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[vsnet-grb-info 40654] LIGO/Virgo/KAGRA S251031dw: Candidates from the Zwicky Transient Facility
by GCN Circulars 05 Nov '25

05 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42594 SUBJECT: LIGO/Virgo/KAGRA S251031dw: Candidates from the Zwicky Transient Facility DATE: 25/11/05 19:02:41 GMT FROM: Shreya Anand <shreyasahasram08(a)gmail.com> Shreya Anand (Stanford), Anirudh Salgundi (UNC), Robert Stein (UMD), Vishwajeet Swain (IIT-B), Yogesh Wagh (IIT-B), Xander J. Hall (CMU), Mansi Kasliwal (Caltech), Eric Bellm (UW), Michael Coughlin (UMN), Theophile Jegou du Laz (Caltech), and Antonella Palmese (CMU) report, On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: We observed the localization region of the LVK low-significance burst trigger S251031dw with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g- and r-band beginning at 2025-11-01 12:22 UTC, approximately 15.2 hours after merger. We covered 23.1% of the reported localization region on 2025-10-31 and 60.9% of the localization on 2025-11-01. This estimate accounts for chip gaps. ~30% of the tiled localization was at a low galactic latitude. Each exposure was 200s with a median r-band depth of 21.1 mag. The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019), removing candidates with history of variability prior to the merger time. After filtering, 58 transient candidates remain, all within the 95.0% localization of the skymap. None of these candidates have fast evolution consistent with kilonovae. We perform additional vetting of these candidates, and highlight 9 candidates that appear to be young and SN-like, or AGN-like, as candidates of interest in the burst search, in the table below: | ZTF Name | IAU Name | RA (deg) | DEC (deg) | MJD | Filt | Mag | MagErr | Note | | ------------ | ---------- | ---------- | ---------- | -------- | ---- | ----- | ------ | -------- | | ZTF25acchitl | -- | 127.996770 | -27.778576 | 60980.52 | r | 20.63 | 0.11 | AGN-like | | ZTF25accnabz | -- | 128.305827 | -23.858020 | 60980.52 | r | 21.60 | 0.19 | AGN-like | | ZTF25acchdbq | -- | 121.061164 | -19.087422 | 60980.50 | r | 20.35 | 0.21 | AGN-like | | ZTF25acchjjz | -- | 127.829510 | -20.792424 | 60980.52 | r | 20.88 | 0.12 | AGN-like | | ZTF25acchljm | -- | 130.363870 | -23.822309 | 60980.52 | r | 20.87 | 0.13 | AGN-like | | ZTF25accniqx | -- | 131.262056 | -20.691176 | 60980.54 | r | 20.16 | 0.15 | AGN-like | | ZTF25acchigq | -- | 128.491126 | -24.746190 | 60980.52 | r | 21.26 | 0.15 | AGN-like | | ZTF25acchszc | AT2025acno | 137.799671 | -22.017226 | 60980.54 | r | 20.93 | 0.13 | SN-like | | ZTF25acchppz | AT2025acep | 135.228502 | -23.983061 | 60980.54 | r | 19.48 | 0.05 | SN-like | ZTF25acchszc appears to be a rising young, blue supernova in a host galaxy (no redshift available). ZTF25acchppz is offset 9" from a potential host galaxy at z=0.082, and is therefore unlikely to be associated with the burst source. Further follow-up is encouraged. 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; Operations are conducted by Caltech's Optical Observatory (COO) and Caltech/IPAC. GROWTH acknowledges the generous support of the NSF under PIRE Grant No 1545949. Alert database searches are done by AMPEL (Nordin et al. 2019) and Kowalski (Duev et al. 2019). The GROWTH India Telescope (GIT, Kumar et al., 2022) is set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. Its operations are partially supported by funding from the IIT Bombay alumni batch of 1994. The Fritz and SkyPortal projects acknowledge the generous support of The Gordon and Betty Moore Foundation. View this GCN Circular online at https://gcn.nasa.gov/circulars/42594. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40653] LIGO/Virgo/KAGRA S251031dw: Candidates from the Zwicky Transient Facility
by GCN Circulars 05 Nov '25

05 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42594 SUBJECT: LIGO/Virgo/KAGRA S251031dw: Candidates from the Zwicky Transient Facility DATE: 25/11/05 19:02:41 GMT FROM: Shreya Anand <shreyasahasram08(a)gmail.com> Shreya Anand (Stanford), Anirudh Salgundi (UNC), Robert Stein (UMD), Vishwajeet Swain (IIT-B), Yogesh Wagh (IIT-B), Xander J. Hall (CMU), Mansi Kasliwal (Caltech), Eric Bellm (UW), Michael Coughlin (UMN), Theophile Jegou du Laz (Caltech), and Antonella Palmese (CMU) report, On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: We observed the localization region of the LVK low-significance burst trigger S251031dw with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g- and r-band beginning at 2025-11-01 12:22 UTC, approximately 15.2 hours after merger. We covered 23.1% of the reported localization region on 2025-10-31 and 60.9% of the localization on 2025-11-01. This estimate accounts for chip gaps. ~30% of the tiled localization was at a low galactic latitude. Each exposure was 200s with a median r-band depth of 21.1 mag. The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019), removing candidates with history of variability prior to the merger time. After filtering, 58 transient candidates remain, all within the 95.0% localization of the skymap. None of these candidates have fast evolution consistent with kilonovae. We perform additional vetting of these candidates, and highlight 9 candidates that appear to be young and SN-like, or AGN-like, as candidates of interest in the burst search, in the table below: | ZTF Name | IAU Name | RA (deg) | DEC (deg) | MJD | Filt | Mag | MagErr | Note | | ------------ | ---------- | ---------- | ---------- | -------- | ---- | ----- | ------ | -------- | | ZTF25acchitl | -- | 127.996770 | -27.778576 | 60980.52 | r | 20.63 | 0.11 | AGN-like | | ZTF25accnabz | -- | 128.305827 | -23.858020 | 60980.52 | r | 21.60 | 0.19 | AGN-like | | ZTF25acchdbq | -- | 121.061164 | -19.087422 | 60980.50 | r | 20.35 | 0.21 | AGN-like | | ZTF25acchjjz | -- | 127.829510 | -20.792424 | 60980.52 | r | 20.88 | 0.12 | AGN-like | | ZTF25acchljm | -- | 130.363870 | -23.822309 | 60980.52 | r | 20.87 | 0.13 | AGN-like | | ZTF25accniqx | -- | 131.262056 | -20.691176 | 60980.54 | r | 20.16 | 0.15 | AGN-like | | ZTF25acchigq | -- | 128.491126 | -24.746190 | 60980.52 | r | 21.26 | 0.15 | AGN-like | | ZTF25acchszc | AT2025acno | 137.799671 | -22.017226 | 60980.54 | r | 20.93 | 0.13 | SN-like | | ZTF25acchppz | AT2025acep | 135.228502 | -23.983061 | 60980.54 | r | 19.48 | 0.05 | SN-like | ZTF25acchszc appears to be a rising young, blue supernova in a host galaxy (no redshift available). ZTF25acchppz is offset 9" from a potential host galaxy at z=0.082, and is therefore unlikely to be associated with the burst source. Further follow-up is encouraged. 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; Operations are conducted by Caltech's Optical Observatory (COO) and Caltech/IPAC. GROWTH acknowledges the generous support of the NSF under PIRE Grant No 1545949. Alert database searches are done by AMPEL (Nordin et al. 2019) and Kowalski (Duev et al. 2019). The GROWTH India Telescope (GIT, Kumar et al., 2022) is set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. Its operations are partially supported by funding from the IIT Bombay alumni batch of 1994. The Fritz and SkyPortal projects acknowledge the generous support of The Gordon and Betty Moore Foundation. View this GCN Circular online at https://gcn.nasa.gov/circulars/42594. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40652] GRB 251105A: Swift/BAT-GUANO localization skymap of a burst
by GCN Circulars 05 Nov '25

05 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42593 SUBJECT: GRB 251105A: Swift/BAT-GUANO localization skymap of a burst DATE: 25/11/05 18:16:19 GMT FROM: Jimmy DeLaunay at Penn State <delauj2(a)gmail.com> James DeLaunay (PSU), Samuele Ronchini (GSSI), Aaron Tohuvavohu (Cosmic Frontier), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (Northwestern) report: Swift/BAT did not localize GRB 251105A onboard (T0: 2025-11-05T04:41:06.40 UTC, Fermi Trig 784010471) 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), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 22.9 in a 16.384 s analysis time bin, starting at T0 + 4.096 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 747 deg2 and the 50% credible area is 279 deg2. The integrated probability inside the coded field of view is <1%. The NITRATES skymap is consistent with the Fermi localization reported in the final position notice (GCN 42584). The combined Fermi/GBM+NITRATES 90% credible area is 129 deg2 and the 50% credible area is 35 deg2. A plot of the probability skymap can be viewed here: [skymap_plot](https://guano.swift.psu.edu/trigger_report?id=784010503/#:~:te… The probability skymap and joint skymap files can be downloaded from the links here [skymap_fits_file](https://guano.swift.psu.edu/files/784010503/0_n_PROBMAP) [joint_skymap_fits_file](https://guano.swift.psu.edu/files/784010503/0_n_JOI… 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=784010503 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/42593. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40651] GRB 251104A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 05 Nov '25

05 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42592 SUBJECT: GRB 251104A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/11/05 18:13:59 GMT FROM: Camila Angulo Valdez at UNAM <camiangulo(a)astro.unam.mx> Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), Camila Angulo (UNAM), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), 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), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM): We imaged the field of the SVOM GRB 251104A (Bernardini et al., GCN Circ. 42581) using the DDRAGO wide-field, two-channel imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-11-05 05:32:28 to 06:59:02 UTC (from 12.02 to 13.46 hours after the trigger) and obtained 64 minutes of exposure in the r and z filters. At the time of the observation the GRB was about 6 degrees from the full Moon. The data were reduced and coadded with the COLIBRÍ pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source at the ECLAIRs source position (Bernardini et al., GCN Circ. 42581) down to the following 5-sigma limit: r > 21.3 z > 20.8 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/42592. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40650] GRB 251105B: AstroSat CZTI detection of a short burst with extended emission
by GCN Circulars 05 Nov '25

05 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42591 SUBJECT: GRB 251105B: AstroSat CZTI detection of a short burst with extended emission DATE: 25/11/05 18:10:53 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> Harsha K. H. (IUCAA), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), A. Goyal (IITB), A. Arya (IITB), G. Waratkar (Caltech/IITB), 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 GRB 251105B which was also detected by SVOM/GRM (Wang et. al., GCN Circ. 42586), Fermi/GBM (Hamburg et. al., GCN Circ. 42589) and Konus-Wind (IPN notices). The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve shows an initial short-duration burst followed by an extended emission which peaks at 2025-11-05 00:58:56.35 UTC. The measured peak count rate associated with the burst is 253 (+94, -8) counts/s above the background in the combined data of all quadrants, with a total of 2711 (+723, -732) counts. The local mean background count rate was 1840 (+6, -6) counts/s. We measure a T90 of 24 (+11, -9) s from the cumulative Veto light curve for the entire burst. 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/42591. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40649] GRB 251023A: SVOM/ECLAIRs detection of a burst through targeted search
by GCN Circulars 05 Nov '25

05 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42590 SUBJECT: GRB 251023A: SVOM/ECLAIRs detection of a burst through targeted search DATE: 25/11/05 16:47:42 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> H. Yang, M. Brunet, O. Godet (IRAP) report on behalf of the SVOM team: The SVOM/ECLAIRs telescope detected GRB 251023A, starting at 2025-10-23T05:57:42.44 UTC (T0), through an offline targeted search with the event-by-event data downloaded through the X-band ground station, which is also detected by Fermi/GBM (Fermi GBM team, GCN#42385), Glowbug (R. Woolf, GCN#42408), and SVOM/GRM (C. Wang, GCN#42451). The burst was detected within several timescales and energy ranges. The best detection is obtained by the image trigger with a signal-to-noise ratio of 6.5 within 8-120 keV over a time window of 40.96 seconds starting at T0. The localization of the source is RA, Dec = 31.661,-7.617 degrees: RA (J2000) = 02h06m26.66s Dec (J2000) = -07d37m01.20s with a 90% C.L. radius of 13.0 arcmin (including systematic error of 6 arcmin added in quadrature). This position is roughly consistent with that measured by Fermi/GBM, with an angular separation of 8.2 degrees. The time-averaged spectrum from T0 to T0+40.96 s in the energy range 5-120 keV is well fitted by a power law. The powerlaw index is 0.8 +/-0.3, consistent with that measured by SVOM/GRM. With this model, the total fluence in 4-120 keV is (1.86 +0.08/-1.00)e-6 erg/cm^2. All quoted errors are at the 68% confidence level. The Space 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. ECLAIRs was developed jointly by APC, CEA, CNES, and IRAP. The SVOM/ECLAIRs point of contact for this event is : Hui Yang (hui.yang(a)irap.omp.eu) Please contact him 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/42590. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40648] Fermi GBM Sub-Threshold Detection of GRB 251105B
by GCN Circulars 05 Nov '25

05 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42589 SUBJECT: Fermi GBM Sub-Threshold Detection of GRB 251105B DATE: 25/11/05 16:40:32 GMT FROM: rhamburg(a)usra.edu R. Hamburg (USRA), P. Veres (UAH), E. Burns (LSU) report on behalf of the Fermi-GBM Team: The SVOM/GRM detected GRB 251105B on 2025-11-05 at 00:58:34.700 UTC (Wang et al 2025, GCN 42586). There was an unrelated Fermi-GBM trigger approximately 2 minutes before this time, which disabled the onboarding triggering for 10 min. The GBM Targeted Search [1], the most sensitive coherent search for short GRB signals in GBM, identified a GRB-like transient starting 0.128 seconds after the SVOM/GRM time, most significantly on the 0.256 s timescale with a "hard" GRB spectrum (i.e., Comptonized function with Epeak = 1500 keV, alpha = -0.5) and an SNR of 60.9. The GRB lightcurve consists of a bright, short peak about 0.5 s in duration seen up to ~1 MeV followed by a period of extended emission out to ~60 s. The Targeted Search localization is RA=279.5 deg, Dec=3.6 deg, with an error of 14.3 deg. (90% CI). [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/42589. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40647] GRB 251103B: Swift/UVOT Upper Limits
by GCN Circulars 05 Nov '25

05 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42588 SUBJECT: GRB 251103B: Swift/UVOT Upper Limits DATE: 25/11/05 13:58:01 GMT FROM: Alice Breeveld at MSSL-UCL <a.breeveld(a)ucl.ac.uk> A.A. Breeveld (UCL-MSSL) and S. Lanava (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 251103B 140 s after the BAT trigger (Lanava et al., GCN Circ. 42556). No optical afterglow consistent with the enhanced XRT position (Evans et al., GCN Circ. 42558)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 140 390 246 >20.2 white 420 1363 245 >21.1 v 470 1413 117 >19.0 b 395 1339 97 >19.8 w1 519 1462 97 >18.8 m2 494 1437 117 >18.8 w2 445 1389 117 >19.1 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.256 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/42588. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40646] LIGO/Virgo/KAGRA S251105aj: Identification of a GW compact binary merger candidate
by GCN Circulars 05 Nov '25

05 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42587 SUBJECT: LIGO/Virgo/KAGRA S251105aj: Identification of a GW compact binary merger candidate DATE: 25/11/05 13:43:35 GMT FROM: Jeremias Sobrinho <jeremiasbezerra.sobrinho(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S251105aj during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-11-05 12:59:19.959 UTC (GPS time: 1446382777.959). The candidate was found by the Aframe [1], cWB [2], cWB BBH [3], GstLAL [4], MBTA [5], PyCBC Live [6], and SPIIR [7] analysis pipelines. S251105aj is an event of interest because its false alarm rate, as estimated by the online analysis, is 8e-13 Hz, or about one in 1e5 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S251105aj The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), or NSBH (<1%). Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [8] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [8] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. The source chirp mass falls with highest probability in the bin (22.0, 44.0) solar masses, assuming the candidate is astrophysical in origin. Two sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [9], distributed via GCN and SCiMMA notices about 27 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [9], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 721 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2071 +/- 545 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] Marx et al. PRD 111, 042010 (2025) doi:10.1103/PhysRevD.111.042010 [2] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004 [3] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018 [4] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008 [5] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [6] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [7] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [8] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [9] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/42587. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40645] GRB 251105B: SVOM/GRM observation of a possible short burst with extended emission
by GCN Circulars 05 Nov '25

05 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42586 SUBJECT: GRB 251105B: SVOM/GRM observation of a possible short burst with extended emission DATE: 25/11/05 13:22:13 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: Marius Brunet (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 251105B (SVOM trigger reference: sb25110501) at 2025-11-05T00:58:34.700 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 narrow hard spike followed by a FRED shape long pulse with a T90 of 43.6 +6.0/-5.4 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251105B.png ECLAIRs was collecting data at the time of this burst but no signal was detected, suggesting the burst localized outside ECLAIRs FoV. 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/42586. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40644] Fermi GRB 251105A: Global MASTER-Net observations report
by GCN Circulars 05 Nov '25

