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[vsnet-grb-info 38375] GRB 250504A: Fermi GBM Observation
by GCN Circulars 05 May '25

05 May '25

TITLE: GCN CIRCULAR NUMBER: 40346 SUBJECT: GRB 250504A: Fermi GBM Observation DATE: 25/05/05 08:00:47 GMT FROM: Elisabetta Bissaldi at Politecnico and INFN Bari <elisabetta.bissaldi(a)ba.infn.it> S. Bala (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 23:25:54.78 UT on 04 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250504A (trigger 768093959/250504976), which was also detected by Swift BAT (M. J. Moss et al. 2025, GCN 40343). The Fermi GBM on-ground location is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 111 degrees. The GBM light curve consists of multiple peaks with a duration (T90) of about 49 s (50-300 keV). The time-averaged spectrum from T0+0.003 to T0+59.393 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.06 +/- 0.08 and the cutoff energy, parameterized as Epeak, is 621 +/- 130 keV. The event fluence (10-1000 keV) in this time interval is (1.20 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+10 s in the 10-1000 keV band is 3.6 +/- 0.3 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/40346. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38374] GRB 250504A: Enhanced Swift-XRT position
by GCN Circulars 05 May '25

05 May '25

TITLE: GCN CIRCULAR NUMBER: 40345 SUBJECT: GRB 250504A: Enhanced Swift-XRT position DATE: 25/05/05 07:32:59 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 940 s of XRT Photon Counting mode data and 2 UVOT images for GRB 250504A, 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 = 269.61806, -40.36676 which is equivalent to: RA (J2000): 17h 58m 28.34s Dec (J2000): -40d 22' 00.3" with an uncertainty of 4.0 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/40345. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38373] Fermi GRB 250504A: Global MASTER-Net observations report
by GCN Circulars 05 May '25

05 May '25

TITLE: GCN CIRCULAR NUMBER: 40344 SUBJECT: Fermi GRB 250504A: Global MASTER-Net observations report DATE: 25/05/05 00:01:03 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 250504A ( Fermi GBM team, GCN 40342) errorbox 1 sec after notice time and 43 sec after trigger time at 2025-05-04 23:26:38 UT, with upper limit up to 17.3 mag. The observations began at zenith distance = 29 deg. The sun altitude is -70.3 deg. The galactic latitude b = -6 deg., longitude l = 350 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2860892 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 49 | 2025-05-04 23:26:38 | MASTER-SAAO | (17h 56m 41.66s , -40d 35m 44.3s) | C | 10 | 16.7 | 77 | 2025-05-04 23:27:07 | MASTER-SAAO | (17h 56m 41.67s , -40d 35m 44.8s) | C | 10 | 16.7 | 111 | 2025-05-04 23:27:36 | MASTER-SAAO | (17h 56m 41.71s , -40d 35m 45.1s) | C | 20 | 17.0 | 151 | 2025-05-04 23:28:15 | MASTER-SAAO | (17h 56m 41.72s , -40d 35m 45.3s) | C | 20 | 17.0 | 249 | 2025-05-04 23:29:43 | MASTER-SAAO | (17h 56m 41.65s , -40d 35m 44.1s) | C | 40 | 17.2 | 313 | 2025-05-04 23:30:42 | MASTER-SAAO | (17h 56m 41.63s , -40d 35m 43.6s) | C | 50 | 17.2 | 387 | 2025-05-04 23:31:51 | MASTER-SAAO | (17h 56m 41.55s , -40d 35m 43.1s) | C | 60 | 17.3 | 466 | 2025-05-04 23:33:10 | MASTER-SAAO | (17h 56m 41.50s , -40d 35m 42.3s) | C | 60 | 17.3 | 545 | 2025-05-04 23:34:29 | MASTER-SAAO | (17h 56m 41.40s , -40d 35m 41.4s) | C | 60 | 17.3 | 624 | 2025-05-04 23:35:48 | MASTER-SAAO | (17h 56m 41.29s , -40d 35m 40.5s) | C | 60 | 17.3 | 703 | 2025-05-04 23:37:08 | MASTER-SAAO | (17h 56m 41.19s , -40d 35m 39.7s) | 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/40344. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38372] GRB 250504A: Swift detection of a burst
by GCN Circulars 04 May '25

