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

[vsnet-grb-info 37898] Swift GRB 250327A: Global MASTER-Net observations report
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39880 SUBJECT: Swift GRB 250327A: Global MASTER-Net observations report DATE: 25/03/27 13:57:44 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), 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-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the Swift GRB 250327A ( T. M. Parsotan et al., GCN 39877) errorbox 22478 sec after notice time and 22599 sec after trigger time at 2025-03-27 13:46:44 UT, with upper limit up to 19.1 mag. The observations began at zenith distance = 56 deg. The sun altitude is -20.9 deg. The galactic latitude b = 40 deg., longitude l = 92 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2825096 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 22690 | MASTER-Tunka | C | 180 | 19.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/39880. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37897] GRB 250327A: DDOTI Optical Observations
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39879 SUBJECT: GRB 250327A: DDOTI Optical Observations DATE: 25/03/27 13:00:18 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Sahil Atri (U Roma), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), and Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observed the field of the Swift/BAT GRB 250327A (Parsotan et al., GCN 39877) also detected by Fermi/GBM (Fermi GBM Team, GCN 39876) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-03-27 UTC. DDOTI observed the Swift/BAT error region (Parsotan et al., GCN 39877) from 08:13 UTC to 10:43 UTC (from T+0.7 h to T+3.2 h after the trigger) with a total exposure of 1.4 hours. Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues and after performed image subtraction against PanSTARRS PS1 DR2, we detect no evident uncatalogued sources within the observed field to a 5-sigma limiting AB magnitude of w > 21.82 This non-detection is consistent with the reported by Ducoin et al. (GCN 39877). We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/39879. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37896] GRB 250327A: COLIBRÍ optical upper limit
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39878 SUBJECT: GRB 250327A: COLIBRÍ optical upper limit DATE: 25/03/27 11:59:15 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Jean-Grégoire Ducoin (CPPM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Rosa L. Becerra (U Roma), Stéphane Basa (LAM), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM) and Ny Avo Rakotondrainibe (LAM) report: We observed the field of the Swift/BAT GRB 250327A (Parsotan et al., GCN 39877) also detected by Fermi/GBM (Fermi GBM Team, GCN 39876) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. We obtained 23 minutes of exposure in the i filter from 2025-03-27 07:50 to 08:34 UTC (20.5 to 64.1 minutes after the trigger). Within the Swift/BAT localization, we do not detect any credible uncatalogued source to a 5-sigma limiting magnitude of: i > 22.9 mag (AB) We also performed an image subtraction using HOTPANTS and the PanSTARRS i-band image as a reference, which did not reveal any credible residuals. The data were coadded with the COLIBRI pipeline and analysed in STDWeb/STDPipe (Karpov 2021). The photometric calibration was performed using nearby stars from the Pan-STARRS DR1 catalog and the magnitude is not corrected for Galactic extinction. Further observations are ongoing. We acknowledge the excellent support from the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/39878. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37895] GRB 250327A: Swift detection of a burst