05 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42585 SUBJECT: Fermi GRB 251105A: Global MASTER-Net observations report DATE: 25/11/05 05:16:15 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 251105A ( Fermi GBM team, GCN 42584) errorbox 129 sec after notice time and 150 sec after trigger time at 2025-11-05 04:43:37 UT, with upper limit up to 18.3 mag. The observations began at zenith distance = 43 deg. The sun altitude is -43.0 deg. The galactic latitude b = -25 deg., longitude l = 190 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3033298 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 166 | 2025-11-05 04:43:37 | MASTER-OAFA | (04h 39m 45.81s , +05d 19m 45.6s) | C | 30 | 17.7 | 207 | 2025-11-05 04:44:13 | MASTER-OAFA | (04h 39m 45.84s , +05d 19m 46.9s) | C | 40 | 17.9 | 258 | 2025-11-05 04:44:59 | MASTER-OAFA | (04h 39m 45.88s , +05d 19m 48.6s) | C | 50 | 18.1 | 319 | 2025-11-05 04:45:55 | MASTER-OAFA | (04h 39m 45.91s , +05d 19m 50.3s) | C | 60 | 18.0 | 390 | 2025-11-05 04:47:01 | MASTER-OAFA | (04h 39m 45.96s , +05d 19m 52.4s) | C | 70 | 18.1 | 957 | 2025-11-05 04:56:33 | MASTER-OAFA | (04h 38m 41.39s , +07d 10m 46.5s) | C | 60 | 18.2 | 1023 | 2025-11-05 04:57:38 | MASTER-OAFA | (04h 38m 41.37s , +07d 10m 48.1s) | C | 60 | 18.3 | 1088 | 2025-11-05 04:58:44 | MASTER-OAFA | (04h 38m 41.40s , +07d 10m 49.8s) | C | 60 | 18.3 | 1154 | 2025-11-05 04:59:50 | MASTER-OAFA | (04h 38m 41.39s , +07d 10m 51.5s) | C | 60 | 18.3 | 1219 | 2025-11-05 05:00:55 | MASTER-OAFA | (04h 38m 41.39s , +07d 10m 53.2s) | C | 60 | 18.3 | 1285 | 2025-11-05 05:02:01 | MASTER-OAFA | (04h 38m 41.39s , +07d 10m 54.7s) | C | 60 | 18.3 | 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/42585. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40643] GRB 251105A: Fermi GBM Final Real-time Localization
by GCN Circulars 05 Nov '25

05 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42584 SUBJECT: GRB 251105A: Fermi GBM Final Real-time Localization DATE: 25/11/05 04:51:43 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 04:41:06 UT on 5 Nov 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251105A (trigger 784010471.401264 / 251105195). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 69.6, Dec = 7.1 (J2000 degrees, equivalent to J2000 04h 38m, 7d 05'), with a statistical uncertainty of 3.3 degrees. The angle from the Fermi LAT boresight is 41.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251105195/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251105195/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251105195/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42584. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40642] Fermi Gamma-ray Burst Monitor trigger 783986701/251104920 is not a GRB
by GCN Circulars 05 Nov '25

05 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42583 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 783986701/251104920 is not a GRB DATE: 25/11/05 01:16:51 GMT FROM: oindabimukherjee(a)gmail.com O. Mukherjee (USRA) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 783986701/251104920 at 22:04:56.89 UT on 04 November 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to solar flare." View this GCN Circular online at https://gcn.nasa.gov/circulars/42583. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40641] GRB 251103B: Fermi GBM observation
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42582 SUBJECT: GRB 251103B: Fermi GBM observation DATE: 25/11/04 21:18:14 GMT FROM: atrigg2(a)lsu.edu A. C. Trigg (NPP, NASA MSFC) report on behalf of the Fermi GBM Team: "At 16:46:36.44 UT on 03 November 2025, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 251103B (trigger 783881201/251103699), which was also detected by the Swift/XRT (Evans et al. 2025, GCN 42557) The Fermi GBM Final Real-time Localization (GCN 42555) is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 70 degrees. The GBM light curve shows/consists of rapid multi-peaked emission with a duration (T90) of about 15 s (50-300 keV). The time-averaged spectrum from T0-0.00 s to T0+10.0 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.07 +/- 0.02 and the cutoff energy, parameterized as Epeak, is 149 +/- 3 keV. The event fluence (10-1000 keV) in this time interval is (2.28 +/- 0.08)E-6 erg/cm^2. The 256-msec peak photon flux measured starting from T0+2.24 s in the 10-1000 keV band is 5.6 +/- 0.5 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 146 +/- 3 keV, alpha = -1.07 +/- 0.01, and beta = -3.3 +/- 0.06. 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/42582. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40640] GRB 251104A: SVOM detection of a burst
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42581 SUBJECT: GRB 251104A: SVOM detection of a burst DATE: 25/11/04 17:59:48 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M.G. Bernardini (INAF-OAB, LUPM), M. Pillas (IAP), N. Dagoneau (CEA), F. Lacreu (IAP) At 2025-11-04T17:30:58 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251104A (SVOM burst-id sb25110404). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Image Trigger (IMT), which produced a sequence of 6 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 10.82 in the [5-8] keV energy band over a time window of 655.36 seconds starting at 2025-11-04T17:28:14. The localization of the best alert is R.A., Dec. 26.5099, 15.5077 degrees: R.A. (J2000) = 1h46m02.39s Dec. (J2000) = 15d30m27.56s with a 90% confidence level (C.L.) radius of 7.39 arcmin (including systematic error of 2 arcmin added in quadrature). No immediate slew was performed on this burst. No X-ray observation could be performed by SVOM/MXT for the time being. No optical observation could be performed by SVOM/VT for the time being. 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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Maria Grazia Bernardini: maria.bernardini(a)inaf.it. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/42581. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40639] GRB 251013C: 7DT detection and Medium-band SED of Afterglow
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42569 SUBJECT: GRB 251013C: 7DT detection and Medium-band SED of Afterglow DATE: 25/11/04 06:14:11 GMT FROM: YoungPyo Hong at Seoul National University <evan77333(a)gmail.com> YoungPyo Hong (SNU ARC/SNU), Donggeun Tak (SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), Hyeonho Choi (SNU ARC/SNU), Seo-Won Chang (SNU ARC/SNU), and Ji Hoon Kim (SNU ARC/SNU) report on behalf of the 7-Dimensional Sky Survey team: At 2025-10-14T00:02:30 UTC (about 6 hours after the GRB), we observed the optical counterpart of GRB 251013C (Fermi GBM team GCN 42221, Rakotondrainibe et al. GCN 42222), first reported by SVOM/VT (Palmerio et al. GCN 42223) using 7-Dimensional Telescope (7DT) at the El Sauce Observatory in Chile. Observations were made with 10 7DT units in g, r, i-band and 14 medium-band filters, in which the numeric values indicate their central wavelengths in nanometers. Each medium-band filter has a bandwidth of 25nm. The counterpart was detected at the following position: RA(J2000) = 345.8356 (deg) / 23h03m20.54s RA(J2000) = -0.2103 (deg) / -00°12'37.08" We report our photometry result with 14 medium-band and g, r, i band filters: Filter Mag Mag_err Exposure Date Time T-T0 --------------------------------------------------------------------------------------------------- g 18.11 0.02 3x100s 2025-10-14T00:06:00 6:15:48 r 17.77 0.02 3x100s 2025-10-14T00:12:58 6:22:46 i 17.55 0.05 3x100s 2025-10-14T00:06:10 6:15:59 m400 18.34 0.08 3x100s 2025-10-14T00:12:53 6:22:42 m425 18.29 0.05 3x100s 2025-10-14T00:13:00 6:22:49 m450 18.00 0.04 3x100s 2025-10-14T00:05:55 6:15:43 m475 18.04 0.03 3x100s 2025-10-14T00:12:53 6:22:42 m500 18.07 0.04 3x100s 2025-10-14T00:13:40 6:23:28 m525 17.98 0.04 3x100s 2025-10-14T00:12:54 6:22:43 m550 17.88 0.04 3x100s 2025-10-14T00:13:00 6:22:49 m575 17.85 0.05 3x100s 2025-10-14T00:06:19 6:16:07 m600 17.86 0.07 3x100s 2025-10-14T00:06:16 6:16:05 m625 17.64 0.08 3x100s 2025-10-14T00:06:03 6:15:52 m650 17.57 0.07 3x100s 2025-10-14T00:05:54 6:15:42 m675 17.73 0.05 3x100s 2025-10-14T00:13:29 6:23:17 m700 17.58 0.06 3x100s 2025-10-14T00:05:57 6:15:46 m750 17.41 0.09 3x100s 2025-10-14T00:05:51 6:15:40 m750 17.36 0.08 3x100s 2025-10-14T00:13:41 6:23:30 Photometric flux calibration was performed using synthetic photometry based on the Gaia DR3 XP catalog (Gaia Collaboration et al. 2022) within the AB magnitude system. This is based on preliminary photometry, and no extinction correction has been applied. The 7-Dimensional Telescope (7DT), located in Chile and comprising 20 wide-field telescopes equipped with 40 medium-bandwidth (~25nm) filters, aims to detect optical counterparts of GW sources and conduct the 7-Dimensional Sky Survey (7DS) of the Southern Hemisphere. Further information about the 7DT is available at [http://7ds.snu.ac.kr/](http://7ds.snu.ac.kr/). View this GCN Circular online at https://gcn.nasa.gov/circulars/42569. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40638] GRB 251028A: Insight-HXMT/HE detection
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42580 SUBJECT: GRB 251028A: Insight-HXMT/HE detection DATE: 25/11/04 15:24:23 GMT FROM: guohx(a)ihep.ac.cn Hao-Xuan Guo, Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng (IHEP) report on behalf of the Insight-HXMT team: At 2025-10-28T03:26:40.000 (T0), Insight-HXMT/HE detected a long burst, GRB 251028A, which is also detected by Fermi/GBM (Fermi GBM team, GCN#42497, GCN#42499), MAXI/GSC (MAXI team, GCN#42498), Glowbug (C.C. Cheung et al., GCN#42506), SVOM/GRM (SVOM/GRM team, SVOM/ECLAIRs team, GCN#42522), GECAM-B (GECAM team, GCN#42523), and Konus-Wind (Konus-Wind team, GCN#42527). The Insight-HXMT/HE light curve mainly consists of a single pulse with a T90 of 80 +21/-30 s. The 1s peak rate, measured from T0-4.5 s, is 450 cnts/sec. Insight-HXMT/HE detected a total of 9154 counts from this burst. The Insight-HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb251028A.png All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org View this GCN Circular online at https://gcn.nasa.gov/circulars/42580. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40637] GRB 251103A: Optical afterglow detection by ZTF’s public survey
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42579 SUBJECT: GRB 251103A: Optical afterglow detection by ZTF’s public survey DATE: 25/11/04 15:14:43 GMT FROM: Amaliya Atamalibekova <aa2569(a)cornell.edu> A. Atamalibekova and A. Y. Q. Ho (Cornell) We report a serendipitous detection of the optical afterglow to GRB 251103A (Hu et al., GCN 42534, Schneider et al., GCN Circ. 42535; Turpin et al., GCN Circ. 42538; Gritsevich et al., GCN Circ. 42539; Izzo et al., GCN Circ. 42540, O'Neill et al., GCN Circ. 42543, Ghosh et al., GCN Circ. 42545, A. A. Breeveld et al., GCN Circ. 42554, R. Hellot et al., GCN Circ. 42559) by the Zwicky Transient Facility Public Survey. The transient ZTF25accpzjo was detected on 2025-11-03 22:39 UTC at g=19.76 +/- 0.21 mag, and two hours later at r = 19.24 +/- 0.11 mag. The last upper limit was two days prior, at 2025-11-01 23:56 UTC (g > 21.10 mag from forced photometry). The combination of fast rise (0.67 mag/day) and red colors g-r = 0.47 +/- 0.23 (corrected for Milky Way extinction) was flagged by a pipeline for discovering afterglows in the ZTF data (e.g. Ho et al. 2020, ApJ, 905, 98). Upon a retrospective search, we identified ZTF25accpzjo as the afterglow to GRB 251103A. View this GCN Circular online at https://gcn.nasa.gov/circulars/42579. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40636] EP251102a: FTW optical and NIR observations
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42578 SUBJECT: EP251102a: FTW optical and NIR observations DATE: 25/11/04 13:49:28 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann, Rasika Deshpande (LMU), Xander Hall, Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU), and Antonella Palmese (Carnegie Mellon U.) report: We observed the counterpart of EP251102a (Schneider et al., GCN 42544; Eyles-Ferris et al., GCN 42546; Liang et al., GCN 42548; Mo et al., GCN 42563; Adami et al., GCN 42575) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J bands simultaneously for 7 x 180 s starting at 2025-11-04T04:50:46 UT (0.94 days after the trigger). We detect the counterpart in all bands and report the following magnitude: r = (21.02 +/- 0.06) AB mag The magnitude is calibrated against the PS1 catalog and not corrected for Galactic extinction. We thank Christoph Ries for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/42578. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40635] GRB 251103A: WFST optical observations
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42577 SUBJECT: GRB 251103A: WFST optical observations DATE: 25/11/04 13:13:47 GMT FROM: ylhua(a)pmo.ac.cn Yan-Long Hua, Chao Wu (NAOC), Jin-Jun Geng, Xue-Feng Wu, Jun-Jie Wei, Tian-Rui Sun, Yi-Fang Liang, Ding-Fang Hu, Guan-Xiao Li, Yuan-Tai Yang, Jia-Zheng Zhu, Ze-Lin Xu, Ning Jiang, Ji-An Jiang report on behalf of the WFST team: Following the detection of GRB 251103A by SVOM(Hu et al., GCN 42534，Benjamin Schneider et al., GCN 42549,Chen-Wei Wang et al., GCN 42552), Fermi/GBM (Fermi GBM Team, GCN 42536, GCN 42553), Swift (J.P. Osborne et al., GCN 42551,A. A. Breeveld et al., GCN 42554). We performed follow-up observations using the Wide Field Survey Telescope (WFST Collaboration; arXiv:2306.07590) at the Lenghu Astronomical Observation Base in Qinghai Province, China. Observations in the r/g band began at 2025-11-03T20:57:29 UTC, approximately 16 hours after the trigger. The afterglow is detected in r/g band we measured the following preliminary magnitude: r = 20.82 +/- 0.16,2025-11-03T20:59:45 UTC g = 21.10 +/- 0.12,2025-11-03T22:30:38 UTC The photometric calibration was performed using nearby stars from the PanSTARRS catalog is in the AB system, and is not corrected for Galactic extinction. We thank the WFST staff for supporting these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/42577. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40634] EP251102a: update of EP-FXT follow-up observation
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42576 SUBJECT: EP251102a: update of EP-FXT follow-up observation DATE: 25/11/04 13:08:10 GMT FROM: Hao Zhou at Purple Mountain Observatory, CAS <haozhou(a)pmo.ac.cn> H. Zhou, Y.-F. Liang (PMO, CAS) and H.-W. Pan (NAO, CAS) report on behalf of the Einstein Probe team: The Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) performed one ToO observation for EP251102a, starting at 2025-11-03T11:21:51 (UTC) with an exposure time of about 2.1 ks. The ground-processed position of EP251102a is R.A. = 113.1622 deg, DEC = 7.3217 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The updated position is consistent with the counterpart reported before (Schneider et al. GCN 42544, Eyles-Ferris et al. GCN 42546, Liang et al. GCN 42548, Adami et al. GCN 42575). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 9.1 x 10^20 cm^-2 and a photon index of 1.93+/-0.36. The derived average unabsorbed 0.5-10 keV flux is (4.8+/-1.3) x 10^(-13) erg/s/cm^2. 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/42576. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40633] EP251102a: OHP/T193 optical observations
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42575 SUBJECT: EP251102a: OHP/T193 optical observations DATE: 25/11/04 11:32:43 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> C. Adami (LAM/Pytheas/AMU), N.A. Rakotondrainibe (LAM), B. Schneider (LAM), S. Basa (UAR Pytheas), E. Le Floc'h (CEA/Irfu) report on behalf of the MISTRAL GRB collaboration: We carried out observations of the EP251102a (Schneider et al., GCN 42544; Eyles-Ferris et al., GCN 42546; Liang et al., GCN 42548; Mo et al., GCN 42563) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 75 min (15 exposures of 5 min) in the r-band at a midtime of 2025-11-04 03:34:45 UT corresponding to T-T0 = 30.2064 hours. The afterglow is detected in r’ after image subtraction performed relative to r-band images from PanSTARRS. We measured the following preliminary magnitude: r’ = 20.94 +/- 0.07 The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the STDWeb/STDPipe tools (Karpov 2025), is in the AB system, and is not corrected for Galactic extinction. We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Yoann Degot-Longhi. View this GCN Circular online at https://gcn.nasa.gov/circulars/42575. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40632] GRB 251103A: OHP/T193 optical observations
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42574 SUBJECT: GRB 251103A: OHP/T193 optical observations DATE: 25/11/04 11:29:23 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> C. Adami (LAM/Pytheas/AMU), N.A. Rakotondrainibe (LAM), B. Schneider (LAM), S. Basa (UAR Pytheas), E. Le Floc'h (CEA/Irfu) report on behalf of the MISTRAL GRB collaboration: We carried out observations of the GRB 251103A (Hu et al., GCN 42534, Schneider et al., GCN 42535; Fermi GBM Team, GCN 42536; Turpin et al., GCN 42538; Gritsevich et al., GCN 42539, Izzo et al., GCN 42540; Osborne et al., GCN 42551; O'Neill et al., GCN 42543; Ghosh et al., GCN 42545; Schneider et al., GCN 42549; Osborne et al., GCN 42551; Wang et al., GCN 42552; Sonawane et al., GCN 42553; Breeveld et al., GCN 42554; Hellot et al., GCN 42559; Mo et al., GCN 42562; Lipunov et al., GCN 42565; Delaunay et al., GCN 42568; Zheng et al., GCN 42571, Ren et al., GCN 42572) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 94 min (1 exposure of 4 min and 18 exposures of 5 min) in the r-band at a midtime of 2025-11-04 05:24:03 UT corresponding to T-T0 = 24.63 hours. The afterglow is detected in r’ and we measured the following preliminary magnitude: r’ = 22.33 +/- 0.16 The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the STDWeb/STDPipe tools (Karpov 2025), is in the AB system, and is not corrected for Galactic extinction. We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Yoann Degot-Longhi. View this GCN Circular online at https://gcn.nasa.gov/circulars/42574. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40631] GRB 251103A: Xinglong 2.16m optical detection
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42573 SUBJECT: GRB 251103A: Xinglong 2.16m optical detection DATE: 25/11/04 11:27:31 GMT FROM: Youdong HU at GXU <huyoudong072(a)hotmail.com> L. P. Xin (NAOC), Y.-D. Hu, X. Tian (GXU), Y. Zhang, J. Wang, J.-Y. Wei (NAOC) report on behalf of SVOM follow-up team: We observed the field of GRB 251103A (Hu et al., GCN 42534; Fermi GBM Team, GCN 42536; Wang et al., GCN 42552; Sonawane et al., GCN 42553; DeLaunay et al., GCN 42568; Ren et al., GCN 42572). using the 2.16-m telescope located at Xinglong observatory, China, equipped with the BFOSC camera. We obtained 9*200s frames in R-band, starting at 21:11:22 UT on 2025-11-03, about 16.7 hrs after the trigger. The optical afterglow (Schneider et al., GCN 42535; Turpin et al., GCN 42538; Gritsevich et al., GCN 42539; Izzo et al., GCN 42540; O'Neill et al., GCN 42543; Ghosh et al., GCN 42545; Schneider et al., GCN 42549; Breeveld et al., GCN 42554; Hellot et al., GCN 42559; Mo et al., GCN 42562; Zheng et al., GCN 42571) was clearly detected in the stacked image with a magnitude of R=20.78+-0.08 mag at the mid time, which calibrate with nearby SDSS stars. We thank the staff at Xinglong observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/42573. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40629] GRB 251103A: Insight-HXMT detection
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42572 SUBJECT: GRB 251103A: Insight-HXMT detection DATE: 25/11/04 10:49:35 GMT FROM: renyz16607(a)163.com GRB 251103A: Insight-HXMT detection Yang-Zhao Ren, Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team: At 2025-11-03T04:46:28.000 (T0), Insight-HXMT/HE detected the burst GRB 251103A, which is also detected by SVOM/ECLAIRs (Hu et al., GCN#42534), Fermi/GBM (Fermi GBM team, GCN #42536), SVOM/GRM (Wang et al., GCN#42552). The Insight-HXMT/HE light curve mainly consists of a single pulse with a T90 of 5.5 +2.5/-2.0 s. The 1s peak rate, measured from T0+0.25 s, is 2447 cnts/sec. The total counts from this burst is 5414 counts. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb251103A.png All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org View this GCN Circular online at https://gcn.nasa.gov/circulars/42572. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40617] GRB 251103A: KAIT optical observations
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42571 SUBJECT: GRB 251103A: KAIT optical observations DATE: 25/11/04 08:07:10 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 GRB 251103A (Hu et al., GCN 42534; Fermi GBM Team, GCN 42536; Wang et al., GCN 42552; Sonawane et al., GCN 42553; DeLaunay et al., GCN 42568) starting at 11:54 UT, 7.13 hours after the burst. A set of clear (roughly R) filter images were obtained. We clearly detected the afterglow (Schneider et al., GCN 42535; Turpin et al., GCN 42538; Gritsevich et al., GCN 42539; Izzo et al., GCN 42540; O'Neill et al., GCN 42543; Ghosh et al., GCN 42545; Schneider et al., GCN 42549; Breeveld et al., GCN 42554; Hellot et al., GCN 42559; Mo et al., GCN 42562) in our coadd image. We measure its brightness to be 19.4 +/- 0.2 mag (Vega) at mid time of 7.72 hours after the burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/42571. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40621] GRB 251103B: Nanshan/HMT optical upper limit
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42570 SUBJECT: GRB 251103B: Nanshan/HMT optical upper limit DATE: 25/11/04 06:19:28 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang (NAOC), S.Y. Fu (HUST), J. An, X. Liu, L.B. He, Z.P. Zhu, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report: We observed the field of GRB 251103B detected by Swift/BAT (Lanava et al., GCN 42556) and Fermi/GBM (Fermi GBM team, GCN 42555) using the HMT-0.5m telescope located at Nanshan, Xinjiang, China. Observations started at 22:31:33 UT on 2025-11-03, i.e., 5.749 hrs after the Swift/BAT trigger, we obtained 25x120 s unfiltered frames. No new optical source is detected in our stacked image within the enhanced XRT error circle (Evans et al., GCN 42558), down to the following 3-sigma limiting magnitude R>20.4 at 6.276 hrs post-burst, calibrated with the nearby PanSTARRS field and the magnitude is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42570. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40618] GRB 251013A: 7DT detection and Medium-band SED of Afterglow
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42569 SUBJECT: GRB 251013A: 7DT detection and Medium-band SED of Afterglow DATE: 25/11/04 06:14:11 GMT FROM: YoungPyo Hong at Seoul National University <evan77333(a)gmail.com> YoungPyo Hong (SNU ARC/SNU), Donggeun Tak (SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), Hyeonho Choi (SNU ARC/SNU), Seo-Won Chang (SNU ARC/SNU), and Ji Hoon Kim (SNU ARC/SNU) report on behalf of the 7-Dimensional Sky Survey team: At 2025-10-14T00:02:30 UTC (about 6 hours after the GRB), we observed the optical counterpart of GRB 251013C (Fermi GBM team GCN 42221, Rakotondrainibe et al. GCN 42222), first reported by SVOM/VT (Palmerio et al. GCN 42223) using 7-Dimensional Telescope (7DT) at the El Sauce Observatory in Chile. Observations were made with 10 7DT units in g, r, i-band and 14 medium-band filters, in which the numeric values indicate their central wavelengths in nanometers. Each medium-band filter has a bandwidth of 25nm. The counterpart was detected at the following position: RA(J2000) = 345.8356 (deg) / 23h03m20.54s RA(J2000) = -0.2103 (deg) / -00°12'37.08" We report our photometry result with 14 medium-band and g, r, i band filters: Filter Mag Mag_err Exposure Date Time T-T0 --------------------------------------------------------------------------------------------------- g 18.11 0.02 3x100s 2025-10-14T00:06:00 6:15:48 r 17.77 0.02 3x100s 2025-10-14T00:12:58 6:22:46 i 17.55 0.05 3x100s 2025-10-14T00:06:10 6:15:59 m400 18.34 0.08 3x100s 2025-10-14T00:12:53 6:22:42 m425 18.29 0.05 3x100s 2025-10-14T00:13:00 6:22:49 m450 18.00 0.04 3x100s 2025-10-14T00:05:55 6:15:43 m475 18.04 0.03 3x100s 2025-10-14T00:12:53 6:22:42 m500 18.07 0.04 3x100s 2025-10-14T00:13:40 6:23:28 m525 17.98 0.04 3x100s 2025-10-14T00:12:54 6:22:43 m550 17.88 0.04 3x100s 2025-10-14T00:13:00 6:22:49 m575 17.85 0.05 3x100s 2025-10-14T00:06:19 6:16:07 m600 17.86 0.07 3x100s 2025-10-14T00:06:16 6:16:05 m625 17.64 0.08 3x100s 2025-10-14T00:06:03 6:15:52 m650 17.57 0.07 3x100s 2025-10-14T00:05:54 6:15:42 m675 17.73 0.05 3x100s 2025-10-14T00:13:29 6:23:17 m700 17.58 0.06 3x100s 2025-10-14T00:05:57 6:15:46 m750 17.41 0.09 3x100s 2025-10-14T00:05:51 6:15:40 m750 17.36 0.08 3x100s 2025-10-14T00:13:41 6:23:30 Photometric flux calibration was performed using synthetic photometry based on the Gaia DR3 XP catalog (Gaia Collaboration et al. 2022) within the AB magnitude system. This is based on preliminary photometry, and no extinction correction has been applied. The 7-Dimensional Telescope (7DT), located in Chile and comprising 20 wide-field telescopes equipped with 40 medium-bandwidth (~25nm) filters, aims to detect optical counterparts of GW sources and conduct the 7-Dimensional Sky Survey (7DS) of the Southern Hemisphere. Further information about the 7DT is available at [http://7ds.snu.ac.kr/](http://7ds.snu.ac.kr/). View this GCN Circular online at https://gcn.nasa.gov/circulars/42569. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40630] GRB 251103A: Swift/BAT-GUANO arcminute localization of a burst
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42568 SUBJECT: GRB 251103A: Swift/BAT-GUANO arcminute localization of a burst DATE: 25/11/04 03:36:10 GMT FROM: Jimmy DeLaunay at Penn State <delauj2(a)gmail.com> James DeLaunay (PSU), Aaron Tohuvavohu (Cosmic Frontier), Samuele Ronchini (GSSI), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (Northwestern) report: Swift/BAT did not localize GRB 251103A onboard (T0: 2025-11-03T04:46:28.11 UTC, Fermi Trig 783837993, SVOM Trig sb25110301). 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 2.048 s analysis time bin starting at T0 - 0.0 s with a sqrt(TS) of 61.6. An arcminute localization is found with DeltaLLHOut of 24 and a DeltaLLHPeak of 10.2. 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 = 146.821, 16.104 deg which is RA(J2000) = 09h 47m 17.04s Dec(J2000) = 16d 06’ 14.4″ 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=783838024 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/42568. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40615] GRB 251103B: MITSuME Akeno optical upper limits
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42567 SUBJECT: GRB 251103B: MITSuME Akeno optical upper limits DATE: 25/11/04 03:30:48 GMT FROM: Ichiro Takahashi at Science Tokyo <itakahashi(a)hp.phys.titech.ac.jp> I. Takahashi, H. Hagio, A. Ochi, Y. Kubo, M. Sasada, R. Kato, H. Seki, S. Joshima, Y. Yatsu and N. Kawai (Science Tokyo) report on behalf of the MITSuME collaboration: We observed the field of GRB 251103B detected by Fermi (Fermi GBM team, GCN 42555) and Swift (Lanava et al., GCN 42556) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno. The observation started at 2025-11-03 16:47:11 UT (35 seconds after the trigger). We stacked the images taken under good conditions. We did not detect any obvious point sources within the enhanced Swift/XRT error region (Evans et al., GCN 42558). We obtained the 5-sigma limits of the stacked images as follows: T0+[sec] | MID-UT | T-EXP[sec] | 5-sigma limits ------------------------------------------------------------------------------------------------ 124 | 2025-11-03 16:48:40 | 80 | Rc>16.6, Ic>16.3 821 | 2025-11-03 17:00:17 | 1020 | g'>17.8, Rc>18.4, Ic>18.1 7041 | 2025-11-03 18:43:57 | 9180 | g'>19.4, Rc>19.5, Ic>19.1 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the trigger T-EXP: Total exposure time We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire) View this GCN Circular online at https://gcn.nasa.gov/circulars/42567. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40623] GRB 251103B: MITSuME Akeno optical upper limits
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42567 SUBJECT: GRB 251103B: MITSuME Akeno optical upper limits DATE: 25/11/04 03:30:48 GMT FROM: Ichiro Takahashi at Science Tokyo <itakahashi(a)hp.phys.titech.ac.jp> I. Takahashi, H. Hagio, A. Ochi, Y. Kubo, M. Sasada, R. Kato, H. Seki, S. Joshima, Y. Yatsu and N. Kawai (Science Tokyo) report on behalf of the MITSuME collaboration: We observed the field of GRB 251103B detected by Fermi (Fermi GBM team, GCN 42555) and Swift (Lanava et al., GCN 42556) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno. The observation started at 2025-11-03 16:47:11 UT (35 seconds after the trigger). We stacked the images taken under good conditions. We did not detect any obvious point sources within the enhanced Swift/XRT error region (Evans et al., GCN 42558). We obtained the 5-sigma limits of the stacked images as follows: T0+[sec] | MID-UT | T-EXP[sec] | 5-sigma limits ------------------------------------------------------------------------------------------------ 124 | 2025-11-03 16:48:40 | 80 | Rc>16.6, Ic>16.3 821 | 2025-11-03 17:00:17 | 1020 | g'>17.8, Rc>18.4, Ic>18.1 7041 | 2025-11-03 18:43:57 | 9180 | g'>19.4, Rc>19.5, Ic>19.1 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the trigger T-EXP: Total exposure time We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire) View this GCN Circular online at https://gcn.nasa.gov/circulars/42567. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40619] GRB 251103B: Swift-XRT refined Analysis
by GCN Circulars 04 Nov '25

