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

[vsnet-grb-info 39220] GRB 250725A: SVOM/GRM observation
by GCN Circulars 25 Jul '25

25 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41164 SUBJECT: GRB 250725A: SVOM/GRM observation DATE: 25/07/25 14:18:41 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 250725A (SVOM trigger reference: sb25072501) at 2025-07-25T01:51:36.300 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#41150), Swift/BAT (P. A. Evans et al., GCN#41152) and Fermi/LAT (A. Holzmann Airasca et al., GCN#41161). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse followed by a narrow spike with a T90 of 9.7 +/-0.3 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250725A.png In addition, the position of this burst, as determined by Swift/BAT (RA= 35.47808, DEC= -82.79131, GCN#41152), is located at about 78 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-2 to T0+12 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.61 +0.15/-0.16 and the cutoff energy, parameterized as Epeak, is 323 +73/-51 keV. The event fluence (10-1000 keV) in this time interval is (8.11 +0.88/-0.80)E-06 erg/cm^2. With the redshift z = 5.26 by VLT/FORS2 (A. L. Thakur et al., GCN#41160), the Eiso (from 1 keV to 10 MeV in rest frame) of this burst is (4.13 +0.58/-0.48)E53 erg. Thus GRB 250725A is more consistent with Type II GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/grb250725A_amati.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41164. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39219] GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.
by GCN Circulars 25 Jul '25

25 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41163 SUBJECT: GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB. DATE: 25/07/25 13:30:56 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.M.Lipunov (Lomonosov MSU, SAI, Moscow), E.Gorbovskoy, N.Tiurina, A.Kuznetsov, A.Sankovich, G.Antipov, P.Balanutsa, P. Rudominskaya, A.Chasovnikov, V.Topolev, K.Zhirkov, Ya.Kechin, V.Senik, D.Vlasenko (Lomonosov MSU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (OAFA), D.Buckley, (SAAO, South Africa) O.Gress, N.Budnev (ISU, Irkutsk), A.Sosnovskij (Crao RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), V.M.Pillet (The Instituto de Astrofisica de Canarias, Spain), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory, Mexico) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov,V.G. Kornilov, E.S. Gorbovskoy, N.V. Tyurina, A.S. Kuznetsov, "ASTRONOMICAL ROBOTIC NETWORKS and OPERATIVE MULTICHANNEL ASTROPHYSICS. Based on the example of the global MASTER network.", The Moscow State University Publishing House. In the series "Works of Outstanding Scientists of Moscow State University", http://www.pereplet.ru/lipunov/625.html#625) located in Argentina (Rudominskaya et al., GCN 41157) and in the South Africa, SAAO; Busckley et al., GCN 41151;) was pointed to the GRB250725A (Fermi GBM 41150, Swift GCN 41152). As we noted out the earlier (Rudominskaya et al., GCN 41157), the gamma-ray burst turned out to be a short GRB (Thakur et al., GCN 41160). Thus, we have images before, during and after GRB250725A. Now the processing of wide-field and polarized frames continues. See also optical observations by Li et al. GCN 41158; Perez-Garcia et al. GCN 41159. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/41163. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39218] GRB 250725A: Swift/UVOT Upper Limits
by GCN Circulars 25 Jul '25

25 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41162 SUBJECT: GRB 250725A: Swift/UVOT Upper Limits DATE: 25/07/25 12:27:21 GMT FROM: s.shilling(a)lancaster.ac.uk S. P. R. Shilling (Lancaster U.) and P. A. Evans (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250725A 880 s after the BAT trigger (Evans et al., GCN Circ. 41152). No optical afterglow consistent with the enhanced XRT position (Osborne et al., GCN Circ. 41153) 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 white_FC 880 1029 147 >21.0 white 880 2562 322 >21.2 v 1036 2439 175 >19.6 b 1134 2537 175 >20.1 u 1110 2340 156 >20.1 w1 1085 2488 175 >19.6 w2 1704 1898 39 >19.5 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.114 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41162. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39217] GRB 250725A: Fermi-LAT detection
by GCN Circulars 25 Jul '25

