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

[vsnet-grb-info 39426] GRB 250813A: AstroSat CZTI detection
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41365 SUBJECT: GRB 250813A: AstroSat CZTI detection DATE: 25/08/14 10:31:51 GMT FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in> M. Tembhurnikar (IUCAA), G. Waratkar (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 a GRB 250813A which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 41343). The source was faintly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-08-13 01:46:01.50 UTC. The measured peak count rate associated with the burst is 72 (+35, -16) counts/s above the background in the combined data of all quadrants, with a total of 485 (+199, -228) counts. The local mean background count rate was 249 (+5, -6) counts/s. Using cumulative rates, we measure a T90 of 12 (+1, -6) s. The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-08-13 01:46:00.12 UTC. The measured peak count rate associated with the burst is 117 (+70, -10) counts/s above the background in the combined data of all quadrants, with a total of 1002 (+403, -457) counts. The local mean background count rate was 1144 (+8, -8) counts/s. We measure a T90 of 13 (+2, -4) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/41365. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39425] LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41364 SUBJECT: LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT DATE: 25/08/14 10:31:50 GMT FROM: Sreeta Roy at University of Warsaw <sreeta.roy(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration with the Fermi GBM team and Swift team report: We identified the compact binary merger candidate S250814bg during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-08-14 07:35:05.587 UTC (GPS time: 1439192123.587). The candidate was found by the GstLAL [1] analysis pipeline. Based on the analysis of gravitational-wave data alone, this candidate does not meet our criteria for a high-significance public alert as its false alarm rate is estimated by the online analysis to be 0.00012 Hz or about one in 2 hours. However, a search performed by the RAVEN pipeline found a significant coincidence between this candidate and Fermi GBM trigger with ID 776849714, which is associated with GRB 250814A. The event’s properties can be found at this URL: https://gracedb.ligo.org/superevents/S250814bg The classification of the GW signal, in order of descending probability, is Terrestrial (>99%), BBH (<1%), NSBH (<1%), or BNS (<1%). Excess noise was present in the L1 detector at the time of this candidate, which may affect the parameters or the significance of the candidate. 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%. [2] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [2] 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 3%. 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 GW-only 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 [3], distributed via GCN and SCiMMA notices about 2 minutes after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [3], distributed via GCN and SCiMMA notices about 6 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 7867 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 13504 +/- 6537 Mpc (a posteriori mean +/- standard deviation). A search performed by the RAVEN pipeline [4] found a temporal coincidence between S250814bg and a Fermi GBM trigger with ID 776849714, which is associated with GRB 250814A (Fermi GBM Team, GCN Circular 41357). The GRB trigger time is 3.7 seconds after the GW candidate event. The estimated joint false alarm rate for the coincidence using just timing info before trials are applied is 7.5e-09 Hz, or about one in 4 years. Combined sky maps are also available: * combined-ext.multiorder.fits,0, an initial localization, distributed via GCN and SCiMMA notices about 2 minutes after the candidate event time. * combined-ext.multiorder.fits,1, an initial localization, distributed via GCN and SCiMMA notices about 6 minutes after the candidate event time. * combined-ext.multiorder.fits,2, an initial localization, distributed via GCN and SCiMMA notices about an hour after the candidate event time. For the combined-ext.multiorder.fits,2 sky map, the 90% credible region is 471 deg2. Considering the overlap of the individual sky maps, the estimated joint false alarm rate for the spatial and temporal coincidence before trials are applied is 1.5e-08 Hz, or about one in 2 years. After including the trials factor of 30, the joint false alarm rate becomes 4.5e-07 Hz, or about 14 per year. Moreover, the GW candidate is 6 seconds after the Swift-BAT trigger 1342439, associated with the same GRB 250814A (Swift Team, GCN Circular 41358). The Swift-BAT GRB is spatio-temporal coincident with the Fermi GBM one, therefore they can be reliably considered the same astrophysical event. Considering the Swift-BAT localization, the estimated joint false alarm rate between the Swift-BAT and the GW candidate for the spatial and temporal coincidence before trials are applied is 1.0e-08 Hz, or about one in 3 years. After including the trials factor of 30, the joint false alarm rate becomes 3.0e-07 Hz, or about 9 per year. 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] 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 [2] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [3] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 [4] Urban, A. L. 2016, Ph.D. Thesis https://dc.uwm.edu/etd/1218 and Piotrzkowski, B. J. 2022, Ph.D. Thesis https://dc.uwm.edu/etd/3060 View this GCN Circular online at https://gcn.nasa.gov/circulars/41364. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39424] GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41363 SUBJECT: GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752 DATE: 25/08/14 10:29:14 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> B. Schneider (LAM), G. Corcoran (UCD), E. Le Floc’h (CEA), A. de Ugarte Postigo (LAM), J. An (NAOC), A. L. Thakur (INAF-IAPS), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), N. R. Tanvir (U. Leicester) report on behalf of the Stargate collaboration: We observed the optical afterglow (Jelinek et al., GCN 41355; de Ugarte Postigo et al., GCN 41356) of GRB 250813B detected by SVOM/ECLAIRs (Xie et al., GCN 41352; Xie et al., GCN 42354) with ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. In images taken with the acquisition camera on Aug 14 05:40 UT (6.82 hr after the ECLAIRs trigger), the optical afterglow is clearly detected in g, r, and z bands. We measured a preliminary magnitude r = 22.24 +/- 0.06 AB (calibrated against the Pan-STARRS PS1 catalog). Our spectra cover the wavelength range 3000-21000 AA, and consist of 4 exposures of 600 s each. Observations started on 2025-08-14 at approximately 05:50 UT (6.98 hr after the SVOM trigger). In a preliminary reduction of the spectra, we detect a faint continuum down to ~3590 AA at the blue end. From the detection of a multitude of absorption lines, which we interpret as due to C II, Si IV, Si II, C IV, C I, Al II, Al III, Mn I, Fe II, Fe II*, Mn II, Mg II, Mg I, Ca II, we infer a redshift of z = 1.752. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Celia Desgrange, Rodrigo Romero, and Akke Corporaal. 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/41363. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39423] GRB 250814A: DDOTI Optical Upper Limit
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41362 SUBJECT: GRB 250814A: DDOTI Optical Upper Limit DATE: 25/08/14 10:26:15 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Sahil Atri (U Roma), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observed the field of GRB 250814A detected by Swift/BAT (Caputo et al., GCN Circ. 41358) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-08-14 UTC. DDOTI observed the XRT position (Caputo et al., GCN Circ. 41358) from 08:50 UTC to 09:18 UTC (from T+ 1.3 h to T+ 1.7 h after the trigger) and obtained a total exposure of 24 minutes. Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect no uncatalogued fading sources within the observed field down to a 3-sigma limiting AB magnitude of: w > 19.6 This value is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41362. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39422] GRB 250813B: EP-FXT counterpart detection
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41361 SUBJECT: GRB 250813B: EP-FXT counterpart detection DATE: 25/08/14 09:01:39 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. Y. Wu, H. Q. Cheng, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 250813B (SVOM/sb25081303, Xie et al. GCN #41352, #41354) at 2025-08-14 00:58:26(UTC), about 2 hours after the SVOM/ECLAIRs trigger, with an exposure time of ~1.3 ks. One uncatalogued source is detected within the ECLAIRs error circle, and the source is spatially consistent with the counterpart reported in optical and X-ray bands (Xie et al. GCN #41352, #41354, Jelinek et al. GCN #41353, #41355, Gill et al. GCN #41356, Page et al. GCN #41359). Preliminary analysis on this source are conducted (note that the exposure time for the analysed data is not complete), with the details listed as follows. Source 1: EPF_J222700.2+122741 RA (J2000): 336.7507 Dec (J2000): 12.4617 Flux: 1.00 x 10^-11 erg/s/cm2 (observed, 0.5-10 kev) Flux_err: 1.2 x 10^-12 erg/s/cm2 (90% C. L.) The position uncertainty of the source is about 10 arcsec in radius (90% C.L. statistical and systematic). 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/41361. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39421] Fermi-LAT Gamma-ray Observations of IceCube-250813A
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41360 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-250813A DATE: 25/08/14 08:20:05 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg), S. Garrappa (Weizmann Institute of Science) and C. Bartolini (INFN Bari) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC250813A neutrino event (GCN 41338) 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 2025-08-13 at 03:21:09.69 UTC (T0) with J2000 position RA = 275.36 (+0.84, -0.94) deg, Decl. = 8.27 (+0.79, -0.75) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC250813A 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 IC250813A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250813A best-fit position, the >100 MeV flux upper limit (95% confidence) is <9.3e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <1.3e-08 (<2.2e-07) 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/41360. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39420] GRB 250813B: Swift-XRT afterglow detection