04 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42566 SUBJECT: GRB 251103B: Swift-XRT refined Analysis DATE: 25/11/04 02:13:00 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.8 ks of XRT data for GRB 251103B, from 62 s to 23.6 ks after the trigger. The data comprise 143 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+10.3 ks) can be modelled with a power-law decay with a decay index of alpha=1.0 (+/-0.4). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.21 (+/-0.08). The best-fitting absorption column is 9.0 (+/-0.7) x 10^21 cm^-2, in excess of the Galactic value of 3.3 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.09 (+0.22, -0.21) and a best-fitting absorption column of 4.9 (+1.2, -1.1) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.0 x 10^-11 (6.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 4.9 (+1.2, -1.1) x 10^21 cm^-2 Galactic foreground: 3.3 x 10^21 cm^-2 Excess significance: 2.5 sigma Photon index: 2.09 (+0.22, -0.21) If the light curve continues to decay with a power-law decay index of 1.0, the count rate at T+24 hours will be 0.014 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.4 x 10^-13 (9.2 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/01409824. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42566. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40628] Fermi GRB 251103A: Global MASTER-Net observations report
by GCN Circulars 03 Nov '25

03 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42565 SUBJECT: Fermi GRB 251103A: Global MASTER-Net observations report DATE: 25/11/03 23:31:13 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-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station) started inspect of the Fermi GRB 251103A ( Fermi GBM team, GCN 42536) errorbox 63596 sec after notice time and 63634 sec after trigger time at 2025-11-03 22:27:02 UT, with upper limit up to 17.2 mag. The observations began at zenith distance = 77 deg. The sun altitude is -58.5 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 251103A errorbox 65141 sec after notice time and 65180 sec after trigger time at 2025-11-03 22:52:48 UT, with upper limit up to 16.8 mag. The observations began at zenith distance = 70 deg. The sun altitude is -52.4 deg. The galactic latitude b = 48 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=3030951 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 63665 | 2025-11-03 22:27:02 | MASTER-Tavrida | (09h 39m 04.69s , +19d 28m 36.2s) | C | 60 | 15.8 | 63743 | 2025-11-03 22:28:21 | MASTER-Tavrida | (09h 45m 39.49s , +18d 09m 40.8s) | C | 60 | 15.6 | 63812 | 2025-11-03 22:29:30 | MASTER-Tavrida | (09h 50m 09.05s , +19d 26m 40.9s) | C | 60 | 15.9 | 63890 | 2025-11-03 22:30:48 | MASTER-Tavrida | (09h 43m 57.72s , +20d 45m 36.4s) | C | 60 | 15.8 | 63957 | 2025-11-03 22:31:54 | MASTER-Tavrida | (09h 34m 46.40s , +18d 09m 53.8s) | C | 60 | 14.9 | 64037 | 2025-11-03 22:33:15 | MASTER-Tavrida | (09h 47m 09.24s , +16d 23m 55.5s) | C | 60 | 15.6 | 64112 | 2025-11-03 22:34:29 | MASTER-Tavrida | (09h 41m 40.15s , +16d 50m 37.4s) | C | 60 | 15.8 | 64187 | 2025-11-03 22:35:45 | MASTER-Tavrida | (09h 54m 59.68s , +20d 46m 42.7s) | C | 60 | 15.6 | 64264 | 2025-11-03 22:37:02 | MASTER-Tavrida | (09h 49m 01.38s , +22d 03m 37.6s) | C | 60 | 16.1 | 64429 | 2025-11-03 22:39:47 | MASTER-Tavrida | (09h 37m 53.16s , +15d 32m 17.9s) | C | 60 | 16.0 | 64597 | 2025-11-03 22:42:34 | MASTER-Tavrida | (09h 52m 28.41s , +16d 52m 15.0s) | C | 60 | 16.0 | 64665 | 2025-11-03 22:43:42 | MASTER-Tavrida | (09h 56m 36.54s , +18d 09m 42.0s) | C | 60 | 15.9 | 64740 | 2025-11-03 22:44:58 | MASTER-Tavrida | (09h 48m 39.02s , +15d 32m 54.2s) | C | 60 | 15.9 | 64817 | 2025-11-03 22:46:15 | MASTER-Tavrida | (10h 01m 15.68s , +19d 27m 16.3s) | C | 60 | 15.9 | 64896 | 2025-11-03 22:47:34 | MASTER-Tavrida | (09h 32m 51.01s , +20d 44m 10.5s) | C | 60 | 15.9 | 65080 | 2025-11-03 22:50:38 | MASTER-Tavrida | (09h 30m 39.62s , +16d 50m 15.8s) | C | 60 | 16.2 | 65210 | 2025-11-03 22:52:48 | MASTER-Kislovodsk | (09h 45m 41.10s , +15d 52m 44.3s) | C | 60 | 15.3 | 65210 | 2025-11-03 22:52:48 | MASTER-Kislovodsk | (09h 45m 37.84s , +16d 14m 48.4s) | C | 60 | 15.3 | 65252 | 2025-11-03 22:53:30 | MASTER-Tavrida | (09h 28m 08.59s , +19d 27m 24.4s) | C | 60 | 16.0 | 65290 | 2025-11-03 22:54:08 | MASTER-Kislovodsk | (09h 45m 42.17s , +15d 53m 49.3s) | C | 60 | 15.3 | 65290 | 2025-11-03 22:54:08 | MASTER-Kislovodsk | (09h 45m 38.78s , +16d 15m 52.2s) | C | 60 | 15.2 | 65329 | 2025-11-03 22:54:47 | MASTER-Tavrida | (10h 03m 23.21s , +16d 50m 53.3s) | C | 60 | 16.0 | 65370 | 2025-11-03 22:55:27 | MASTER-Kislovodsk | (09h 45m 44.69s , +16d 14m 55.7s) | C | 60 | 14.4 | 65407 | 2025-11-03 22:56:04 | MASTER-Tavrida | (09h 59m 28.09s , +15d 33m 03.1s) | C | 60 | 16.1 | 65450 | 2025-11-03 22:56:47 | MASTER-Kislovodsk | (09h 45m 37.64s , +16d 14m 01.1s) | C | 60 | 13.0 | 65492 | 2025-11-03 22:57:30 | MASTER-Tavrida | (09h 45m 09.73s , +14d 16m 08.9s) | C | 60 | 16.0 | 65572 | 2025-11-03 22:58:49 | MASTER-Tavrida | (09h 43m 15.43s , +23d 20m 25.8s) | C | 60 | 15.9 | 65652 | 2025-11-03 23:00:09 | MASTER-Tavrida | (09h 23m 45.21s , +18d 09m 40.8s) | C | 60 | 16.3 | 65719 | 2025-11-03 23:00:47 | MASTER-Kislovodsk | (09h 45m 40.53s , +16d 14m 40.7s) | C | 120 | 12.0 | 65732 | 2025-11-03 23:01:29 | MASTER-Tavrida | (09h 55m 49.49s , +14d 15m 39.6s) | C | 60 | 16.1 | 65813 | 2025-11-03 23:02:51 | MASTER-Tavrida | (10h 07m 38.94s , +18d 09m 58.4s) | C | 60 | 15.8 | 65859 | 2025-11-03 23:03:06 | MASTER-Kislovodsk | (09h 45m 43.46s , +16d 16m 15.9s) | C | 120 | 13.2 | 65998 | 2025-11-03 23:05:26 | MASTER-Kislovodsk | (09h 45m 42.35s , +15d 53m 35.0s) | C | 120 | 13.1 | 65998 | 2025-11-03 23:05:26 | MASTER-Kislovodsk | (09h 45m 38.38s , +16d 15m 33.9s) | C | 120 | 13.8 | 66058 | 2025-11-03 23:05:26 | MASTER-Kislovodsk | (09h 45m 38.38s , +16d 15m 33.9s) | C | 240 | 14.9 | Coadd 65983 | 2025-11-03 23:05:41 | MASTER-Tavrida | (10h 00m 15.07s , +22d 04m 18.9s) | C | 60 | 15.7 | 66063 | 2025-11-03 23:07:01 | MASTER-Tavrida | (09h 34m 27.78s , +14d 15m 40.9s) | C | 60 | 15.2 | 66108 | 2025-11-03 23:07:46 | MASTER-Kislovodsk | (09h 45m 38.40s , +16d 16m 40.2s) | C | 60 | 14.3 | 66143 | 2025-11-03 23:08:21 | MASTER-Tavrida | (10h 06m 05.12s , +20d 46m 52.5s) | C | 60 | 14.8 | 66188 | 2025-11-03 23:09:05 | MASTER-Kislovodsk | (09h 45m 44.30s , +16d 15m 44.3s) | C | 60 | 14.6 | 66268 | 2025-11-03 23:10:25 | MASTER-Kislovodsk | (09h 45m 37.28s , +16d 14m 49.5s) | C | 60 | 15.0 | 66328 | 2025-11-03 23:10:25 | MASTER-Kislovodsk | (09h 45m 37.28s , +16d 14m 49.4s) | C | 180 | 16.6 | Coadd 66322 | 2025-11-03 23:11:19 | MASTER-Tavrida | (09h 27m 05.34s , +15d 31m 34.4s) | C | 60 | 16.1 | 66676 | 2025-11-03 23:17:14 | MASTER-Kislovodsk | (09h 45m 43.23s , +16d 16m 03.7s) | C | 60 | 16.3 | 66676 | 2025-11-03 23:17:14 | MASTER-Kislovodsk | (09h 45m 50.89s , +15d 54m 01.9s) | C | 60 | 16.5 | 66708 | 2025-11-03 23:17:45 | MASTER-Tavrida | (09h 26m 34.95s , +22d 02m 43.8s) | C | 60 | 16.9 | 66756 | 2025-11-03 23:18:34 | MASTER-Kislovodsk | (09h 45m 46.97s , +15d 55m 46.6s) | C | 60 | 16.7 | 66756 | 2025-11-03 23:18:34 | MASTER-Kislovodsk | (09h 45m 39.21s , +16d 17m 48.1s) | C | 60 | 16.3 | 66789 | 2025-11-03 23:19:07 | MASTER-Tavrida | (09h 54m 31.91s , +23d 22m 17.1s) | C | 60 | 17.1 | 66836 | 2025-11-03 23:19:54 | MASTER-Kislovodsk | (09h 45m 46.98s , +15d 53m 57.9s) | C | 60 | 16.7 | 66836 | 2025-11-03 23:19:54 | MASTER-Kislovodsk | (09h 45m 39.10s , +16d 15m 58.7s) | C | 60 | 16.3 | 66896 | 2025-11-03 23:19:54 | MASTER-Kislovodsk | (09h 45m 39.10s , +16d 15m 58.7s) | C | 180 | 16.8 | Coadd 66917 | 2025-11-03 23:21:14 | MASTER-Kislovodsk | (09h 45m 51.06s , +15d 55m 42.0s) | C | 60 | 16.8 | 66917 | 2025-11-03 23:21:14 | MASTER-Kislovodsk | (09h 45m 43.07s , +16d 17m 42.5s) | C | 60 | 16.5 | 66968 | 2025-11-03 23:22:05 | MASTER-Tavrida | (09h 31m 55.01s , +23d 19m 40.3s) | C | 60 | 17.2 | 66996 | 2025-11-03 23:22:34 | MASTER-Kislovodsk | (09h 45m 45.14s , +15d 55m 04.0s) | C | 60 | 16.3 | 66996 | 2025-11-03 23:22:34 | MASTER-Kislovodsk | (09h 45m 37.01s , +16d 17m 04.4s) | C | 60 | 16.1 | 67076 | 2025-11-03 23:23:54 | MASTER-Kislovodsk | (09h 45m 45.15s , +15d 56m 08.7s) | C | 60 | 16.6 | 67076 | 2025-11-03 23:23:54 | MASTER-Kislovodsk | (09h 45m 36.92s , +16d 18m 08.8s) | C | 60 | 16.3 | 67157 | 2025-11-03 23:25:14 | MASTER-Kislovodsk | (09h 45m 41.84s , +16d 17m 11.6s) | C | 60 | 16.4 | 67157 | 2025-11-03 23:25:14 | MASTER-Kislovodsk | (09h 45m 50.18s , +15d 55m 11.6s) | C | 60 | 16.5 | 67237 | 2025-11-03 23:26:34 | MASTER-Kislovodsk | (09h 45m 35.80s , +16d 16m 16.3s) | C | 60 | 16.4 | 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/42565. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40620] LIGO/Virgo/KAGRA S251103f: Identification of a GW compact binary merger candidate
by GCN Circulars 03 Nov '25

03 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42564 SUBJECT: LIGO/Virgo/KAGRA S251103f: Identification of a GW compact binary merger candidate DATE: 25/11/03 22:36:28 GMT FROM: Dripta Bhattacharjee <dripta.bhattacharjee(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S251103f during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-11-03 22:05:26.540 UTC (GPS time: 1446242744.540). The candidate was found by the Aframe [1], cWB [2], cWB BBH [3], GstLAL [4], MBTA [5], PyCBC Live [6], and SPIIR [7] analysis pipelines. S251103f is an event of interest because its false alarm rate, as estimated by the online analysis, is 4.2e-14 Hz, or about one in 1e6 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S251103f The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), NSBH (<1%), or BNS (<1%). Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [8] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [8] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. The source chirp mass falls with highest probability in the bin (11.0, 22.0) solar masses, assuming the candidate is astrophysical in origin. Two sky maps are available at this time and can be retrieved from the GraceDB event page: * amplfi.multiorder.fits,0, an initial localization generated by AMPLFI [9], distributed via GCN and SCiMMA notices about 20 seconds after the candidate event time. * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [10], distributed via GCN and SCiMMA notices about 4 minutes after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,0. For the bayestar.multiorder.fits,0 sky map, the 90% credible region is 981 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2158 +/- 568 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] Marx et al. PRD 111, 042010 (2025) doi:10.1103/PhysRevD.111.042010 [2] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004 [3] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018 [4] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008 [5] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [6] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [7] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [8] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [9] Chatterjee et al. MLST 5, 045030 (2024) doi:10.1088/2632-2153/ad8982 [10] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/42564. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40625] EP251102a: NIR observations with WINTER
by GCN Circulars 03 Nov '25

03 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42563 SUBJECT: EP251102a: NIR observations with WINTER DATE: 25/11/03 22:02:24 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Caltech/Carnegie), Tomas Ahumada (Caltech), Viraj Karambelkar (Columbia/CCA), Benjamin Schneider (LAM), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of EP251102a (Liang et al., GCN 42548) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began at 2025-11-03T10:34:56 UTC in the J band (13.2 hours after the EP trigger), consisting of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) We do not detect a source at the optical counterpart location (Schneider et al., GCN 42544; Eyles-Ferris et al., GCN 42546) after image subtraction performed relative to J-band images from the UKIRT Hemisphere survey (Dye et al., 2017). We set a 3-sigma upper limit of J ~ 19.6 mag (AB) and a 5-sigma upper limit of J ~ 19.1 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/42563. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40624] GRB 251103A: J-band detection with WINTER
by GCN Circulars 03 Nov '25

03 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42562 SUBJECT: GRB 251103A: J-band detection with WINTER DATE: 25/11/03 22:00:37 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Caltech/Carnegie), Benjamin Schneider (LAM), Tomas Ahumada (Caltech), Viraj Karambelkar (Columbia), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 251103A (Hu et al., GCN 42534, Fermi GBM Team, GCN 42536; Osborne et al., GCN 42551; Wang et al., GCN 42552; Sonawane et al., GCN 42553) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Two epochs of observations were performed in the J band, beginning at 2025-11-03T10:02 UTC (+5.3 hours after the GRB trigger) and at 2025-11-03T11:39:53 UTC (+6.9 hours), each consisting of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) We detect a source at the optical counterpart location (Schneider et al., GCN 42535; Turpin et al., GCN 42538; Gritsevich et al., GCN 42539; Izzo et al., GCN 42540; O'Neill et al., GCN 42543; Ghosh et al., GCN 42545; Schneider et al., GCN 42549; Breeveld et al., GCN 42554; Hellot et al., GCN 42559) in the first epoch, with magnitude J ~ 19.4 mag (AB). In the second epoch, we set a 3-sigma upper limit of J ~ 19.7 mag (AB) and a 5-sigma upper limit of J ~ 19.3 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/42562. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40627] Swift GRB 251103B: Global MASTER-Net observations report
by GCN Circulars 03 Nov '25

03 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42561 SUBJECT: Swift GRB 251103B: Global MASTER-Net observations report DATE: 25/11/03 21:35:01 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 251103B ( S. Lanava et al., GCN 42556) errorbox 16520 sec after notice time and 16537 sec after trigger time at 2025-11-03 21:22:14 UT, with upper limit up to 18.3 mag. The observations began at zenith distance = 70 deg. The sun altitude is -40.6 deg. The galactic latitude b = -8 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=3031294 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 16628 | MASTER-SAAO | C | 180 | 18.3 | 16628 | MASTER-SAAO | C | 180 | 17.4 | 16840 | MASTER-SAAO | C | 180 | 17.4 | 16840 | MASTER-SAAO | C | 180 | 18.3 | 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/42561. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40622] GRB 251103B: GROWTH-India Telescope optical upper limits
by GCN Circulars 03 Nov '25

03 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42560 SUBJECT: GRB 251103B: GROWTH-India Telescope optical upper limits DATE: 25/11/03 21:20:07 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> T. Mohan, V. Vijaykumar, V. Swain, S. Patil, A.P. Saikia, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of GRB 251103B, detected by Fermi (Fermi GBM team, GCN 42555) and Swift (Lanava et al., GCN 42556), using the 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-11-03 20:09:26 UT, i.e., 3.38 hours after the GRB trigger and obtained multiple exposures in the r' and g' filters. No optical counterpart was detected within the Swift-XRT localization region (Evans et al., GCN 42558). The photometric upper limits are as follows: | MJD (mid) | Filter | tmid-t0 (hours) | Exposure Time (sec) | Upper limit (AB) | | ------------ | ------ | ------------ | ---------------------- | ---------------- | | 60982.84498 | g' | 3.5 | 360 | 19.4 | | 60982.85227 | r' | 3.68 | 4x360 | 20.5 | 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/42560. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40616] GRB 251103A: Kilonova-Catcher optical afterglow detection
by GCN Circulars 03 Nov '25

03 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42559 SUBJECT: GRB 251103A: Kilonova-Catcher optical afterglow detection DATE: 25/11/03 21:17:21 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> R. Hellot, M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (OCA/IJCLab), M. Coughlin (UMN), S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 251103A detected by SVOM (Hu et al., GCN 42534; Wang et al., GCN 42552) and Fermi/GBM (Fermi GBM team GCN 45536) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with a TEC160FL telescope operated by M. Freeberg and a CDK17 telescope located at AITP San Pedro Chile Observatory operated by R. Hellot. Our observations started at TGRB+3.2hr and were taken with sdss ri filters. In our stacked frames, subtracted from the PanSTARRS DR2 template image, we detect the optical counterpart reported by the NOT (Schneider et al., GCN 42535), LCOGT/1m (Turpin et al., GCN 42538; Ghosh et al., GCN 42545), BOOTES-2/TELMA (Gritsevich et al., GCN 42539), GOTO (O'Neill et al., GCN 42543), SVOM/COLIBRÍ (FM-GFT) (Schneider et al., GCN 42549), Swift/UVOT (Breeveld et al., GCN 42554). We report part of our follow-up results in the table below: +---------------+-----------+--------+----------------+--------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+===========+========+================+==============+ | 3.62 | 10 x 180s | r (AB) | 18.66 +/- 0.06 | CDK17 AITP | | 4.89 | 10 x 180s | r (AB) | 19.02 +/- 0.12 | TEC160FL | | 5.46 | 10 x 180s | i (AB) | 19.33 +/- 0.28 | TEC160FL | +---------------+-----------+--------+----------------+--------------+ All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan filters were calibrated using the PanSTARRS DR1 catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/) View this GCN Circular online at https://gcn.nasa.gov/circulars/42559. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40626] GRB 251103B: Enhanced Swift-XRT position
by GCN Circulars 03 Nov '25

03 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42558 SUBJECT: GRB 251103B: Enhanced Swift-XRT position DATE: 25/11/03 20:12:14 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team. Using 1251 s of XRT Photon Counting mode data and 1 UVOT images for GRB 251103B, 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 = 105.87339, -24.87217 which is equivalent to: RA (J2000): 07h 03m 29.61s Dec (J2000): -24d 52' 19.8" 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 https://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/42558. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40614] LIGO/Virgo/KAGRA S251031cq: Identification of a GW compact binary merger candidate
by GCN Circulars 31 Oct '25

31 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42529 SUBJECT: LIGO/Virgo/KAGRA S251031cq: Identification of a GW compact binary merger candidate DATE: 25/10/31 19:29:26 GMT FROM: Dripta Bhattacharjee <dripta.bhattacharjee(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S251031cq during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-10-31 18:59:15.906 UTC (GPS time: 1445972373.906). The candidate was found by the Aframe [1], cWB [2], cWB BBH [3], GstLAL [4], MBTA [5], MLy [6], and PyCBC Live [7] analysis pipelines. S251031cq is an event of interest because its false alarm rate, as estimated by the online analysis, is 7e-10 Hz, or about one in 45 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S251031cq The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), NSBH (<1%), or BNS (<1%). Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [8] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [8] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. The source chirp mass falls with highest probability in the bin (22.0, 44.0) solar masses, assuming the candidate is astrophysical in origin. Two sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [9], distributed via GCN and SCiMMA notices about 24 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [9], distributed via GCN and SCiMMA notices about 4 minutes after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,2. For the bayestar.multiorder.fits,2 sky map, the 90% credible region is 709 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2083 +/- 562 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] Marx et al. PRD 111, 042010 (2025) doi:10.1103/PhysRevD.111.042010 [2] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004 [3] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018 [4] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008 [5] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [6] Skliris et al. PRD 110, 104034 (2024) doi:10.1103/PhysRevD.110.104034 [7] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [8] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [9] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/42529. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40613] GRB 251031A: Swift/BAT-GUANO localization skymap of a burst
by GCN Circulars 31 Oct '25

