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[vsnet-grb-info 38677] GRB 250606A: Fermi GBM Final Real-time Localization
by GCN Circulars 06 Jun '25

06 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40640 SUBJECT: GRB 250606A: Fermi GBM Final Real-time Localization DATE: 25/06/06 04:39:12 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 04:28:41 UT on 6 Jun 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250606A (trigger 770876926.822872 / 250606187). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 32.3, Dec = -78.2 (J2000 degrees, equivalent to J2000 02h 09m, -78d 12'), with a statistical uncertainty of 2.8 degrees. The angle from the Fermi LAT boresight is 50.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250606187/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250606187/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250606187/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40640. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38676] Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
by GCN Circulars 06 Jun '25

06 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40639 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB DATE: 25/06/06 04:37:18 GMT FROM: oindabimukherjee(a)gmail.com Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB O. Mukherjee (USRA) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 770867684/250606080 at 01:54:39.00 UT on 06 June 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to local particles." View this GCN Circular online at https://gcn.nasa.gov/circulars/40639. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38675] Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
by GCN Circulars 06 Jun '25

06 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40638 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB DATE: 25/06/06 04:33:56 GMT FROM: oindabimukherjee(a)gmail.com Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB O. Mukherjee (USRA) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 770867684/250606080 at 01:54:39.00 UT on 06 June 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to local particles." View this GCN Circular online at https://gcn.nasa.gov/circulars/40638. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38674] Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
by GCN Circulars 06 Jun '25

06 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40638 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB DATE: 25/06/06 04:33:56 GMT FROM: oindabimukherjee(a)gmail.com Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB O. Mukherjee (USRA) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 770867684/250606080 at 01:54:39.00 UT on 06 June 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to local particles." View this GCN Circular online at https://gcn.nasa.gov/circulars/40638. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38673] GRB 250602A: GECAM detection
by GCN Circulars 06 Jun '25

06 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40637 SUBJECT: GRB 250602A: GECAM detection DATE: 25/06/06 04:33:43 GMT FROM: zhengchao_astro(a)foxmail.com Chao Zheng, Chen-Wei Wang, Yan-Qiu Zhang, Shao-Lin Xiong, Yue Huang (IHEP) report on behalf of GECAM team: GECAM-A detected burst GRB 250602A at 2025-06-02T03:04:31.310 UTC (denoted as T0), which was also detected by Fermi/GBM (Fermi GBM team, GCN #40602). According to the GECAM-A light curves in about 70-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of about 8.68 s. The GECAM-A light curve can be found here: https://www.bursthub.cn//admin/static/gecamgrb250602A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/40637. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38672] Fermi trigger No 770867684: Global MASTER-Net observations report
by GCN Circulars 06 Jun '25

06 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40636 SUBJECT: Fermi trigger No 770867684: Global MASTER-Net observations report DATE: 25/06/06 04:16:29 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 GRB250606.08 (trigger No 770867684,11h 54m 36.00s , -54d 01m 12.0s, R=8.02) errorbox 145 sec after notice time and 170 sec after trigger time at 2025-06-06 01:57:29 UT, with upper limit up to 18.0 mag. The observations began at zenith distance = 81 deg. The sun altitude is -44.9 deg. MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB250606.08 errorbox 146 sec after notice time and 171 sec after trigger time at 2025-06-06 01:57:30 UT, with upper limit up to 19.4 mag. The observations began at zenith distance = 33 deg. The sun altitude is -54.5 deg. The galactic latitude b = 8 deg., longitude l = 295 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2893923 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 185 | 2025-06-06 01:57:29 | MASTER-SAAO | (12h 05m 40.89s , -53d 37m 11.1s) | C | 30 | 16.5 | 235 | 2025-06-06 01:57:29 | MASTER-SAAO | (12h 05m 40.89s , -53d 37m 11.2s) | C | 130 | 17.2 | Coadd 185 | 2025-06-06 01:57:29 | MASTER-SAAO | (12h 08m 35.38s , -53d 52m 45.4s) | C | 30 | 17.3 | 235 | 2025-06-06 01:57:29 | MASTER-SAAO | (12h 08m 35.39s , -53d 52m 45.4s) | C | 130 | 18.0 | Coadd 187 | 2025-06-06 01:57:30 | MASTER-OAFA | (12h 08m 13.05s , -53d 38m 46.7s) | C | 30 | 18.6 | 228 | 2025-06-06 01:58:06 | MASTER-OAFA | (12h 08m 13.09s , -53d 38m 46.8s) | C | 40 | 18.8 | 239 | 2025-06-06 01:58:18 | MASTER-SAAO | (12h 05m 41.09s , -53d 37m 07.5s) | C | 40 | 16.7 | 239 | 2025-06-06 01:58:18 | MASTER-SAAO | (12h 08m 35.55s , -53d 52m 43.0s) | C | 40 | 17.5 | 279 | 2025-06-06 01:58:53 | MASTER-OAFA | (12h 08m 13.22s , -53d 38m 46.8s) | C | 50 | 19.0 | 308 | 2025-06-06 01:59:17 | MASTER-SAAO | (12h 05m 41.36s , -53d 37m 03.8s) | C | 60 | 16.8 | 308 | 2025-06-06 01:59:17 | MASTER-SAAO | (12h 08m 35.78s , -53d 52m 40.3s) | C | 60 | 17.6 | 341 | 2025-06-06 01:59:49 | MASTER-OAFA | (12h 08m 13.38s , -53d 38m 46.5s) | C | 60 | 18.9 | 387 | 2025-06-06 02:00:36 | MASTER-SAAO | (12h 05m 41.68s , -53d 37m 00.3s) | C | 60 | 16.8 | 387 | 2025-06-06 02:00:36 | MASTER-SAAO | (12h 08m 36.14s , -53d 52m 38.0s) | C | 60 | 17.6 | 419 | 2025-06-06 02:01:08 | MASTER-OAFA | (12h 31m 47.57s , -49d 44m 44.7s) | C | 60 | 19.0 | 754 | 2025-06-06 02:06:43 | MASTER-OAFA | (12h 44m 15.34s , -49d 44m 12.4s) | C | 60 | 19.2 | 932 | 2025-06-06 02:09:40 | MASTER-OAFA | (12h 31m 52.61s , -49d 44m 50.8s) | C | 60 | 19.3 | 1008 | 2025-06-06 02:10:57 | MASTER-OAFA | (12h 38m 34.16s , -51d 38m 58.0s) | C | 60 | 19.1 | 1341 | 2025-06-06 02:16:30 | MASTER-OAFA | (12h 51m 33.85s , -51d 38m 22.8s) | C | 60 | 19.0 | 1417 | 2025-06-06 02:17:46 | MASTER-OAFA | (12h 44m 10.98s , -49d 45m 06.6s) | C | 60 | 19.3 | 1596 | 2025-06-06 02:20:44 | MASTER-OAFA | (12h 31m 50.62s , -49d 43m 18.2s) | C | 60 | 19.1 | 1672 | 2025-06-06 02:22:01 | MASTER-OAFA | (12h 38m 36.25s , -51d 38m 57.0s) | C | 60 | 18.6 | 1999 | 2025-06-06 02:27:28 | MASTER-OAFA | (12h 51m 34.74s , -51d 38m 15.9s) | C | 60 | 19.4 | 2077 | 2025-06-06 02:28:46 | MASTER-OAFA | (12h 44m 12.10s , -49d 45m 00.3s) | C | 60 | 19.3 | 2255 | 2025-06-06 02:31:43 | MASTER-OAFA | (12h 31m 52.06s , -49d 43m 09.8s) | C | 60 | 18.6 | 2331 | 2025-06-06 02:33:00 | MASTER-OAFA | (12h 38m 37.81s , -51d 38m 37.7s) | C | 60 | 18.2 | 2665 | 2025-06-06 02:38:33 | MASTER-OAFA | (12h 51m 36.64s , -51d 38m 08.1s) | C | 60 | 18.5 | 2740 | 2025-06-06 02:39:48 | MASTER-OAFA | (12h 44m 14.95s , -49d 44m 53.5s) | C | 60 | 18.8 | 2916 | 2025-06-06 02:42:45 | MASTER-OAFA | (12h 31m 53.39s , -49d 43m 00.2s) | C | 60 | 18.8 | 2992 | 2025-06-06 02:44:00 | MASTER-OAFA | (12h 38m 39.38s , -51d 38m 29.8s) | C | 60 | 18.7 | 3322 | 2025-06-06 02:49:30 | MASTER-OAFA | (12h 51m 38.28s , -51d 38m 00.7s) | C | 60 | 18.9 | 3398 | 2025-06-06 02:50:46 | MASTER-OAFA | (12h 44m 15.32s , -49d 44m 46.9s) | C | 60 | 19.1 | 3575 | 2025-06-06 02:53:43 | MASTER-OAFA | (12h 31m 54.88s , -49d 42m 52.8s) | C | 60 | 19.1 | 3650 | 2025-06-06 02:54:59 | MASTER-OAFA | (12h 38m 40.97s , -51d 38m 22.6s) | C | 60 | 19.1 | 3985 | 2025-06-06 03:00:34 | MASTER-OAFA | (12h 51m 38.79s , -51d 37m 54.3s) | C | 60 | 18.7 | 4066 | 2025-06-06 03:01:55 | MASTER-OAFA | (12h 44m 18.16s , -49d 44m 41.8s) | C | 60 | 18.6 | 4245 | 2025-06-06 03:04:54 | MASTER-OAFA | (12h 31m 56.32s , -49d 42m 44.8s) | C | 60 | 18.0 | 4323 | 2025-06-06 03:06:12 | MASTER-OAFA | (12h 38m 42.60s , -51d 38m 21.7s) | C | 60 | 17.8 | 4653 | 2025-06-06 03:11:42 | MASTER-OAFA | (12h 51m 41.88s , -51d 37m 49.9s) | C | 60 | 16.9 | 4729 | 2025-06-06 03:12:57 | MASTER-OAFA | (12h 44m 17.92s , -49d 44m 38.6s) | C | 60 | 17.4 | 4915 | 2025-06-06 03:16:04 | MASTER-OAFA | (12h 31m 57.78s , -49d 42m 33.6s) | C | 60 | 17.7 | 4993 | 2025-06-06 03:17:21 | MASTER-OAFA | (12h 38m 44.26s , -51d 38m 29.4s) | C | 60 | 17.7 | 5321 | 2025-06-06 03:22:50 | MASTER-OAFA | (12h 51m 43.99s , -51d 37m 46.6s) | C | 60 | 18.0 | 5398 | 2025-06-06 03:24:07 | MASTER-OAFA | (12h 44m 19.80s , -49d 44m 36.2s) | C | 60 | 17.8 | 5573 | 2025-06-06 03:27:02 | MASTER-OAFA | (12h 31m 59.29s , -49d 42m 59.2s) | C | 60 | 17.6 | 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/40636. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38671] The EP-WXT trigger 01709177873 is likely a flaring star
by GCN Circulars 06 Jun '25