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41359 SUBJECT: GRB 250813B: Swift-XRT afterglow detection DATE: 25/08/14 08:09:11 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K.L. Page, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: We have analysed 1.6 ks of XRT data for GRB 250813B, from 9.6 to 16.3 ks after the SVOM/ECLAIRs trigger (GCN Circ. 41354). The data are entirely in Photon Counting (PC) mode. We find an uncatalogued X-ray source at RA, Dec = 336.7505, +12.4613 which is equivalent to: RA (J2000): 22 27 00.13 Dec(J2000): +12 27 40.5 with an uncertainty of 3.7 arcsec (radius, 90% confidence). There is no evidence for fading during this interval, with the X-ray source showing a mean count rate of 0.17 +/- 0.02 count s^-1. However, the localisation of this source is consistent with the fading optical afterglow found by Ondrejov D50 (GCN Circ. 41353, 41355) and SVOM/COLIBRI (GCN Circ. 41356), and so we consider it the X-ray afterglow. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.1 (+0.4, -0.3). The best-fitting absorption column is 2.5 (+1.3, -1.1) × 10^21 cm^-2, in excess of the Galactic value of 6.2 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 6.2 x 10^-12 (9.3 x 10^-12) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.5 (+1.3, -1.1) x 10^21 cm^-2 Galactic foreground: 6.2 x 10^20 cm^-2 Photon index: 2.1 (+0.4, -0.3) This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41359. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39419] GRB 250813B: Swift-XRT afterglow detection
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41359 SUBJECT: GRB 250813B: Swift-XRT afterglow detection DATE: 25/08/14 08:09:11 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K.L. Page, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: We have analysed 1.6 ks of XRT data for GRB 250813B, from 9.6 to 16.3 ks after the SVOM/ECLAIRs trigger (GCN Circ. 41354). The data are entirely in Photon Counting (PC) mode. We find an uncatalogued X-ray source at RA, Dec = 336.7505, +12.4613 which is equivalent to: RA (J2000): 22 27 00.13 Dec(J2000): +12 27 40.5 with an uncertainty of 3.7 arcsec (radius, 90% confidence). There is no evidence for fading during this interval, with the X-ray source showing a mean count rate of 0.17 +/- 0.02 count s^-1. However, the localisation of this source is consistent with the fading optical afterglow found by Ondrejov D50 (GCN Circ. 41353, 41355) and SVOM/COLIBRI (GCN Circ. 41356), and so we consider it the X-ray afterglow. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.1 (+0.4, -0.3). The best-fitting absorption column is 2.5 (+1.3, -1.1) × 10^21 cm^-2, in excess of the Galactic value of 6.2 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 6.2 x 10^-12 (9.3 x 10^-12) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.5 (+1.3, -1.1) x 10^21 cm^-2 Galactic foreground: 6.2 x 10^20 cm^-2 Photon index: 2.1 (+0.4, -0.3) This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41359. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39418] GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41358 SUBJECT: GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger DATE: 25/08/14 07:58:28 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> R. Caputo (GSFC), A. P. Beardmore (U Leicester), P. A. Evans (U Leicester), R. A. J. Eyles-Ferris (U Leicester), C. Gronwall (PSU), A. Y. Lien (U Tampa) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team: At 07:34:59 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250814A (trigger=1342439). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 306.329, +48.391 which is RA(J2000) = 20h 25m 19s Dec(J2000) = +48d 23' 27" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure structure with a duration of about 20 sec. The peak at ~T+26 s in the 15-25 keV band raw light curve is likely due to detector noise, though further ground data is required to confirm this. The peak count rate was ~500 counts/sec (15-350 keV), at ~10 sec after the trigger. The XRT began observing the field at 07:37:54.1 UT, 174.3 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source with an enhanced position: RA, Dec 306.30802, 48.39903 which is equivalent to: RA(J2000) = 20h 25m 13.92s Dec(J2000) = +48d 23' 56.5" with an uncertainty of 2.2 arcseconds (radius, 90% containment). This location is 57 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 6.51 x 10^21 cm^-2 (Willingale et al. 2013). The initial flux in the 2.5 s image was 7.47e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 250 seconds with the U filter starting 179 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.2 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18.0 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 1.066. This GRB is temporally and spatially coincident with the subthreshold GW trigger S250814bg which occurred 6 s after the BAT trigger. The XRT position is towards the edge of the GW localisation. Given the low significance of the GW event (a false alarm rate of ~10/day) this is probably a chance coincidence; however, follow up of this GRB is advised. Burst Advocate for this burst is R. Caputo (regina.caputo AT nasa.gov). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/41358. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39417] GRB 250814A: Fermi GBM Final Real-time Localization
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41357 SUBJECT: GRB 250814A: Fermi GBM Final Real-time Localization DATE: 25/08/14 07:45:48 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 07:35:09 UT on 14 Aug 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250814A (trigger 776849714.277078 / 250814316). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 298.0, Dec = 47.5 (J2000 degrees, equivalent to J2000 19h 52m, 47d 30'), with a statistical uncertainty of 8.6 degrees. The angle from the Fermi LAT boresight is 30.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250814316/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250814316/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250814316/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41357. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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