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

[vsnet-grb-info 38440] GRB 250509A: Prompt enhanced Swift-XRT position
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40410 SUBJECT: GRB 250509A: Prompt enhanced Swift-XRT position DATE: 25/05/09 23:32:52 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-XRT team: Using 426 s of promptly downlinked XRT event data for GRB 250509A, we find an enhanced XRT position of the afterglow: RA, Dec: 46.44960, -38.84128 which is equivalent to: RA (J2000) = 03 05 47.90 Dec (J2000) = -38 50 28.6 with an uncertainty of 1.9 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/1311764. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40410. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38439] Fermi GRB 250509A: Global MASTER-Net observations report
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40409 SUBJECT: Fermi GRB 250509A: Global MASTER-Net observations report DATE: 25/05/09 23:31:05 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 250509A ( Fermi GBM team, GCN 40406) errorbox 7 sec after notice time and 64 sec after trigger time at 2025-05-09 22:34:33 UT, with upper limit up to 18.4 mag. Observations started at twilight. The observations began at zenith distance = 70 deg. The sun altitude is -9.7 deg. The galactic latitude b = -60 deg., longitude l = 237 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2866536 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 70 | 2025-05-09 22:34:33 | MASTER-OAFA | (03h 18m 00.28s , -38d 23m 19.1s) | C | 10 | 14.1 | 104 | 2025-05-09 22:35:03 | MASTER-OAFA | (03h 18m 00.24s , -38d 23m 19.1s) | C | 20 | 14.5 | 138 | 2025-05-09 22:35:42 | MASTER-OAFA | (03h 18m 00.14s , -38d 23m 18.9s) | C | 10 | 14.4 | 174 | 2025-05-09 22:36:18 | MASTER-OAFA | (03h 18m 00.11s , -38d 23m 18.5s) | C | 10 | 14.4 | 215 | 2025-05-09 22:36:53 | MASTER-OAFA | (03h 18m 00.10s , -38d 23m 18.6s) | C | 20 | 14.7 | 265 | 2025-05-09 22:37:39 | MASTER-OAFA | (03h 18m 00.12s , -38d 23m 19.3s) | C | 30 | 14.8 | 865 | 2025-05-09 22:46:44 | MASTER-OAFA | (03h 18m 00.32s , -38d 23m 28.0s) | C | 140 | 14.8 | 1041 | 2025-05-09 22:49:30 | MASTER-OAFA | (03h 18m 00.52s , -38d 23m 31.2s) | C | 160 | 16.3 | 1227 | 2025-05-09 22:52:36 | MASTER-OAFA | (03h 18m 00.73s , -38d 23m 34.3s) | C | 160 | 16.5 | 1414 | 2025-05-09 22:55:42 | MASTER-OAFA | (03h 18m 01.03s , -38d 23m 38.0s) | C | 160 | 17.0 | 1424 | 2025-05-09 22:55:43 | MASTER-OAFA | (03h 06m 24.43s , -38d 43m 44.4s) | C | 180 | 18.2 | 1600 | 2025-05-09 22:58:49 | MASTER-OAFA | (03h 18m 01.35s , -38d 23m 42.3s) | C | 160 | 17.1 | 1610 | 2025-05-09 22:58:49 | MASTER-OAFA | (03h 06m 24.67s , -38d 43m 47.0s) | C | 180 | 18.4 | 1786 | 2025-05-09 23:01:55 | MASTER-OAFA | (03h 18m 01.74s , -38d 23m 46.7s) | C | 160 | 17.1 | 1796 | 2025-05-09 23:01:55 | MASTER-OAFA | (03h 06m 24.96s , -38d 43m 50.0s) | C | 180 | 18.3 | 1972 | 2025-05-09 23:05:01 | MASTER-OAFA | (03h 18m 02.05s , -38d 23m 50.9s) | C | 160 | 17.1 | 1983 | 2025-05-09 23:05:02 | MASTER-OAFA | (03h 06m 25.27s , -38d 43m 53.2s) | C | 180 | 18.2 | 2159 | 2025-05-09 23:08:08 | MASTER-OAFA | (03h 18m 02.30s , -38d 23m 55.2s) | C | 160 | 17.1 | 2169 | 2025-05-09 23:08:08 | MASTER-OAFA | (03h 06m 25.58s , -38d 43m 56.5s) | C | 180 | 18.1 | 2356 | 2025-05-09 23:11:14 | MASTER-OAFA | (03h 06m 25.97s , -38d 44m 00.1s) | C | 180 | 18.0 | 2531 | 2025-05-09 23:14:20 | MASTER-OAFA | (03h 18m 02.98s , -38d 24m 03.8s) | C | 160 | 17.1 | 2542 | 2025-05-09 23:14:20 | MASTER-OAFA | (03h 06m 26.35s , -38d 44m 03.6s) | C | 180 | 18.0 | 2718 | 2025-05-09 23:17:26 | MASTER-OAFA | (03h 18m 03.37s , -38d 24m 09.0s) | C | 160 | 17.2 | 2728 | 2025-05-09 23:17:27 | MASTER-OAFA | (03h 06m 26.66s , -38d 44m 06.7s) | C | 180 | 18.0 | 2904 | 2025-05-09 23:20:33 | MASTER-OAFA | (03h 18m 03.73s , -38d 24m 14.1s) | C | 160 | 17.1 | 2914 | 2025-05-09 23:20:33 | MASTER-OAFA | (03h 06m 26.94s , -38d 44m 08.8s) | C | 180 | 17.6 | 3090 | 2025-05-09 23:23:39 | MASTER-OAFA | (03h 18m 04.07s , -38d 24m 19.9s) | C | 160 | 16.9 | 3100 | 2025-05-09 23:23:39 | MASTER-OAFA | (03h 06m 27.22s , -38d 44m 12.4s) | C | 180 | 17.4 | 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/40409. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38438] Swift GRB 250509A: Global MASTER-Net observations report
