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[vsnet-grb-info 37548] EP250227a: Optical upper limits with Kinder observations
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39534 SUBJECT: EP250227a: Optical upper limits with Kinder observations DATE: 25/02/28 16:56:52 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> A. Aryan (NCU), A. K. H. Kong (NTHU), T.-W. Chen, H.-Y. Hsiao, C.-S. Lin (all NCU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), Y. J. Yang, A. Sankar. K, Y.-C. Pan, C.-C. Ngeow, W.-J. Hou, M.-H. Lee, H.-C. Lin, C.-H. Lai, J.-K. Guo (all NCU), S. Yang, L. L. Fan, Z. N. Wang, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP250227a (Wen et al., GCN 39532) using the 40cm SLT telescope at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2024, arXiv:2406.09270). The first SLT epoch of observations in the i band started at 15:53 UT on the 27th of February 2025 (MJD = 60733.662), ~11.22 hrs after the EP trigger, while the first SLT epoch of observations in the r band started at 16:28 UT on the 27th of February 2025 (MJD = 60733.686), ~11.79 hrs after the EP trigger. We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. We did not detect any uncataloged optical counterpart candidate within the EP-WXT localization error circle of radius 2.7 arcminutes. We further employed the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform PSF photometry on our stacked frames. The details of the observations and measured three sigma upper limits (in the AB system) were as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass SLT | i | 60733.662 | 11.22 | 300 * 6 | >21.1 | 1".47 | 1.80 SLT | r | 60733.686 | 11.79 | 300 * 12 | >21.5 | 1".46 | 1.49 The non-detection of any prominent optical counterpart is consistent with Malesani et al., (GCN 39533). The presented upper limits were calibrated using the field stars from the Pan-STARRS1 catalog and were not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_i = 0.12 mag and A_r = 0.16 mag, respectively, in the direction of the transient (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/39534. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37547] EP250227a: NOT optical observations
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39533 SUBJECT: EP250227a: NOT optical observations DATE: 25/02/28 16:36:03 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Martin-Carrillo (UCD), A. J. Levan (Radboud Univ and Warwick Univ.), F. E. Bauer (PUC), P. G. Jonker (Radboud Univ), M. Alejandra Diaz Teodori (NOT and Turku Univ.), Roar H. Rasmussen (NOT and Aarhus Univ.), Saskia Schlagenhauf (QUB), report for a larger collaboration: We obtained observations of the field of the fast X-ray transient EP250227a (Wen et al. GCN 39532) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations started on 2025 Feb 28.126 UT (22.37 hr after the EP trigger) and were carried out in the r and z filters. No new source is visible within the EP/FXT X-ray error circle (Wen et al. GCN 39532), down to a 3-sigma limiting magnitude r > 23.7 AB, calibrated against nearby Pan-STARRS objects. At the edge of the error circle, we note the presence of a source, visible also in the Legacy Survey and whose brightness is consistent with the archival value. While this is a potential host galaxy for EP250227a, its chance association probability is not negligible. We also performed image subtraction on our stacked r-band image using the Legacy Survey as template. A single variable source is identified at coordinates (inconsistent with those of the EP/FXT error circle): R.A.(J2000) = 13:36:29.37 Dec.(J2000) = -13:49:00.16 This source is located about 1” to the NE of the nucleus of a galaxy visible in the Legacy Survey with magnitude r = 18.8. We measure for the variable source r = 22.5 +/- 0.1 AB. The nature of this source and its association with EP250227a are unclear at the moment. Further observations are planned and deep r-band photometry of the field is encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/39533. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37546] EP250227a: Einstein Probe detected of a fast X-ray transient
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39532 SUBJECT: EP250227a: Einstein Probe detected of a fast X-ray transient DATE: 25/02/28 15:52:07 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> W.F. Wen (SZTU), J. H. Wu (GZHU), H. Z. Wu (HUST), B. -T. Wang (YNAO, CAS), Z. X. Ling(NAO, CAS) report on behalf of the Einstein Probe team: We report on the detection of a fast X-ray transient EP250227a (trigger ID: 11916647689) at 2025-02-27 04:39:40 (UTC) by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The position of the source is R.A. = 204.133 deg, DEC = -13.820 deg (J2000) with an uncertainty of 2.7 arcmin (radius, 90% C.L. statistical and systematic). The transient event lasted for about 40 seconds. The 0.5-4.0 keV spectrum can be fitted with an absorbed powerlaw model, with nH fixed at 1.87 x 10^20 cm^-2 and a photon index of -0.07(+2.18/-1.22). The unabsorbed 0.5-4.0 keV flux is 2.1 (+2.6/-1.2) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. We performed a follow-up target of opportunity observation with EP-FXT. The observation began at 2025-02-27 15:19:07 (UTC) with an exposure time of 3020 seconds, about 10.7 hours after the detection by EP-WXT. Within the WXT error cirlce, an uncatalogued X-ray source was detected at R.A. = 204.1444 deg, DEC = -13.8216 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The X-ray spectrum can be fitted with an absorbed powerlaw with the nH fixed at the Galactic value and a photon index of 1.2 (-0.8, +0.8). The derived unabsorbed 0.5-10 keV flux is 2.4 (-1.4, +5.2) x 10^-13 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/39532. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37545] EP250228a: updates on the EP observations
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39531 SUBJECT: EP250228a: updates on the EP observations DATE: 25/02/28 15:49:46 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H.Y. Liu (NAO, CAS), J.Q. Peng (IHEP, CAS), W. F. Wen(SZTU), J. H. Wu (GZHU), C.C. Jin (NAO, CAS) report on behalf of the Einstein Probe team: The X-ray transient EP250228a (GCN 39525) triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission at 2025-02-28T03:59:09 (UTC) and an autonomous observation was performed by the Follow-up X-ray Telescope (FXT) around 45 s later. The on-ground analysis of the FXT data shows that an uncatalogued source was detected at R.A. = 103.6059, DEC = -41.5710 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with that reported by the Swift XRT Team (GCN 39527). Given that the localisation of this source is well aligned with the position of Gaia DR3 5563280076339409920, EP250228a is likely a stellar flare associated with this star. The FXT spectrum can be well fitted by a 4T apec model with kT= 6.6(+3.4/-1.3), 1.4(+0.69/-0.35), 0.63(+0.16/-0.23), and 0.17(+0.04/-0.06) keV, respectively, and the derived flux is around 1.87 (+0.09/-0.09) x 10^-11 erg/s/cm^2 in 0.5-10 keV. The uncertainties are at the 90% confidence level for the above parameters. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with onboard X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/39531. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37544] GRB 250226A: Fermi GBM Observation
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39530 SUBJECT: GRB 250226A: Fermi GBM Observation DATE: 25/02/28 14:49:24 GMT FROM: Utkarsh Pathak at IIT Bombay <utkarshpathak.07(a)gmail.com> U. Pathak (IITB) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 06:34:57.33 UT on 26 February 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250226A (trigger 762244502/250226274) which was also detected by EP/WXT and EP/FXT (Jiang et al. 2024, GCN 39482). It was also detected by INTEGRAL SPI-ACS and PICsIT (Thakur et al. 2025, GCN 39518), GECAM-B (Zhang et al. 2025, GCN 39492). Optical follow-ups have been done with TRT (An et al. 2025, GCN 39486), COLIBRI/DDRAGO (Magnani et al. 2025, GCN 39488), GSP (Li et al. 2025, GCN 39489), Kinder (Aryan et al. 2025, GCN 39509), 1.6m Mephisto (Zhou et al. 2025, GCN 39511), SVOM/VT (Li et al. 2025, GCN 39514), Xinglong (Jin et al. 2025, GCN 39515). The spectroscopic redshift of the optical counterpart observed by VLT/X-shooter (Zhu et al. 2025, GCN 39487) is 3.315. The Fermi GBM on-ground location is consistent with the EP/FXT position. The angle from the Fermi LAT boresight is 108 degrees. The GBM light curve consists of multiple spikes from a single emission episode with a duration (T90) of about 61 s (50-300 keV). The time-averaged spectrum from T0-2.6 to T0+62.0 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.36 +/- 0.03, and the cutoff energy, parameterized as Epeak, is 4408 +/- 1160 keV. The event fluence (10-1000 keV) in this time interval is (1.96 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+3.4 s in the 10-1000 keV band is 4.7 +/- 0.3 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 2864 +/- 2100 keV, alpha = -1.35 +/- 0.04 and beta = -1.8 +/- 0.2. As the burst occurred near SAA entry, the spectral results of both fits to the data (especially Epeak) are likely to have some contamination and thus may not reflect the burst's true spectral nature. 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/39530. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37543] EP250225a: EP-FXT follow-up observation
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39529 SUBJECT: EP250225a: EP-FXT follow-up observation DATE: 25/02/28 14:11:40 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S. Q. Jiang, T. Zhao (NAO, CAS), B.-T. Wang (YNAO, CAS), H. Z. Wu (HUST), Y. J. Song, Y. Liu (NAO, CAS) report on behalf of the Einstein Probe team: We performed one follow-up observation of the X-ray transient EP250225a (Jiang et al., GCN 39475) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started at 2025-02-26 11:53:56 (UTC), about 23.67 hours after the WXT detection, with an exposure of ~3 ks. No source was detected within the WXT error circle. The 0.5-10 keV upper limit at the NOT candidate position (Malesani et al., GCN 39516) is about 7e-14 erg/s/cm^2 (90% C. L.). Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/39529. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37542] EP250223a: J band upper limit by SYSU 80cm telescope
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39528 SUBJECT: EP250223a: J band upper limit by SYSU 80cm telescope DATE: 25/02/28 11:41:02 GMT FROM: Wei-Sen Huang at SYSU <huangws5(a)mail2.sysu.edu.cn> Wei-Sen Huang, Jin-Ji Li, Chun Chen, Zhong-Nan Dong, Jia-Qi Lin, Pu Lin, Hao-Nan Yang, Yan Yu, Hao-Ran Zhang, Si-Yuan Zhu, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm telescope team: We observed the field of EP250223a (Lian et al., GCN 39429; Kennea et al., GCN 39437; Wang et al., GCN 39448) using the Sun Yat-sen University 80cm infrared telescope in J band. The calculated position is R.A. = 98.2712, DEC = -22.4449 (J2000), from EP/FXT observation. Our first observations began at 2025-02-24 12:10:00 UTC, 21.09 hours after the EP trigger, with 180 x 20 s exposures. The second observations began at 2025-02-25 12:54:00 UTC, 45.82 hours after the EP trigger, with 90 x 20 s exposures. We do not detect any counterpart in the stacked images at the position of the optical afterglow(Lipunov et al., GCN 39434; Hauptmann et al., GCN 39436; Levan et al., GCN 39438; Wu et al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo et al., GCN 39441; Xin et al., GCN 39445; Guo et al., GCN 39447; An et al., GCN 39449; Ducoin et al., GCN 39453; O’Neill et al., GCN 39455; Aryan et al., GCN 39464; Saikia et al., GCN 39472; Wang et al., GCN 39476; Mazaeva et al., GCN39496), down to a 5-sigma depth of J~17.2 Vega magnitudes on 2025-02-24 and J~17.0 Vega magnitudes on 2025-02-25. View this GCN Circular online at https://gcn.nasa.gov/circulars/39528. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37541] EP250228a: Swift/XRT localisation
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39527 SUBJECT: EP250228a: Swift/XRT localisation DATE: 25/02/28 10:52:50 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K.L. Page, P.A. Evans (U.Leicester) and J. DeLaunay (PSU) report on behalf of the Swift XRT Team: On 2025 February 28, at 05:53 UT, Swift obtained an Target of Opportunity observation of EP250228a (GCN Circ. 39525), collecting ~340 s of data around 1.9 hr after the Einstein Probe trigger. The XRT data show an uncatalogued X-ray source, consistent with the FXT source reported by the EP team, at a position of RA, Dec = 103.60631, -41.57160, which is equivalent to RA (J2000): 06h 54m 25.51s Dec (J2000): -41d 34′ 17.8″ with an uncertainty of 4.4 arcsec (radius, 90% confidence). The flux of this source was (5.4 +/- 0.9) x 10^-12 erg cm^-2 s^-1 (0.3 - 10 keV). View this GCN Circular online at https://gcn.nasa.gov/circulars/39527. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37540] EP250228a: Global MASTER-Net observations report
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39526 SUBJECT: EP250228a: Global MASTER-Net observations report DATE: 25/02/28 08:18:36 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 EP250228a ( EP Team et al., GCN 39525) errorbox 229 sec after notice time and 12029 sec after trigger time at 2025-02-28 07:19:38 UT, with upper limit up to 19.2 mag. The observations began at zenith distance = 74 deg. The sun altitude is -36.6 deg. The galactic latitude b = -17 deg., longitude l = 252 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2794721 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 12059 | 2025-02-28 07:19:38 | MASTER-OAFA | (06h 55m 12.36s , -41d 21m 41.5s) | C | 60 | 19.2 | 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/39526. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37539] EP250228a: Einstein Probe detection of an X-ray transient
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39525 SUBJECT: EP250228a: Einstein Probe detection of an X-ray transient DATE: 25/02/28 07:09:00 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H.Y. Liu (NAO, CAS), J.Q. Peng (IHEP, CAS), W. F. Wen(SZTU), J. H. Wu (GZHU), C.C. Jin (NAO, CAS) report on behalf of the Einstein Probe team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250228a. The transient triggered EP-WXT (ID: 01709132122) at 2025-02-28T03:59:09 (UTC). The WXT position of the source is R.A. = 103.607 deg, DEC = -41.581 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error cirlce, an uncatalogued X-ray source was detected at R.A. = 103.6021 deg, DEC = -41.5715 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/39525. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37538] GRB 250226A / EP250226a: LCO detection of the afterglow
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39524 SUBJECT: GRB 250226A / EP250226a: LCO detection of the afterglow DATE: 25/02/27 23:22:56 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> F. Poidevin, I. Pérez-Fournon (IAC and ULL), D. Cano-Morales, I. Correa-Plasencia, and A.E. Hernández-Díaz (ULL) We observed the location of the long-duration GRB 250226A / EP250226a discovered by Fermi GBM (Fermi GBM team, GCN circ. 39479) and EP WXT and FXT (Jiang et al., GCN circ. 39482; Jiang et al., GCN circ. 39513) and detected also by GECAM-B (Zhang et al., GCN circ. 39492) and INTEGRAL SPI-ACS and PICsIT (Thakur et al., GCN circ. 39518) with two Las Cumbres Observatory Global Telescope network (LCOGT) 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Sutherland Observatory (South Africa). Simultaneous 300-sec exposures were obtained in the SDSS i' and r' filters starting at about 18.89 hr after the Fermi trigger. We detect the optical afterglow at the location reported by An et al. (GCN circ. 39486) and with optical detections by other groups (Zhu et al., GCN circ. 39487; Magnani et al., GCN circ. 39488; Li et al., GCN circ. 39489; Aryan et al., GCN circ. 39509; Zou et al., GCN circ. 39511; Li et al., GCN circ. 39514; and Junjie-Jin et al., GCN circ. 39515). A redshift of z = 3.315 has been reported by Zhu et al. (GCN circ. 39487). We measure the following magnitudes, calibrated against Pan-STARRS DR2 stars and not corrected for Galactic extinction: Date | UT start | t_mid - t0 (hours) | mag | error | filter | ---------------------------------------------------------------------- 2025-02-27 01:28:39 18.94 21.22 0.29 i' 2025-02-27 01:28:40 18.94 21.44 0.36 r' 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/39524. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37537] LIGO/Virgo/KAGRA S250227e: Updated Sky localization
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39523 SUBJECT: LIGO/Virgo/KAGRA S250227e: Updated Sky localization DATE: 25/02/27 17:40:48 GMT FROM: ethan.payne(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 S250227e (GCN Circular 39506). 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/S250227e For the Bilby.multiorder.fits,0 sky map, the 90% credible region is well fit by an ellipse with an area of 280 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(19h19m, +06d18m, 14.62d, 6.11d, 101.52d) Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2004 +/- 527 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. (2023) arXiv:2307.13380 View this GCN Circular online at https://gcn.nasa.gov/circulars/39523. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37536] LIGO/Virgo/KAGRA S250226dl: Updated Sky localization
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39522 SUBJECT: LIGO/Virgo/KAGRA S250226dl: Updated Sky localization DATE: 25/02/27 17:34:46 GMT FROM: ethan.payne(a)ligo.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S250226dl (GCN Circular 39504). 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/S250226dl For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 1218 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3361 +/- 1041 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. (2023) arXiv:2307.13380 View this GCN Circular online at https://gcn.nasa.gov/circulars/39522. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37535] GRB 250225B: VLT/Xshooter imaging
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39521 SUBJECT: GRB 250225B: VLT/Xshooter imaging DATE: 25/02/27 17:12:33 GMT FROM: Yu-Han Yang at University of Rome Tor Vergata <yyang(a)roma2.infn.it> Yu-Han Yang (U Rome), Eleonora Troja (U Rome), and Rosa Becerra (U Rome) report on behalf of the ERC BHianca team: We observed the field of GRB 250225B (Williams et al., GCN 39473) with the Xshooter spectrograph on the ESO VLT UT3 (Melipal). Observations began at T+38.0 hours and, due to visibility constraints, only 2x600s spectra were acquired. Using the acquisition and guiding (A&G) camera, imaging in the I filter was carried out at an average airmass of about 2.1. No source is detected at the position of the optical and nIR candidate counterpart (Schneider et al. GCN 39494, Yang et al. GCN 39495) down to a 3-sigma limit I>22.4 AB mag calibrated using nearby stars in the Legacy Survey DR10 (Dey et al. 2019) catalogue. Compared to our previous measurement (Yang et al. GCN 39495), these observations provide tentative evidence for fading by ~0.3 mag. Further observations are planned. 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/39521. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37534] GRB 250205A / EP250205A: further radio observations with the VLA
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39520 SUBJECT: GRB 250205A / EP250205A: further radio observations with the VLA DATE: 25/02/27 15:43:06 GMT FROM: Stefano Giarratana at INAF-OAB <s.giarratana(a)ira.inaf.it> S. Giarratana (INAF-OAB), M. Giroletti (INAF-IRA), G. Ghirlanda (INAF-OAB), N. Di Lalla (Stanford Univ.), N. Omodei (Stanford Univ.), O. S. Salafia (INAF-OAB) At 06:32:26 UT on 2025 Feb 8 (T_mid = 2.41 days post-burst) and at 05:58:32 UT on 2025 Feb 13 (T_mid = 7.39 days post-burst) the Karl G. Jansky VLA observed the field of GRB 250205A / EP250205A (Saccardi et al., GCN 39154; Mukherjee et al., GCN 39171) in three bands, with central frequencies of 6, 10 and 15 GHz. The standard 3C286 was used as bandpass and flux density calibrator, while J0741+3112 was used as phase calibrator. The preliminary analysis yields the following results: ================================================================ T_mid Freq Peak U.L. r.m.s. Beam PA [days] [GHz] [uJy/b] [uJy] [uJy/b] [arcsec^2] [deg] ================================================================ 2.41 6 - 21 7 0.34x0.31 47 2.41 10 38 - 8 0.23x0.20 49 2.41 15 - 21 7 0.14x0.12 34 7.39 6 - 24 8 0.38x0.31 65 7.39 10 - 21 7 1.47x0.16 68 7.39 15 - 24 8 0.16x0.12 54 ================================================================ where U.L. are the upper limits (3 sigma) for the non-detections. We would like to thank the staff of the VLA for approving, executing, and processing the observations. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. These observations were carried out as part of project SF171028, approved in the framework of the Fermi - NRAO joint program agreement. View this GCN Circular online at https://gcn.nasa.gov/circulars/39520. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37533] GRB 250226B: INTEGRAL SPI-ACS and PICsIT detection
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39519 SUBJECT: GRB 250226B: INTEGRAL SPI-ACS and PICsIT detection DATE: 25/02/27 14:32:17 GMT FROM: Aishwarya L Thakur at INAF-IAPS, Rome <aishth(a)outlook.com> James Craig Rodi(a), Aishwarya Linesh Thakur(a), Patrizia Barria(a,b), Giulia Gianfagna(a), Lorenzo Natalucci(a,b), Luigi Piro(a), report: GRB 250226B was discovered by Fermi/GBM (GCN 39503) at 2025-02-26T22:30:23 (UTC). In a SPI-ACS light curve above 80 keV, we find a signal temporally coincident with the GBM detection, having an approximate duration of ~ 20 sec. The signal consists of multiple pulses over this duration. The strongest pulse of this signal is also detected in the IBIS/PICsIT data. The approximate peak count rate in SPI-ACS is 95,000 cts/s for E>80 keV, over a median background rate of 63,000 cts/s. This work is based on observations with INTEGRAL, an ESA project with instruments and a science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, and Spain), and with the participation of Russia and the USA. The SPI-ACS detector system has been provided by MPE Garching/Germany. ----- (a) INAF/IAPS-Rome (b) ICSC National Research Centre for High-Performance Computing View this GCN Circular online at https://gcn.nasa.gov/circulars/39519. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37532] GRB 250226B: INTEGRAL SPI-ACS and PICsIT detection
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39519 SUBJECT: GRB 250226B: INTEGRAL SPI-ACS and PICsIT detection DATE: 25/02/27 14:32:17 GMT FROM: Aishwarya L Thakur at INAF-IAPS, Rome <aishth(a)outlook.com> James Craig Rodi(a), Aishwarya Linesh Thakur(a), Patrizia Barria(a,b), Giulia Gianfagna(a), Lorenzo Natalucci(a,b), Luigi Piro(a), report: GRB 250226B was discovered by Fermi/GBM (GCN 39503) at 2025-02-26T22:30:23 (UTC). In a SPI-ACS light curve above 80 keV, we find a signal temporally coincident with the GBM detection, having an approximate duration of ~ 20 sec. The signal consists of multiple pulses over this duration. The strongest pulse of this signal is also detected in the IBIS/PICsIT data. The approximate peak count rate in SPI-ACS is 95,000 cts/s for E>80 keV, over a median background rate of 63,000 cts/s. This work is based on observations with INTEGRAL, an ESA project with instruments and a science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, and Spain), and with the participation of Russia and the USA. The SPI-ACS detector system has been provided by MPE Garching/Germany. ----- (a) INAF/IAPS-Rome (b) ICSC National Research Centre for High-Performance Computing View this GCN Circular online at https://gcn.nasa.gov/circulars/39519. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37531] EP250226a/GRB 250226A: INTEGRAL SPI-ACS and PICsIT detection
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39518 SUBJECT: EP250226a/GRB 250226A: INTEGRAL SPI-ACS and PICsIT detection DATE: 25/02/27 14:31:11 GMT FROM: Aishwarya L Thakur at INAF-IAPS, Rome <aishth(a)outlook.com> Aishwarya Linesh Thakur(a), James Craig Rodi(a), Patrizia Barria(a,b), Giulia Gianfagna(a), Luigi Piro(a), Lorenzo Natalucci(a,b) report: EP250226a/GRB 250226A was discovered by Fermi/GBM (GCN 39479) and EP-WXT (GCN 39482) at 2025-02-26T06:34:57 (UTC) and has also been detected by GECAM-B (GCN 39492) In a SPI-ACS light curve above 80 keV, we find a signal temporally coincident with the GBM and EP-WXT detections, having an approximate duration of ~ 15 sec. The signal consists of a single pulse over this duration. This signal is also detected marginally in the IBIS/PICsIT data. The approximate peak count rate in SPI-ACS is 74,000 cts/s for E>80 keV, over a median background rate of 67,600 cts/s. This work is based on observations with INTEGRAL, an ESA project with instruments and a science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, and Spain), and with the participation of Russia and the USA. The SPI-ACS detector system has been provided by MPE Garching/Germany. ----- (a) INAF/IAPS-Rome (b) ICSC National Research Centre for High-Performance Computing View this GCN Circular online at https://gcn.nasa.gov/circulars/39518. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37530] GRB 250225B: INTEGRAL SPI-ACS detection
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39517 SUBJECT: GRB 250225B: INTEGRAL SPI-ACS detection DATE: 25/02/27 14:29:04 GMT FROM: Aishwarya L Thakur at INAF-IAPS, Rome <aishth(a)outlook.com> Aishwarya Linesh Thakur(a), Patrizia Barria(a,b), James Craig Rodi(a), Giulia Gianfagna(a), Luigi Piro(a), Lorenzo Natalucci(a,b) report: GRB 250225B was discovered by Swift/BAT (GCN 39479) at 2025-02-25T19:39:13 (UTC) and has also been detected by SVOM/GRM (GCN 39493), Konus Wind (GCN 39498) and Fermi/GBM (GCN 39502). In a SPI-ACS light curve above 80 keV, we find a signal temporally coincident with these detections, having an approximate duration of ~ 3 sec. The signal consists of a single pulse over this duration. The approximate peak count rate in SPI-ACS is 90,000 cts/s for E>80 keV, over a median background rate of 70,800 cts/s. This work is based on observations with INTEGRAL, an ESA project with instruments and a science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, and Spain), and with the participation of Russia and the USA. The SPI-ACS detector system has been provided by MPE Garching/Germany. ----- (a) INAF/IAPS-Rome (b) ICSC National Research Centre for High-Performance Computing View this GCN Circular online at https://gcn.nasa.gov/circulars/39517. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37529] EP250225a: NOT optical candidate counterpart
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39516 SUBJECT: EP250225a: NOT optical candidate counterpart DATE: 25/02/27 12:49:18 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> Daniele B. Malesani (DAWN/NBI and Radboud Univ.), Andrew J. Levan (Radboud Univ. and DAWN/NBI), Antonio Martin-Carrillo (UCD), Franz E. Bauer (PUC), Peter G. Jonker (Radboud Univ.), Maria E. Ravasio (Radboud Univ.), M. Alejandra Diaz Teodori (NOT and Turku Univ.), Roar H. Rasmussen (NOT), report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP250225a (Jiang et al., GCN 39475) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were carried out in the r and z filters, with mean times 2025 Feb 26.98 and 27.00 UT (1.47 and 1.49 days after the trigger, respectively). Template subtraction of the NOT images using the Legacy Survey as reference yields a potential faint candidate at the edge of the EP/WXT error circle, located at coordinates: RA(J2000) = 09:25:04.07 Dec(J2000) = -04:53:40.2 This position is consistent with an object in the Legacy Survey (with magnitudes g = 23.22, r = 22.48, i = 21.53, z = 21.57). The object looks point-like both in our data (PSF 0.75" in the z band) and in the Legacy Survey. Photometry confirms a brightening of 0.50 +- 0.05 and 0.33 +- 0.10 mag in the r and z bands, respectively, when compared to the archival fluxes in the Legacy Survey. The point-like nature of the source suggests either a transient on top of a compact host galaxy or stellar variability. Further observations are planned (and encouraged) to establish the nature of this object and its association with EP250225a. View this GCN Circular online at https://gcn.nasa.gov/circulars/39516. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37528] EP250226a/GRB 250226A:Xinglong optical follow-up observations
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39515 SUBJECT: EP250226a/GRB 250226A:Xinglong optical follow-up observations DATE: 25/02/27 12:36:12 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), Sen-Liu (NAOC), JinLei-Zhang (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report: We observed the field of the fast X-ray transient EP250226a/GRB 250226a (Jiang et al., GCN #39482; The Fermi team, GCN #39479) using the the Xinglong 2.16-m telescope located at Xinglong, Hebei, China. We obtained 3600 s R and I-band with the time of 2025-02-26T17:04:55 . The optical object reported by An et al. (GCN #39486) is detected in our image. We measure a preliminary magnitude of R = 21.19 +/- 0.07 and I = 21.68 +/- 0.05 mag (AB), calibrated against nearby stars from the Pan-STARRS catalog. We summarize our observation results as follows: Obs. No. | Time (UTC) | Exposure Time (s) | Filter | Apparent mag (AB) | Telescope Name 1 | 2025-02-26T17:04:55 | 3600 s | R |21.19 +/- 0.07| Xinglong 2.16-cm Telescope 2 | 2025-02-26T18:05:21 | 3600 s | I | 21.68 +/- 0.0 | Xinglong 2.16-m Telescope View this GCN Circular online at https://gcn.nasa.gov/circulars/39515. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37527] EP250226a / GRB 250226A: SVOM/VT optical observations
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39514 SUBJECT: EP250226a / GRB 250226A: SVOM/VT optical observations DATE: 25/02/27 11:48:14 GMT FROM: Xuhui Han at NAOC/SVOM <hxh(a)nao.cas.cn> R. Z. Li (YNAO), Z. Q. Wang (GXU), W. K. Zheng (UCB), X. H. Han, L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. N. Ma, H. B. Cai, J. Wang, Y. Xu, J. Y. Wei (NAOC), J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM team: The SVOM/VT conducted a ToO follow-up observation of the EP250226a/GRB 250226A (Jiang et al., GCN 39482; Fermi GBM team, GCN 39479; Zhang et al., GCN 39492; INTEGRAL/SPI-ACS (triNum #11070)) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously with an exposure time of 18*100 seconds. The afterglow (An et. al., GCN 39486; Zhu et. al., GCN 39487; Magnani et al., GCN 39488; Li et. al., GCN 39489; Aryan et al., GCN 39509; Zou et al., GCN 39511; Zhu et al., GCN 39487) was detected with a brightness of 22.58+/-0.14 mag (AB) in VT_B and 21.56+/-0.10 mag (AB) in VT_R, at the mid-time of 20.45 hours post 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/39514. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37526] EP250226a/GRB 250226A: refined analysis of the EP-WXT and FXT observations
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39513 SUBJECT: EP250226a/GRB 250226A: refined analysis of the EP-WXT and FXT observations DATE: 25/02/27 09:18:11 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S. Q. Jiang (NAO, CAS), B.-T. Wang (YNAO, CAS), H. Z. Wu (HUST), T. Zhao, Y. J. Song, Y. Liu (NAO, CAS) report on behalf of the Einstein Probe team: The X-ray transient EP250226a/GRB 250226A triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Jiang et al., GCN 39482), which is also detected by Fermi/GBM (Fermi GBM team, GCN 39479), GECAM-B (Zhang et al., GCN 39492) and INTEGRAL/SPI-ACS (triNum #11070), and followed by several optical telescopes (An et al., GCN 39486, Magnani et al., GCN 39488, Li et al., GCN 39489, Aryan et al., GCN 39509, Zou et al., GCN 39511) at the redshift of 3.315 (Zhu et al., GCN 39487). The refined analysis of the WXT data shows that the event started at 2025-02-26T06:34:54 (UTC) and lasted for 22 s with the peak flux of 9.8 x 10^(-9) erg/s/cm^2, before the observation was interrupted by the autonomous follow-up observation. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed about 44 minutes later as blocked by the Earth. The on-ground analysis shows that an uncatalogued source was detected at R.A. = 224.2641, DEC = 20.9754 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic equivalent hydrogen column density of 3.7 x 10^20 cm^-2 and a photon index of 2.07 (-/+0.06). The derived average unabsorbed 0.5-10 keV flux is 2.89 (-/+0.08) x 10^(-11) erg/s/cm^2. Further FXT observation performed at about 11.9 hours after the trigger showed an average unabsorbed 0.5-10 keV flux is 1.83 (-/+0.18) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/39513. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37525] EP250225a: TRT optical upper limits
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39512 SUBJECT: EP250225a: TRT optical upper limits DATE: 25/02/27 09:15:26 GMT FROM: Zipei Zhu at NAOC <zpzhu(a)nao.cas.cn> Z.P. Zhu, J. An, X. Liu, S.Q. Jiang, S.Y. Fu (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of EP250225a (Jiang et al., GCN 39475) using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. Observations started at 02:45:51 UTC on 2025-02-26, 6 x 300 s and 5 x 300s frames were obtained in Sloan-r and Sloan-z band, respectively. No new optical source is detected in the stacked images within or beside the ~ 2.8 arc min EP/WXT error circle (Jiang et al., GCN 39475), consistent with the non-detection (Li et al., GCN 39477; Lipunov et al., GCN 39478), down to a 5-sigma limiting magnitude of r ~ 21.8 and z ~ 19.5, calibrated with Pan-STARRS sources in the field and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/39512. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37524] EP250226a/GRB 250226A: 1.6m Mephisto observations
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39511 SUBJECT: EP250226a/GRB 250226A: 1.6m Mephisto observations DATE: 25/02/27 08:51:56 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn> Xingzhu Zou, Brajesh Kumar, Wenqiang Fan, Tao Wang, Jiayu Qi, Yuan Fang, Guowang Du, Jinghua Zhang, Helong Guo, Edoardo P. Lagioia, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team: The field of EP250226a/GRB 250226A (Jiang et al., GCN 39482; The Fermi team, GCN 39479) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Three exposures of 300s each in the MEPHISTO u, v, g, and r bands were simultaneously (ug, vr) obtained starting from 2025-02-26T17:59:42 (~ 11.5h after the trigger). In our stacked g and r band images, we detect a source at the position of the optical candidate (An et. al., GCN 39486; Zhu et. al., GCN 39487; Magnani et al., GCN 39488; Li et. al., GCN 39489; Aryan et al., GCN 39509) but not in u, v bands. The preliminary magnitudes and the 3-sigma upper limits are below: Start_Time(UT) | Band | Exp(s) | Mag/LimMag(AB) --------------------|------|--------|--------------- 2025-02-26T17:59:42 | u | 300*3 | > 22.6 2025-02-26T18:17:11 | v | 300*3 | > 23.0 2025-02-26T17:59:42 | g | 300*3 | 22.2 +/- 0.2 2025-02-26T18:17:11 | r | 300*3 | 21.2 +/- 0.1 ------------------------------------------------------------------------------------------------- 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/39511. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37523] LIGO/Virgo/KAGRA S250206dm: Upper limits from SVOM/GRM Observations
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39510 SUBJECT: LIGO/Virgo/KAGRA S250206dm: Upper limits from SVOM/GRM Observations DATE: 25/02/27 08:37:53 GMT FROM: Yue Wang <m18509381757(a)163.com> Yue Wang, Chen-Wei Wang, Shao-Lin Xiong, Shi-Jie Zheng, Ping Wang (IHEP) and Ce Cai (HEBNU) report on behalf of the SVOM team: At the event time 2025-02-06T21:25:30.439 (UTC) of S250206dm (GCN 39175; GCN 39178; GCN 39231), SVOM/GRM was observing normally and monitored 96.6% of the localization probability region of this GW event. There was no SVOM/GRM in-flight trigger around the event time of S250206dm. The routine blind search of SVOM/GRM data also found no burst candidate. Considering three typical GRB spectral models (i.e. soft, normal and hard Band functions), three timescales and the center region of GW localization (RA= 38.21°, Dec = 53.47°), the 3 sigma upper limits of the GRB energy flux (15 keV-5000 keV, in units of 10^-7 erg/s/cm^2) are reported below: |Timescale (s) | Soft | Normal | Hard| | ------------ | ------------ | ------------ | ------------ | |0.1| 0.63 | 1.36 | 17.09 | |1| 0.20 | 0.43 | 5.40 | |10| 0.06 | 0.14 | 1.71 | With the median luminosity distance of 373 Mpc from the GW detection (GCN 39231), we further calculate the following upper limits of the GRB intrinsic luminosity (1 keV-10 MeV, in units of 10^49 erg/s): |Timescale (s) | Soft | Normal | Hard| | ------------ | ------------ | ------------ | ------------ | |0.1| 0.17 |0.25|4.35| |1| 0.05 |0.08|1.38| |10| 0.01 |0.03|0.44| We note that all these results are preliminary and refined analysis will be reported. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Yue Wang (IHEP) (yuewang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/39510. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37522] EP250226a/GRB 250226A: Kinder optical follow-up observations
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39509 SUBJECT: EP250226a/GRB 250226A: Kinder optical follow-up observations DATE: 25/02/27 05:20:39 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> A. Aryan, T.-W. Chen, H.-Y. Hsiao (all NCU), A. K. H. Kong (NTHU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), Y. J. Yang, A. Sankar. K, Y.-C. Pan, C.-C. Ngeow, W.-J. Hou, M.-H. Lee, H.-C. Lin, C.-H. Lai, C.-S. Lin, J.-K. Guo (all NCU), S. Yang, L. L. Fan, Z. N. Wang, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP250226a/GRB 250226a (Jiang et al., GCN 39482; The Fermi team, GCN 39479) using the Lulin One-meter Telescope (LOT) at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2024, arXiv:2406.09270). The first LOT epoch of observations in the g band started at 19:34 UT on the 26th of February 2025 (MJD = 60732.815), ~12.98 hrs after the EP trigger; while the first LOT epoch of observations in the r band started at 19:59 UT on the 26th of February 2025 (MJD = 60732.826), ~13.25 hrs after the EP trigger. We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. In the stacked r-band image, we marginally detected the optical counterpart candidate proposed by An et al. (GCN 39486) and confirmed by several other observations (e.g., Zhu et al., GCN 39487; Magnani et al., GCN 39488; and Li et al., GCN 39489). We employed the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform PSF photometry on our stacked frames. The details of the observations and measured photometry (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass LOT | g | 60732.815 | 12.98 | 300 * 3 | >21.1 | 0".92 | 1.02 LOT | r | 60732.826 | 13.25 | 300 * 3 | 21.73 +/- 0.17 | 0".91 | 1.01 The presented magnitudes were calibrated using the field stars from the Pan-STARRS1 catalog and were not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_g = 0.16 mag and A_r = 0.11 mag, respectively, in the direction of the transient (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/39509. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37521] LIGO/Virgo/KAGRA S250223dk: Insight-HXMT/HE sub-threshold detection of a burst (HEB 250223501)
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39508 SUBJECT: LIGO/Virgo/KAGRA S250223dk: Insight-HXMT/HE sub-threshold detection of a burst (HEB 250223501) DATE: 25/02/27 03:06:58 GMT FROM: yqzhang_cl(a)163.com Ce Cai (HEBNU), Shao-Lin Xiong, Xiao-Bo Li, Shu-Xu Yi, Shuang-Nan Zhang (IHEP) report on behalf of the Insight-HXMT team: At the event time (T0 = 2025-02-23T12:01:15.360 UTC) of the LIGO/Virgo/KAGRA S250223dk event, which was reported to be possibly associated with a sub-threshold burst candidate by Swift/BAT (GCN 39443, 39499), Insight-HXMT was observing 99.97% of the localization probability region based on the combined skymap and there is no Insight-HXMT/HE triggers from the on-ground automated blind search around this event. Thus, we implemented a targeted search [1] for sub-threshold burst signals within the window of T0+/-30 s using the central region of the joint LVK-Swift/BAT localization probability map (i.e. RA = 85.341 deg, Dec = -47.554 deg) and three types of GRB spectra. Our targeted search detected a burst candidate (named as HEB 250223501) with about 4 sigma on the 1-second timescale, starting at T0 - 9.50 s. We note that the time of this Insight-HXMT/HE burst candidate is well consistent with the start time of the Swift/BAT candidate (T0 - 10.240 s, GCN 39443), but the duration is much shorter, which could be explained as the detection energy band of Insight-HXMT/HE is higher than that of Swift/BAT in terms of GRB observation. We note that these results are very preliminary. Refined analysis will be reported later. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://hxmten.ihep.ac.cn/. [1] Cai, C., Xiong, S. L., Li, C. K., et al. 2021, MNRAS, 508, 3910S View this GCN Circular online at https://gcn.nasa.gov/circulars/39508. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37520] LIGO/Virgo/KAGRA S250227y: Retraction of GW compact binary merger candidate
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39507 SUBJECT: LIGO/Virgo/KAGRA S250227y: Retraction of GW compact binary merger candidate DATE: 25/02/27 01:38:00 GMT FROM: chl20171(a)outlook.com The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: The trigger S250227y is no longer considered to be a candidate of interest. This candidate was initially identified by one or more early-warning analyses by matching partial signal templates to the data. Analysis of additional data up to the putative merger time, with full signal templates, did not make a significant detection, indicating that the initial candidate was likely due to transient noise. View this GCN Circular online at https://gcn.nasa.gov/circulars/39507. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37519] LIGO/Virgo/KAGRA S250227e: Identification of a GW compact binary merger candidate
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39506 SUBJECT: LIGO/Virgo/KAGRA S250227e: Identification of a GW compact binary merger candidate DATE: 25/02/27 00:59:12 GMT FROM: chl20171(a)outlook.com The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250227e during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-02-27 00:12:45.474 UTC (GPS time: 1424650383.474). The candidate was found by the GstLAL [1] analysis pipeline. S250227e is an event of interest because its false alarm rate, as estimated by the online analysis, is 2.6e-12 Hz, or about one in 1e4 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250227e After parameter estimation by RapidPE-RIFT [2], the classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), NSBH (<1%), or BNS (<1%). There is evidence for excess noise in L1 coinciding with the merger time. There is evidence for nonstationary noise in V1 around the event time. These data quality issues may affect the parameters or the significance of the candidate. Assuming the candidate is astrophysical in origin, the probability that the lighter compact object is consistent with a neutron star mass (HasNS) is <1%. [3] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [3] Both HasNS and HasRemnant consider the support of several neutron star equations of state. 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 [4], distributed via GCN notice about 26 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [4], 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 500 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2077 +/- 642 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. (2023) arXiv:2305.05625 [2] Rose et al. (2022) arXiv:2201.05263 and Pankow et al. PRD 92, 023002 (2015) doi:10.1103/PhysRevD.92.023002 [3] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [4] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/39506. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37518] Fermi GRB 250226B: Global MASTER-Net observations report
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39505 SUBJECT: Fermi GRB 250226B: Global MASTER-Net observations report DATE: 25/02/26 23:31:13 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 250226B ( Fermi GBM team, GCN 39503) errorbox 99 sec after notice time and 134 sec after trigger time at 2025-02-26 22:32:37 UT, with upper limit up to 16.4 mag. Observations started at twilight. The observations began at zenith distance = 75 deg. The sun altitude is -13.9 deg. The galactic latitude b = -7 deg., longitude l = 24 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2792989 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 150 | 2025-02-26 22:32:37 | MASTER-Tunka | (18h 59m 50.08s , -12d 13m 54.5s) | C | 30 | 16.4 | 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/39505. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37517] LIGO/Virgo/KAGRA S250226dl: Identification of a GW compact binary merger candidate
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39504 SUBJECT: LIGO/Virgo/KAGRA S250226dl: Identification of a GW compact binary merger candidate DATE: 25/02/26 23:30:23 GMT FROM: chl20171(a)outlook.com The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250226dl during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2025-02-26 22:48:38.699 UTC (GPS time: 1424645336.699). The candidate was found by the CWB [1], CWB BBH [2], GstLAL [3], MBTA [4], PyCBC Live [5], and SPIIR [6] analysis pipelines. S250226dl is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.2e-12 Hz, or about one in 1e4 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250226dl 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 the lighter compact object 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. 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 28 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 1479 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3587 +/- 1101 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. (2023) arXiv:2305.05625 [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] 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/39504. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37516] GRB 250226B: Fermi GBM Final Real-time Localization
