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[vsnet-grb-info 37980] GRB 250331D: Fermi GBM Final Real-time Localization
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39961 SUBJECT: GRB 250331D: Fermi GBM Final Real-time Localization DATE: 25/03/31 05:59:53 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 05:49:17 UT on 31 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250331D (trigger 765092962.014718 / 250331243). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 21.1, Dec = 55.7 (J2000 degrees, equivalent to J2000 01h 24m, 55d 42'), with a statistical uncertainty of 13.9 degrees. The angle from the Fermi LAT boresight is 12.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250331243/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250331243/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250331243/… View this GCN Circular online at https://gcn.nasa.gov/circulars/39961. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37979] GRB 250331C: Prompt enhanced Swift-XRT position
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39960 SUBJECT: GRB 250331C: Prompt enhanced Swift-XRT position DATE: 25/03/31 05:45:04 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Using 1.6 ks of promptly downlinked XRT event data for GRB 250331C, we find an enhanced XRT position of the afterglow: RA, Dec: 80.95640, 33.06317 which is equivalent to: RA (J2000) = 05 23 49.54 Dec (J2000) = +33 03 47.4 with an uncertainty of 1.9 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/1299967. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39960. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37978] GRB 250331C: Swift detection of a burst
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39959 SUBJECT: GRB 250331C: Swift detection of a burst DATE: 25/03/31 04:55:40 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> S. B. Cenko (GSFC), C. Gronwall (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 04:37:40 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250331C (trigger=1299967). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 80.993, +33.029 which is RA(J2000) = 05h 23m 58s Dec(J2000) = +33d 01' 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 25 sec. The peak count rate was ~800 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 04:39:51.5 UT, 130.9 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 80.95740, 33.06310 which is equivalent to: RA(J2000) = 05h 23m 49.78s Dec(J2000) = +33d 03' 47.2" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 163 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 6.49 x 10^21 cm^-2 (Willingale et al. 2013). The initial flux in the 2.5 s image was 1.04e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 139 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the large, but uncertain, extinction expected. Burst Advocate for this burst is S. B. Cenko (brad.cenko 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/39959. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37977] GRB 250331B: Swift detection of a burst
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39958 SUBJECT: GRB 250331B: Swift detection of a burst DATE: 25/03/31 04:47:31 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> S. B. Cenko (GSFC), C. Gronwall (PSU), R. Gupta (NASA GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 04:19:43 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250331B (trigger=1299965). Swift slewed to the burst after a brief delay to clear an observing constraint. The BAT on-board calculated location is RA, Dec 71.381, +43.805 which is RA(J2000) = 04h 45m 31s Dec(J2000) = +43d 48' 17" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peak structure with a duration of about 8 sec. The peak count rate was ~1400 counts/sec (15-350 keV), at ~2 sec after the trigger. The XRT began observing the field at 04:24:57.3 UT, 313.9 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 71.37364, 43.81080 which is equivalent to: RA(J2000) = 04h 45m 29.67s Dec(J2000) = +43d 48' 38.9" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 28 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. We cannot determine whether the source is fading at the present time. A power-law fit to a spectrum formed from promptly downlinked event data does not constrain the column density. UVOT took a finding chart exposure of 150 seconds with the White filter starting 317 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the large, but uncertain, extinction expected. Burst Advocate for this burst is S. B. Cenko (brad.cenko 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/39958. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37976] GRB 250330A: SVOM/VT optical upper limit
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39957 SUBJECT: GRB 250330A: SVOM/VT optical upper limit DATE: 25/03/31 04:35:08 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Z.M. Wang, A. Li (BNU), L.P. Xin, H.L. Li, Y. L. Qiu, C. Wu, Z.H. Yao, Y. Xu, P.P. Zhang, J. Wang, Y.N. Ma, X.H. Han, H.B. Cai, J.Y. Wei(NAOC) report on behalf of the SVOM/VT team: SVOM performed two Target of Opportunity observations of GRB 250330A (Cenko et al., GCN 39938; Pathak, GCN 39944; Osborne et al., GCN 39947) in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously， starting at 2025-03-30T09:17:44 UT, and 2025-03-30T12:40:58 UT, respectively. No sources were detected in the stacked images within the XRT source position (Page, GCN 39940). The 3 sigma limits in VT_R is 21.7 mag (AB) with the exposure time of 3 x 100s at the medium time of 3.2 hours after the Swift BAT trigger, and 23.0 mag with the exposure of 12*120s, at the medium time of 6.8 hours after the burst. This result is consistent with the reports (Becerra, GCN 39941; Siegel et al., GCN 39948; Perez-Garcia et al., GCN 39949; Lipunov et al., GCN 39950). 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/39957. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37975] GRB 250331A: MAXI/GSC detection
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39956 SUBJECT: GRB 250331A: MAXI/GSC detection DATE: 25/03/31 03:44:29 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> K. Takagi, M. Nakajima (Nihon U.), Y. Kawakubo, M. Serino (AGU), H. Negoro, Y. Kudo, H. Shibui, H. Takahashi, K. Tatano, H. Nishio (Nihon U.), T. Mihara, S. Yamada, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, H. Hiramatsu, H. Nishikawa, Y. Kondo, S. Sasao, A. Yoshida (AGU), Y. Tsuboi, H. Sugai, N. Nagashima (Chuo U.), M. Shidatsu, Y. Niida, C. Kang, T. Nakamoto (Ehime U.), I. Takahashi, M. Niwano, N. Higuchi, Y. Yatsu (Tokyo Tech), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, Y. Okada, K. Fujiwara (Kyoto U.), M. Yamauchi, Y. Otsuki, T. Hasegawa, M. Nishio (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.) report on behalf of the MAXI team: The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 01:40:54 UT on March 31, 2025. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (124.987 deg, -18.636 deg) = (08 19 56, -18 38 09) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.25 deg and 0.2 deg, respectively. The roll angle of long axis from the north direction is 168.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 146 +- 23 mCrab (4.0-10.0keV, 1 sigma error). Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners: (124.498, -17.690) deg = (08 17 59, -17 41 24) (J2000) (124.178, -17.935) deg = (08 16 42, -17 56 05) (J2000) (125.521, -19.513) deg = (08 22 05, -19 30 46) (J2000) (125.843, -19.266) deg = (08 23 22, -19 15 57) (J2000) There was no significant excess flux in the previous transit at 0:08 UT and in the next transit at 03:14 UT with an upper limit of 20 mCrab for each. View this GCN Circular online at https://gcn.nasa.gov/circulars/39956. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37974] SVOM/sb25033102: SVOM detection of an X-ray transient
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39955 SUBJECT: SVOM/sb25033102: SVOM detection of an X-ray transient DATE: 25/03/31 03:40:23 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Yinuo MA, Chao WU, Donghua ZHAO, Wenjin XIE (NAOC), Hatsune GOTO (CEA, Kanazawa Univ) on behalf of the SVOM mission team. At 2025-03-31T02:04:18 UTC (Tb) SVOM/ECLAIRs triggered on the X-ray transient labelled sb25033102 (SVOM burst-id sb25033102). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. This transient was only detected by the Count-Rate Trigger (CRT), which produced a sequence of 1 alerts. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 15.10 in the [8-120] keV energy band over a time window of 20.48 seconds starting at Tb. The localization of the best alert is R.A., Dec 289.235, -18.527 degrees: RA (J2000) = 19h16m56.51s Dec (J2000) = -18d31m37.10s with a 90% C.L. radius of 5.48 arcmin (including systematic error of 2 arcmin added in quadrature). We notice that this transient also triggered SVOM/ECLAIRs at the 1.57 hours before, at 2025-03-31T00:29:51.04 (SVOM/sb25033101). Due to an external ToO was performing by SVOM, no immediate slew was performed on this transient. 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. The Burst Advocate (BA) on shift for this burst is Yinuo MA: mayn(a)bao.ac.cn Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/39955. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37973] GRB 250314A: VLA detection
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39954 SUBJECT: GRB 250314A: VLA detection DATE: 25/03/31 02:49:59 GMT FROM: Tanmoy Laskar at U of Utah <tanmoylaskar(a)gmail.com> Nayana A. J. (UC Berkeley), T. Laskar (University of Utah), R. Margutti (UC Berkeley), K. D. Alexander (University of Arizona), R. Chornock (UC Berkeley), E. Berger (Harvard University), W. Fong (Northwestern University), P. Schady (University of Bath), and G. Schroeder (Cornell University) report: "We carried out Karl G. Jansky Very Large Array (VLA) observations of the high-redshift (z ~ 7.3; Malesani et al., GCN 39732; Rakotondrainibe et al., GCN 39743) SVOM/ECLAIRs GRB 250314A (Wang et al., GCN 39719) beginning on 2025 March 21 06:26 UTC (6.7 days after the burst) at multiple frequencies. In preliminary analysis, we detect a radio counterpart with a flux density of ~ 0.1 mJy at 17 GHz, and position: RA (J2000) = 13:25:12.16 Dec (J2000) = -05:16:55.07 with a (statistical) uncertainty of 0.6" in each coordinate. This position is consistent with the optical position (Malesani et al., GCN 39727). Further observations are planned. We thank the VLA staff for scheduling and executing these observations" View this GCN Circular online at https://gcn.nasa.gov/circulars/39954. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37972] LIGO/Virgo/KAGRA S250331o: Identification of a GW compact binary merger candidate
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39953 SUBJECT: LIGO/Virgo/KAGRA S250331o: Identification of a GW compact binary merger candidate DATE: 25/03/31 02:06:54 GMT FROM: Gyoik Kim at Yonsei University <gyoik_kim(a)yonsei.ac.kr> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250331o during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-03-31 01:34:48.438 UTC (GPS time: 1427420106.438). The candidate was found by the cWB [1], cWB BBH [2], GstLAL [3], PyCBC Live [4], and SPIIR [5] analysis pipelines. S250331o is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.2e-10 Hz, or about one in 1e2 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250331o After parameter estimation by RapidPE-RIFT [6], 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%. [7] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [7] 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,0, an initial localization generated by BAYESTAR [8], distributed via GCN notice about 23 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [8], distributed via GCN notice 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 27 deg2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis): icrs; ellipse(02h07m, +31d24m, 4.57d, 1.87d, 116.86d) Marginalized over the whole sky, the a posteriori luminosity distance estimate is 582 +/- 120 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] 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] Rose et al. (2022) arXiv:2201.05263 and Pankow et al. PRD 92, 023002 (2015) doi:10.1103/PhysRevD.92.023002 [7] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [8] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/39953. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37971] Fermi GRB 250330B: Global MASTER-Net observations report
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39952 SUBJECT: Fermi GRB 250330B: Global MASTER-Net observations report DATE: 25/03/30 23:15:59 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 GRB 250330B ( Fermi GBM team, GCN 39951) errorbox 54 sec after notice time and 92 sec after trigger time at 2025-03-30 21:53:54 UT, with upper limit up to 17.4 mag. The observations began at zenith distance = 77 deg. The sun altitude is -59.7 deg. The galactic latitude b = 16 deg., longitude l = 206 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2828695 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 102 | 2025-03-30 21:53:54 | MASTER-SAAO | (07h 22m 19.10s , +12d 01m 03.3s) | C | 20 | 17.1 | 141 | 2025-03-30 21:54:33 | MASTER-SAAO | (07h 22m 19.82s , +12d 01m 05.9s) | C | 20 | 17.0 | 186 | 2025-03-30 21:55:12 | MASTER-SAAO | (07h 22m 20.65s , +12d 01m 08.5s) | C | 30 | 17.1 | 240 | 2025-03-30 21:56:01 | MASTER-SAAO | (07h 22m 21.73s , +12d 01m 11.2s) | C | 40 | 17.0 | 304 | 2025-03-30 21:57:00 | MASTER-SAAO | (07h 22m 23.03s , +12d 01m 14.3s) | C | 50 | 16.9 | 378 | 2025-03-30 21:58:10 | MASTER-SAAO | (07h 22m 24.54s , +12d 01m 18.1s) | C | 60 | 16.9 | 629 | 2025-03-30 22:02:21 | MASTER-SAAO | (07h 36m 00.30s , +13d 19m 14.0s) | C | 60 | 17.4 | 709 | 2025-03-30 22:03:40 | MASTER-SAAO | (07h 36m 01.77s , +13d 19m 17.5s) | C | 60 | 17.4 | 788 | 2025-03-30 22:04:59 | MASTER-SAAO | (07h 36m 03.30s , +13d 19m 20.6s) | C | 60 | 17.4 | 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/39952. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37970] GRB 250330B: Fermi GBM Final Real-time Localization
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39951 SUBJECT: GRB 250330B: Fermi GBM Final Real-time Localization DATE: 25/03/30 22:03:10 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 SHORT GRB At 21:52:22 UT on 30 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250330B (trigger 765064347.102666 / 250330911). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 114.1, Dec = 13.3 (J2000 degrees, equivalent to J2000 07h 36m, 13d 18'), with a statistical uncertainty of 3.1 degrees. The angle from the Fermi LAT boresight is 81.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250330911/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250330911/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250330911/… View this GCN Circular online at https://gcn.nasa.gov/circulars/39951. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37969] Fermi GRB 250330A: Global MASTER-Net observations report
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39950 SUBJECT: Fermi GRB 250330A: Global MASTER-Net observations report DATE: 25/03/30 19:16:02 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 GRB 250330A ( Fermi GBM team, GCN 39944) errorbox 41642 sec after notice time and 41678 sec after trigger time at 2025-03-30 17:42:16 UT, with upper limit up to 18.5 mag. Observations started at twilight. The observations began at zenith distance = 69 deg. The sun altitude is -14.6 deg. The galactic latitude b = -16 deg., longitude l = 316 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2828018 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 41709 | 2025-03-30 17:42:16 | MASTER-SAAO | (16h 01m 09.95s , -72d 45m 24.7s) | C | 60 | 18.1 | 41788 | 2025-03-30 17:43:36 | MASTER-SAAO | (16h 28m 26.03s , -72d 45m 15.7s) | C | 60 | 18.2 | 41868 | 2025-03-30 17:44:56 | MASTER-SAAO | (16h 02m 18.38s , -74d 39m 19.9s) | C | 60 | 18.0 | 41947 | 2025-03-30 17:46:15 | MASTER-SAAO | (16h 32m 49.13s , -74d 37m 47.3s) | C | 60 | 18.3 | 42026 | 2025-03-30 17:47:34 | MASTER-SAAO | (15h 04m 24.83s , -74d 37m 14.9s) | C | 60 | 18.4 | 42106 | 2025-03-30 17:48:54 | MASTER-SAAO | (15h 34m 57.62s , -74d 38m 25.7s) | C | 60 | 18.4 | 42186 | 2025-03-30 17:50:14 | MASTER-SAAO | (15h 09m 38.19s , -72d 45m 00.7s) | C | 60 | 18.2 | 42265 | 2025-03-30 17:51:33 | MASTER-SAAO | (15h 36m 45.01s , -72d 44m 01.7s) | C | 60 | 18.3 | 42345 | 2025-03-30 17:52:52 | MASTER-SAAO | (16h 01m 11.29s , -72d 45m 24.8s) | C | 60 | 18.2 | 42424 | 2025-03-30 17:54:12 | MASTER-SAAO | (16h 28m 23.83s , -72d 44m 12.1s) | C | 60 | 18.2 | 42866 | 2025-03-30 18:01:34 | MASTER-SAAO | (16h 02m 13.55s , -74d 39m 54.2s) | C | 60 | 17.9 | 42945 | 2025-03-30 18:02:53 | MASTER-SAAO | (16h 32m 48.33s , -74d 40m 05.2s) | C | 60 | 18.3 | 43025 | 2025-03-30 18:04:13 | MASTER-SAAO | (15h 04m 23.51s , -74d 37m 45.9s) | C | 60 | 18.4 | 43104 | 2025-03-30 18:05:32 | MASTER-SAAO | (15h 34m 50.67s , -74d 39m 22.5s) | C | 60 | 18.5 | 43184 | 2025-03-30 18:06:52 | MASTER-SAAO | (15h 09m 34.64s , -72d 44m 00.2s) | C | 60 | 18.2 | 43263 | 2025-03-30 18:08:11 | MASTER-SAAO | (15h 36m 38.09s , -72d 44m 59.8s) | C | 60 | 18.3 | 43343 | 2025-03-30 18:09:31 | MASTER-SAAO | (16h 01m 06.13s , -72d 44m 09.8s) | C | 60 | 18.2 | 45719 | 2025-03-30 18:49:07 | MASTER-SAAO | (16h 28m 13.93s , -72d 47m 17.6s) | C | 60 | 18.2 | 45798 | 2025-03-30 18:50:26 | MASTER-SAAO | (16h 02m 10.31s , -74d 39m 28.3s) | C | 60 | 18.1 | 45878 | 2025-03-30 18:51:46 | MASTER-SAAO | (16h 32m 34.04s , -74d 40m 31.3s) | C | 60 | 18.3 | 46778 | 2025-03-30 19:06:46 | MASTER-SAAO | (15h 04m 04.80s , -74d 39m 00.1s) | C | 60 | 18.5 | 46858 | 2025-03-30 19:08:05 | MASTER-SAAO | (15h 34m 34.17s , -74d 41m 15.3s) | C | 60 | 18.4 | 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/39950. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37968] GRB 250330A: BOOTES-7 early optical upper limit