31 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42528 SUBJECT: GRB 251031A: Swift/BAT-GUANO localization skymap of a burst DATE: 25/10/31 18:52:57 GMT FROM: Jimmy DeLaunay at Penn State <delauj2(a)gmail.com> James DeLaunay (PSU), Samuele Ronchini (GSSI), Aaron Tohuvavohu (Cosmic Frontier), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (Northwestern) report: Swift/BAT did not localize GRB 251031A onboard (T0: 2025-10-31T07:21:00.49 UTC, Fermi Trig 783588065) 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), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 8.4 in a 16.384 s analysis time bin, starting at T0 + 8.192 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 8,620 deg2 and the 50% credible area is 269 deg2. The integrated probability inside the coded field of view is 1%. The NITRATES skymap is consistent with the Fermi localization reported in the final position notice (GCN 42525). The combined Fermi/GBM+NITRATES 90% credible area is 168 deg2 and the 50% credible area is 47 deg2. A plot of the probability skymap can be viewed here: [skymap_plot](https://guano.swift.psu.edu/trigger_report?id=783588097/#:~:te… The probability skymap and joint skymap files can be downloaded from the links here [skymap_fits_file](https://guano.swift.psu.edu/files/783588097/0_n_PROBMAP) [joint_skymap_fits_file](https://guano.swift.psu.edu/files/783588097/0_n_JOI… 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=783588097 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/42528. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40612] Konus-Wind detection of GRB 251028A
by GCN Circulars 31 Oct '25

31 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42527 SUBJECT: Konus-Wind detection of GRB 251028A DATE: 25/10/31 16:09:13 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 251028A (Ferm-GBM detection: The Fermi GBM team, GCN 42497; Veres and Meegan, GCN 42520; BALROG localization: Preis & Greiner, GCN 42499; MAXI-GSC detection: Sugai et al., GCN 42498; Glowbug detection: Cheung et al., GCN 42506; SVOM-GRM detection: Guo et al., GCN 42522; GECAM-B detection: Guo et al., GCN 42523) triggered Konus-Wind at T0=12396.343 s UT (03:26:36.343). The burst light curve starts with a possible rise of a weak emission at ~T0-67 s, which, at ~T0-5.5 s, evolves into the main multi-peaked emission episode with a duration of ~38 s. The emission is seen up to ~5 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB251028_T12396/ As observed by Konus-Wind, the burst had the total fluence of 3.95(-0.25,+0.27)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+19.568 s, of 3.17(-0.62,+0.64)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the main episode (measured from T0 to T0+33.024 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.70(-0.12,+0.13), the high energy photon index beta = -2.81(-0.39,+0.22), the peak energy Ep = 229(-15,+16) keV (chi2 = 92/97 dof). The spectrum near the maximum count rate (measured from T0+16.640 to T0+24.832 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.31(-0.20,+0.22), the high energy photon index beta = -3.22(-1.23,+0.42), the peak energy Ep = 217(-15,+17) keV (chi2 = 77/82 dof). 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/42527. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40611] GRB 251031A: BALROG localization (Fermi Trigger 783588065 / GRB 251031306)
by GCN Circulars 31 Oct '25

31 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42526 SUBJECT: GRB 251031A: BALROG localization (Fermi Trigger 783588065 / GRB 251031306) DATE: 25/10/31 07:43:38 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 783588065 at 07:21:00 on 31 Oct. 2025 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 188.3 deg Decl.(2000.0) = -17.9 deg The 1 sigma statistical error radius is 2.8 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB251031306/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB251031306/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB251031306/json View this GCN Circular online at https://gcn.nasa.gov/circulars/42526. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40610] GRB 251031A: Fermi GBM Final Real-time Localization
by GCN Circulars 31 Oct '25

31 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42525 SUBJECT: GRB 251031A: Fermi GBM Final Real-time Localization DATE: 25/10/31 07:31:22 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 07:21:00 UT on 31 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251031A (trigger 783588065.486224 / 251031306). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 190.3, Dec = -17.6 (J2000 degrees, equivalent to J2000 12h 41m, -17d 36'), with a statistical uncertainty of 3.3 degrees. The angle from the Fermi LAT boresight is 49.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251031306/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251031306/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251031306/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42525. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40609] GRB 251025C: SVOM/GRM observation
by GCN Circulars 30 Oct '25

30 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42524 SUBJECT: GRB 251025C: SVOM/GRM observation DATE: 25/10/30 17:03:31 GMT FROM: tanwj(a)ihep.ac.cn SVOM/GRM team: Wen-Jun Tan, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Sebastien Guillot (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 251025C (SVOM burst-id sb25102505) at 2025-10-25T23:08:41.000 (T0), which is also detected by Fermi/GBM (Fermi/GBM team, GCN # 42449), CALET (S. Torii, et al. GCN # 42467), AstroSat CZTI (A. Arya, et al. GCN # 42469) and Glowbug (R. Woolf, et al. GCN # 42490). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a significant peak followed by weak emission with a T90 of 30.4 +13.2/-12.6 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251025C.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 170.7, Dec = 54.9 , GCN #42449), is located at about 89 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization given by Fermi/GBM, the time-averaged spectrum from T0-2 to T0+30 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.97 +0.16/-0.14 and the cutoff energy, parameterized as Epeak, is 1450 +680/-440 keV. The event fluence (10-1000 keV) in this time interval is (1.06 +0.09/-0.27)E-05 erg/cm^2. The localization of GRB 251025C in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251025C_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: Wen-Jun Tan (IHEP)(tanwj(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42524. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40608] GRB 251028A: GECAM-B detection
by GCN Circulars 30 Oct '25

30 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42523 SUBJECT: GRB 251028A: GECAM-B detection DATE: 25/10/30 15:46:39 GMT FROM: guohx(a)ihep.ac.cn Hao-Xuan Guo, Chen-Wei Wang, Chao Zheng, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by a long burst, GRB 251028A, at 2025-10-28T03:26:40.000 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN#42497, GCN#42499), MAXI/GSC (MAXI team, GCN#42498), Glowbug (C.C. Cheung et al., GCN#42506) and SVOM/GRM (SVOM/GRM team, SVOM/ECLAIRs team, GCN#42522). According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 38 +4/-5 s. shi The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251028A.png The time-averaged spectrum from T0-10 s to T0+45 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.05 +0.11/-0.11 and the cutoff energy, parameterized as Epeak, is 259 +38/-25 keV. The event fluence (10-1000 keV) in this time interval is (3.12 +0.20/-0.17)E-05 erg/cm^2. The 'Amati' relation diagram of GRB 251028A is shown at: https://www.bursthub.cn//admin/static/gecambgrb251028A_amati.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/42523. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40607] GRB 251028A: SVOM/GRM observation
by GCN Circulars 30 Oct '25

30 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42522 SUBJECT: GRB 251028A: SVOM/GRM observation DATE: 25/10/30 13:47:16 GMT FROM: Haoxuan Guo <skyairsama(a)gmail.com> SVOM/GRM team: Hao-Xuan Guo, Chen-Wei Wang, Zheng-Hang Yu, Chao Zheng,, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)SVOM/ECLAIRs team: Report on behalf of the SVOM team: SVOM/ECLAIRs team: Sebastien Guillot (IRAP) SVOM/GRM was triggered in-flight by a burst GRB 251028A (SVOM trigger reference: sb25102801) at 2025-10-28T03:26:37.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN#42497, GCN#42499), MAXI/GSC (MAXI team, GCN#42498) and Glowbug (C.C. Cheung et al., GCN#42506). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple peaks with a T90 of 31.0 +6.5/-3.0 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251028A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 149.5, DEC= 20.2, GCN#42497), is located at about 157 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view, but this burst still clearly detected by ECLAIRs due to the reflection of the Earth atmosphere. With this localization, the time-averaged spectrum from T0-10 to T0+45 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.31 +0.14/-0.16 and the cutoff energy, parameterized as Epeak, is 345 +107/-64 keV. The event fluence (10-1000 keV) in this time interval is (4.56 +0.24/-0.27)E-5 erg/cm^2. The localization of GRB 251028A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251028A_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: Hao-Xuan Guo (IHEP)(guohx(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42522. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40606] IceCube-251025A: Two Transient Candidates from the Zwicky Transient Facility
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42521 SUBJECT: IceCube-251025A: Two Transient Candidates from the Zwicky Transient Facility DATE: 25/10/29 23:11:01 GMT FROM: Robert David Stein at JSI <rdstein(a)umd.edu> Akshay Eranhalodi (DESY), Robert Stein (JSI), Jannis Necker (Leiden University) and Anna Franckowiak (Ruhr University Bochum) report: On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: As part of the ZTF neutrino follow up program (Stein et al. 2023), we observed the localization region of the neutrino event IceCube-251025A (Zegarelli et. al, GCN 42436) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g- and r-band beginning at 2025-10-26 11:02 UTC, approximately 21.2 hours after event time. We covered 98.9% (2.1 sq deg) of the reported localization region. This estimate accounts for chip gaps. Each exposure was 300s with a typical depth of 21.0 mag. The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019) . We are left with the following high-significance transient candidates by our pipeline, all lying within the 90.0% localization of the skymap. ±–––––––––––––––––––––––––––––––––––––––-+ | ZTF Name | IAU Name | RA (deg) | DEC (deg) | Filter | Mag | MagErr | ±–––––––––––––––––––––––––––––––––––––––-+ | ZTF25acammho | AT 2025abwy | 144.8380039 | +15.6961873 | g | 21.13 | 0.21 | | ZTF25acamsai | AT 2025abtz | 146.0869065 | +14.6023944 | r | 20.75 | 0.12 | ±–––––––––––––––––––––––––––––––––––––––-+ Amongst our candidates, we find two unclassified transients of potential interest. ZTF25acammho/AT 2025abwy was inititally detected on 2025-10-03 in r-band, and was then redetected in our ToO observations three weeks later. The source appears to be hostless, with a current magnitude of 21.13. ZTF25acamsai/AT 2025abtz was first detected on 2025-10-22, and appears coincident with a host galaxy of photometric redshift z=0.2. This would imply a magnitude of M=-19.5. The source appears to be blue. We encourage spectrscopic observations to confirm the nature of these two transients. In addition, we also recover one known supernova, ZTF25abvepyj/SN2025zno. The source was first detected by ZTF on 2025-10-02, and is classified as Type Ia Supernova at a redshift of 0.064. Type Ia supernovae are not predicted to be significant neutrino emitters, so we conclude that this source is unrelated to the neutrino. We further find one likely AGN (ZTF19aaixfxw) with W1-W2=0.8. This source does not display any evidence of flaring coincident with the neutrino, and we see no reason to associate it with IC251025A. The neutrino localisation was also observed by DDOTI (Becerra et al., GCN 42457) who report no uncatalogued source with w > 20. These observations are consistent with our observations reported here. ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA; WIS, Israel; OKC, Sweden; JSI/UMd, USA; DESY, Germany; TANGO, Taiwan; UW Milwaukee, USA; LANL, USA; TCD, Ireland; IN2P3, France. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert database searches are done by AMPEL (Nordin et al. 2019). View this GCN Circular online at https://gcn.nasa.gov/circulars/42521. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40605] GRB 251028A: Fermi GBM Observation
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42520 SUBJECT: GRB 251028A: Fermi GBM Observation DATE: 25/10/29 20:08:12 GMT FROM: Peter Veres at University of Alabama in Huntsville <veresp(a)gmail.com> P. Veres (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 03:26:31.86 UT on 28 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251028A (trigger 783314796/251028143) which was also detected by MAXI (Negoro et al. 2025, GCN 42498) and Glowbug (Cheung et al. 2025, GCN 42506). The Fermi GBM on-ground location is consistent with the MAXI position. The angle from the Fermi LAT boresight is 50 degrees. The GBM light curve consists of multiple overlapping pulses with a duration (T90) of about 30 s (50-300 keV). The time-averaged spectrum from T0 to T0+39.9 s is best fit by a Band function with Epeak = 244 +/- 14 keV, alpha = -0.91 +/- 0.03, and beta = -2.4 +/- 0.1. The event fluence (10-1000 keV) in this time interval is (3.13 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+24 s in the 10-1000 keV band is 10.8 +/- 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/42520. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40604] GRB 251026B: SOAR Classification of GOTO25jgl/SN2025absf as a Type Ia supernova
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42519 SUBJECT: GRB 251026B: SOAR Classification of GOTO25jgl/SN2025absf as a Type Ia supernova DATE: 25/10/29 20:04:03 GMT FROM: jcarney(a)unc.edu Jonathan Carney (UNC), Xander J. Hall (CMU), Igor Andreoni (UNC), Brendan O’Connor (CMU), Malte Busmann (LMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report: We observed the source SN 2025absf reported by Belkin et al. (GCN 42470), a possible counterpart to short GRB 251026B (GCN 42455), with the Goodman High Throughput Spectrograph (GHTS; Clemens 2004) on the Southern Astrophysical Telescope (SOAR). We used a grating of 400 lines/mm and a 1.0'' wide slit mask in the M1 spectroscopic setup (hereafter 400M1) with 2x2 binning using the GHTS Red Camera. The 400M1 spectra cover a wavelength range of 3800 -- 7040 Å. The spectra were reduced using Pypeit (Prochaska 2020), using arcs taken immediately after target observation and calibration images from the same night. Flux calibration was performed using observations of HR7596 taken on the same night as the observations with an identical 400M1 setup and 2x2 binning. Using SNID (Blondin et al. 2011) and NGSF (AstroNote 2022-191), we find good template matches to a Ia-norm SN at z ~ 0.044. Thus, we classify SN 2025absf as a type Ia supernova. We therefore conclude that SN 2025absf is not the optical counterpart to GRB 251026B. We thank the CTIO and NOIRLab staff for supporting these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/42519. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40603] GRB 251022A: Swift-XRT confirmation of fading
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42518 SUBJECT: GRB 251022A: Swift-XRT confirmation of fading DATE: 25/10/29 19:49:57 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> D.N. Burrows (PSU), S. Lanava (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Capalbi (INAF-OAR), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has conducted further observations of the field of the Fermi/LAT-detected burst GRB 251022A. The observations now extend from T0+38.6 ks to T0+575.9 ks and have a total exposure time of 6.6 ks. . The previously-reported "Source 4" (Burrows et al., GCN Circ. 42417), coincident with GOTO25iym, is now found to be fading with >3-sigma significance, and is therefore likely the GRB afterglow. The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/00021864. The results of the full analysis of the tiled XRT observations are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00139. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42518. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40602] GRB 251026B: LBT near-infrared observations
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42517 SUBJECT: GRB 251026B: LBT near-infrared observations DATE: 25/10/29 17:44:10 GMT FROM: Yu-Han Yang at University of Rome Tor Vergata <yyang(a)roma2.infn.it> Yu-Han Yang, Eleonora Troja, Massine El Kabir, Muskan Yadav (U Rome) report on behalf of the ERC BHianca team: Following the detection of GRB 251026B by Fermi/GBM (Dafčíková et al., GCN 42455), we observed the candidate optical counterpart GOTO25jgl/AT2025absf (Belkin et al., GCN 42470) in the J filter with the LUCI near-infrared imager mounted on the Large Binocular Telescope (LBT). Observations started at 2025-10-29T11:28:17 (~ 3.2 d after the GBM trigger) with an average airmass of 1.5. We detect the source previously reported as a candidate from GOTO (Belkin et al., GCN 42470) with a preliminary magnitude of J ~ 19.2 AB mag, calibrated using nearby stars from the 2MASS catalog (Skrutskie et al. 2006), uncorrected for Galactic extinction. Our measurement is consistent with the near-infrared upper limit derived by PRIME (Kabir et al. GCN 42501). Compared to the predicted optical magnitude L~19.3 at the same epoch using the magnitudes and decay trend reported by GOTO (Belkin et al., GCN 42470), we find no evidence for a red color excess. Based on the lack of X-ray emission (Osborne et al. GCN 42491) and blue color, the properties of GOTO25jgl do not appear consistent with standard afterglow or kilonova emission, therefore its association with GRB 251026B cannot be confirmed. We acknowledge excellent support from the LBTO and LBT-INAF staff, particularly Ester Marini. View this GCN Circular online at https://gcn.nasa.gov/circulars/42517. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40601] GRB 250926B: VZLUSAT-2 detection
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42516 SUBJECT: GRB 250926B: VZLUSAT-2 detection DATE: 25/10/29 16:40:33 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU) -- the VZLUSAT-2/GRB payload collaboration. The long-duration GRB 250926B (Fermi/GBM detection: GCN 42012) was detected by the GRB detector on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/) The data acquisition was performed by the GRB detector unit no. 0. The detection was confirmed at the peak time 2025-09-26 19:50:31 UTC. The T90 duration is 26 s and the significance during T90 reaches 5.4 sigma. The light curve obtained by VZLUSAT-2 is available here: https://vzlusat2.konkoly.hu/static/share/GRB250926B_GCN_VZLUSAT2.pdf All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/ The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral. View this GCN Circular online at https://gcn.nasa.gov/circulars/42516. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40600] GRB 250926A: VZLUSAT-2 detection
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42515 SUBJECT: GRB 250926A: VZLUSAT-2 detection DATE: 25/10/29 16:39:53 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU) -- the VZLUSAT-2/GRB payload collaboration. The long-duration GRB 250926A (Fermi/GBM detection: GCN 41993; AstroSat/CZTI detection: GCN 42008; INSIGHT-HXMT/HE detection: GCN 42013; CALET/CGBM detection: GCN 42027; Wind/Konus detection trigger at 2025-09-26 00:21:25.489 UTC) was detected by the GRB detectors on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/) The data acquisition was performed by the GRB detector units no. 0 and no. 1. The detection was confirmed at the peak time 2025-09-26 00:21:23 UTC. The T90 duration is 1 s (2 s) and the significance during T90 reaches 5 sigma (17 sigma) for detector unit no. 0 (no. 1). The light curve obtained by VZLUSAT-2 is available here: https://vzlusat2.konkoly.hu/static/share/GRB250926A_GCN_VZLUSAT2.pdf All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/ The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral. View this GCN Circular online at https://gcn.nasa.gov/circulars/42515. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40599] GRB 250925A: VZLUSAT-2 detection
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42514 SUBJECT: GRB 250925A: VZLUSAT-2 detection DATE: 25/10/29 16:38:52 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU) -- the VZLUSAT-2/GRB payload collaboration. The long-duration GRB 250925A (Swift/BAT detection: GCN 41985) was detected by the GRB detector on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/) The data acquisition was performed by the GRB detector unit no. 0. The detection was confirmed at the peak time 2025-09-25 17:04:21 UTC. The T90 duration is 22 s and the significance during T90 reaches 6.6 sigma. The light curve obtained by VZLUSAT-2 is available here: https://vzlusat2.konkoly.hu/static/share/GRB250925A_GCN_VZLUSAT2.pdf All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/ The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral. View this GCN Circular online at https://gcn.nasa.gov/circulars/42514. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40598] GRB 251026B: Fermi GBM Observation
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42513 SUBJECT: GRB 251026B: Fermi GBM Observation DATE: 25/10/29 14:40:22 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova (MUNI) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 07:18:53.33 UT on 26 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251026B (trigger 783155938/251026305). The angle from the Fermi LAT boresight is 19 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 6 s (50-300 keV). The time-averaged spectrum from T0-1.3 to T0+3.7 s is best fit by a simple power law function with index -1.38 +/- 0.04. The event fluence (10-1000 keV) in this time interval is (7.2 +/- 0.7)E-07 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.32 s in the 10-1000 keV band is 1.6 +/- 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/42513. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40597] GRB 251026A/EP251026a: SVOM/VT optical counterpart
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42512 SUBJECT: GRB 251026A/EP251026a: SVOM/VT optical counterpart DATE: 25/10/29 14:28:29 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, C. Wu, L. P. Xin, Y. L. Qiu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, Z. H. Yao, Y. N. Ma, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu., J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), J.X Cao (GXU), X. Tian (GXU) report on behalf of the SVOM/VT team. SVOM/VT performed an automatic slew on the long burst triggered by SVOM/ECLAIRs (Cao et al., GCN 42454) and EP-WXT (Li et al.., GCN 42482). SVOM/VT began observing the field automatically on 2025-10-26T08:34:26, i.e., 424 sec with the slew of the platform triggered on-board, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X band downlinked data, an uncatalogued and fading optical counterpart within EP-FXT's error box (Li et al., GCN 42511) was detected in both channels, compared to the PanSTARRS catalogue. The position is at R.A., Dec. = 72.653080, 51.763733 degrees, equivalent to: R.A. (J2000) = 04:50:36.74 Dec. (J2000) = +51:45:49.44 with an uncertainty of 0.5 arcsec. This location is 3.6 arcminutes from the ECLAIRs onboard position and 2.1 arcminutes from the MXTs position (Cao et al., GCN 42454). The afterglow was fading with a temporal slope of -0.7 from VT_R~19.51+/-0.05 mag, VT_B~21.35+/-0.18 mag at 445 sec, followed by a bump with the peak of VT_R~20.8+/-0.1 mag at the mid time of 3.3 hours post trigger. With the check of VT VHF data, the optical counterpart was also detected in source list and 1 bit images of both channels in Sequence 1. Our photometry was estimated in AB magnitude and not corrected for Galactic extinction. Given the heavy extinction of the Galactic plane (Av = 3.7), the burst was intrinsically optically bright. 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/42512. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40596] GRB 251026A/EP251026a: EP-FXT follow-up observation
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42511 SUBJECT: GRB 251026A/EP251026a: EP-FXT follow-up observation DATE: 25/10/29 13:22:19 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> A. Li (BNU), J. H. Wu (GZHU), H. Q. Cheng and H. Sun (NAOC) on behalf of the Einstein Probe (EP) team: EP-FXT performed two follow-up observations of GRB 251026A/EP251026a (GCN 42454) at 2025-10-27T09:41:08 and 2025-10-28T01:39:45 (UTC), respectively, about 25 and 41 hours after the ECLAIRs' trigger, with an exposure time of 2.7 and 6.0 ks. No source was detected in the first observation. The second observation detected a weak uncatalogued source within the WXT error circle at R.A. = 72.6573, DEC = 51.7653 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). Based on the spectral fitting result, we got a powerlaw spectrum with the absorption fixed at the Galactic value of 3.77x10^21 cm^-2 and the photon index of 2.5, the flux in 0.5-10 keV is derived to be approximately 5.4x10^-14 erg/s/cm2 from the FXT count rate. 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/42511. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40595] The EP-WXT trigger 01709247588 is likely a flaring star
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42510 SUBJECT: The EP-WXT trigger 01709247588 is likely a flaring star DATE: 25/10/29 12:02:08 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Author list: J. P. Feng, B. Zhang (USTC), Y. Wang, Y. F. Liang (PMO, CAS), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: Content: The EP-WXT trigger 01709247588 at the time of 2025-10-29T06:43:17 UTC, is likely a stellar flare associated with Emission-line Star--PM J04472+2038. The estimated flux of the flare is around 1.6e-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 1e31 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/42510. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40594] GRB 251028B: Fermi/GBM observation
by GCN Circulars 29 Oct '25