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39503 SUBJECT: GRB 250226B: Fermi GBM Final Real-time Localization DATE: 25/02/26 22:40:51 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 22:30:23 UT on 26 Feb 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250226B (trigger 762301828.12293 / 250226938). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 284.4, Dec = -10.8 (J2000 degrees, equivalent to J2000 18h 57m, -10d 48'), with a statistical uncertainty of 1.9 degrees. The angle from the Fermi LAT boresight is 71.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250226938/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250226938/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250226938/… View this GCN Circular online at https://gcn.nasa.gov/circulars/39503. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37515] GRB 250225B: Fermi GBM Observation
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39502 SUBJECT: GRB 250225B: Fermi GBM Observation DATE: 25/02/26 22:38:04 GMT FROM: Matt Godwin <msg0028(a)uah.edu> M. Godwin (UAH), C. Meegan (UAH), P. Veres (UAH) and R. Hamburg (USRA) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 19:39:13.83 UT on 25 February 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250225B (trigger 762205158/250225819). which was also detected by Swift BAT (H. A. Krimm et al. 2025, GCN 39473), Konus-Wind (A. Tsvetkova et al. 2025, GCN 39498), and VLT/FORS2 (Schneider et al. 2025, GCN 39494) The Fermi GBM on-ground location is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 55 degrees. The GBM light curve consists of one bright peak followed my multiple short peaks with a duration (T90) of about 335 s. The time-averaged spectrum from T0-3.6 to T0+340.5 s is best fit by a power law function with an exponential high-energy cutoff.The power law index is -1.30 +/- 0.05 and the cutoff energy, parameterized as Epeak, is 218 +/- 28 keV. The event fluence (10-1000 keV) in this time interval is (2.14 +/- 0.11)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.3 s in the 10-1000 keV band is 21.9 +/- 0.3 ph/s/cm^2. The time-averaged spectrum of the first peak from T0 to T0+3.6 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.06 +/- 0.02 and the cutoff energy, parameterized as Epeak, is 568 +/- 42 keV. The Band function fits the spectrum equally well, with an Epeak of 547 +/- 46 keV, alpha = -1.05 +/- 0.03 and beta = -2.85 +/-0.67. 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/39502. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37514] GRB 250221A: ATCA Detections and Upper Limits
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39501 SUBJECT: GRB 250221A: ATCA Detections and Upper Limits DATE: 25/02/26 21:23:21 GMT FROM: agul8829(a)uni.sydney.edu.au A. Gulati (USyd), G. E. Anderson (Curtin), Claire Morley (Curtin), S. Chastain (UNM), J. K. Leung (UofT/HUJI), A. J. van der Horst (GWU), and L. Rhodes (TSI/McGill) on behalf of the ATCA PanRadio GRB collaboration We observed long GRB 250221A (Palmer et al., GCN 39396) as part of The Australia Telescope Compact Array (ATCA) "PanRadio GRB" Large Project C3542 (PI: G. Anderson) at 5.5 and 9 GHz on 2025-02-21 (starting 6 minutes post-burst, for 10 hours), and on 2025-02-23 (starting 2.2 days post burst for 4 hours). No radio sources were detected near the Swift/XRT enhanced position (Beardmore et al., GCN 39404) in the first epoch, with a 3-sigma upper limit of 24 uJy at 9 GHz. We detect a radio counterpart in the second epoch at a position consistent with the Swift/XRT enhanced position, with a flux of 233 +/- 15 uJy at 9 GHz. This value significantly exceeds the 10 GHz VLA detection at 1.95 days (Ricci et al., GCN 39433), possibly due to strong interstellar scintillation near the typical 10 GHz transition frequency. We thank the CSIRO Space and Astronomy staff for supporting these observations. We acknowledge the Gomeroi people as the traditional owners of the Observatory site. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) which is funded by the Australian Government for operation as a National Facility managed by CSIRO. View this GCN Circular online at https://gcn.nasa.gov/circulars/39501. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37513] GRB 250225B: REM NIR upper limits
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39500 SUBJECT: GRB 250225B: REM NIR upper limits DATE: 25/02/26 19:12:09 GMT FROM: Matteo Ferro at INAF-OAB <matteo.ferro(a)inaf.it> M. Ferro, R. Brivio, P. D'Avanzo, S. Covino, D. Fugazza, S. Campana (INAF-OAB), and L. Izzo (INAF-OACn and DARK/NBI) report on behalf of the REM team: We observed the field of Swift detected GRB250225B (Williams et al., GCN 39473), also seen by SVOM (Zhang et al., GCN 39493) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the J, H, and K bands, started on 2025 February 26 at 08:27:46 UT (i.e. 12.8 hr after the burst), and lasted for about 1 hour. From preliminary inspection inside the BAT error circle, we do not find any counterpart at the position of the reported optical/NIR candidate counterpart (Schneider et al., GCN 39494, Yang et al., GCN 39495) down to the following 3sigma limit: H > 17.5 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 13.2 hours after the trigger J > 17.1 (Vega; calibrated against the 2MASS catalogue) at a mid-time of 13.4 hours after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/39500. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37512] LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Updated Sky localization and Coincidence with External Event
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39499 SUBJECT: LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Updated Sky localization and Coincidence with External Event DATE: 25/02/26 18:26:53 GMT FROM: ethan.payne(a)ligo.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration along with the Swift/BAT-GUANO team 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 S250223dk (GCN Circular 39443). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.offline0.multiorder.fits,0, distributed via GCN Notice, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S250223dk For the Bilby.offline0.multiorder.fits,0 sky map, the 90% credible region is 18323 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 9589 +/- 6347 Mpc (a posteriori mean +/- standard deviation). A search performed by the RAVEN pipeline [2] found a temporal coincidence between S250223dk and a sub-threshold Swift/BAT trigger with ID 762004910 (GCN circular 39443). The GRB trigger time is 10.24 seconds before the GW candidate event. The estimated joint false alarm rate for the coincidence using just timing info is 1.9e-07 Hz, or about one in a month. The GRB candidate was found during a joint targeted search between the LIGO/Virgo/KAGRA collaboration and Swift/BAT-GUANO, and has a false alarm rate of 7.4e-05 Hz, or about one in 3 hours. RAVEN has also identified an additional detection from Fermi GBM. Combined sky maps are also available: * combined-ext.multiorder.fits,0, an initial localization, distributed via GCN notice about 12 hours after the candidate event time. * combined-ext.multiorder.fits,1, an initial localization, distributed via GCN notice about 12 hours after the candidate event time. * combined-ext.multiorder.fits,2, an initial localization, distributed via GCN notice about 13 hours after the candidate event time. * combined-ext.multiorder.fits,3, an initial localization, distributed via GCN notice about 15 hours after the candidate event time. * combined-ext.multiorder.fits,5, an updated localization, distributed via GCN notice about 3 days after the candidate event time. The joint LVK-Swift/BAT localization probability map peaks at RA = 85.341 deg, Dec = -47.554 deg. A circle with a radius of 10 arcmin around this position contains 52% of the integrated joint probability. For the combined-ext.multiorder.fits,5 sky map, the 90% credible region is 1 deg2. Considering the overlap of the individual sky maps, the estimated joint false alarm rate for the spatial and temporal coincidence is 1.7e-08 Hz, or about one in 2 years. After considering trials factors, this means the joint FAR is larger than the ‘'high significance’' alert threshold and this joint event is no longer considered significant. 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. (2023) arXiv:2307.13380 [2] Urban, A. L. 2016, Ph.D. Thesis https://dc.uwm.edu/etd/1218 and Piotrzkowski, B. J. 2022, Ph.D. Thesis https://dc.uwm.edu/etd/3060 View this GCN Circular online at https://gcn.nasa.gov/circulars/39499. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37511] Konus-Wind detection of GRB 250225B
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39498 SUBJECT: Konus-Wind detection of GRB 250225B DATE: 25/02/26 18:14:00 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 long-duration GRB 250225B (Swift-BAT detection: Williams et al., GCN 39473; SVOM/GRM detection: Zhang et al., GCN 39493) triggered Konus-Wind at T0=70750.895 s UT (19:39:10.895). The burst light curve shows a bright initial pulse which starts at ~T0-2.2 s and has a total duration of ~3.3 s, followed by two weaker emission episodes centered around ~T0+60 s and T0+108 s. The emission is seen up to ~6 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250225_T70750/ As observed by Konus-Wind, the burst had a fluence of 1.54(-0.18,+0.28)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+0.262 s, of 1.14(-0.24,+0.35)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the initial pulse (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.14(-0.16,+0.18) and Ep = 634(-181,+393) keV (chi2 = 66/84 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -1.7 (chi2 = 66/83 dof). The time-averaged spectrum of the second emission episode (measured from T0+57.600 to T0+65.792 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model with alpha = -1.23(-0.21,+0.28) and Ep = 361(-118,+292) keV (chi2 = 97/99 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -1.7 (chi2 = 95/98 dof). The time-averaged spectrum of the third emission episode (measured from T0+106.752 to T0+114.944 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model with alpha = -0.91(-0.69,+1.12) and Ep = 187(-74,+228) keV (chi2 = 110/99 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -1.7 (chi2 = 110/98 dof). 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/39498. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37510] LIGO/Virgo/KAGRA S250223dk: DECam optical detections of Swift X-ray sources
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39497 SUBJECT: LIGO/Virgo/KAGRA S250223dk: DECam optical detections of Swift X-ray sources DATE: 25/02/26 17:49:58 GMT FROM: Antonella Palmese at Carnegie Mellon University <apalmese(a)andrew.cmu.edu> Antonella Palmese (CMU), Lei Hu (CMU), Xander J. Hall (CMU), Tomás Cabrera (CMU), Igor Andreoni (UNC), Brendan O’Connor (CMU), Keerthi Kunnumkai (CMU), report on behalf of the GW-MMADS team: The high probability area of the joint LVK/Swift-GUANO alert for the gravitational wave candidate S250223dk (GCN 39443) was observed using the wide-field Dark Energy Camera (DECam) on the 4m Blanco telescope (GCN 39462), and we analyzed the data from observations starting 2025-02-24T03:45:38 and 2025-02-25T00:50:13 (GCN 39468). We detect a variable source consistent with the location of the Swift XRT source S250223dk_X1 (GCN 39485) at the position of a Quaia (Storey-Fisher et al. 2024) likely quasar source (unWISE source id 0850m470o0042962, RA, dec=85.499,-47.358 [J2000]) with a photometric redshift of 1.4+-0.2, consistent with the distance of the GW alert. Stacked difference imaging with respect to templates from the Dark Energy Survey data reveals a clear source (AT 2025csi) in the griz bands. Our preliminary photometry on the difference imaging results in the following magnitudes: | MJD | Band | mag | | ---------- | ---- | -------------- | | 60730.1567 | g | 20.90 +- 0.01 | | 60730.1748 | i | 20.38 +- 0.01 | | 60731.0349 | g | 20.82 +- 0.007 | | 60731.0530 | i | 20.41 +- 0.009 | We also inspected archival DECam data at this location and note that this possible quasar showed a steady ~1 mag increase in brightness in all bands between 2013 and 2018. Some archival detections are also present from ATLAS forced photometry over the past two years. The archival detections suggest that the source variability may be unrelated to the GW alert, although we encourage follow-up observations to establish the nature of this object and whether it is currently experiencing flaring activity. We also detect a transient (AT 2025cpu) in the griz bands consistent with the location of S250223dk_X5 at position RA, dec= 85.51643, -47.70934 [J2000], with the following magnitudes: | MJD | Band | mag | | ---------- | ---- | ------------- | | 60730.1569 | g | 22.71 +- 0.03 | | 60730.1748 | i | 22.63 +- 0.07 | | 60731.0349 | g | 22.55 +- 0.03 | | 60731.0530 | i | 22.74 +- 0.05 | We note that this source appears as a nuclear transient in a possible galaxy with photometric redshift of 0.797+-0.088 (from the DESI Legacy Survey photometric redshift catalog). The archival DECam observations for this source show variability of up to a magnitude, thus we cannot exclude that these detections are due to AGN variability. Further analysis of these sources is planned and follow-up observations are encouraged. We thank the CTIO and NOIRLab staff for supporting observations and data calibration. View this GCN Circular online at https://gcn.nasa.gov/circulars/39497. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37509] EP250223a: CrAO ZTSH optical observation
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39496 SUBJECT: EP250223a: CrAO ZTSH optical observation DATE: 25/02/26 17:18:16 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> E. Mazaeva (IKI), V. Rumyantsev (CrAO), A. Pozanenko (IKI), N. Pankov (HSE, IKI), A. Volnova (IKI) report on behalf of IKI GRB-FuN collaboration: We observed the field of EP250223a (Lian et al., GCN 39429) 2.6-meter ZTSh telescope of CrAO starting on (UT) 2025-02-25 18:01:15. The optical counterpart of EP250223a (Hauptmann et al., GCN 39436; Wu et al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo et al., GCN 39441; Xin et al., GCN 39445; Guo et al., GCN 39447; An et al., GCN 39449; Ducoin et al., GCN 39453; O’Neill et al., GCN 39455; Aryan et al., GCN 39464; Saikia et al., GCN 39472; Wang et al., GCN 39476) at the redshift of 2.756 (Levan et al., GCN 39438) is clearly detected. The preliminary photometry of the optical counterpart is the following: Date UT start T-T0 Exp. Filter OT Err. UL(3sigma) (mid, days) (s) 2025-02-25 18:01:15 2.15250 41x120 R 20.62 0.05 22.2 The magnitudes were calibrated using nearby PS1 stars using Lupton transformations to R-magnitude. No correction has been made for a Galactic extinction towards the counterpart. View this GCN Circular online at https://gcn.nasa.gov/circulars/39496. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37508] GRB 250225B: VLT optical and near-infrared candidate counterpart
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39495 SUBJECT: GRB 250225B: VLT optical and near-infrared candidate counterpart DATE: 25/02/26 16:31:57 GMT FROM: Yu-Han Yang at University of Rome Tor Vergata <yyang(a)roma2.infn.it> Yu-Han Yang (U Rome), Brendan O’Connor (CMU), Eleonora Troja (U Rome), Rosa Becerra (U Rome) and Muskan Yadav (U Rome) report: We observed the field of GRB 250225B (Williams et al., GCN 39473) with the FORS2 imager on the ESO VLT UT1 (Antu) and the HAWKI imager on the ESO VLT UT4 (Yepun). Observations began at T+13.7 hours and were carried out at an average airmass of about 2.6 in the I filter and in the J filter, respectively. We detect the source reported by Schneider et al. (GCN 39494) at a preliminary magnitude J~21.4 AB mag calibrated using nearby stars in the 2MASS Catalogue. In comparison with archival imaging, the source appears brighter by ~0.5 mag in both the i- and the J-band, thus confirming the brightening reported by Schneider et al. (GCN 39494). Although the probability of a chance alignment with the nearby galaxy ESO 340-26 remains small (P_cc<3%; Dichiara et al. 2020), we note that the observed color and magnitude of the candidate counterpart do not match the behavior of the kilonova AT2017gfo, if placed at a distance of 78 Mpc. If confirmed as the GRB afterglow, our observations favor the association with the underlying fainter galaxy, visible in the Legacy Survey (P_cc ~0.8%; Bloom et al. 2002) 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/39495. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37507] GRB 250225A: VLT optical and near-infrared candidate counterpart
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39495 SUBJECT: GRB 250225A: VLT optical and near-infrared candidate counterpart DATE: 25/02/26 16:31:57 GMT FROM: Yu-Han Yang at University of Rome Tor Vergata <yyang(a)roma2.infn.it> Yu-Han Yang (U Rome), Brendan O’Connor (CMU), Eleonora Troja (U Rome), Rosa Becerra (U Rome) and Muskan Yadav (U Rome) report: We observed the field of GRB 250225A (Williams et al., GCN 39473) with the FORS2 imager on the ESO VLT UT1 (Antu) and the HAWKI imager on the ESO VLT UT4 (Yepun). Observations began at T+13.7 hours and were carried out at an average airmass of about 2.6 in the I filter and in the J filter, respectively. We detect the source reported by Schneider et al. (GCN 39494) at a preliminary magnitude J~21.4 AB mag calibrated using nearby stars in the 2MASS Catalogue. In comparison with archival imaging, the source appears brighter by ~0.5 mag in both the i- and the J-band, thus confirming the brightening reported by Schneider et al. (GCN 39494). Although the probability of a chance alignment with the nearby galaxy ESO 340-26 remains small (P_cc<3%; Dichiara et al. 2020), we note that the observed color and magnitude of the candidate counterpart do not match the behavior of the kilonova AT2017gfo, if placed at a distance of 78 Mpc. If confirmed as the GRB afterglow, our observations favor the association with the underlying fainter galaxy, visible in the Legacy Survey (P_cc ~0.8%; Bloom et al. 2002) 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/39495. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37506] GRB 250225B: VLT/FORS2 candidate optical afterglow
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39494 SUBJECT: GRB 250225B: VLT/FORS2 candidate optical afterglow DATE: 25/02/26 14:07:48 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> B. Schneider (LAM), A. J. Levan (Radboud and Warwick), D. B. Malesani (DAWN/NBI and Radboud), R. A. J. Eyles-Ferris (Leicester), N. R. Tanvir (Leicester), L. Izzo (INAF/OACn and DARK/NBI), A. Martin-Carrillo (UCD), P. D’Avanzo (INAF/OAB), S. D. Vergani (CNRS, Paris Obs./LUX), report on behalf of the Stargate collaboration: We observed the location of the Swift/BAT GRB 250225B (Williams et al., GCN 39473) with the FORS2 instrument on the VLT UT1. Observations began on 2025 Feb 26.40 UT (13.94 hr after the GRB), and a total of 5x50 s of observations were obtained, at large airmass ~2.3 and deep in twilight. Image subtraction against the z-band template from the Legacy Survey reveals a transient source at coordinates: RA(J2000) = 20:24:33.81 DEC(J2000) = -41:28:25.4 This source is consistent with a faint, extended object visible in the Legacy Survey (with a reported photometric redshift 1.12 +/- 0.18), and photometry suggests it has brightened by about 0.6 magnitudes from the time of the Legacy Survey observations. We consider this a candidate afterglow for GRB 250225B, although we note that detection of fading or an X-ray association will be required to robustly establish its nature. The source is offset by ~3 arcmin (65 kpc in projection) from the bright galaxy ESO 340-26. Although this is well within the range of offsets seen for merger-driven GRBs, if this transient is indeed the afterglow of GRB 250225B, the presence of an underlying source in the Legacy Survey suggests the proximity to ESO 340-26 is a chance association. Our subtraction shows no sign of any other transients within the BAT error circle, including within or close to ESO 340-26. The 5-sigma limiting magnitude for any such transient corresponds to z > 22.7 (M_z > -12 at redshift z = 0.018). We thank the staff at ESO, among which Marco Berton, for their assistance in obtaining these challenging observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39494. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37505] GRB 250225B: SVOM/GRM observation of a long burst
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39493 SUBJECT: GRB 250225B: SVOM/GRM observation of a long burst DATE: 25/02/26 14:06:50 GMT FROM: yqzhang_cl(a)163.com SVOM/GRM team: Yan-Qiu Zhang, Chao Zheng, Chen-Wei Wang, Shi-Jie Zheng, Wen-Jun Tan, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Nicolas Dagoneau (CEA), Maria-Grazia Bernardini (INAF-OAB), Jean-Luc Atteia (IRAP) report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by a long burst GRB 250225B at 2025-02-25T19:39:14.000 (T0), which was also observed by Swift/BAT (M.A. Williams et al., GCN #39473), Fermi/GBM (triNum #762205158) and INTEGRAL/SPI-ACS (triNum #11068). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-pulses with a T90 of 293.0 +/- 31.2 s in the 15-5000 keV band. In addition, the position of this burst, as determined by Swift/BAT (GCN #39473, RA: 306.145 deg, DEC: -41.4845 deg, Error: 3 arcmin), is located at about 113 degrees from the SVOM optical axis, and outside the ECLAIRs field of view. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250225B.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Yan-Qiu Zhang (IHEP) (zhangyanqiu(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/39493. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37504] GRB 250226A: GECAM-B detection
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39492 SUBJECT: GRB 250226A: GECAM-B detection DATE: 25/02/26 14:05:27 GMT FROM: yqzhang_cl(a)163.com GRB 250226A: GECAM-B detection Yan-Qiu Zhang (IHEP), Shao-Lin Xiong (IHEP), Chen-Wei Wang (IHEP) report on behalf of the GECAM team: GECAM-B was triggered both in-flight and on-ground by a long burst, GRB 250226A, at 2025-02-26T06:34:56.000 UTC (T0), which was also detected by Fermi/GBM (Fermi GBM team, GCN #39479), EP/WXT (EP250226a/GRB 250226A, S.Q. Jiang et al., GCN #39482) and INTEGRAL/SPI-ACS (triNum #11070). According to the GECAM-B light curves in about 5-2000 keV, this burst mainly consists of multiple pulses with a duration (T90) of about 63.5 +/- 11.7 s. The GECAM light curve could be found here: https://www.bursthub.cn//admin/static/gecamgrb250226A.png We note that these results are very preliminary. Refined analysis will be reported later. Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two microsatellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/39492. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37503] GRB 250221A: EP-FXT detection of the X-ray afterglow
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39491 SUBJECT: GRB 250221A: EP-FXT detection of the X-ray afterglow DATE: 25/02/26 12:12:31 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> E. Troja (U Rome), R. L. Becerra (U Rome), W. J. Zhang, T. Y. Lian, H. W. Pan (NAO, CAS), Y. Wang (PMO, CAS), and Y. -H. Yang (U Rome) report: We performed a follow-up observation of GRB 250221A detected by Swift/BAT (Caputo et al., GCN 39396) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation began at 2025-02-23 05:16:58 (UTC), about ~ 2.1 days after the trigger, for a total exposure time of 5.2 ks. At the position of the XRT counterpart (Beardmore et al., GCN 39404), an uncatalogued X-ray source is detected by both FXT-A and FXT-B. This position is also consistent with the optical (Watson et al., GCN 39397; Cotter et al., GCN 39413; Muenter et al., GCN 39417; Shilling et al. GCN 39409; Kumar et al. GCN 39412; Pozanenko et al., GCN 39422; Ghosh et al., GCN 39425; Iskandar et al., GCN 39446) and radio afterglow (Ricci et al., GCN 39433). From a preliminary analysis we derive an observed flux of (1.7 +/- 0.2)*10^-13 erg/cm^2/s (0.3-10.0 keV), consistent with the latest Swift/XRT measurement (Salvaggio et al., GCN 39414) and indicative of a possible rebrightening (Pankov et al., GCN 39427). Further observations are planned. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES. View this GCN Circular online at https://gcn.nasa.gov/circulars/39491. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37502] GRB 250214A: SVOM/GRM observation
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39490 SUBJECT: GRB 250214A: SVOM/GRM observation DATE: 25/02/26 11:48:23 GMT FROM: zhengchao_astro(a)foxmail.com SVOM/GRM team: Chao Zheng, Shi-Jie Zheng, Shao-Lin Xiong, Yue Huang, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Piron (LUPM), Nicolas Dagoneau (CEA), Maria-Grazia Bernardini (INAF-OAB), Jean-Luc Atteia (IRAP) report on behalf of the SVOM team: SVOM/GRM detected GRB 250214A at 2025-02-14T05:32:06 UT (T0), which was also observed by Fermi/GBM (Fermi GBM team, GCN #39320). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-pulses with a duration of about 6 seconds in the 15-600 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250214A.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Chao Zheng (IHEP) (zhengchao97(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/39490. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37501] EP250226a/GRB 250226A: GSP detects optical counterpart
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39489 SUBJECT: EP250226a/GRB 250226A: GSP detects optical counterpart DATE: 25/02/26 10:57:41 GMT FROM: Wenxiong Li <liwenxiong1992(a)gmail.com> W. X. Li, S. J. Xue (NAOC), M. Andrews, J. Farah, D. A. Howell, M. Newsome, E. Padilla Gonzalez, C. McCully, and G. Terreran (Las Cumbres Observatory), on behalf of a larger collaboration, report: Following the detection of the fast X-ray transient EP250226a/GRB 250226A by the Einstein Probe (Jiang et al., GCN 39482), we initiated observations of the fast X-ray transient location starting on Feb 26 at 9:23 UT (~3 hours after the EP/WXT trigger) in the i and z bands. These observations were conducted using the 1-meter telescope at the Las Cumbres Observatory node located at the Cerro Tololo Inter-American Observatory in Chile. The optical counterpart (An et al., GCN 39486; Magnani et al., GCN 39488) was detected in the co-added images with i ~19.0 and z~19.3 mag. These observations were taken as part of the Global Supernova Project. View this GCN Circular online at https://gcn.nasa.gov/circulars/39489. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37500] EP250226a/GRB 250226A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39488 SUBJECT: EP250226a/GRB 250226A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart DATE: 25/02/26 10:37:22 GMT FROM: Francesco <francesco.magnani.work(a)gmail.com> Francesco Magnani (CPPM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), Benjamin Schneider (LAM), Alan M. Watson (UNAM), Kin Ocelotl López (UNAM), William H. Lee (UNAM), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Antonio de Ugarte Postigo (LAM) report: We observed the field of EP250226a (Jiang et al., GCN Circ. 39482), consistent with the likely long GRB 250226A detected by Fermi/GBM (Fermi GCN Circ. 39479), 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 2025-02-26 07:56:43 to 09:14:20 UTC (82 minutes to 164 minutes after the trigger) and obtained 50 minutes of exposure in the i filter. The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2021), with photometric calibration against Pan-STARRS DR1 and image subtraction against Pan-STARRS DR2. Our photometry is in the AB system and is not corrected for Galactic extinction. In our stacked image we detect a source at the position of the optical candidate reported by An et. al. (GCN Circ. 39486) and Zhu et. al. (GCN Circ. 39487) with magnitude: i = 19.05 +/- 0.03 We encourage continued monitoring of this source. 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/39488. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37499] EP250226a / GRB 250226A: VLT/X-shooter redshift of z = 3.315
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39487 SUBJECT: EP250226a / GRB 250226A: VLT/X-shooter redshift of z = 3.315 DATE: 25/02/26 10:21:06 GMT FROM: Zipei Zhu at NAOC <zpzhu(a)nao.cas.cn> Z. P. Zhu (NAOC), A. Saccardi (CEA/Irfu), B. Schneider (LAM), L. Izzo (INAF-OACn and DARK/NBI), J. T. Palmerio (CEA/Irfu), D. Xu (NAOC), N. R. Tanvir (U. Leicester), D. B. Malesani (DAWN/NBI and Radboud Univ.), G. Pugliese (API-UvA), A. J. Levan (Radboud and Warwick), S. D. Vergani (CNRS, Obs. Paris/LUX) report on behalf of the Stargate collaboration: We observed the optical afterglow (An et al., GCN 39486) of EP250226a / GRB 250226A (Fermi GBM team, GCN 39479; Jiang et al., GCN 39482) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-25000 AA, and consist of 2x600 s. The observation mid-time was 2025 Feb. 26 at 08:43:57 (2.15 hr after the GBM trigger). In a 15 s image taken with the acquisition camera on Feb. 26 at 08:27:06 UT, we detect the optical afterglow, for which we measure a magnitude r =19.17 +/- 0.03 AB (calibrated against nearby stars from the Pan-STARRS catalogue). In a preliminary reduction of the spectra, we clearly detect a continuum down to 4000 AA. From the detection of a broad Lya absorption at ~5230 AA and multiple narrow absorption features, including O I, O I*, Si II, Si II*, C II, C II*, C IV, Si IV, Al II, Fe II, Fe II*, Al III, Ni II, Ni II*, Zn II, Cr II, Mg II, Mg I, Ca II we infer the redshift of the GRB to be z = 3.315. We acknowledge expert support from the ESO staff in Paranal, in particular Diego Parraguez and Marco Berton. View this GCN Circular online at https://gcn.nasa.gov/circulars/39487. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37498] EP250226a / GRB 250226A: TRT optical counterpart observation
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39486 SUBJECT: EP250226a / GRB 250226A: TRT optical counterpart observation DATE: 25/02/26 08:35:09 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> J. An, S.Q. Jiang, X. Liu, S.Y. Fu, Z.P. Zhu, D. Xu (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang (NAOC) report on behalf of a large collaboration: We observed the field of EP250226a detected by EP/WXT (Jiang et al., GCN 39482), which is very likely the same event of GRB 250226A detected by Fermi/GBM (Fermi GBM team, GCN 39479), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. We obtained several 300 s frames in the Sloan-r filter. An uncatalogued and decaying optical source is detected within the EP/FXT error circle (Jiang et al., GCN 39482) at coordinates R.A. (J2000) = 14:57:03.63 Dec. (J2000) = +20:58:32.31 with an uncertainty of about 1.0 arcsec. The source has r ~ 17.7 mag at 21.8 min after the EP trigger, calibrated with PanSTARRS DR2 stars and not corrected for Galactic extinction. We think that the source is the optical counterpart of EP250226a / GRB 250226A. View this GCN Circular online at https://gcn.nasa.gov/circulars/39486. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37497] LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39485 SUBJECT: LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources DATE: 25/02/26 08:33:05 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.J. Delaunay (PSU), K.L. Page (U. Leicester), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), S.B. Cenko (NASA/GSFC), R.A.J. Eyles-Ferris (U. Leicester), A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), A.A. Breeveld (UCL-MSSL), S. Campana (INAF-OAB), M. De Pasquale (University of Messina), S. Dichiara (PSU), P. D’Avanzo (INAF-OAB), A. D’Aì (INAF-IASFPA) , V. D’Elia (ASI-SSDC & INAF-OAR), C. Gronwall (PSU), D. Hartmann (Clemson University), N. Klingler (NASA-GSFC / UMBC / CRESST II), N.P.M. Kuin (UCL-MSSL), S. Laha (NASA/GSFC), S.R. Oates (U. Birmingham), J.P. Osborne (U. Leicester), P. O’Brien (U. Leicester), M.J. Page (UCL-MSSL), G. Raman (PSU) S. Ronchini (PSU), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), E. Troja (U Tor Vergata, INAF) report on behalf of the Swift team: Swift has carried out 1 observation of the combined LVK/Swift-BAT-GUANO error region for the GW trigger S250223dk, centred on the most-probable location (RA,Dec = 85.4260, -47.5420 [J2000]). We gathered 5.5 ks of data from 106 ks to 140 ks after the LVK trigger. This observations covers 73% of the probability in the combined skymap. We have detected 7 X-ray sources. Each source is assigned a rank of 1-4 which describes how likely it is to be related to the GW trigger, with 1 being the most likely and 4 being the least likely. The ranks are described at https://www.swift.ac.uk/ranks.php. We have found: * 0 sources of rank 1 * 0 sources of rank 2 * 7 sources of rank 3 * 0 sources of rank 4 RANK 3 sources ============== These are uncatalogued X-ray sources, however they are not brighter than previous upper limits, so do not stand out as likely counterparts to the GW trigger. | Source ID | RA | Dec | Err90 | | S250223dk_X1 | 05h 41m 59.75s | -47d 21' 33.8" | 6.8" | | S250223dk_X2 | 05h 42m 11.19s | -47d 23' 57.3" | 6.4" | | S250223dk_X3 | 05h 41m 58.45s | -47d 33' 26.5" | 6.5" | | S250223dk_X4 | 05h 42m 19.59s | -47d 34' 02.3" | 6.9" | | S250223dk_X5 | 05h 42m 03.87s | -47d 42' 35.1" | 6.4" | | S250223dk_X6 | 05h 42m 01.25s | -47d 43' 06.8" | 6.3" | | S250223dk_X7 | 05h 41m 25.44s | -47d 26' 58.1" | 6.4" | For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2, and photon index (Gamma)=1.7, unless otherwise stated. The results of the XRT automated analysis, including details of the sources listed above, are online at https://www.swift.ac.uk/LVC/S250223dk This circular is an official product of the Swift XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39485. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37496] EP250226a: Global MASTER-Net observations report
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39484 SUBJECT: EP250226a: Global MASTER-Net observations report DATE: 25/02/26 08:09:29 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 EP250226a ( EP Team et al., GCN 39482) errorbox 460 sec after notice time and 3834 sec after trigger time at 2025-02-26 07:39:10 UT, with upper limit up to 20.4 mag. The observations began at zenith distance = 56 deg. The sun altitude is -32.9 deg. The galactic latitude b = 60 deg., longitude l = 28 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2792303 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 3865 | 2025-02-26 07:39:10 | MASTER-OAFA | (14h 57m 01.08s , +20d 57m 34.1s) | C | 60 | 20.4 | 4736 | 2025-02-26 07:53:41 | MASTER-OAFA | (14h 57m 24.39s , +21d 12m 59.9s) | C | 60 | 20.4 | 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/39484. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37495] Swift GRB 250225B: Global MASTER-Net observations report
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39483 SUBJECT: Swift GRB 250225B: Global MASTER-Net observations report DATE: 25/02/26 07:32:53 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 GRB 250225B ( M. A. Williams et al., GCN 39473) errorbox 41481 sec after notice time and 41703 sec after trigger time at 2025-02-26 07:14:16 UT, with upper limit up to 16.6 mag. The observations began at zenith distance = 83 deg. The sun altitude is -37.0 deg. The galactic latitude b = -35 deg., longitude l = 360 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2791924 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 41793 | MASTER-OAFA | C | 180 | 16.6 | 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/39483. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37494] EP250226a/GRB 250226A: EP-WXT detection and FXT follow-up observation of an X-ray transient
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39482 SUBJECT: EP250226a/GRB 250226A: EP-WXT detection and FXT follow-up observation of an X-ray transient DATE: 25/02/26 07:30:36 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S. Q. Jiang (NAO, CAS), B.-T. Wang (YNAO, CAS), H. Z. Wu (HUST), T. Zhao, Y.J. Song, Y. Liu (NAO, CAS) report on behalf of the Einstein Probe team: We report on the detection of an X-ray transient EP250226a at 2025-02-26 06:35:16 (UTC) by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The WXT position of the source is R.A. = 224.273 deg, DEC = 20.973 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The trigger time and the position are generally consistent with the likely long GRB 250226A detected by Fermi (GCN 39479). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error cirlce, an uncatalogued X-ray source was detected at R.A. = 224.2668 deg, DEC = 20.9743 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/39482. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37493] Fermi GRB 250226A: Global MASTER-Net observations report
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39481 SUBJECT: Fermi GRB 250226A: Global MASTER-Net observations report DATE: 25/02/26 07:19:05 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) started inspect of the Fermi GRB 250226A ( Fermi GBM team, GCN 39479) errorbox 24 sec after notice time and 42 sec after trigger time at 2025-02-26 06:35:39 UT, with upper limit up to 20.6 mag. The observations began at zenith distance = 68 deg. The sun altitude is -42.6 deg. The galactic latitude b = 63 deg., longitude l = 32 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2792277 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 47 | 2025-02-26 06:35:39 | MASTER-OAFA | (14h 37m 17.00s , +28d 44m 10.7s) | C | 10 | 17.3 | 62 | 2025-02-26 06:35:39 | MASTER-OAFA | (14h 37m 17.01s , +28d 44m 10.7s) | C | 40 | 18.0 | Coadd 48 | 2025-02-26 06:35:40 | MASTER-OAFA | (14h 47m 34.56s , +29d 06m 42.6s) | C | 10 | 18.8 | 73 | 2025-02-26 06:35:40 | MASTER-OAFA | (14h 47m 34.57s , +29d 06m 42.7s) | C | 60 | 19.9 | Coadd 133 | 2025-02-26 06:35:40 | MASTER-OAFA | (14h 47m 34.56s , +29d 06m 42.7s) | C | 180 | 20.5 | Coadd 97 | 2025-02-26 06:36:24 | MASTER-OAFA | (14h 37m 16.85s , +28d 44m 13.0s) | C | 20 | 17.7 | 98 | 2025-02-26 06:36:25 | MASTER-OAFA | (14h 47m 34.39s , +29d 06m 43.3s) | C | 20 | 19.2 | 132 | 2025-02-26 06:37:04 | MASTER-OAFA | (14h 37m 16.73s , +28d 44m 14.3s) | C | 10 | 17.3 | 143 | 2025-02-26 06:37:04 | MASTER-OAFA | (14h 47m 34.22s , +29d 06m 43.3s) | C | 30 | 19.5 | 168 | 2025-02-26 06:37:40 | MASTER-OAFA | (14h 37m 16.62s , +28d 44m 15.1s) | C | 10 | 17.2 | 193 | 2025-02-26 06:37:40 | MASTER-OAFA | (14h 37m 16.64s , +28d 44m 15.1s) | C | 60 | 18.5 | Coadd 178 | 2025-02-26 06:37:40 | MASTER-OAFA | (14h 47m 34.11s , +29d 06m 43.3s) | C | 30 | 19.6 | 223 | 2025-02-26 06:37:40 | MASTER-OAFA | (14h 47m 34.28s , +29d 06m 43.1s) | C | 120 | 20.0 | Coadd 209 | 2025-02-26 06:38:16 | MASTER-OAFA | (14h 37m 16.46s , +28d 44m 15.8s) | C | 20 | 17.8 | 219 | 2025-02-26 06:38:16 | MASTER-OAFA | (14h 47m 33.97s , +29d 06m 42.9s) | C | 40 | 19.7 | 260 | 2025-02-26 06:39:02 | MASTER-OAFA | (14h 37m 16.25s , +28d 44m 16.5s) | C | 30 | 18.0 | 270 | 2025-02-26 06:39:02 | MASTER-OAFA | (14h 47m 33.77s , +29d 06m 42.4s) | C | 50 | 19.9 | 321 | 2025-02-26 06:39:58 | MASTER-OAFA | (14h 37m 15.96s , +28d 44m 16.6s) | C | 40 | 18.3 | 331 | 2025-02-26 06:39:58 | MASTER-OAFA | (14h 47m 33.52s , +29d 06m 41.8s) | C | 60 | 19.9 | 439 | 2025-02-26 06:41:46 | MASTER-OAFA | (14h 38m 47.22s , +23d 27m 51.0s) | C | 60 | 18.4 | 529 | 2025-02-26 06:41:46 | MASTER-OAFA | (14h 38m 47.22s , +23d 27m 51.0s) | C | 240 | 19.5 | Coadd 449 | 2025-02-26 06:41:46 | MASTER-OAFA | (14h 48m 37.68s , +23d 50m 29.6s) | C | 80 | 20.2 | 559 | 2025-02-26 06:41:46 | MASTER-OAFA | (14h 48m 37.68s , +23d 50m 29.7s) | C | 300 | 20.6 | Coadd 535 | 2025-02-26 06:43:12 | MASTER-OAFA | (14h 38m 46.84s , +23d 27m 50.2s) | C | 80 | 18.6 | 545 | 2025-02-26 06:43:12 | MASTER-OAFA | (14h 48m 37.34s , +23d 50m 28.1s) | C | 100 | 20.2 | 652 | 2025-02-26 06:44:59 | MASTER-OAFA | (14h 38m 46.33s , +23d 27m 48.1s) | C | 100 | 18.8 | 662 | 2025-02-26 06:44:59 | MASTER-OAFA | (14h 48m 36.92s , +23d 50m 26.1s) | C | 120 | 20.2 | 793 | 2025-02-26 06:47:04 | MASTER-OAFA | (14h 38m 45.75s , +23d 27m 45.8s) | C | 130 | 18.7 | 953 | 2025-02-26 06:47:04 | MASTER-OAFA | (14h 38m 45.75s , +23d 27m 45.8s) | C | 450 | 19.7 | Coadd 803 | 2025-02-26 06:47:05 | MASTER-OAFA | (14h 48m 36.39s , +23d 50m 23.4s) | C | 150 | 20.2 | 973 | 2025-02-26 06:49:50 | MASTER-OAFA | (14h 38m 45.03s , +23d 27m 41.9s) | C | 160 | 18.8 | 983 | 2025-02-26 06:49:50 | MASTER-OAFA | (14h 49m 41.16s , +23d 48m 31.7s) | C | 180 | 20.2 | 1163 | 2025-02-26 06:49:50 | MASTER-OAFA | (14h 49m 41.16s , +23d 48m 31.8s) | C | 540 | 20.6 | Coadd 1167 | 2025-02-26 06:53:04 | MASTER-OAFA | (14h 38m 44.30s , +23d 27m 37.0s) | C | 160 | 18.7 | 1177 | 2025-02-26 06:53:04 | MASTER-OAFA | (14h 49m 40.51s , +23d 48m 27.3s) | C | 180 | 20.1 | 1362 | 2025-02-26 06:56:19 | MASTER-OAFA | (14h 38m 43.40s , +23d 27m 31.4s) | C | 160 | 18.6 | 1372 | 2025-02-26 06:56:19 | MASTER-OAFA | (14h 49m 39.69s , +23d 48m 22.0s) | C | 180 | 20.1 | 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/39481. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37492] Fermi trigger No 762205158: Global MASTER-Net observations report
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39480 SUBJECT: Fermi trigger No 762205158: Global MASTER-Net observations report DATE: 25/02/26 07:18:11 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) started inspect of the Fermi GRB250225.82 (trigger No 762205158,20h 13m 48.00s , -40d 49m 58.8s, R=4.37) errorbox 40804 sec after notice time and 40845 sec after trigger time at 2025-02-26 06:59:59 UT, with upper limit up to 17.7 mag. The observations began at zenith distance = 83 deg. The sun altitude is -39.2 deg. The galactic latitude b = -33 deg., longitude l = 0 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2791902 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 40925 | 2025-02-26 06:59:59 | MASTER-OAFA | (20h 11m 46.26s , -42d 14m 07.7s) | C | 160 | 17.6 | 41131 | 2025-02-26 07:03:24 | MASTER-OAFA | (20h 11m 46.06s , -42d 12m 55.8s) | C | 160 | 17.7 | 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/39480. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37491] GRB 250226A: Fermi GBM Final Real-time Localization
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39479 SUBJECT: GRB 250226A: Fermi GBM Final Real-time Localization DATE: 25/02/26 06:42:51 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 06:34:57 UT on 26 Feb 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250226A (trigger 762244502.334384 / 250226274). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 222.1, Dec = 23.8 (J2000 degrees, equivalent to J2000 14h 48m, 23d 48'), with a statistical uncertainty of 3.9 degrees. The angle from the Fermi LAT boresight is 111.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250226274/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250226274/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250226274/… View this GCN Circular online at https://gcn.nasa.gov/circulars/39479. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37490] EP250225a: Global MASTER-Net observations report
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39478 SUBJECT: EP250225a: Global MASTER-Net observations report DATE: 25/02/26 05:31:23 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 EP250225a ( EP Team et al., GCN 39475) errorbox 364 sec after notice time and 58846 sec after trigger time at 2025-02-26 04:34:36 UT, with upper limit up to 20.5 mag. The observations began at zenith distance = 30 deg. The sun altitude is -50.1 deg. The galactic latitude b = 31 deg., longitude l = 238 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2792193 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 58876 | 2025-02-26 04:34:36 | MASTER-OAFA | (09h 24m 15.36s , -04d 59m 40.0s) | C | 60 | 20.5 | 60307 | 2025-02-26 04:58:27 | MASTER-OAFA | (09h 24m 17.17s , -05d 00m 37.2s) | C | 60 | 20.4 | 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/39478. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37489] EP250225a: GSP optical upper limit
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39477 SUBJECT: EP250225a: GSP optical upper limit DATE: 25/02/26 05:25:33 GMT FROM: Wenxiong Li <liwenxiong1992(a)gmail.com> W. X. Li, S. J. Xue (NAOC), M. Andrews, J. Farah, D. A. Howell, M. Newsome, E. Padilla Gonzalez, C. McCully, and G. Terreran (Las Cumbres Observatory), on behalf of a larger collaboration, report: Following the detection of the fast X-ray transient EP250225a by the Einstein Probe (Jiang et al., GCN 39475) with the Sinistro instrument mounted on the 1-m telescope of the LCO, we initiated observations of the fast X-ray transient location starting on 2025 Feb 26th at 04:50:50 UT (~15 hours after the EP/WXT trigger) in the r band. These observations were conducted using the 1-meter telescope at the Las Cumbres Observatory node located at the Cerro Tololo Inter-American Observatory in Chile. No new optical source was detected in the co-added images within the EP/WXT error box down to ~21.5 mag. These observations were taken as part of the Global Supernova Project. View this GCN Circular online at https://gcn.nasa.gov/circulars/39477. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37488] EP250223a: GMG Optical Observation
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39476 SUBJECT: EP250223a: GMG Optical Observation DATE: 25/02/26 04:26:24 GMT FROM: Boting Wang at Yunnan Observatories, CAS <wangbaiting(a)ynao.ac.cn> B.-T. Wang, R.-Z. Li, F.-F. Song, J. Mao, D.-Q. Wang, and J.-M. Bai (YNAO, CAS) report: We observed the field of EP250223a (Lian et al., GCN 39429, T0 at 2025-02-23T15:04:35.749) using the GMG-2.4m telescope at the Lijiang Observatory. The observation began at 2025-02-25T12:45:36.92, about 45.68 hours after the trigger. The optical counterpart of EP250223a (Hauptmann et al., GCN 39436; Wu et al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo et al., GCN 39441; Xin et al., GCN 39445; Guo et al., GCN 39447; An et al., GCN 39449; Ducoin et al., GCN 39453; O’Neill et al., GCN 39455; Aryan et al., GCN 39464; Saikia et al., GCN 39472), with a redshift of 2.756 (Levan et al., GCN 39438), was detected within the error box of EP/FXT (Lian et al., GCN 39429). The preliminary analysis results are shown as follows: | tmid-t0 (hours) | Filter | Exposure (s) | Magnitude (AB) | 5-sigma U.L. | | ----------- |------- | ------------------ | -------------- | ------ | | 45.85 | sdssr | 1200 | 20.82 +/- 0.08 | 21.9 | The given magnitudes are derived based on calibration against Pan-STARRS1 field stars and are not corrected for the expected Galactic foreground extinction. We warmly thank the staff at the Lijiang Observatory for their efforts in conducting the observation. View this GCN Circular online at https://gcn.nasa.gov/circulars/39476. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37487] EP250225a: Einstein Probe detected of a fast X-ray transient
by GCN Circulars 26 Feb '25

