:16 (T-TGRB ~ 22.5 hrs), and the exposure time is about 5.2 ks. 3 uncatalogued sources were detected both by FXTA and FXTB in the 90% localization error circle provided by SVOM/ECLAIRs (with a radius of 12.2 arcmin centered at RA, DEC = 200.822 deg, +1.766 deg), as listed below (the FXT flux is taken from FXTB module). Source name | RA | DEC | Estimated Flux | SNR | Dist from SVOM/ECLAIRs | | deg | deg | (erg/s/cm^2) | | offset (in arcmin) | ----------------------------------------------------------------------------- EP J132305.4+015154 | 200.7724 | 1.865 | 4.7(+/-1.3) x 10^-14 | 4.0 | 6.64 | EP J132344.5+015453 * | 200.9355 | 1.9148 | 1.3(+/-0.3) x 10^-13 | 8.1 | 11.23 | EP J132351.8+015429 | 200.9659 | 1.908 | 7.8(+/-1.8) x 10^-14 | 5.1 | 12.13 | ----------------------------------------------------------------------------- Note: * EP J132344.5+015453 was also detected by Swift/XRT (GCN #40517) in a ~2.8 ks observation conducted at 2025-05-21T23:46:50, with a flux of ~2.4e-13 erg/s/cm^2. The source thus exhibits a decreasing trend in the X-ray flux within two epochs. The above observation was made with the EP-FXT instrument. 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). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES. View this GCN Circular online at https://gcn.nasa.gov/circulars/40532. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38563] GRB 250522B: Fermi GBM Final Localization
by GCN Circulars 23 May '25

23 May '25

TITLE: GCN CIRCULAR NUMBER: 40531 SUBJECT: GRB 250522B: Fermi GBM Final Localization DATE: 25/05/23 00:55:12 GMT FROM: Matt Godwin <msg0028(a)uah.edu> The Fermi GBM team reports the detection of a likely LONG GRB "At 17:08:52.84 UT on 22 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250522B (trigger 769626537/250522714). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 285.32, Dec = -54.30 (J2000 degrees, equivalent to J2000 19h 1m, -54d 17'), with a statistical uncertainty of 11.40 degrees. The angle from the Fermi LAT boresight is 80 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250522714/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250522714/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250522714/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/40531. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38562] GRB 250521D: SVOM/VT optical observations
by GCN Circulars 23 May '25

23 May '25

TITLE: GCN CIRCULAR NUMBER: 40530 SUBJECT: GRB 250521D: SVOM/VT optical observations DATE: 25/05/23 00:26:24 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> W. Zheng (UCB), L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. N. Ma, X. H. Han, J. Wang (NAOC), Y. F. Liang (PMO), Z. Q. Wang (GXU) report on behalf of the SVOM/VT team: SVOM performed a Target of Opportunity observation of GRB 250521D detected by Fermi/GBM (Fermi GBM team, GCN 40516). SVOM/VT began observing the position of the counterpart candidate reported by LAST (Konno et al., GCN 40520) at 2025-05-22T05:58:37 UTC, 7.61 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. We clearly detected the candidate in VT both channels. The brightness in AB magnitude was estimated to be: Mid time (hour) | Band | Exposure Time (second) | Magnitude | Magnitude error 7.819 | VT_B | 15*100 | 19.66 | 0.02 7.819 | VT_R | 15*100 | 19.45 | 0.02 However, considering that there is no significant fading in brightness, and also this candidate was detected by GOTO (O'Neill et al., GCN 40522) before the GBM trigger, we also suggest that this candidate is an unrelated object. 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/40530. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38561] GRB 250522A: Fermi GBM Final Real-time Localization
by GCN Circulars 22 May '25

22 May '25

TITLE: GCN CIRCULAR NUMBER: 40529 SUBJECT: GRB 250522A: Fermi GBM Final Real-time Localization DATE: 25/05/22 22:12:30 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 22:01:59 UT on 22 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250522A (trigger 769644124.77991 / 250522918). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 37.3, Dec = -5.4 (J2000 degrees, equivalent to J2000 02h 29m, -5d 24'), with a statistical uncertainty of 16.9 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/2025/bn250522918/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250522918/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250522918/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40529. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38560] EP#01709176612: Swift-XRT counterpart detection of flaring star
by GCN Circulars 22 May '25

