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

[vsnet-grb-info 39240] GRB 250727A: AST3-2 Upper limit
by GCN Circulars 28 Jul '25

28 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41184 SUBJECT: GRB 250727A: AST3-2 Upper limit DATE: 25/07/28 10:02:21 GMT FROM: Tianrui Sun at Purple Mountain Obs,CAS <trsun(a)pmo.ac.cn> Tian-Rui Sun, Yan-Long Hua (Purple Mountain Observatory, CAS), Kun Ma, Jiali Chen, Kai-wen Zheng, Yi-Qiao Yang, Xiao-Yan Li(Nanjing Institute of Astronomical Optics & Technology, CAS), Jin-Jun Geng, Wenlong Zhang, Xue-Feng Wu (Purple Mountain Observatory, CAS), report on behalf of the AST3 Team: Following the detection of GRB 250727A by ECLAIRs onboard SVOM (Cao et al., GCN 41176), we carried out follow-up observations using the Antarctic Survey Telescope AST3-2 located at Dome A, Antarctica (Lat. −80.4173°, Long. 77.0950°). Observations began at 2025-07-27T11:09:43.449 UT. No significant optical counterpart was detected within the ECLAIRs error circle (~9 arcmin radius), compared to the Gaia DR2 catalog. The stacked image (71 × 30 s exposures) in the i-band reached a 5σ limiting magnitude of ~18.9. This non-detection is consistent with the non-detection reported by SVOM/VT (Li et al., GCN 41181). Photometric calibration was performed using the ATLAS Reference Catalog (Tonry et al. 2018). We thank Prof. Michael Ashley (UNSW) for his continuous support in the operation of AST3-2. View this GCN Circular online at https://gcn.nasa.gov/circulars/41184. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39239] LIGO/Virgo/KAGRA S250727cl: Updated Sky localization
by GCN Circulars 28 Jul '25

28 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41183 SUBJECT: LIGO/Virgo/KAGRA S250727cl: Updated Sky localization DATE: 25/07/28 09:51:17 GMT FROM: Elise Sänger at Max Planck Institute for Gravitational Physics (AEI Potsdam) <elise.sanger(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), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250727cl (GCN Circular 41178). 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/S250727cl For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 205 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2152 +/- 515 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 View this GCN Circular online at https://gcn.nasa.gov/circulars/41183. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39238] GRB 250727A: EP-FXT counterpart detection
by GCN Circulars 28 Jul '25

28 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41182 SUBJECT: GRB 250727A: EP-FXT counterpart detection DATE: 25/07/28 04:00:11 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.-H. I. Yin (NJU), R. D. Liang, 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 250727A (SVOM/sb25072701) (Cao et al. GCN 41176) at 2025-07-27T12:37:29 (UTC), about 1.7 hours after the SVOM/ECLAIRs trigger, with an exposure time of 4209s. Three uncatalogued sources are detected within the ECLAIRs error circle, among which Source 3 is spatially consistent with the candidate counterpart Source 1 (SWIFT J234539.1-811248) detected by Swift/XRT (Evans et al. GCN 41180). Preliminary analysis on these source are automatically conducted, and the details are listed as follows. Source 1: EPF_J234436.3-810410 RA (J2000): 356.1514 Dec (J2000): -81.0694 Flux: 4.96 x 10^-14 erg/s/cm^2 (observed, 0.5-10 keV) Flux_err: 2.00 x 10^-14 erg/s/cm^2 (1 sigma) Source 2: EPF_J234357.8-811244 RA (J2000): 355.9909 Dec (J2000): -81.2121 Flux: 6.82 x 10^-14 erg/s/cm^2 (observed, 0.5-10 keV) Flux_err: 2.18 x 10^-14 erg/s/cm^2 (1 sigma) Source 3: EPF_J234541.4-811245 RA (J2000): 356.4225 Dec (J2000): -81.2124 Flux: 1.36 x 10^-13 erg/s/cm^2 (observed, 0.5-10 keV) Flux_err: 3.44 x 10^-14 erg/s/cm^2 (1 sigma) Note: This source is spatially consistent with the candidate counterpart Source 1 (SWIFT J234539.1-811248) detected by Swift/XRT. The Source 2, and 3 are detected by both FXT-A and FXT-B, while Source 1 is detected only by FXT-A. The positional uncertainty of the sources are 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/41182. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39237] GRB250727A: SVOM/VT optical upper limit
by GCN Circulars 27 Jul '25