26 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39475 SUBJECT: EP250225a: Einstein Probe detected of a fast X-ray transient DATE: 25/02/26 04:23:32 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S.Q. Jiang (NAO, CAS), B.-T. Wang (YNAO, CAS), H.Z. Wu (HUST), T. Zhao, Y.J. Song, Y. Liu (NAO, CAS) report on behalf of the Einstein Probe team: We report on the detection of a fast X-ray transient EP250225a at 2025-02-25T12:13:50 (UTC) by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The position of the source is R.A. = 141.272 deg, DEC = -4.932 deg (J2000) with an uncertainty of 2.8 arcmin (radius, 90% C.L. statistical and systematic). The transient event lasted for about 600 seconds. The average 0.5-4 keV spectrum can be fitted with an absorbed powerlaw model, with nH fixed at the Galactic value of 3.0 x 10^20 cm^-2 and a photon index of 2.5 (-0.9/+1.1). The unabsorbed average 0.5-4 keV flux is estimated to be 4.3 (-1.3/+2.1) x 10^-11 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters. Further FXT observations are scheduled. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/39475. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37486] Fermi GRB 250225A: Global MASTER-Net observations report
by GCN Circulars 25 Feb '25

25 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39474 SUBJECT: Fermi GRB 250225A: Global MASTER-Net observations report DATE: 25/02/25 21:03:06 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 250225A ( Fermi GBM team, GCN 39467) errorbox 44698 sec after notice time and 44737 sec after trigger time at 2025-02-25 18:51:00 UT, with upper limit up to 19.1 mag. The observations began at zenith distance = 33 deg. The sun altitude is -19.6 deg. The galactic latitude b = -49 deg., longitude l = 244 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2790801 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 44768 | 2025-02-25 18:51:00 | MASTER-SAAO | (03h 54m 49.41s , -40d 48m 54.8s) | C | 60 | 18.8 | 44847 | 2025-02-25 18:52:19 | MASTER-SAAO | (04h 05m 18.27s , -40d 47m 21.7s) | C | 60 | 18.7 | 44926 | 2025-02-25 18:53:39 | MASTER-SAAO | (03h 48m 24.30s , -38d 53m 35.9s) | C | 60 | 18.5 | 45006 | 2025-02-25 18:54:58 | MASTER-SAAO | (03h 58m 33.77s , -38d 54m 13.2s) | C | 60 | 18.5 | 45085 | 2025-02-25 18:56:18 | MASTER-SAAO | (04h 01m 53.31s , -42d 42m 05.9s) | C | 60 | 18.6 | 45167 | 2025-02-25 18:57:39 | MASTER-SAAO | (04h 12m 37.11s , -42d 43m 05.4s) | C | 60 | 18.9 | 45246 | 2025-02-25 18:58:59 | MASTER-SAAO | (03h 41m 13.44s , -42d 41m 11.6s) | C | 60 | 18.8 | 45325 | 2025-02-25 19:00:18 | MASTER-SAAO | (03h 52m 04.78s , -42d 42m 33.9s) | C | 60 | 19.0 | 45423 | 2025-02-25 19:01:56 | MASTER-SAAO | (03h 54m 49.21s , -40d 47m 23.4s) | C | 60 | 18.7 | 45503 | 2025-02-25 19:03:15 | MASTER-SAAO | (04h 05m 16.54s , -40d 47m 55.2s) | C | 60 | 18.9 | 45741 | 2025-02-25 19:07:13 | MASTER-SAAO | (03h 48m 17.83s , -38d 54m 45.8s) | C | 60 | 18.6 | 45820 | 2025-02-25 19:08:33 | MASTER-SAAO | (03h 58m 39.26s , -38d 54m 26.3s) | C | 60 | 18.5 | 45900 | 2025-02-25 19:09:52 | MASTER-SAAO | (04h 01m 51.26s , -42d 40m 43.1s) | C | 60 | 18.9 | 45979 | 2025-02-25 19:11:12 | MASTER-SAAO | (04h 12m 42.31s , -42d 42m 16.8s) | C | 60 | 18.8 | 46058 | 2025-02-25 19:12:31 | MASTER-SAAO | (03h 41m 16.02s , -42d 40m 55.7s) | C | 60 | 19.1 | 46137 | 2025-02-25 19:13:50 | MASTER-SAAO | (03h 52m 03.12s , -42d 41m 27.8s) | C | 60 | 19.0 | 46217 | 2025-02-25 19:15:09 | MASTER-SAAO | (03h 54m 43.40s , -40d 46m 27.2s) | C | 60 | 18.8 | 46296 | 2025-02-25 19:16:29 | MASTER-SAAO | (04h 05m 22.17s , -40d 47m 26.6s) | C | 60 | 18.7 | 46376 | 2025-02-25 19:17:48 | MASTER-SAAO | (03h 48m 17.65s , -38d 54m 21.8s) | C | 60 | 18.5 | 46456 | 2025-02-25 19:19:08 | MASTER-SAAO | (03h 58m 39.07s , -38d 54m 08.0s) | C | 60 | 18.8 | 46535 | 2025-02-25 19:20:28 | MASTER-SAAO | (04h 01m 51.71s , -42d 40m 26.7s) | C | 60 | 18.6 | 46614 | 2025-02-25 19:21:47 | MASTER-SAAO | (04h 12m 43.06s , -42d 42m 11.9s) | C | 60 | 18.7 | 46695 | 2025-02-25 19:23:08 | MASTER-SAAO | (03h 41m 17.18s , -42d 40m 34.0s) | C | 60 | 18.6 | 46784 | 2025-02-25 19:24:37 | MASTER-SAAO | (03h 52m 01.84s , -42d 41m 05.5s) | C | 60 | 18.9 | 46863 | 2025-02-25 19:25:56 | MASTER-SAAO | (03h 54m 44.70s , -40d 46m 04.3s) | C | 60 | 18.6 | 46943 | 2025-02-25 19:27:15 | MASTER-SAAO | (04h 05m 22.62s , -40d 47m 03.2s) | C | 60 | 18.4 | 47022 | 2025-02-25 19:28:34 | MASTER-SAAO | (03h 48m 17.09s , -38d 53m 59.3s) | C | 60 | 18.5 | 47102 | 2025-02-25 19:29:55 | MASTER-SAAO | (03h 58m 38.43s , -38d 53m 36.6s) | C | 60 | 18.4 | 47182 | 2025-02-25 19:31:14 | MASTER-SAAO | (04h 01m 52.00s , -42d 39m 55.2s) | C | 60 | 18.8 | 47267 | 2025-02-25 19:32:39 | MASTER-SAAO | (04h 12m 43.40s , -42d 41m 44.3s) | C | 60 | 18.4 | 47346 | 2025-02-25 19:33:59 | MASTER-SAAO | (03h 41m 15.66s , -42d 39m 54.0s) | C | 60 | 18.7 | 47426 | 2025-02-25 19:35:18 | MASTER-SAAO | (03h 52m 01.71s , -42d 40m 43.5s) | C | 60 | 18.6 | 47505 | 2025-02-25 19:36:38 | MASTER-SAAO | (03h 54m 44.12s , -40d 45m 42.3s) | C | 60 | 18.5 | 47585 | 2025-02-25 19:37:57 | MASTER-SAAO | (04h 05m 22.69s , -40d 46m 41.4s) | C | 60 | 18.5 | 47664 | 2025-02-25 19:39:17 | MASTER-SAAO | (03h 48m 17.11s , -38d 53m 37.9s) | C | 60 | 18.3 | 47744 | 2025-02-25 19:40:36 | MASTER-SAAO | (03h 58m 38.68s , -38d 53m 36.3s) | C | 60 | 18.3 | 47823 | 2025-02-25 19:41:56 | MASTER-SAAO | (04h 01m 52.08s , -42d 39m 55.6s) | C | 60 | 18.3 | 47907 | 2025-02-25 19:43:20 | MASTER-SAAO | (04h 12m 43.76s , -42d 41m 01.5s) | C | 60 | 18.3 | 47987 | 2025-02-25 19:44:39 | MASTER-SAAO | (03h 41m 15.72s , -42d 39m 30.2s) | C | 60 | 18.6 | 48066 | 2025-02-25 19:45:58 | MASTER-SAAO | (03h 52m 02.90s , -42d 40m 21.6s) | C | 60 | 18.3 | 48145 | 2025-02-25 19:47:18 | MASTER-SAAO | (03h 54m 42.90s , -40d 45m 20.4s) | C | 60 | 17.8 | 48226 | 2025-02-25 19:48:38 | MASTER-SAAO | (04h 05m 21.63s , -40d 46m 19.8s) | C | 60 | 18.5 | 48307 | 2025-02-25 19:49:59 | MASTER-SAAO | (03h 48m 16.28s , -38d 53m 16.1s) | C | 60 | 18.0 | 48386 | 2025-02-25 19:51:18 | MASTER-SAAO | (03h 58m 38.73s , -38d 52m 47.9s) | C | 60 | 17.4 | 48465 | 2025-02-25 19:52:38 | MASTER-SAAO | (04h 01m 52.05s , -42d 39m 32.2s) | C | 60 | 17.3 | 48545 | 2025-02-25 19:53:57 | MASTER-SAAO | (04h 12m 44.00s , -42d 40m 40.8s) | C | 60 | 17.4 | 48624 | 2025-02-25 19:55:16 | MASTER-SAAO | (03h 41m 16.82s , -42d 39m 08.2s) | C | 60 | 16.4 | 48705 | 2025-02-25 19:56:38 | MASTER-SAAO | (03h 52m 01.56s , -42d 40m 01.8s) | C | 60 | 17.2 | 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/39474. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37485] GRB 250225B: Swift detection of a burst
by GCN Circulars 25 Feb '25