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39949 SUBJECT: GRB 250330A: BOOTES-7 early optical upper limit DATE: 25/03/30 18:13:56 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Perez-Garcia, A. J. Castro-Tirado, E. Fernandez-Garcia, S.-Y. Wu, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy (IAA-CSIC), C. Perez del Pulgar (Univ. de Malaga), G. Garcia-Segura (Inst. de Astronomia, UNAM), M. Gritsevich (Univ. of Helsinki), D. R. Xiong (Yunnan Observatories of CAS), Y.-D. Hu (GuangXi Univ.), B.-B. Zhang (Nanjing Univ.) and A. Maury (Space, San Pedro de Atacama), on behalf of a larger collaboration, report: Following the detection of GRB 250330A by Swift/BAT (Cenko et al., GCNC [39938](https://gcn.nasa.gov/circulars/39938)) and Fermi (Fermi GRB Team, GCNC [39944](https://gcn.nasa.gov/circulars/39944)), the 0.6m BOOTES-7 robotic telescope at San Pedro de Atacama (Chile) responded to the alert on Nov. 9, 06:08:48 UT (i.e. 57s after trigger, and 70s after the event). Within the reported Swift/XRT error circle (Page et al., GCNC [39940](https://gcn.nasa.gov/circulars/39940)) , no optical transient is detected down to 17.6 mag (clear filter). On a coadd (620s) of images at 06:31:17 UT (mid exposure time; i.e. 23.8 min post burst), nothing is detected down to 19.3 mag, in agreement with the deeper VLT/FORS2 observations taken later on (Becerra et al., GCNC [39941](https://gcn.nasa.gov/circulars/39941)). We thank the staff at San Pedro de Atacama Celestial Observations for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/39949. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37967] GRB 250330A: Swift/UVOT Upper Limits
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39948 SUBJECT: GRB 250330A: Swift/UVOT Upper Limits DATE: 25/03/30 17:15:45 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H. Siegel (PSU) and S. B. Cenko (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250330A 3944 s after the BAT trigger (Cenko et al., GCN Circ. 39938). No optical afterglow consistent with the XRT position (Osborne et al., GCN Circ. 39947) 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 3944 4094 147 >21.2 white 3944 4094 147 >21.2 v 4101 4300 197 >20.0 b 4921 5109 185 >20.9 u 4716 4915 197 >20.0 w1 4511 4711 197 >21.3 m2 4306 4505 197 >19.8 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.147 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/39948. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37966] GRB 250330A: Swift-XRT afterglow detection
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39947 SUBJECT: GRB 250330A: Swift-XRT afterglow detection DATE: 25/03/30 16:52:55 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne (U. Leicester), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAR), D.N. Burrows (PSU), M. A. Williams (PSU), S. Dichiara (PSU), K.L. Page (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Swift-BAT-detected burst GRB 250330A. We searched for X-ray sources in 1.4 ks of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 5.1 ks, obtained between T0+3.9 ks and T0+28.0 ks. Two uncatalogued X-ray sources are detected within the estimated 3-sigma Swift-BAT error region (296 arcsec), of which one ("Source 1") is above the LSXPS 3-sigma upper limit at this position and fading with >3-sigma significance, and is therefore likely the GRB afterglow. Using 1474 s of PC mode data and 4 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 252.94482, -86.88053 which is equivalent to: RA (J2000): 16h 51m 46.76s Dec(J2000): -86d 52' 49.9" with an uncertainty of 2.3 arcsec (radius, 90% confidence). This position is 48 arcsec from the Swift-BAT position. The light curve can be modelled with a power-law decay with a decay index of alpha=1.01 (+0.15, -0.14). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.3 (+0.4, -0.3). The best-fitting absorption column is 4.9 (+1.9, -1.5) x 10^21 cm^-2, in excess of the Galactic value of 1.2 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 3.6 x 10^-11 (7.0 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 4.9 (+1.9, -1.5) x 10^21 cm^-2 Galactic foreground: 1.2 x 10^21 cm^-2 Excess significance: 3.9 sigma Photon index: 2.3 (+0.4, -0.3) If the light curve continues to decay with a power-law decay index of 1.01, the count rate at T+24 hours will be 7.8 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.8 x 10^-13 (5.4 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01299776. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/01299776. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39947. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37965] GRB 250328A: 1.6m Mephisto optical observations
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39946 SUBJECT: GRB 250328A: 1.6m Mephisto optical observations DATE: 25/03/30 16:19:25 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn> Brajesh Kumar, Jianhui Lian, Xinlei Chen, Xufeng Zhu, Fanchuan Kong, Yaosong Yu, Xingzhu Zou, Yu Pan, Guowang Du, Yuan Fang, Jinghua Zhang, Helong Guo, Tao Wang, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team: The field of SVOM/ECLAIRs-detected GRB 250328A (burst-id sb25032803; Brunet et al., GCN 39910) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Our observations were started from 2025-03-28T18:19:29 (~1.4 hr after the trigger) under moderate sky conditions. Multiple frames in uvgriz bands were simultaneously (ugi, vrz) acquired with different exposure time. There is a marginal detection of an afterglow candidate in our stacked g and r band images at the location reported in VLT/HAWK-I observations (Schneider et al.; GCN 39919), also consistent with the XRT source #2. There is no optical detection in uviz bands. Considering the fading nature of the source reported in later epoch of observations at the same location (Schneider et al., GCN 39920; Li et al., GCN 39923; Li et al, GCN 39936), the candidate in our stacked images is likely the optical counterpart of GRB 250328A (Li et al, GCN 39936). The preliminary photometric magnitudes (without Galactic extinction correction) and 3 sigma limiting magnitudes in different bands are below: Start_Time(UT) | Band | Exp(s) | Mag/LimMag(AB) ---------------------|------|--------|-------------------- 2025-03-28T18:19:29 | u | 180*3 | >20.17 2025-03-28T18:28:23 | v | 180*4 | >21.02 2025-03-28T18:19:29 | g | 50*10 | 21.53 +/- 0.22 2025-03-28T18:28:23 | r | 50*12 | 21.44 +/- 0.15 2025-03-28T18:19:29 | i | 79*7 | >21.62 2025-03-28T18:28:23 | z | 79*8 | >20.94 ---------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21. ---------------------------------------------------------- View this GCN Circular online at https://gcn.nasa.gov/circulars/39946. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37964] GRB 250329B: SVOM/COLIBRÍ (F-GFT) optical upper limit
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39945 SUBJECT: GRB 250329B: SVOM/COLIBRÍ (F-GFT) optical upper limit DATE: 25/03/30 15:32:15 GMT FROM: J.-G. Ducoin at CPPM <ducoin(a)cppm.in2p3.fr> Ny Avo Rakotondrainibe (LAM), Jean-Grégoire Ducoin (CPPM), Jean-Luc Atteia (IRAP), Margarita Pereyra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM) report: We imaged the field of GRB 250329B detected by SVOM/ECLAIRs as trigger sb25032902, (Xie et al., GCN Circ. 39925) 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 observed from 2025-03-30 04:04 to 05:50 UTC (15.9 to 17.66 hours after the trigger) and obtained 80 minutes of exposure in the i filter. The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction. At the XRT localization (Beardmore et al., GCN Circ. 39939), we do not find any optical counterpart to a 3-sigma limiting magnitude of: i > 23.73. Our result is consistent with previous optical non-detections (Xie et al., GCN Circ. 39926; Chen et al., GCN Circ. 39929; Xin et al., GCN Circ. 39931; and Wu et al., GCN Circ 39935) We acknowledge the excellent support of the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and thank the COLIBRÍ and DDRAGO engineering teams. View this GCN Circular online at https://gcn.nasa.gov/circulars/39945. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37963] GRB 250330A: Fermi GBM Final Localization
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39944 SUBJECT: GRB 250330A: Fermi GBM Final Localization DATE: 25/03/30 12:59:41 GMT FROM: Utkarsh Pathak at IIT Bombay <utkarshpathak.07(a)gmail.com> The Fermi GBM team reports the detection of a likely LONG GRB "At 06:07:38.42 UT on 30 March 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250330A (trigger 765007663/250330255). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 254.96, Dec = -66.02 (J2000 degrees, equivalent to J2000 16h 51m, -86d 52'), with a statistical uncertainty of 6.9 degrees. This localization is consistent with Swift-BAT location (Cenko et al. 2025, GCN 39938) and Swift-XRT (Page et al. 2025, 39940). The angle from the Fermi LAT boresight is 46 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250330255/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250330255/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250330255/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/39944. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37962] IceCube-250330A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39943 SUBJECT: IceCube-250330A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/03/30 11:02:08 GMT FROM: Giacomo Sommani at Ruhr-Universität Bochum <gsommani(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 2025-03-30 08:31:06.33 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_Bronze alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 1.7612 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/140729_49427574.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 2025-03-30 Time: 08:31:06.33 UT RA: 307.53 (+0.57, -0.47 deg 90% PSF containment) J2000 Dec: 11.07 (+0.45, -.47 deg 90% PSF containment) J2000 We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of the event. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/39943. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37961] IceCube Alert 250330.35: Global MASTER-Net observations report
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39942 SUBJECT: IceCube Alert 250330.35: Global MASTER-Net observations report DATE: 25/03/30 10:39:28 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-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 IceCube Alert 250330.35 (trigger No 49427574,20h 29m 18.48s , +10d 58m 33.6s, R=0.51) errorbox 91 sec after notice time and 148 sec after trigger time at 2025-03-30 08:33:34 UT, with upper limit up to 19.2 mag. The observations began at zenith distance = 69 deg. The sun altitude is -28.6 deg. The galactic latitude b = -16 deg., longitude l = 55 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2828042 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 154 | 2025-03-30 08:33:34 | MASTER-OAFA | (20h 20m 09.80s , +10d 22m 06.8s) | C | 10 | 16.4 | 179 | 2025-03-30 08:33:34 | MASTER-OAFA | (20h 20m 09.79s , +10d 22m 06.9s) | C | 60 | 17.3 | Coadd 164 | 2025-03-30 08:33:35 | MASTER-OAFA | (20h 29m 20.45s , +10d 45m 17.7s) | C | 30 | 17.7 | 209 | 2025-03-30 08:33:35 | MASTER-OAFA | (20h 29m 20.45s , +10d 45m 17.7s) | C | 120 | 18.4 | Coadd 454 | 2025-03-30 08:33:35 | MASTER-OAFA | (20h 29m 20.44s , +10d 45m 17.7s) | C | 610 | 18.3 | Coadd 194 | 2025-03-30 08:34:10 | MASTER-OAFA | (20h 20m 10.00s , +10d 22m 13.8s) | C | 20 | 16.8 | 205 | 2025-03-30 08:34:11 | MASTER-OAFA | (20h 29m 20.56s , +10d 45m 22.0s) | C | 40 | 17.9 | 246 | 2025-03-30 08:34:57 | MASTER-OAFA | (20h 20m 10.18s , +10d 22m 21.5s) | C | 30 | 16.9 | 256 | 2025-03-30 08:34:57 | MASTER-OAFA | (20h 29m 20.73s , +10d 45m 26.7s) | C | 50 | 17.9 | 307 | 2025-03-30 08:35:53 | MASTER-OAFA | (20h 20m 10.41s , +10d 22m 29.9s) | C | 40 | 17.0 | 367 | 2025-03-30 08:35:53 | MASTER-OAFA | (20h 20m 10.41s , +10d 22m 29.9s) | C | 160 | 17.5 | Coadd 318 | 2025-03-30 08:35:54 | MASTER-OAFA | (20h 29m 20.96s , +10d 45m 32.0s) | C | 60 | 17.9 | 398 | 2025-03-30 08:35:54 | MASTER-OAFA | (20h 29m 20.96s , +10d 45m 32.0s) | C | 220 | 18.5 | Coadd 378 | 2025-03-30 08:36:59 | MASTER-OAFA | (20h 20m 10.57s , +10d 22m 37.6s) | C | 50 | 17.1 | 389 | 2025-03-30 08:36:59 | MASTER-OAFA | (20h 29m 21.10s , +10d 45m 37.1s) | C | 70 | 18.0 | 464 | 2025-03-30 08:38:15 | MASTER-OAFA | (20h 20m 10.80s , +10d 22m 47.2s) | C | 70 | 17.0 | 475 | 2025-03-30 08:38:15 | MASTER-OAFA | (20h 29m 21.27s , +10d 45m 43.8s) | C | 90 | 17.9 | 571 | 2025-03-30 08:39:52 | MASTER-OAFA | (20h 20m 11.10s , +10d 22m 57.3s) | C | 90 | 17.3 | 696 | 2025-03-30 08:39:52 | MASTER-OAFA | (20h 20m 11.09s , +10d 22m 57.2s) | C | 340 | 17.9 | Coadd 581 | 2025-03-30 08:39:52 | MASTER-OAFA | (20h 29m 21.47s , +10d 45m 50.8s) | C | 110 | 18.2 | 751 | 2025-03-30 08:39:52 | MASTER-OAFA | (20h 29m 21.47s , +10d 45m 50.6s) | C | 450 | 18.7 | Coadd 697 | 2025-03-30 08:41:48 | MASTER-OAFA | (20h 20m 11.33s , +10d 23m 08.5s) | C | 110 | 17.3 | 707 | 2025-03-30 08:41:48 | MASTER-OAFA | (20h 29m 21.71s , +10d 45m 59.7s) | C | 130 | 17.9 | 848 | 2025-03-30 08:44:04 | MASTER-OAFA | (20h 20m 11.45s , +10d 23m 18.4s) | C | 140 | 17.5 | 858 | 2025-03-30 08:44:04 | MASTER-OAFA | (20h 29m 21.88s , +10d 46m 08.9s) | C | 160 | 18.2 | 1024 | 2025-03-30 08:46:50 | MASTER-OAFA | (20h 20m 11.60s , +10d 23m 29.1s) | C | 160 | 17.3 | 1034 | 2025-03-30 08:46:50 | MASTER-OAFA | (20h 29m 22.17s , +10d 46m 20.1s) | C | 180 | 18.0 | 1210 | 2025-03-30 08:49:56 | MASTER-OAFA | (20h 20m 11.76s , +10d 23m 40.7s) | C | 160 | 17.6 | 1370 | 2025-03-30 08:49:56 | MASTER-OAFA | (20h 20m 11.76s , +10d 23m 40.8s) | C | 480 | 18.1 | Coadd 1221 | 2025-03-30 08:49:56 | MASTER-OAFA | (20h 29m 22.37s , +10d 46m 30.8s) | C | 180 | 18.4 | 1408 | 2025-03-30 08:53:04 | MASTER-OAFA | (20h 29m 22.58s , +10d 46m 41.4s) | C | 180 | 18.4 | 1584 | 2025-03-30 08:56:10 | MASTER-OAFA | (20h 20m 12.02s , +10d 24m 01.1s) | C | 160 | 17.6 | 1594 | 2025-03-30 08:56:10 | MASTER-OAFA | (20h 29m 22.74s , +10d 46m 51.5s) | C | 180 | 18.4 | 1774 | 2025-03-30 08:56:10 | MASTER-OAFA | (20h 29m 22.75s , +10d 46m 51.5s) | C | 540 | 18.9 | Coadd 1770 | 2025-03-30 08:59:15 | MASTER-OAFA | (20h 20m 12.11s , +10d 24m 09.8s) | C | 160 | 17.6 | 1780 | 2025-03-30 08:59:16 | MASTER-OAFA | (20h 29m 22.89s , +10d 47m 00.1s) | C | 180 | 18.4 | 1956 | 2025-03-30 09:02:22 | MASTER-OAFA | (20h 20m 12.11s , +10d 24m 17.4s) | C | 160 | 17.6 | 2116 | 2025-03-30 09:02:22 | MASTER-OAFA | (20h 20m 12.11s , +10d 24m 17.3s) | C | 480 | 18.2 | Coadd 1966 | 2025-03-30 09:02:22 | MASTER-OAFA | (20h 29m 23.02s , +10d 47m 08.9s) | C | 180 | 18.6 | 2142 | 2025-03-30 09:05:28 | MASTER-OAFA | (20h 20m 12.15s , +10d 24m 26.4s) | C | 160 | 17.8 | 2152 | 2025-03-30 09:05:28 | MASTER-OAFA | (20h 29m 23.11s , +10d 47m 17.6s) | C | 180 | 18.6 | 2332 | 2025-03-30 09:05:28 | MASTER-OAFA | (20h 29m 23.11s , +10d 47m 17.6s) | C | 540 | 19.1 | Coadd 2328 | 2025-03-30 09:08:34 | MASTER-OAFA | (20h 20m 12.13s , +10d 24m 34.2s) | C | 160 | 17.7 | 2338 | 2025-03-30 09:08:34 | MASTER-OAFA | (20h 29m 23.16s , +10d 47m 25.6s) | C | 180 | 18.7 | 2514 | 2025-03-30 09:11:40 | MASTER-OAFA | (20h 20m 12.11s , +10d 24m 42.9s) | C | 160 | 17.7 | 2674 | 2025-03-30 09:11:40 | MASTER-OAFA | (20h 20m 12.11s , +10d 24m 42.9s) | C | 480 | 18.2 | Coadd 2525 | 2025-03-30 09:11:40 | MASTER-OAFA | (20h 29m 23.23s , +10d 47m 33.9s) | C | 180 | 18.6 | 2700 | 2025-03-30 09:14:46 | MASTER-OAFA | (20h 20m 11.96s , +10d 24m 49.3s) | C | 160 | 17.7 | 2710 | 2025-03-30 09:14:46 | MASTER-OAFA | (20h 29m 23.24s , +10d 47m 41.1s) | C | 180 | 18.6 | 2890 | 2025-03-30 09:14:46 | MASTER-OAFA | (20h 29m 23.24s , +10d 47m 41.1s) | C | 540 | 19.2 | Coadd 2886 | 2025-03-30 09:17:52 | MASTER-OAFA | (20h 20m 11.87s , +10d 24m 55.7s) | C | 160 | 17.7 | 2897 | 2025-03-30 09:17:52 | MASTER-OAFA | (20h 29m 23.23s , +10d 47m 47.9s) | C | 180 | 18.6 | 3073 | 2025-03-30 09:20:58 | MASTER-OAFA | (20h 20m 11.77s , +10d 25m 01.5s) | C | 160 | 17.9 | 3233 | 2025-03-30 09:20:58 | MASTER-OAFA | (20h 20m 11.77s , +10d 25m 01.5s) | C | 480 | 18.3 | Coadd 3083 | 2025-03-30 09:20:59 | MASTER-OAFA | (20h 29m 23.17s , +10d 47m 54.3s) | C | 180 | 18.8 | 3259 | 2025-03-30 09:24:05 | MASTER-OAFA | (20h 20m 11.65s , +10d 25m 07.5s) | C | 160 | 17.8 | 3270 | 2025-03-30 09:24:05 | MASTER-OAFA | (20h 29m 23.08s , +10d 48m 00.1s) | C | 180 | 18.8 | 3450 | 2025-03-30 09:24:05 | MASTER-OAFA | (20h 29m 23.08s , +10d 48m 00.1s) | C | 540 | 19.2 | Coadd 3446 | 2025-03-30 09:27:11 | MASTER-OAFA | (20h 20m 11.57s , +10d 25m 14.3s) | C | 160 | 17.8 | 3456 | 2025-03-30 09:27:12 | MASTER-OAFA | (20h 29m 22.99s , +10d 48m 06.0s) | C | 180 | 18.8 | 3631 | 2025-03-30 09:30:17 | MASTER-OAFA | (20h 20m 11.32s , +10d 25m 17.7s) | C | 160 | 17.9 | 3791 | 2025-03-30 09:30:17 | MASTER-OAFA | (20h 20m 11.32s , +10d 25m 17.7s) | C | 480 | 18.3 | Coadd 3642 | 2025-03-30 09:30:18 | MASTER-OAFA | (20h 29m 22.85s , +10d 48m 10.9s) | C | 180 | 18.9 | 3818 | 2025-03-30 09:33:23 | MASTER-OAFA | (20h 20m 11.05s , +10d 25m 20.8s) | C | 160 | 17.9 | 3828 | 2025-03-30 09:33:24 | MASTER-OAFA | (20h 29m 22.71s , +10d 48m 15.8s) | C | 180 | 18.8 | 4008 | 2025-03-30 09:33:24 | MASTER-OAFA | (20h 29m 22.70s , +10d 48m 15.8s) | C | 540 | 19.2 | Coadd 4004 | 2025-03-30 09:36:30 | MASTER-OAFA | (20h 20m 10.69s , +10d 25m 22.7s) | C | 160 | 17.7 | 4014 | 2025-03-30 09:36:30 | MASTER-OAFA | (20h 29m 22.52s , +10d 48m 19.4s) | C | 180 | 18.8 | 4191 | 2025-03-30 09:39:37 | MASTER-OAFA | (20h 20m 10.39s , +10d 25m 26.8s) | C | 160 | 17.8 | 4351 | 2025-03-30 09:39:37 | MASTER-OAFA | (20h 20m 10.39s , +10d 25m 26.8s) | C | 480 | 18.2 | Coadd 4201 | 2025-03-30 09:39:37 | MASTER-OAFA | (20h 29m 22.33s , +10d 48m 23.2s) | C | 180 | 18.7 | 4377 | 2025-03-30 09:42:43 | MASTER-OAFA | (20h 20m 10.20s , +10d 25m 32.4s) | C | 160 | 17.6 | 4387 | 2025-03-30 09:42:43 | MASTER-OAFA | (20h 29m 22.13s , +10d 48m 27.3s) | C | 180 | 18.5 | 4564 | 2025-03-30 09:45:49 | MASTER-OAFA | (20h 20m 09.80s , +10d 25m 34.1s) | C | 160 | 17.6 | 4574 | 2025-03-30 09:45:50 | MASTER-OAFA | (20h 29m 21.90s , +10d 48m 30.3s) | C | 180 | 18.5 | 4750 | 2025-03-30 09:48:56 | MASTER-OAFA | (20h 20m 09.46s , +10d 25m 36.8s) | C | 160 | 17.5 | 4910 | 2025-03-30 09:48:56 | MASTER-OAFA | (20h 20m 09.48s , +10d 25m 36.8s) | C | 480 | 17.6 | Coadd 4760 | 2025-03-30 09:48:56 | MASTER-OAFA | (20h 29m 21.60s , +10d 48m 33.2s) | C | 180 | 17.9 | 4937 | 2025-03-30 09:52:02 | MASTER-OAFA | (20h 20m 09.11s , +10d 25m 38.9s) | C | 160 | 17.2 | 5122 | 2025-03-30 09:55:08 | MASTER-OAFA | (20h 20m 08.75s , +10d 25m 41.4s) | C | 160 | 16.9 | 5308 | 2025-03-30 09:58:14 | MASTER-OAFA | (20h 20m 08.40s , +10d 25m 43.9s) | C | 160 | 16.5 | 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/39942. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37960] GRB 250330A: VLT/FORS2 Optical Observations
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39941 SUBJECT: GRB 250330A: VLT/FORS2 Optical Observations DATE: 25/03/30 10:22:23 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa Becerra (U Rome), Eleonora Troja (U Rome), Muskan Yadav (U Rome), Roberto Ricci (U Rome) report on behalf of the ERC BHianca team: We observed the field of GRB 250330A (Cenko et al., GCN 39938) with the FORS2 imager on the ESO VLT UT1 (Antu). Observations began at T+1.25 hours after the trigger and were carried out in the R filter at an average seeing of 0.7" and airmass about 2.2. Image subtraction against the SkyMapper Southern Survey (SMSS) Fourth Data Release (DR4) catalog (Onken et al., 2024) shows no new uncataloged source down to r~21.5 AB. Several fainter objects are visible within the XRT position (Page et al., GCN 39940), however, additional observations are required to assess their variability We thank the staff at the VLT for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39941. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37959] GRB 250330A: Prompt Swift-XRT position
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39940 SUBJECT: GRB 250330A: Prompt Swift-XRT position DATE: 25/03/30 09:00:27 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K.L. Page and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: Because of the location of Swift with respect to the South Atlantic Anomaly at the time of the burst, XRT began collecting Photon Counting mode data for GRB 250330A (GCN Circ. 39938) around 4 ks after the trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec = 252.9515, -86.87972 which is equivalent to RA (J2000): 16h 51m 48.36s Dec (J2000): -86d 52' 47.0" with an uncertainty of 3.9 arcsec (radius, 90% confidence). This is 47 arcseconds from the BAT position, inside the BAT error circle. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39940. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37958] GRB 250329B: Swift-XRT afterglow detection
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39939 SUBJECT: GRB 250329B: Swift-XRT afterglow detection DATE: 25/03/30 08:26:45 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), J.A. Kennea (PSU), D.N. Burrows (PSU), M. A. Williams (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: We have analysed 1.1 ks of XRT data for the SVOM/ECLAIRs-detected burst GRB 250329B, from 7.4 ks to 8.5 ks after the SVOM/ECLAIRs trigger. The data are entirely in Photon Counting (PC) mode. An uncatalogued X-ray source is found which is substantially brighter than an upper limit derived from the Rosat All-Sky Survey and is thus likely the afterglow. Using 1140 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 207.66921, +52.82343 which is equivalent to: RA (J2000): 13h 50m 40.61s Dec(J2000): +52d 49' 24.3" with an uncertainty of 3.3 arcsec (radius, 90% confidence). This position is 3.7 arcmin from the SVOM/ECLAIRs position. We cannot at this time determine whether the source is fading. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 3.2 (+0.9, -0.8). The best-fitting absorption column is 7.1 (+4.0, -3.1) x 10^21 cm^-2, in excess of the Galactic value of 1.3 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 2.6 x 10^-11 (1.4 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 7.1 (+4.0, -3.1) x 10^21 cm^-2 Galactic foreground: 1.3 x 10^20 cm^-2 Excess significance: 3.8 sigma Photon index: 3.2 (+0.9, -0.8) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00019667. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39939. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37957] GRB 250330A: Swift detection of a burst
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39938 SUBJECT: GRB 250330A: Swift detection of a burst DATE: 25/03/30 06:28:16 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> S. B. Cenko (GSFC), K. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 06:07:38 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250330A (trigger=1299776). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 252.790, -86.870 which is RA(J2000) = 16h 51m 10s Dec(J2000) = -86d 52' 11" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single peak structure with a duration of about 10 sec. The peak count rate was ~5800 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 06:08:51.3 UT, 73.2 seconds after the BAT trigger. Due to the proximity of Swift to the SAA, XRT centroided on a cosmic ray. Given the short visibility window, no other data are available at this time. UVOT data are not available at this time. Although this trigger occurred while Swift was close to the SAA, the BAT light-curve shows a definite peak, and Fermi-GBM also triggered at the same time. Burst Advocate for this burst is S. B. Cenko (brad.cenko 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/39938. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37956] Swift GRB250330.26: Global MASTER-Net observations report
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39937 SUBJECT: Swift GRB250330.26: Global MASTER-Net observations report DATE: 25/03/30 06:21:28 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-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 Swift GRB250330.26 (trigger No 1299776,16h 51m 09.60s , -86d 52m 12.0s, R=0.05) errorbox 47 sec after notice time and 74 sec after trigger time at 2025-03-30 06:08:53 UT, with upper limit up to 19.1 mag. The observations began at zenith distance = 56 deg. The sun altitude is -55.5 deg. The galactic latitude b = -26 deg., longitude l = 306 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2827980 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 80 | MASTER-OAFA | C | 10 | 18.6 | 115 | MASTER-OAFA | C | 20 | 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/39937. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37955] GRB250328A: A fading optical afterglow confirmed by SVOM/VT
by GCN Circulars 30 Mar '25

30 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39936 SUBJECT: GRB250328A: A fading optical afterglow confirmed by SVOM/VT DATE: 25/03/30 03:36:32 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, J. Wang, W. J. Xie, B.T. Wang (YNAO, CAS), Z. H. Yao, Y. N. Ma, Y. Xu, P. P. Zhang, X. H. Han, Y. J. Xiao, H. B. Cai, J. Y. Wei (NAOC)，M. Brunet, J. Malzac (IRAP) report on behalf of the SVOM team: SVOM/VT performed a second ToO observation on the burst triggered by SVOM/ECLAIRs (Brunet et al., GCN 39910). The observation began from about 20.65 hours to 21.5 hours after the burst in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The candidate reported (Schneider et al., GCN 39919, Schneider et al., GCN 39920) was fading by about one magnitude in stack images in both channels, compared to the previous brightness reported by Li et al. GCN 39923. The magnitude is VT_R = 22.8+/-0.2 mag(AB) at the mid time of 21.05 hours after the burst. The photometry has not been corrected for the Galactic extinction. We proposed that this candidate is the optical counterpart of GRB 250328A. 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/39936. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37954] GRB 250329B: SVOM/C-GFT optical upper limit
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39935 SUBJECT: GRB 250329B: SVOM/C-GFT optical upper limit DATE: 25/03/29 23:27:41 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Chao WU (NAOC), W.J. Xie (NAOC), Y.H. Cheng (SWIFAR, YNU), B.T. Wang (YNAO, CAS), Zhe Kang (CHO), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei, Qiu(NAOC), Jing Wang(NAOC), Jianyan Wei (NAOC) report on behalf of the SVOM/C-GFT team: We observed the field of GRB 250329B detected by SVOM/ECLAIRs (sb25032902) with C-GFT. Our observations were started on 2025-03-29T12:50:31 UTC, ~40.20 mins after the trigger. No any source was detected in our stacked image within the source error circle of the X-ray Swift/XRT (source #1: https://www.swift.ac.uk/SVOM/SVOM_FIELD00008/ ). The limiting magnitude(3 sigma) in i band is 19.80 mag at the middle time of 41.95 minutes after the burst. The photometry was calibrated with UCAC4 catalog. This result is consistent with the reports (Xin et al., GCN 39926, Chen et al., GCN 39929, and Xin et al., GCN 39931). We thank the observation assistants Yinhuai Hao and Bowen Li at Jilin observatory for their excellent support. Chinese Ground Follow-up Telescope of SVOM mission is located at Jilin, Changchun Observatory, National Astronomical Observatories, CAS. It has FOV of 1.28 deg x 1.28 deg with a 4k*4k CMOS detector mounted on the primary focus of 1.2-meter-aperure telescope. View this GCN Circular online at https://gcn.nasa.gov/circulars/39935. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37953] LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 1)
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39934 SUBJECT: LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 1) DATE: 25/03/29 22:30:24 GMT FROM: Isaac McMahon at University of Zürich <isaac.mcmahon(a)ligo.org> S. MacBride (UZH), I. McMahon (UZH), M. Soares-Santos (UZH), reporting on behalf of the Dark Energy Survey Gravitational Wave (DESGW) Team: At 01:43 UTC, March 29th, the Dark Energy Camera (DECam) began the first epoch of observations in response to the LVK alert issued for the candidate gravitational-wave event S250328ae (GCN 39898). We observed eight fields centered on the following ICRS coordinates: (145.286221, 10.615360) (145.996500, 12.108130) (143.786221, 10.715360) (144.496500, 12.208130) (144.069167, 9.115670) (143.344621, 7.609550) (145.900667, 13.593470) (142.620092, 6.103430) These pointings cover the 90% localization region of candidate gravitational-wave event S250328ae. All fields were observed in DECam r, i, and z filters with 90-second exposures. The limiting magnitude achieved is ~22.7 in r-band, ~22.1 in i-band, and ~21.4 in z-band. We process the images with our difference imaging pipeline (Herner et al. 2020) using DES and public DECam images as templates. We employ the autoscan machine learning code (Goldstein et al 2015) to reject subtraction artifacts. Candidates were selected by requiring at least two high signal to noise detections. We also require an autoscan score of at least 0.7 on at least one of those detections. We also match our candidates against the ALLWISE, Milliquas, and Quaia AGN catalogs (Secrest et al 2015, Flesch 2023, Storey-Fisher et al 2024) within the LVK localization volume to determine if any correspond to known active galactic nuclei. After candidate selection, we report the 20 high confidence candidates listed below. After vetting and identification, 8 candidates are classified as nuclear candidates (likely active galactic nuclei), 8 candidates as possible supernovae, and 3 other candidates do not fall in either category. 1 additional candidate (2292763) has been identified as a known AGN WISEA J093710.05+082057.2. We have numerous other transient candidates which require further observation to confidently classify. Further observations are ongoing, and we encourage followup of the 20 candidates identified herein. | TYPE | ID | ATNAME | RA | DEC | MAG_R | MAG_R_ERR | MAG_I | MAG_I_ERR | MAG_Z | MAG_Z_ERR | | -------- | ------- | --------- | ---------- | ---------- | ----- | ---- | ----- | ---- | ----- | ---- | | SN_LIKE | 2290892 | AT2025gei | 143.636743 | 9.980209 | N/A | N/A | 20.59 | 0.03 | N/A | N/A | | OTHER | 2292987 | AT2025gej | 143.183373 | 6.893136 | 21.37 | 0.04 | 21.45 | 0.08 | N/A | N/A | | AGN_LIKE | 2290036 | AT2025gek | 145.199481 | 10.828527 | 20.77 | 0.04 | 20.62 | 0.03 | 20.69 | 0.1 | | SN_LIKE | 2290467 | AT2020woa | 144.388798 | 10.255536 | 19.87 | 0.02 | N/A | N/A | 20.1 | 0.04 | | SN_LIKE | 2290524 | AT2025gel | 144.524917 | 10.199936 | N/A | N/A | N/A | N/A | 20.47 | 0.06 | | OTHER | 2290001 | AT2025avp | 144.806008 | 10.632223 | 20.36 | 0.02 | 20.19 | 0.02 | 20.22 | 0.06 | | SN_LIKE | 2291473 | AT2025gem | 144.706509 | 11.560317 | 20.92 | 0.03 | N/A | N/A | 21.22 | 0.1 | | AGN_LIKE | 2293190 | AT2025cvb | 144.191297 | 10.828462 | 20.86 | 0.03 | 20.87 | 0.03 | N/A | N/A | | AGN_LIKE | 2290623 | AT2025gen | 144.112464 | 11.641817 | 21.4 | 0.04 | 21.3 | 0.08 | 21.37 | 0.12 | | SN_LIKE | 2292782 | AT2025geo | 144.928578 | 10.349243 | 20.92 | 0.04 | 21.07 | 0.04 | N/A | N/A | | SN_LIKE | 2291779 | AT2025gej | 143.182187 | 6.894174 | N/A | N/A | N/A | N/A | 20.76 | 0.06 | | OTHER | 2290762 | AT2025gep | 144.259773 | 11.511316 | 21.29 | 0.04 | N/A | N/A | N/A | N/A | | SN_LIKE | 2290334 | AT2025geq | 145.235616 | 12.469694 | 20.22 | 0.02 | 20.57 | 0.03 | N/A | N/A | | AGN_LIKE | 2290970 | AT2025ger | 142.543835 | 6.090899 | 21.71 | 0.05 | 21.43 | 0.06 | 21.28 | 0.09 | | AGN_LIKE | 2292040 | AT2025ges | 144.438216 | 9.885617 | 21.72 | 0.07 | 21.75 | 0.11 | 21.93 | 0.17 | | SN_LIKE | 2292645 | AT2025get | 144.053408 | 11.422277 | N/A | N/A | 22.67 | 0.21 | N/A | N/A | | AGN_LIKE | 2293517 | AT2025geu | 145.956024 | 12.381673 | 21.73 | 0.08 | 21.65 | 0.07 | N/A | N/A | | AGN_LIKE | 2291833 | AT2025gev | 143.241035 | 8.651865 | 22.16 | 0.09 | 21.99 | 0.13 | 22.22 | 0.22 | | AGN_LIKE | 2294074 | AT2025gew | 144.291829 | 8.349302 | 22.23 | 0.1 | 21.85 | 0.11 | N/A | N/A | | AGN | 2292763 | AT2025gex | 146.071329 | 11.839902 | 21.89 | 0.11 | 21.92 | 0.12 | 21.05 | 0.1 | The DECam Search & Discovery Program for Optical Signatures of Gravitational Wave Events (DESGW) is carried out by the Dark Energy Survey (DES) collaboration in partnership with wide-ranging groups in the community. DESGW uses data obtained with the Dark Energy Camera (DECam), which was constructed by the DES collaboration with support from the Department of Energy and member institutions, and utilizes data as distributed by the Science Data Archive at NOIRLAB. NOIRLAB is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. We thank the Cerro Tololo observatory staff for their support in acquiring these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39934. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37952] GRB 250327B: ALMA detection