06 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40635 SUBJECT: The EP-WXT trigger 01709177873 is likely a flaring star DATE: 25/06/06 02:53:28 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> T. Y. Lian, R. D. Liang (NAOC), H. L. Peng (NNU), T. C. Zheng (PMO), W. Yuan (NAOC) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709177873 at the time of 2025-06-05T18:51:47, is likely a stellar flare associated with RX J1553.0+4457. The estimated flux of the flare is around 1.2e-10 erg/s/cm^2 in 0.5-10.0 keV, corresponding to an X-ray luminosity of around 2e31 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/40635. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38670] GRB 250605A: LT optical observations
by GCN Circulars 05 Jun '25

05 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40634 SUBJECT: GRB 250605A: LT optical observations DATE: 25/06/05 22:51:33 GMT FROM: Ben Gompertz at U of Birmingham <b.gompertz(a)bham.ac.uk> B. P. Gompertz (U. Birmingham), Dimple (U. Birmingham), A. Martin-Carrillo (UCD), G. Corcoran (UCD) and D. B. Malesani (DAWN/NBI and Radboud), report on behalf of a larger collaboration: We initiated follow-up observations of GRB 250605A (Gupta et al., GCN 40633) with the IO:O camera on the 2m robotic Liverpool Telescope (LT). Observations began at 20:48:52.89 UT, ~2 hours after the Swift/BAT trigger, and consisted of 10x60 s exposures in the SDSS i filter. Observations were taken close to twilight, at high airmass, and the target was 28 deg from the moon at 77% illumination. Within the Swift/XRT error box, we detect a possible optical counterpart, not present in archival imaging, with an AB magnitude of i ~ 21.1 at RA = 11:07:49.7, Dec = -19:47:15.4. However, this detection is only significant at the 2-sigma level and further, deeper observations are required to confirm its reality. Formally, we measure a 3-sigma upper limit of i > 20.6 within the XRT localisation region. We also note the presence of a faint source visible in the Legacy Survey archival imaging with an AB magnitude of i = 23.54. The source position is consistent with the possible optical counterpart, and may be the host galaxy of GRB 250605A. Magnitudes are calibrated against nearby Pan-STARRS stars and not corrected for galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40634. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38669] GRB 250605A: Swift detection of a burst
by GCN Circulars 05 Jun '25

05 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40633 SUBJECT: GRB 250605A: Swift detection of a burst DATE: 25/06/05 19:08:03 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> R. Gupta (NASA GSFC), J. J. DeLaunay (PSU), S. Dichiara (PSU), C. Gronwall (PSU), N. J. Klingler (GSFC/UMBC/CRESSTII), H. A. Krimm (NSF), M. J. Moss (GSFC), K. L. Page (U Leicester), T. M. Parsotan (GSFC), M. H. Siegel (PSU) and M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 18:52:31.27 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250605A (trigger=1321323). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 166.977, -19.795 which is RA(J2000) = 11h 07m 54s Dec(J2000) = -19d 47' 42" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a complex light curve with one strong pulse between T0-2 sec to T0+10 sec and a second dimmer but broad pulse between T0+40 sec to T0+100 sec. The peak count rate was 4,000 counts/sec (15-350 keV), at ~2 sec after the trigger. The XRT began observing the field at 18:54:09.2 UT, 98.0 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 166.9571, -19.7882 which is equivalent to: RA(J2000) = 11h 07m 49.70s Dec(J2000) = -19d 47' 17.5" with an uncertainty of 5.5 arcseconds (radius, 90% containment). This location is 71 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. UVOT took a finding chart exposure of 144 seconds with the White filter starting 106 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 0.039. Burst Advocate for this burst is R. Gupta (rahulbhu.c157 AT gmail.com). 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/40633. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38668] Swift GRB250605.79: Global MASTER-Net observations report
by GCN Circulars 05 Jun '25

05 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40632 SUBJECT: Swift GRB250605.79: Global MASTER-Net observations report DATE: 25/06/05 18:56:40 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 GRB250605.79 (trigger No 1321323,11h 07m 54.48s , -19d 47m 42.0s, R=0.05) errorbox 16 sec after notice time and 37 sec after trigger time at 2025-06-05 18:53:08 UT, with upper limit up to 17.9 mag. The observations began at zenith distance = 31 deg. The sun altitude is -39.9 deg. The galactic latitude b = 37 deg., longitude l = 273 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2893644 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 43 | MASTER-SAAO | C | 10 | 17.9 | 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/40632. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38667] Konus-Wind detection of GRB 250601A
by GCN Circulars 05 Jun '25