27 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41181 SUBJECT: GRB250727A: SVOM/VT optical upper limit DATE: 25/07/27 23:03:23 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, Y. L. Qiu, L. P. Xin, C. Wu, 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. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), J. X. Cao (GXU) report on behalf of the SVOM team. SVOM/VT performed ToO follow-up observations on the GRB 250727A (SVOM burst-id sb25072701, Cao et al., GCN 41176) in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The observation started on 2025-07-27T12:45:24 UT, about 1.82 hours after the SVOM T0 time. No uncatalogued sources are detected in single or stacked images at the position of the Swift/XRT (Evans et al., GCN 41180), compared to the Legacy survey. The 3 sigma upper limit magnitudes are derived as below: Mid_time | Band | Exposure Time | Upper limit (AB) 2.16 hour VT_B 36*70 sec 23.5 mag 2.16 hour VT_R 35*70 sec 23.4 mag Also no apparent variation is found for the catalogued sources that lie within the errorbox of the Swift/XRT source 2 (Evans et al., GCN 41180). 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/41181. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39236] GRB 250727A: Swift-XRT observations
by GCN Circulars 27 Jul '25

27 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41180 SUBJECT: GRB 250727A: Swift-XRT observations DATE: 25/07/27 21:03:14 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 250727A, collecting 1.6 ks of Photon Counting (PC) mode data between T0+2.2 ks and T0+8.3 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 J234539.1-811248): ================================== RA (J2000.0): 356.4132 = 23h 45m 39.17s Dec (J2000.0): -81.2136 = -81d 12' 49.0" Error: 4.9 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 7.7 arcmin from the SVOM/ECLAIRs position. Mean rate: 0.0155 +/- 0.0041 ct s^-1 Mean flux: (5.2 +/- 1.4)e-13 erg cm^-2 s^-1 Peak rate: 0.0155 +/- 0.0041 ct s^-1 Peak flux: (5.2 +/- 1.4)e-13 erg cm^-2 s^-1 ECF: 3.37e-11 erg cm^-2 ct^-1, assuming NH=9.71e+20 cm^-2, gamma=1.97; determined from a spectral fit. XMM UL: 4.6e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 29.9-sigma below this 3-sigma upper limit. There is no evidence for fading. Source 2 (SWIFT J234406.8-810315): ================================== RA (J2000.0): 356.0284 = 23h 44m 06.82s Dec (J2000.0): -81.0543 = -81d 03' 15.5" Error: 8.5 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 4.9 arcmin from the SVOM/ECLAIRs position. Mean rate: (5.2 [+2.6, -2.0])e-3 ct s^-1 Mean flux: (1.52 [+0.77, -0.59])e-13 erg cm^-2 s^-1 Peak rate: (5.2 [+2.6, -2.0])e-3 ct s^-1 Peak flux: (1.52 [+0.77, -0.59])e-13 erg cm^-2 s^-1 ECF: 2.93e-11 erg cm^-2 ct^-1, assuming NH=3.26e+22 cm^-2, gamma=4.66; determined from a spectral fit. XMM UL: 1.9e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 25.1-sigma below this 3-sigma upper limit. There is no evidence for fading. 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_FIELD00025. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41180. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39235] LIGO/Virgo/KAGRA S250727dc: Identification of a GW compact binary merger candidate
by GCN Circulars 27 Jul '25

27 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41179 SUBJECT: LIGO/Virgo/KAGRA S250727dc: Identification of a GW compact binary merger candidate DATE: 25/07/27 20:24:58 GMT FROM: aubrey_laity(a)uri.edu The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250727dc during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-07-27 20:01:48.457 UTC (GPS time: 1437681726.457). The candidate was found by the cWB BBH [1], GstLAL [2], MBTA [3], PyCBC Live [4], and SPIIR [5] analysis pipelines. S250727dc is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.1e-18 Hz, or about one in 1e10 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250727dc 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%. [6] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [6] 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 [7], distributed via GCN and SCiMMA notices about 24 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [7], 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 well fit by an ellipse with an area of 23 deg^2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis): icrs; ellipse(06h27m, -36d17m, 3.74d, 1.98d, 29.70d) Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1172 +/- 256 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] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018 [2] 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 [3] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [4] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [5] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [6] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [7] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/41179. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39234] LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
by GCN Circulars 27 Jul '25

27 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41178 SUBJECT: LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate DATE: 25/07/27 19:02:50 GMT FROM: aubrey_laity(a)uri.edu The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250727cl during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-07-27 18:03:29.655 UTC (GPS time: 1437674627.655). The candidate was found by the cWB [1], cWB BBH [2], GstLAL [3], MBTA [4], MLy [5], PyCBC Live [6], and SPIIR [7] analysis pipelines. S250727cl is an event of interest because its false alarm rate, as estimated by the online analysis, is 4e-20 Hz, or about one in 1e12 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250727cl The classification of the GW signal, in order of descending probability, is BBH (>99%), BNS (<1%), NSBH (<1%), or Terrestrial (<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 31 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 379 deg^2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1817 +/- 454 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] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004 [2] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018 [3] 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 [4] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [5] Skliris et al. PRD 110, 104034 (2024) doi:10.1103/PhysRevD.110.104034 [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/41178. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39233] LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
by GCN Circulars 27 Jul '25

