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[vsnet-grb-info 37588] EP250225a: the candidate optical counterpart is an AGN
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39573 SUBJECT: EP250225a: the candidate optical counterpart is an AGN DATE: 25/03/03 15:25:46 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> D. B. Malesani (DAWN/NBI and Radboud Univ.), D. Mata-Sanchez (IAC and ULL), A. Martin-Carrillo (UCD), A. J. Levan (Radboud Univ.), P. G. Jonker (Radboud Univ.), report on behalf of a larger collaboration: We observed again the variable object (Malesani et al., GCN 39516) located inside the X-ray localization of the fast X-ray transient EP250225a (Jiang et al., GCN 39475; Jiang et al., GCN 39529) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. The observation mid time was 2025 Feb 27.93 UT (2.42 days after the trigger) and a total of 5x300 s was secured in the r band. The object is detected with a flux consistent with our previous observation (Malesani et al., GCN 39516) to within ~0.1 mag, and still brighter than the archival value from the Legacy Survey. Image subtraction confirms no significant variability between the two NOT epochs. A spectrum of this source was secured with the Gran Telescopio Canarias (GTC). Observations started on 2025 Feb 28.98 UT (3.47 days after the trigger), and consisted of a single 1800 s exposure with grism R1000R, yielding usable data in the wavelength range 5000-9000 AA. Detection of two broad features (FWHM ~ 3500 km s^-1), identified as Hbeta and Hgamma, as well as of narrow [O III] 5008, allows us to measure a redshift z = 0.587. The large velocities and the point-like PSF indicate that this is an active galactic nucleus. Given the slow variability and the AGN nature of this source, its relationship to EP250225b is unclear, and the two may well be unrelated. We acknowledge significant support from the observing staff at the NOT, in particular, Alejandra Diaz Teodori (NOT and Turku Univ.), Roar Rasmussen (NOT and Aarhus Univ.), and Saskia Schlagenhauf (QUB), and at the GTC, in particular Antonio Cabrera-Lavers (GTC). View this GCN Circular online at https://gcn.nasa.gov/circulars/39573. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37587] EP250302a: Kinder optical follow-up observations
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39572 SUBJECT: EP250302a: Kinder optical follow-up observations DATE: 25/03/03 14:21:48 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> A. Aryan, T.-W. Chen, C.-S. Lin (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, H.-Y. Hsiao, 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 EP250302a (Zhu et al., GCN 39550; Dai et al., GCN 39556) using the 40cm SLT 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 r band started at 18:30 UT on the 2nd of March 2025 (MJD = 60736.771), ~2.91 hrs after the EP trigger. We took a total of 12 frames in r-band spanning a period of about 2.91hr to 5.22hr since the EP-WXT trigger. The optical counterpart candidate proposed by Zhu et al., (GCN 39550 ) and confirmed by several other observations (Busmann et al., GCN 39551; Leonini et al., GCN 39553; Wu et al., GCN 39555; Xin et al., GCN 39558; Adami et al., GCN 39560; Yang et al., GCN 39561; Becerra et al., GCN 39562; and Izzo et al., GCN 39564), was clearly detected in almost each of the individual frame (besides the last frame). We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform PSF photometry on individual frames. The details of the observation and measured photometry from the first frame (in the AB system) were as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | Seeing | Airmass SLT | r | 60736.771 | 2.91 | 300 * 1 | 19.60 +/- 0.05 | 1".25 | 1.14 The presented magnitude was calibrated using the field stars from the Pan-STARRS1 catalog and was not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_r = 0.06 mag, respectively, in the direction of the transient (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/39572. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37586] LIGO/Virgo/KAGRA S250302av: 2 counterpart neutrino candidate events from an IceCube neutrino search