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39933 SUBJECT: GRB 250327B: ALMA detection DATE: 25/03/29 21:34:47 GMT FROM: Tanmoy Laskar at U of Utah <tanmoylaskar(a)gmail.com> T. Laskar (University of Utah), N. Franz, C. Christy, K. D. Alexander (University of Arizona), E. Berger (Harvard University), R. Chornock (UC Berkeley), W. Fong (Northwestern University), R. Margutti (UC Berkeley), P. Schady (University of Bath), and G. Schroeder (Cornell University), report on behalf of a larger collaboration: “We observed GRB 250327B (Bouchet et al., GCN 39888) with the Atacama Large Millimeter/Submillimeter Array (ALMA) at 97.5 GHz beginning on 2025 March 29 at 01:45 UT (28.5 hours after the burst). Preliminary analysis reveals a mm source with flux density of ~ 0.5 mJy at position: RA (J2000) = 11:47:06.72 Dec (J2000) = +29:50:24.71 with an uncertainty of 0.05" in each coordinate. This is consistent with the X-ray position (Bouchet et al., GCN 39888; Page et al. GCN 39895), optical position (Moskvitin et al., GCN 39889; Xin et al., GCN 39890), and radio position (Christy et al., GCN 39932). We thank the JAO staff, AoD, P2G, and the entire ALMA team for their help with these observations." View this GCN Circular online at https://gcn.nasa.gov/circulars/39933. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37951] GRB 250327B: VLA detection
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39932 SUBJECT: GRB 250327B: VLA detection DATE: 25/03/29 21:32:49 GMT FROM: Tanmoy Laskar at U of Utah <tanmoylaskar(a)gmail.com> C. Christy, N. Franz (University of Arizona), T. Laskar (University of Utah), K. D. Alexander (University of Arizona), E. Berger (Harvard University), R. Chornock (UC Berkeley), W. Fong (Northwestern University), R. Margutti (UC Berkeley), P. Schady (University of Bath), and G. Schroeder (Cornell University), report on behalf of a larger collaboration: “We observed GRB 250327B (Bouchet et al., GCN 39888) with the Karl G. Jansky Very Large Array (VLA) at multiple frequencies beginning on 2025 March 29 at 03:00 UT (29.8 hours after the burst). In preliminary analysis, we detect a radio counterpart at 15.1 GHz with a flux density of ~0.2 mJy at the position: RA (J2000) = 11:47:06.72 +/- 0.08” Dec (J2000) = +29:50:24.89 +/- 0.05” This is consistent with the X-ray position (Bouchet et al., GCN 39888; Page et al. GCN 39895) and optical position (Moskvitin et al., GCN 39889; Xin et al., GCN 39890). Further observations are planned. We thank the VLA staff for scheduling and executing these observations.” View this GCN Circular online at https://gcn.nasa.gov/circulars/39932. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37950] GRB 250329B: SVOM/VT optical upper limit
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39931 SUBJECT: GRB 250329B: SVOM/VT optical upper limit DATE: 25/03/29 19:13:49 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L.P. Xin, H.L. Li, Y. L. Qiu, C. Wu, Z.H. Yao, Y. Xu, P.P. Zhang, J. Wang, Y.N. Ma, X.H. Han, H.B. Cai, J.Y. Wei, W.J. Xie (NAOC), Y.H. Cheng (SWIFAR, YNU), B.T. Wang (YNAO, CAS), J. T. Palmerio (CEA) report on behalf of the SVOM/VT team: SVOM performed a Target of Opportunity observation of GRB 250329B (Xie et al., GCN 39925), starting at 2025-03-29T15:00:16 UT, ~2.85 hours after the SVOM/Eclairs trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. No any source was detected in the stacked images within the errorbox of the X-ray Swift/XRT [source #1]( https://www.swift.ac.uk/SVOM/SVOM_FIELD00008/) . The 3 sigma limits in VT_R is 23.1 mag (AB) at the middle time of 4.0 hours after the burst. This result is consistent with the reports (Xin et al., GCN 39926, Chen et al., GCN 39929). Deeper or redder follow-ups are encouraged to investigate the nature of the burst. 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/39931. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37949] GRB 250329B: SVOM/VT optical upper limit
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39931 SUBJECT: GRB 250329B: SVOM/VT optical upper limit DATE: 25/03/29 19:13:49 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L.P. Xin, H.L. Li, Y. L. Qiu, C. Wu, Z.H. Yao, Y. Xu, P.P. Zhang, J. Wang, Y.N. Ma, X.H. Han, H.B. Cai, J.Y. Wei, W.J. Xie (NAOC), Y.H. Cheng (SWIFAR, YNU), B.T. Wang (YNAO, CAS), J. T. Palmerio (CEA) report on behalf of the SVOM/VT team: SVOM performed a Target of Opportunity observation of GRB 250329B (Xie et al., GCN 39925), starting at 2025-03-29T15:00:16 UT, ~2.85 hours after the SVOM/Eclairs trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. No any source was detected in the stacked images within the errorbox of the X-ray Swift/XRT [source #1]( https://www.swift.ac.uk/SVOM/SVOM_FIELD00008/) . The 3 sigma limits in VT_R is 23.1 mag (AB) at the middle time of 4.0 hours after the burst. This result is consistent with the reports (Xin et al., GCN 39926, Chen et al., GCN 39929). Deeper or redder follow-ups are encouraged to investigate the nature of the burst. 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/39931. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37948] GRB 250327B: SVOM/COLIBRÍ (F-GFT) Further Observations
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39930 SUBJECT: GRB 250327B: SVOM/COLIBRÍ (F-GFT) Further Observations DATE: 25/03/29 19:02:34 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Jean-Grégoire Ducoin (CPPM), Noémie Globus (UNAM), Camila Angulo (UNAM), Sarah Antier (OCA), Ramandeep Gill (UNAM), Stéphane Basa (LAM), William H. Lee (UNAM), Dalya Akl (AUS), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Hui Yang (IRAP) report: We observed the field of SVOM/ECLAIRs GRB 250327B (Bouchet et al. GCN Circ. 39888) 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 50 minutes of exposure in the i filter from 2025-03-29 03:49 and 11:32 (44.3 and 52.0 hours after the trigger). Our observations were not continuous, but rather were at the start and end of this interval with a long interruption for observations of other sources. We observed through thick clouds. 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. At the position of the previously reported optical transient (Moskvitin et al., GCN Circ. 39889; Xin et al., GCN Circ. 39890; O’Neill et al., GCN Circ. 39891; Malesani et al., GCN Circ. 39893; Lian et al., GCN Circ. 39894; Page et al., GCN Circ. 39895; Shrestha et al., GCN Circ. 39896; Perley & Bochenek, GCN Circ. 39902; Kumar et al., GCN Circ. 39904; Dennefeld et al., GCN Circ. 39905; Pankov et al., GCN Circ. 39906; Pérez-Fournon et al., GCN Circ. 39912; Tarasenkov et al., GCN Circ. 39913; Mo et al., GCN Circ. 39914), we detect a source with i = 22.23 +/- 0.15. Compared to our previous observation at about 7.65 hours after the trigger, the temporal decay index is about -1.0. We acknowledge the excellent support of the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and thank the COLIBRÍ and DDRAGO engineering teams. View this GCN Circular online at https://gcn.nasa.gov/circulars/39930. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37947] GRB 250329B: 1.6m Mephisto Optical Upper Limits
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39929 SUBJECT: GRB 250329B: 1.6m Mephisto Optical Upper Limits DATE: 25/03/29 18:00:42 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn> Xinlei Chen, Brajesh Kumar, Jianhui Lian, Xufeng Zhu, Fanchuan Kong, Yaosong Yu, Yu Pan, Xingzhu Zou, Guowang Du, Yuan Fang, Jinghua Zhang, Tao Wang, Helong Guo, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team: We observed the field of SVOM/ECLAIRs-detected GRB 250329B (Xie et al., GCN 39925) with 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Simultaneous uvgriz band observations were started from 2025-03-29 UT13:29:03 (~1.3 hr after the trigger) and multiple frames with different exposure times were taken under moderate sky conditions. In our stacked images, no new optical source was detected, consistent with Xin et al. (GCN 39926). The 5-sigma limiting magnitudes in different bands are below: Start_Time(UT) | Band | Exp(s) | LimMag(AB) ---------------------|------|--------------|------------ 2025-03-29T13:29:05 | u | 180*2, 300*2 | >19.93 2025-03-29T13:43:31 | v | 180*1, 300*2 | >19.76 2025-03-29T13:29:04 | g | 50*6, 300*2 | >20.58 2025-03-29T13:43:30 | r | 50*3, 300*2 | >20.55 2025-03-29T13:29:03 | i | 79*4, 300*2 | >20.68 2025-03-29T13:43:30 | z | 79*2, 300*2 | >19.65 ------------------------------------------------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21. ------------------------------------------------------------------------------------------------- View this GCN Circular online at https://gcn.nasa.gov/circulars/39929. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37946] LIGO/Virgo/KAGRA S250329fl: 2 counterpart neutrino candidate events from an IceCube neutrino search
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39928 SUBJECT: LIGO/Virgo/KAGRA S250329fl: 2 counterpart neutrino candidate events from an IceCube neutrino search DATE: 25/03/29 16:53:25 GMT FROM: Zsuzsa Marka at IceCube/Columbia University <zsuzsa(a)astro.columbia.edu> IceCube Collaboration (http://icecube.wisc.edu/) reports: We have performed a search for track-like muon neutrino candidate events detected by IceCube consistent with the sky localization of the low-significance gravitational-wave candidate event S250329fl in a time range of 1000 seconds centered on the alert event time (2025-03-29T14:58:44.29 UTC to 2025-03-29T15:15:24.29 UTC) [1,2]. During this time period, IceCube was collecting good quality data. A single hypothesis test was conducted using a Bayesian approach to quantify the joint GW + neutrino event significance, which assumes a binary merger scenario and accounts for known astrophysical priors, such as GW source distance, in the statistical significance estimation [3]. Two track-like events were found in spatial and temporal coincidence with the gravitational-wave candidate S250329fl calculated from the map circulated in the S250329fl-2-Preliminary notice. This represents an overall p-value of 5.05e-05 for the Bayesian search. The p-value measures the consistency of the observed track-like events with the known atmospheric backgrounds for this single map (not accounting for statistical trials from multiple GW events). Further details are available at https://gcn.nasa.gov/missions/icecube and at https://roc.icecube.wisc.edu/public/LvkNuTrackSearch. Properties of the coincident events are shown below: dt(s) RA(deg) Dec(deg) Angular uncertainty(deg) p-value(Bayesian) ------------------------------------------------------------------------------------- 390.16 279.03 -49.69 0.98 0.0000505 153.42 87.16 47.51 4.07 0.0915 where: dt = Time of track event minus time of GW trigger (sec) Angular uncertainty = Angular uncertainty of track event: the radius of a circle representing 90% CL containment by area. p-value = the p-value for this specific track event from this search. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu [1] M. G. Aartsen et al 2020 ApJL 898 L10 [2] Abbasi et al. Astrophys.J. 944 (2023) 1, 80 [3] I. Bartos et al. 2019 Phys. Rev. D 100, 083017 View this GCN Circular online at https://gcn.nasa.gov/circulars/39928. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37945] GRB250329A: REM optical afterglow detection
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39927 SUBJECT: GRB250329A: REM optical afterglow detection DATE: 25/03/29 16:25:26 GMT FROM: Matteo Ferro at INAF-OAB <matteo.ferro(a)inaf.it> M. Ferro, R. Brivio, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB), and A. Melandri (INAF-OAR) report on behalf of the REM team: We observed the field of GRB250329A (Wang et al., GCN 39916) with the REM 60cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, K bands, starting on 2025 March 29 at 04:19:30 UT (i.e. 96 s after the SVOM trigger), and lasting for about 3 hours. From preliminary photometry we detect the counterpart in the optical images at the position of the optical afterglow (Watson et al., GCN 39915; Wang et al., GCN 39917; Schneider et al., GCN 39918; Ghosh et al., GCN 39922) with the following magnitude: r = 17.2 +/- 0.1 (AB; calibrated against the Pan-STARRS catalogue) at a mid-time of t - t0 = 165 s after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/39927. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37944] GRB 250329B: GWAC-F50A optical upper limit
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39926 SUBJECT: GRB 250329B: GWAC-F50A optical upper limit DATE: 25/03/29 13:31:32 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin(NAOC), Y. G. Yang(HNU), X. H. Han, C. WU, Y. L. Qiu, J. Wang, H. L. Li, X .M. Lu, R. S. Zhang, Y. Xu, L. Huang, H. B. Cai, Y. J. Xiao, P. P. Zhang, L. Lan, W. J. Xie, Z. H. Yao, J. Y. Wei(NAOC), X. G. Wang, E. W. Liang(GXU) report on behalf of the SVOM/F50A team: We began to observe GRB 250328A (Xie et al., GCN 39925) with 50cm telescope (GWAC-F50A) at Xinglong station, China, at 2025-03-29T12:27:17.58 (UT), about 7.0 min after the burst. With the first observations with exposure time of 4*100 sec, no any uncatalogued source was detected in our stacked image down to a 3 sigma limit magnitude of 18.5 mag in R band, at the mid time of 10.3 min after the burst, comparing to several nearby USNO B1.0 stars. Further observations are ongoing. We acknowledge the excellent support from observation assistant Yangtong Zheng and Winlong Dong. View this GCN Circular online at https://gcn.nasa.gov/circulars/39926. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37943] GRB 250329B: SVOM detection of a faint transient
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39925 SUBJECT: GRB 250329B: SVOM detection of a faint transient DATE: 25/03/29 13:24:22 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> W.J. Xie (NAOC), Y.H. Cheng (SWIFAR, YNU), B.T. Wang (YNAO, CAS), O. Godet, S. Guillot (IRAP), S. Schanne (CEA), M. Brunet (IRAP) on behalf of the SVOM mission team. SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250329B (SVOM burst-id sb25032902) starting at 2025-03-29T12:10:18 UTC (Tb). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected by the Image Trigger (IMT), which produced a sequence of 2 alerts. IMT provided the alert with the best signal-to-noise-ratio (SNR) of 7.33 in the 8-120 keV energy band over a time window of 40.96 seconds starting at Tb. The localization of the best alert is R.A., Dec 207.6731, 52.8853 degrees: RA (J2000) = 13h50m41.55s Dec (J2000) = 52d53m07.02s with a 90% C.L. radius of 10.69 arcmin (including systematic error of 2 arcmin added in quadrature). No immediate slew was performed on this burst, because its significance was below the slew threshold. A SVOM ToO will be performed. 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. The Burst Advocate (BA) on shift for this burst is Wenjin XIE: xiewj(a)bao.ac.cn. Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/39925. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37942] GRB 250329A: Swift-XRT afterglow detection
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39924 SUBJECT: GRB 250329A: Swift-XRT afterglow detection DATE: 25/03/29 12:53:30 GMT FROM: P.A. Evans at U. Leicester <pae9(a)leicester.ac.uk> S. Dichiara (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: We have analysed 1.6 ks of XRT data for the SVOM/ECLAIRs-detected burst GRB 250329A, from 6.8 ks to 13.1 ks after the SVOM/ECLAIRs trigger. The data are entirely in Photon Counting (PC) mode. Using 1005 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 197.44646, +9.49619 which is equivalent to: RA (J2000): 13h 09m 47.15s Dec(J2000): +09d 29' 46.3" with an uncertainty of 4.7 arcsec (radius, 90% confidence). This position is 51 arcsec from the SVOM/ECLAIRs position, and 3.3 arcsec from the optical candidate first reported by Watson et al., (GCN. Circ 39915). The source has a mean count rate of 3.0e-02 ct/sec and shows weak (1.4-sigma) indications of fading. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00019666. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39924. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37941] GRB 250328A: SVOM/VT optical observation
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39923 SUBJECT: GRB 250328A: SVOM/VT optical observation DATE: 25/03/29 12:50:45 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L.P. Xin, Y. L. Qiu, C. Wu, J. Wang, W.J. Xie, Z. H. Yao, Y. Xu, P. P. Zhang, X. H. Han, Y. J. Xiao, H. B. Cai, J. Y. Wei (NAOC)，M. Brunet, J. Malzac (IRAP) report on behalf of the SVOM team: SVOM performed a ToO observation on the burst triggered by SVOM/ECLAIRs (Brunet et al., GCN 39910). SVOM/VT began observing the field from about 2 hours to 7 hours after the burst in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X band downlinked data, the candidate reported (Schneider et al., GCN 39919, Schneider et al., GCN 39920) was clearly detected in stack images in both channels. The magnitudes are: VT_R=21.7+/- 0.1 mag(AB) and VT_B=22.0+/0.1 mag(AB) with the mid time of 4.85 hours after the burst. The photometry has not been corrected for the Galactic extinction. No any significant fading with larger than 0.2 mag during our observations was found. Further observations are ongoing. 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/39923. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37940] GRB 250329A: Fading optical counterpart detection by LCO.