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39877 SUBJECT: GRB 250327A: Swift detection of a burst DATE: 25/03/27 08:11:09 GMT FROM: Jamie Kennea at Penn State <jak51(a)psu.edu> T. M. Parsotan (GSFC), J. J. DeLaunay (PSU), R. Gupta (NASA GSFC), J. A. Kennea (PSU) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team: At 07:30:04 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250327A (trigger=1299088). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 248.197, +61.595 which is RA(J2000) = 16h 32m 47s Dec(J2000) = +61d 35' 43" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 40 sec. The peak count rate was ~1648 counts/sec (15-350 keV), at ~3 sec after the trigger. Due to an observing constraint, Swift did not get data immediately. We will report on XRT data in a later GCN. Burst Advocate for this burst is T. M. Parsotan (tyler.parsotan 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/39877. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37894] GRB 250327A: Fermi GBM Final Real-time Localization
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39876 SUBJECT: GRB 250327A: Fermi GBM Final Real-time Localization DATE: 25/03/27 07:40:37 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 07:30:06 UT on 27 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250327A (trigger 764753411.32631 / 250327313). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 246.1, Dec = 62.3 (J2000 degrees, equivalent to J2000 16h 24m, 62d 17'), with a statistical uncertainty of 3.6 degrees. The angle from the Fermi LAT boresight is 47.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250327313/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250327313/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250327313/… View this GCN Circular online at https://gcn.nasa.gov/circulars/39876. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37893] Fermi trigger No 764700395: Global MASTER-Net observations report
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39875 SUBJECT: Fermi trigger No 764700395: Global MASTER-Net observations report DATE: 25/03/27 00:17:45 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB250326.70 (trigger No 764700395,20h 23m 40.80s , -38d 57m 36.0s, R=9.31) errorbox 21402 sec after notice time and 21440 sec after trigger time at 2025-03-26 22:43:51 UT, with upper limit up to 18.3 mag. The observations began at zenith distance = 79 deg. The sun altitude is -60.5 deg. The galactic latitude b = -35 deg., longitude l = 3 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2823964 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 21471 | 2025-03-26 22:43:51 | MASTER-SAAO | (19h 31m 14.42s , -44d 23m 39.6s) | C | 60 | 17.6 | 22457 | 2025-03-26 23:00:16 | MASTER-SAAO | (19h 31m 09.11s , -44d 23m 35.8s) | C | 60 | 17.9 | 23441 | 2025-03-26 23:16:41 | MASTER-SAAO | (19h 31m 11.68s , -44d 24m 08.8s) | C | 60 | 18.1 | 23760 | 2025-03-26 23:21:59 | MASTER-SAAO | (19h 51m 37.14s , -40d 37m 28.5s) | C | 60 | 18.0 | 23840 | 2025-03-26 23:23:19 | MASTER-SAAO | (20h 02m 03.62s , -40d 38m 43.3s) | C | 60 | 17.9 | 24085 | 2025-03-26 23:27:25 | MASTER-SAAO | (19h 31m 10.94s , -44d 25m 46.3s) | C | 60 | 18.2 | 24428 | 2025-03-26 23:33:08 | MASTER-SAAO | (19h 51m 36.38s , -40d 37m 36.0s) | C | 60 | 18.1 | 24508 | 2025-03-26 23:34:27 | MASTER-SAAO | (20h 02m 03.88s , -40d 38m 48.3s) | C | 60 | 18.1 | 24746 | 2025-03-26 23:38:25 | MASTER-SAAO | (19h 31m 09.95s , -44d 26m 12.3s) | C | 60 | 18.2 | 24825 | 2025-03-26 23:39:44 | MASTER-SAAO | (19h 58m 05.51s , -38d 43m 52.8s) | C | 60 | 18.0 | 24904 | 2025-03-26 23:41:04 | MASTER-SAAO | (20h 08m 21.86s , -38d 43m 07.6s) | C | 60 | 18.0 | 25063 | 2025-03-26 23:43:42 | MASTER-SAAO | (19h 51m 30.03s , -40d 38m 44.7s) | C | 60 | 18.2 | 25142 | 2025-03-26 23:45:02 | MASTER-SAAO | (20h 02m 08.19s , -40d 38m 53.4s) | C | 60 | 18.1 | 25380 | 2025-03-26 23:49:00 | MASTER-SAAO | (19h 31m 12.73s , -44d 24m 47.9s) | C | 60 | 18.3 | 25459 | 2025-03-26 23:50:19 | MASTER-SAAO | (19h 58m 04.80s , -38d 44m 00.9s) | C | 60 | 18.2 | 25539 | 2025-03-26 23:51:38 | MASTER-SAAO | (20h 08m 21.86s , -38d 43m 13.0s) | C | 60 | 18.0 | 25618 | 2025-03-26 23:52:58 | MASTER-SAAO | (20h 17m 35.18s , -38d 45m 24.9s) | C | 60 | 18.0 | 25698 | 2025-03-26 23:54:17 | MASTER-SAAO | (20h 27m 56.49s , -38d 45m 32.8s) | C | 60 | 17.9 | 25777 | 2025-03-26 23:55:36 | MASTER-SAAO | (19h 51m 31.85s , -40d 37m 07.5s) | C | 60 | 18.3 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/39875. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37892] LIGO/Virgo/KAGRA S250326y: Updated Sky localization
by GCN Circulars 26 Mar '25