25 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39473 SUBJECT: GRB 250225B: Swift detection of a burst DATE: 25/02/25 20:00:29 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> M. A. Williams (PSU), S. Dichiara (PSU), R. Gupta (NASA GSFC), H. A. Krimm (NSF), M. J. Moss (GSFC), K. L. Page (U Leicester) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team: At 19:39:13 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250225B (trigger=1291459). Swift could not slew immediately due to an observing constraint. The BAT on-board calculated location is RA, Dec 306.145, -41.484 which is RA(J2000) = 20h 24m 35s Dec(J2000) = -41d 29' 03" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multiple-peaked structure (well-separated peaks at T+1, T+60, T+110) with a total duration of about 120 sec. The peak count rate was ~13000 counts/sec (15-350 keV), at ~1 sec after the trigger. Due to a Moon observing constraint, Swift cannot slew to the BAT position until 05:11 UT on 2025 February 26. There will thus be no XRT or UVOT data for this trigger before this time. We note the presence of the Emission-line Galaxy ESO 340-26 in the BAT error box. This is a bright (B=14.8, R=10.9) extended (1.4 arcmin) galaxy at z ~ 0.018 . Burst Advocate for this burst is M. A. Williams (mjw6837 AT psu.edu). 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/39473. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37484] EP250223a: GROWTH-India Telescope optical observations
by GCN Circulars 25 Feb '25