05 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40631 SUBJECT: Konus-Wind detection of GRB 250601A DATE: 25/06/05 15:52:19 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The short-duration GRB 250601A (Fermi GBM detection: Fermi GBM team, GCN 40596; Sharma et al., GCN 40621; Swift/BAT-GUANO localization: DeLaunay et al., GCN 40600) triggered Konus-Wind at T0=62975.326 s UT (17:29:35.326). The burst light curve shows a multi-peaked pulse, which starts at ~T0-0.5 s and has a total duration of ~0.8 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/GRB250601_T62975/ As observed by Konus-Wind, the burst had a fluence of 2.02(-0.28,+0.31)x10^-6 erg/cm2, and a 16-ms peak flux, measured from T0-0.004 s, of 7.00(-2.01,+2.06)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). Since the brightest peak of the burst light curve was detected before the trigger, the spectral analysis was performed using the KW 3-channel light curve data. Modelling the KW 3-channel time-integrated spectrum (measured from T0-0.492 s to T0+0.276 s) by a power law with exponential cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep), yields alpha = 0.31(-0.37,+0.52) and Ep = 436(-62,+76) keV. 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/40631. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38666] IPN triangulation of GRB 250404B
by GCN Circulars 05 Jun '25

05 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40630 SUBJECT: IPN triangulation of GRB 250404B DATE: 25/06/05 15:32:58 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the HEND/Mars Odyssey team, 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, A. Tohuvavohu, and J. DeLaunay on behalf of the Swift-BAT team, G. Waratkar, J.Joshi, V. Bhalerao, D. Bhattacharya, and S. Vadawale, on behalf of the Astrosat-CZTI team, and W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report: The short-duration GRB 250404B (AstroSat CZTI detection: Salunke et al., GCN Circ. 40078) was detected by Konus-Wind, Swift (BAT), AstroSat (CZTI), and Mars-Odyssey (HEND) at about 66970 s UT (18:36:10). 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: 273.629 (18h 14m 31s) -2.251 ( -2d 15' 03") Corners: 273.108 (18h 12m 26s) -2.676 ( -2d 40' 35") 274.127 (18h 16m 31s) -1.659 ( -1d 39' 32") 274.151 (18h 16m 36s) -1.842 ( -1d 50' 30") 273.131 (18h 12m 31s) -2.866 ( -2d 51' 58") --------------------------------------------- The error box area is 768 sq. arcmin, and its maximum dimension is 1.6 deg (the minimum one is 9 arcmin). The Sun distance was 100 deg. This localization may be improved. A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB250404_T66970/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/40630. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38665] IPN triangulation of GRB 250529A
by GCN Circulars 05 Jun '25

05 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40629 SUBJECT: IPN triangulation of GRB 250529A DATE: 25/06/05 15:23:42 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the HEND/Mars Odyssey team, D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi GBM team, S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, A. Tohuvavohu, and J. DeLaunay on behalf of the Swift-BAT team, and W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report: The long-duration GRB 250529A (Fermi-GBM detection: Fermi GBM team, GCN 40567) was detected by Fermi (GBM), Konus-Wind, Swift (BAT), and Mars-Odyssey (HEND) at about 13576 s UT (03:46:16). 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: 18.193 (01h 12m 46s) +58.274 (+58d 16' 25") Corners: 21.244 (01h 24m 58s) +56.039 (+56d 02' 19") 14.840 (00h 59m 22s) +60.456 (+60d 27' 22") 14.829 (00h 59m 19s) +60.366 (+60d 21' 57") 21.225 (01h 24m 54s) +55.944 (+55d 56' 37") --------------------------------------------- The error box area is 1252 sq. arcmin, and its maximum dimension is 5.6 deg (the minimum one is 4 arcmin). The Sun distance was 48 deg. This localization may be improved. The IPN localization is consistent with, but reduces the area of, the Fermi-GBM (GCN 40567) localization. A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB250529_T13600/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/40629. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38664] The EP-WXT trigger 01709177837 is likely a flaring star
by GCN Circulars 05 Jun '25

05 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40628 SUBJECT: The EP-WXT trigger 01709177837 is likely a flaring star DATE: 25/06/05 09:41:18 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S. Q. Jiang (NAOC), T. C. Zheng (PMO), X. Y. Zhou (PRIC), H. W. Pan (NAOC) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709177837 at the time of 2025-06-05T09:24:19, is likely a stellar flare associated with RV Crt. 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 4e32 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/40628. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38663] Fermi Gamma-ray Burst Monitor trigger 770470765/250601486 is not a GRB
by GCN Circulars 04 Jun '25

04 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40627 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 770470765/250601486 is not a GRB DATE: 25/06/04 15:35:09 GMT FROM: Joe Mangan at IJCLab <joseph.mangan(a)ijclab.in2p3.fr> J. Mangan (IJCLab/CNRS) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 770470765/250601486 at 11:39:20.34 UT on 01 June 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to local particles." View this GCN Circular online at https://gcn.nasa.gov/circulars/40627. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38662] GRB 250601A: PRIME H band upper limit.
by GCN Circulars 04 Jun '25

04 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40626 SUBJECT: GRB 250601A: PRIME H band upper limit. DATE: 25/06/04 15:02:32 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva(a)uniroma1.it> N. Passaleva (U Rome), O. Guiffreda (UMD), J. Durbak (UMD), M. Elkabir (U Rome), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC) Following the Fermi Gamma-ray Burst Monitor (GBM) detection (GCN 40596), and the Swift/BAT-GUANO arcminutes localization of same event, we observed the transient field in H filter with PRIME ~47.5 hours after the initial Fermi detection. Using Two Micron All Sky Survey (2MASS) for preliminary calibration we do not detect any uncatalogued source down to H>20.6 AB (3-sigma) not corrected for galactic extinction at the position of the candidates reported by Swift/XRT (Page et al. GCN 40604, Salvaggio et al., GCN 40606) and EP/FXT (Liu et al., GCN 40607). PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023, Durbak et al. 2024). We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40626. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38661] GRB 250530A: SVOM/GRM analysis
by GCN Circulars 04 Jun '25

04 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40625 SUBJECT: GRB 250530A: SVOM/GRM analysis DATE: 25/06/04 03:52:55 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Chao Zheng, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: M. G. Bernardini (INAF-OAB, LUPM) Report on behalf of the SVOM team: SVOM/GRM detected the burst GRB 250530A at 2025-05-30T06:31:54.99 UTC (T0), which is also detected by SVOM/ECLAIRs (Wang et al., GCN #40576). With the event-by-event data downloaded through the X-band ground station, we conducted the standard analysis pipeline of GRB 250530A. The GRM light curve shows that this burst consists of a single pulse with a T90 of 15.0 +3.0/-4.0 s in the 15-5000 keV band, which is consistent with the result from VHF data. With the localization of ECLAIRs (RA=186.71, DEC=-2.5648), the time-averaged spectrum from T0 to T0+15 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.26 +0.18/-0.13 and the cutoff energy, parameterized as Epeak, is 707 +1140/-360 keV. The event fluence (10-1000 keV) in this time interval is (2.8 +/-0.4)E-06 erg/cm^2. Thus GRB 250530A 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/grb250530A_amati.png Further follow-up observations are encouraged. We note that the calibration of SVOM/GRM is undergoing thus these results are preliminary. Refined analysis will be reported later. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Chen-Wei Wang (IHEP) (cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/40625. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38660] GRB 250601A: PRIME J band upper limit.
by GCN Circulars 03 Jun '25