29 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42509 SUBJECT: GRB 251028B: Fermi/GBM observation DATE: 25/10/29 11:59:34 GMT FROM: Christian Malacaria at INAF-OAR <cmalacaria.astro(a)gmail.com> C. Malacaria (INAF-OAR) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 07:48:06.71 UT on 28 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251028B (trigger 783330491/251028325), which was also detected by the Glowbug (Woolf et al. 2025, GCN 42507) and Swift/BAT-GUANO (DeLaunay et al. 2025, GCN 42508). A final Fermi/GBM localization correction was issued in GCN 42502. The GBM light curve consists of two main pulses with a duration (T90) of about 14 s (50-300 keV). The time-averaged spectrum from T0-0.3 s to T0+12.0 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.77 +/- 0.10 and the cutoff energy, parameterized as Epeak, is 125 +/- 8 keV. The event fluence (10-1000 keV) in this time interval is (3.9 +/- 0.2)E-06 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+8.9 s in the 10-1000 keV band is 6.4 +/- 0.4 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak = 113 +/- 11 keV, alpha = -0.68 +/- 0.14 and beta = -2.8 +/- 0.4. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog." View this GCN Circular online at https://gcn.nasa.gov/circulars/42509. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40593] GRB 251028B: Swift/BAT-GUANO localization skymap of a burst
by GCN Circulars 28 Oct '25

28 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42508 SUBJECT: GRB 251028B: Swift/BAT-GUANO localization skymap of a burst DATE: 25/10/28 18:52:40 GMT FROM: Jimmy DeLaunay at Penn State <delauj2(a)gmail.com> James DeLaunay (PSU), Samuele Ronchini (GSSI), Aaron Tohuvavohu (Caltech), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (Northwestern) report: Swift/BAT did not localize GRB 251028B onboard (T0: 2025-10-28T07:48:06.71 UTC, Fermi Trig 783330491, CALET Trig 1445672396, Glowbug GCN 42507) 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), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 12.3 in a 1.024 s analysis time bin, starting at T0 + 8.704 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 6,959 deg2 and the 50% credible area is 1,123 deg2. The integrated probability inside the coded field of view is 1%. The NITRATES skymap is consistent with the Fermi localization reported in the final position notice (GCN 42502). The combined Fermi/GBM+NITRATES 90% credible area is 436 deg2 and the 50% credible area is 92 deg2. A plot of the probability skymap can be viewed here: [skymap_plot](https://guano.swift.psu.edu/trigger_report?id=783330523/#:~:te… The probability skymap and joint skymap files can be downloaded from the links here [skymap_fits_file](https://guano.swift.psu.edu/files/783330523/0_n_PROBMAP) [joint_skymap_fits_file](https://guano.swift.psu.edu/files/783330523/0_n_JOI… 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=783330523 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/42508. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40592] GRB 251028B: Glowbug gamma-ray detection
by GCN Circulars 28 Oct '25

28 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42507 SUBJECT: GRB 251028B: Glowbug gamma-ray detection DATE: 25/10/28 18:24:36 GMT FROM: richard.s.woolf.civ(a)us.navy.mil R. Woolf, C.C. Cheung, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 251028B, which was also detected by Fermi GBM (GCN 42502) and CALET (GCN 42505). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-28 07:48:04.672 with a duration of 22.5 s and a total significance of about 30.5 sigma. The light curve comprises two primary peaks. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42507. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40591] GRB 251028A: Glowbug gamma-ray detection
by GCN Circulars 28 Oct '25

28 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42506 SUBJECT: GRB 251028A: Glowbug gamma-ray detection DATE: 25/10/28 17:54:20 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 251028A, which was also detected by Fermi/GBM (GCN 42497, 42499) and MAXI/GSC (GCN 42498). Using an adaptive window with a resolution of 32-ms, and taking the GBM-reported T0 (2025-10-28 03:26:31 UT), the burst onset is determined to be T0+22.48s with a duration of 2.0 s and a total significance of about 7.5 sigma. The single peak observed by Glowbug corresponds to the maximum in the Fermi/GBM light curve (GCN 42497). Additional lower-level emission from ~T0+5s to T0+20s may be present in the Glowbug light curve at low significance. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42506. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40590] GRB 251028B: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 28 Oct '25

28 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42505 SUBJECT: GRB 251028B: CALET Gamma-Ray Burst Monitor detection DATE: 25/10/28 16:08:21 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 251028B (Fermi GBM Final Localization Correction: Fermi GBM team, GCN Circ. 42502) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 07:48:06.24 UTC on 28 October 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1445672396/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure that starts at T-0.5 sec, peaks at T+9.9 sec, and ends at T+11.5 sec. The T90 and T50 durations measured by the SGM data are 11.3 +/- 0.4 sec and 8.5 +/- 0.3 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1445672396/ 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/42505. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40589] Fermi GRB 251028B: Global MASTER-Net observations report
by GCN Circulars 28 Oct '25

28 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42504 SUBJECT: Fermi GRB 251028B: Global MASTER-Net observations report DATE: 25/10/28 14:00:39 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-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB 251028B ( Fermi GBM team, GCN 42502) errorbox 19936 sec after notice time and 19967 sec after trigger time at 2025-10-28 13:20:54 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 6 deg. The sun altitude is -33.5 deg. The galactic latitude b = -10 deg., longitude l = 99 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3025691 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 19998 | 2025-10-28 13:20:54 | MASTER-Tunka | (22h 31m 44.47s , +45d 04m 55.7s) | C | 60 | 18.6 | 19998 | 2025-10-28 13:20:54 | MASTER- | (22h 30m 56.32s , +45d 13m 01.0s) | C | 60 | 18.3 | 20070 | 2025-10-28 13:22:06 | MASTER-Tunka | (22h 34m 25.03s , +46d 58m 00.3s) | C | 60 | 17.5 | 20070 | 2025-10-28 13:22:06 | MASTER- | (22h 33m 35.14s , +47d 06m 10.6s) | C | 60 | 17.3 | 20146 | 2025-10-28 13:23:22 | MASTER-Tunka | (22h 30m 48.12s , +43d 08m 44.4s) | C | 60 | 13.9 | 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/42504. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40588] GRB 251025B: GROWTH-India Telescope continued multiband optical observations and rebrightening
by GCN Circulars 28 Oct '25

28 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42503 SUBJECT: GRB 251025B: GROWTH-India Telescope continued multiband optical observations and rebrightening DATE: 25/10/28 12:33:26 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> T. Mohan, V. Swain, S. Patil, A.P. Saikia, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of SVOM GRB 251025B (Hussein et al., GCN 42437), with 0.7m GROWTH-India Telescope (GIT). Our second epoch started at 2025-10-25 22:07:53 UT, i.e. about 7.73 hours after the SVOM trigger. Multiple exposures were obtained in the r′ and i' filters, and we detect the optical afterglow in our stacked images. The photometry result follows as: | MJD (mid) | tmid - t0 (hours) | Filter | Exposure (s) | Magnitude (AB) | | --------- | ----------------- | ------ | ------------ | -------------- | |60973.93279| 7.99 | r' | 5 x 360 | 19.97 +- 0.08 | |60973.95429| 8.5 | i' | 5 x 360 | 19.82 +- 0.16 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. The optical counterpart has rebrightened by ~0.4 mag over a period of about 5.8 hours since our earlier observation (Mohan et al., GCN 42447), consistent with other reports by Li et al., GCN 42453; Pereyra et al., GCN 42452; Freeberg et al., GCN 42474. 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/42503. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40587] GRB 251028B: Fermi GBM Final Localization Correction
by GCN Circulars 28 Oct '25

28 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42502 SUBJECT: GRB 251028B: Fermi GBM Final Localization Correction DATE: 25/10/28 10:12:02 GMT FROM: Christian Malacaria at INAF-OAR <cmalacaria.astro(a)gmail.com> The Fermi GBM team reports the detection of a likely LONG GRB "At 07:48:06.71 UT on 28 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251028B (trigger 783330491/251028325). This trigger was initially classified as Distant Particles by the flight software, but is in fact a GRB. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 337.82, Dec = 45.75 (J2000 degrees, equivalent to J2000 22h 31m, +45d 45'), with a statistical uncertainty of 3.69 degrees. The angle from the Fermi LAT boresight is 119 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028325/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028325/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028325/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/42502. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40586] GRB251026B: PRIME H-band upper limit
by GCN Circulars 28 Oct '25

28 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42501 SUBJECT: GRB251026B: PRIME H-band upper limit DATE: 25/10/28 10:04:28 GMT FROM: Massine El Kabir <m.elkabir(a)campus.unimib.it> M. El Kabir (U Rome), N. Passaleva (U Rome), J. Durbak (UMD), O. Guiffreda (UMD), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC) Following the detection of a candidate optical counterpart (Belkin et al., GCN 42470), we observed the field of GOTO GOTO25jgl/AT2025absf in the H filter with PRIME. Observations started ~ 2 d after the initial Fermi trigger (Dafčíková et al., GCN 42455). At the GOTO position (Belkin et al., GCN 42470), no obvious counterpart is detected on the top of the bright nearby galaxy. Due to the bright galaxy background, it is hard to assess the presence of a faint transient source without a template. Using GALFIT, we modelled the galaxy with a single Sersic profile and, after subtraction, derive a 3-sigma upper limit of H > 19 AB mag 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/42501. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40585] GRB251025B: 3.6m DOT Optical Observations
by GCN Circulars 28 Oct '25

28 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42500 SUBJECT: GRB251025B: 3.6m DOT Optical Observations DATE: 25/10/28 07:35:28 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180(a)gmail.com> Anshika Gupta, Kumar Pranshu, Dhruv Jain, Debolina Kar, Pankaj Pawar, and Kuntal Misra (ARIES) report: We observed the field of GRB 251025B detected by SVOM/ECLAIRs (Hussein et al. 2025; GCN 42437) with the 3.6m Devasthal Optical Telescope (DOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2025-10-27 at 04:20:49.73 UT, i.e., ~1.58 days after the SVOM trigger. We have taken multiple frames with an exposure time of 300s in the R filter. We stacked the images after the alignment. We detect an optical counterpart in our stacked image within the error box of SVOM telescope (Hussein et al. 2025; GCN 42437) and Swift-XRT (Beardmore et al. 2025; GCN 42445). We obtain the following preliminary magnitude in the stacked image: Date Start_UT T_start-T0 (days) Filter Exp time (s) Magnitude ================================================================== 2025-10-27 04:20:49.73 ~1.58 ~ R 300s*8 20.866 +/-0.007 Our detection is consistent with Wu et al. 2025 (GCN 42438); Gress et al. 2025 (GCN 42439); Wu et al. 2025 (GCN 42440); Beardmore et al. 2025 (GCN 42445); Mohan et al. 2025 (GCN 42447); Hernández Fung et al. 2025 (GCN 42450); Pereyra et al. 2025 (GCN 42452); Li et al. 2025 (GCN 42453); Mo et al. 2025 (GCN 42459); Rakotondrainibe et al. 2025 (GCN 42460); Rajabov et al. 2025 (GCN 42466); Saccardi et al. 2025 (GCN 42472); Freeberg et al. 2025 (GCN 42474); Volnova et al. 2025 (GCN 42475). The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the USNO-B1.0 catalog. View this GCN Circular online at https://gcn.nasa.gov/circulars/42500. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40584] GRB 251028A: BALROG localization (Fermi Trigger 783314796 / GRB 251028143)
by GCN Circulars 28 Oct '25