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39571 SUBJECT: LIGO/Virgo/KAGRA S250302av: 2 counterpart neutrino candidate events from an IceCube neutrino search DATE: 25/03/03 13:51:37 GMT FROM: Zsuzsa Marka at IceCube/Columbia University <zsuzsa(a)astro.columbia.edu> IceCube Collaboration (http://icecube.wisc.edu/) reports: We have performed a search for track-like muon neutrino candidate events detected by IceCube consistent with the sky localization of the low-significance gravitational-wave candidate event S250302av in a time range of 1000 seconds centered on the alert event time (2025-03-02 13:57:15 UTC to 2025-03-02 14:13:55 UTC) [1,2]. During this time period, IceCube was collecting good quality data. A single hypothesis test was conducted using a Bayesian approach to quantify the joint GW + neutrino event significance, which assumes a binary merger scenario and accounts for known astrophysical priors, such as GW source distance, in the statistical significance estimation [3]. Two track-like events were found in spatial and temporal coincidence with the gravitational-wave candidate S250302av calculated from the map circulated in the S250302av-2-Preliminary notice. This represents an overall p-value of 0.0084 for the Bayesian search. The p-value measures the consistency of the observed track-like events with the known atmospheric backgrounds for this single map (not accounting for statistical trials from multiple GW events). Further details are available at https://gcn.nasa.gov/missions/icecube and at https://roc.icecube.wisc.edu/public/LvkNuTrackSearch. Properties of the coincident event are shown below: dt(s) RA(deg) Dec(deg) Angular uncertainty(deg) p-value(Bayesian) ------------------------------------------------------------------------------------- 76.86 114.87 3.25 1.16 0.0298 211.98 191.11 58.45 5.39 0.0137 where: dt = Time of track event minus time of GW trigger (sec) Angular uncertainty = Angular uncertainty of track event: the radius of a circle representing 90% CL containment by area. p-value = the individual p-value for the specific track event from this search. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu [1] M. G. Aartsen et al 2020 ApJL 898 L10 [2] Abbasi et al. Astrophys.J. 944 (2023) 1, 80 [3] I. Bartos et al. 2019 Phys. Rev. D 100, 083017 View this GCN Circular online at https://gcn.nasa.gov/circulars/39571. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37585] EP250302a: Swift/UVOT detection
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39570 SUBJECT: EP250302a: Swift/UVOT detection DATE: 25/03/03 12:58:05 GMT FROM: Sam Shilling at Lancaster University <shilling.sam(a)gmail.com> S. P. R. Shilling (Lancaster U.) and A. A. Breeveld (UCL-MSSL) reports on behalf of the Swift UVOT team: Swift/UVOT observed the field of EP250302a (Dai et al., GCN 39556) for 1029 seconds in the U-band starting at 16:36:56 UT, 1 hour after the detection by Einstein Probe WXT. A source consistent with the EP-FXT position (Dai et al., GCN 39556) is detected and appears to be fading. The preliminary detection magnitudes reported below are calculated using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373). The magnitude at the start of the observation is 17.64 +/- 0.05 (1 hour post trigger) and decays to 18.88 +/- 0.12 (~2 hours post trigger). We note that an X-ray source at the EP-FXT position was independently observed by the Swift/XRT (Page et al., GCN 39557). We also note that, in addition to the Swift/UVOT, various other facilities have observed an optical counterpart at this position (Zhu et al., GCN 39550; Busmann et al., GCN 39551; Leonini et al., GCN 39553; Wu et al., GCN 39555; Xin et al., GCN 39558; Lipunov et al., GCN 39559; Adami et al., GCN 39560; Becerra et al., GCN 39562; Pankov et al., GCN 39565; Reguitti et al., GCN 39568; Komesh et al., GCN 39569). View this GCN Circular online at https://gcn.nasa.gov/circulars/39570. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37584] EP250302a: NUTTelA-TAO Early Measurments
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39569 SUBJECT: EP250302a: NUTTelA-TAO Early Measurments DATE: 25/03/03 12:18:23 GMT FROM: Toktarkhan Komesh at Nazarbayev University <toktarkhan.komesh(a)nu.edu.kz> T. Komesh (NU), Z. Abdullayev (NU), Z. Maksut (NU), D. Berdikhan (NU), B. Grossan (UCB, NU), M. Krugov (FAI) and E. Abdikamalov (NU) report on behalf of the Energetic Cosmos Laboratory: The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) pointed at EP250302a on receipt of an automated GCN / EP position alert, observing in Sloan g' and r' bands, with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32, 14). We started observations at 15:42:43 UT on 2025-03-02, 399 seconds after the Einstein Probe trigger (Dai et al., GCN 39556). Observations were made in partially cloudy conditions. A new and changing source consistent with the XRT position (Page et al., GCN 38761) was detected. We report the following photometric