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[vsnet-grb-info 38792] GRB 250615A / EP250615a: AstroSat CZTI detection
by GCN Circulars 17 Jun '25

17 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40752 SUBJECT: GRB 250615A / EP250615a: AstroSat CZTI detection DATE: 25/06/17 05:50:31 GMT FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in> M. Tembhurnikar (IUCAA), G. Waratkar (IITB), Harsha K. H. (IUCAA), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long duration GRB 250615A / EP250615a which was also detected by Swift/BAT (Dichiara et al., GCN Circ. 40736) and Einstein Probe/WXT (Yang et al., GCN Circ. 40743). The burst location was at an angle of 84 deg from the pointing axis of AstroSat CZTI. The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-06-15 22:25:17.50 UTC. The measured peak count rate associated with the burst is 99 (+31, -11) counts/s above the background in the combined data of two quadrants (out of four), with a total of 983 (+231, -222) counts. The local mean background count rate was 155 (+1, -2) counts/s. Using cumulative rates, we measure a T90 of 22 (+15, -5) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-06-15 22:25:22.52 UTC. The measured peak count rate associated with the burst is 490 (+70, -50) counts/s above the background in the combined data of all quadrants, with a total of 7176 (+826, -898) counts. The local mean background count rate was 1329 (+7, -8) counts/s. We measure a T90 of 34 (+6, -10) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/40752. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38791] Fermi Gamma-ray Burst Monitor trigger 771803204/250616907 is not a GRB
by GCN Circulars 16 Jun '25

16 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40751 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 771803204/250616907 is not a GRB DATE: 25/06/16 22:57:17 GMT FROM: eliza.neights(a)gmail.com E. Neights (GWU, NASA GSFC) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 771803204/250616907 at 21:46:39.32 UT on 16 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/40751. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38790] SVOM sb25061207: AbAO AS-32 Optical Upper Limit
by GCN Circulars 16 Jun '25

16 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40750 SUBJECT: SVOM sb25061207: AbAO AS-32 Optical Upper Limit DATE: 25/06/16 18:56:01 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), R. Ya. Inasaridze (AbAO) report on behalf of IKI-GRB-FuN: We performed optical observations of the field of an X-Ray transient sb25061207 (Zhang et. al, GCN 40697; Evans et. al, GCN 40711; Song et. al, GCN 40718) using the 0.7-meter AS-32 telescope of the Abastumani Astrophysical Observatory (AbAO). The observations began on 2025-06-12 at 17:42:06 UT, i.e. ~0.32 days since the SVOM trigger. The series of images has taken in the R-band. We do not detect the optical counterpart (Li et. al, GCN 40707) in the stacked image of 65*60 sec. The preliminary upper limit is given below: Date UT start t-T0 Exp. Filter OT Err. UL (mid, days) (n*s) (3sigma) 2025-06-12 17:42:06 0.32447 65*60 R n/d n/d 20.0 The photometry has calibrated using nearby stars from USNO-B1.0 (R2 magnitudes) and has not corrected for the Galactic extinction. The result is in agreement with optical upper limits reported by (Becerra et. al, GCN 40723; Li et. al, GCN 40731; Adami et. al, GCN 40744). View this GCN Circular online at https://gcn.nasa.gov/circulars/40750. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38789] GRB 250615A: COLIBRÍ optical upper limit
by GCN Circulars 16 Jun '25

16 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40749 SUBJECT: GRB 250615A: COLIBRÍ optical upper limit DATE: 25/06/16 15:32:51 GMT FROM: Francesco at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work(a)gmail.com> Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the Swift GRB 250615A (Dichiara et al., GCN Circ. 40736) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-06-16 08:40 to 2025-06-16 10:46 UTC (from 10.3 to 12.3 hours after the trigger) and obtained 96 minutes of exposure in the i filter. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In our stacked image, we do not detect any new source at the enhanced Swift-XRT position (Goad et al., GCN Circ. 40739) down to a 3-sigma limiting AB magnitude of: i > 22.8 Our upper limit is consistent with the non-detection reported by Swift/UVOT (Kuin et al., GCN Circ. 40747) and DDOTI (Becerra et al., GCN Circ. 40748). 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/40749. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38788] GRB 250615A: DDOTI Optical Upper Limit
by GCN Circulars 16 Jun '25