25 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39472 SUBJECT: EP250223a: GROWTH-India Telescope optical observations DATE: 25/02/25 19:15:48 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> A.P. Saikia, T. Mohan, V. Swain, V. Bhalerao (IITB), D. Eappachen, G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of EP250223a reported by EP-WXT (Lian et al., GCN 39429) with the 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-02-23T17:05:58 UT, i.e., 2.02 hours after the EP trigger. We obtained a single exposure of 420 seconds each in r' and g' filters. We clearly detected the afterglow in our image at the position given by NOT (Hauptmann et. al., GCN 39436). The photometry result follows as: | MJD (mid) | tmid-t0 (hours) | Filter | Total Exposure (s) | Magnitude (AB) | Limiting Magnitude | | ----------------- | ----------- |------- | ------------------ | -------------- | ------ | | 60729.714907 | 2.08 | r' | 1x420 | 19.18 +/- 0.18 | 19.66 | | 60729.720081 | 2.15 | g' | 1x420 | - | 19.62 | Our result is consistent with Hauptmann et al., (GCN 39436), Wu et al., (GCN 39439), Péréz-Fournon et al., (GCN 39440), Izzo et al., (GCN 39441), Xin et al., (GCN 39445), Guo et al., (GCN 39447). The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/39472. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37483] GRB 250221A: Swift-BAT refined analysis
by GCN Circulars 25 Feb '25