values for the optical transient: tc-t0(s) g'(mag) err r'(mag) err exposure_time (s) -------------------------------------------------------------- 424 - 18.36 0.08 50 628 - 18.35 0.08 300 928 - 18.80 0.13 300 1273 - 18.76 0.07 240 1513 - 18.55 0.06 240 1753 - 18.12 0.04 240 1993 - 17.71 0.03 240 2233 - 17.58 0.02 240 2686 - 17.48 0.03 240 2926 - 17.54 0.02 240 3166 - 17.58 0.02 240 3406 - 17.65 0.02 240 3646 - 17.68 0.03 240 3886 - 17.73 0.03 240 4126 - 17.85 0.03 240 4366 - 17.88 0.04 240 4606 - 17.95 0.03 240 4846 - 18.08 0.04 240 5086 - 18.11 0.03 240 5326 - 18.18 0.04 240 5566 - 18.32 0.04 240 5806 - 18.47 0.04 240 6046 - 18.56 0.04 240 6348 18.93 0.05 18.56 0.04 240 6588 18.99 0.06 18.76 0.04 240 6828 19.01 0.05 18.86 0.05 240 7068 19.05 0.05 18.86 0.05 240 7308 19.06 0.05 18.90 0.05 240 7548 19.12 0.05 18.94 0.05 240 7788 19.28 0.07 19.01 0.06 240 8028 19.43 0.08 19.01 0.06 240 8269 19.53 0.08 19.19 0.07 240 8509 19.34 0.06 19.19 0.06 240 tc-t0 = trigger time minus image center time. Calibration was done with 4 bright Pan-STARRS catalog stars on our images. Our results are in agreement with those reported in previously published circulars (Zhu et. al, GCN 39550; Wu et. al, GCN 39555; Xin et. al, GCN 39558; Pankov et al., GCN 39565). We caution the reader that these are preliminary results, without color or other corrections, and will likely change in small measure. Please also note that times are approximate. ---------------------------------- NU = Nazarbayev University, Astana, Kazakhstan UCB = University of California, Berkeley, USA FAI = Fesenkov Astrophysical Institute, Kazakhstan This research has been funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP26103591). The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazkhstan. View this GCN Circular online at https://gcn.nasa.gov/circulars/39569. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37583] EP250302a: optical observation from the INAF Asiago Observatory
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39568 SUBJECT: EP250302a: optical observation from the INAF Asiago Observatory DATE: 25/03/03 11:27:12 GMT FROM: Andrea Reguitti at INAF - Osservatorio Astronomico di Brera <andreareguitti(a)gmail.com> A. Reguitti (INAF-OAB) reports on behalf of the CIBO (Coordinamento Italiano Burst Ottici) collaboration: We observed the field of EP250302a (Zhu et al., GCN 39550) from the INAF - Padova Astronomical Observatory located in Asiago (Italy) with the 67/92 Schmidt robotic telescope. The observation was carried in the Sloan-i filter, started on 2025 March 02 at 20:01:15 UT (i.e. 4.4 hr after the burst), and lasted for 15 minutes. In our stacked images, the optical counterpart is detected at the coordinates reported by Zhu et al., GCN 39550: i = 19.98+-0.17 mag (AB; calibrated against the PS1 catalogue), at a mid-time of about 4.5 hours after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/39568. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37582] EP250302a: REM NIR upper limits
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39567 SUBJECT: EP250302a: REM NIR upper limits DATE: 25/03/03 10:11:26 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 EP250302a (Dai et al., GCN 39556) 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 March 03 at 02:15:53 UT (i.e. 10.66 hr after the burst), and lasted for about 1 hour. From preliminary analysis, we do not find any counterpart at the position of the reported optical afterglow (Zhu et al., GCN 39550; Busmann et al., GCN 39551; Leonini et al., GCN 39553; Wu et al., GCN 39555; Xin et al., GCN 39558; Adami et al., GCN 39560; Yang et al., GCN 39561; Becerra et al., GCN 39562; Izzo et al., GCN 39564; Pankov et al., 39565) down to the following 3sigma limit: H > 16.1 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 11.09 hours after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/39567. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37581] IceCube-241113A: MASTER flaring blazar 5BZB J1311+0853 with Zhirkov effect
