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

[vsnet-grb-info 39285] GRB 250804B: SVOM/GRM observation of a short burst
by GCN Circulars 04 Aug '25

04 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41229 SUBJECT: GRB 250804B: SVOM/GRM observation of a short burst DATE: 25/08/04 16:01:26 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Jean-Luc Atteia, Sebastien Guillot (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 250804B (SVOM trigger reference: sb25080401) at 2025-08-04T04:44:51.600 UTC (T0). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 0.37 +0.09/-0.15 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250804B.png The SVOM/GRM on-ground localization of this burst is (J2000): RA: 36.3 deg DEC: -42.1 deg Error: 4.3 deg (1sigma, statistical only) We caution that the calibration of SVOM/GRM is undergoing and this localization is subject to systematic errors. In addition, the position of this burst, as determined by GRM, is located at about 56 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. Nonetheless, the burst is seen (via analysis of X-band data) in the ECLAIRs data above 50 keV at the T0 given by GRM, likely through the ECLAIRs shielding. With this localization, the time-averaged spectrum from T0-0.5 to T0+0.4 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.78 +0.07/-0.08 and the cutoff energy, parameterized as Epeak, is 1650 +38/-28 keV. The event fluence (10-1000 keV) in this time interval is (2.63 +/-0.13)E-06 erg/cm^2. Thus GRB 250804B is consistent with Type II GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/grb250804B_amati.png 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) View this GCN Circular online at https://gcn.nasa.gov/circulars/41229. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39284] GRB 250804A: Fermi GBM Final Localization
by GCN Circulars 04 Aug '25

04 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41228 SUBJECT: GRB 250804A: Fermi GBM Final Localization DATE: 25/08/04 15:33:20 GMT FROM: rhamburg(a)usra.edu The Fermi GBM team reports the detection of a likely SHORT GRB. "At 11:38:03.48 UT on 04 August 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250804A (trigger 776000288/250804485). This trigger was initially classified as Below Horizon by the flight software, but is in fact a GRB. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 114.09, Dec = 42.02 (J2000 degrees, equivalent to J2000 7h 36m, +42d 1'), with a statistical uncertainty of 19.32 degrees. The angle from the Fermi LAT boresight is 44 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250804485/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250804485/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250804485/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/41228. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39283] EP250802a: additional Liverpool Telescope upper limits
by GCN Circulars 04 Aug '25

04 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41227 SUBJECT: EP250802a: additional Liverpool Telescope upper limits DATE: 25/08/04 12:15:11 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris and N. R. Tanvir (U of Leicester) report on behalf of a larger collaboration: We observed the field of the X-ray transient EP250802a (Yin et al., GCN 41221) with the 2m Liverpool Telescope using the IO:O instrument. We obtained 8x150s exposures in each of the SDSS r’ and SDSS z’ filters starting at 2025-08-03 22:17:48 UT, approximately 35.7 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. Similarly to Bochanek et al. (GCN 41224), the bright stars in the error region affected our subtractions, however, no new sources are detected in either the subtractions or stacked images. Our results are consistent with Mohan et al. (GCN 41222), Lipunov et al. (GCN 41223) and Bochanek et al. (GCN 41224). At the position of the X-ray source, we derive 3-sigma upper limits of r’ > 22.44 and z’ > 21.73 with photometry calibrated to Pan-STARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41227. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39282] EP250730a: SVOM/VT optical upper limit
by GCN Circulars 04 Aug '25

04 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41226 SUBJECT: EP250730a: SVOM/VT optical upper limit DATE: 25/08/04 09:37:30 GMT FROM: zhyao(a)bao.ac.cn Z. H. Yao, H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Y. N. Ma, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), B. T. Wang (YNAO) report on behalf of the SVOM/VT team. SVOM performed a Target of Opportunity observation of EP250730a detected by EP/WXT (Wang et al., GCN 41207). SVOM/VT began observing the field at 2025-07-31T10:36:57.506 UTC, 28.5 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. No uncataloged candidates were detected in our single or stacked images within the error box provided by EP/WXT (Wang et al., GCN 41207), the three sigma limits are: mid-time (UTC) | exposure time (s) | band | upper limit (AB) --------------------|-------------------------|------|----------------- 2025-07-31T11:47:09 | 19*100 | VT_B | 23.5 2025-07-31T11:47:09 | 19*100 | VT_R | 23.0 Our results are consistent with COLIBRÍ (Magnani et al., GCN 41209) and Global MASTER-Net (Lipunov et al., GCN 41210). 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/41226. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39281] Fermi Gamma-ray Burst Monitor trigger 775945985/250803856 is not a GRB
by GCN Circulars 04 Aug '25