25 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41161 SUBJECT: GRB 250725A: Fermi-LAT detection DATE: 25/07/25 10:33:39 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> A. Holzmann Airasca (UniTrento and INFN Bari), F. Longo (University and INFN, Trieste), D. Depalo (Politecnico and INFN Bari) and R. Gupta (NASA/GSFC) report on behalf of the Fermi-LAT Collaboration: On July 25, 2025, Fermi-LAT detected high-energy emission from GRB 250725A, which was also detected by Fermi-GBM (trigger 775101099 / 250725077, GCN 41150), Swift-BAT (GCN 41152), Swift-XRT (GCN 41153), MASTER-OAFA (GCN 41157), SVOM/VT (GCN 41158), BOOTES-7 (GCN 41159) and VLT/FORS2 (GCN 41160). The best LAT on-ground location is found to be: RA, Dec = 34.6, -83.2 (J2000) with an error radius of 1.1 deg (90 % containment, statistical error only). This was 24 deg from the LAT boresight at the time of the GBM trigger (T0 = 01:51:34.81 UT). The data from the Fermi-LAT shows a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0 - 90 s after the GBM trigger is (1.26 ± 0.50) E-5 ph/cm2/s. The estimated photon index above 100 MeV is -2.07 ± 0.40. The highest-energy photon is a 1 GeV event which is observed ~ 15 seconds after the GBM trigger. The Fermi-LAT point of contact for this burst is Francesco Longo (francesco.longo(a)ts.infn.it). 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/41161. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39216] GRB 250725A: VLT/FORS2 spectroscopic redshift z = 5.26
by GCN Circulars 25 Jul '25

25 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41160 SUBJECT: GRB 250725A: VLT/FORS2 spectroscopic redshift z = 5.26 DATE: 25/07/25 10:24:26 GMT FROM: Nusrin Habeeb at University of Leicester <nh312(a)leicester.ac.uk> A. L. Thakur (INAF-IAPS), N. R. Tanvir (Univ. of Leicester), A. de Ugarte Postigo (LAM), A. Saccardi (CEA/Irfu), L. Izzo (INAF/OACn and DARK/NBI), A. Kumar (RHUL), S. D. Vergani (LUX-Paris Obs.) report on behalf of the Stargate collaboration: We observed the optical counterpart (Buckley et al. GCN 41151; Li et al. GCN 41158; Perez-Garcia et al. GCN 41159) of GRB 250725A (Fermi GBM Team, GCN 41150; Evans et al. GCN 41152) using the ESO/VLT UT1 (Antu) equipped with the FORS2 spectrograph. In a 60 s acquisition image obtained in I-band starting on 2025 July 25 at 07:44:31 UT (5.88 hrs after the burst), the afterglow is well detected with I(AB) = 20.5+/-0.1 mag, calibrated against nearby stars from the SkyMapper catalog. We obtained a single exposure of 1800 s using grism 300I+11 starting on 2025 July 25 at 08:04:47 UT (6.22 hrs after the burst). In a preliminary reduction of the spectrum, a trough due to Lyman-alpha is visible at 7610AA. From the detection of metals absorption features, which we interpret as due to O I and Si II, plus a tentative Si II* fine structure line, we infer a redshift of z = 5.26. At that same redshift we also detect an absorption feature consistent with Lyman-beta from the host galaxy, within the Lyman forest. We acknowledge the excellent support from the ESO observing staff in Paranal, in particular Carlos La Fuente and Lorena Faundez. View this GCN Circular online at https://gcn.nasa.gov/circulars/41160. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39215] GRB 250725A: BOOTES-7 early optical detection
by GCN Circulars 25 Jul '25

25 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41159 SUBJECT: GRB 250725A: BOOTES-7 early optical detection DATE: 25/07/25 10:03:36 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Perez-Garcia, E. Fernandez-Garcia, S.-Y. Wu, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar (Univ. of Malaga), L. Hernandez-Garcia (Univ. of Valparaiso), M. Gritsevich (Univ. of Helsinki), Y.-D. Hu (GXU), B.-B. Zhang (Nanjing Univ.), and A. Maury (Space Obs., San Pedro de Atacama), on behalf of a larger collaboration, report: Following the detection of GRB 250725A by Swift, the 0.6m BOOTES-7 robotic telescope at Space Observatory (San Pedro de Atacama, Chile) automatically responded to this high-energy event starting on July 25, 01:52:17 UT (i.e. 41 sec after detection). Series of images in clear filter were gathered and we detect an optical source consistent with the one reported by Buckley et al. (GCN 41151) and Li et al. (GCN 41158). Using GaiaDR3 Gmag as a reference, we measure an initial magnitude of 15.5 +/- 0.1 in the first 10 sec exposure image. In subsequent stacked images of 1 sec images we do not detect any source up to mag 15.7, mid exposure time on July 25, 01:53:27. Further analysis of the additional images is ongoing. We would like to thank the staff at San Pedro de Atacama Space Observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/41159. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39214] GRB 250725A: SVOM/VT optical candidate
by GCN Circulars 25 Jul '25