27 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41177 SUBJECT: LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates DATE: 25/07/27 18:06:49 GMT FROM: xjh(a)andrew.cmu.edu Xander Hall (CMU), Lei Hu (CMU), Tomás Cabrera (CMU), Antonella Palmese (CMU), Igor Andreoni (UNC), Keerthi Kunnumkai (CMU), Brendan O’Connor (CMU), on behalf of the Gravitational Wave MultiMessenger Astronomy DECam Survey (GW-MMADS) team DECam observed the southern high probability area of the LVK gravitational wave candidate S250725j (GCN 41154) using the wide-field Dark Energy Camera (DECam) on the 4m Blanco telescope. Observations started at 2025-07-25 23:13:43 UTC (Prop ID: 2025A-227091; PI Soares-Santos) and covered the highest 90% probability region of the event (GCN 41168). We run the SFFT difference imaging (Hu et al. 2022) on the available images, filter out likely stars and moving objects, visually inspect the remaining transients, and remove transients showing SNR>5 detections predating the gravitational wave alert from ATLAS forced photometry. We reported on TNS new transients within the LVK 99% CI area, and we report here those matched to a NED galaxy (GCN 41165): | id | AT name | ra | dec | discovery_date (UT) | mag_g | mag_g_err | mag_g-mag_r | NED separation | | ------------------------ | ---------- | ---------- | ---------- | ----------------------- | ------ | ----- | ----- | ----- | | T202507251524174m373721 | AT 2025shz | 231.072434 | -37.622634 | 2025-07-25 23:29:54.630 | 22.63 | 0.06 | 0.37 | 17.0” | T202507251542117m350010* | AT 2025sib | 235.548892 | -35.002876 | 2025-07-25 23:15:43.009 | 22.5 | 0.1 | 0.7 | 2.1” | T202507251538092m361517 | AT 2025sia | 234.538140 | -36.254760 | 2025-07-25 23:19:38.393 | 21.74 | 0.03 | 1.06 | 1.1” \* - *We note that these transients may have tentative low SNR pre-detections from ATLAS forced photometry.* We note that AT 2025shz cannot be excluded as a variable star and that it shows an extremely quick rise in the rz filters between two observations in the same night with a rise of several mag/day. We also note that AT 2025sib, shows a gradual decline in the grz filters between two observations with an average decline of ~0.5 mag/day. Further analysis is underway. We thank the CTIO and NOIRLab staff for supporting these observations and the data calibration. View this GCN Circular online at https://gcn.nasa.gov/circulars/41177. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39232] GRB 250727A: SVOM detection of a burst
by GCN Circulars 27 Jul '25

27 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41176 SUBJECT: GRB 250727A: SVOM detection of a burst DATE: 25/07/27 11:55:37 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> J. X. Cao (GXU), W. J. Xie (NAOC), M. Brunet, J-L. Atteia (IRAP), M. G. Bernardini (INAF-OAB, LUPM), report on behalf of the SVOM mission team: At 2025-07-27T10:55:41 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250727A (SVOM burst-id sb25072701). 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 3 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.45 in the [8-50] keV energy band over a time window of 163.84 seconds starting at 2025-07-27T10:53:39. The localization of the best alert is R.A., Dec. 355.7990, -81.1275 degrees: R.A. (J2000) = 23h43m11.76s Dec. (J2000) = -81d07m39.00s with a 90% confidence level (C.L.) radius of 9.33 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve showed a featureless structure with a T90 duration in the [5-120] keV energy band of about 70 (-14, +16) s. This burst was also detected by SVOM/GRM with low significance. No immediate slew was performed on this burst. A SVOM ToO has 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 Jiaxin Cao: cjx(a)st.gxu.edu.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41176. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39231] LIGO/Virgo/KAGRA S250725l: Updated Sky localization
by GCN Circulars 27 Jul '25

27 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41175 SUBJECT: LIGO/Virgo/KAGRA S250725l: Updated Sky localization DATE: 25/07/27 11:06:08 GMT FROM: Lorenzo Pompili at Max Planck Institute for Gravitational Physics <lorenzo.pompili(a)aei.mpg.de> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250725l (GCN Circular 41155). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.offline0.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S250725l For the Bilby.offline0.multiorder.fits,0 sky map, the 90% credible region is 1532 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2567 +/- 766 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 View this GCN Circular online at https://gcn.nasa.gov/circulars/41175. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0