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39566 SUBJECT: IceCube-241113A: MASTER flaring blazar 5BZB J1311+0853 with Zhirkov effect DATE: 25/03/03 09:56:46 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> K. Labzina, K.Zhirkov, V.Lipunov, E.Gorbovskoy, G.Antipov, D.Vlasenko, A.Kuznetsov, N.Tyurina, P.Balanutsa, A.Chasovnikov, D.Kuvshinov, V.Topolev,Ya.Kechin,Yu.Tselik, K.Minkina(Lomonosov Moscow State University, SAI, Physics Department), O.Gress, N.Budnev, O.Ershova (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), D.Buckley (SAAO), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started IceCube-241113 (IceCube, Zegarelli et al. GCN#38200) to the IceCube Alert 241113.02 (trigger No 30891383, 13h 04m 46.32s , +08d 29m 27.6s, R=0.53) errorbox 477 sec after notice time and 554 sec after trigger time at 2024-11-13 00:31:35 UT, with upper limit up to 16.0 mag. (Lipunov et al. GCN#38186) MASTER cover map: https://master.sai.msu.ru/site/master2/observ.php?id=2668204 We analyzed MASTER archive images since 2012 of the sources, that can be related with this event. We detected blazar J131155.76+085340.9 inside 3 sigma https://vizier.cds.unistra.fr/viz-bin/VizieR?-source=&-out.add=_r&-out.add=… and we detected its brightening up to 16.9m during last nights observations. The MASTER archive light curve from 2010 year is available at http://observ.pereplet.ru/MASTER_IC241113A.jpg Light curve shows that after neutrino alert the blazar J131155.76+085340.9 was in a dim state 20.2m, after which, within an half hour, it increased its brightness to 16.9m. This, we report observation of an Zhirkov effect, discovered earlier (The Astrophysic Jornal Letters, 896, L19, 2020 https://ui.adsabs.harvard.edu/abs/2020ApJ...896L..19L/abstract ). View this GCN Circular online at https://gcn.nasa.gov/circulars/39566. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37580] EP250302a: Mondy Observations and Optical Light Curve
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39565 SUBJECT: EP250302a: Mondy Observations and Optical Light Curve DATE: 25/03/03 09:54:00 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Moskvitin (SAO RAS), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN: We performed optical observations of the field of a fast X-Ray transient EP250302a (Zhu et. al, GCN 39550; Busmann et. al, GCN 39551; Leonini et. al, GCN 39553; Wu et. al, GCN 39555; Dai et. al, GCN 39556; Page et. al, GCN 39557; Xin et. al, GCN 39558; Lipunov et. al, GCN 39559; Adami et. al, GCN 39560; Yang et al., GCN 39561; Becerra et al., GCN 39562; Izzo et al., GCN 39564) in the R filter with the AZT-33IK 1.5-meter telescope of Mondy observatory. The observations began on 2025-03-02 (UT) 15:50:41.578, i.e. 0.01083 days since trigger. The optical counterpart (firstly reported by Zhu et. al, GCN 39550) is clearly detected in each image of an exposure of 120 sec. The optical light curve displays variable behavior. Initially, the light curve fades until ~1.5e-2 days since trigger, then it is brightening until it reaches peak magnitude of R = 17.26 +/- 0.03 mag at 2025-03-02 (UT) 16:14:42 (0.02751 days since trigger). The further brightness evolution is a decay by the times indicated in Adami et. al, GCN 39560. Our photometry is based on nearby stars from the USNO-B1.0 catalog (see the list below) and has not been corrected for the Galactic extinction. Ref. stars RA Dec R2 11:18:11.14 +33:32:45.34 15.74 11:17:47.64 +33:30:50.19 17.69 The light curve image is available at: http://grb.rssi.ru/EP250302a/EP250302a_LC.jpg View this GCN Circular online at https://gcn.nasa.gov/circulars/39565. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37579] EP250302a: VLT/MUSE optical redshift z = 1.131
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39564 SUBJECT: EP250302a: VLT/MUSE optical redshift z = 1.131 DATE: 25/03/03 09:11:58 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> L. Izzo (INAF/OACn and DARK/NBI), R. A. J. Eyles-Ferris (Univ. Leicester), D. Xu (NAOC), A. Saccardi (CEA/Irfu), B. Schneider (LAM), D. B. Malesani (DAWN/NBI and Radboud Univ.), J. T. Palmerio (CEA/Irfu), N. R. Tanvir (Univ. Leicester), P. G. Jonker (Radboud Univ.), S. D. Vergani (CNRS - Paris Observatory/LUX), A. J. Levan (Radboud Univ. and Warwick Univ.), report on behalf of the Stargate collaboration: We observed the optical/NIR counterpart (Zhu et al., GCN 39550; Busmann et al., GCN 39551; Leonini et al., GCN 39553; Wu et al., GCN 39555; Xin et al., GCN 39558; Adami et al., GCN 39560; Becerra et al., GCN 39562) of the fast X-ray transient EP250302a (Dai et al., GCN 39556) using the ESO VLT UT4 (Yepun) equipped with the MUSE integral-field spectrograph. The observation mid-epoch is 2025 March 3.193 UT (13.03 hr after the initial high-energy trigger), the total exposure time is 76.5 min, and the covered wavelength range is 4750-9300 AA. The optical counterpart (Zhu et al., GCN 39550) is well detected in the wavelength-stacked “white light” image, as well as in continuum spectroscopy. We also observe several clear absorption features, which we interpret as due to Mg I (2853), Mg II (2804, 2796), and Fe II (2600, 2587, 2383, 2374, 2344), all at a common redshift z = 1.131. Given the overall good S/N of the spectrum, and the fact that there are no features left un-identified, we consider z = 1.131 to be most likely the redshift of EP250302a. Our spectra do not cover the blue region where the z = 0.549 features reported by Yang et al. (GCN 39561) would fall, so we cannot confirm the presence of that system, which could be an intervening absorber. No emission lines at z = 0.549 appear in our data. Thanks to the large MUSE field of view (1' x 1'), further to the optical transient, two neighboring bright galaxies were covered in our observation, including the one noted by Busmann et al. (GCN 39551) and Yang et al. (GCN 39561). For them, we measure the following redshifts: 1) RA = 11:18:05.26, Dec = +33:35:05.6: z = 0.127 from Na I D, Mg b, Hbeta, G band absorption; 2) RA = 11:18:01.03, Dec = +33:35:30.8: z = 0.127 from Halpha, [N II] and [S II] emission. We conclude that these objects are not physically associated with EP250302a. We thank Malte Busmann and Brendan O’Connor for sharing a finding chart of the field, and the ESO observing staff in Paranal, in particular Claudia Cid, Monika Petr-Gotzens, and Jonathan Smoker, for efficiently carrying out these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39564. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37578] INTEGRAL: end of scientific operations
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39563 SUBJECT: INTEGRAL: end of scientific operations DATE: 25/03/03 08:52:32 GMT FROM: Carlo Ferrigno <carlo.ferrigno(a)unige.ch> From 2025-03-04 at 12:08:04 UT, data from the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) will not be transmitted anymore to the INTEGRAL science data centre (ISDC) owing to the end of scientific operations, more than 22 years after its launch. As a consequence, the INTEGRAL Burst Alert System (IBAS) will be discontinued and no more alerts nor GCN notices distributed (see https://gcn.gsfc.nasa.gov/integral.html for the current INTEGRAL GCN notices). The IBAS team thanks all the scientific community for the continuous support. View this GCN Circular online at https://gcn.nasa.gov/circulars/39563. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37577] EP250302A: VLT near-infrared observations
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39562 SUBJECT: EP250302A: VLT near-infrared observations DATE: 25/03/03 08:26:32 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa Becerra (U Rome), Yu-Han Yang (U Rome), Muskan Yadav (U Rome), Eleonora Troja (U Rome) report on behalf of the ERC BHianca team: We observed the field of EP250302A (Dai et al., GCN 39556) with the HAWKI imager on the ESO VLT UT4 (Yepun). Observations began at T+14.1 h days and were carried out at an average airmass of about 1.9 in the J, H, and K filter. We detect the optical counterpart (Zhu et al., GCN 39550; Busmann et al., GCN 39551; Leonini et al., GCN 39553; Wu et al., GCN 39555, Xin et al., GCN 39558) in all three filters at a magnitude J~20 mag (Vega) calibrated using nearby stars in the 2MASS Catalogue. 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/39562. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37576] EP250302A: VLT/X-shooter tentative redshift
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39561 SUBJECT: EP250302A: VLT/X-shooter tentative redshift DATE: 25/03/03 08:21:14 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(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 EP250302A (Dai et al., GCN 39556) with the X-Shooter spectrograph on the ESO VLT UT3 (Melipal). Observations began at T+13.6 hours and obtained a total of 4x600s spectra at an average airmass of about 1.9. At the position of the optical counterpart (Zhu et al., GCN 39550; Busmann et al., GCN 39551; Leonini et al., GCN 39553; Wu et al., GCN 39555, Xin et al., GCN 39558) we detect a strong continuum in all three arms. Based on a preliminary analysis, we identify weak absorption lines consistent with Fe II and the Mg II doublet at redshift z=0.549. Our observations suggest that the EP transient is not related to the nearby galaxy noted by Busmann et al., GCN 39551, but lies at higher redshift. 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/39561. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37575] EP250302A: VLT/X-shooter tentative redshift