03 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40624 SUBJECT: GRB 250601A: PRIME J band upper limit. DATE: 25/06/03 22:03:13 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva(a)uniroma1.it> N. Passaleva (U Rome), O. Guiffreda (UMD), J. Durbak (UMD), M. Elkabir (U Rome), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC) Following the Fermi Gamma-ray Burst Monitor (GBM) detection (GCN 40596), and the Swift/BAT-GUANO arcminute localization of same event, we observed the transient field in J filter with PRIME ~23.5 hours after the initial Fermi detection. Using nearby VISTA Hemispherical Survey (VHS) we do not detect any uncatalogued source down to J>20.3 AB (3-sigma) at the position of the candidates reported by Swift/XRT (Page et al. GCN 40604, Salvaggio et al., GCN 40606) and EP/FXT (Liu et al., GCN 40607). PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023, Durbak et al. 2024). We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40624. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38659] Fermi Gamma-ray Burst Monitor trigger 770675211/250603852 is not a GRB
by GCN Circulars 03 Jun '25

03 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40623 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 770675211/250603852 is not a GRB DATE: 25/06/03 21:37:43 GMT FROM: Lorenzo Scotton at UAH <lscottongcn(a)outlook.com> L. Scotton (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 770675211/250603852 at 20:26:46.25 UT on 03 June 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to local particles." View this GCN Circular online at https://gcn.nasa.gov/circulars/40623. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38658] GRB 250601A: VLT/FORS2 Optical Observation
by GCN Circulars 03 Jun '25

03 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40622 SUBJECT: GRB 250601A: VLT/FORS2 Optical Observation DATE: 25/06/03 19:31:34 GMT FROM: Roberto Ricci at INAF-IRA <ricci(a)ira.inaf.it> Roberto Ricci (U Rome), 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 250601A (Fermi GBM team GCN 40596; DeLaunay et al., GCN 40600) with the FORS2 imager on the ESO VLT UT1 (Antu). Observations began 29.8 hours after the trigger and were carried out in the R filter with an average airmass of ~2.3. Our field covers the candidates reported by Swift/XRT (Page et al. GCN 40604, Salvaggio et al., GCN 40606) and EP/FXT (Liu et al., GCN 40607). Compared with the Legacy Survey DR10 (Dey et al. 2019) catalogue, we do not detect any uncatalogued source down to R>24 AB (3-sigma). Further observations are planned. 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/40622. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38657] GRB 250601A: Fermi GBM Observation
by GCN Circulars 03 Jun '25

03 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40621 SUBJECT: GRB 250601A: Fermi GBM Observation DATE: 25/06/03 15:42:16 GMT FROM: Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma(a)nasa.gov> V. Sharma (NASA-GSFC/UMBC) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 17:29:35 UT on 1 Jun 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250601A (trigger 770491780 / 250601729). which was also detected by Swift/BAT-GUANO (J. DeLaunay et al. 2025, GCN 40600) and Swift/XRT (K.L. Page et al. 2025, GCN 40604). The Fermi GBM on-ground location is consistent with the Swift/BAT-GUANO position. The angle from the Fermi LAT boresight is 24 degrees. The GBM light curve consists of main emission episode with a duration (T90) of about 3 s (50-300 keV). The time-averaged spectrum from T0-0.5 to T0+2.4 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.58 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 873 +/- 142 keV. The event fluence (10-1000 keV) in this time interval is (2.7 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1 s in the 10-1000 keV band is 4.9 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/40621. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38656] GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
by GCN Circulars 03 Jun '25

03 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40620 SUBJECT: GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization DATE: 25/06/03 15:06:50 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 continued our follow-up campaign of GRB 250602A, detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 40602) 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 2025-06-03 UTC. DDOTI observed the Fermi/LAT error region (Holzmann Airasca et al., GCN Circ. 40611), from 03:51 UTC to 05:01 UTC (from T+24.7 h to T+ 25.9 h after the trigger), obtaining a total exposure time of 48 minutes. By comparing our observations with the USNO-B1 and Pan-STARRS PS1 DR2 catalogs, and performing image subtraction using a Pan-STARRS PS1 DR2 template, we detect no uncatalogued sources within the observed field down to a 10-sigma limiting AB magnitude of: w > 20.0 Unfortunately, the Fermi/LAT error region was not included in the field observed on the night of 2025-06-02 UTC (Atri et al., GCN Circ. 40610). 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/40620. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38655] GRB 250603A: Swift/UVOT Upper Limits
by GCN Circulars 03 Jun '25

03 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40619 SUBJECT: GRB 250603A: Swift/UVOT Upper Limits DATE: 25/06/03 13:14:52 GMT FROM: Samantha Oates at University of Birmingham <samantha.oates(a)alumni.ucl.ac.uk> S. R. Oates (Lancaster U.) and T. M. Parsotan (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250603A 105 s after the BAT trigger (Parsotan et al., GCN Circ. 40613). No optical afterglow consistent with the enhanced XRT position (Beardmore et al., GCN Circ. 40616) 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 white_FC 105 255 147 >20.4 u_FC 318 567 246 >19.7 white 105 1531 382 >21.0 v 647 5129 190 >19.0 b 573 1516 97 >19.6 u 318 1491 324 >19.8 w1 697 1467 78 >18.7 m2 672 1442 97 >18.5 w2 623 5029 294 >19.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 1.89 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40619. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38654] GRB 250603A: Swift-XRT refined Analysis
by GCN Circulars 03 Jun '25

03 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40618 SUBJECT: GRB 250603A: Swift-XRT refined Analysis DATE: 25/06/03 12:58:34 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> S. Campana (INAF-OAB), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), D.N. Burrows (PSU), M.A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 7.3 ks of XRT data for GRB 250603A, from 92 s to 34.7 ks after the trigger. The data comprise 3 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=1.17 (+0.09, -0.08). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.48 (+0.32, -0.30). The best-fitting absorption column is 1.6 (+0.5, -0.4) x 10^22 cm^-2, in excess of the Galactic value of 6.9 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 7.6 x 10^-11 (1.1 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.6 (+0.5, -0.4) x 10^22 cm^-2 Galactic foreground: 6.9 x 10^21 cm^-2 Excess significance: 3.3 sigma Photon index: 1.48 (+0.32, -0.30) If the light curve continues to decay with a power-law decay index of 1.17, the count rate at T+24 hours will be 8.8 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.7 x 10^-14 (9.8 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01320335. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40618. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38653] Fermi trigger No 770638414: Global MASTER-Net observations report
by GCN Circulars 03 Jun '25

03 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40617 SUBJECT: Fermi trigger No 770638414: Global MASTER-Net observations report DATE: 25/06/03 11:32:32 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 GRB250603.43 (trigger No 770638414,19h 14m 55.20s , +26d 21m 36.0s, R=7.82) errorbox 165 sec after notice time and 195 sec after trigger time at 2025-06-03 10:16:44 UT, with upper limit up to 16.8 mag. Observations started at twilight. The observations began at zenith distance = 73 deg. The sun altitude is -14.5 deg. The galactic latitude b = 7 deg., longitude l = 59 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2890867 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 215 | 2025-06-03 10:16:44 | MASTER-OAFA | (19h 39m 27.79s , +30d 15m 05.9s) | C | 40 | 16.8 | 266 | 2025-06-03 10:17:31 | MASTER-OAFA | (19h 39m 27.74s , +30d 15m 07.5s) | C | 50 | 16.8 | 327 | 2025-06-03 10:18:27 | MASTER-OAFA | (19h 39m 27.67s , +30d 15m 08.4s) | C | 60 | 16.8 | 399 | 2025-06-03 10:19:33 | MASTER-OAFA | (19h 39m 27.58s , +30d 15m 09.3s) | C | 70 | 16.8 | 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/40617. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38652] GRB 250603A: Enhanced Swift-XRT position
by GCN Circulars 03 Jun '25