04 May '25

TITLE: GCN CIRCULAR NUMBER: 40343 SUBJECT: GRB 250504A: Swift detection of a burst DATE: 25/05/04 23:44:16 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> M. J. Moss (GSFC), C. Gronwall (PSU), R. Gupta (NASA GSFC), J. A. Kennea (PSU), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 23:25:57 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250504A (trigger=1310284). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 269.612, -40.349 which is RA(J2000) = 17h 58m 27s Dec(J2000) = -40d 20' 57" 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 60 sec. The peak count rate was ~4000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 23:27:15.3 UT, 77.9 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 269.61691, -40.36642 which is equivalent to: RA(J2000) = 17h 58m 28.06s Dec(J2000) = -40d 21' 59.1" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 64 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 consistent with the Galactic value of 2.12 x 10^21 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of 250 seconds with the U filter starting 137 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. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. The 8'x8' region for the list of sources generated on-board covers 0.00% of the XRT error circle. No correction has been made for the expected extinction corresponding to E(B-V) of 0.191. Burst Advocate for this burst is M. J. Moss (mikejmoss3 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/40343. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38371] GRB 250504A: Fermi GBM Final Real-time Localization
by GCN Circulars 04 May '25

04 May '25

TITLE: GCN CIRCULAR NUMBER: 40342 SUBJECT: GRB 250504A: Fermi GBM Final Real-time Localization DATE: 25/05/04 23:36:31 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 23:25:54 UT on 4 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250504A (trigger 768093959.78286 / 250504976). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 265.4, Dec = -40.9 (J2000 degrees, equivalent to J2000 17h 41m, -40d 53'), with a statistical uncertainty of 2.1 degrees. The angle from the Fermi LAT boresight is 113.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40342. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38370] Swift GRB250504.98: Global MASTER-Net observations report
by GCN Circulars 04 May '25

04 May '25

TITLE: GCN CIRCULAR NUMBER: 40341 SUBJECT: Swift GRB250504.98: Global MASTER-Net observations report DATE: 25/05/04 23:35:52 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 GRB250504.98 (trigger No 1310284,17h 58m 26.88s , -40d 20m 56.4s, R=0.05) errorbox 14 sec after notice time and 40 sec after trigger time at 2025-05-04 23:26:38 UT, with upper limit up to 16.7 mag. The observations began at zenith distance = 29 deg. The sun altitude is -70.3 deg. The galactic latitude b = -9 deg., longitude l = 352 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2860822 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 46 | MASTER-SAAO | C | 10 | 16.7 | 75 | MASTER-SAAO | C | 10 | 16.7 | 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/40341. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38369] GRB 250502A: Swift/UVOT Follow up
by GCN Circulars 04 May '25

04 May '25

TITLE: GCN CIRCULAR NUMBER: 40340 SUBJECT: GRB 250502A: Swift/UVOT Follow up DATE: 25/05/04 20:03:01 GMT FROM: Paul Kuin at MSSL <npkuin(a)gmail.com> Paul Kuin (MSSL/UCL) reports on behalf of the Swift/UVOT team: The Swift/UVOT began observations of the field of SVOM detected GRB 250502A 72ks after the SVOM ECLAIR trigger (Wang et al., GCN Circ. 40313). A source consistent with the position reported by Ny Avo Rakotondraine et al. (GCN Circ. 40315) has been detected in the initial UVOT exposures. The detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start T_stop Exp(s) Mag (Vega) Wh 78ks 95ks 880 21.5+/- 0.35 u 72ks 106ks 3664 >21.3 (3-sigma UL) View this GCN Circular online at https://gcn.nasa.gov/circulars/40340. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38368] GRB 250502A: Mondy and Tien-Shan Optical Observations
by GCN Circulars 04 May '25