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39561 SUBJECT: EP250302A: VLT/X-shooter tentative redshift DATE: 25/03/03 08:21:14 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(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 EP250302A (Dai et al., GCN 39556) with the X-Shooter spectrograph on the ESO VLT UT3 (Melipal). Observations began at T+13.6 hours and obtained a total of 4x600s spectra at an average airmass of about 1.9. At the position of the optical counterpart (Zhu et al., GCN 39550; Busmann et al., GCN 39551; Leonini et al., GCN 39553; Wu et al., GCN 39555, Xin et al., GCN 39558) we detect a strong continuum in all three arms. Based on a preliminary analysis, we identify weak absorption lines consistent with Fe II and the Mg II doublet at redshift z=0.549. Our observations suggest that the EP transient is not related to the nearby galaxy noted by Busmann et al., GCN 39551, but lies at higher redshift. 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/39561. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37574] EP250302a: OHP/T193 optical and spectroscopic observations
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39560 SUBJECT: EP250302a: OHP/T193 optical and spectroscopic observations DATE: 25/03/03 08:13:10 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> C. Adami (LAM/Pytheas/AMU), B. Schneider (LAM), S. Basa (LAM/OHP/Pytheas/AMU), M. Dennefeld (IAP/CNRS/Sorbonne U.), E. Le Floc'h (CEA/Irfu), J. P. Palmerio (CEA/Irfu), A. Saccardi (CEA/Irfu), J. Schmitt (OHP/Pytheas/AMU), F. Schüssler (CEA/DPhP), D. Turpin (CEA/Irfu), S. D. Vergani (CNRS, Paris Obs./LUX) report on behalf of the larger collaboration: We observed the field of the EP250302a (Dai et al. GCN 39556) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 2 exposures (2x600 s) in the r-band. The first epoch started at 23:38:10 UT on 2025-03-02 (8.03h after the trigger) and the second one at 01:02:41 UT on 2025-03-03 (9.43h after the trigger). In both images, we clearly detected the optical counterpart reported by Zhu et al., GCN 39550, Busmann et al., GCN 39551, Leonini et al., GCN 39553 and Xin et al., GCN 39558. The preliminary magnitudes derived for that source are: r = 20.75 +/- 0.06 mag (AB) r = 20.85 +/- 0.07 mag (AB) The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. In addition, we obtained 2x30 min exposures with the MISTRAL spectroscopic blue setting, covering from 4200 to 8000 AA starting at 00:20:45UT (midtime = T0+8h45). In a preliminary reduction of the spectrum, we detect a very faint continuum at the GRB position, covering the whole spectral range and suggesting a redshift lower than 2.5. We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Neda Heidari and Stephane Favard for the MISTRAL observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39560. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37573] EP250302a: Global MASTER-Net observations report
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39559 SUBJECT: EP250302a: Global MASTER-Net observations report DATE: 25/03/03 08:09:37 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 EP250302a ( EP Team et al., GCN 39556) errorbox 328 sec after notice time and 57360 sec after trigger time at 2025-03-03 07:32:04 UT, with upper limit up to 19.8 mag. The observations began at zenith distance = 73 deg. The sun altitude is -35.3 deg. The galactic latitude b = 70 deg., longitude l = 190 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2797947 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 57390 | 2025-03-03 07:32:04 | MASTER-OAFA | (11h 18m 00.44s , +33d 56m 34.8s) | C | 60 | 19.8 | 58371 | 2025-03-03 07:48:24 | MASTER-OAFA | (11h 18m 02.25s , +33d 57m 27.8s) | C | 60 | 19.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/39559. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37572] EP250302a: Xinglong F60B optical observation
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39558 SUBJECT: EP250302a: Xinglong F60B optical observation DATE: 25/03/03 07:52:34 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, X. H. Han, P. P. Zhang, J. Wang, C. Wu, Y. L. Qiu, H. B. Cai, H. L. Li, X. M. Lu, R. S. Zhang, Y. J. Xiao, J. S. Deng, Z. H. Yao, Y. N. Ma, J. Y. Wei (NAOC), X. G. Wang, E. W. Liang (GXU) report: We observed location of EP250302a (Trigger ID: 01709132186, Dai et al., GCN 39556) with F60B telescope in R band at Xinglong observatory, China. Observations started at 15:42:43 UT on 2025-03-02, 6.5 min after the EP-WXT trigger. The optical counterpart reported (Zhu et al., GCN 39550, Busmann et al., GCN 39553, Leonini et al., GCN 39553, Wu et al., GCN 39555) within the FXT and XRT locations (Dai et al., GCN 39556, Page et al., GCN 39557) was clearly detected in the stacked image with an exposure time of 10*50 sec. The brightness was estimated to be R=18.36+/-0.13 mag calibrated to USNO B1.0 R2 magnitude. View this GCN Circular online at https://gcn.nasa.gov/circulars/39558. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37571] EP250302a: Swift-XRT observations of a fading X-ray source