16 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40748 SUBJECT: GRB 250615A: DDOTI Optical Upper Limit DATE: 25/06/16 12:02:03 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Sahil Atri (U Roma), 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 250615A detected by Swift (Dichiara et al., GCN Circ. 40736) 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 2025-06-16 UTC. DDOTI observed the enhanced Swift-XRT position (Goad et al., GCN Circ. 40739) from 05:18 UTC to 09:55 UTC (from T+6.9 h to T+ 11.5 h after the trigger), obtaining a total exposure of 1.6 hours, alternating with other scientific programs. Comparing our observations to Pan-STARRS PS1 DR2 catalogues, we detect no uncatalogued fading sources within the observed field down to a 3-sigma limiting AB magnitude of: w >19.3 This upper limit is consistent with the non-detection reported by Swift/UVOT (Kuin et al., GCN Circ. 40747). This value is not corrected for Galactic extinction, which is significant due to the burst’s proximity to the Galactic plane. 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/40748. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38787] GRB 250615A: Swift/UVOT Upper Limits
by GCN Circulars 16 Jun '25

16 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40747 SUBJECT: GRB 250615A: Swift/UVOT Upper Limits DATE: 25/06/16 11:38:35 GMT FROM: Paul Kuin at MSSL <npkuin(a)gmail.com> N.P.M.Kuin (UCL/MSSL) and S. Dichiara (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250615A 152 s after the BAT trigger (Dichiara et al., GCN Circ. 40736). No optical afterglow consistent with the enhanced XRT position (Goad et al., GCN Circ. 40739) 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 u_FC 152 402 246 >19.8 white 432 1722 284 >21.0 v 483 1772 156 >19.5 b 408 1697 136 >20.7 u 152 1672 363 >20.0 w1 532 1821 136 >19.5 w2 804 1747 78 >19.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 1.165 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40747. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38786] Konus-Wind detection of GRB 250612C (short/hard with extended emission)
by GCN Circulars 16 Jun '25

16 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40746 SUBJECT: Konus-Wind detection of GRB 250612C (short/hard with extended emission) DATE: 25/06/16 11:33:32 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The bright GRB 250612C (Fermi GBM detection: Fermi GBM team, GCN 40704; Neights & Meegan, GCN 40713; SVOM/GRM observation: Wang et al., GCN 40708; GRID detection: Yang et al., GCN 40732) triggered Konus-Wind (KW) at T0=53591.512 s UT (14:53:11.512). The burst light curve shows a very bright, multi-peaked emission episode, which starts at ~T0-0.05 s and has a duration of ~1.3 s. This episode is followed by a much weaker extended emission tail visible to ~T0+25 s. The emission is seen up to ~15 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250612_T53591/ As observed by Konus-Wind, the burst had the total fluence of (6.92 ± 0.50)x10^-5 erg/cm^2 and a 16-ms peak energy flux, measured from T0+0.016, of (3.01 ± 0.38)x10^-4 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the initial episode (measured from T0 to T0+1.280 s) is best fit in the 20 keV - 20 MeV range by a power law with exponential cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.90(-0.03,+0.02) and Ep = 2084 (-97,+103) keV (chi2 = 91.8/74 dof). Fitting this spectrum by a Band function yields similar, within errors, values of alpha and Ep, and an upper limit on the high energy photon index beta of -4.0 (chi2 = 91.7/73 dof). The spectrum near the peak count rate (measured from T0 to T0+0.064 s) is best fit in the 20 keV - 20 MeV range by a CPL model with alpha = -0.14(-0.13,+0.14) and Ep = 2073 (-214,+263) keV (chi2 = 38.7/35 dof). Fitting this spectrum by a Band function yields the same values of alpha and Ep, and an upper limit on the high energy photon index beta of -2.0 (chi2 = 38.4/34 dof). The spectrum of the extended emission, measured from T0+1.280 s to T0+25.856 s, is best fit in the 20 keV - 20 MeV range by a simple power law (PL) function with the photon PL index of -1.68 ± 0.12. All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40746. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38785] GRB 250615A: Swift-XRT refined Analysis
by GCN Circulars 16 Jun '25