28 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42499 SUBJECT: GRB 251028A: BALROG localization (Fermi Trigger 783314796 / GRB 251028143) DATE: 25/10/28 04:28:32 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 783314796 at 03:26:31 on 28 Oct. 2025 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 145.7 deg Decl.(2000.0) = 16.8 deg The 1 sigma statistical error radius is 2.1 deg. We estimate an additional systematic error of 2 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB251028143/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB251028143/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB251028143/json View this GCN Circular online at https://gcn.nasa.gov/circulars/42499. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40583] GRB 251028A: MAXI/GSC detection
by GCN Circulars 28 Oct '25

28 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42498 SUBJECT: GRB 251028A: MAXI/GSC detection DATE: 25/10/28 04:17:17 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> H. Sugai (Chuo U.), Y. Kawakubo, M. Serino (AGU), H. Negoro, M. Nakajima, K. Takagi, H. Takahashi, H. Nishio (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, H. Hiramatsu, Y. Kondo, A. Yoshida (AGU), Y. Tsuboi, N. Nagashima, Y. Ishihara (Chuo U.), M. Shidatsu, C. Kang, T. Nakamoto (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), 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.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U) report on behalf of the MAXI team: The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 03:27:06 UT on October 28, 2025. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (149.003 deg, 17.518 deg) = (09 56 00, +17 31 04) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.27 deg and 0.21 deg, respectively. The roll angle of long axis from the north direction is 49.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 267 +- 43 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: (148.423, 18.362) deg = (09 53 41, +18 21 43) (J2000) (148.075, 17.954) deg = (09 52 17, +17 57 14) (J2000) (149.164, 17.109) deg = (09 56 39, +17 06 32) (J2000) (149.513, 17.514) deg = (09 58 03, +17 30 50) (J2000) There was no significant excess flux in the previous transit at 02:15 UT with an upper limit of 20 mCrab. View this GCN Circular online at https://gcn.nasa.gov/circulars/42498. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40582] GRB 251028A: Fermi GBM Final Real-time Localization
by GCN Circulars 28 Oct '25

28 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42497 SUBJECT: GRB 251028A: Fermi GBM Final Real-time Localization DATE: 25/10/28 03:36:52 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 03:26:31 UT on 28 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251028A (trigger 783314796.860488 / 251028143). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 149.5, Dec = 20.2 (J2000 degrees, equivalent to J2000 09h 58m, 20d 11'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 53.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028143/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028143/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251028143/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42497. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40581] The EP-WXT trigger 01709247525 is not a real source
by GCN Circulars 28 Oct '25

28 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42496 SUBJECT: The EP-WXT trigger 01709247525 is not a real source DATE: 25/10/28 01:44:18 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. H. Wu (GZHU), A. Li (BNU), H. Q. Cheng and H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709247525 at the time of 2025-10-27T03:28:52.59, is not a real source. View this GCN Circular online at https://gcn.nasa.gov/circulars/42496. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40580] SVOM trigger sb25102702/GRB 251027A is not a GRB
by GCN Circulars 28 Oct '25