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39557 SUBJECT: EP250302a: Swift-XRT observations of a fading X-ray source DATE: 25/03/03 07:43:50 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 March 02 at 16:36 UT, Swift started observing EP250302a, 3.6 ks after the trigger (GCN Circ. 39556). A fading X-ray source was identified, at a position of RA, Dec = 169.51508, +33.5858, which is equivalent to RA (J2000): 11h 18m 03.62s Dec (J2000): +33d 35′ 09.0″ with an uncertainty of 2.6 arcsec (radius, 90% confidence). This position is consistent with the optical counterpart reported in GCNs 39550, 39551, 39553 and 39555. The X-ray flux at the start of the observation was (5.0 +-/ 1.1) x 10^-11 erg cm^-2 s^-1 (0.3 - 10 keV), fading to a value of (7.1 +/- 0.9) x 10^-12 erg cm^-2 s^-1 at 8 ks post trigger. The decay can be fitted with a power-law slope of alpha = 2.36 (+0.37/-0.32). View this GCN Circular online at https://gcn.nasa.gov/circulars/39557. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37570] EP250302a: Einstein Probe detection of an X-ray transient
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39556 SUBJECT: EP250302a: Einstein Probe detection of an X-ray transient DATE: 25/03/03 07:23:40 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C. Y. Dai (NJU), Y.Q. Zhao (USTC, PRIC), X. Mao, S. X. Wen, W. Yuan (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 EP250302a. The transient triggered EP-WXT (ID: 01709132186) at 2025-03-02T15:36:04 (UTC). The light curve shows a burst lasting at least 30s, with a peak of about 9 x 10^(-9) erg/s/cm^2. The spectrum can be fitted by an absorbed power-law with a photon index of 0.6(-0.4/+0.4) (with the column density fixed at the Galactic one of 2.36 x 10^20 cm^-2). The derived average unabsorbed 0.5-4 keV flux is 7.0(-1.6, +2.0) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 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. = 169.5151 deg, DEC = 33.5851 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). A secondary burst is detected starting at 2025-03-02T15:56:06 (UTC) and last for ~500 s, the spectrum during the flare can be fitted by an absorbed power-law with a photon index of 1.8(-0.05/+0.0.5) (with the column density fixed at the Galactic one of 2.36 x 10^20 cm^-2), and the derived average unabsorbed 0.5-10 keV flux is 9.6(-0.4, +0.4) x 10^(-11) erg/s/cm^2. Additionally, we note that the optical counterparts (GCN 39550, GCN 39551, GCN 39553, and GCN 39555) lie within the positional uncertainty of EP-FXT. Further follow-up observations are encouraged to identify the nature of this X-ray transient. 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/39556. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37569] EP250302a: SVOM/C-GFT optical observations
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39555 SUBJECT: EP250302a: SVOM/C-GFT optical observations DATE: 25/03/03 05:21:19 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Chao WU (NAOC), Zhe Kang (CHO), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei, Qiu(NAOC), Jing Wang(NAOC), Jianyan Wei (NAOC) report on behalf of the SVOM/C-GFT team: We observed the field of EP250302a detected by Einstein Probe (Trigger ID: 01709132186) with C-GFT. Our observations were started on 2025-03-02T15:43:07 UTC, ~7.05 mins after the trigger. The optical counterpart (reported by Zhu et al. GCN 39550, Busmann et al., GCN 9551,Leonini et al., GCN 39553) was clearly detected in stacked images of band g,r and i. The results are, (T-T0)_mid(sec) mag mag_err band ------------------------------------------ 462 18.13 +/- 0.10 i 553 18.31 +/- 0.09 g 664 18.14 +/- 0.07 r The photometry was calibrated with nearby Pan-STARRS1 stars. Further analysis is on-going. We thank the observation assistants Bowen Li at Jilin observatory for their excellent support. Chinese Ground Follow-up Telescope of SVOM mission is located at Jilin, Changchun Observatory, National Astronomical Observatories, CAS. It has FOV of 1.28 deg x 1.28 deg with a 4k*4k CMOS detector mounted on the primary focus of 1.2-meter-aperure telescope. View this GCN Circular online at https://gcn.nasa.gov/circulars/39555. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37568] GRB250226A: GRANDMA Optical Observations