16 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40745 SUBJECT: GRB 250615A: Swift-XRT refined Analysis DATE: 25/06/16 10:56:50 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> D.N. Burrows (PSU), M.A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-OAR) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.2 ks of XRT data for GRB 250615A, from 93 s to 40.3 ks after the trigger. The data comprise 106 s in Windowed Timing (WT) mode 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=1.62 (+0.07, -0.06). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.62 (+0.27, -0.26). The best-fitting absorption column is 2.4 (+0.6, -0.5) x 10^22 cm^-2, in excess of the Galactic value of 5.5 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.0 (+0.4, -0.3) and a best-fitting absorption column of 2.4 (+0.7, -0.6) x 10^22 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 6.7 x 10^-11 (1.5 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.4 (+0.7, -0.6) x 10^22 cm^-2 Galactic foreground: 5.5 x 10^21 cm^-2 Excess significance: 5.3 sigma Photon index: 2.0 (+0.4, -0.3) If the light curve continues to decay with a power-law decay index of 1.62, the count rate at T+24 hours will be 2.2 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.5 x 10^-14 (3.3 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/01324646. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40745. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38784] sb25061207/SVOM: T120 OHP optical upper limit
by GCN Circulars 16 Jun '25

16 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40744 SUBJECT: sb25061207/SVOM: T120 OHP optical upper limit DATE: 25/06/16 10:28:28 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> C. Adami (LAM/Pytheas/AMU), B. Schneider (LAM), Y. Degot-Longui (Pytheas/OHP), S. Basa (LAM/OHP/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), report on behalf of a larger collaboration: We observed the field of the SVOM sb25061207 X-ray transient (Zhang et al., GCN 40697; Li et al., GCN 40707; Evans et al.,GCN 40711; Li et al., GCN 40707; Zhang et al., GCN 40697) using the T120cm telescope at Observatoire de Haute-Provence (France). We obtained 54.5 minutes in the r-band, from 2025-06-12T20:32:03.91 to 2025-06-12T21:44:45.14 (from 9.9 to 11.3 hr after the trigger). In the stacked image, we do not detect the VT optical counterpart (Li et al., GCN 40707) down to the following 3-sigma limit (AB): r > 22.1 The photometric calibration was performed using nearby stars from the PanStarrs catalog and the magnitude is not corrected for Galactic extinction. We acknowledge the excellent support from Observatoire de Haute-Provence and in particular the students and professors from the summer camp OHP 2025 (Institut Origines). View this GCN Circular online at https://gcn.nasa.gov/circulars/40744. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38783] EP250615a/GRB 250615A: EP-WXT detection of a fast X-ray transient
by GCN Circulars 16 Jun '25

16 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40743 SUBJECT: EP250615a/GRB 250615A: EP-WXT detection of a fast X-ray transient DATE: 25/06/16 09:31:10 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> G. J. Yang, M. J. Liu (NAO, CAS), Y. Q. Zhao (USTC,PRIC), Y. P. Zhou (NJU), X. L. Chen (YNU), Q. Y. Wu, C. C. Jin (NAO,CAS) on behalf of the Einstein Probe team: We report on the detection of a fast X-ray transient, designated EP250615a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at 2025-06-15T22:25:17 (UTC). The position of the source is R.A. = 290.379 deg, DEC = 4.678 deg (J2000) with an uncertainty of 2.181 arcmin in radius (90% C.L. statistical and systematic). The transient event lasts for more than 50 seconds. The lightcurve of the transient observed by the WXT exhibits a rapid brightening profile. The average 0.5-4 keV spectrum can be fitted by an absorbed power law with a photon index of 2.2 (+1.5/-1.4) with a column density value of 2.1 (+1.7/-1.6) x 10^22 cm^-2. The derived average unabsorbed 0.5-4 keV flux is 1.0 (+4.3/-0.6) x 10^-8 erg/s/cm^2. The peak flux is around 6.3 x 10^-7 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. The trigger time and position of this X-ray transient are consistent with that of GRB 250615A (GCN 40736, GCN 40737, GCN 40739). 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/40743. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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