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

[vsnet-grb-info 39379] GRB 250809A: Swift-BAT refined analysis
by GCN Circulars 11 Aug '25

11 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41321 SUBJECT: GRB 250809A: Swift-BAT refined analysis DATE: 25/08/11 18:09:12 GMT FROM: D. R. Sadaula at NASA GSFC <dev.r.sadaula(a)nasa.gov> D. Sadaula (GSFC/UMBC), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250809A (trigger #1340954) (Parsotan, et al., GCN Circ. 41303). The BAT ground-calculated position is RA, Dec = 233.034, -53.314 deg which is RA(J2000) = 15h 32m 08.2s Dec(J2000) = -53d 18' 50.6" with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 96%. The BAT light curve showed a complex structure with a duration of about 32 sec. T90 (15-350 keV) is 17.79 +- 2.77 sec (estimated error including systematics). The time-averaged spectrum from T+1.01 to T+20.94 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.83 +- 0.20. The fluence in the 15-150 keV band is 3.9 +- 0.5 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+11.58 sec in the 15-150 keV band is 0.6 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1340954 View this GCN Circular online at https://gcn.nasa.gov/circulars/41321. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39378] Fermi Gamma-ray Burst Monitor trigger 776620220/250811660 is not a GRB
by GCN Circulars 11 Aug '25

11 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41320 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 776620220/250811660 is not a GRB DATE: 25/08/11 17:10:25 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118(a)uah.edu> Jacob Smith (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: The Fermi Gamma-ray Burst Monitor (GBM) trigger 776620220/250811660 at 15:50:15.05 UT on 11 August 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to local particles. View this GCN Circular online at https://gcn.nasa.gov/circulars/41320. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39377] GRB 250309B: 1.3m DFOT Optical observations
by GCN Circulars 11 Aug '25

11 Aug '25

TITLE: GCN CIRCULAR NUMBER: 39679 SUBJECT: GRB 250309B: 1.3m DFOT Optical observations DATE: 25/03/12 06:18:47 GMT FROM: Amit Kumar Ror at ARIES <mitturor77894(a)gmail.com> Amit K. Ror, Anshika Gupta, Pranshu, Shashi B. Pandey, Kuntal Mishra (ARIES) report: We observed the field of GRB 230509B detected by the Swift and Fermi (Evans et al. 2025, GCN 39633; Fermi GBM team, GCN 39635, 39642) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2025-03-10 at 20:25:19 UT, i.e., ~ 1.53 days after the Ferm-GBM trigger. We have taken multiple frames with an exposure time of 300s in the R filter. We stacked the images after the alignment. We detected an optical afterglow reported by Stein et al. 2025 (GCN 39639) in our stacked image. We obtain the following preliminary magnitude in the stacked image: Date Start_UT T_start-T0 (days) Filter Exp time (s) Magnitude ========================================================= 2025-03-10 20:25:19 ~1.53 R 300s*24 20.36 +/- 0.10 Our detection is consistent with Stein et al. 2025 (GCN 39639); Lipunov et al. 2025 (GCN 39641); Pérez-Fournon et al. 2025 (GCN 39643); Stein et al. 2025 (GCN 39644); Moskvitin et al. 2025 (GCN 39645); Perley et al. 2025 (GCN 39646); Malesani et al. 2025 (GCN 39647); Ducoin et al. 2025 (GCN 39650); Shin et al. 2025 (GCN 39654); Moskvitin et al. 2025 (GCN 39658); Wang et al. 2025 (GCN 39661) and Guiffreda et al. 2025 (GCN 39670). 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 catalogue. This circular may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/39679. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39376] Fermi-LAT Gamma-ray Observations of IceCube-250804A
by GCN Circulars 11 Aug '25

11 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41319 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-250804A DATE: 25/08/11 15:13:15 GMT FROM: Simone Garrappa at Weizmann Institute of Science <simone.garrappa(a)weizmann.ac.il> S. Garrappa (Weizmann Institute of Science), L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) 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 IC250804A neutrino event (GCN 41235) 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 2025-08-04 at 20:16:26.65 UTC (T0) with J2000 position RA = 79.50 (+0.51, -0.52) deg, Decl. = 16.65 (+0.49, -0.45) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC250804A 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 IC250804A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250804A best-fit position, the >100 MeV flux upper limit (95% confidence) is <1.2e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <4.0e-08 (<2.5e-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 source, the Fermi-LAT contact person is S. Garrappa (simone.garrappa at weizmann.ac.il). 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/41319. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39375] GRB 250807B: Swift-BAT refined analysis
by GCN Circulars 11 Aug '25

11 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41318 SUBJECT: GRB 250807B: Swift-BAT refined analysis DATE: 25/08/11 14:04:39 GMT FROM: Mike Moss at NASA GSFC <mikejmoss3(a)gmail.com> R. Gupta (GSFC), S. D. Barthelmy (GSFC), N. J. Klingler (GSFC/UMBC/CRESSTII), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+520 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250807A (trigger #1340514) (Klingler, et al., GCN Circ. 41262). The BAT ground-calculated position is RA, Dec = 51.435, -47.882 deg which is RA(J2000) = 03h 25m 44.4s Dec(J2000) = -47d 52' 54.4" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 72%. The mask-weighted light curve displays a complex structure with several pulses. T90 (15-350 keV) is 75.46 +- 2.19 sec (estimated error including systematics). The time-averaged spectrum from T-20.35 to T+119.49 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.32 +- 0.03. The fluence in the 15-150 keV band is 2.5 +- 0.0 x 10^-05 erg/cm2. The 1-sec peak photon flux measured from T+33.82 sec in the 15-150 keV band is 16.7 +- 0.5 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1340514 View this GCN Circular online at https://gcn.nasa.gov/circulars/41318. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39374] LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
by GCN Circulars 11 Aug '25