03 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40616 SUBJECT: GRB 250603A: Enhanced Swift-XRT position DATE: 25/06/03 06:07:13 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team. Using 1415 s of XRT Photon Counting mode data and 1 UVOT images for GRB 250603A, 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 = 129.93745, -39.29287 which is equivalent to: RA (J2000): 08h 39m 44.99s Dec (J2000): -39d 17' 34.3" with an uncertainty of 2.3 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/40616. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38651] GRB 250603A: Swift-XRT position and confirmation of GRB nature
by GCN Circulars 03 Jun '25

03 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40615 SUBJECT: GRB 250603A: Swift-XRT position and confirmation of GRB nature DATE: 25/06/03 05:40:03 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K.L. Page and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: The XRT began observing the field of GRB 250603A (GCN Circ. 40613) at 01:12:04.7 UT, 101.7 seconds after the BAT trigger. Using promptly-collected data (although downlinked after a delay), we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 129.93750, -39.29289 which is equivalent to: RA(J2000) = 08h 39m 45.00s Dec(J2000) = -39d 17' 34.4" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 104 arcseconds from the BAT onboard position, within the BAT error circle. Given the nature of the fading X-ray light-curve, we confirm this trigger as GRB 250603A, and not a new Galactic transient. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40615. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38650] Swift GRB250603.05: Global MASTER-Net observations report
by GCN Circulars 03 Jun '25

03 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40614 SUBJECT: Swift GRB250603.05: Global MASTER-Net observations report DATE: 25/06/03 02:48:43 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 Swift GRB250603.05 (trigger No 1320335,08h 39m 40.32s , -39d 16m 04.8s, R=0.05) errorbox 19 sec after notice time and 41 sec after trigger time at 2025-06-03 01:11:04 UT, with upper limit up to 19.2 mag. The observations began at zenith distance = 57 deg. The sun altitude is -44.5 deg. The galactic latitude b = 2 deg., longitude l = 260 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2890204 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 46 | MASTER-OAFA | C | 10 | 17.9 | 62 | MASTER-OAFA | C | 10 | 17.9 | 78 | MASTER-OAFA | C | 10 | 17.9 | 99 | MASTER-OAFA | C | 20 | 18.3 | 126 | MASTER-OAFA | C | 20 | 18.3 | 157 | MASTER-OAFA | C | 30 | 18.5 | 198 | MASTER-OAFA | C | 40 | 18.7 | 245 | MASTER-OAFA | C | 40 | 18.6 | 296 | MASTER-OAFA | C | 50 | 18.7 | 362 | MASTER-OAFA | C | 70 | 19.0 | 443 | MASTER-OAFA | C | 80 | 19.0 | 539 | MASTER-OAFA | C | 100 | 19.1 | 656 | MASTER-OAFA | C | 120 | 19.1 | 794 | MASTER-OAFA | C | 140 | 19.2 | 955 | MASTER-OAFA | C | 170 | 19.2 | 1138 | MASTER-OAFA | C | 180 | 19.2 | 1324 | MASTER-OAFA | C | 180 | 19.1 | 1511 | MASTER-OAFA | C | 180 | 19.1 | 1697 | MASTER-OAFA | C | 180 | 19.1 | 1884 | MASTER-OAFA | C | 180 | 19.1 | 2070 | MASTER-OAFA | C | 180 | 19.1 | 2257 | MASTER-OAFA | C | 180 | 19.1 | 2443 | MASTER-OAFA | C | 180 | 19.1 | 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/40614. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38649] GRB 250603A: Swift detection of a burst or new Galactic transient Swift J0839.7-3916
by GCN Circulars 03 Jun '25

03 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40613 SUBJECT: GRB 250603A: Swift detection of a burst or new Galactic transient Swift J0839.7-3916 DATE: 25/06/03 01:51:05 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> T. M. Parsotan (GSFC), R. Brivio (INAF-OAB), R. Gupta (NASA GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL) and C. Salvaggio (INAF-OAB) report on behalf of the Neil Gehrels Swift Observatory Team: At 01:10:23 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250603A (trigger=1320335). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 129.918, -39.268 which is RA(J2000) = 08h 39m 40s Dec(J2000) = -39d 16' 05" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 18 sec with a possible short spike at T0+16 sec. The peak count rate was ~1,300 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 01:12:04.7 UT, 101.7 seconds after the BAT trigger. No source was detected in the 2.5-s promptly available image. We are waiting for the full dataset to detect and localise the XRT counterpart. Although the initial 2.5s of XRT data do not show a clear X-ray afterglow, the high significance of the BAT image (7.82 sigma) gives us confidence that this is an astrophysical source. Further analysis awaits the full downlinked dataset. We note the presence of Fermi-GBM event at ~T+10 minutes (GBM trigger: 770606412) with a position consistent (to its 25Â° error radius) with this source location. Given the location of the BAT detection at 1.42Â° from the Galactic plane, persistent flux over 10 minutes would suggest a Galactic transient. If so, we would name it Swift J0839.7-3916 . Burst Advocate for this burst is T. M. Parsotan (tyler.parsotan 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/40613. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38648] GRB 250602A: Fermi GBM Observation
by GCN Circulars 03 Jun '25

03 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40612 SUBJECT: GRB 250602A: Fermi GBM Observation DATE: 25/06/03 01:47:35 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118(a)uah.edu> Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: At 03:04:31.31 UT on 02 June 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250602A (trigger 770526276/250602128). which was also detected by Fermi-LAT (A. Holzmann Airasca, et al. 2025, GCN 40611). The Fermi GBM on-ground location is consistent with the Fermi-LAT position. The angle from the Fermi LAT boresight is 111 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 14.6 s (50-300 keV). The time-averaged spectrum from T0+0.003 to T0+8.768 s is best fit 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 120 +/- 10 keV. The event fluence (10-1000 keV) in this time interval is (1.7 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.0 s in the 10-1000 keV band is 5.8 +/- 0.3 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 102 +/- 22 keV, alpha = -0.7 +/- 0.3 and beta = -2.2 +/- 0.2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/ View this GCN Circular online at https://gcn.nasa.gov/circulars/40612. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38647] GRB 250602A: Fermi-LAT detection
by GCN Circulars 02 Jun '25

02 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40611 SUBJECT: GRB 250602A: Fermi-LAT detection DATE: 25/06/02 20:13:59 GMT FROM: Rahul Gupta at NASA GSFC <rahul.gupta(a)nasa.gov> A. Holzmann Airasca (UniTrento and INFN Bari), S. Lopez (CNRS / IN2P3), R. Gupta (NASA GSFC), F. Longo (University and INFN, Trieste), N. Di Lalla (Stanford Univ.), and J. Racusin (NASA GSFC) report on behalf of the Fermi-LAT Collaboration: On June 02, 2025, Fermi-LAT detected high-energy emission from GRB 250602A, which was also detected by Fermi-GBM (trigger 770526276 / 250602128, GCN 40602). The best LAT on-ground location is found to be: RA, Dec = 111.9, 56.9 (J2000) with an error radius of 0.4 deg (90 % containment, statistical error only). This was 111 deg from the LAT boresight at the time of the GBM trigger (T0 = 03:04:31.31 UT). The data from the Fermi-LAT shows a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 3000 - 8000 s after the GBM trigger is (8.2 ± 3.2) E-7 ph/cm2/s. The estimated photon index above 100 MeV is -2.17 ± 0.33. The highest-energy photon is a 1.6 GeV event which is observed ~ 4800 seconds after the GBM trigger. The Fermi-LAT point of contact for this burst is Rahul Gupta (rahul.gupta(a)nasa.gov). The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/40611. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38646] GRB 250602A: DDOTI Optical Upper Limit
by GCN Circulars 02 Jun '25