22 May '25

TITLE: GCN CIRCULAR NUMBER: 40528 SUBJECT: EP#01709176612: Swift-XRT counterpart detection of flaring star DATE: 25/05/22 19:17:02 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), M. Capalbi (INAF-IASFPA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected source EP#01709176612, collecting 2.0 ks of Photon Counting (PC) mode data between T0+4.2 ks and T0+9.7 ks after the trigger. A candidate counterpart has been found. The details of this source are: Source 1 (SWIFT J122501.5-521613): ================================== RA (J2000.0): 186.2566 = 12h 25m 01.58s Dec (J2000.0): -52.2705 = -52d 16' 13.8" Error: 3.5 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 23 arcsec from the Einstein Probe/WXT position. Mean rate: 2.883 +/- 0.078 ct s^-1 Mean flux: (9.45 +/- 0.26)e-11 erg cm^-2 s^-1 Peak rate: 5.3 +/- 1.1 ct s^-1 Peak flux: (1.74 +/- 0.37)e-10 erg cm^-2 s^-1 ECF: 3.28e-11 erg cm^-2 ct^-1, assuming NH=2.18e+21 cm^-2, gamma=2.19; determined from a spectral fit. This matches a catalogued X-ray source XMMSL3 J122501.2-521616 in the XMM-NEWTON/XMMSLEWCLN catalogue. Details: Separation: 2.9" from the XRT source Cat Rate: 6.3e-01 +/- 2.6e-01 ct s^-1 Cat Flux: 5.5e-12 +/- 2.3e-12 erg cm^-2 s^-1 (0.3-10 keV) so the source is 4.5-sigma above the catalogued flux. The source may be fading, at the 1.0-sigma level. A SIMBAD object `WISEA J122501.45-521614.6' is 1.5" away. There are 2 2MASS objects within the source's 3-sigma error radius. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. This is most likely a stellar flare of a Young Stellar Object Candidate Gaia DR3 6077506855610363648 (GCN 40523, Song et al.) The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/EP. This circular is an officicial product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40528. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38559] Fermi GRB 250521D: Global MASTER-Net observations report
by GCN Circulars 22 May '25

22 May '25

TITLE: GCN CIRCULAR NUMBER: 40527 SUBJECT: Fermi GRB 250521D: Global MASTER-Net observations report DATE: 25/05/22 19:15:49 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 250521D ( Fermi GBM team, GCN 40516) errorbox 74439 sec after notice time and 74480 sec after trigger time at 2025-05-22 19:03:16 UT, with upper limit up to 18.2 mag. The observations began at zenith distance = 63 deg. The sun altitude is -20.4 deg. The galactic latitude b = 10 deg., longitude l = 52 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2877804 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 74510 | 2025-05-22 19:03:16 | MASTER-Kislovodsk | (18h 46m 09.15s , +22d 14m 31.3s) | C | 60 | 17.9 | 74594 | 2025-05-22 19:04:40 | MASTER-Kislovodsk | (18h 54m 44.61s , +22d 15m 50.5s) | C | 60 | 17.4 | 74879 | 2025-05-22 19:09:25 | MASTER-Kislovodsk | (18h 31m 37.29s , +20d 22m 21.4s) | C | 60 | 18.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40527. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38558] Fermi trigger No 769533898: Global MASTER-Net observations report
by GCN Circulars 22 May '25

22 May '25

TITLE: GCN CIRCULAR NUMBER: 40526 SUBJECT: Fermi trigger No 769533898: Global MASTER-Net observations report DATE: 25/05/22 16:31:05 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB250521.64 (trigger No 769533898,19h 21m 48.00s , -31d 22m 01.2s, R=12.57) errorbox 44915 sec after notice time and 44947 sec after trigger time at 2025-05-22 03:54:01 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 41 deg. The sun altitude is -76.5 deg. The galactic latitude b = -20 deg., longitude l = 7 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2877526 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 44968 | 2025-05-22 03:54:01 | MASTER-OAFA | (18h 31m 55.71s , -33d 31m 15.7s) | C | 40 | 17.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40526. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38557] Fermi trigger No 769499303: Global MASTER-Net observations report
by GCN Circulars 22 May '25