28 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42495 SUBJECT: SVOM trigger sb25102702/GRB 251027A is not a GRB DATE: 25/10/28 00:05:44 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y. H.Cheng (YNU), Y. F. Liang (PMO), M. Brunet (IRAP), D. Turpin (CEA), report on behalf of the SVOM mission team: At 2025-10-27T09:38:17 SVOM issued an alert with burst-id: sb25102702. The following circular(s) have been published regarding this event: GCN 42471, 42480, 42481, 42486. After reprocessing the data with the full telemetry, this trigger is no longer considered as an astrophysical source but is due to coding noise from the Crab in the field of view. We apologize for any inconvenience this may have caused. The Burst Advocate (BA) on shift for this alert is Yehao Cheng: yhcheng(a)mail.ynu.edu.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/42495. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40579] IceCube-251025A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42494 SUBJECT: IceCube-251025A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/10/27 22:10:59 GMT FROM: Yuhua Yao at IceCube/UW-Madison <yyao255(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-251025A (https://gcn.nasa.gov/circulars/42436) in a time range of 1000 seconds centered on the alert event time (2025-10-25 13:39:33.261 UTC to 2025-10-25 13:56:13.261 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-251025A. We report a p-value of 1.00 in this time window. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.4e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-251025A in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 1e+05 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-10-24 13:47:53.261 UTC to 2025-10-26 13:47:53.261 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.6e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-251025A in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/42494. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40578] GRB 251025B: Swift-XRT confirmation of fading
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42493 SUBJECT: GRB 251025B: Swift-XRT confirmation of fading DATE: 25/10/27 20:42:45 GMT FROM: P.A. Evans at U. Leicester <pae9(a)leicester.ac.uk> P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has reobserved the X-ray afterglow of GRB 251025B (Hussein et al., GCN Circ. 42437, Beardmore et al., GCN Circ. 42245), gathering a further 2.6 ks of exposure from T0+131 ks to T0+154 ks. The X-ray source is detected but has faded significantly, from 0.30 +/- 0.02 ct/sec to 0.009 (+0.003, -0.002) ct/sec (0.3-10 keV), further confirming its identity as the afterglow of this GRB. The best-fitting power-law decay index is 0.95 (+0.15, -0.12). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42493. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40577] GRB 251013C : 3.4-m telescope of Iranian National Observatory (INO340) optical observations
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42492 SUBJECT: GRB 251013C : 3.4-m telescope of Iranian National Observatory (INO340) optical observations DATE: 25/10/27 20:37:15 GMT FROM: soroush shakeri at Iranian National Observatory (INO) - Isfahan University of Technology (IUT) <soroush.physic(a)gmail.com> **Authors: INO340 Transient Follow-up Team** (H. G. Khosroshahi (INO), S. Shakeri (IUT/INO), H. Altafi (INO/IUT), S. Karimi Mianrudi (IUT), Parisa Hashemi (IUT), H. Torkzadeh (IUT), Reza Rezaei (SUT) and Yu Wang (ICRANet). We report optical follow-up observations of the long-duration **GRB 251013C**, detected by the Fermi/GBM team (GCN [42221](https://gcn.nasa.gov/circulars/42221?view=index&query=GRB+251013C&st…) at 2025-10-13 17:39:41 UT, and subsequently observed by SVOM and Swift/XRT. We observed the field of GRB 251013C with **3.4 m Telescope of Iranian National Observatory** ([INO340](https://ino.org.ir/en/)) by using SDSS g, r, and i filters on 2025 October 13, 15, and 16 (UT). We detected the source at the following position R.A. (J2000.0): 23 03 16 Dec.(J2000.0): -00 12 21 Our first observation was done at 20:36:20 UT on October 13, corresponding to ~10,578 s after the trigger of the Fermi/GBM, and the observation extended to ~2.17 days post-trigger. Photometric calibration was carried out using nearby reference stars from Pan-STARRS and SDSS catalogs. The afterglow shows a consistent fading trend typical of long GRB afterglows and a slight brightening in the second day, with magnitudes decreasing from i = 16.3 ± 0.018 → 21.61 ± 0.34, r = 16.63 ±0.20 → 21.99 ± 0.25, and g = 16.75 ± 0.017→ 22.44 ± 0.16. The deepest stacked images (exp:500s) from the third night reached g = 22.44 ± 0.16 mag. The optical images [ GRB 251013C - Filter-r - 13 Oct](https://www.dropbox.com/scl/fi/5104th21jqrydd9box07q/grb251013C13oct.j… [GRB 251013C - Filter-r - 15 Oct](https://www.dropbox.com/scl/fi/dx9iwokwdc2k2s2bqjz2z/grb251013C15oct.j… **We thank the INO340 technical and scientific staff**, M. Bidar, A. Javadi, A. Farhang, H. Shalchian, R. Shomali, R. Ravanmehr, H. Jenab, S. M. Mohajer, H. Sadeghi, M. Rostamian, A. Behnam, A. Karimzadeh, T. Shokatpour, R. Mirzaei, H. Alirezaei, S. Masoudieh. View this GCN Circular online at https://gcn.nasa.gov/circulars/42492. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40576] GRB 251026B: Swift-XRT observations of GOTO25jgl/AT2025absf
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42491 SUBJECT: GRB 251026B: Swift-XRT observations of GOTO25jgl/AT2025absf DATE: 25/10/27 20:04:15 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne (U. Leicester), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Lanava (PSU), S. Dichiara (PSU), K.L. Page (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Fermi/GBM-detected burst GRB 251026B, collecting 2.0 ks of Photon Counting (PC) mode data between T0+116.7 ks and T0+122.7 ks, centred on the tentative GOTO optical counterpart candidate (GCN Circ. 42470). No X-ray sources have been detected consistent with the estimated 3-sigma GOTO error region (0.8 arcsec). The 3-sigma upper limit in the field ranges from ~0.004 to ~0.005 ct s^-1, corresponding to a 0.3-10 keV observed flux of 1.7e-13 to 2.1e-13 erg cm^-2 s^-1 (assuming a typical GRB spectrum). 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/00021872. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42491. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40575] GRB 251025C: Glowbug gamma-ray detection
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42490 SUBJECT: GRB 251025C: Glowbug gamma-ray detection DATE: 25/10/27 19:37:00 GMT FROM: richard.s.woolf.civ(a)us.navy.mil R. Woolf, C.C. Cheung, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 251025C, which was also detected by Fermi GBM (GCN 42449), CALET (GCN 42467), and AstroSat CZTI (GCN 42469). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-25 23:08:38.104 with a duration of 22.5 s and a total significance of about 46.8 sigma. The light curve comprises an initial fast rise/decay component in the T0 to T0+5s window, followed by secondary emission with slow exponential decay extending to T0+22.5s. Note that data from ~T0 to T0+1.5s and ~T0+3s to T0+5.5s suffered from deadtime in various detectors. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42490. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40574] Fermi-LAT Gamma-ray Observations of IceCube-251025A
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42489 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-251025A DATE: 25/10/27 17:51:55 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) and S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC251025A neutrino event (GCN 42436) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 25-10-25 at 13:47:53.26 UTC (T0) with J2000 position RA = 145.63 (+0.88, -0.88) deg, Decl. = 15.06 (+0.65, -0.62) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC251025A localization error (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC251025A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC251025A best-fit position, the >100 MeV flux upper limit (95% confidence) is <2.8e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <2.8e-09 (<4.6e-08) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this analysis, the Fermi-LAT contact person is L. Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de). 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/42489. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40573] GRB 251023B: Swift-UVOT Upper Limits
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42488 SUBJECT: GRB 251023B: Swift-UVOT Upper Limits DATE: 25/10/27 17:38:43 GMT FROM: noelklin(a)umbc.edu Swift-UVOT has performed follow-up observations of the EP-detected burst GRB 251023B (Wu et al. GCN 42415), collecting 1.7 ks of observations between T0+6.6 ks and T0+26.9 ks. No source was detected in the UVOT data at the position of the optical afterglow (Mandarakas et al., 42404; He at al., GCN 42418; Adami et al., 42421; Méndez et al. 42424). 3-sigma upper limits (AB) using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are: Filter T_start(s) T_stop(s) Exp(s) Mag U 6573 26943 1737 >21.92 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.416 in the direction of the burst (Schlegel et al. 1998). We note that in the first snapshot (1531.80 s worth of data), the optical afterglow's position landed on a UVOT detector patch of small scale sensitivity inhomogeneity. In the U-band this can cause a source's flux to appear 5-16% lower than it actually is. The above limits are not corrected for this. See https://swift.gsfc.nasa.gov/analysis/uvot_digest/sss_check.html for more information. View this GCN Circular online at https://gcn.nasa.gov/circulars/42488. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40572] Konus-Wind detection of GRB 251022A
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42487 SUBJECT: Konus-Wind detection of GRB 251022A DATE: 25/10/27 17:16:14 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 long GRB 251022A (Fermi-GBM detection: The Fermi GBM team, GCN 42380; Mukherjee & Meegan, GCN 42410; Fermi-LAT detection: Di Lalla et al., GCN 42384; SVOM/GRM observation: Ren et al., GCN 42484) triggered Konus-Wind (KW) at T0=81287.312 s UT (22:34:47.312). The burst consists of multiple emission pulses in the interval from T0-35 s to T0+90; the total duration of the burst is ~125 s. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB251022_T81287/ As observed by Konus-Wind, the burst had a fluence of (4.14 ± 0.71)x10^-5 erg/cm^2 and a 64-ms peak energy flux, measured from T0 + 23.168 s, of (1.09 ± 0.36)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum (measured from T0 to T0+90.368 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) function with the following model parameters: the low-energy photon index alpha = -1.37 (-0.08,+0.07), the high energy photon index beta = -2.06 (-0.22,+0.13), the peak energy Ep = 178 (-38,+80) keV, chi2 = 96/97 dof. The spectrum near the peak count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.71 (-0.42,+0.80), the high energy photon index beta = -2.13 (-0.84,+0.24), the peak energy Ep = 161 (-56,+84) keV, chi2 = 91/97 dof. 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/42487. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40571] GRB 251027A: Swift-XRT observations
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42486 SUBJECT: GRB 251027A: Swift-XRT observations DATE: 25/10/27 16:36:26 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-OAR), 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 251027A, collecting 1.6 ks of Photon Counting (PC) mode data between T0+4.5 ks and T0+12 ks after the trigger. We have detected 2 sources. These have been automatically classified as follows: * 0 likely counterparts * 0 candidate counterparts * 2 uncatalogued X-ray sources * 0 known X-ray sources Uncatalogued X-ray sources -------------------------- Source 1 (SWIFT J062052.1+114644): ================================== RA (J2000.0): 95.2175 = 06 20 52.20 Dec (J2000.0): +11.7792 = +11 46 45.1 Error: 7.5 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 5.8 arcmin from the SVOM/ECLAIRs position. Mean rate: (5.4 [+2.7, -2.0])e-3 ct s^-1 Mean flux: (1.90 [+0.95, -0.72])e-10 erg cm^-2 s^-1 Peak rate: (5.4 [+2.7, -2.0])e-3 ct s^-1 Peak flux: (1.90 [+0.95, -0.72])e-10 erg cm^-2 s^-1 ECF: 3.52e-08 erg cm^-2 ct^-1 assuming NH=1.86e+24 cm^-2, gamma=-3.00 determined from a spectral fit. XMM UL: 2.1e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 2.2-sigma above this 3-sigma upper limit. There is no evidence for fading. A SIMBAD object `NVSS J062052+114645' is 0.1" away. There are 4 2MASS objects within the source's 3-sigma error radius. Source 3 (SWIFT J062105.2+112959): ================================== RA (J2000.0): 95.2720 = 06 21 05.28 Dec (J2000.0): +11.4998 = +11 29 59.3 Error: 8.8 (arcsec, radius, 90% confidence). Detect flag: POOR Distance: 12.3 arcmin from the SVOM/ECLAIRs position. Mean rate: (5.7 [+3.5, -2.5])e-3 ct s^-1 Mean flux: (2.4 [+1.5, -1.1])e-13 erg cm^-2 s^-1 Peak rate: (5.7 [+3.5, -2.5])e-3 ct s^-1 Peak flux: (2.4 [+1.5, -1.1])e-13 erg cm^-2 s^-1 XMM UL: 3.3e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading. There are 5 2MASS objects 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/SVOM_FIELD00046. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42486. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40570] EP251027.145: COLIBRÍ optical upper limits
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42485 SUBJECT: EP251027.145: COLIBRÍ optical upper limits DATE: 25/10/27 15:48:00 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> William H. Lee (UNAM), Damien Dornic (CPPM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU),Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Kin Ramandeep Gill (UNAM), Noémie Globus (UNAM), Ocelotl López (UNAM), Diego López-Cámara (UNAM), Nikos Mandarakas (LAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the EP251027.145 (ID=01709247525) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-27 07:47 to 09:09 UTC (from 4.3 to 5.7 hours after the trigger) and obtained 64 minutes of simultaneous exposure in the r and z filters. 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 the stacked image, we do not detect any uncatalogued source at the EP/WXT position down to the following 5-sigma limit: r > 23.6 z > 22.3 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/42485. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40569] GRB 251022A: SVOM/GRM observation
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42484 SUBJECT: GRB 251022A: SVOM/GRM observation DATE: 25/10/27 15:46:15 GMT FROM: renyz16607(a)163.com GRB 251022A: SVOM/GRM observation SVOM/GRM team: Yang-Zhao Ren, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Nicolas Dagoneau (CEA), Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 251022A at 2025-10-22T22:34:19.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #42380), Swift/BAT (James DeLaunay et al., GCN#42409) and Fermi/LAT ( N. Di Lalla et al., GCN #42384), With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 106 +6/-2 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251022A.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 74.5, Dec = -22.7, GCN #42380), is located at about 102 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-20 to T0+101 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.49 +0.12/-0.11 and the cutoff energy, parameterized as Epeak, is 330 +162/-80 keV. The event fluence (10-1000 keV) in this time interval is (4.07 +0.27/-0.27)E-05 erg/cm^2. The localization of GRB 251022A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251022A_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: Yang-Zhao Ren (IHEP)(renyz(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42484. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40568] GRB 251026B: Swift ToO observations
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42483 SUBJECT: GRB 251026B: Swift ToO observations DATE: 25/10/27 15:40:49 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 ToO observation of the Fermi/GBM-detected event GRB 251026B. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021872 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 Fermi/GBM 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/42483. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40567] GRB 251026A/EP251026a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42482 SUBJECT: GRB 251026A/EP251026a: Einstein Probe detection of a fast X-ray transient DATE: 25/10/27 15:36:49 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> A. Li (BNU), J. H. Wu (GZHU), H. Q. Cheng and H. Sun (NAOC) 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 EP251026a. The ground analysis of the WXT data shows that the event started at T0=2025-10-26T08:26:33 (UTC). The WXT position of the source is R.A. = 72.663 deg, DEC = 51.775 deg (J2000) with an uncertainty of 2.1 arcmin in radius (90% C.L. statistical and systematic). This transient is temporally and spatially coincident with GRB 251026A (GCN 42454). The analysis of the WXT data shows that the event lasted for about 500 seconds. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 3.77 x 10^21 cm^-2 and a photon index of 1.00 (-0.37/+0.38). The derived average unabsorbed 0.5-4 keV flux is 1.35 (-0.6/+0.7) x 10^-9 erg/s/cm^2. The peak flux is around 2.1 x 10^-9 erg/s/cm^2 with a fixed Galactic hydrogen column density of 3.77 x 10^21 cm^-2 and a photon index of 1.07 (-0.53/+0.55). We note that the late release of this transient is mostly due to the delay in the data transmission. Follow-up observations with EP-FXT has been scheduled and more information will be reported when the telemetry data arrives. 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/42482. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40566] GRB 251027A: LCO optical upper limit