02 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40610 SUBJECT: GRB 250602A: DDOTI Optical Upper Limit DATE: 25/06/02 19:56:39 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 GRB 250602A detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 40602) 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 2025-06-02 UTC. DDOTI observed the Fermi/GBM error region, covering about 88% of the statistical error region (Fermi GBM Team, GCN Circ. 40602). DDOTI observed the field of GRB 250602A from 04:05 UTC to 06:05 UTC (from T+1.01 h to T+ 3.02 h after the trigger) and obtained a total exposure of 50 minutes, 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 > 20.0 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/40610. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38645] GRB 250530C: Swift-BAT refined analysis
by GCN Circulars 02 Jun '25

02 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40609 SUBJECT: GRB 250530C: Swift-BAT refined analysis DATE: 25/06/02 19:11:33 GMT FROM: Mike Moss at NASA GSFC <mikejmoss3(a)gmail.com> D. Sadaula (GSFC/UMBC), S. D. Barthelmy (GSFC), R. Caputo (NASA/GSFC), R. Gupta (GSFC), 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), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+885 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250530C (trigger #1319125) (Caputo, et al., GCN Circ. 40585). The BAT ground-calculated position is RA, Dec = 55.146, -22.457 deg which is RA(J2000) = 03h 40m 35.1s Dec(J2000) = -22d 27' 26.1" with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 96%. The mask-weighted light curve displays a complex structure with multiple dim pulses. The T90 (15-350 keV) is 42.86 +- 6.04 sec (estimated error including systematics). The time-averaged spectrum from T-29.77 to T+21.26 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.32 +- 0.17. The fluence in the 15-150 keV band is 8.5 +- 0.9 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T-0.28 sec in the 15-150 keV band is 0.8 +- 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/1319125 View this GCN Circular online at https://gcn.nasa.gov/circulars/40609. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38644] GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
by GCN Circulars 02 Jun '25

02 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40608 SUBJECT: GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj DATE: 25/06/02 16:07:14 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> A. Martin-Carrillo (UCD), B. Schneider (LAM), L. Izzo (INAF/OACN and DARK/NBI), A. de Ugarte Postigo (LAM), G. Corcoran (UCD), B. Gompertz (U. Birmingham), D. B. Malesani (DAWN/NBI and Radboud), R. H. Rasmussen (NOT and Aarhus Univ.), report on behalf of a larger collaboration. We carried out spectroscopic observations 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 4x900 s exposures starting at 21:16 UT on 2025-05-31 (10.3 days after the Fermi trigger) with a wavelength coverage of 3800-9500 AA. The spectrum shows a blue, featureless continuum, peaking at around 4500 AA. Redward of the peak, the continuum is consistent with a power law F_lambda propto lambda^-2.7. The overall shape does not resemble a power-law spectrum, which would be typical of GRB afterglows, nor a SN spectrum, given the lack of any features. Although the spectrum does not fully resemble those of dwarf novae in outbursts, the spectral energy distribution is overall consistent with previous examples (e.g. Aviles et al. 2018, doi:10.14482/INDES.30.1.303.661). In summary, our spectroscopic observations confirm that AT2025mgj is not associated with GRB250521C, as already suggested by Busmann et al. (GCN 40597) and Gillanders et al. (GCN 40605) based on photometric observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40608. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38643] GRB 250601A: EP-FXT follow-up observation and afterglow candidates
by GCN Circulars 02 Jun '25

02 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40607 SUBJECT: GRB 250601A: EP-FXT follow-up observation and afterglow candidates DATE: 25/06/02 15:46:51 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. C. Liu (THU), X. Y. Zhou (PRIC), H. L. Peng (NNU), B. B. Zhang (BNU) and Y. Liu (NAO,CAS) report on behalf of the Einstein Probe (EP) team : We performed a follow-up observation of GRB 250601A (detected through on-broad trigger of Fermi/GBM, Fermi, GCN #40596, and localized by Swift/BAT, DeLaunay, GCN #40600; followed by Swift/XRT, Page et al., GCN #40604), with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation began at 2025-06-02T02:10:26 (T-TGRB ~ 8.7 hrs) with an exposure time of about 5.8 ks. Two uncatalogued sources were detected by FXT-A and FXT-B in the 3-sigma Swift/BAT error circle with a radius of 493 arcsecond centered at RA, DEC = 90.0709 deg, -57.2892 deg, as listed below (the FXT flux is taken from FXT-B module). EP J060023.3-571631 has a separation of 11.6 arcsecond from the XRT source 3, and EP J060048.7-571413 has a separation of 4.8 arcsecond from the XRT source 2. Source name | RA | DEC | Estimated Flux | SNR | Dist from Swift/BAT | | deg | deg | (erg/s/cm^2) | | offset (in arcmin) | EP J060023.3-571631 | 90.0971 | -57.2752 | 3.2(+/-1.2) x 10^-14 | 4.1 | 1.19 | EP J060048.7-571413 * | 90.2037 | -57.2368 | 1.0(+/-0.2) x 10^-13 | 9.4 | 5.33 | Note: * EP J060048.7-571413 was also detected by Swift/XRT (GCN #40604) in a ~4.6 ks observation conducted at T-TGRB ~ 4.8 hrs, with a flux of ~ 4e-13 erg/s/cm^2. The source thus exhibits a decreasing trend in the X-ray flux within the 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/40607. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38642] GRB 250601A: Swift/XRT candidate afterglow
by GCN Circulars 02 Jun '25

02 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40606 SUBJECT: GRB 250601A: Swift/XRT candidate afterglow DATE: 25/06/02 15:13:44 GMT FROM: Chiara Salvaggio at INAF OABrera <chiara.salvaggio(a)inaf.it> C. Salvaggio (INAF-OAB), S. B. Cenko (GSFC), B. Sbarufatti (INAF-OAB) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Fermi/GBM, Swift/BAT-GUANO detected burst GRB 250601A (GCN 40596, 40600). Two XRT sources have been previously reported in GCN 40604. One of the two sources (source 2) has an eROSITA counterpart, while XRT source 3 is a new transient. Therefore we consider source 3 a candidate afterglow for GRB 250601A. Source 3: RA (J2000.0): 90.0936 = 06:00:22.47 Dec (J2000.0): -57.2778 = -57:16:40.0 Error: 5.7 arcsec (radius, 90% conf.) Count-rate: (3.6 [+1.6, -1.3])e-3 ct s^-1 Distance: 60 arcsec from Swift/BAT position. Flux: (1.00 [+0.45, -0.35])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) More Swift/XRT observations are planned to (un)confirm the afterglow detection. 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/ToO_GRBs/00021844. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40606. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38641] GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
by GCN Circulars 02 Jun '25