22 May '25

TITLE: GCN CIRCULAR NUMBER: 40525 SUBJECT: Fermi trigger No 769499303: Global MASTER-Net observations report DATE: 25/05/22 10:47:55 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB250521.24 (trigger No 769499303,12h 46m 07.20s , -30d 31m 48.0s, R=12.01) errorbox 60162 sec after notice time and 60196 sec after trigger time at 2025-05-21 22:31:35 UT, with upper limit up to 19.0 mag. Observations started at twilight. The observations began at zenith distance = 39 deg. The sun altitude is -10.4 deg. The galactic latitude b = 32 deg., longitude l = 302 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2877064 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 60216 | 2025-05-21 22:31:35 | MASTER-OAFA | (13h 05m 11.76s , -37d 11m 03.5s) | C | 40 | 16.7 | 60227 | 2025-05-21 22:31:35 | MASTER-OAFA | (13h 16m 35.65s , -36d 46m 35.5s) | C | 60 | 12.6 | 60386 | 2025-05-21 22:34:25 | MASTER-OAFA | (13h 05m 09.04s , -35d 17m 27.8s) | C | 40 | 17.0 | 60397 | 2025-05-21 22:34:25 | MASTER-OAFA | (13h 16m 15.99s , -34d 53m 05.7s) | C | 60 | 18.7 | 60555 | 2025-05-21 22:37:14 | MASTER-OAFA | (12h 52m 33.75s , -29d 34m 03.7s) | C | 40 | 17.4 | 60566 | 2025-05-21 22:37:14 | MASTER-OAFA | (13h 03m 00.21s , -29d 09m 57.2s) | C | 60 | 19.0 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40525. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38556] GRB 250521D: DDOTI Optical Upper Limit
by GCN Circulars 22 May '25

22 May '25

TITLE: GCN CIRCULAR NUMBER: 40524 SUBJECT: GRB 250521D: DDOTI Optical Upper Limit DATE: 25/05/22 10:30:43 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Sahil Atri (U Roma), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observed the field of GRB 250521D detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 40516) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-05-22 UTC. DDOTI observed the field of GRB 250521D from 05:34 UTC to 09:09 UTC (from T+7.2 h to T+ 10.8 h after the trigger) and obtained a total exposure of 1.7 hours, alternating with other scientific programs. Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect no uncatalogued fading sources within the observed field down to a 10-sigma limiting AB magnitude of: w > 21.0 This value is not corrected for the Galactic extinction. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40524. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38555] The EP-WXT trigger 01709176612 is likely a flaring star
by GCN Circulars 22 May '25

22 May '25

TITLE: GCN CIRCULAR NUMBER: 40523 SUBJECT: The EP-WXT trigger 01709176612 is likely a flaring star DATE: 25/05/22 06:37:57 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. J. Song (NAO, CAS), Q. C. Shui (IHEP, CAS), H. Q. Cheng, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709176612 at the time of 2025-05-22T05:56:51, is likely a stellar flare associated with a Young Stellar Object Candidate Gaia DR3 6077506855610363648. The estimated flux of the flare is around 6e-11 erg/s/cm^2 in 0.5-4 keV, corresponding to an X-ray luminosity of around 1.15e32 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/40523. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38554] GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
by GCN Circulars 22 May '25