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40408 SUBJECT: Swift GRB 250509A: Global MASTER-Net observations report DATE: 25/05/09 23:06:47 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 GRB 250509A ( M. H. Siegel et al., GCN 40407) errorbox 1296 sec after notice time and 1332 sec after trigger time at 2025-05-09 22:55:43 UT, with upper limit up to 18.4 mag. Observations started at twilight. The observations began at zenith distance = 76 deg. The sun altitude is -14.1 deg. The galactic latitude b = -59 deg., longitude l = 244 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2866479 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 1423 | MASTER-OAFA | C | 180 | 18.2 | 1609 | MASTER-OAFA | C | 180 | 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/40408. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38437] GRB 250509A: Swift detection of a burst
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40407 SUBJECT: GRB 250509A: Swift detection of a burst DATE: 25/05/09 22:49:14 GMT FROM: Mike Siegel at PSU/Swift MOC <siegel(a)swift.psu.edu> M. H. Siegel (PSU), S. Dichiara (PSU), R. Gupta (NASA GSFC) and B. Sbarufatti (INAF-OAB) report on behalf of the Neil Gehrels Swift Observatory Team: At 22:33:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250509A (trigger=1311764). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 46.455, -38.853 which is RA(J2000) = 03h 05m 49s Dec(J2000) = -38d 51' 11" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi peak structure with a duration of about 60 sec. The peak count rate was ~2800 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 22:34:41.7 UT, 71.1 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 46.45032, -38.84173 which is equivalent to: RA(J2000) = 03h 05m 48.08s Dec(J2000) = -38d 50' 30.2" with an uncertainty of 3.6 arcseconds (radius, 90% containment). This location is 42 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 (2.03 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 9.2 (+3.98/-3.41) x 10^21 cm^-2 (90% confidence). The initial flux in the 2.5 s image was 7.21e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of nominal 150.000 seconds with the White filter starting 80 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. Data from the 2.7'x2.7' sub-image are not available at this time. 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 0.021. Burst Advocate for this burst is M. H. Siegel (siegel AT swift.psu.edu) 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/40407. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38436] GRB 250509A: Fermi GBM Final Real-time Localization
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40406 SUBJECT: GRB 250509A: Fermi GBM Final Real-time Localization DATE: 25/05/09 22:43:58 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 22:33:29 UT on 9 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250509A (trigger 768522814.285632 / 250509940). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 46.0, Dec = -35.3 (J2000 degrees, equivalent to J2000 03h 04m, -35d 17'), with a statistical uncertainty of 3.0 degrees. The angle from the Fermi LAT boresight is 89.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250509940/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250509940/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250509940/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40406. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38435] GRB 250506A: NOT optical upper limits