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39922 SUBJECT: GRB 250329A: Fading optical counterpart detection by LCO. DATE: 25/03/29 11:20:41 GMT FROM: ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994(a)gmail.com> Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Rahul Gupta (NASA GSFC), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES) on behalf of a larger collaboration. We observed the field of the GRB 250329A triggered by the SVOM/ECLAIRs (Wang et al., GCN 39916) in the B, V filter of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at McDonald Observatory. The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel). Observations began on March 29, 2025, starting 1.49 hours after the GRB trigger. We clearly detect the optical transient (OT) reported by GCNs (Watson et al., GCN 39915, Wang et al. GCN 39917, Schneider et al., GCN 39918) in our B, V band image. -------------------------------------------------------------------------------------------------- |Date| |UTstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| -------------------------------------------------------------------------------------------------- 2025-03-21 05:46:30.432 1.49 1 x 600 B B = 22.28 +/- 0.08 2025-03-21 05:47:59.424 1.51 3 x 300 V V = 21.95 +/- 0.16 -------------------------------------------------------------------------------------------------- The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/39922. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37939] GRB 250328A: SVOM/C-GFT optical upper limit
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39921 SUBJECT: GRB 250328A: SVOM/C-GFT optical upper limit DATE: 25/03/29 11:16:01 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Zhe Kang (CHO), J. Malzac(OMP)，M. Brunet(OMP), Liping Xin(NAOC), Xuhui Han(NAOC), Chao WU (NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei, Qiu(NAOC), Jing Wang(NAOC), Jianyan Wei (NAOC) report on behalf of the SVOM/C-GFT team: We observed the field of GRB 250328A detected by SVOM/ECLAIRs (sb25032803) with C-GFT. Our observations were started on 2025-03-28T17:14:26 UTC, ~17.50 mins fter the trigger. A series of g, r, and i-band images were obtained. No uncataloged optical counterpart candidates were detected within the SVOM/ECLARIRS source error circle (GCN 39910). Additionally, no sources were detected at the positions of the Swift/XRT Source #2 and the location reported by Schneider et al. (GCN 39919) and Schneider et al. (GCN 3920) in our coadded images. The upper limit magnitudes(3sigma) are, (T-T0)_mid(mins) upper_limit(3sigma) band ---------------------------------------------------------------- 22.65 >20.00 i 24.15 >20.20 g 25.63 >20.11 r The photometry was calibrated with UCAC4 catalog. This result is consistent with the report from Xin et al.(39911). We thank the observation assistants Bowen Li at Jilin observatory for their excellent support. Chinese Ground Follow-up Telescope of SVOM mission is located at Jilin, Changchun Observatory, National Astronomical Observatories, CAS. It has FOV of 1.28 deg x 1.28 deg with a 4k*4k CMOS detector mounted on the primary focus of 1.2-meter-aperure telescope. View this GCN Circular online at https://gcn.nasa.gov/circulars/39921. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37938] GRB 250328A: SVOM/COLIBRÍ (F-GFT) optical afterglow candidate
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39920 SUBJECT: GRB 250328A: SVOM/COLIBRÍ (F-GFT) optical afterglow candidate DATE: 25/03/29 11:09:27 GMT FROM: COLIBRI at COLIBRI Consortium <gcn(a)colibri-obs.org> Benjamin Schneider (LAM), Jean-Grégoire Ducoin (CPPM), Sarah Antier (OCA/IJCLAB), Ramandeep Gill (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Francesco Magnani (CPPM), Diego López-Cámara (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Antonio de Ugarte Postigo (LAM) report: We observed the field of the SVOM/ECLAIRs GRB 250328A (Brunet et al., GCN 39910) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (F-GFT) telescope. We obtained 50 min of exposures in the i-band starting at 06:57:58 UT on 2025-03-29 (14.0 hr after the SVOM trigger). In the stacked image, we detect a source at the near-infrared afterglow candidate position reported by Schneider et al., GCN 39919 and consistent with the XRT source #2. At that position, no source is visible either in the PanSTARRS survey or the Legacy Survey. The preliminary magnitude derived for that source is i = 22.04 +/- 0.24 mag (AB). The data were coadded with the Colibri pipeline and analyzed with STDWeb/STDPipe (Karpov 2021). The photometric calibration was performed using nearby stars from the PanSTARRS 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/39920. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37937] GRB 250328A: VLT/HAWK-I near-infrared afterglow candidate
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39919 SUBJECT: GRB 250328A: VLT/HAWK-I near-infrared afterglow candidate DATE: 25/03/29 09:37:08 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> B. Schneider (LAM), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), G. Corcoran (UCD), report on behalf of the Stargate collaboration: We observed the location of the SVOM/ECLAIRs GRB 250328A (Brunet et al., GCN 39910) using the ESO/VLT UT4 (Yepun) equipped with the HAWK-I camera. Observations started on March 29 at 07:13:31 UT (14.3 hr after the SVOM trigger). A series of 15 images of 60 s were obtained in the J-band. Consistent with the location of the X-ray Swift/XRT [source #2](https://www.swift.ac.uk/SVOM/SVOM_FIELD00006/), we detect an object which is not visible in the Legacy Survey, at coordinates: RA(J2000) = 14:23:50.41 = 215.9601 Dec(J2000) = +25:55:55.0 = +25.9319 We measure J = 21.9 +/- 0.1 (AB) calibrated against nearby stars in the 2MASS catalogue. This object is a viable afterglow candidate for GRB 250328A, although we note that we lack deep enough reference imaging in the J band, and the X-ray light curve of XRT source #2 does not show obvious fading. Further observations are thus required to robustly confirm the nature of this NIR and X-ray source. We acknowledge excellent support from the ESO observing staff in Paranal. View this GCN Circular online at https://gcn.nasa.gov/circulars/39919. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37936] GRB 250329A: VLT/X-shooter redshift z = 2.921
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39918 SUBJECT: GRB 250329A: VLT/X-shooter redshift z = 2.921 DATE: 25/03/29 08:38:33 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> B. Schneider (LAM), G. Corcoran (UCD), E. Le Floc’h (CEA), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), N. R. Tanvir (Leicester), report on behalf of the Stargate collaboration: We observed the optical counterpart (Watson et al., GCN 39915, Wang et al. GCN 39917) of the SVOM/ECLAIRs GRB 250329A (Wang et al., GCN 39916) using the ESO/VLT UT3 (Melipal) equipped with the X-shooter spectrograph. In a 10-s r-band exposure taken with the acquisition camera (1.58 hr after the SVOM trigger), a source is well detected at the location of the counterpart reported by Watson et al., GCN 39915 with a magnitude r = 21.9 +/- 0.1 (AB, calibrated against a single Pan-STARRS object). Our measurement is consistent with Wang et al. GCN 39917 and confirms the fast fading nature of this source and its likely association with GRB 250329A. Our spectra, covering the wavelength range 3000-21000 AA, consist of 4 exposures of 600 s each. The observation mid time was on 2025 Mar 29.2611 UT (1.97 hr after the SVOM trigger). In a preliminary reduction of the spectra, a break is visible at ~4775 AA, which we identify as due to HI Lyman-alpha absorption. From the detection of multiple narrow absorption features, including OI, Si II, C II, Si IV, C IV, Fe II, Al II, Al III, Mg I, Ni II*, Fe II*, Mg II, Ca II, we infer a redshift of z = 2.921. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Martina Baratella, Felipe Gaete, Rob van Holstein, and Vincent Megevand. We would like to thank especially the two visitors at UT3, Helmut Wiesemeyer and Mario van den Ancker for their patience while our observation was being taken. View this GCN Circular online at https://gcn.nasa.gov/circulars/39918. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37935] GRB 250329A: SVOM/VT optical counterpart confirmation
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39917 SUBJECT: GRB 250329A: SVOM/VT optical counterpart confirmation DATE: 25/03/29 08:01:15 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> B.-T. Wang (YNAO, CAS), Y.H. Cheng (SWIFAR, YNU), W.J. Xie, L.P. Xin, Y. L. Qiu, H. L. Li, C. Wu (NAOC), J. T. Palmerio(CEA/Irfu), Z. H. Yao, Y. Xu, P. P. Zhang, J. Wang, X. H. Han, Y. J. Xiao, H. B. Cai, J. Y. Wei (NAOC) report on behalf of the SVOM team: SVOM performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Wang et al., GCN 39916). SVOM/VT began observing the field automatically with the slew of the platform triggered on-board, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With VHF downlinked data, an uncatalogued source was found in VT_R channel, and fading for about 0.4 mag in the third and fourth sequences. The coordinates are R.A (J2000) =13:09:47.23 (197.44674 deg) DEC.(J2000) = +09:29:43.2 (+9.49532 deg) Error=0.5 arcseconds. The coordinates are consistent with the candidate reported (Watson et al., GCN 39915). The magnitude is VT_R=20.1+/- 0.04 mag(AB) and VT_B>22.0 mag(AB,3sigma) with the mid time of 1.25 hours after the burst. We propose it is possible a medium/high redshift GRB, given on red coulor (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/39917. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37934] GRB 250329A: SVOM detection of a burst
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39916 SUBJECT: GRB 250329A: SVOM detection of a burst DATE: 25/03/29 05:34:15 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> B.-T.Wang(YNAO, CAS), Y.H. Cheng (SWIFAR, YNU), W.J. Xie, D.H. Zhao (NAOC), C.W. Wang (IHEP), and D. Götz (CEA) on behalf of the SVOM mission team. At 2025-03-29T04:17:54 UTC (Tb) SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250329A (SVOM burst-id sb25032901). 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 Count-Rate Trigger (CRT), which produced a sequence of 17 alerts. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 37.28 in the [8-50] keV energy band over a time window of 5.10 seconds starting at Tb. The localization of the best alert is R.A., Dec 197.4374, 9.4849 degrees (J2000) with a 90% C.L.radius of 2.88 arcmin (including systematic error of 2 arcmin added in quadrature). The burst was also detected by GRM. The GRM light curve shows that this burst consists of a single main pulse. The SVOM/GRM lightcurve can be found here: https://www.bursthub.cn//admin/static/svgrb250329A.png SVOM slewed to the burst position. MXT began observing the field at 2025-03-29T04:20:20 UTC, 146 seconds after Tb. Using onboard processed data we found a faint uncatalogued X-ray source located at R.A., Dec 197.4168, 9.5412 degrees: RA (J2000) = 13h09m40s DEC (J2000) = 9d32m28s with a 90% C.L. radius of 2.5 arc minutes. This location is 3.59 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments. 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. The Burst Advocate (BA) on shift for this burst is Boting Wang: wangbaiting(a)ynao.ac.cn. Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/39916. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37933] GRB 250329A: SVOM/COLIBRÍ (F-GFT) Detection of a Bright Optical Counterpart Candidate
by GCN Circulars 29 Mar '25

29 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39915 SUBJECT: GRB 250329A: SVOM/COLIBRÍ (F-GFT) Detection of a Bright Optical Counterpart Candidate DATE: 25/03/29 05:20:22 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Alan M. Watson (UNAM), Ramandeep Gill (UNAM), Sarah Antier (OCA/IJCLAB), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Francesco Magnani (CPPM), Diego López-Cámara (UNAM), Benjamin Schneider (LAM), Dalya Akl (AUS), Camila Angulo (UNAM), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the SVOM/ECLAIRs GRB 250329A (sb25032901) with the DDRAGO wide-field imager on the SVOM/COLIBRÍ (F-GFT) telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. We observed from 2025-03-29 04:18 to 04:55 UTC (55 to 2256 seconds after the trigger) and obtained 26 minutes of exposure in the i filter. The data were coadded with custom software and analyzed in STDWeb/STDPipe (Karpov 2024), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction. Within the SVOM/ECLAIRs error box, we detect a bright uncatalogued source at RA = 197.44679 and Dec = 9.49533 (J2000) with a magnitude of i = 17.91 +/- 0.03 Further observations are planned. We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/39915. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37932] GRB 250327B: J-band observations with WINTER
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39914 SUBJECT: GRB 250327B: J-band observations with WINTER DATE: 25/03/28 20:44:14 GMT FROM: Geoffrey Mo at MIT <gmo(a)mit.edu> Geoffrey Mo (MIT), Benjamin Schneider (LAM), Tomas Ahumada (Caltech), Danielle Frostig (CfA), Viraj Karambelkar (Caltech), Robert Stein (UMD), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 250327B (Bouchet et al., GCN 39888) in the near-infrared J-band with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began under poor weather conditions at 2025-03-28T10:04:53 UTC (12.9 hours after the GRB), consisting of 13 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565). We do not detect a source at the optical and X-ray counterpart location (Moskvitin et al., GCN 39889; Xin et al., GCN 39890; O’Neill et al., GCN 39891; Malesani et al., GCN 39893; Lian et al., GCN 39894; Page et al., GCN 39895; Shrestha et al., GCN 39896; Duncoin et al., GCN 39897; Perley et al., GCN 39902; Kumar et al., GCN 39904; Dennefeld et al., GCN 39905; Pankov et al., GCN 39906; Pérez-Fournon et al., GCN 39912). We obtain the following 5-sigma upper limit: J ~ 17.5 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/39914. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37931] GRB 250327B: MASTER detection of OT rebrightening
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39913 SUBJECT: GRB 250327B: MASTER detection of OT rebrightening DATE: 25/03/28 20:43:27 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> A.Tarasenkov, V.Lipunov, A.Kuznetsov, G.Antipov, K..Zhirkov, P.Balanutsa, N.Tyurina, E.Gorbovskoy, Ya.Kechin, A.Chasovnikov, V.Topolev, V.Senik, K.Labzina (Lomonosov MSU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), D.Buckley (SAAO), A.Sosnovskij (Crao RAS), O.Gress, N.Budnev, O.Ershova (ISU), 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,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, started SVOM GRB 250327B (Bouchet et al. GCN 39888, Ttrigger=2025-03-27T21:11:27UT) at 2025-03-28 06:46:31UT with mlim=21m at 600s summary exposition. There is optical source with m_OT=19.9 +-0.3m(by GAIA reference stars) at two single images and at summary one at Moskvitin et al. (GCN 39889) position (also observed by SVOM/VT (GCN 39890), GOTO (GCN 398901), NOT (39893), Mephisto (GCN 39894), LCOGT (GCN 39896, GCN 39912, GCN 39904), COLIBRI (GCN 39897), LT (GCN 39902), OHP (GCN 39905), CrAO/SAORAS (GCN 39906)). that means rebrightening 9.5h after trigger time This message may by cited View this GCN Circular online at https://gcn.nasa.gov/circulars/39913. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37930] GRB 250327B: LCO optical counterpart detection
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39912 SUBJECT: GRB 250327B: LCO optical counterpart detection DATE: 25/03/28 18:04:55 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, I. Correa-Plasencia, A.E. Hernández-Díaz (ULL), and A. López-Oramas (IAC and ULL) We report Las Cumbres Observatory Global Telescope network (LCOGT) observations of GRB 250327B, detected by SVOM ECLAIRs and MXT (Bouchet et al., GCN circ. 39888) and VT (Xin et al., GCN circ. 39890) and Swift XRT (Page et al., GCN circ. 39895) at a redshift of z = 3.035 (Malesani et. al, GCN circ. 39893; Dennefeld et al., GCN circ. 39905). We observed the field of GRB 250327B with the two LCOGT 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Teide Observatory (Tenerife, Spain) in the SDSS r, g, and i filters, starting at 2025-03-27 23:55:43 UT, about 2.74 hours after the SVOM trigger. An uncatalogued source is clearly detected at the position of the optical counterpart reported by Moskvitin et al., GCN circ. 39889; Xin et al., GCN circ. 39890; O’Neill et al., GCN circ. 39891; Malesani et al., GCN circ. 39893; Lian et al., GCN circ. 39894; Shrestha et al., GCN circ. 39896; Ducoin et al., GCN circ. 39897; Perley and Bochenek, GCN circ. 39902; Kumar et al., GCN circ. 39904; Dennefeld et al., GCN circ. 39905; and Pankov et al., GCN circ. 39906). We measure the following magnitudes, calibrated against Pan-STARRS DR2 stars and not corrected for Galactic extinction: Date | UT start | mag | error | filter | exposure time (sec) --------------------------------------------------------------------- 2025-03-27 23:55:43 18.24 0.02 r 180 2025-03-28 00:31:11 20.07 0.06 g 180 2025-03-28 00:34:41 18.19 0.04 i 180 2025-03-28 02:12:57 18.79 0.06 i 180 2025-03-28 03:04:23 19.35 0.05 r 300 2025-03-28 03:09:13 21.25 0.14 g 180 This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF). View this GCN Circular online at https://gcn.nasa.gov/circulars/39912. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37929] GRB 250328A: GWAC-F50A optical upper limit
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39911 SUBJECT: GRB 250328A: GWAC-F50A optical upper limit DATE: 25/03/28 17:58:43 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin(NAOC), Y. G. Yang(HNU), X. H. Han, C. WU, Y. L. Qiu, J. Wang, H. L. Li, X .M. Lu, R. S. Zhang, Y. Xu, L. Huang, H. B. Cai, Y. J. Xiao, P. P. Zhang, L. Lan, W. J. Xie, Z. H. Yao, J. Y. Wei(NAOC), X. G. Wang, E. W. Liang(GXU) report on behalf of the SVOM/F50A team: We began to observe GRB 250328A (Brunet et al., GCN 39910) with 50cm telescope (GWAC-F50A) at Xinglong station, China, at 2025-03-28T16:59:19 (UT), about 145s after the burst. With the first observations with exposure time of 6*100 sec, no any uncatalogued source was detected in our stacked image down to a 3 sigma limit magnitude of 19.0 mag in R band, at the mid time of 7.5 min after the burst, comparing to several nearby USNO B1.0 stars. We acknowledge the excellent support from observation assistant Yangtong Zheng and Winlong Dong. View this GCN Circular online at https://gcn.nasa.gov/circulars/39911. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37928] GRB 250328A: SVOM detection of a burst
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39910 SUBJECT: GRB 250328A: SVOM detection of a burst DATE: 25/03/28 17:32:16 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, J. Malzac, L. Bouchet, O. Godet (IRAP), C. Plasse (CEA), L.P. Xin (NAOC) on behalf of the SVOM mission team. SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250328A (SVOM burst-id sb25032803) starting at 2025-03-28T16:56:56.3 UTC (Tb). 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 Count-Rate Trigger (CRT), which produced a sequence of 1 alerts. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 6.85 in the [8-120] keV energy band over a time window of 20.48 seconds starting at Tb. The light curve showed a single structure with a duration of about 15s The localization of the best alert is R.A., Dec 215.9771, 25.8825 degrees: RA (J2000) = 14h23m54.51s Dec (J2000) = 25d52m56.83s with a 90% C.L. radius of 11.42 arcmin (including systematic error of 2 arcmin added in quadrature). No immediate slew was performed on this burst, because its significance was below the slew threshold. A SVOM ToO will be performed. 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. The Burst Advocate (BA) on shift for this burst is Marius Brunet: marius.brunet(a)irap.omp.eu. Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/39910. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37927] FRB 20250316A: FTW optical observations