22 May '25

TITLE: GCN CIRCULAR NUMBER: 40522 SUBJECT: GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB DATE: 25/05/22 06:31:47 GMT FROM: Ben Gompertz at U of Birmingham <b.gompertz(a)bham.ac.uk> D. O'Neill, A. Kumar, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022) in response to the Fermi/GBM alert for GRB 250521D (GCN 40516, Fermi GBM team). During targeted follow-up of GRB 250521D (Fermi GBM team, GCN 40516), we detected the counterpart candidate reported by LAST in GCN 40520 (Konno et al., GCN 40520) with L = 19.72 ± 0.10 AB mag (+3.19h post trigger), and L = 19.68 ± 0.19 AB mag (+5.08h post trigger). We note however that we have a pre-trigger 5-sigma detection of the source at 2025-05-21 01:24:41 (-20.95h pre-trigger ) with L = 19.38 ±0.19 AB mags, indicating this is likely an unrelated event. The GOTO-L (400-700nm) and LAST unfiltered (comparable to Gaia Bp) bandpasses are roughly equivalent, and the combined GOTO and LAST observations suggest a variable source. 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 and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/40522. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38553] GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 22 May '25

22 May '25

TITLE: GCN CIRCULAR NUMBER: 40521 SUBJECT: GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/05/22 05:38:13 GMT FROM: Camila Angulo Valdez at UNAM <camiangulo(a)astro.unam.mx> Camila Angulo (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), A. Foisseau (APC) and C. Lachaud (APC): We imaged the field of the SVOM GRB 250521B (Foisseau et al., GCN Circ. 40513) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-05-22 03:29 to 04:08 UTC (from 23.2 to 23.8 hours after the trigger) and obtained 32 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 ECLAIRs source position (Foisseau et al., GCN Circ. 40513) down to the following 5-sigma limit: i > 22.8 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/40521. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38552] GRB 250521D: LAST tentative optical counterpart candidate
by GCN Circulars 22 May '25

22 May '25

TITLE: GCN CIRCULAR NUMBER: 40520 SUBJECT: GRB 250521D: LAST tentative optical counterpart candidate DATE: 25/05/22 04:07:48 GMT FROM: Ruslan Konno at Weizmann Institute of Science <ruslankonno(a)gmail.com> R. Konno (WIS), S. Garrappa (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), S. Fainer (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), S. Spitzer (WIS), and K. Rybicki (WIS) on behalf of the LAST Collaboration We report observations of GRB 250521D (GCN #40516), detected by Fermi-GBM, with the Large Array Survey Telescope (LAST; Ofek et al. 2023; Ben-Ami et al. 2023). We observe the field of GRB 250521D using 20 telescopes, each with a FoV of 7.4 deg^2 and no filter (clear - similar to the GAIA Bp band) over several epochs. In each epoch, we coadd 20x20s images. The standard limiting magnitude of a single 20x20s coadd is about 20.5 (AB mag). We began observations at 2025-05-21 22:47:38 UTC (T-T0 = 25.7 min). The observations are performed by tiling the 90% confidence area, supplied by the glg_healpix_all_bn250521932.fit map, with predefined LAST observation fields. We cover a total area of about 240 deg^2, corresponding to an integrated localization probability of about 56%. We found one new optical transient candidate, reported as AT 2025kze to TNS, in our automatic transient-detection pipeline (Konno et al., in prep.) which showed a brightening during observations. The candidate coordinates are RA, Dec = 278.4350830, 17.5896389 deg, which is 1.95 deg away from the best-fit position reported in GCN #40516. The associated photometry is | JD | T-T0 (h) | Mag | |----------------|----------|-------------------| | 2460817.45206228 | 0.48 | 20.50 (UL) | | 2460817.46226134 | 0.73 | 20.50 (UL) | | 2460817.48502633 | 1.27 | 20.105 ± 0.098 | | 2460817.50906663 | 1.85 | 19.722 ± 0.083 | The reported magnitudes are in the AB system, calibrated against the GAIA DR3 catalog, with no filter (clear). The position shows no LAST detections prior to the GRB trigger time, with the latest observations dating to 2025-04-21 01:33:59 UTC. Neither do we find any evidence of this source prior to the GRB trigger time in the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021). There is a faint ambiguous extended underlying source at the candidate position visible in survey images provided by the SDSS SkyServer. Follow-up observations are encouraged to determine the nature of this candidate or the underlying source present in survey images. LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/). View this GCN Circular online at https://gcn.nasa.gov/circulars/40520. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38551] GRB 250520A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 22 May '25