25 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39471 SUBJECT: GRB 250221A: Swift-BAT refined analysis DATE: 25/02/25 14:19:03 GMT FROM: Mike Moss at NASA GSFC <mikejmoss3(a)gmail.com> D. M. Palmer (LANL), S. D. Barthelmy (GSFC), R. Caputo (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), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-479 to T+600 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250221A (trigger #1290305) (R. Caputo, et al., GCN Circ. 39396). The BAT ground-calculated position is RA, Dec = 59.476, -15.137 deg which is RA(J2000) = 03h 57m 54.4s Dec(J2000) = -15d 08' 11.8" with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment). The partial coding was 19%. The mask-weighted light curve displays a single short pulse. T90 (15-350 keV) is 1.80 +- 0.32 sec (estimated error including systematics). The time-averaged spectrum from T-0.22 to T+1.84 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.43 +- 0.23. The fluence in the 15-150 keV band is 3.9 +- 0.6 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+0.42 sec in the 15-150 keV band is 2.9 +- 0.5 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1290305 View this GCN Circular online at https://gcn.nasa.gov/circulars/39471. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37482] GRB 250223C: SVOM/GRM observation of a long burst
by GCN Circulars 25 Feb '25

25 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39470 SUBJECT: GRB 250223C: SVOM/GRM observation of a long burst DATE: 25/02/25 13:44:49 GMT FROM: yqzhang_cl(a)163.com SVOM/GRM team: Yan-Qiu Zhang, Chao Zheng, Chen-Wei Wang, Shi-Jie Zheng, Wen-Jun Tan, Chen-Wei Wang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Nicolas Dagoneau (CEA), Maria-Grazia Bernardini (INAF-OAB), Jean-Luc Atteia (IRAP) report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by a long burst GRB 250223C at 2025-02-23T16:18:36.500 UTC (T0), which was also observed by Fermi/GBM (Fermi GBM team, GCN #39459). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-pulses with a T90 of 40.50 +/- 15.03 s in the 15-2000 keV band. ECLAIRs was not collecting data at the time of this burst. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250223C.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Yan-Qiu Zhang (IHEP) (zhangyanqiu(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/39470. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37481] EP250215A: J band upper limit by SYSU 80cm telescope
by GCN Circulars 25 Feb '25

25 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39469 SUBJECT: EP250215A: J band upper limit by SYSU 80cm telescope DATE: 25/02/25 07:01:01 GMT FROM: yanghn8(a)mail2.sysu.edu.cn Hao-Nan Yang, Jia-Qi Lin, Si-Yuan Zhu, Zhong-Nan Dong, Wei-Sen Huang, Pu Lin, Jin-Ji Li, Yan Yu, Hao-Ran Zhang, Chun Chen, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm telescope team: We observed the field of EP250215A (Fermi GCN 39327; EP GCN 39329) using the Sun Yat-sen University 80cm infrared telescope with 180 x 20 s exposures in J band. The calculated position is RA. = 156.3301 deg, DEC =-27.6997 deg J2000, from EP/FXT observation. Our observations began at 2025-2-15 17:52:00 UTC, 11.39 hours after the EP trigger. We do not detect any counterpart at the position of the optical afterglow(Liu et al. GCN 39330; Xie et al., GCN 39333; Malesani et al., GCN 39339; and Malesani et al. GCN 39341; R. Sanchez-Ramirez et al. GCN 39343; Jean-Grégoire Ducoin (CPPM) et al. GCN 39344; I. Pérez-Fournon et al. GCN 39348; R.Ruffini et al. GCN 39366; D.Svinkin et al. GCN 39375), down to a 5-sigma depth of J~17.5 Vega magnitudes. View this GCN Circular online at https://gcn.nasa.gov/circulars/39469. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37480] LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: DECam GW-MMADS candidates
by GCN Circulars 25 Feb '25

25 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39468 SUBJECT: LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: DECam GW-MMADS candidates DATE: 25/02/25 06:46:50 GMT FROM: xjh(a)andrew.cmu.edu Lei Hu (CMU), Xander J. Hall (CMU), Tomás Cabrera (CMU), Antonella Palmese (CMU), Igor Andreoni (UNC), Brendan O’Connor (CMU), Keerthi Kunnumkai (CMU), on behalf of the GW-MMADS team The high probability area of the joint LVK/Swift-GUANO alert for the gravitational wave candidate S250223dk (GCN 39443) was observed using the wide-field Dark Energy Camera (DECam) on the 4m Blanco telescope by the Dark Energy Survey Gravitational Wave (DESGW) program (PI: Soares-Santos; GCN 39462). Observations started at 2025-02-24T03:45:38 on the night of the alert, and at 2025-02-25T00:50:13 on the following night. We find that the median 5sigma depths of the exposures are r\~24.7 mag on the first night and r\~24.9 mag on the second night. As part of the Gravitational Wave Multi-Messenger Astronomy DECam Survey (GW-MMADS), we run the SFFT difference imaging (Hu et al. 2022) on the available images using templates from DES, filter out likely stars and moving objects, visually inspect the remaining transients. We posted on TNS new transients from this analysis and report here the most likely extragalactic transients we find within the joint LVK-GUANO skymap 95% credible interval area: | id | AT name | ra | dec | discovery_date (UT) | mag_r | mag_r_err | mag_r-mag_i | | ------------------------ | ---------- | ---------- | ---------- | ----------------------- | ------ | ----- | ----- | | C202502240542297m473928 | AT 2025cqb | 85.623700 | -47.657680 | 2025-02-24T03:58:42 | 23.04 | 0.05 | 0.20 | C202502240549253m474247 | AT 2025cqf | 87.355530 | -47.713117 | 2025-02-24T03:58:42 | 24.44 | 0.20 | N/A | A202502240541155m473906* | AT 2025cpv | 85.314435 | -47.651722 | 2025-02-24T03:45:38 | 23.55 | 0.08 | 0.21 | C202502240541459m473517 | AT 2025cql | 85.441205 | -47.588088 | 2025-02-24T04:24:50 | 24.77 | 0.25 | N/A | C202502240545203m483410 | AT 2025cqm | 86.334777 | -48.569306 | 2025-02-24T03:58:42 | 24.00 | 0.13 | N/A | T202502240543468m475332 | AT 2025cqc | 85.944938 | -47.892308 | 2025-02-24T03:45:38 | 23.00 | 0.05 | 0.21 | C202502240544410m483014 | AT 2025cqe | 86.170896 | -48.503829 | 2025-02-24T03:58:42 | 23.75 | 0.10 | 0.49 | A202502240546005m475901* | AT 2025cqd | 86.502090 | -47.983653 | 2025-02-24T03:45:38 | 22.48 | 0.03 | 0.23 * Possible stellar origin Magnitudes reported are from the discovery date and not corrected from Milky Way extinction. Further analysis is underway. We thank the CTIO and NOIRLab staff for supporting observations and data calibration. View this GCN Circular online at https://gcn.nasa.gov/circulars/39468. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37479] GRB 250225A: Fermi GBM Final Real-time Localization
by GCN Circulars 25 Feb '25

25 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39467 SUBJECT: GRB 250225A: Fermi GBM Final Real-time Localization DATE: 25/02/25 06:35:59 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 06:25:23 UT on 25 Feb 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250225A (trigger 762157528.045892 / 250225268). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 60.0, Dec = -40.5 (J2000 degrees, equivalent to J2000 04h 00m, -40d 30'), with a statistical uncertainty of 12.1 degrees. The angle from the Fermi LAT boresight is 72.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250225268/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250225268/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250225268/… View this GCN Circular online at https://gcn.nasa.gov/circulars/39467. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37478] LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: AstroSat CZTI non-detection and upper limits
by GCN Circulars 25 Feb '25

25 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39466 SUBJECT: LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: AstroSat CZTI non-detection and upper limits DATE: 25/02/25 04:51:53 GMT FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in> G. Waratkar (IITB), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (TIFR), S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: We have carried a search [1] for X-ray candidates in Astrosat CZTI data in a 100 sec window around the trigger time of the event S250223dk (UTC 2025-02-23 12:01:15). We use the combined-ext.multiorder.fits map (https://gracedb.ligo.org/api/superevents/S250223dk/files/combined-ext.multi…) for our analysis. CZTI is a coded aperture mask instrument that has considerable effective area for about 29% of the entire sky, but is also sensitive to brighter transients from the entire sky. At the time of the merger, Astrosat's nominal pointing is RA,DEC = 15:49:17.1, 70:18:47.9 (237.32, 70.31), which is ~153 deg away from the maximum probability location. At the time of the merger event, the Earth-satellite-transient angle corresponding to the BAT location is ~126 deg and hence is not occulted by Earth in satellite's frame. In a time interval of 100 sec around the event, the region of the localisation map which is not occulted by Earth in the satellite's frame has a total probability of 1.0 (100%). CZTI data were de-trended to remove orbit-wise background variation. We then searched data from the four independent, identical quadrants to look for coincident spikes in the count rates. Searches were undertaken by binning the data in 0.1s, 1s, and 10s respectively. Statistical fluctuations in background count rates were estimated by using data from 5 preceding orbits. We selected confidence levels such that the probability of a false trigger in a 100 sec window is 10^-4. We do not find any evidence for any hard X-ray transient in this window, in the CZTI energy range of 20-200 keV. We use a detailed mass model of the satellite to calculate the direction-dependent instrument response for points in the visible sky. We then assume the source is modelled as a power law with photon index alpha = -1, and convert our count rate upper limits to direction-dependent flux limits. We obtain the following upper limits for source flux in the 20-200 keV band by taking a probability weighted mean over the visible sky: | Bin (s) | Flux Limit (ergs/cm^2/s) | Fluence Limit (ergs/cm^2) | | ------------ | ------------ | ------------ | | 0.1 | 7.01e-06 | 7.01e-07 | | 1.0 | 1.73e-06 | 1.73e-06 | | 10.0 | 3.01e-07 | 3.01e-06 | CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI EMGW detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=emgw [1] Waratkar et al. ApJ 976, 123 (2024) doi:10.3847/1538-4357/ad84e6 View this GCN Circular online at https://gcn.nasa.gov/circulars/39466. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37477] LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Magellan upper limits.
by GCN Circulars 25 Feb '25

25 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39465 SUBJECT: LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Magellan upper limits. DATE: 25/02/25 02:44:55 GMT FROM: Harsh Kumar at Center for Astrophysics | Harvard & Smithsonian <harshkosli13(a)gmail.com> H. Kumar, E. Berger, A. Villar, D. Hiramatsu, P. K. Blanchard, K. D. Soto, S. K. Yadavalli, A. Gagliano, C. Ransome, Anya Nugent, Y. Dong (Harvard) report: We obtained imaging with the IMACS imager on the 6.5m Magellan Baade telescope to search for an optical counterpart following the announcement of Swift/BAT-GUANO 762004910 (GCN #39443) event, coincident with gravitational wave event S250223dk. We obtained 4 x 120-second images in each of g- and r-band, starting about 16.6 hours after the GW trigger, targeting the Swift/BAT-GUANO localization of 5 arcmin around RA(J2000)= 85.341 deg, Dec(J2000)= -47.554, covering ~95% of the joint LVK-Swift/BAT localization 50% credible region. We do not detect new transients above 5-sigma level up to ~23.7 mag in the g-band and ~23.5 mag in the r-band after performing image subtraction with Legacy Survey-DECam images as a reference. We checked for the DECam DESGW candidates (GCN #39462) in our images. One source (AT2025cpq) falls in the area covered by Magellan. The source is marginally detected at <3 Sigma. We performed forced photometry and obtained the following magnitudes: —------------------------------------------ Name | Filter | Magnitude +/- e_magnitude —------------------------------------------ AT2025cpq | g | 24.04 +/- 0.48 AT2025cpq | r | 23.78 +/- 0.28 —------------------------------------------- We thank Yuri Beletsky for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39465. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37476] EP250223a: Kinder optical follow-up observations
by GCN Circulars 25 Feb '25

25 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39464 SUBJECT: EP250223a: Kinder optical follow-up observations DATE: 25/02/25 01:49:48 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> A. Aryan (NCU), A. K. H. Kong (NTHU), T.-W. Chen, W.-J. Hou, H.-Y. Hsiao (all NCU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), Y. J. Yang, A. Sankar. K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, H.-C. Lin, C.-H. Lai, C.-S. Lin, J.-K. Guo (all NCU), S. Yang, L. L. Fan, Z. N. Wang, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP250223a (Lian et al., GCN 39429) using the 40cm SLT telescope and Lulin One-meter Telescope (LOT) at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2024, arXiv:2406.09270). The first SLT epoch of observations in the i-band started at 12:00:02 UT on the 24th of February 2024 (MJD = 60730.500), 20.92 hrs after the EP trigger. The first LOT epoch of observations in the r-band started at 14:42:53 UT on the 24th of February 2024 (MJD = 60730.613), 23.64 hrs after the EP trigger. We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. In the stacked images, we clearly detected the optical counterpart candidate proposed by Hauptmann et al. (GCN 39436) and confirmed by several other observations (e.g., Levan et al al., GCN 39438; Wu et al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo et al., GCN 39441; Xin et al., GCN 39445; Guo et al., GCN 39447; An et al., GCN 39449; Ducoin et al., GCN 39453; and O’Neill et al., GCN39455). We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform PSF photometry on our stacked frames. The details of the observations and measured photometry (in the AB system) are as follows: --------------------------------------------------------------------------------------------------------------------------- Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass SLT | i | 60730.500 | 20.92 | 300 * 24 | 19.23 +/- 0.03 | 2".06 | 1.51 LOT | r | 60730.613 | 23.64 | 300 * 6 | 19.79 +/- 0.01 | 1".43 | 2.10 The presented magnitudes were calibrated using the field stars from the Pan-STARRS1 catalog and were not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_i = 0.16 mag and A_r = 0.22 mag, respectively, in the direction of the transient (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/39464. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37475] GRB 250207a: ATCA Radio Upper Limits
by GCN Circulars 25 Feb '25