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39909 SUBJECT: FRB 20250316A: FTW optical observations DATE: 25/03/28 16:50:28 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann, Jennifer Fabà, Daniel Gruen, Mathias Mucke, Xiaoxiong Zuo (LMU), Brendan O'Connor, and Antonella Palmese (CMU) report on behalf of a larger collaboration: We observed the localization of FRB 20250316A (Ng et al., ATel #17081; Andrew et al., GCN 39886). With the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the g and i band on multiple nights. Observations started 2.53d after the FRB or 5.8h after the discovery of an uncataloged X-ray source EP J120944.2+585060 by Einstein Probe (GCN 39834). | Time (UT) | t - t0 (d) | Band | Exposures | Depth (3 sigma, AB mag) | Depth Diff (3 sigma, AB mag) | |---------------------|------------|------|-----------|-------------------------|------------------------------| | 2025-03-18T21:14:03 | 2.53 | g | 10x 180 s | 24.3 | Used as Reference | | 2025-03-18T21:14:03 | 2.53 | i | 10x 180 s | 23.7 | Used as Reference | | 2025-03-22T20:05:28 | 6.48 | g | 16x 180 s | 21.9 | - | | 2025-03-22T20:05:28 | 6.48 | i | 16x 180 s | 21.6 | - | | 2025-03-23T23:11:05 | 7.61 | g | 15x 180 s | 24.4 | 23.5 | | 2025-03-23T23:11:05 | 7.61 | i | 15x 180 s | 23.8 | 23.0 | | 2025-03-28T03:33:48 | 11.79 | g | 10x 180 s | 23.0 | 22.9 | | 2025-03-28T03:33:48 | 11.79 | i | 10x 180 s | 22.5 | 22.5 | We performed difference imaging against templates from the LegacySurvey (g) and PS1 (i). We also used our first observation as a template and do not detect any excess flux at the FRB location in either case. This is consistent with the observations of Becerra et al. (ATel #17082, GCN 39843, 39853), Niino et al.(ATel #17084), Hashimoto (ATel #17095), Yang et al. (ATel #17101), Troja et al. (ATel #17109, GCN 39869), Dong et al. (ATel #17112), Aryan et al. (GCN 39839), Pereyra et al. (GCN 39858), Jiang et al. (GCN 39864), Gillanders et al. (GCN 39883), and Simha et al. (ATel #17116, GCN 39887). The magnitudes are calibrated against the PS1 catalog and are not corrected for galactic extinction. We thank Christoph Ries and Michael Schmidt from the Wendelstein Observatory staff for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39909. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37926] LIGO/Virgo/KAGRA S250328ae: NED Galaxies in the 4-Update Localization Volume
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39908 SUBJECT: LIGO/Virgo/KAGRA S250328ae: NED Galaxies in the 4-Update Localization Volume DATE: 25/03/28 15:33:03 GMT FROM: David Cook at Caltech/IPAC-NED <dcook(a)ipac.caltech.edu> David O. Cook (Caltech/IPAC), Rick Ebert (Caltech/IPAC), George Helou (Caltech/IPAC), Joseph M. Mazzarella (Caltech/IPAC), Marion Schmitz (Caltech/IPAC), and Leo Singer (NASA/GSFC) On behalf of the NASA/IPAC Extragalactic Database (NED) Team. We spatially cross-matched the LVK S250328ae-4-Update sky localization with the NED Local Volume Sample (NED-LVS; Cook et al. 2023), which is a subset of NED with a redshift or redshift-independent distance less than 1000 Mpc. We find 839 galaxies within the 90% containment volume, and we list here the top 20 galaxies sorted by the joint probability of the 3D localization and the WISE W1 luminosity (an observable proxy for stellar mass). For the full or top 20 list of galaxies in the 90% volume go either to the NED Gravitational Wave Followup service at https://ned.ipac.caltech.edu/uri/NED::GWF/ or click on the following links: Full List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S250328ae/4 Top 20 List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S250328ae/4/20 The NED-GWF service provides downloadable galaxy lists and visualizations for candidate host galaxies. For each GW alert, these products are automatically generated and made available within minutes to expedite efficient electromagnetic follow-up observations. The NED top 20 list is sorted by the joint probability of the 3D localization and the WISE W1 luminosity, but users can sort on additional pre-computed prioritization metrics (star formation rate, P_3D * P_SFR; and specific star formation rate, P_3D * P_sSFR; etc.) which are available via downloading the entire galaxy list inside the event's probability volume. | objname| ra| dec|objtype| DistMpc|DistMpc_unc| m_NUV| m_NUV_unc| m_Ks| m_Ks_unc| m_W1| m_W1_unc| P_3D|P_3D_LumW1| |-------------------------|--------------|--------------|-------|-----------|-----------|------------|------------|------------|------------|------------|------------|--------|----------| |WISEA J094227.03+110047.4| 145.61266| 11.01318| G| 612.35| null| null| null| 12.661| 0.096| 10.577| 0.006|2.63e-06| 5.47e-08| |WISEA J093435.61+082700.3| 143.64838| 8.45010| G| 507.10| 0.11| null| null| 13.186| 0.203| 10.854| 0.006|3.85e-06| 4.28e-08| |WISEA J093458.83+094902.6| 143.74516| 9.81741| G| 564.56| 0.09| null| null| 14.250| 0.157| 10.944| 0.007|2.12e-06| 2.69e-08| |WISEA J093555.60+093752.8| 143.98169| 9.63134| G| 589.67| 0.08| null| null| 13.465| 0.202| 11.501| 0.007|2.87e-06| 2.37e-08| |WISEA J093938.05+110947.9| 144.90857| 11.16332| G| 482.07| 0.08| null| null| 13.597| 0.141| 12.972| 0.014|1.58e-05| 2.25e-08| |WISEA J094028.13+111733.4| 145.11722| 11.29263| G| 556.24| 0.11| null| null| 13.110| 0.111| 12.941| 0.015|9.93e-06| 1.94e-08| |WISEA J094035.77+103104.6| 145.14905| 10.51795| G| 495.66| 0.07| null| null| 13.045| 0.080| 12.298| 0.012|6.77e-06| 1.90e-08| |WISEA J093657.39+085125.0| 144.23916| 8.85696| G| 557.28| 0.06| null| null| null| null| 11.769| 0.007|3.22e-06| 1.86e-08| |WISEA J094109.87+105038.6| 145.29116| 10.84407| G| 439.67| 0.07| null| null| 12.109| 0.080| 12.120| 0.012|6.55e-06| 1.70e-08| |WISEA J094121.23+112617.1| 145.33849| 11.43811| G| 564.36| 0.09| null| null| 13.311| 0.123| 13.095| 0.017|9.76e-06| 1.70e-08| |WISEA J094025.05+111347.9| 145.10441| 11.23000| G| 557.91| 0.09| null| null| 13.243| 0.108| 13.078| 0.020|9.62e-06| 1.66e-08| |WISEA J093619.16+091944.6| 144.07983| 9.32906| G| 588.58| 0.11| null| null| 13.919| 0.167| 12.015| 0.007|3.16e-06| 1.62e-08| |WISEA J093619.13+091936.4| 144.07971| 9.32680| G| 591.85| 0.08| null| null| 12.365| 0.106| 12.060| 0.010|3.00e-06| 1.49e-08| |WISEA J093747.49+101024.7| 144.44789| 10.17354| G| 432.26| 0.05| null| null| 12.881| 0.108| 12.438| 0.013|7.81e-06| 1.46e-08| |WISEA J093417.20+081006.5| 143.57167| 8.16848| G| 347.36| 0.08| 21.156| 0.071| 13.681| 0.191| 10.002| 0.006|1.22e-06| 1.39e-08| |WISEA J094125.76+110548.3| 145.35737| 11.09678| G| 557.02| 0.07| null| null| 13.696| 0.126| 13.350| 0.021|9.58e-06| 1.28e-08| |WISEA J094051.38+102028.4| 145.21409| 10.34125| G| 444.19| 0.03| null| null| 15.275| 0.145| 12.091| 0.007|4.61e-06| 1.25e-08| |WISEA J094106.66+105024.2| 145.27777| 10.84008| G| 487.71| null| null| null| 14.219| 0.109| 13.198| 0.021|1.00e-05| 1.18e-08| |WISEA J093537.73+091115.6| 143.90721| 9.18768| G| 552.71| 0.11| null| null| 13.648| 0.222| 12.528| 0.013|4.10e-06| 1.16e-08| |WISEA J093620.06+092335.0| 144.08362| 9.39307| G| 582.84| 0.07| 20.401| 0.231| 13.508| 0.189| 12.534| 0.014|3.60e-06| 1.12e-08| Table 1: Top 20 galaxies in NED-LVS that fall in the 90% probability volume for S250328ae sorted by the joint probability of 3D position and WISE W1 luminosity (P_3D * P_LumW1). Galaxy is the NED preferred name. RA and Dec are the Equatorial coordinates in degrees (J2000). Objtype is the object type of the galaxy candidate. Distance is the distance to the galaxy in Mpc. m_NUV and mErr_NUV are the apparent magnitude and error from GALEX. m_Ks and mErr_Ks are the apparent magnitude and error from 2MASS. m_W1 and mErr_W1 are the apparent magnitude and error from AllWISE. P_3D is the probability that the galaxy is in the volume given the distance of GW event. P_3D_LumW1 is the joint probability within the volume weighted by the WISE1 luminosity of the galaxy (P_3D * P_LumW1). View this GCN Circular online at https://gcn.nasa.gov/circulars/39908. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37925] EP250302a: upper limit of SPI-ACS/INTEGRAL
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39907 SUBJECT: EP250302a: upper limit of SPI-ACS/INTEGRAL DATE: 25/03/28 13:40:48 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> P. Minaev (IKI), A. Pozanenko (IKI), S. Grebenev (IKI), I. Chelovekov (IKI) and IKI GRB-FuN We searched the INTEGRAL dataset for gamma-ray emission from the X-ray transient EP250302a, detected with WXT EP (Dai et al., GCN 39556). No significant excess above the background was detected during the EP250302a in any of the detectors. The source EP250302a is located 71 degrees off-axis of the INTEGRAL telescopes' field of view. In particular, for the SPI-ACS detector, the upper limit (3-sigma) for the fluence from an event with a duration of 100 sec (during the first and second EP250302a episodes) is 3.2e-6 erg*cm^-2 using the softest simulated CPL spectrum with Ep = 20 keV. The SPI-ACS estimating is based on the calibration given in the paper https://ui.adsabs.harvard.edu/abs/2023MNRAS.525.2411M We thank the INTEGRAL Observatory and all the staff who have served it for over 22 years. Blessed be the memory of its deeds. View this GCN Circular online at https://gcn.nasa.gov/circulars/39907. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37924] GRB 250327B: CrAO and SAO RAS Optical Observations
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39906 SUBJECT: GRB 250327B: CrAO and SAO RAS Optical Observations DATE: 25/03/28 13:37:10 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> N. Pankov (HSE, IKI), A. Moskvitin (SAO RAS), V. Rumyantsev (CrAO), O. I. Spiridonova (SAO RAS), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We performed optical observations of the field of GRB 250327A (Bouchet et. al, GCN 39888; Page et. al, GCN 39895) at the redshift of z = 3.035 (Malesani et. al, GCN 39893; Dennefeld et al., GCN 39905) with the 2.6-meter Shajn telescope (ZTSh) of the Crimean Astrophysical Observatory (CrAO) and the 1-meter Zeiss-1000 telescope of the Special Astrophysical Observatory of the RAS (SAO RAS). The observations started on (UT) 2025-03-27 22:24:22 at CrAO, i.e. about 0.05 days since GBM trigger. We obtained the series of frames in the VRI filters with ZTSh and the series of frames in the BVRI filters with Zeiss-1000. We clearly detect the bright optical afterglow (Moskvitin et. al, GCN 39889; Xin et. al, GCN 39890; O’Neill et. al, GCN 39891; Malesani et. al, GCN 39893; Lian et. al, GCN 39894; Shrestha et. al, GCN 39896; Ducoin et. al, GCN 39897; Perley & Bochenek, GCN 39902) in the images from both telescopes. The preliminary photometry of the afterglow in the end of each series is as follows: Date UT start t-T0 Exp. Filter OT Err Telescope (mid, days) (s) 2025-03-27 23:12:18 0.08410 30 I 16.45 0.07 ZTSh 2025-03-27 23:13:36 0.08500 30 R 17.15 0.08 ZTSh 2025-03-27 23:12:59 0.08457 30 V 17.80 0.10 ZTSh 2025-03-27 00:25:24 0.14229 4*300 Rc 18.22 0.05 Zeiss-1000 The photometry is based on nearby stars of USNO-B1.0 (R2 magnitudes; same as in Moskvitin et. al, GCN 39889) and has not been corrected for the Galactic extinction. Using the R-filter photometry between 0.01 and 0.1 days after trigger, we estimate a power law decay of the light curve to be alpha = -1.87 +/- 0.03. View this GCN Circular online at https://gcn.nasa.gov/circulars/39906. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37923] GRB 250327B: OHP/T193 spectroscopic observations and redshift confirmation
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39905 SUBJECT: GRB 250327B: OHP/T193 spectroscopic observations and redshift confirmation DATE: 25/03/28 12:49:52 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> M. Dennefeld (IAP/CNRS/Sorbonne U.), B. Schneider (LAM), C. Adami (LAM/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), A. Saccardi (CEA/Irfu), S. Vergani (CNRS, Obs. de Paris, LUX), S. Basa (Pytheas/OHP/LAM) report on behalf of the MISTRAL-GRB collaboration: We observed the SVOM/ECLAIRs GRB 250327B (Bouchet et al., GCN 39888) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager in red setting. We obtained 1x60 s in the r’, i’, z’ and Y bands starting at 22:44:30 UT on 2025-03-27 (T0+1.55 h after the trigger). The optical afterglow reported by Moskvitin et al. GCN 39889; Xin et al. GCN 39890; O’Neill et al. GCN 39891; Malesani et al. GCN 39893; Lian et al. GCN 39894; Shrestha et al. GCN 39896; Ducoin et al., GCN39897; Perley et al., GCN 39902; and Kumar et al., GCN 39904 is well detected at r = 17.25 +/- 0.05 mag (AB). The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitude is not corrected for Galactic extinction. In addition, we obtained 3x15 min of spectroscopic observations covering from 6400 to 9950 AA starting at 2025-03-27 22:52:55 UT (T0+1.69 h). In the stacked spectrum, we clearly detect multiple absorption features, which we interpret as being due to Si II, Si II*, C IV, Fe II, Fe II*, Al II, Al III, Mg I, Ni II* at a common redshift of z = 3.038 +/- 0.005. The detection of fine-structure lines robustly associates this system to the high-energy transient. This value is also consistent with the value reported by Malesani et al. (GCN 39893). We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Stéphane Favard. View this GCN Circular online at https://gcn.nasa.gov/circulars/39905. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37922] GRB 250327B: further optical observations by LCOGT
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39904 SUBJECT: GRB 250327B: further optical observations by LCOGT DATE: 25/03/28 12:22:25 GMT FROM: Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK <amitkundu515(a)gmail.com> Amit Kumar (RHUL/Warwick), Raya Dastidar (UNAB), Giuliano Pignata (UTA), Danny Steeghs, Thomas Killestein (Warwick), David O’Neill (Birmingham), Jonathan Andrés Pineda García (UNAB) and Mauricio Ramirez (UNAB) report on behalf of the wider collaboration: We conducted optical follow-up observations of the optical counterpart to the SVOM/ECLAIRs-detected GRB 250327B (Bouchet et al., GCN 39888) using the LCOGT 0.4-m telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Teide Observatory, Tenerife, Spain, equipped with the SCICAM-QHY600 camera. Observations were carried out on 2025-03-28 between 02:18:54 UT and 03:34:29 UT, corresponding to approximately 5.1 to 6.4 hours post-burst. Each epoch comprised a series of 6 × 300 sec exposures in the B-band. In the stacked image, we clearly detect the optical counterpart with a B-band magnitude of ~21.9 ± 0.2. The detected position is consistent with the location of the optical counterpart reported by Moskvitin et al. GCN 39889 (a.k.a. GOTO25bhx, AT 2025gcz), with supporting detections from Xin et al. (GCN 39890), O’Neill et al. (GCN 39891), Malesani et al. (GCN 39893), Lian et al. (GCN 39894), Shrestha et al. (GCN 39896), Ducoin et al. (GCN 39897), and Perley & Bochenek (GCN 39902). The reported magnitude is calibrated against the USNO-B1 catalog and is not corrected for Galactic extinction in the direction of the event. Further analysis and follow-up observations are ongoing. This circular may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/39904. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37921] EP250315a: Pan-STARRS r and i-band imaging and photometry
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39903 SUBJECT: EP250315a: Pan-STARRS r and i-band imaging and photometry DATE: 25/03/28 10:04:31 GMT FROM: James Gillanders at University of Oxford <jhgillanders.astro(a)gmail.com> J. H. Gillanders (Oxford), M. Huber, K. C. Chambers (IfA, Univ. Hawaii), S. J. Smartt, K. W. Smith, S. Srivastav (Oxford), M. Nicholl, D. Young, M. Fulton (QUB), T.-W. Chen (NCU, Taiwan) A. S. B. Schultz, T. de Boer, J. Fairlamb, G. Paek, C. C. Lin, T. Lowe, E. Magnier, P. Minguez, I. A. Smith, R. J. Wainscoat (IfA, Univ. Hawaii). We observed the optical counterpart of EP250315a (Peng et al., GCN 39731; Quirola-Vasquez et al., GCN 39733), using the Pan-STARRS telescope system (Chambers et al., 2016, arXiv e-prints, 1612.05560) on MJD 60755.50 (2025-03-21 12:00 UTC), approximately 6.25 days after the EP-WXT detection (Peng et al., GCN 39731). The Pan-STARRS system consists of two 1.8m telescope units located at the summit of Haleakala on the Hawaiian island of Maui, employing an SDSS-like filter system denoted as grizy, and a broad w-filter, which is a composite of the gri-filters. Our observation consisted of 6x150s exposures in both the r and i filters with Pan-STARRS1. The images were processed with the Pan-STARRS pipeline. After astrometric and photometric calibration, reference images were subtracted from the target stacked images (Magnier et al., 2020a, ApJS, 251, 3; Magnier et al., 2020b, ApJS, 251, 6; Waters et al., 2020, ApJS, 251, 4). From these difference images, we do not detect the optical counterpart discovered by Quirola-Vasquez et al., GCN 39733. At the reported optical counterpart position, we measure 3.5-sigma limiting AB magnitudes of r~21.7 and i~21.7. View this GCN Circular online at https://gcn.nasa.gov/circulars/39903. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37920] GRB 250327b: Liverpool Telescope optical observations
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39902 SUBJECT: GRB 250327b: Liverpool Telescope optical observations DATE: 25/03/28 09:30:33 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> D. A. Perley and A.Bochenek (LJMU) report: We observed the field of GRB250327b (Bouchet et al., GCN 39888) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 1x100s exposures in the SDSS g, r, i, and z filters, starting at 2025-03-28 00:17:25 UT, approximately 3.1 hours after the trigger. We report a detection in all our images at the position of the optical counterpart (Moskvitin et al., GCN 39889), given in the table below. Our results agree with previous optical observations (Moskvitin et al. GCN 39889; Xin et al. GCN 39890; O’Neill et al. GCN 39891; Malesani et al. GCN 39893; Lian et al. GCN 39894; Shrestha et al. GCN 39896; Ducoin et al., GCN39897). MJD (mid) T_mid - T_0 Filter Mag. (AB) 60762.01268 3.11 hours r 18.47 ± 0.02 60762.01412 3.14 hours i 17.98 ± 0.04 60762.01556 3.18 hours g 19.87 ± 0.05 60762.01706 3.21 hours z 17.82 ± 0.06 The photometry was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/39902. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37919] GRB 250322A: GRANDMA/TNOT optical upper limits
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39901 SUBJECT: GRB 250322A: GRANDMA/TNOT optical upper limits DATE: 25/03/28 09:01:10 GMT FROM: duverne(a)apc.in2p3.fr E. Elhosseiny (NRIAG), N. Kochiashvili (AbAO), O. Pyshna (Caltech), Haichang Zhu (THU), A. Iskandar(XAO), Xiaofeng Wang (THU), Letian Wang (XAO) C. Andrade (UMN), S. Antier (OCA/IJCLAB), M. Coughlin (UMN), P-A. Duverne (APC), N. Guessoum (AUS), P. Hello (IJCLAB), S. Karpov (FZU), T. Pradier (Unistra/IPHC), D. Turpin (CEA-Saclay/Irfu) on behalf of the GRANDMA and Kilonova-Catcher collaborations: The field of GRB 250322A (Gupta et al., GCN 39835, Goad et al. GCN 39841, Perri et al. GCN 39855, Sadaula et al. GCN 39867) has been imaged with the 80~cm Tsinghua-Nanshan Optical Telescope (TNOT) located at Nanshan Station of Xinjiang Astronomy observatory 1.1h post trigger with the r' filter for a total exposure of 100s. We do not detect any new source at the enhanced Swift-XRT position (Goad et al. GCN 39841) down to r<21.2 AB mag (5-sigma) calibrated with nearby Pan-STARRS stars and without Galactic extinction correction. All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2025 Acta Polytechnica, 65(1), 50-64). We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/). View this GCN Circular online at https://gcn.nasa.gov/circulars/39901. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37918] LIGO/Virgo/KAGRA S250328ae: Updated Sky localization
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39900 SUBJECT: LIGO/Virgo/KAGRA S250328ae: Updated Sky localization DATE: 25/03/28 08:07:05 GMT FROM: Aaron Zimmerman at U. of Texas at Austin <aaron.zimmerman(a)utexas.edu> 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 S250328ae (GCN Circular 39898). 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/S250328ae For the Bilby.multiorder.fits,0 sky map, the 90% credible region is well fit by an ellipse with an area of 15 deg2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis): icrs; ellipse(09h39m, +10d53m, 4.94d, 0.99d, 116.27d) Marginalized over the whole sky, the a posteriori luminosity distance estimate is 511 +/- 82 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/39900. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37917] GRB 250327A: SVOM/VT upper limits on the XRT position