22 May '25

TITLE: GCN CIRCULAR NUMBER: 40519 SUBJECT: GRB 250520A: CALET Gamma-Ray Burst Monitor detection DATE: 25/05/22 02:30:45 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> Y. Asaoka (ICRR), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, 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 short GRB 250520A (Swift Detection: Eyles-Ferris et al., GCN Circ. 40491; SVOM/GRM observation: Wang et al., GCN Circ. 40495; AstroSat CZTI detection: Tembhurnikar et al., GCN Circ. 40497; Konus-Wind detection: Frederiks et al., GCN Circ. 40512) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 02:42:16.72 UTC on 20 May 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1431743946/index.html). The burst signal was seen by all CGBM detectors. The burst light curve shows a single pulse that starts at T+0.06 sec, peaks at T+0.19 sec, and ends at T+0.31 sec. The T90 and T50 durations measured by the SGM data are 0.21 +/- 0.04 sec and 0.09 +/- 0.01 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1431743946/ 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/40519. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38550] GRB 250520A: 10 GHz VLA radio source
by GCN Circulars 22 May '25

22 May '25

TITLE: GCN CIRCULAR NUMBER: 40518 SUBJECT: GRB 250520A: 10 GHz VLA radio source DATE: 25/05/22 02:15:16 GMT FROM: Genevieve Schroeder at Cornell University <genevieveschroeder(a)u.northwestern.edu> G. Schroeder (Cornell), J. Rastinejad, W. Fong (Northwestern), T. Laskar (Utah) report: We observed the location of the short-duration GRB 250520A (Eyles-Ferris et al., GCN 40491; SVOM/GRM Team, GCN 40495; Tembhurnikar et al., GCN 40497; Frederiks et al., GCN 40512) with the Karl G. Jansky Very Large Array (VLA) in D->C configuration under program 25A-063 (PI Schroeder) at a mid time of 2025 May 21 at 09:22 UT (1.28 days post-burst) for 1.25 hours at a mean frequency of 10 GHz. In preliminary analysis, we detect a 4-sigma radio source with a flux density of ~18 microJy at the position: RA(J2000) = 18:49:08.57 Dec(J2000) = -11:52:07.7 with an uncertainty of ~0.8" in each coordinate. This position is consistent with the X-ray position (Goad et al., GCN 40494) but offset (~2") from the optical source reported by Xin et al. (GCN 40500), which has not yet shown any evidence for fading (Yang et al., GCN 40511). At the position of the radio source, we do not detect any optical emission in Gemini i-band imaging (Rastinejad et al., GCN 40504). Further observations are planned to assess the variability of the radio source and its connection, if any, to GRB 250520A. We thank the VLA staff for quickly approving and executing these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40518. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38549] GRB 250521B: Swift ToO observations
by GCN Circulars 21 May '25

21 May '25

TITLE: GCN CIRCULAR NUMBER: 40517 SUBJECT: GRB 250521B: Swift ToO observations DATE: 25/05/21 23:45:15 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a ToO observation of the SVOM/ECLAIRs-detected event GRB 250521B. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021830 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the SVOM/ECLAIRs event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration. Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40517. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38548] GRB 250521D: Fermi GBM Final Real-time Localization
by GCN Circulars 21 May '25

21 May '25

TITLE: GCN CIRCULAR NUMBER: 40516 SUBJECT: GRB 250521D: Fermi GBM Final Real-time Localization DATE: 25/05/21 22:32:26 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 22:21:56 UT on 21 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250521D (trigger 769558921.008874 / 250521932). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 281.6, Dec = 21.3 (J2000 degrees, equivalent to J2000 18h 46m, 21d 18'), with a statistical uncertainty of 2.6 degrees. The angle from the Fermi LAT boresight is 65.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250521932/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250521932/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250521932/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40516. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38547] GRB 250521C: Fermi GBM Final Localization
by GCN Circulars 21 May '25