04 May '25

TITLE: GCN CIRCULAR NUMBER: 40339 SUBJECT: GRB 250502A: Mondy and Tien-Shan Optical Observations DATE: 25/05/04 11:59:20 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), E. Klunko (ISTP), I. Reva (FAI), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We performed follow-up observations of the optical counterpart (Rakotondrainibe et. al, GCN 40315) to GRB 250502A (Wang et al., GCN 40313) using the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy), and the 1-meter Zeiss-1000 telescope of the Tien-Shan Astronomical Observatory (TSHAO). The optical source was observed also by (An et. al, GCN 40319; Li et. al, GCN 40320; Ghosh et. al, GCN 40322; Ugarte Postigo et. al, GCN 40328; Pérez-Fournon et. al, GCN 40330; Odeh et. al, GCN 40331; Bochenek & Perley, GCN 40333; Corcoran et. al, GCN 40334; Leonini et. al, GCN 40337; Zheng et. al, GCN 40338). The redshift z = 2.163 was determined by Ugarte Postigo et. al, GCN 40328. The X-Ray counterpart was detected by XRT (Dichiara et. al, GCN 40336). Our observations began on 02.05.2025 (UT) 15:48 at Mondy Observatory and 2025-05-03 18:25:43 at Tien-Shan Observatory. We detect the optical counterpart in the stacked image in the first observation. The preliminary photometry is as follows: Date UTstart Exptime t-T0 Filter OT Err UL (s) (mid, days) (3sigma) 2025-05-02 15:48:58 30*120 0.31425 R 19.74 0.10 22.5 2025-05-03 18:25:43 20*120 1.41617 R n/d n/d 21.0 The photometry is based on nearby USNO-B1.0 stars and has not been corrected for the Galactic extinction. Reference stars RA Dec R2 206.5862 -10.7663 14.69 206.4706 -10.7622 16.20 206.5453 -10.7644 17.95 View this GCN Circular online at https://gcn.nasa.gov/circulars/40339. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38367] GRB 250502A: KAIT optical observations
by GCN Circulars 04 May '25

04 May '25

TITLE: GCN CIRCULAR NUMBER: 40338 SUBJECT: GRB 250502A: KAIT optical observations DATE: 25/05/04 08:20:51 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, observed the field of SVOM GRB 250502A (Wang et al., GCN 40313) starting at 08:58, May 02 UT, about 12 minutes after the burst. Observations were performed in 3 x 3 tiling mode, a set of clear (roughly R) filter images were obtained. We detected the optical afterglow (Rakotondrainibe et al., GCN 40315; An et al., GCN 40319; Li et al., GCN 40320; Gosh et al., GCN 40322; de Ugarte Postigo et al., GCN 40328; Perez-Fournon et al., GCN 40330; Odeh & Guessoum, GCN 40331; Bochenek & Perley, GCN 40333; Corcoran et al., GCN 40334 and Leonini et al., GCN 40337), which decayed from 17.4 +/- 0.1 mag (Vega) at 963s to 18.7 +/- 0.2 mag at 7.6ks after the burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/40338. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38366] GRB 250502A: Montarrenti Observatory optical detection
by GCN Circulars 03 May '25

03 May '25

TITLE: GCN CIRCULAR NUMBER: 40337 SUBJECT: GRB 250502A: Montarrenti Observatory optical detection DATE: 25/05/03 21:54:31 GMT FROM: Simone Leonini at Montarrenti Observatory (Siena, Italy) <s.leonini(a)iol.it> S. Leonini, M. Conti, P. Rosi, L.M. Tinjaca Ramirez (Montarrenti Observatory, Siena, Italy, part of UAI/SSV-GRB section), M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy) and K. Kalinowski (Aarhus University, Department of Physics and Astronomy) report: we observed the field of GRB 250502A detected by SVOM/ECLAIRs (Wang et al., GCN 40313) with the automated and remoted 0.53m Ritchey-Chretien telescope at Montarrenti Observatory (Siena, Italy, IAU code C88). The observations were started at 2025-05-02 20:42:17 UT (approximately 12 hours after burst) stacking a set of Rc-band CCD images. Observations were performed under thin cloud cover in the second part of the night. The optical afterglow (Rakotondrainibe et al., GCN 40315; An et al., GCN 40319; Li et al., GCN 40320; Gosh et al., GCN 40322; de Ugarte Postigo et al. with a redshift of z = 2.163, GCN 40328 ; Perez-Fournon et al., GCN 40330; Odeh & Guessoum, GCN 40331; Bochenek & Perley, GCN 40333; Corcoran et al., GCN 40334 and Dichiara et al., GCN 40336) was barely detected (S/N =2.1) at the following position: RA (J2000.0) 13h 46m 05.60s +/-0.23 Decl. (J2000.0) -10° 45' 31.70" +/-0.16 Preliminary photometry was obtained using nearby PanSTARRS stars as follows: Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Err. 2025-05-02 21:31:19 UT 12.75 140x40s Rc 20.70 +/- 0.15 Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied. View this GCN Circular online at https://gcn.nasa.gov/circulars/40337. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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