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39899 SUBJECT: GRB 250327A: SVOM/VT upper limits on the XRT position DATE: 25/03/28 06:44:48 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> H.L. Li(NAOC), L. Zhang (IHEP), Y.D. Hu (GXU), X.L. Chen (YNU), Y. L. Qiu, L.P. Xin, C. Wu, Z.H. Yao, Y. Xu, P.P. Zhang, J. Wang, Y.N. Ma, X.H. Han, H.B. Cai, W. J. Xie, J.Y. Wei (NAOC), J. T. Palmerio (CEA)report on behalf of the SVOM/VT team: SVOM performed a Target of Opportunity observation of GRB 250327A (Fermi GBM team, GCN 39876; Parsotan et al., GCN 39877). SVOM/VT began observing the field at 2025-03-27T11:25:40.50 UT, ~3.9 hours after the Swift/BAT trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With the full X-band data, no any source was detected in the stacked images within the errorbox of Swift/XRT (Burrows et al. GCNC39892). The 3 sigma limits in AB magnitude were derived as follows: --------------------------------------------------------- (t-T0)_mid(hr) exptime(ks) Band upperlim (3sigma) 5.9 7.32 VT_R 23.8 5.9 7.38 VT_B 23.8 Deeper or redder observations are encouraged to investigate the nature of the burst. 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/39899. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37916] LIGO/Virgo/KAGRA S250328ae: Identification of a GW compact binary merger candidate
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39898 SUBJECT: LIGO/Virgo/KAGRA S250328ae: Identification of a GW compact binary merger candidate DATE: 25/03/28 06:27:04 GMT FROM: Sayantan Ghosh at Indian Institute of Technology Bombay <stanghosh(a)iitb.ac.in> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250328ae during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-03-28 05:40:27.419 UTC (GPS time: 1427175645.419). 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. S250328ae is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.2e-10 Hz, or about one in 1e2 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250328ae After parameter estimation by RapidPE-RIFT [8], 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%. [9] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [9] 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 7%. 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 [10], distributed via GCN notice about 32 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [10], distributed via GCN notice 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 22 deg2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis): icrs; ellipse(09h39m, +10d34m, 7.42d, 0.95d, 115.70d) Marginalized over the whole sky, the a posteriori luminosity distance estimate is 492 +/- 91 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] Skliris et al. (2020) arXiv:2009.14611 [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] Rose et al. (2022) arXiv:2201.05263 and Pankow et al. PRD 92, 023002 (2015) doi:10.1103/PhysRevD.92.023002 [9] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [10] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/39898. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37915] GRB 250327B: SVOM/COLIBRÍ (F-GFT) follow-up observations
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39897 SUBJECT: GRB 250327B: SVOM/COLIBRÍ (F-GFT) follow-up observations DATE: 25/03/28 06:11:29 GMT FROM: J.-G. Ducoin at CPPM <ducoin(a)cppm.in2p3.fr> Jean-Grégoire Ducoin (CPPM), Enrique Moreno Méndez (UNAM), Stéphane Basa (LAM), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), 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), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the SVOM/ECLAIRs GRB 250327B (Bouchet et al. GCN Circ. 39888) 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 observed from 2025-03-28 04:33 to 05:04 UTC (7.4 to 7.9 hours after the trigger) and obtained 11 minutes of exposure in the r filter at a mean observing time of T+7.6 hours. The data were coadded with custom software and analyzed with STDpipe (Karpov 2024) with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction. We detect the afterglow (Moskvitin et al. GCN Circ. 39889, Xin et al. GCN Circ. 39890, O’Neill et al. GCN Circ. 39891, Burrows et al. GCN Circ. 39892, Malesani et al. GCN Circ. 39893, Lian et al. GCN Circ. 39894, Page et al. GCN Circ. 39895, Shrestha et al. GCN Circ. 39896) with a magnitude of r = 20.01 +/- 0.02 Further observations are ongoing. We acknowledge the excellent support from the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and thank the COLIBRÍ and DDRAGO engineering teams View this GCN Circular online at https://gcn.nasa.gov/circulars/39897. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37914] GRB 250327B: Las Cumbres optical counterpart detection
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39896 SUBJECT: GRB 250327B: Las Cumbres optical counterpart detection DATE: 25/03/28 04:43:23 GMT FROM: Manisha Shrestha at University of Arizona <mshrestha1(a)arizona.edu> M. Shrestha (Univ. of Arizona), D. Sand (Univ. of Arizona), K. D. Alexander (Univ. of Arizona), J. Andrews (Gemini), J. Pearson (Univ. of Arizona), N. Smith (Univ. of Arizona), K. Bostroem (Univ. of Arizona), C. Christy (Univ. of Arizona), N. Franz (Univ. of Arizona), D. A. Howell (LCO/UCSB), C. McCully (LCO/UCSB), M. Newsome (LCO/UCSB), J. Farah (LCO/UCSB) report on behalf of a wider Global Supernova Project collaboration: We observed the field of GRB 250327B (SVOM team, GCN 39888) with the 1-m telescope, starting on 025-03-28T02:38:50.16 UT (60762.11 MJD, ~5.5 hours after the trigger) using the Sinistro instrument in g, r, i bands (exposure of 2×200 s). We clearly detect the optical counterpart as reported in previous circulars ( Moskvitin+ GCN 39889, Xin+ GCN 39890, O’Neill+ GCN 39891, Malesani+ GCN 39893, Lian+ GCN 39894). Preliminary photometric data are as follows: g = 20.7 +-0.1 r = 19.4 +-0.1 i = 18.8 +- 0.1 These values were calculated with respect to ATLAS-REFCAT2 (Tonry et al. 2018, ApJ 867 105) catalog. They are not corrected for galactic extinction. This source is fading compared to the magnitude reported in Malesani+ GCN 39893. View this GCN Circular online at https://gcn.nasa.gov/circulars/39896. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37913] GRB 250327B: Swift-XRT detection of the X-ray afterglow
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39895 SUBJECT: GRB 250327B: Swift-XRT detection of the X-ray afterglow DATE: 25/03/28 03:39:17 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K.L. Page, P.A. Evans (U. Leicester) and C.A. Gronwall (PSU) report on behalf of the Swift-XRT Team On 2025 March 27 at 21:35 UT, Swift began a Target-of-Opportunity observation of the SVOM-discovered burst GRB 250327B (GCN Circ. 39888). 750 s of data were collected, starting 1.7 ks after the SVOM/ECLAIRs trigger. A bright, fading X-ray source was found, at a position of RA, Dec = 176.77890, 29.83953, which is equivalent to RA (J2000) = 11h 47m 06.94s Dec (J2000) = +29d 50' 22.3" with an uncertainty of 3.5 arcseconds (radius, 90% confidence). This is consistent with the optical afterglow (GCN Circs. 39889, 39890, 39891, 39894), with a measured redshift of 3.035 (GCN Circ. 39893). The light curve can be modelled with a power-law decay with a decay index of alpha=1.20 (+0.73, -0.66). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.47 (+/- 0.09) and the Galactic column density of 1.76 x 10^20 cm^-2 (Willingale et al. 2013). If the light curve continues to decay with a power-law decay index of 1.20, the count rate at T+24 hours will be 0.048 count s^-1 View this GCN Circular online at https://gcn.nasa.gov/circulars/39895. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37912] GRB 250327B: 1.6m Mephisto optical observations
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39894 SUBJECT: GRB 250327B: 1.6m Mephisto optical observations DATE: 25/03/28 01:40:32 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn> Jianhui Lian, Brajesh Kumar, Xufeng Zhu, Fanchuan Kong, Yaosong Yu, Yu Pan, Guowang Du, Xingzhu Zou, Yuan Fang, Xinzhong Er, Jinghua Zhang, Tao Wang, Xinlei Chen, Helong Guo, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team: The field of SVOM GRB 250327B (Bouchet et al., GCN 39888) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. 1 exposures of 180s in the MEPHISTO u, v, 3 exposures of 50s in the MEPHISTO g, r bands, and 2 exposures of 80s in the MEPHISTO i, z bands were obtained starting from 2025-03-27 T21:14:19 (~3min after the trigger). The afterglow candidate (Moskvitin et al., GCN 39889; Xin et al., GCN 39890; O’Neill et al., GCN 39891; Malesani et al., GCN 39893) is clearly detected in each v, g, r, i, z band, with v-r, g-i color of 3.99 and 1.80 mag, respectively. The preliminary magnitudes of the first detections are below: Start_Time(UT) |Band | Exp(s) | Mag(AB) --------------------|-----|--------|---------------- 2025-03-27T21:18:21 | v | 180*1 | 18.66 +/- 0.075 2025-03-27T21:14:19 | g | 50*3 | 16.53 +/- 0.013 2025-03-27T21:18:21 | r | 50*3 | 14.67 +/- 0.003 2025-03-27T21:14:19 | i | 80*2 | 14.73 +/- 0.004 2025-03-27T21:18:21 | z | 50*3 | 13.83 +/- 0.004 ------------------------------------------------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21. ------------------------------------------------------------------------------------------------- View this GCN Circular online at https://gcn.nasa.gov/circulars/39894. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37911] GRB 250327B: NOT spectroscopic redshift z = 3.035
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39893 SUBJECT: GRB 250327B: NOT spectroscopic redshift z = 3.035 DATE: 25/03/28 00:17:12 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> D. B. Malesani (DAWN/NBI and Radboud), B. Schneider (LAM), A. Martin-Carrillo (UCD), J. T. Palmerio (CEA/Irfu), G. Corcoran (UCD), B. Gompertz (Birmingham), A. de Ugarte Postigo (LAM), T. Pursimo (NOT), report on behalf of a larger collaboration: We observed the optical afterglow (Moskvitin et al., GCN 39889; Xin et al., GCN 39890; O'Neill et al., GCN 39891) of the SVOM GRB 250327B (Bouchet et al., GCN 39888) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC spectrograph. The covered wavelength range (grism #4) is 3200 - 9600 AA. In an image of 2x180 s in the r-band, starting on 2025 Mar. 27 at 22:48:21 (1.7 hr after the trigger), we measure r = 17.13 +/- 0.04 (AB). The photometric calibration was performed using nearby stars from the Pan-STARRS catalog and the magnitude is not corrected for Galactic extinction. Based on a preliminary reduction, the spectrum shows bright continuum all the way to the red, with a strong trough around 4900 AA and a break blueward of it, typical of DLA absorption and Lyman forest. From detection of multiple absorption features, which we interpret as due to, among others, Si II, C II, S IV, C IV, Fe II, Al II, we measure a redshift z = 3.035. View this GCN Circular online at https://gcn.nasa.gov/circulars/39893. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37910] GRB 250327A: Swift-XRT refined Analysis
by GCN Circulars 28 Mar '25

28 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39892 SUBJECT: GRB 250327A: Swift-XRT refined Analysis DATE: 25/03/28 00:07:39 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> D.N. Burrows (PSU), M. A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 8.0 ks of XRT data for GRB 250327A, from 12.1 ks to 47.5 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The refined XRT position is RA, Dec = 248.1950, +61.6164 which is equivalent to: RA (J2000): 16 32 46.80 Dec(J2000): +61 36 58.9 with an uncertainty of 3.6 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=0.92 (+0.22, -0.21). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.38 (+0.32, -0.29). The best-fitting absorption column is 3.0 (+1.1, -1.0) x 10^21 cm^-2, in excess of the Galactic value of 2.6 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.1 x 10^-11 (5.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.0 (+1.1, -1.0) x 10^21 cm^-2 Galactic foreground: 2.6 x 10^20 cm^-2 Excess significance: 4.6 sigma Photon index: 2.38 (+0.32, -0.29) If the light curve continues to decay with a power-law decay index of 0.92, the count rate at T+24 hours will be 0.016 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.1 x 10^-13 (9.3 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01299088. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39892. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37909] GRB 250327B: GOTO optical counterpart detection
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39891 SUBJECT: GRB 250327B: GOTO optical counterpart detection DATE: 25/03/27 23:19:12 GMT FROM: d.s.oneill(a)bham.ac.uk D. O’Neill, A. Kumar, B. Godson, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, F. Jimenez-Ibarra, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Palle and D. Pollacco report on behalf of the GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the SVOM/ECLAIRS sb2503270 (Bouchet et al. 39888). The observations were conducted between 2025-03-27 21:14:55 (208 sec post-trigger) and 2025-03-27 22:24:37.72 (76.42 min post-trigger). Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings. We detect the optical counterpart reported by SAO RAS and SVOM/VT (Moskvitin et al., GCN 39889; Xin et al., GCN 39890) as an initially rising source that reached a peak magnitude of L=15.098 ± 0.012 at 8.43 min after trigger, before decaying at a rate of approximately t^-0.8 to a magnitude of 17.011 ± 0.004 at t0+76.42 min post-trigger. We find no evidence of the source prior to the GRB trigger time in previous GOTO observations, the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021). Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. Observations are ongoing. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/39891. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37908] GRB 250327B: SVOM/VT optically bright counterpart
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39890 SUBJECT: GRB 250327B: SVOM/VT optically bright counterpart DATE: 25/03/27 22:50:19 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L.P. Xin, Y. L. Qiu, H. L. Li, C. Wu (NAOC),J. T. Palmerio(CEA/Irfu), Z. H. Yao, Y. Xu, P. P. Zhang, W. J. Xie, J. Wang, X. H. Han, Y. J. Xiao, H. B. Cai, J. Y. Wei (NAOC), Laurent Bouchet, Hui Yang(IRAP) report on behalf of the SVOM team: SVOM performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Bouchet et al., GCN 39888). SVOM/VT began observing the field automatically with the slew of the platform triggered on-board, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With VHF downlinked data, a very bright uncatalogued source was found in both channels, and brightening in the first and second sequences, compared to DESI catalog. The coordinates are R.A =11:47:06.70, DEC.=+29:50:24.8 Error=0.5 arcseconds. J2000 The magnitude is VT_B~15.8 mag(AB) and VT_R~14.2 mag(AB) in the first sequence with the mid time of 461 seconds after the burst. The coordinates and the brightness are consistent with the candidate reported (Moskvitin et al., GCN 39889). We proposed that this is the optical counterpart of the burst. 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/39890. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37907] GRB 250327B: SAO RAS optical candidate
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39889 SUBJECT: GRB 250327B: SAO RAS optical candidate DATE: 25/03/27 22:33:49 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. S. Moskvitin, O. I. Spiridonova (SAO RAS), A. S. Pozanenko (IKI) report on behalf of a larger collaboration. We observed the field of the field of the SVOM GRB 250327B (Bouchet et al., GCN 39888) with the SAO RAS 1-m telescope Zeiss-1000. The observations started on 21:28:15 UT (~17 minutes after SVOM trigger) We found a bright uncatalogued source with R = 14.1 +/- 0.1 (calibrated against R2 magnitudes of nearby USNO-B1 stars) and the coordinates R.A. = 11:47:06.72 Dec. = +29:50:24.7 (+/- 0".5, Epoch = 2000.0) The observations are ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/39889. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37906] GRB 250327B: SVOM detection of a burst
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39888 SUBJECT: GRB 250327B: SVOM detection of a burst DATE: 25/03/27 22:12:14 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Laurent Bouchet, Hui Yang, Olivier Godet, Marius Brunet (IRAP), Clara Plasse (CEA) on behalf of the SVOM mission team. SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250327B (SVOM burst-id sb25032706) starting at 2025-03-27T21:11:27 UTC (Tb). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 10 alerts. IMT provided the alert with the best signal-to-noise-ratio (SNR) of 12.05 in the [8-120] keV energy band over a time window of 40.96 seconds starting at Tb. The light curve shows that the burst duration is about 300 s and the burst is still detected after the slew. The localization of the best alert is R.A., Dec 176.7763, 29.8765 degrees (J2000) with a 90% C.L. radius of 6.70 arcminutes (including systematic error of 2 arcminutes added in quadrature). SVOM slewed to the burst. MXT began observing the field at 2025-03-27T21:14:41 UTC, 193 seconds after Tb. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec 176.788, 29.832 degrees: RA (J2000) = 11h47m09.15s DEC (J2000) = 29d49m55.57s with a 90% C.L. radius of 25 arcseconds. This MXT location is within the ECLAIRs error circle. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments. 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. The Burst Advocate (BA) on shift for this burst is Hui Yang: hui.yang(a)irap.omp.eu. Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/39888. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37905] FRB 20250316A: Gemini Imaging and Spectroscopy of the Sub-arcsecond Localization Region of FRB 20250316A
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39887 SUBJECT: FRB 20250316A: Gemini Imaging and Spectroscopy of the Sub-arcsecond Localization Region of FRB 20250316A DATE: 25/03/27 21:54:43 GMT FROM: Wen-fai Fong at Northwestern University <wfong(a)northwestern.edu> S. Simha (U. Chicago-Northwestern), T. Eftekhari (Northwestern) report on behalf of the CHIME/FRB Collaboration: The CHIME/FRB Collaboration reports on optical imaging and spectroscopy of the sub-arcsecond CHIME Outrigger localization (ATel #17114, GCN #39886) of the nearby, bright FRB 20250316A (ATel #17081). We obtained deep g-band observations starting at 24 March 2025 12:39:44 UT (PI: T. Eftekhari; 15 x 120-sec exposures) with the Gemini-North Multi-Object Spectrograph (GMOS-N) mounted on the 8-m Gemini North telescope at Maunakea, Hawai'i. Observations were taken in clear conditions with an average airmass of 1.6 and seeing of 0.8". We do not detect any strong, possible transient (point source) optical emission at the FRB location (1-sigma; ATel #17114) and measure a 3-sigma point-source limiting magnitude at this location of g > 23.8 mag (AB). However, we detect a clump of extended optical emission in the host galaxy, offset from the FRB localization region by ~1.2" (measured from the brightest pixel in the g-band image). At a distance to NGC 4141 of ~40 Mpc, the corresponding projected physical distance between the FRB and this clump is ~250 pc. We also obtained long-slit optical spectroscopy with GMOS-N starting at 25 March 2025 10:41:44 (PI: T. Eftekhari; 8 x 900-sec exposures) at an airmass of ~1.33. We used a 1" slit width, the B480 grating, and the GG455 blocking filter at central wavelengths of 640 and 650 nm. The slit was oriented at a position angle of 10.6 degrees East of North to cover both the FRB localization region and the nearby extended optical emission. While we do not detect any transient spectral features or features at the FRB position, we detect strong nebular emission from the nearby optical clump, including H-beta, H-alpha, and [OIII] at a common redshift of z~0.0065, consistent with emission from a star-forming region within the host. We thank Gemini Observatory staff, including Jennifer Andrews, for assistance with planning and executing the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39887. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37904] FRB 20250316A: The sub-arcsecond localization of FRB 20250316A using CHIME/FRB Outriggers coincides with reported X-ray counterparts