04 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41225 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 775945985/250803856 is not a GRB DATE: 25/08/04 05:23:28 GMT FROM: sumanbala2210(a)gmail.com S. Bala (USRA) and V. Sharma (GSFC/UMBC) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 775945985/250803856 at 20:33:00.34 UT on 03 August 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/41225. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39280] EP250802a: Liverpool Telescope optical upper limits
by GCN Circulars 04 Aug '25

04 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41224 SUBJECT: EP250802a: Liverpool Telescope optical upper limits DATE: 25/08/04 01:27:27 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek and D. A. Perley (LJMU) report: We observed the field of the fast X-ray transient EP250802a (Yin et al., GCN 41221) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 4x120s exposures in the SDSS r’ and i’ filters starting at 2025-08-03 21:42:37 UT, approximately 35 hours after the trigger. The images were stacked, and their background was subtracted relative to Pan-STARRS-1 using PSF matching with the help of PSFEx. We do not detect any new object at the EP/WXT error region of the transient: the 3-sigma limiting magnitudes on the stacked images are r > 22.67 mag and i > 22.33 mag, in line with Mohan et al. (GCN 41222) and Lipunov et al. (GCN 41223). However, we note that there are a few bright, saturated stars inside the error region on our images, impacting the image subtraction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41224. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39279] EP250802a: Global MASTER-Net observations report
by GCN Circulars 04 Aug '25

04 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41223 SUBJECT: EP250802a: Global MASTER-Net observations report DATE: 25/08/04 00:09:32 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-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 EP250802a ( EP Team et al., GCN 41221) errorbox 39315 sec after notice time and 1 days 47045 sec after trigger time at 2025-08-03 23:41:13 UT, with upper limit up to 18.0 mag. The observations began at zenith distance = 62 deg. The sun altitude is -70.6 deg. The galactic latitude b = -6 deg., longitude l = 65 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2958029 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 133475 | 2025-08-03 23:41:13 | MASTER-SAAO | (20h 11m 03.23s , +24d 50m 38.4s) | C | 60 | 18.0 | 133475 | 2025-08-03 23:41:13 | MASTER-SAAO | (20h 12m 56.78s , +24d 35m 32.1s) | C | 60 | 17.3 | 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/41223. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39278] EP250802a: GROWTH-India Telescope optical upper limit
by GCN Circulars 03 Aug '25

03 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41222 SUBJECT: EP250802a: GROWTH-India Telescope optical upper limit DATE: 25/08/03 19:17:03 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> T. Mohan, V. Swain, A.P. Saikia, V. Bhalerao (IITB), D. Eappachen, G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of EP transient EP250802a (Yin et al., GCN 41221), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-08-03 16:11:32 UT, i.e., ~29.5 hours after the EP trigger and obtained an exposure in r' filter. We do not detect any afterglow candidates within the uncertainty region of WXT localization. The photometric upper limit is as follows: | MJD (mid) | Filter | tmid-t0 (day) | Exposure Time (sec) | Upper limit (AB) | | ------------ | ------ | ------------- | ------------------- | ---------------- | | 60890.67467 | r' | 1.23 | 300 | 20.8 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/41222. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39277] EP250802a: Einstein Probe detection of an X-ray transient
by GCN Circulars 03 Aug '25

03 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41221 SUBJECT: EP250802a: Einstein Probe detection of an X-ray transient DATE: 25/08/03 12:45:12 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.-H. I. Yin (NJU), X. Mao, T. Zhao, C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by EP-WXT through ground data analysis, designated EP250802a (ObsID:06800000790). The transient was detected at 2025-08-02 10:37:08 (UTC). The WXT position of the source is R.A. = 303.321 deg, DEC = 24.814 deg (J2000) with an uncertainty of 3.1 arcmin (radius, 90% C.L. statistical and systematic). The transient event lasted for about 650 seconds. The average 0.5-4 keV spectrum can be fitted with an absorbed powerlaw model, with absorption fixed at the Galactic value of 3.5 x 10^21 cm^-2 and a photon index of 2.81 (+/-0.47). The unabsorbed average 0.5-4 keV flux is estimated to be 3.81 (-0.57, +0.67) x 10^-11 erg/s/cm2. The peak flux is about 1.16 (-0.20, +0.25) x 10^-10 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters. Further FXT observations are scheduled. 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/41221. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39276] LIGO/Virgo/KAGRA S250802dn: Updated Sky localization
by GCN Circulars 03 Aug '25

03 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41220 SUBJECT: LIGO/Virgo/KAGRA S250802dn: Updated Sky localization DATE: 25/08/03 05:18:45 GMT FROM: lucy.thomas(a)ligo.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S250802dn (GCN Circular 41218). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S250802dn For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 3209 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3070 +/- 1219 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040 View this GCN Circular online at https://gcn.nasa.gov/circulars/41220. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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