25 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39463 SUBJECT: GRB 250207a: ATCA Radio Upper Limits DATE: 25/02/25 01:32:43 GMT FROM: agul8829(a)uni.sydney.edu.au A. Gulati (USyd), G. E. Anderson (Curtin), S. Chastain (UNM), A. J. van der Horst (GWU), J. K. Leung (UofT/HUJI), and L. Rhodes (TSI/McGill) on behalf of the ATCA PanRadio GRB collaboration We observed Swift and Fermi-detected GRB 250207A (Ferro et al., GCN 39182; Fermi GBM Collaboration, GCN 39181) as part of The Australia Telescope Compact Array (ATCA) "PanRadio GRB" Large Project C3542 (PI: G. Anderson) at 5.5 and 9 GHz on 2025-02-12, 2025-02-14 and 2025-02-21. No radio sources were detected near the Swift/XRT enhanced position (Osborne et al., GCN 39217 )in any of the observation epochs. The 3-sigma upper limits for the 9 GHz observations are 174, 96, and 60 uJy respectively. We thank the CSIRO Space and Astronomy staff for supporting these observations. We acknowledge the Gomeroi people as the traditional owners of the Observatory site. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) which is funded by the Australian Government for operation as a National Facility managed by CSIRO. View this GCN Circular online at https://gcn.nasa.gov/circulars/39463. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37474] LIGO/Virgo/KAGRA S250223dk: DECam DESGW Candidates
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39462 SUBJECT: LIGO/Virgo/KAGRA S250223dk: DECam DESGW Candidates DATE: 25/02/24 22:36:16 GMT FROM: Isaac McMahon at University of Zürich <isaac.mcmahon(a)ligo.org> I. McMahon (UZH), S. MacBride (UZH), H. T. Diehl (FNAL), S. Kaur (UZH), L. Joseph (Benedictine U.), N. Sherman (Boston U.), K. Herner (Fermilab), M. Soares-Santos (UZH), reporting on behalf of the Dark Energy Survey Gravitational Wave (DESGW) Team: At 03:45:38 UTC, the Dark Energy Camera (DECam) began observing in response to the joint LVK/Swift-BAT RAVEN alert issued for the candidate gravitational-wave event S250223dk (GCN 39443). We observed two fields centered on the following ICRS coordinates (85.80,-47.60) (85.83,-47.63) Both fields were observed in DECam g, r, i, and z filters with 360 second exposures. The limiting magnitude achieved is 23.36 in r-band. Images were processed by 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 initially selected by requiring at least two high signal to noise detections, which were separated in time in order to reject moving objects. We also require an autoscan score of at least 0.7 on at least one of those detections. After candidate selection, we report five high confidence candidates (listed below). After vetting and identification, four candidates were classified as nuclear candidates (likely AGNs), one candidate (2017239) has been labeled as a possible supernova. All candidates have a host galaxy match within 1 arcsecond. None of the candidate hosts are included in the ALLWISE and MILLIQUAS AGN catalogs (Secrest et. al 2015, Flesch 2023). No other candidates were found in the area. We encourage followup of the five candidates identified herein. | id | AT name | ra | dec | discovery_date (UT) | mag_g | mag_g_err | mag_r | mag_r_err | mag_i | mag_i_err | mag_z | mag_z_err | | --------------- | ---------- | ---------- | ---------- | ----------------------- | ------ | ----- | ------ | ----- | ------ | ----- | ------ | ----- | | 2014974 | AT2025cpl | 86.327994 | -47.827215 | 2025-02-24 03:45:38.271 | 22.487 | 0.043 | 22.151 | 0.031 | 21.744 | 0.053 | 21.894 | 0.106 | | 2014991 | AT2025cpm | 86.516403 | -47.893872 | 2025-02-24 03:45:38.271 | 23.448 | 0.107 | 22.905 | 0.060 | 22.453 | 0.103 | 22.308 | 0.153 | | 2015571 | AT2025cpo | 86.105565 | -47.689987 | 2025-02-24 03:45:38.271 | 22.972 | 0.053 | N/A | N/A | 22.423 | 0.084 | 22.765 | 0.203 | | 2015600 | AT2025cpp | 86.176728 | -47.763957 | 2025-02-24 03:52:10.108 | 21.980 | 0.024 | N/A | N/A | 22.097 | 0.061 | 22.312 | 0.132 | | 2017239 | AT2025cpq | 85.552523 | -47.577823 | 2025-02-24 03:58:42.138 | 24.503 | 0.268 | 23.980 | 0.161 | 23.972 | 0.320 | 24.265 | 0.851 | 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/39462. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37473] LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39461 SUBJECT: LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations DATE: 25/02/24 19:45:19 GMT FROM: Lorenzo Scotton at UAH <lscottongcn(a)outlook.com> L. Scotton (UAH) reports on behalf of the Fermi-GBM Team: For S250223dk and the Swift/BAT-GUANO ID 762004910 (The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration along with the Swift/BAT-GUANO team, GCN 39443) and using the combined skymap combined-ext.multiorder.fits,3, Fermi-GBM was observing 100% of the localization probability at event time. There was no Fermi-GBM onboard trigger around the event time of the LIGO/Virgo/KAGRA (LVK) detection of GW trigger S250223dk, neither for the Swift/BAT-GUANO trigger ID 762004910. An automated, blind search for short gamma-ray bursts below the onboard triggering threshold in Fermi-GBM also identified no counterpart candidates. The GBM targeted search, the most sensitive, coherent search for GRB-like signals, was run from +/-30 s around merger time, and also identified no counterpart candidates. Part of the joint localization region is behind the Earth for Fermi, located at RA=267.1, Dec=-5.5 with a radius of 68.0 degrees. We therefore set upper limits on impulsive gamma-ray emission for the joint localization region visible to Fermi at merger time. Using the representative soft, normal, and hard GRB-like templates described in arXiv:1612.02395, we set the following 3 sigma flux upper limits over 10-1000 keV, weighted by the joint LVK-Swift/BAT localization probability (in units of 10^-7 erg/s/cm^2): Timescale Soft Normal Hard ------------------------------------ 0.128 s: 2.00 2.90 6.40 1.024 s: 0.69 0.95 1.90 8.192 s: 0.23 0.32 0.63 Assuming the median luminosity distance of 6033 Mpc from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^50 erg/s): Timescale Soft Normal Hard ------------------------------------ 0.128s: 14.15 16.94 64.06 1.024s: 4.88 5.55 19.02 8.192s: 1.63 1.87 6.31 View this GCN Circular online at https://gcn.nasa.gov/circulars/39461. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37472] GRB 250119B: VZLUSAT-2 detection
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39460 SUBJECT: GRB 250119B: VZLUSAT-2 detection DATE: 25/02/24 18:21:07 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU) -- the VZLUSAT-2/GRB payload collaboration. The long-duration GRB 250119B (FERMI/GBM detection: GCN 38979; INTEGRAL/SPI-ACS detection: GCN Circular 38997; Swift/BAT-GUANO detection: GCN 39007; Konus/Wind detection: GCN 39016; NuSTAR detection at 2025-01-19 08:27:23 UTC) was detected by the GRB detector on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/). The data acquisition was performed by the GRB detector unit no. 1. The detection was confirmed at the peak time 2025-01-19 08:27:44 UTC. The T90 duration is 41 s and the significance during T90 reaches 66 sigma. The light curve obtained by VZLUSAT-2 is available here: https://vzlusat2.konkoly.hu/static/share/GRB250119B_GCN_VZLUSAT2.pdf All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/ The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral. View this GCN Circular online at https://gcn.nasa.gov/circulars/39460. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37471] GRB 250223C: Fermi GBM Final Real-time Localization
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39459 SUBJECT: GRB 250223C: Fermi GBM Final Real-time Localization DATE: 25/02/24 17:27:23 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 16:18:20 UT on 23 Feb 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250223C (trigger 762020305.175056 / 250223679). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 262.6, Dec = 41.0 (J2000 degrees, equivalent to J2000 17h 30m, 41d 00'), with a statistical uncertainty of 5.1 degrees. The angle from the Fermi LAT boresight is 41.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250223679/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250223679/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250223679/… View this GCN Circular online at https://gcn.nasa.gov/circulars/39459. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37470] GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39458 SUBJECT: GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert DATE: 25/02/24 16:54:52 GMT FROM: d.s.oneill(a)bham.ac.uk D. O’Neill, B. P. Gompertz, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, F. Jimenez-Ibarra, A. Kumar, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Pall'e and D. Pollacco report on behalf of the GOTO collaboration: We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the joint LVK/Swift-BAT RAVEN alert (LIGO, Virgo, KAGRA and Swift/BAT-GUANO teams, GCN 39443). Targeted observations of the combined 90% credible region (using the combined-ext.multiorder.fits,2 skymap) were performed by GOTO-South between 2025-02-24 09:41:31 UT (+21.67h) and 2025-02-24 13:18:31 (+25.28h) UT. Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks. In the 5 arcmin circle centred at RA = 85.341, Dec = -47.544, containing 52% of the integrated joint probability (LIGO, Virgo, KAGRA and Swift/BAT-GUANO teams, GCN 39443), no credible counterpart candidates are identified to a 3-sigma limiting magnitude of L > 21.1 mag. Furthermore, no candidate optical counterparts are identified within the <1 deg2 combined 90% LVK+Swift/BAT-GUANO credible region. In addition to the targeted response, serendipitous imaging from the all-sky survey was obtained for the 90% credible region defined by the NITRATES search, starting from 2025-02-23 12:03:34 UT (+0.04h). This resulted in a total coverage of 1621 deg^2 within the 90% localisation contour of Swift/BAT-GUANO, corresponding to ~41.6% of its total 2D localisation probability. No credible optical counterparts were identified within this region. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and not corrected for Galactic extinction. 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/39458. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37469] GRB 250202B: VZLUSAT-2 detection
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39457 SUBJECT: GRB 250202B: VZLUSAT-2 detection DATE: 25/02/24 15:10:59 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU) -- the VZLUSAT-2/GRB payload collaboration. The long-duration GRB 250202B (FERMI/GBM: GCN Circular 39120; AstroSat/CZTI: GCN Circular 39122; NuSTAR detection: GCN 39135; Konus/Wind detection: GCN 39149; CALET/CGBM detection: trigger no. 1422503847; INTEGRAL/SPI-ACS peak detection at 2025-02-02 ~03:57:20 UTC) was detected by the GRB detector on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/). The data acquisition was performed by the GRB detector unit no. 1. The detection was confirmed at the peak time 2025-02-02 03:57:18 UTC. The T90 duration is 87 s and the significance during T90 reaches 80 sigma. The light curve obtained by VZLUSAT-2 is available here: https://vzlusat2.konkoly.hu/static/share/GRB250202B_GCN_VZLUSAT2.pdf All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/ The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral. View this GCN Circular online at https://gcn.nasa.gov/circulars/39457. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37468] GRB 250219A: EP-FXT afterglow detection
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39456 SUBJECT: GRB 250219A: EP-FXT afterglow detection DATE: 25/02/24 14:43:44 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> D. Turpin (CEA), P. Y. Han, C. X. Zhang (HUST), J. Yang (NJU), X. Tian (GXU), D. F. Hu (PMO, CAS), W. Chen (NAO, CAS), J. Guan, C. K. Li, Y . Chen, S. M. Jia, W. W. Cui, D. W. Han, W. Li, C. Z. Liu, F . J. Lu, L. M. Song, J. Wang, J. J. Xu, J. Zhang, S. N. Zhang, H. S. Zhao, X. F . Zhao (IHEP , CAS), Y . Liu, C. C. Jin, C. Zhang, Z. X. Ling (NAOC,CAS), B. Cordier (CEA) on behalf of the SVOM and Einstein Probe teams We performed a follow-up observation of GRB 250219A (Daigne et al., GCN 39376) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started at 2025-02-21T07:04:16 (T-TGRB ~ 1.63 days) for about 3ks of exposure in total. An uncatalogued X-ray source is detected by both FXT-A and FXT-B at the position of the x-ray afterglow candidate reported by Swift/XRT (Kennea et al., GCN 39379). This position is also consistent with the optical afterglow detected by SVOM/VT (Xin et al., GCN 39380), COLIBRÍ (Magnani et al. GCN 39382) and the NOT (Fu et al., GCN 39383). A preliminary analysis shows that the spectrum can be fitted with an absorbed power law with nH=1.53*10^20 cm^-2 and a photon index of 1.53 (-0.68/+0.70) . The observed flux in the 0.3-10.0 keV is 4.4 (+2.2/-1.1)*10^-13 erg/s/cm^2. Compared to the Swift/XRT epoch Kennea et al., GCN 39379), the observed source flux has faded by almost one order of magnitude with a temporal slope alpha~-0.56. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES. View this GCN Circular online at https://gcn.nasa.gov/circulars/39456. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37467] EP250223a: GOTO optical afterglow detections
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39455 SUBJECT: EP250223a: GOTO optical afterglow detections DATE: 25/02/24 13:59:07 GMT FROM: d.s.oneill(a)bham.ac.uk D. O’Neill, B. P. Gompertz, A. J. Levan, K. Ulaczyk, G. Ramsay, A. Kumar, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, F. Jimenez-Ibarra, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Pall'e and D. Pollacco report on behalf of the GOTO collaboration: We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the EP/WXT alert WXT01709131863 (Lian et al. GCN 39429). Three epochs of targeted observations were performed: at 2025-02-24 09:56:36 UT (+18.9h post trigger), 2025-02-24 11:04:37 UT (+20.0h post trigger), and 2025-02-24 12:12:37 UT (+21.1h post trigger). 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 afterglow (Hauptmann et al., GCN 39436; Levan et al., GCN 39438; Wu et al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo et al., GCN 39441; Xin et al., GCN 39445; Guo et al., GCN 39447; An et al., GCN 39449; Brivio et al., GCN 39450; Ducoin et al., GCN 39453) with magnitudes of L (400-700 nm) = 20.04 ± 0.15 mag (+18.9h), L = 19.78 ± 0.11 mag (+20.0h) and L = 19.97 ± 0.14 mag (+21.1h). Our measurements indicate no fading of the afterglow between 18 and 21 hours after trigger, continuing the shallow evolution noted by Ducoin et al. during the first 6 - 15 hours (GCN 39453). 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/39455. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37466] GRB 250222A: SVOM/GRM observation of a burst
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39454 SUBJECT: GRB 250222A: SVOM/GRM observation of a burst DATE: 25/02/24 13:15:04 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Piron (LUPM), Nicolas Dagoneau (CEA), Maria-Grazia Bernardini (INAF-OAB), Jean-Luc Atteia, Sébastien Guillot (IRAP) report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a long burst GRB 250222A (SVOM trigger reference: sb25022201) at 2025-02-22T14:24:26.100 UTC (T0). With the event-by-event data downloaded through the X-band ground station, the GRM light curve of 15 to 600 keV shows that this burst consists of multi-pulses with a T90 of 4.3 +0.6/-0.5 s. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250222A.png The SVOM/GRM on-ground localization of this burst is (J2000): RA: 284.2 deg DEC: -61.0 deg Error: 1.6 deg (1sigma, statistical only) We caution that the calibration of SVOM/GRM is undergoing and this localization is subject to systematic errors. In addition, this burst was detected by the Count-Rate Trigger onboard ECLAIRs, as an increase in counts over background, but it was not localized by the coded-mask imaging process, which confirms that the burst occurred outside the ECLAIRs field of view. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Chen-Wei Wang (IHEP) (cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/39454. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37465] EP250223a: COLIBRÍ/DDRAGO Detection of the Optical Counterpart and Slow Fading
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39453 SUBJECT: EP250223a: COLIBRÍ/DDRAGO Detection of the Optical Counterpart and Slow Fading DATE: 25/02/24 13:00:21 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Jean-Grégoire Ducoin (CPPM), Francesco Magnani (CPPM), Benjamin Schneider (LAM), Alan M. Watson (UNAM), Kin Ocelotl López (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Antonio de Ugarte Postigo (LAM) report: We imaged the field of EP250223a (Lian et al., GCN Circ. 39429), detected also by Swift/XRT (Kennea et al., GCN Circ. 39437), 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 2025-02-24 04:59 to 07:19 UTC (13.9 to 16.3 hours after the trigger) and obtained 96 minutes of exposure in the r filter. The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2021), with photometric calibration against Pan-STARRS DR1 and image subtraction against Pan-STARRS DR2. Our photometry is in the AB system and is not corrected for Galactic extinction. In a stacked image of our first 50 minutes of exposure, we detect a source at the position of the optical afterglow candidate reported by Hauptmann et al. (GCN Circ. 39436) and many other groups (GCN Circs. 39439, 39440, 39441, 39445, 39447, and 39449) with magnitude: r = 19.87 +/- 0.01 Comparing our r magnitude to the similar ones reported by Hauptmann et al. (GCN Circ. 39436) and Pérez-Fournon et al. (GCN Circ. 39440), we see no more than slow fading between about 6 and 15 hours. We encourage continued monitoring of this source. 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/39453. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37464] GRB 250210A: VZLUSAT-2 detection
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39452 SUBJECT: GRB 250210A: VZLUSAT-2 detection DATE: 25/02/24 12:50:48 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU) -- the VZLUSAT-2/GRB payload collaboration. The long-duration GRB 250210A (FERMI/GBM: GCN Circular 39262; AstroSat/CZTI: GCN Circular 39267; INTEGRAL/SPI-ACS: CGN Circular 39268; SVOM/GRM: CGN Circular 39282; GRBAlpha detection: GCN 39313) was detected by the GRB detector on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/). The data acquisition was performed by the GRB detector unit no. 0. The detection was confirmed at the peak time 2025-02-10 05:31:59 UTC. The T90 duration is 49 s and the significance during T90 reaches 10 sigma. The light curve obtained by VZLUSAT-2 is available here: https://vzlusat2.konkoly.hu/static/share/GRB250210A_GCN_VZLUSAT2.pdf All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/ The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral. View this GCN Circular online at https://gcn.nasa.gov/circulars/39452. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37463] GRB 250206A: VZLUSAT-2 detection
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39451 SUBJECT: GRB 250206A: VZLUSAT-2 detection DATE: 25/02/24 12:41:13 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU) -- the VZLUSAT-2/GRB payload collaboration. The long-duration GRB 250206A (Fermi/GBM detection: GCN 39172; Fermi/LAT detection: GCN 39233; EIRSAT-1/GMOD detection: GCN 39236; Konus/Wind detection: GCN 39283; INTEGRAL/SPI-ACS peak detection at 2025-02-06 ~19:51:45 UTC) was detected by the GRB detectors on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/). The data acquisition was performed by the GRB detector units no. 0 and no. 1. The detection was confirmed at the peak time 2025-02-06 19:51:43 (19:51:46) UTC. The T90 duration is 67 s (63 s) and the significance during T90 reaches 11 sigma (17 sigma) for detector unit no. 0 (no. 1). The light curve obtained by VZLUSAT-2 is available here: https://vzlusat2.konkoly.hu/static/share/GRB250206A_GCN_VZLUSAT2.pdf All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/ The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral. View this GCN Circular online at https://gcn.nasa.gov/circulars/39451. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37462] EP250223a: REM NIR upper limit
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39450 SUBJECT: EP250223a: REM NIR upper limit DATE: 25/02/24 11:40:05 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of EP250223a (Lian et al., GCN 39429; Wang et al., GCN 39448), also detected by Swift/XRT (Kennea et al., GCN 39437) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the J, H, and K bands, started on 2025 February 24 at 01:29:31 UT (i.e. 10.4 hr after the burst), and lasted for about 1 hour. From preliminary inspection, we do not find any counterpart at the position of the reported optical afterglow (Hauptmann et al., GCN 39436; Levan et al., GCN 39438; Wu et al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo & Malesani, GCN 39441; Xin et al., GCN 39445; Guo et al., GCN 39447; An et al., GCN 39449) down to the following 3sigma limit: H > 17.6 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 10.85 hours after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/39450. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37461] EP250223a: TRT optical afterglow observation
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39449 SUBJECT: EP250223a: TRT optical afterglow observation DATE: 25/02/24 11:34:23 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> J. An, S.Q. Jiang, N.C. Sun (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), Z. Fan, W.X. Li, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of EP250223a detected by EP (Lian et al., GCN 39429; Wang et al., GCN 39448), and observed by Swift/XRT (Kennea et al., GCN 39437), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. Observations started at 00:37:15.66 UTC on 2025-02-24, i.e., 9.544 hrs after the EP trigger, and a series of 200 s frames were obtained in B, V, R and I bands. The optical afterglow (Wu et al., GCN 39439; Guo et al., GCN 39447; Izzo et al., GCN 39441; Xin et al., GCN 39445; Pérez-Fournon et al., GCN 39440; Hauptmann et al., GCN 39436; Levan et al., GCN 39438) is clearly detected in our stacked images with: | T (mid) - T0 (hours)| band | mag | error | | 9.816 | B | 21.32 | 0.14 | | 9.996 | V | 20.17 | 0.07 | | 10.176 | R | 19.86 | 0.07 | | 10.356 | I | 19.41 | 0.12 | calibrated with Panstarrs-DR2 stars in the field and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/39449. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37460] EP250223a: refined analysis of the EP-WXT and FXT observations
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39448 SUBJECT: EP250223a: refined analysis of the EP-WXT and FXT observations DATE: 25/02/24 10:08:07 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wang (PMO, CAS), T. Y. Lian, W. J. Zhang (NAOC, CAS), X. Tian (GXU), R. Z. Li(YNAO, CAS), H. W. Pan (NAOC, CAS) report on behalf of the Einstein Probe team: The X-ray transient EP250223a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Lian et al., GCN 39429), and followed by the Swift XRT (Kennea et al., GCN 39437) and several optical telescopes (Levan et al., GCN 39436, Wu et al., GCN 39439, Pérez-Fournon et al., GCN 39440, Izzo et al., GCN 39441, Xin et al., GCN 39445) at the redshift of 2.756 (Levan et al., GCN 39438). The refined analysis of the WXT data shows that the event started at 2025-02-23T15:02:05.66 (UTC) and lasted for 140 s with the peak flux of 2 x 10^(-9) erg/s/cm^2, before the observation was interrupted by the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 1.36 x 10^21 cm^-2 and a photon index of 2.1 (-/+0.6). The derived average unabsorbed 0.5-4 keV flux is 4.4 (-1.1/+1.4) x 10^(-10) erg/s/cm^2. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed about two minutes later. The on-ground analysis shows that an uncatalogued source was detected at R.A. = 98.2748, DEC = -22.4443 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic equivalent hydrogen column density of 1.36 x 10^21 cm^-2 and a photon index of 1.97 (-/+0.05). The derived average unabsorbed 0.5-10 keV flux is 2.5 (-/+0.1) x 10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Further follow-up observations with EP-FXT have been scheduled. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/39448. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37459] EP250223a: 1.6m Mephisto and 50cm array observations
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39447 SUBJECT: EP250223a: 1.6m Mephisto and 50cm array observations DATE: 25/02/24 10:02:52 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn> Helong Guo, Guowang Du, Yu Pan, Xinlei Chen, Brajesh Kumar, Xiaotong Chen, Yiheng Xie, Yuan Fang, Xingzhu Zou, Yuanpei Yang, Jinghua Zhang, Dezi Liu, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team: The field of EP250223a detected by EP Team (Lian et al., GCN 39429) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) and 50cm array facilities of Yunnan University located at Lijiang Observatory. Simultaneous uvgr band images with different exposure times were acquired with Mephisto starting from 15:20:12 2025-02-23 UT (~15.6 minutes after the trigger) and with 50cm array in iz bands starting from 15:49:08 2025-02-23 UT (~44.5 minutes after the trigger). The afterglow candidate (Lipunov et al., GCN 39434; Hauptmann et al., GCN 39436; Kennea et al., GCN 39437; Levan et al., GCN 39438; Wu et al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo et al., GCN 39441; Xin et al., GCN 39445) is clearly detected in each v, g, r band and in the stacked u band images taken with Mephisto. The candidate is also visible in the stacked i band image of 50 cm array but not in the stacked z band. The preliminary magnitudes and 3-sigma upper limit are below: 1.6m Mephisto Start_Time(UT) | Band | Exp(s) | Mag/LimMag(AB) --------------------|------|--------|---------------- 2025-02-23T16:00:53 | u | 300*3 | 20.97 +/- 0.29 2025-02-23T15:25:14 | v | 180 | 19.93 +/- 0.22 2025-02-23T15:20:12 | g | 10 | 18.11 +/- 0.12 2025-02-23T15:25:14 | r | 50 | 18.17 +/- 0.07 50CM array Start_Time(UT) | Band | Exp(s) | Mag/LimMag(AB) --------------------|------|--------|--------------- 2025-02-23T15:49:08 | i | 300*3 | 18.89 +/- 0.11 2025-02-23T15:49:08 | z | 300*3 | >18.81 ------------------------------------------------------------------------------------------------- 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. The 50cm array consists of two 50cm telescopes for wide-field surveys and also serves as the supporting facility for monitoring the Mephisto detected targets. ------------------------------------------------------------------------------------------------- View this GCN Circular online at https://gcn.nasa.gov/circulars/39447. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37458] GRB 250221A: TNOT detection of the optical counterpart
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39446 SUBJECT: GRB 250221A: TNOT detection of the optical counterpart DATE: 25/02/24 09:24:45 GMT FROM: Xiaofeng Wang at Tsinghua University <wang_xf(a)mail.tsinghua.edu.cn> A. Iskandar（XAO), H.-C. Zhu (THU)，X.-F. Wang, and L.-T. Wang (XAO) report the optical detection of the afterglow of GRB 250221A (Francile et al., GCN 39395; Caputo et al., GCN 39396; Watson et al., GCN 39397; Melandri et al., GCN 39406; Shilling et al., GCN 39409; Guo et al., GCN 39412; Muenter et al., GCN 39417; Palmerio et al., GCN 39418; Pankov et al., GCNs 39422,39424,39426,39427; Ghosh et al., GCN 39425). We obtained the r-band images (~2.40 days after the burst) with the 80~cm Tsinghua-Nanshan Optical Telescope (TNOT) located at Nanshan Station of Xinjiang Astronomy Observatory, starting on 2025-02-23 (UT) 13:05:49. The afterglow is clearly detected on the stacked images, with the following magnitude: r = 20.46 +- 0.17 mag (MJD =60698.5457) The above photometric result is calibrated against the Pan-STARRS catalog without a correction for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/39446. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37457] EP250223a: SVOM/VT optical observation
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39445 SUBJECT: EP250223a: SVOM/VT optical observation DATE: 25/02/24 07:51:36 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> L.P. Xin, Y.L. Qiu(NAOC), Y. Wang(PMO),H.L. Li, C. Wu, Z.H. Yao, Y. N. Ma, X.H. Han, H.B. Cai, J. Wang, Y. Xu, J.Y. Wei(NAOC), J. T. Palmerio(CEA/Irfu) report on behalf of the SVOM team: The SVOM/VT conducted a ToO follow-up observations of the EP250223a (Lian et al., GCN 39429) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. The afterglow(Benjamin et al., GCN 39436) was clearly detected within the errorbox of EP/FXT (Lian et al., GCN 39429) in VT_R and VT_B images. The afterglow was fading during our observations and the brightness was estimated to be 19.21+/-0.05 mag in AB magnitude in VT_R, and 20.11+/-0.05 mag in AB magnitude in VT_B, at the mid time of 3.7 hours post 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/39445. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37456] LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39444 SUBJECT: LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart DATE: 25/02/24 04:53:21 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Alan M. Watson (UNAM), William H. Lee (UNAM), Océlotl López (UNAM), Camila Angulo Valdez (UNAM), Rosa L. Becerra (U Roma), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), and Margarita Pereyra (UNAM), and Eleonora Troja (U Roma) report: We imaged the field of the Swift/BAT-GUANO trigger possibly associated with LIGO/Virgo/KAGRA S250223dk (GCN Circ. 39443) with the DDOTI wide-field imager at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico (http://ddoti.astroscu.unam.mx). We observed the whole BAT error region from 2025-02-24 03:56 UTC to 04:24 UTC (15.9 to 16.4 hours after the GW event) at extremely high airmass. We obtained a total exposure of 24 minutes. Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues, we detect no uncatalogued sources within the observed BAT error region to a 5-sigma AB limiting magnitude of w > 20.0. Our photometry is in the AB system and is not corrected for Galactic extinction. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/39444. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37455] LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO trigger with ID 762004910: Identification of a GW compact binary merger candidate possibly associated with a sub-threshold Swift/BAT-GUANO trigger
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39443 SUBJECT: LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO trigger with ID 762004910: Identification of a GW compact binary merger candidate possibly associated with a sub-threshold Swift/BAT-GUANO trigger DATE: 25/02/24 03:12:15 GMT FROM: minghuidu1993(a)gmail.com The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration along with the Swift/BAT-GUANO team report: We identified the compact binary merger candidate S250223dk during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at T0 = 2025-02-23 12:01:15.360 UTC (GPS time: 1424347293.360). The candidate was found by the GstLAL [1] analysis pipeline. S250223dk is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.4e-05 Hz, or about one in 19 hours. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250223dk The classification of the GW signal, in order of descending probability, is Terrestrial (92%), BBH (8%), NSBH (<1%), or BNS (<1%). Assuming the candidate is astrophysical in origin, the probability that the lighter compact object is consistent with a neutron star mass (HasNS) is <1%. [2] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [2] Both HasNS and HasRemnant consider the support of several neutron star equations of state. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. Five GW-only sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [3], distributed via GCN notice about a minute after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [3], distributed via GCN notice about 5 minutes after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [3], distributed via GCN notice about 12 hours after the candidate event time. * bayestar.multiorder.fits,3, an initial localization generated by BAYESTAR [3], distributed via GCN notice about 12 hours after the candidate event time. * bayestar.multiorder.fits,4, an initial localization generated by BAYESTAR [3], distributed via GCN notice about 13 hours after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,4. For the bayestar.multiorder.fits,4 sky map, the 90% credible region is 3203 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 6033 +/- 1778 Mpc (a posteriori mean +/- standard deviation). The LVK notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; [4]). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-45,+45] seconds around the time of the GW alert. All the requested event mode data was delivered to the ground. The BAT likelihood search, NITRATES [5], performed on the temporal window [T0-20 s, T0+20 s], detects a burst candidate with a sqrt(TS) of 8.0 in a 8.192 s analysis time bin, starting at T0 - 10.240 s The 90% credible area is 2666 deg2 and the 50% credible area is <1 deg2. The integrated probability inside the coded field of view is 83%. The joint LVK-Swift/BAT localization probability map peaks at RA = 85.341 deg, Dec = -47.554 deg. A circle with a radius of 5 arcmin around this position contains 52% of the integrated joint probability. Swift has already initiated TOO followup of this position with XRT and UVOT. Results will be reported in future circulars. We encourage followup by other, more sensitive, facilities. A plot of the Swift/BAT probability skymap can be viewed here: https://guano.swift.psu.edu/trigger_report?id=762004910/#:~:text=Probabilit… The Swift/BAT probability skymap file can be downloaded from the link here: https://guano.swift.psu.edu/files/762004910/0_n_PROBMAP Instructions on how to read and manipulate this map can be found here: https://guano.swift.psu.edu/documentation More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=762004910 A search performed by the RAVEN pipeline [6] found a temporal coincidence between S250223dk and a sub-threshold Swift/BAT trigger with ID 762004910. The GRB trigger time is 10.24 seconds before the GW candidate event. The estimated joint false alarm rate for the coincidence using just timing info is 1.9e-07 Hz, or about one in a month. The GRB candidate was found during a joint targeted search between the LIGO/Virgo/KAGRA collaboration and Swift/BAT-GUANO, and has a false alarm rate of 7.4e-05 Hz, or about one in 3 hours.Combined sky maps are also available: * combined-ext.multiorder.fits,0, an initial localization, distributed via GCN notice about 12 hours after the candidate event time. * combined-ext.multiorder.fits,1, an initial localization, distributed via GCN notice about 12 hours after the candidate event time. * combined-ext.multiorder.fits,2, an initial localization, distributed via GCN notice about 13 hours after the candidate event time. For the combined-ext.multiorder.fits,2 sky map, the 90% credible region is <1 deg2. The joint localization is dominated by the Swift/BAT-GUANO candidate. Considering the overlap of the individual sky maps, the estimated joint false alarm rate for the spatial and temporal coincidence is 5.1e-09 Hz, or about one in 6 years. For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. (2023) arXiv:2305.05625 [2] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [3] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 [4] Tohuvavohu et al. ApJ, 900, 1 (2020) [5] DeLaunay & Tohuvavohu, ApJ, 941, 169 (2022) [6] Urban, A. L. 2016, Ph.D. Thesis https://dc.uwm.edu/etd/1218 and Piotrzkowski, B. J. 2022, Ph.D. Thesis https://dc.uwm.edu/etd/3060 View this GCN Circular online at https://gcn.nasa.gov/circulars/39443. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37454] The EP-WXT trigger 01709131882 is likely a flaring star
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39442 SUBJECT: The EP-WXT trigger 01709131882 is likely a flaring star DATE: 25/02/24 02:20:45 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wang (PMO, CAS), H. Z. Wu (HUST), H. He, S.-E. Xu (WHU), W. Yuan (NAOC, CAS) report on behalf of the Einstein Probe team: The EP-WXT trigger (ID: 01709131882) on 2025-02-23 21:47:14 (UTC) is likely a stellar flare associated with a BY Dra Variable V1217 Cen. The estimated flux of the flare is around 1.0 x 10^-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 5.1 x 10^31 erg/s. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with onboard X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/39442. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37453] EP250223a: OASDG optical observations
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39441 SUBJECT: EP250223a: OASDG optical observations DATE: 25/02/24 00:06:24 GMT FROM: luca.izzo(a)inaf.it L. Izzo (INAF-OACn and DARK/NBI), and D. B. Malesani (DAWN/NBI and Radboud Univ.) report: We observed the field of EP250223a (Lian et al., GCN #39429) using the 0.5-m T1 telescope of the Osservatorio Astronomico S. Di Giacomo, located in Agerola, Italy. Our observations started on 2025 February 23 at 18:15 UT, approximately 3.19 hours after the GRB trigger. We acquired a series of 6x300 s images in the Rc filter. In the stacked image, we detect a faint source consistent with the X-ray afterglow reported by EP/FXT (Lian et al., GCN #39429), and by Swift-XRT (Kennea et al., GCN #39437), and with the optical counterpart reported by several other telescopes (Hauptmann et al., GCN #39436; Levan et al., GCN #39438; Wu et al., GCN #39439; Perez-Fournon et al., GCN #39440). We measure a preliminary magnitude of Rc = 19.6 +/- 0.2 mag (AB), calibrated against nearby stars from the Pan-STARRS catalog. View this GCN Circular online at https://gcn.nasa.gov/circulars/39441. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37452] EP250223a: LCO detection of the afterglow
by GCN Circulars 23 Feb '25