21 May '25

TITLE: GCN CIRCULAR NUMBER: 40515 SUBJECT: GRB 250521C: Fermi GBM Final Localization DATE: 25/05/21 18:36:09 GMT FROM: Lorenzo Scotton at UAH <lscottongcn(a)outlook.com> The Fermi GBM team reports the detection of a likely SHORT GRB "At 13:31:01.20 UT on 21 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250521C (trigger 769527066/250521563). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 105.00, Dec = 65.63 (J2000 degrees, equivalent to J2000 7h 0m, +65d 37'), with a statistical uncertainty of 16.05 degrees. The angle from the Fermi LAT boresight is 91 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250521563/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250521563/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250521563/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/40515. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38546] GRB 250521A: DDOTI Optical Upper Limit
by GCN Circulars 21 May '25

21 May '25

TITLE: GCN CIRCULAR NUMBER: 40514 SUBJECT: GRB 250521A: DDOTI Optical Upper Limit DATE: 25/05/21 17:03:34 GMT FROM: sahil.atri(a)students.uniroma2.eu Sahil Atri (U Roma), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observed the field of the GRB 250521A detected by Fermi/GBM (Fermi GBM Team, GCN 40508) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-05-21 UTC. DDOTI observed the Fermi/GBM error region, covering about 93% of the error region (Fermi GBM Team, GCN Circ. 40508). DDOTI observed the field of GRB 250521A from 04:41 UTC to 11:25 UTC (from T+0.2 h to T+ 6.7 h after the trigger) and obtained a total exposure of 2.5 hours, alternating with other scientific programs. Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect no uncatalogued fading sources within the observed field to a 10-sigma limiting AB magnitude of: w > 20.91 This value is not corrected for the Galactic extinction. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40514. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38545] GRB 250521B: SVOM detection of a burst through offline search
by GCN Circulars 21 May '25

21 May '25

TITLE: GCN CIRCULAR NUMBER: 40513 SUBJECT: GRB 250521B: SVOM detection of a burst through offline search DATE: 25/05/21 16:50:38 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Foisseau, C. Lachaud (APC), M. Brunet (IRAP), N. Dagoneau (CEA) report on behalf of the SVOM team: The SVOM/ECLAIRs telescope detected a transient source, labelled GRB 250521B, starting at 2025-05-21T04:19:17.8 UTC (Tb), through an offline search with the event-by-event data downloaded through the X-band ground station. The burst was detected within several energy ranges in a 5.12 seconds timescale. The best detection is obtained by the image trigger with a signal-to-noise ratio of 7.2 within 8-50 keV over a time window of 5.12 seconds starting at Tb. The lightcurve consists of a single pulse lasting around 5s. The localization of the source is RA, Dec = 200.822, 1.766 degrees: RA (J2000) = 13h23m17.3s Dec (J2000) = 01d45m57.6s with a 90% C.L. radius of 12.2 arcmin (including systematic error of 6 arcmin added in quadrature). We note that no bright X-ray sources are found in the error box. 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. ECLAIRs was developed jointly by APC, CEA, CNES, and IRAP. The SVOM point of contact for this event is : A. Foisseau : foisseau(a)apc.in2p3.fr Please contact him by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/40513. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38544] Konus-Wind detection of GRB 250520A (short/hard)
by GCN Circulars 21 May '25

21 May '25

TITLE: GCN CIRCULAR NUMBER: 40512 SUBJECT: Konus-Wind detection of GRB 250520A (short/hard) DATE: 25/05/21 14:42:50 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The short GRB 250520A (Swift detection: Eyles-Ferris et al., GCN 40491; SVOM/GRM observation: Wang et al., GCN 40495) triggered Konus-Wind (KW) at T0=9741.866 s UT (02:42:21.866). The burst light curve shows a single pulse, which starts at ~T0-0.07 s and has a duration of ~0.26 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/GRB250520_T09741/ As observed by Konus-Wind, the burst had the total fluence of (3.38 ± 0.75)x10^-6 erg/cm^2 and a 16-ms peak energy flux, measured from T0-0.032, of (3.49 ± 0.81)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst (measured from T0 to T0+0.192 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.48 (-0.27,+0.41), the high energy photon index beta = -2.51 (-1.99,+0.47), the peak energy Ep = 671 (-211,+247) keV, chi2 = 37/27 dof. The spectrum near the peak count rate (measured from T0 to T0+0.064 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.67 (-0.27,+0.46), the high energy photon index beta = -2.39 (-7.61,+0.53), the peak energy Ep = 1099 (-505,+876) keV, chi2 = 11/17 dof. All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40512. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38543] GRB 250520A: VLT/FORS2 Optical Observation
by GCN Circulars 21 May '25