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40405 SUBJECT: GRB 250506A: NOT optical upper limits DATE: 25/05/09 09:37:58 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> Z. P. Zhu (NAOC), B. Schneider (LAM), A. Martin-Carrillo (UCD), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), D. Xu (NAOC), T. T. Hansen, W. M. Ali, P. H. Chan, N. Hölinger, E. Lamprou, R. Lesley, H. Lundberg, J. Pajak, L. Peschieras, and N. Valsamidis (all Stockholm University), report on behalf of a larger collaboration. We observed the field of GRB 250506A detected by SVOM/ECLAIRs (Wang et al., GCN 40358) and Fermi/GBM (Sonawane et al., GCN 40362), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT) centered at the X-ray source detected by EP/FXT (Zhang et al. GCN 40365). We obtained exposures in the SDSS r (3x600 s) and z (4x300 s) bands starting at 23:44:29 UT on 2025-05-06 (21.35 hr after the SVOM/ECLAIRs trigger). No new optical source is detected at a position consistent with the Swift/XRT error region (the best currently available for this event; Burrows et al., GCN 40378) in the stacked images of either band down to the 5-sigma limiting AB magnitudes of r > 23.6 and z > 22.5, calibrated against nearby Pan-STARRS stars. View this GCN Circular online at https://gcn.nasa.gov/circulars/40405. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38434] EP250508a: Liverpool Telescope optical upper limits
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40404 SUBJECT: EP250508a: Liverpool Telescope optical upper limits DATE: 25/05/09 09:01:45 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris, P. T. O’Brien and R. L. C. Starling (U of Leicester) report: We observed the field of the X-ray transient EP250508a (Liang et al., GCN 40390; Zhao et al., GCN 40399; Liang et al., GCN 40403) with the 2m Liverpool Telescope using the IO:O instrument. We obtained 6x150s exposures in the SDSS r’ filter starting at 2025-05-08 21:07:19 UT and 6x150s exposures in the SDSS z’ filter starting at 2025-05-08 21:24:25 UT, approximately 15.1 hours after the X-ray detection. We performed image subtraction on the stacked images using reference images from Pan-STARRS and also compared the stacked and reference images manually. Consistent with Ugarte Postigo et al. (GCN 40391), Lipunov et al. (GCN 40393), Brivio et al. (GCN 40395) and Zheng et al. (GCN 40401), we identify no new sources within the error region of the EP/FXT source. At the position of the optical counterpart candidate identified by Xin et al. (GCN 40402), we derive 3-sigma upper limits of r’ > 21.5 and z’ > 21.5 with photometry calibrated to Pan-STARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40404. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38433] EP250508a: Liverpool Telescope optical upper limits
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40404 SUBJECT: EP250508a: Liverpool Telescope optical upper limits DATE: 25/05/09 09:01:45 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris, P. T. O’Brien and R. L. C. Starling (U of Leicester) report: We observed the field of the X-ray transient EP250508a (Liang et al., GCN 40390; Zhao et al., GCN 40399; Liang et al., GCN 40403) with the 2m Liverpool Telescope using the IO:O instrument. We obtained 6x150s exposures in the SDSS r’ filter starting at 2025-05-08 21:07:19 UT and 6x150s exposures in the SDSS z’ filter starting at 2025-05-08 21:24:25 UT, approximately 15.1 hours after the X-ray detection. We performed image