11 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41317 SUBJECT: LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification DATE: 25/08/11 08:16:05 GMT FROM: Soichiro Morisaki at U. of Tokyo <soichiro.morisaki(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1) and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250810ck (GCN Circular 41315). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S250810ck Based on posterior support from parameter estimation [1], under the assumption that the candidate S250810ck is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass above one solar 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] HasRemnant is assumed to be zero when the heavier component mass is below 1 solar mass. 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 probability that the lighter compact object is below 1 solar mass (HasSSM) is <1%. The source chirp mass falls with highest probability in the bin (5.5, 11.0) solar masses after parameter estimation [1], assuming the candidate is astrophysical in origin. For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 180 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 621 +/- 129 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] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040 [2] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe View this GCN Circular online at https://gcn.nasa.gov/circulars/41317. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39373] GRB 250809A: Swift/UVOT Detection
by GCN Circulars 10 Aug '25

10 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41316 SUBJECT: GRB 250809A: Swift/UVOT Detection DATE: 25/08/10 16:51:32 GMT FROM: Paul Kuin at MSSL <npkuin(a)gmail.com> N.P.M. Kuin (UCL/MSSL) and T. M. Parsotan (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250809A 128 s after the BAT trigger (Parsotan et al., GCN Circ. 41303). A source consistent with the XRT position ( Evans et al. GCN Circ. 41304 ) is detected in the initial UVOT exposures. Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag v 435 755 58 17.62 +/- 0.21 b 384 1038 97 18.86 +/- 0.19 u 128 1013 452 19.57 +/- 0.21 w1 484 805 58 >18.4 m2 459 780 58 >20.1 w2 410 1064 78 >18.8 The earliest exposures were fainter; these detections are near the peak of the light curve. The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 1.919 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41316. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39372] LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate
by GCN Circulars 10 Aug '25

10 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41315 SUBJECT: LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate DATE: 25/08/10 14:58:38 GMT FROM: Anna Moreso Serra at ICCUB <anna.moreso-serra(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250810ck during real-time processing of data from LIGO Hanford Observatory (H1) and Virgo Observatory (V1) at 2025-08-10 14:23:57.336 UTC (GPS time: 1438871055.336). The candidate was found by the GstLAL [1] analysis pipeline. S250810ck is an event of interest because its false alarm rate, as estimated by the online analysis, is 5.4e-20 Hz, or about one in 1e12 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250810ck The classification of the GW signal, in order of descending probability, is BBH (>99%), NSBH (<1%), Terrestrial (<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%. [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 9%. The source chirp mass falls with highest probability in the bin (5.5, 11.0) 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 [3], distributed via GCN and SCiMMA notices about 25 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [3], 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 3454 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 628 +/- 164 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] 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 View this GCN Circular online at https://gcn.nasa.gov/circulars/41315. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39371] Corrected Swift-XRT Refined Analysis of GRB 250809A
by GCN Circulars 10 Aug '25

10 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41314 SUBJECT: Corrected Swift-XRT Refined Analysis of GRB 250809A DATE: 25/08/10 10:35:32 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K.L. Page (U. Leicester) reports on behalf of the Swift-XRT team: GCN Circ. 41313 provided an incomplete automatic modelling of the XRT light-curve of GRB 250809A. The first snapshot of data is dominated by a large flare, peaking at 240 s after the BAT trigger. The underlying decay can be modelled as a power-law with alpha = 3.0 +/- 0.2. If the light curve continues to decay with a power-law decay index of 3.0, the count rate at T+24 hours will be 2.3 x 10^-8 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.3 x 10^-20 (1.5 x 10^-19) erg cm^-2 s^-1. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41314. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39370] GRB 250809A: Swift-XRT refined Analysis
by GCN Circulars 10 Aug '25

10 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41313 SUBJECT: GRB 250809A: Swift-XRT refined Analysis DATE: 25/08/10 09:44:16 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), A. Melandri (INAF-OAR), M.A. Williams (PSU), S. Dichiara (PSU), J.A. Kennea (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 6.7 ks of XRT data for GRB 250809A, from 113 s to 51.4 ks after the trigger. The data comprise 910 s in Windowed Timing (WT) mode (the first 8 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The best available XRT position (using the promptly downlinked event data, the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue) is RA, Dec = 233.00043, -53.29626 which is equivalent to: RA (J2000): 01h 00m 00.00s Dec(J2000): -53d 00' 00.0" with an uncertainty of 3.0 arcsec (radius, 90% confidence). The light curve can be modelled with an initial rise, with a power-law index of alpha=-1.5 (NaN, NaN), followed by a break at T+281 s to an alpha of 8.0 (NaN, NaN). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.41 (+/-0.13). The best-fitting absorption column is 2.05 (+0.18, -0.17) x 10^22 cm^-2, in excess of the Galactic value of 8.0 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.9 x 10^-11 (1.6 x 10^-10) erg cm^-2 count^-1. A summary of the WT-mode spectrum is thus: Total column: 2.05 (+0.18, -0.17) x 10^22 cm^-2 Galactic foreground: 8.0 x 10^21 cm^-2 Excess significance: 11.9 sigma Photon index: 2.41 (+/-0.13) If the light curve continues to decay with a power-law decay index of 2.96, the count rate at T+24 hours will be 3.7 x 10^-8 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.8 x 10^-18 (6.1 x 10^-18) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01340954. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41313. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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