02 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40605 SUBJECT: GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry DATE: 25/06/02 15:01:40 GMT FROM: James Gillanders at University of Oxford <jhgillanders.astro(a)gmail.com> J. H. Gillanders (Oxford), M. Huber, K. C. Chambers (IfA, Univ. Hawaii), S. J. Smartt, K. W. Smith, (Oxford/QUB), S. Srivastav (Oxford), M. Nicholl, D. Young, M. Fulton (QUB), T.-W. Chen (NCU, Taiwan) A. S. B. Schultz, T. de Boer, J. Fairlamb, G. Paek, C. C. Lin, T. Lowe, E. Magnier, P. Minguez, I. A. Smith, R. J. Wainscoat (IfA, Univ. Hawaii). We observed the fast-fading transient AT2025mgj (Andreoni et al., GCN 40566), tentatively associated with the short-GRB 250521C (Fermi GBM Team, GCN 40515) using the Pan-STARRS telescope system (Chambers et al., 2016, arXiv e-prints, 1612.05560) on MJDs 60825.26 and 60827.26 (approximately 8.7 and 10.7 days post-GRB, respectively). The Pan-STARRS system consists of two 1.8m telescope units located at the summit of Haleakala on the Hawaiian island of Maui, employing an SDSS-like filter system denoted as grizy, and a broad w-filter, which is a composite of the gri-filters. Our observations consisted of 120s (MJD 60825.26) and 200s exposures (MJD 60827.26) in grizy-bands. All images were processed with the Pan-STARRS pipeline. After astrometric and photometric calibration, reference images were subtracted from the target images (Magnier et al., 2020a, ApJS, 251, 3; Magnier et al., 2020b, ApJS, 251, 6; Waters et al., 2020, ApJS, 251, 4). From these difference images, we recover the following photometry measurements: MJD Filter AB mag 60825.26 g 18.97 +/- 0.06 60825.26 r 19.18 +/- 0.08 60825.26 i 19.29 +/- 0.08 60825.26 z 19.5 +/- 0.2 60827.26 g 19.29 +/- 0.05 60827.26 r 19.39 +/- 0.06 60827.26 i 19.62 +/- 0.06 60827.26 z 19.57 +/- 0.08 From our multi-band Pan-STARRS photometry, we estimate a fade rate of ~0.1 mag/day in r-band. Our rate of fading across our photometric bands match those reported previously by Martin-Carrillo et al. (GCN 40584), Becerra et al. (GCN 40590), and Busmann et al. (GCN 40597). The rate of fading and persistent blue colour, with some indication of cooling, are all reminiscent of typical CV behaviour. While the connection to GRB 250521C cannot be definitively ruled out, the data match the lightcurve behaviour of CVs. Late-time, deep imaging is required to unambiguously uncover the nature of AT2025mgj. A point source would confirm AT2025mgj is indeed a CV, whereas an extended source in its vicinity would indicate that it was the afterglow of GRB 250521C. View this GCN Circular online at https://gcn.nasa.gov/circulars/40605. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38640] GRB 250601A: Swift-XRT observations
by GCN Circulars 02 Jun '25

02 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40604 SUBJECT: GRB 250601A: Swift-XRT observations DATE: 25/06/02 08:18:00 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Swift/BAT-detected burst GRB 250601A, collecting 4.6 ks of Photon Counting (PC) mode data between T0+17.2 ks and T0+35.3 ks. Two uncatalogued X-ray sources have been detected within the estimated 3-sigma Swift/BAT error region (493 arcsec), however none of them is above the RASS limit or shows definitive signs of fading. Therefore, at the present time we cannot identify which, if any, is the afterglow. Details of these sources are given below: Source 2: RA (J2000.0): 90.2023 = 06:00:48.56 Dec (J2000.0): -57.2379 = -57:14:16.6 Error: 7.3 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: (7.8 +/- 1.9)e-3 ct s^-1 Distance: 315 arcsec from Swift/BAT position. Flux: (4.2 +/- 1.0)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 3: RA (J2000.0): 90.0936 = 06:00:22.47 Dec (J2000.0): -57.2778 = -57:16:40.0 Error: 5.7 arcsec (radius, 90% conf.) Count-rate: (3.6 [+1.6, -1.3])e-3 ct s^-1 Distance: 60 arcsec from Swift/BAT position. Flux: (1.00 [+0.45, -0.35])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Another uncatalogued source was also detected, however this was too far from the GRB position to be the afterglow. 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/ToO_GRBs/00021844. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40604. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38639] Fermi GRB 250601A: Global MASTER-Net observations report
by GCN Circulars 02 Jun '25