subtraction on the stacked images using reference images from Pan-STARRS and also compared the stacked and reference images manually. Consistent with Ugarte Postigo et al. (GCN 40391), Lipunov et al. (GCN 40393), Brivio et al. (GCN 40395) and Zheng et al. (GCN 40401), we identify no new sources within the error region of the EP/FXT source. At the position of the optical counterpart candidate identified by Xin et al. (GCN 40402), we derive 3-sigma upper limits of r’ > 21.5 and z’ > 21.5 with photometry calibrated to Pan-STARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40404. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38432] EP250508a: follow-up observation with EP-FXT
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40403 SUBJECT: EP250508a: follow-up observation with EP-FXT DATE: 25/05/09 08:07:31 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R. D. Liang, T. Zhao, H. Q. Cheng, W. D. Zhang (NAOC, CAS) on behalf of the Einstein Probe (EP) team: Following the detection of the fast X-ray transient EP250508a (Liang et al., GCN 40390, Zhao et al. GCN 40399) and its multi-wavelength follow-up observations (Postigo et al., GCN 40391; Lipunov et al., GCN 40393; Brivio et al., GCN 40395; Zheng GCN 40401; Xin et al. GCN 40402), we performed an observation with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe mission. The observations began at 2025-05-08 13:41:03 (UTC), about 7.6 hours after the EP-WXT detection. The exposure time is 7250 seconds. Preliminary analysis shows that the source was detected in this epoch. The spectrum in the 0.5-10 keV band can be fitted with an absorbed power-law model with NH fixed at the Galactic value of 3.56e20 cm^-2 and a photon index of 2.22(-0.47, +0.47). The unabsorbed 0.5-10 keV flux is 4.53(-1.88, +1.88)e-14 erg/s/cm^2 (90% C.L.), about five times lower than that detected in the autonomous FXT follow-up observation (Zhao et al. GCN 40399), demonstrating a rapid decay trend in the source's X-ray emission. EP-FXT will continue monitoring the source. More follow-up observations are encouraged. The contact TA of EP250508a is R. D. Liang. Please contact him via email liangrd(a)bao.ac.cn if needed. 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/40403. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38431] EP250508a: SVOM/VT optical candidate
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40402 SUBJECT: EP250508a: SVOM/VT optical candidate DATE: 25/05/09 05:40:30 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. N. Ma, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei, T. Zhao, R. D. Liang, H. Q. Cheng, W. D. Zhang (NAOC, CAS), Y. D. Hu (GXU), L. Zhang (IHEP), X. L. Chen(YNU) report on behalf of the SVOM and EP Teams: SVOM/VT observed the X-ray transient EP250508a (Liang et al., GCN 40390，Zhao et al., GCN 40399) in ToO mode in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The observation started at 2025-05-08T11:38:19 UT, about 5.6 hours after the trigger. An uncatalogued faint candidate is detected in both channels within FXT error circle, compared to Legacy Survey, with the coordinate: RA= 11:53:01.05 (178.25438 deg) DEC=-19:55:24.2 (-19.92339 deg) Error = 0.5 arcseconds J2000 The brightness of the candidate is derived as below : Mid-time band mag(AB) exposure 6.74 hour VT_R 23.0+/-0.2 71*70 sec 6.75 hour VT_B 23.6+/-0.3 71*70 sec Our photometry was estimated in AB magnitude and not corrected for Galatic extinction. Give the faintness of the candidate, we cannot determine whether it is fading. More follow-ups are encouraged to confirm the nature of the transient. 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/40402. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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