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[vsnet-grb-info 40656] GRB 251105C: Fermi GBM Final Localization Correction
by GCN Circulars 05 Nov '25

05 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42595 SUBJECT: GRB 251105C: Fermi GBM Final Localization Correction DATE: 25/11/05 21:49:53 GMT FROM: Angus Jameson <abj0023(a)uah.edu> The Fermi GBM team reports the detection of a likely LONG GRB "At 18:45:56.05 UT on 05 November 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251105C (trigger 784061161/251105782). This trigger was initially classified as Below horizon by the flight software, but is in fact a GRB. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 212.18, Dec = 37.29 (J2000 degrees, equivalent to J2000 14h 8m, +37d 17'), with a statistical uncertainty of 11.28 degrees. The angle from the Fermi LAT boresight is 68 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251105782/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251105782/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251105782/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/42595. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40655] GRB 251105C: Fermi GBM Final Localization Correction
by GCN Circulars 05 Nov '25

05 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42595 SUBJECT: GRB 251105C: Fermi GBM Final Localization Correction DATE: 25/11/05 21:49:53 GMT FROM: Angus Jameson <abj0023(a)uah.edu> The Fermi GBM team reports the detection of a likely LONG GRB "At 18:45:56.05 UT on 05 November 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251105C (trigger 784061161/251105782). This trigger was initially classified as Below horizon by the flight software, but is in fact a GRB. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 212.18, Dec = 37.29 (J2000 degrees, equivalent to J2000 14h 8m, +37d 17'), with a statistical uncertainty of 11.28 degrees. The angle from the Fermi LAT boresight is 68 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251105782/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251105782/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251105782/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/42595. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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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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