02 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40603 SUBJECT: Fermi GRB 250601A: Global MASTER-Net observations report DATE: 25/06/02 04:45:45 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 250601A ( Fermi GBM team, GCN 40596) errorbox 31266 sec after notice time and 31297 sec after trigger time at 2025-06-02 02:11:13 UT, with upper limit up to 18.8 mag. The observations began at zenith distance = 80 deg. The sun altitude is -41.7 deg. The galactic latitude b = -31 deg., longitude l = 264 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2888853 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 31328 | 2025-06-02 02:11:13 | MASTER-SAAO | (05h 23m 33.62s , -61d 25m 21.7s) | C | 60 | 18.1 | 31328 | 2025-06-02 02:11:13 | MASTER-SAAO | (05h 27m 12.25s , -61d 40m 47.0s) | C | 60 | 16.8 | 32079 | 2025-06-02 02:23:44 | MASTER-SAAO | (05h 23m 32.93s , -61d 25m 26.3s) | C | 60 | 18.2 | 32079 | 2025-06-02 02:23:44 | MASTER-SAAO | (05h 27m 11.81s , -61d 40m 51.9s) | C | 60 | 16.9 | 32832 | 2025-06-02 02:36:17 | MASTER-SAAO | (05h 23m 35.76s , -61d 24m 34.2s) | C | 60 | 18.2 | 32832 | 2025-06-02 02:36:17 | MASTER-SAAO | (05h 27m 14.94s , -61d 39m 58.9s) | C | 60 | 16.9 | 32926 | 2025-06-02 02:37:51 | MASTER-SAAO | (05h 01m 57.98s , -57d 37m 48.3s) | C | 60 | 18.3 | 32926 | 2025-06-02 02:37:51 | MASTER-SAAO | (05h 05m 13.56s , -57d 53m 13.1s) | C | 60 | 16.9 | 33492 | 2025-06-02 02:47:17 | MASTER-SAAO | (05h 23m 29.69s , -61d 25m 33.6s) | C | 60 | 18.3 | 33492 | 2025-06-02 02:47:17 | MASTER-SAAO | (05h 27m 09.27s , -61d 40m 57.8s) | C | 60 | 16.9 | 33586 | 2025-06-02 02:48:51 | MASTER-SAAO | (05h 01m 58.51s , -57d 38m 06.3s) | C | 60 | 18.6 | 33586 | 2025-06-02 02:48:51 | MASTER-SAAO | (05h 05m 14.44s , -57d 53m 30.3s) | C | 60 | 17.1 | 33679 | 2025-06-02 02:50:24 | MASTER-SAAO | (05h 17m 04.95s , -57d 38m 12.0s) | C | 60 | 18.3 | 33679 | 2025-06-02 02:50:24 | MASTER-SAAO | (05h 20m 20.73s , -57d 53m 36.1s) | C | 60 | 17.0 | 34244 | 2025-06-02 02:59:49 | MASTER-SAAO | (05h 23m 26.94s , -61d 25m 56.2s) | C | 60 | 18.2 | 34348 | 2025-06-02 03:01:33 | MASTER-SAAO | (05h 01m 56.88s , -57d 38m 26.6s) | C | 60 | 18.6 | 34348 | 2025-06-02 03:01:33 | MASTER-SAAO | (05h 05m 13.07s , -57d 53m 50.3s) | C | 60 | 17.2 | 34441 | 2025-06-02 03:03:06 | MASTER-SAAO | (05h 17m 02.63s , -57d 38m 31.9s) | C | 60 | 18.3 | 34441 | 2025-06-02 03:03:06 | MASTER-SAAO | (05h 20m 18.63s , -57d 53m 56.0s) | C | 60 | 17.0 | 35007 | 2025-06-02 03:12:32 | MASTER-SAAO | (05h 23m 27.32s , -61d 26m 18.0s) | C | 60 | 18.4 | 35101 | 2025-06-02 03:14:06 | MASTER-SAAO | (05h 01m 55.99s , -57d 38m 46.4s) | C | 60 | 18.6 | 35101 | 2025-06-02 03:14:06 | MASTER-SAAO | (05h 05m 12.55s , -57d 54m 10.0s) | C | 60 | 17.2 | 35194 | 2025-06-02 03:15:39 | MASTER-SAAO | (05h 17m 02.39s , -57d 38m 52.0s) | C | 60 | 18.4 | 35194 | 2025-06-02 03:15:39 | MASTER-SAAO | (05h 20m 18.72s , -57d 54m 16.2s) | C | 60 | 17.0 | 35288 | 2025-06-02 03:17:13 | MASTER-SAAO | (05h 02m 24.56s , -54d 08m 10.8s) | C | 60 | 17.0 | 35381 | 2025-06-02 03:18:46 | MASTER-SAAO | (05h 12m 59.55s , -53d 50m 37.6s) | C | 60 | 18.5 | 35381 | 2025-06-02 03:18:46 | MASTER-SAAO | (05h 15m 57.34s , -54d 06m 02.3s) | C | 60 | 16.7 | 35661 | 2025-06-02 03:23:26 | MASTER-SAAO | (05h 11m 01.98s , -51d 56m 40.6s) | C | 60 | 18.5 | 35661 | 2025-06-02 03:23:26 | MASTER-SAAO | (05h 13m 52.04s , -52d 12m 05.7s) | C | 60 | 16.8 | 35757 | 2025-06-02 03:25:02 | MASTER-SAAO | (05h 01m 55.75s , -57d 41m 01.1s) | C | 60 | 18.6 | 35757 | 2025-06-02 03:25:02 | MASTER-SAAO | (05h 05m 12.76s , -57d 56m 25.1s) | C | 60 | 17.3 | 35851 | 2025-06-02 03:26:36 | MASTER-SAAO | (05h 17m 02.21s , -57d 39m 55.6s) | C | 60 | 18.5 | 35851 | 2025-06-02 03:26:36 | MASTER-SAAO | (05h 20m 18.88s , -57d 55m 20.0s) | C | 60 | 17.2 | 36038 | 2025-06-02 03:29:43 | MASTER-SAAO | (05h 12m 58.98s , -53d 52m 22.2s) | C | 60 | 18.4 | 36038 | 2025-06-02 03:29:43 | MASTER-SAAO | (05h 15m 56.70s , -54d 07m 48.0s) | C | 60 | 17.0 | 36318 | 2025-06-02 03:34:23 | MASTER-SAAO | (05h 11m 01.70s , -51d 56m 54.3s) | C | 60 | 18.7 | 36318 | 2025-06-02 03:34:23 | MASTER-SAAO | (05h 13m 51.53s , -52d 12m 20.2s) | C | 60 | 17.0 | 36411 | 2025-06-02 03:35:56 | MASTER-SAAO | (05h 24m 08.15s , -51d 57m 10.8s) | C | 60 | 18.4 | 36411 | 2025-06-02 03:35:56 | MASTER-SAAO | (05h 26m 57.92s , -52d 12m 36.4s) | C | 60 | 17.0 | 36504 | 2025-06-02 03:37:29 | MASTER-SAAO | (05h 05m 10.11s , -57d 56m 43.4s) | C | 60 | 17.4 | 36504 | 2025-06-02 03:37:29 | MASTER-SAAO | (05h 01m 53.17s , -57d 41m 19.2s) | C | 60 | 18.7 | 36597 | 2025-06-02 03:39:02 | MASTER-SAAO | (05h 20m 17.51s , -57d 55m 46.9s) | C | 60 | 17.3 | 36597 | 2025-06-02 03:39:02 | MASTER-SAAO | (05h 17m 00.88s , -57d 40m 22.3s) | C | 60 | 18.6 | 36784 | 2025-06-02 03:42:09 | MASTER-SAAO | (05h 15m 55.94s , -54d 07m 49.4s) | C | 60 | 17.0 | 36784 | 2025-06-02 03:42:09 | MASTER-SAAO | (05h 12m 57.97s , -53d 52m 23.8s) | C | 60 | 18.6 | 36973 | 2025-06-02 03:45:18 | MASTER-SAAO | (05h 04m 12.35s , -56d 01m 02.3s) | C | 60 | 17.5 | 36973 | 2025-06-02 03:45:18 | MASTER-SAAO | (05h 01m 05.36s , -55d 45m 37.7s) | C | 60 | 18.8 | 37066 | 2025-06-02 03:46:51 | MASTER-SAAO | (05h 13m 57.11s , -52d 13m 36.4s) | C | 60 | 17.2 | 37066 | 2025-06-02 03:46:51 | MASTER-SAAO | (05h 11m 06.80s , -51d 58m 10.9s) | C | 60 | 18.7 | 37159 | 2025-06-02 03:48:24 | MASTER-SAAO | (05h 26m 51.17s , -52d 13m 53.2s) | 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/40603. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38638] GRB 250602A: Fermi GBM Final Real-time Localization
by GCN Circulars 02 Jun '25

02 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40602 SUBJECT: GRB 250602A: Fermi GBM Final Real-time Localization DATE: 25/06/02 03:14:49 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 03:04:31 UT on 2 Jun 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250602A (trigger 770526276.307432 / 250602128). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 111.7, Dec = 67.8 (J2000 degrees, equivalent to J2000 07h 26m, 67d 47'), with a statistical uncertainty of 4.9 degrees. The angle from the Fermi LAT boresight is 111.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250602128/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250602128/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250602128/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40602. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38637] Fermi trigger No 770470765: Global MASTER-Net observations report
by GCN Circulars 02 Jun '25

02 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40601 SUBJECT: Fermi trigger No 770470765: Global MASTER-Net observations report DATE: 25/06/02 00:48:11 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 GRB250601.49 (trigger No 770470765,03h 02m 00.00s , -51d 57m 00.0s, R=11.63) errorbox 43681 sec after notice time and 43715 sec after trigger time at 2025-06-01 23:47:55 UT, with upper limit up to 19.0 mag. The observations began at zenith distance = 80 deg. The sun altitude is -71.3 deg. The galactic latitude b = -55 deg., longitude l = 267 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2888592 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 43745 | 2025-06-01 23:47:55 | MASTER-SAAO | (01h 44m 18.74s , -52d 18m 33.7s) | C | 60 | 16.4 | 43745 | 2025-06-01 23:47:55 | MASTER-SAAO | (01h 41m 30.62s , -52d 03m 14.0s) | C | 60 | 18.7 | 44762 | 2025-06-02 00:04:51 | MASTER-SAAO | (01h 44m 12.09s , -52d 18m 24.7s) | C | 60 | 16.8 | 44762 | 2025-06-02 00:04:51 | MASTER-SAAO | (01h 41m 22.46s , -52d 02m 58.5s) | C | 60 | 18.8 | 45994 | 2025-06-02 00:25:24 | MASTER-SAAO | (01h 44m 18.84s , -52d 18m 56.3s) | C | 60 | 17.2 | 45994 | 2025-06-02 00:25:24 | MASTER-SAAO | (01h 41m 28.06s , -52d 03m 32.4s) | 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/40601. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38636] GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
by GCN Circulars 01 Jun '25

01 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40600 SUBJECT: GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst DATE: 25/06/01 22:21:42 GMT FROM: Samuele Ronchini at PSU <sjs8171(a)psu.edu> James DeLaunay (PSU), Samuele Ronchini (PSU), Aaron Tohuvavohu (Caltech), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report: Swift/BAT did not localize GRB 250601A onboard (T0: 2025-06-01T17:29:35.54 UTC, Fermi GCN 40596). 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 position is found with standard imaging, with an SNR = 8.7. The duration of the burst is ~1 sec. The BAT position is RA, Dec = 90.0709, -57.2892 deg which is RA(J2000) = 06h 00m 17.02s Dec(J2000) = -57d 17’ 21.1″ with an estimated uncertainty of 3 arcmin radius. More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=770491811 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/40600. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38635] GRB 250601A: Swift ToO observations
by GCN Circulars 01 Jun '25

01 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40599 SUBJECT: GRB 250601A: Swift ToO observations DATE: 25/06/01 22:17:16 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 250601A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021844 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/40599. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[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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