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39886 SUBJECT: FRB 20250316A: The sub-arcsecond localization of FRB 20250316A using CHIME/FRB Outriggers coincides with reported X-ray counterparts DATE: 25/03/27 21:19:58 GMT FROM: shiona(a)mit.edu We have derived a sub-arcsecond VLBI localization for FRB 20250316A (see ATel #17081, ATel #17086; this is the first such localization using the full CHIME/FRB Outriggers array. This consists of the CHIME core and the KKO Outrigger (Lanman et al. 2024) near Penticton, BC, and two additional Outrigger stations at Green Bank Observatory (GBO) and Hat Creek Radio Observatory (HCO). The position below is consistent with the ~10" position of the potential X-ray counterpart EP J120944.2+585060 detected by the Einstein Probe (ATel #17100) but is inconsistent with the 90% confidence interval reported from Swift/XRT observations (ATel #17109). We derive our position by referencing delays on each of the three CHIME-Outrigger baselines to nearby in-beam International Celestial Reference Frame (ICRF) calibrators observed simultaneously with the FRB (Andrew et al. 2024). On all CHIME-Outrigger baselines, we phase reference our visibilities to the calibrator RFC J1204+5202 (https://astrogeo.org/sol/rfc/rfc_2024b/; Petrov & Kovalev 2025), located ~6 degrees away from the FRB. Five additional in-beam ICRF calibrators were observed on all three baselines between CHIME and its Outriggers, which we use to derive a representative error budget for the FRB localization. The calibrators completely surround the FRB, spanning ~+/- 1 degree in hour angle and +50/-20 degrees in declination relative to CHIME zenith, while the FRB is located ~0.2 degrees east and ~10 degrees north of CHIME zenith. We check for imperfect calibrator selection and direction-dependent effects by 1) calibrating the target to all other usable calibrators, and 2) calibrating known calibrator positions to other calibrators, which maximizes on-sky angular separations. Both procedures give RMS delay errors no larger than 1 ns, 3 ns, and 6ns on the CHIME-KKO, CHIME-HCO and CHIME-GBO baselines, respectively. This yields the following 1-sigma (stat+sys) localization ellipse for the location of FRB 20250316A: Right Ascension = 12h09m44.31s Declination = +58d50m56.70s a_err = 150 milliarcsec b_err = 100 milliarcsec theta = 2.4 degrees East of North All coordinates are in the ICRF. We have included our one-sigma localization contour over the Epoch 1 r-band MMT image reported in ATel #17112. We note that to account for astrometric offsets due to optical-radio reference frame ties, we have inflated our localization errors in the plot by 150mas (added in quadrature). The full four-station array is still being commissioned, and its astrometric performance will be fully characterized in an upcoming work. However, we note that the error from our bootstrapping procedure is consistent with our archival test localizations of over 200 ICRF calibrators and well-localized pulsars at similar target-calibrator separations and at cross-correlation signal-to-noise ratios lower than those in the dataset used here. Furthermore, the abundance of in-beam calibrators may enable additional improvements on the preliminary position quoted here. Follow-up observations are strongly encouraged to definitively establish whether EP J120944.2+585060 is spatially coincident with FRB 20250316A, and to characterize the nature of this potential X-ray counterpart. Link to MMT Image https://storage.googleapis.com/chimefrb-dev.appspot.com/FRB20250316A/FRB202… View this GCN Circular online at https://gcn.nasa.gov/circulars/39886. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37903] GRB 250327A: J-band observations with WINTER
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39885 SUBJECT: GRB 250327A: J-band observations with WINTER DATE: 25/03/27 19:40:58 GMT FROM: Geoffrey Mo at MIT <gmo(a)mit.edu> Geoffrey Mo (MIT), Benjamin Schneider (LAM), Tomas Ahumada (Caltech), Danielle Frostig (CfA), Viraj Karambelkar (Caltech), Robert Stein (UMD), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 250327A (Fermi GBM Team, GCN 39876; Parsotan et al., GCN 39877, Kienlin et al., GCN 39882) in the near-infrared J-band with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations were triggered automatically and began at 2025-03-27T07:41:48 UTC (12 min after the GRB), consisting of 5 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565). We do not detect a source at the SVOM/VT counterpart location (Xin et al., GCN 39884), and also do not detect any new sources in the Swift/BAT localization after visual comparison to archival PanSTARRS-1 (Chambers et al. 2016) y-band imaging. This is consistent with other observations (Ducoin et al., GCN 39878; Becerra et al., GCN 39879; Lipunov et al., GCN 39880; Lipunov et al., GCN 39881). We obtain the following 5-sigma upper limit: J ~ 18.3 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/39885. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37902] GRB 250327A: SVOM/VT optical candidate
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39884 SUBJECT: GRB 250327A: SVOM/VT optical candidate DATE: 25/03/27 16:42:22 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> L.P. Xin (NAOC), J. T. Palmerio (CEA), L. Zhang (IHEP), Y.D. Hu (GXU), X.L. Chen (YNU), Y. L. Qiu, H.L. Li., C. Wu, Z.H. Yao, Y.N. Ma, X.H. Han, H.B. Cai, J.Y. Wei (NAOC), B. Cordier (CEA), report on behalf of the SVOM/VT team: SVOM performed a Target of Opportunity observation of GRB 250327A (Fermi GBM team, GCN 39876; Parsotan et al., GCN 39877). SVOM/VT began observing the field at 2025-03-27T11:25:40.50 UT, ~3.9 hours after the Swift/BAT trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. An uncatalogued candidate is detected inside the Swift/BAT error circle at ra=248.18018, dec=61.63347 (J2000), corresponding to: RA (J2000) = 16:32:43.2 Dec (J2000) = +61:38:00.5 with an uncertainty of 1.0 arcsec. This source is not present in the archival Legacy Survey. The source is detected in the VT_R stacked image with exposure time of 47x60 seconds with VT_R = 22.8 +/- 0.3 mag (AB). The 3 sigma upper limit in the VT_B is 23.4 mag (AB). We thank D.B. Malesani for helpful discussion. 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/39884. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37901] FRB 20250316A: Pan-STARRS r and i-band imaging and photometry
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39883 SUBJECT: FRB 20250316A: Pan-STARRS r and i-band imaging and photometry DATE: 25/03/27 15:42:08 GMT FROM: James Gillanders at University of Oxford <jhgillanders.astro(a)gmail.com> J. H. Gillanders (Oxford), M. Huber, K. C. Chambers (IfA, Univ. Hawaii), S. J. Smartt, K. W. Smith, S. Srivastav (Oxford), M. Nicholl, D. Young, M. Fulton (QUB), T.-W. Chen (NCU, Taiwan) A. S. B. Schultz, T. de Boer, J. Fairlamb, G. Paek, C. C. Lin, T. Lowe, E. Magnier, P. Minguez, I. A. Smith, R. J. Wainscoat (IfA, Univ. Hawaii). We observed the field of FRB 20250316A (Ng et al., ATel 17081) and EP J120944.2+585060 (Sun et al., ATel 17100, GCN 39834) using the Pan-STARRS telescope system (Chambers et al., 2016, arXiv e-prints, 1612.05560) on MJD 60757.42 (2025-03-23 10:04 UTC), ~7.06 days after the FRB detection (Ng et al., ATel 17081). The Pan-STARRS system consists of two 1.8m telescope units located at the summit of Haleakala on the Hawaiian island of Maui, employing an SDSS-like filter system denoted as grizy, and a broad w-filter, which is a composite of the gri-filters. Our observation consisted of 6x150s exposures in i-band, and 3x150s in r-band. The images were processed with the Pan-STARRS pipeline, where they underwent astrometric and photometric calibration, and stacking (Magnier et al., 2020a, ApJS, 251, 3; Magnier et al., 2020b, ApJS, 251, 6; Waters et al., 2020, ApJS, 251, 4). From these stacked target images, which cover the entire localisation region of FRB 20250316A (Leung et al., ATel 17086) and the EP-FXT error region of EP J120944.2+585060 (Sun et al., ATel 17100, GCN 39834), we do not detect any new optical sources down to 5-sigma limiting AB magnitudes of r~23.5 and i~23.5. These non-detections are consistent with previously reported observations by Becerra et al., ATel 17082, GCN 39853; Niino et al., ATel 17084; Hashimoto ATel 17095; Yang et al., ATel 17101; Troja et al., ATel 17109, GCN 39869; Aryan et al., GCN 39839; Pereyra et al., GCN 39858; Jiang et al., GCN 39864. View this GCN Circular online at https://gcn.nasa.gov/circulars/39883. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37900] GRB 250327A: Fermi GBM observation
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39882 SUBJECT: GRB 250327A: Fermi GBM observation DATE: 25/03/27 14:52:00 GMT FROM: Andreas von Kienlin at MPE <azk(a)mpe.mpg.de> A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: "At 07:30:06.33 UT on 27 March 2025, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 250327A (trigger 764753411 / 250327313), which was also detected by the Swift/BAT (Parsotan et al. 2025, GCN 39877). The Fermi GBM Final Real-time Localization (GCN 39876) is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 47 degrees. The GBM light curve shows a structured emission episode with a duration (T90) of about 160 s (50-300 keV). The time-averaged spectrum from T0-1.024s to T0+90.114s is best fit by a Band function with Epeak = 480 +/- 50 keV, alpha = -1.08 +/- 0.03, and beta = -2.14 +/- 0.15. The event fluence (10-1000 keV) in this time interval is (2.97 +/- 0.07)E-05 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+0.704 s in the 10-1000 keV band is 5.08 +/- 0.23 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/39882. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37899] Fermi GRB 250327A: Global MASTER-Net observations report
by GCN Circulars 27 Mar '25

27 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39881 SUBJECT: Fermi GRB 250327A: Global MASTER-Net observations report DATE: 25/03/27 14:01:03 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) started inspect of the Fermi GRB 250327A ( Fermi GBM team, GCN 39876) errorbox 22555 sec after notice time and 22597 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 = 41 deg., longitude l = 93 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2825101 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 22688 | 2025-03-27 13:46:44 | MASTER-Tunka | (16h 33m 04.03s , +61d 29m 19.4s) | 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/39881. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[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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[vsnet-grb-info 37888] EP250321a: Mondy AZT-33IK Continued Optical Observations
by GCN Circulars 25 Mar '25

25 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39870 SUBJECT: EP250321a: Mondy AZT-33IK Continued Optical Observations DATE: 25/03/25 17:27:37 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), E. Klunko (ISTP), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We continued optical observations of the field of EP250321a (Hu et. al, GCN 39800; Page et. al, GCN 39811, Hu et. al, GCN 39833) at the redshift of z = 4.368 (Zhu et. al, GCN 39769) in the R filter with the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The observations started on (UT) 2025-03-22 15:35:42, i.e. about 1.4 days since trigger. The optical afterglow (Fu et. al, GCN 39804; Perez-Garcia et. al, GCN 39805; Brivio et. al, GCN 39807; Zhu et. al, GCN 39809; Becerra et. al, GCN 39810; Pérez-Fournon et. al, GCN 39812; Lee et. al, GCN 39815; Han et. al, GCN 39817; Jin et. al, GCN 39822; Zhu et. al, GCN 39827; Gill et. al, GCN 39831; Zheng et. al, GCN 39832; Bochenek & Perley, GCN 39837; Zhu et. al, GCN 39854) is not detected in the stacked images. The preliminary photometry is as follows: Date UT start t-T0 Exp. Filter OT Err UL(3sigma) (mid, days) (s) 2025-03-22 15:35:42 1.40467 17*120 R n/d n/d 22.3 2025-03-23 16:02:48 2.45336 60*120 R n/d n/d 23.6 The photometry is based on nearby stars of SDSS-DR12 and has not been corrected for the Galactic extinction. SDSS-DR12 RA Dec R(Lupton transformations, 2005) 179.2552 +17.3825 18.123 +/- 0.049 179.2436 +17.3713 18.846 +/- 0.012 View this GCN Circular online at https://gcn.nasa.gov/circulars/39870. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37887] Swift follow-up observations of FRB250316A and EP J120944.2+585060
by GCN Circulars 25 Mar '25

25 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39869 SUBJECT: Swift follow-up observations of FRB250316A and EP J120944.2+585060 DATE: 25/03/25 17:26:37 GMT FROM: Eleonora <nora.gsfc(a)gmail.com> E. Troja ( U Rome), Y.-H. Yang ( U Rome), S. Dichiara (PSU), M. E. Kabir (U Rome) and H. Sun (NAO, CAS) report: We reobserved the field of FRB 20250316A (ATel #17081) with Swift starting on 2025-03-23 (~7 days after the FRB) for a total exposure of 10 ks. A blind search does not identify any X-ray source consistent with the CHIME localization (ATel #17086). However, a targeted search at the position of EP J120944.2+585060 (Sun et al., ATel #17100) finds a weak X-ray source at RA, Dec (J2000) = 182.4369, 58.8471 deg with a 90% error radius of 6 arcsec (stat+sys), as derived by xrtcentroid. The detection is significant at the >99.7% confidence level (Kraft, Nousek, and Burrows, 1991). A finder chart can be found at: https://nora.users.roma2.infn.it/FRB250316A.png Based on a preliminary analysis, we infer a count rate of (7 +/- 3)E-4 cts/s which corresponds to an observed flux of (2.4 +/- 1.0)E-14 erg/cm2/s (0.3-10 keV) assuming an absorbed power-law spectrum with a photon index of 2 and NH = 1.4E+20 cm^-2. Our observations are consistent with the reported flux for EP J120944.2+585060 (Sun et al., ATel #17100) and do not show substantial variability. We performed an independent analysis of the first epoch of Swift observations, taken at 12 hrs after the burst (Yang et al., ATel #17101). Using the above XRT position, we derive a 90% upper limit of 7E-4 cts/s, consistent with our reported value. Within the XRT localization, no optical counterpart is visible in the Swift UVOT White images down to >22.3 AB mag We thank the Swift team for scheduling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39869. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37886] GRB 250322A: third epoch of NOT optical observations
by GCN Circulars 25 Mar '25

25 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39868 SUBJECT: GRB 250322A: third epoch of NOT optical observations DATE: 25/03/25 17:11:56 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> D. B. Malesani (DAWN/NBI and Radboud), B. Schneider (LAM), A. Martin-Carrillo (UCD), A. M. Kadela (NOT and NBI) report on behalf of a larger collaboration: We secured a third observation of the field of GRB 250322A (Gupta et al., GCN 39835; Tembhurnikar et al., GCN 39849) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC imager. Our observation consisted of 5x600 s in the r-band, with mean time 2025 Mar 24.86 UT (2.19 days after the GRB). This observation reaches a depth comparable to our first epoch (Martin-Carrillo et al., GCN 39842), taken at 4.65 hr after the GRB, unlike our second epoch (Schneider et al., GCN 39863), which suffered from worse seeing. Image subtraction of our third epoch from the first was carried out using HOTPANTS. No residuals are detected in the difference image, down to a limiting magnitude r > 23.8 AB (calibrated against Pan-STARRS). This limit is consistent with, but strengthens, our earlier determination r > 23.2 (Schneider et al., GCN 39863). View this GCN Circular online at https://gcn.nasa.gov/circulars/39868. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37885] EP250321a: Xinglong 216 decaying optical observations
by GCN Circulars 25 Mar '25

25 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39822 SUBJECT: EP250321a: Xinglong 216 decaying optical observations DATE: 25/03/21 19:24:45 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Jinlei-Zhang (NAOC), Pengliang-Du (NAOC), Feng-Xiao(NAOC),Zhou-Fan (NAOC), Hong-Wu (NAOC) We performed optical observations of the field of a fast X-Ray transient EP250321a (Hu et al., GCN 39800) in the Free filter using 2.16-m telescope located at Xinglong, Hebei, China. In the band a 600 s exposures were taken , with a median observation time of 2025-03-02T20:32:28. No uncatalogued optical transient is detected in the stacked images within the 3 arcmin EP/WXT error circle (Li et al., GCN 36405), down to 3-sigma limiting magnitudes of g ~ 20.5, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. View this GCN Circular online at https://gcn.nasa.gov/circulars/39822. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37884] GRB 250322A: Swift-BAT refined analysis
by GCN Circulars 25 Mar '25

25 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39867 SUBJECT: GRB 250322A: Swift-BAT refined analysis DATE: 25/03/25 14:56:16 GMT FROM: Rahul Gupta at NASA GSFC <rahulbhu.c157(a)gmail.com> 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-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250322A (trigger #1297832) (Gupta, et al., GCN Circ. 39835). The BAT ground-calculated position is RA, Dec = 106.775, 7.197 deg which is RA(J2000) = 07h 07m 06.1s Dec(J2000) = +07d 11' 47.8" with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment). The partial coding was 100%. The mask-weighted BAT light curve shows multi-peak emission. T90 (15-350 keV) is 0.62 +- 0.05 sec (estimated error including systematics). The time-averaged spectrum from T+0.00 to T+0.67 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 0.65 +- 0.19. The fluence in the 15-150 keV band is 1.5 +- 0.2 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T-0.16 sec in the 15-150 keV band is 1.4 +- 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/1297832 View this GCN Circular online at https://gcn.nasa.gov/circulars/39867. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37883] The EP-WXT trigger 01709133021 (designated as EP250324a) is not a real source
by GCN Circulars 25 Mar '25

25 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39866 SUBJECT: The EP-WXT trigger 01709133021 (designated as EP250324a) is not a real source DATE: 25/03/25 04:12:20 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> T. Y. Lian (NAO, CAS), J. Q. Peng (IHEP,CAS), X. Fan, S. E. Xu (WHU), C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: Based on the telemetry data analysis, the EP-WXT trigger 01709133021 (designated as EP250324a) at the time of 2025-03-24T09:38:23(UTC), is not a real source. View this GCN Circular online at https://gcn.nasa.gov/circulars/39866. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37882] GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
by GCN Circulars 24 Mar '25

24 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39865 SUBJECT: GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit DATE: 25/03/24 17:11:05 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Schmalz (KIAM), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We performed optical observations of the field of GRB 250321B (Schanne et. al, GCN 39818; Capalbi et. al, GCN 39856) in the Clear light with the 0.36-meter RC-36 telescope of the ISON-Kitab observatory. The observations started on (UT) 2025-03-21 17:31:49, i.e. about 0.59 days since trigger. We do not detect an optical afterglow candidate in the stacked image. The preliminary photometry is as follows: Date UT start t-T0 Exp. Filter OT Err UL(3sigma) (mid, days) (s) 2025-03-21 17:31:49 0.59330 38*60 Clear n/d n/d 17.0 Ref. stars RA Dec r 169.5809 +39.4176 13.063 169.7213 +39.4809 13.341 The photometry is based on nearby stars of SDSS-DR12 (r-magnitudes) and has not been corrected for the Galactic extinction. Our result is consistent with non-detections of an optical (Ducoin et. al, GCN 39840) and an X-Ray (Capalbi et. al, GCN 39856) counterpart. View this GCN Circular online at https://gcn.nasa.gov/circulars/39865. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37881] FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
by GCN Circulars 24 Mar '25

24 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39864 SUBJECT: FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060 DATE: 25/03/24 17:09:34 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang, Z.P. Zhu, X. Liu, J. An (NAOC), S.Y. Fu (HUST), D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), A. M. Kadela, A. A. Djupvik (NOT) report on behalf of a large collaboration: We observed the field of the X-ray candidate EP J120944.2+585060 (Sun et al., GCN 39834; ATel #17100) possibly associated with FRB 250316A (Ng et al., ATel #17081; Leung et al., ATel #17086), using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. The mid time of the observations is 01:00:20.3 UTC on 2025-03-23, and a series of 300 s frames were obtained in the Sloan r-band. No new optical source is detected in the stacked image within the EP/FXT error region by subtracting the stacked image against the Legacy Survey template. The 5-sigma limiting magnitude of the observations is r > 24.0, calibrated with Legacy Survey DR 10 and not corrected for Galactic extinction. The non-detection of an optical counterpart is consistent with previous reports by Becerra et al. (ATel #17082; GCN 39843; GCN 39853), Niino et al. (ATel #17084), Hashimoto et al. (ATel #17095), Yang et al. (ATel #17101), Aryan et al. (GCN 39839) and Pereyra et al. (GCN 39858). View this GCN Circular online at https://gcn.nasa.gov/circulars/39864. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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