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42481 SUBJECT: GRB 251027A: LCO optical upper limit DATE: 25/10/27 15:13:55 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), C. Wu (NAOC), J. T. Palmerio (CEA/Irfu), L. P. Xin (NAOC), D. Turpin (CEA/Irfu), B. Cordier (CEA/Irfu), Y. H. Cheng (YNU), Y. F. Liang (PMO), report on behalf of the SVOM mission team: We observed the field of the GRB 251027A detected by SVOM/ECLAIRs (Cheng et al., GCN 42471) with the LCO 1m telescope at McDonald Observatory equipped with the Sinistro instrument. Our observation started on 2025-10-27 at 10:22:43 UT (~45 min after the trigger) and we obtained 3x200 s exposures using the SDSS r filter. In the stacked image, we did not detect any new optical source at the SVOM/ECLAIRs position (Cheng et al., GCN 42471), in agreement with the results reported by Dornic et al. (GCN 42480). We derived the following upper limit r > 22 AB mag (5-sigma) calibrated against Pan-STARRS1 catalogue and not corrected for Galactic extinction. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/42481. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40565] GRB 251027A: LCO optical upper limit
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42481 SUBJECT: GRB 251027A: LCO optical upper limit DATE: 25/10/27 15:13:55 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), C. Wu (NAOC), J. T. Palmerio (CEA/Irfu), L. P. Xin (NAOC), D. Turpin (CEA/Irfu), B. Cordier (CEA/Irfu), Y. H. Cheng (YNU), Y. F. Liang (PMO), report on behalf of the SVOM mission team: We observed the field of the GRB 251027A detected by SVOM/ECLAIRs (Cheng et al., GCN 42471) with the LCO 1m telescope at McDonald Observatory equipped with the Sinistro instrument. Our observation started on 2025-10-27 at 10:22:43 UT (~45 min after the trigger) and we obtained 3x200 s exposures using the SDSS r filter. In the stacked image, we did not detect any new optical source at the SVOM/ECLAIRs position (Cheng et al., GCN 42471), in agreement with the results reported by Dornic et al. (GCN 42480). We derived the following upper limit r > 22 AB mag (5-sigma) calibrated against Pan-STARRS1 catalogue and not corrected for Galactic extinction. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/42481. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40564] GRB 251027A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42480 SUBJECT: GRB 251027A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/10/27 14:47:37 GMT FROM: J.-G. Ducoin at CPPM <ducoin(a)cppm.in2p3.fr> Damien Dornic (CPPM), William H. Lee (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), 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), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Y. H.Cheng (YNU) and Y. F. Liang (PMO) : We imaged the field of the SVOM GRB 251027A (Cheng et al., GCN Circ. 42471) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-10-27T10:08:34 to 2025-10-27T10:47:17 UTC (from 31 to 69 minutes after the trigger) and obtained 32x60 seconds of exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and analyzed 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 (Av>2). In the stacked image, we do not detect any new source at the ECLAIRs source position (Cheng et al., GCN Circ. 42471) down to the following 5-sigma limit: r > 23.57 z > 22.26 Further analysis is 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/42480. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40563] GRB 251017A: Mondy AZT-33IK and Koshka Zeiss-1000 optical observations
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42479 SUBJECT: GRB 251017A: Mondy AZT-33IK and Koshka Zeiss-1000 optical observations DATE: 25/10/27 13:47:19 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), E. Klunko (ISTP), A. Novichonok (Petrozavodsk State University, KIAM), I. Nikolenko (INASAN), A. Pozanenko (IKI), N. Pankov (HSE, IKI), report on behalf of IKI-GRB-FuN: We observed the optical counterpart (Perez-Garcia et al., 42323; Antier et al., 42325; Sasada et al., 42329; Lipunov et al., 42330; Fu et al., 42331; Mo et al., 42336; Adami et al., 42339; Xin et al., 42341; Izzo et al., 42350; Shilling et al., 42355; Akl et al., 42368; Midavaine et al., 42370; Volnova et al., 42477) of the Swift GRB 251017A (Gupta et al., GCN 42322) in the R-filter with 1.5-meter AZT-33IK telescope of Sayan Solar Observatory (Mondy) on Oct. 17,18,23, 2025, and in the Rb filter with 1-meter Zeiss-1000 telescope of the Koshka Observatory (INASAN) on Oct. 20, 2025. Preliminary photometry and observation details are the following: Date UT start t-T0 Exp. Filter OT Err. UL Site/Instrum (mid,days) (n*s) (3sigma) 2025-10-17 11:25:01 0.14333 20*120 R 20.41 0.07 21.8 Mondy/AZT-33IK 2025-10-17 12:49:15 0.19065 26*120 R 20.88 0.07 22.3 Mondy/AZT-33IK 2025-10-18 11:40:09 1.14891 35*120 R 21.79 0.13 22.5 Mondy/AZT-33IK 2025-10-20 16:36:07 3.37307 40*180 R n/d n/d 21.1 Koshka/Zeiss-1000 2025-10-23 13:18:38 6.22425 45*120 R n/d n/d 22.5 Mondy/AZT-33IK The photometry is based on several nearby PS1 stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42479. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40562] GRB 251023B / EP251023b: Mondy optical upper limit
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42478 SUBJECT: GRB 251023B / EP251023b: Mondy optical upper limit DATE: 25/10/27 13:44:29 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), A. Pozanenko (IKI) , N. Pankov (HSE, IKI), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN: We observed the field of the GRB 251023B / EP251023b (Kang et al., GCN Circ. 42392; Nakahira et al., GCN Circ. 42402; Wu et al., GCN Circ. 42415; Cheung et al., GCN Circ. 42407) in the R-filter with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) starting Oct. 25, 2025, 17:50:36 UT, and taking several frames with 120 s exposures. The optical candidate reported by Mandarakas et al. (GCN Circ. 42404) is not detected in the stacked frame. Photometry and observational details are the following: Date UT start t-T0 Exp. Filter OT Err. UL (mid,days) (n*s) (3sigma) 2025-10-25 17:50:36 2.40386 40*120 R n/d n/d 22.7 The photometry is based on several nearby SDSS stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42478. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40561] GRB 251017A: INASAN-Kislovodsk optical observations
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42477 SUBJECT: GRB 251017A: INASAN-Kislovodsk optical observations DATE: 25/10/27 13:36:52 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), A.N. Tarasenkov (INASAN), A. Pozanenko (IKI), N. Pankov (HSE) report on behalf of IKI GRB-FuN: We observed the field of the Swift GRB 251017A (Gupta et al., GCN 42322) with RC500 telescope of the INASAN-Kislovodsk observatory. We took several 120-seconds frames in the R-band starting Oct. 17, 2025, 15:09:15 (UT). In the stacked image the optical counterpart (Perez-Garcia et al., 42323; Antier et al., 42325; Sasada et al., 42329; Lipunov et al., 42330; Fu et al., 42331; Mo et al., 42336; Adami et al., 42339; Xin et al., 42341; Izzo et al., 42350; Shilling et al., 42355; Akl et al., 42368; Midavaine et al., 42370) is clearly detected. Preliminary photometry is the following: Date UT start t-T0 Exp. Filter OT Err. UL (mid,days) (n*s) (3sigma) 2025-10-17 15:09:15 0.34348 100*120 R 21.45 0.16 22.0 The photometry is based on several nearby PS1 stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42477. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40560] GRB 251026A: Mondy optical upper limit
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42476 SUBJECT: GRB 251026A: Mondy optical upper limit DATE: 25/10/27 13:34:08 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), A. Pozanenko (IKI) , N. Pankov (HSE, IKI), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN: We observed the field of GRB 251026A detected by SVOM/ECLAIRs (Cao et al., GCN 42454) in the R-filter with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) starting Oct. 26, 2025, 20:15:58 (UT) taking several frames with 120 s exposures. Inside the error box of the SVOM/MXT (Cao et al., GCN 42454) we did not detect any new uncatalogued source. Photometry and observational details are the following: Date UT start t-T0 Exp. Filter OT Err. UL (mid,days) (n*s) (3sigma) 2025-10-26 20:15:58 0.51293 30*120 R n/d n/d 22.4 The photometry is based on several nearby PS1 stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42476. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40559] GRB 251025B: Mondy optical observations
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42475 SUBJECT: GRB 251025B: Mondy optical observations DATE: 25/10/27 13:31:43 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), A. Pozanenko (IKI) , N. Pankov (HSE, IKI), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN: We observed the field of the GRB 251025B (Hussein et al., GCN 42437) in the R-filter with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) starting Oct. 26, 2025, 16:25:44 UT, and taking several frames with 120 s exposures. The optical counterpart (Wu et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440; Beardmore et al., GCN 42445; Mohan et al., GCN 42447; Hernández Funget al., GCN 42450; Pereyra et al., GCN 42452; Li et al., GCN 42453; Mo et al., GCN 42459; Rakotondrainibe et al., GCN 42460; Rajabov et al., 42466; Saccardi et al., 42472; Freeberg et al., 42474) is clearly detected in the stacked frame. Preliminary photometry is the following: Date UT start t-T0 Exp. Filter OT Err. UL (mid,days) (n*s) (3sigma) 2025-10-26 16:25:44 1.10532 60*120 R 20.50 0.05 23.1 The photometry is based on several nearby SDSS stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42475. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40558] GRB 251025B: Kilonova-Catcher optical afterglow detection
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42474 SUBJECT: GRB 251025B: Kilonova-Catcher optical afterglow detection DATE: 25/10/27 12:53:57 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> M. Freeberg, R. Hellot (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (OCA/IJCLab), M. Coughlin (UMN), S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 251025B detected by SVOM (Hussein et al., GCN 42437) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with a TEC160FL and a 0.43m Dall-Kirkham telescopes operated by M. Freeberg and a CDK17 telescope located at AITP San Pedro Chile Observatory operated by R. Hellot. Our observations started at TGRB+5.7hr and were taken with BRc and sdss ri filters. In our stacked frames, subtracted from the PanSTARRS DR2 template image, we detect the optical counterpart reported by SVOM/C-GFT (Wu et al., GCN 42438), MASTER (Gress et al., GCN 42439), SVOM/VT (Wu et al., GCN 42440), Swift/XRT (Beardmore et al., GCN 42445), GROWTH (Mohan et al., GCN 42447), IAC80 (Hernández Fung et al., GCN 42450), SVOM/COLIBRÍ (FM-GFT) (Pereyra et al., GCN 42452), WINTER (Mo et al., GCN 42459), OHP/T193 (Rakotondrainibe et al., GCN 42460), the MAO/AZT-22 (Rabajov et al., GCN 42466) and VLT/MUSE (Saccardi et al., GCN 42472). We report part of our follow-up results in the table below: +---------------+-----------+-----------+----------------+---------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+===========+===========+================+===============+ | 6.28 | 20 x 180s | B (Vega) | 20.58 +/- 0.16 | 0.43/DK | | 12.46 | 12 x 300s | r (AB) | 19.93 +/- 0.10 | CDK17 AITP | | 13.37 | 40 x 180s | r (AB) | 20.37 +/- 0.13 | TEC160FL | +---------------+-----------+-----------+----------------+---------------+ All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan filters were calibrated using the PanSTARRS DR1 catalog. Images obtained with the Johnson-cousins filters were calibrated using the GAIA DR3 synphot catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/) View this GCN Circular online at https://gcn.nasa.gov/circulars/42474. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40557] Konus-Wind detection of GRB 251016A (short/hard)
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42473 SUBJECT: Konus-Wind detection of GRB 251016A (short/hard) DATE: 25/10/27 12:47:24 GMT FROM: Valentina Panteleeva at Ioffe Institute <panteleevav228(a)gmail.com> V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The short-duration GRB 251016A (SVOM/ECLAIRs detection: Basa et al., GCN 42308; Brunet et al., GCN 42374; Fermi-GBM detection: The Fermi GBM team, GCN 42309; Smith and Meegan, GCN 42365; Glowbug detection: Woolf et al., GCN 42313; CALET-GBM detection: Kawakubo et al., GCN 42321; AstroSat-CZTI detection: Arya et al., GCN 42327; Insight-HXMT/HE detection: Zao et al., GCN 42359) triggered Konus-Wind at T0=53956.564 s UT (14:59:16.564). The burst light curve shows a single pulse which starts at ~T0-0.2 s and has a total duration of ~0.5 s. The emission is seen up to ~3 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB251016_T53956/ As observed by Konus-Wind, the burst had the total fluence of 6.32(-0.91,+1.04)x10^-6 erg/cm2, and the 16-ms peak flux, measured from T0+0.018 s, of 2.46(-0.52,+0.58)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+0.256 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.44(-0.20,+0.35), the high energy photon index beta = -2.14(-0.72,+0.34), the peak energy Ep = 825(-282,+293) keV (chi2 = 30/25 dof). 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/42473. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40556] GRB 251025B: VLT/MUSE spectroscopic redshift z = 2.003
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42472 SUBJECT: GRB 251025B: VLT/MUSE spectroscopic redshift z = 2.003 DATE: 25/10/27 11:30:46 GMT FROM: Andrea Saccardi at CEA/Irfu <andrea.saccardi(a)cea.fr> A. Saccardi (CEA/Irfu), L. Izzo (INAF/OACn & DARK/NBI), P. Schady (University of Bath), D. B. Malesani (DAWN/NBI and Radboud), J. An (NAOC), A. A. Chrimes (ESA/ESTEC & Radboud Univ.), G. Corcoran (UCD), A. Martin-Carrillo (UCD), B. Schneider (LAM), N. R. Tanvir (U. Leicester), S. D. Vergani (LUX-Paris Obs.), report on behalf of the Stargate collaboration: We observed the field of the SVOM/ECLAIRs GRB 251025B (Hussein et al., GCN 42437), using the ESO VLT UT4 (Yepun) equipped with the MUSE spectrograph. Our observation started at 03:27:23 UT on 2025 October 27 (1.54 days after the GRB trigger), and consisted of 4 exposures of 700 s each. The optical counterpart (Wu et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440; Mohan et al., GCN 42447; Hernández Fung et al., GCN 42450; Pereyra et al., GCN 42452; Li et al., GCN 42453; Mo et al., GCN 42459; Rakotondrainibe et al., GCN 42460; Rajabov et al., GCN 42466) is well detected in the wavelength-stacked “white light” image. The afterglow has a synthetic magnitude Rc = 21.22 +/- 0.04 (AB). Our spectra cover the wavelength range 4750 - 9330 AA. In a preliminary reduction, we detect a continuum over the entire covered wavelength range. From the detection of several absorption features that we identify as due to Al II, Al III, Fe II, Mg II, and Mg I, we infer a common redshift of z = 2.003 for the GRB. Additionally, we note the presence of an intervening absorber at z = 0.73 with Mg II (and likely Mg I) absorption lines. As first noted by Pereyra et al. (GCN 42452), an archival object is visible in the Legacy Survey underlying the optical afterglow (g = 24.02 +/- 0.15; r = 23.32 +/- 0.21; z = 22.18 +/- 0.16). If this is the GRB host, at z = 2.0 it would have an absolute magnitude of M(2000 Å) ~ -21.6 AB. We acknowledge expert support from the observing staff in Paranal. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) View this GCN Circular online at https://gcn.nasa.gov/circulars/42472. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40555] GRB 251027A: SVOM detection of a faint burst
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42471 SUBJECT: GRB 251027A: SVOM detection of a faint burst DATE: 25/10/27 10:41:32 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y. H.Cheng (YNU), Y. F. Liang (PMO), O. Godet, S. Guillot (IRAP), S. Schanne (CEA), L. Zhang (IHEP) At 2025-10-27T09:38:17 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251027A (SVOM burst-id sb25102702). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Count-Rate Trigger (CRT), which produced a sequence of 1 alert. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.33 in the [5-20] keV energy band over a time window of 20.40 seconds starting at 2025-10-27T09:37:56. The localization of the best alert is R.A., Dec. 95.1860, 11.6869 degrees: R.A. (J2000) = 6h20m44.64s Dec. (J2000) = 11d41m12.73s with a 90% confidence level (C.L.) radius of 9.46 arcmin (including systematic error of 2 arcmin added in quadrature). The GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251027A.png Due to the ECLAIRs detection significance being below the slew threshold, no immediate slew was performed on this burst. But follow-up observations with SVOM/MXT and SVOM/VT have been requested. 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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Yehao Cheng: yhcheng(a)mail.ynu.edu.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/42471. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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