26 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39874 SUBJECT: LIGO/Virgo/KAGRA S250326y: Updated Sky localization DATE: 25/03/26 15:19:25 GMT FROM: A. Domiciano at Côte d’Azur Observatory <armando.domiciano(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 S250326y (GCN Circular 39871). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN Notice, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S250326y For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 1460 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 5412 +/- 1720 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/39874. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37891] Konus-Wind detection of GRB 250322A (short)
by GCN Circulars 26 Mar '25

26 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39873 SUBJECT: Konus-Wind detection of GRB 250322A (short) DATE: 25/03/26 12:50:11 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The short-duration GRB 250322A (Swift-BAT detection: Gupta et al., GCN 39835; Sadaula et al., GCN 39867; AstroSat-CZTI detection: Tembhurnikar et al., GCN 39849) triggered Konus-Wind at T0=57974.215 s UT (16:06:14.215). The burst light curve shows a multipeaked structure, which starts at T0-0.102 s and has a total duration of ~0.18 s. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250322_T57974/ As observed by Konus-Wind, the burst had a fluence of 1.02(-0.13,+0.14)x10^-6 erg/cm2, and a 16-ms peak flux, measured from T0-0.086 s, of 1.05(-0.24,+0.25)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). Since the brightest peak of the burst light curve was detected before the trigger, the spectral analysis was performed using the KW 3-channel light curve data. Modelling the KW 3-channel time-integrated spectrum (measured from T0-0.102 s to T0+0.078 s) by a power law with exponential cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep), yields alpha = 0.22(-0.39,+0.52) and Ep = 472(-64,+85) keV. Assuming the redshift z=0.42 (Fong et al., GCN 39852; Yang et al. GCN 39859) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy release E_iso is 4.9(-0.6,+0.7)x10^50 erg, the peak luminosity L_iso is 7.1(-1.6,+1.7)x10^51 erg/s, the rest-frame peak energy of the time-averaged spectrum Ep,i,z is 670(-91,+121) keV. With the obtained estimates, GRB 250322A is a clear outlier in the 'Amati' relation derived for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021). Meanwhile, in both Eiso-Ep,z and Liso-Ep,z planes, the GRB 250322A position is consistent with short-hard (Type I) GRB population, see http://www.ioffe.ru/LEA/GRBs/GRB250322_T57974/GRB250322A_rest_frame.pdf All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/39873. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37890] IPN triangulation of GRB 250322B
by GCN Circulars 26 Mar '25

26 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39872 SUBJECT: IPN triangulation of GRB 250322B DATE: 25/03/26 12:46:47 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the HEND/Mars Odyssey team, D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, E. Burns on behalf of the IPN, S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, A. Tohuvavohu, and J. DeLaunay on behalf of the Swift-BAT team, G. Waratkar, J.Joshi, V. Bhalerao, D. Bhattacharya, and S. Vadawale, on behalf of the Astrosat-CZTI team, and W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report: The bright, long-duration GRB 250322B (AstroSat-CZTI detection: Tembhurnikar et al., GCN 39848; NuSTAR CsI shield detection: Grefenstette et al., GCN 39857) was detected by AstroSat (CZTI), NuSTAR (CsI shield), Konus-Wind, Swift (BAT), and Mars-Odyssey (HEND) at about 72435 s UT (20:07:15). The burst was outside the coded field of view of the BAT. We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 319.668 (21h 18m 40s) -24.964 (-24d 57' 51") Corners: 319.574 (21h 18m 18s) -23.375 (-23d 22' 29") 319.886 (21h 19m 33s) -26.698 (-26d 41' 53") 319.642 (21h 18m 34s) -26.204 (-26d 12' 13") 319.155 (21h 16m 37s) -22.325 (-22d 19' 29") --------------------------------------------- The error box area is 2638 sq. arcmin, and its maximum dimension is 4.4 deg (the minimum one is 12.2 arcmin). The Sun distance was 48 deg. This localization may be improved. A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB250322_T72435/IPN/ The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/39872. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37889] LIGO/Virgo/KAGRA S250326y: Identification of a GW compact binary merger candidate
by GCN Circulars 26 Mar '25

26 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39871 SUBJECT: LIGO/Virgo/KAGRA S250326y: Identification of a GW compact binary merger candidate DATE: 25/03/26 02:38:50 GMT FROM: Chia-Hsuan Hsiung <sw56540(a)gmail.com> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250326y during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-03-26 01:54:06.153 UTC (GPS time: 1426989264.153). The candidate was found by the cWB [1], cWB BBH [2], GstLAL [3], MBTA [4], PyCBC Live [5], and SPIIR [6] analysis pipelines. S250326y is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.6e-12 Hz, or about one in 1e4 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250326y After parameter estimation by RapidPE-RIFT [7], 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%. [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%. 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 [9], distributed via GCN notice about 31 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [9], distributed via GCN notice 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 1687 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 6237 +/- 1766 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] Aubin et al. CQG 38, 095004 (2021) doi:10.1088/1361-6382/abe913 [5] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [6] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [7] Rose et al. (2022) arXiv:2201.05263 and Pankow et al. PRD 92, 023002 (2015) doi:10.1103/PhysRevD.92.023002 [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/39871. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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