23 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39440 SUBJECT: EP250223a: LCO detection of the afterglow DATE: 25/02/23 23:49:41 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon, F. Poidevin, D. Aguado, J.A. Acosta-Pulido, A. López-Oramas, D. Nespral (IAC and ULL), F. Acero (CEA Saclay and IAC), N.C. Sun (UCAS), W. Li, Y. Wang, Z. Niu (NAOC), D. Cano-Morales, I. Correa-Plasencia, and A.E. Hernández-Díaz (ULL) We observed the location of EP250223a (Lian et al., GCN circ. 39429), detected also by Swift XRT (Kennea et al., GCN circ. 39437), with two Las Cumbres Observatory Global Telescope network (LCOGT) 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Sutherland Observatory (South Africa). We obtained first a 600-sec exposure in the SDSS r' filter, that started at 2025-02-23 19:47:12 UT, e.g. 4.71 hr after the EP trigger, followed by 300-sec exposures in the SDSS i' and g' filters. The optical afterglow candidate reported by Hauptmann et al. (GCN circ. 39436) is clearly detected in the three images. We measured the following magnitudes, calibrated against PanSTARRS DR2 stars and not corrected for Galactic extinction: Date | UT start | T (mid) - T0 (hours) | mag | error | filter | ---------------------------------------------------------------------- 2025-02-23 19:47:12 4.79 19.73 0.03 r' 2025-02-23 21:38:41 6.61 19.74 0.06 i' 2025-02-23 21:42:28 6.67 20.77 0.10 g' A redshift of z = 2.756 has been reported by Levan et al. (GCN circ. 39438). 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/39440. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37451] EP250223a: early optical detection by BOOTES-4
by GCN Circulars 23 Feb '25

23 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39439 SUBJECT: EP250223a: early optical detection by BOOTES-4 DATE: 25/02/23 23:38:26 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct(a)iaa.es> S.-Y. Wu, I. Perez-Garcia, E. Fernandez-Garcia, M. D. Caballero-Garcia, G. Garcia-Segura, S. Guziy, R. Sanchez-Ramirez and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar (Univ. de Malaga), M. Gritsevich (Univ. of Helsinki), Y.-D. Hu (GXU), and D. R. Xiong, J. M. Bai, Y. F. Fan, C. J. Wang, Y. X. Xin, X. H. Zhao, J. R. Mao, B. K. Lun, K. Ye (Yunnan Observatories/CAS, Kunming) on behalf of a larger collaboration, report: Following the detection of EP250223a by EP/WXT (Lian et al. GCNC 39429), the 0.6m BOOTES-4/MET robotic telescope at Lijiang Astronomical Observatory (China) automatically responded to this burst starting on Feb. 23, 15:16:38 UT (~12 min after trigger). At the position of the EP/FXT X-ray source (also recorded by Swift/XRT, Kennea et al. GCNC 39437), an optical counterpart is detected, for which we measure a magnitude of 18.4 +/- 0.1 (60s, clear filter, comparable with Gmag of Gaia DR3), which also consistent with the object reported by NOT at a later stage (Hauptmann et al. GCNC 39426, Levan et al. GCNC 39438). Further analysis of the additional images is ongoing. We thank the staff at Lijiang observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/39439. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37450] EP250223a: NOT redshift z = 2.756
by GCN Circulars 23 Feb '25

23 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39438 SUBJECT: EP250223a: NOT redshift z = 2.756 DATE: 25/02/23 23:17:57 GMT FROM: Andrew Levan at Radboud University <a.levan(a)astro.ru.nl> Andrew J. Levan (Radboud and Warwick), Luca Izzo (INAF, Naples and DARK/NBI), Daniele B. Malesani (DAWN/NBI and Radboud), Antonio Martin-Carrillo (UCD), Franz E. Bauer (PUC), Peter G. Jonker (Radboud), Benjamin N. Hauptmann (NOT and DTU Space), Yfke Bethlehem (Kapteyn Astronomical Institute, Groningen, and ING), and Dong Xu (NAOC), report on behalf of a larger collaboration: Further to the identification of the likely optical counterpart (Hauptmann et al., GCN 39436) of EP 250223a (Lian et al., GCN 39429), we obtained spectroscopic observations with the Nordic Optical Telescope, beginning at 21:18 UT. A total of 4x900 s observations were obtained using grism #4. The observations reveal a strong continuum with a pronounced suppression at ~4550 AA, which we interpret as arising from damped Lyman-alpha absorption. In addition we detect a number of narrow metal lines, among which Fe II, Al II, C II, O I, Si II, which allow us to fix the redshift to z = 2.756. The spectral shape and redshift, as well as the detection of an X-ray counterpart at a consistent position with Swift (Kennea et al., GCN 39437), secure the source as the counterpart of EP250223a. View this GCN Circular online at https://gcn.nasa.gov/circulars/39438. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37449] EP250223a: Swift/XRT localization
by GCN Circulars 23 Feb '25

23 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39437 SUBJECT: EP250223a: Swift/XRT localization DATE: 25/02/23 21:48:18 GMT FROM: Jamie Kennea at Penn State <jak51(a)psu.edu> J. A. Kennea, C. Gronwall (PSU) and P. A. Evans (Leicester) report on behalf of the Swift Team: At 16:36:15UT Swift began a target-of-opportunity observation of the transient EP250223a (GCN #39429), approximately 1.6 hours after the Einstein Probe trigger. We detect an an uncatalogued point source above the RASS limit at the following location: RA/Dec(J2000) = 98.27464, -22.4449, which is equivalent to: RA(J2000) = 06h 33m 05.91s, Dec(J2000) = -22° 26′ 41.8″, with an estimated uncertainty radius of 3.8 arc-seconds (90% confidence). This position lies 8.5 arc-seconds from the EP WXT position reported in GCN #39429. The peak flux during the XRT observation was 5.4 (±1.0) × 10^-12 erg cm^-2 s^-1 (0.3 - 10 keV). View this GCN Circular online at https://gcn.nasa.gov/circulars/39437. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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