25 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41158 SUBJECT: GRB 250725A: SVOM/VT optical candidate DATE: 25/07/25 09:38:16 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, Y. N. Ma, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. Palmerio (CEA), J. S. Deng, J. Y. Wei (NAOC), R. Z. Li (YNAO), X. L. Chen (YNU) report on behalf of the SVOM/VT team. SVOM performed a Target of Opportunity observation of GRB 250725A detected by Fermi/GBM (Fermi GBM Team, GCN 41150) and Swift/BAT (Evans et al., GCN 41152). SVOM/VT began observing the field at 2025-07-25 02:27:11 UTC, 36.1 min after the Swfit trigger time, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. An uncatalogued source compared to DESI catalogue, is found using VT X-band data, within the error box of Swift/XRT (Osborne et al., GCN 41153) at R.A., Dec 35.480401, -82.791125 degrees: RA (J2000) = 02:21:55.30 Dec (J2000) = -82:47:28.05 with an uncertainty of 0.5 arcsec. The source is detected in both VT_R and VT_B. It was fading in VT_R by 0.3 mag within about one hour during our observation. The AB magnitudes are: Mid time | exposure time | band | mag (AB) | mag err --------------------|-------------------|------|----------|-------- 0.93 hour | 70×13 sec | VT_B | 22.30 | 0.10 0.93 hour | 70×10 sec | VT_R | 19.33 | 0.02 Our measurements are not corrected for Galactic extinction. This source is proposed to be the optical candidate of the burst. Considerring the red color of VT_B-VT_R of about 2.9, the burst is supposed to be probable at medium/high redshift (Wang et al. 2020). 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/41158. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39213] GRB 250725A: MASTER-OAFA optical detection of very fast afterglow
by GCN Circulars 25 Jul '25

25 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41157 SUBJECT: GRB 250725A: MASTER-OAFA optical detection of very fast afterglow DATE: 25/07/25 08:51:52 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> P. Rudominskaya (Lomonosov, MSU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (OAFA), V.Lipunov (Lomonosov MSU), E.Gorbovskoy, A.Kuznetsov, G.Antipov, P.Balanutsa, A.Chasovnikov, N.Tiurina, V.Topolev, K.Zhirkov, Ya.Kechin, V.Senik, D.Vlasenko (Lomonosov MSU), O.Gress, N.Budnev (ISU), A.Sosnovskij (Crao RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the GRB250725.08 26 sec after notice time and 45 sec after trigger time at 2025-07-25 01:52:22 UT. On our first (10s exposure) set we found 1 optical transient within Swift error-box (ra=35.3833 dec=-82.7836 r=0.05) brighter than 17.7. T-Tmid Date Time Expt. Ra Dec Mag ---------|---------------------|-------|-----------------|-----------------|------- 50 2025-07-25 01:52:22 10 (02h 21m 55.67s , -82d 47m 28.1s) 15.8 The 5-sigma upper limit has been about 17.7mag The automatical light curve is the very fast fall F ~ t^-2 This very similar to short GRB behavior. The large optical telescope observation is very welcome! The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/41157. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39212] LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate
by GCN Circulars 25 Jul '25

25 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41156 SUBJECT: LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate DATE: 25/07/25 04:54:50 GMT FROM: Junjie Zhao at Henan Academy of Sciences <junjiezhao(a)hnas.ac.cn> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250725l during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-07-25 04:20:50.940 UTC (GPS time: 1437452468.940). The candidate was found by the GstLAL [1], MBTA [2], and PyCBC Live [3] analysis pipelines. S250725l is an event of interest because its false alarm rate, as estimated by the online analysis, is 3e-08 Hz, or about one in 1 year, 23 days. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250725l The classification of the GW signal, in order of descending probability, is BBH (99%), Terrestrial (1%), BNS (<1%), or NSBH (<1%). Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [4] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [4] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. The source chirp mass falls with highest probability in the bin (11.0, 22.0) solar masses, assuming the candidate is astrophysical in origin. Two sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [5], distributed via GCN and SCiMMA notices about 31 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [5], 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,2. For the bayestar.multiorder.fits,2 sky map, the 90% credible region is 1990 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2186 +/- 673 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] Allene et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [3] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [4] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [5] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/41156. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39211] LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate
by GCN Circulars 25 Jul '25

25 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41155 SUBJECT: LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate DATE: 25/07/25 04:53:42 GMT FROM: Kiet Pham <kiet.pham(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250725l during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-07-25 04:20:50.940 UTC (GPS time: 1437452468.940). The candidate was found by the GstLAL [1], MBTA [2], and PyCBC Live [3] analysis pipelines. S250725l is an event of interest because its false alarm rate, as estimated by the online analysis, is 3e-08 Hz, or about one in 1 year, 23 days. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250725l The classification of the GW signal, in order of descending probability, is BBH (99%), Terrestrial (1%), BNS (<1%), or NSBH (<1%). Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [4] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [4] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. The source chirp mass falls with highest probability in the bin (11.0, 22.0) solar masses, assuming the candidate is astrophysical in origin. Two sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [5], distributed via GCN and SCiMMA notices about 31 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [5], 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,2. For the bayestar.multiorder.fits,2 sky map, the 90% credible region is 1990 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2186 +/- 673 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] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [3] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [4] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [5] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/41155. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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