21 May '25

TITLE: GCN CIRCULAR NUMBER: 40511 SUBJECT: GRB 250520A: VLT/FORS2 Optical Observation DATE: 25/05/21 14:13:02 GMT FROM: Yu-Han Yang at University of Rome Tor Vergata <yyang(a)roma2.infn.it> Yu-Han Yang (U Rome), Rosa L. Becerra (U Rome) and Eleonora Troja (U Rome) report on behalf of the ERC BHianca team: We observed the field of GRB 250520A (Eyles-Ferris et al., GCN 40491) with the FORS2 imager on the ESO VLT UT1 (Antu). Observations began 27.8 hours after the trigger and were carried out in the R filter with an average airmass of ~1. We detect the source previously reported as a candidate from SVOM/VT (Xin et al., GCN 40500) with a preliminary magnitude of R~23 AB mag, calibrated using nearby stars from the Pan-STARRS DR2 (Flewelling et al., 2020, ApJS, 251, 7), uncorrected for Galactic extinction. Compared to the magnitude reported by SVOM/VT (Xin et al., GCN 40500), we find no evidence of fading. No other source is detected within the XRT error circle (Goad et al. GCN 40494) down to R>24.6 (3-sigma). We thank the staff at the VLT for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40511. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38542] GRB 250502A: Tautenburg observations
by GCN Circulars 21 May '25

21 May '25

TITLE: GCN CIRCULAR NUMBER: 40510 SUBJECT: GRB 250502A: Tautenburg observations DATE: 25/05/21 14:09:26 GMT FROM: Sylvio Klose at TLS Tautenburg <klose(a)tls-tautenburg.de> K. Kritik, L. Berthel, T. Ranganathan, J. Kahl, S. Schmidl (all FSU Jena), M. Hartmann, B. Stecklum, S. Klose (all Tautenburg) report: We observed the field of GRB 250502A (Wang et. al., GCN 40313) with the 1.3m Schmidt telescope using the prime focus CCD camera. Observations started on May 2, 2025, at 22:18:13 UT, about 13.5 hrs after the SVOM trigger, at a mean airmass of 2.2. The optical transient first reported by Rakotondrainibe et. al. (GCN 40315) was clearly detected. Based on 40 min of exposure, at a midtime of 22:38 UT, we measure a preliminary r-band magnitude (AB) of 20.88 +/- 0.20 mag, calibrated against Pan-STARRS DR1. We apologize for the late submission of this circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/40510. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38541] GRB 250520A: Swift/UVOT Upper Limits
by GCN Circulars 21 May '25

21 May '25

TITLE: GCN CIRCULAR NUMBER: 40509 SUBJECT: GRB 250520A: Swift/UVOT Upper Limits DATE: 25/05/21 13:02:53 GMT FROM: Samantha Oates at University of Birmingham <samantha.oates(a)alumni.ucl.ac.uk> S. R. Oates (Lancaster U.) and R. A. J. Eyles-Ferris (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250520A 127 s after the BAT trigger (Eyles-Ferris et al., GCN Circ. 40491). No optical afterglow consistent with the enhanced XRT position (Goad et al., GCN Circ. 40494) or the SVOM/VT optical candidate (Xin et al., GCN Circ. 40500) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag/3sigUL white 149 298 147 >20.9 white 149 1373 392 >21.3 v 127 1251 110 >18.9 b 481 1349 97 >19.7 u 456 1324 97 >19.3 uvw1 432 1300 97 >19.1 uvm2 407 1275 78 >18.6 uvw2 358 1394 112 >19.2 We caution that the photometry may not be accurate, as the source region used to determine the optical/UV limits, is on an area of the UVOT detector with low sensitivity. The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.754 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40509. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[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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