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39554 SUBJECT: GRB250226A: GRANDMA Optical Observations DATE: 25/03/03 04:48:59 GMT FROM: Lydia Nyambane at UMN <nyamb021(a)umn.edu> M. Tanasan (NARIT), L. Nyambane (UMN), H. Muenter (UMN), C. Andrade (UMN), Y. Rajabov (UBAI), F. Magnani (CPPM), M. Masek (FZU), S. Alshamsi (AUS), W. Corradi (LNA), T. Almeida (LNA), K. Noysena (NARIT), L. Fraga (LNA), N. Sasaki (LNA), A. Takey (NRIAG), Y. Hendy (NRIAG), M. Abdelkareem (NRIAG), E. Elhosseiny F. Navarete (NOIRLab/SOAR), S. Antier (OCA/IJCLAB), M. Coughlin (UMN), S. Karpov (FZU), P. Hello (IJCLAB), P-A. Duverne (APC), T. Pradier (Unistra/IPHC), N. Guessoum (AUS) on behalf of the GRANDMA and Kilonova-Catcher collaborations: The GRANDMA collaboration imaged the field of a fast X-ray transient GRB 250226A 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). GRANDMA observations were performed at RA = 224.2651, DEC = 20.9756 with the OPD/60cm, TRT-SBO, KAO, Lisnyky/AZT-8 and AbAO-T70 telescopes starting ~0.4 days post T0 in the R and i' bands. We detect the optical afterglow and report some of the observations at the following magnitudes: | T-start (UTC) | Magnitude | UL (5sigma) | Filter | Telescope | | 2025-02-26 17:19:21 | 21.5 +/- 0.2 | 21.5 | R (AB) | TRT-SBO | | 2025-02-27 01:39:46 | 21.15+/-0.15 | 22.6 | i’ (AB) | KAO | | 2025-02-27 05:28:50 | 22.0+/-0.25 | 21.8 | R (AB) | OPD/60cm | Our findings were consistent with the MEPHISTO telescope (Zou et al., GCN 39511), the Xinglong Observatory ( Jiang et al., GCN 39515), and the Las Cumbres Observatory Global Telescope network (LCOGT) (Poidevin et al., GCN 39524). All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained in Johnson Cousin filters were calibrated using the Gaia DR3 and PS1 catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/). View this GCN Circular online at https://gcn.nasa.gov/circulars/39554. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37567] EP250302a: Montarrenti Observatory optical detection
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39553 SUBJECT: EP250302a: Montarrenti Observatory optical detection DATE: 25/03/02 23:05:33 GMT FROM: Simone Leonini at Montarrenti Observatory (Siena, Italy) <s.leonini(a)iol.it> S. Leonini, M. Conti, P. Rosi, L.M. Tinjaca Ramirez (Montarrenti Observatory, Siena, Italy, part of UAI/SSV-GRB section), M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy) and K. Kalinowski (Aarhus University, Department of Physics and Astronomy) report: we observed the field of the X-ray transient EP250302a (Einstein Probe mission, Trigger ID 01709132186) with the automated and remoted 0.53m Ritchey-Chretien telescope at Montarrenti Observatory (Siena, Italy, IAU code C88). The observations were started at 2025-03-02 20:40:11 UT (approximately 5 hours after the EP-WXT trigger) stacking 50x40s calibrated Rc-band CCD images. We detect an optical transient candidate at the position reported by Zhu et al. (GCN 39550). Preliminary photometry was obtained using nearby PanSTARRS stars as follows: Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Err. 2025-03-02 20:57:42 UT 5.35 50x40s Rc 20.36 +/-0.08 consistent with other observation reported by Busmann et al., GCN 39551. Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied. Further observations are ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/39553. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37566] Fermi GRB 250302A: Global MASTER-Net observations report
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39552 SUBJECT: Fermi GRB 250302A: Global MASTER-Net observations report DATE: 25/03/02 21:33:42 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 250302A ( Fermi GBM team, GCN 39548) errorbox 21539 sec after notice time and 21575 sec after trigger time at 2025-03-02 19:46:08 UT, with upper limit up to 20.4 mag. The observations began at zenith distance = 43 deg. The sun altitude is -36.5 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 250302A errorbox 22677 sec after notice time and 22713 sec after trigger time at 2025-03-02 20:05:06 UT, with upper limit up to 17.7 mag. The observations began at zenith distance = 77 deg. The sun altitude is -50.2 deg. The galactic latitude b = 46 deg., longitude l = 22 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2796892 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 21605 | 2025-03-02 19:46:08 | MASTER-Tunka | (15h 31m 17.49s , +16d 30m 25.9s) | C | 60 | 19.8 | 21665 | 2025-03-02 19:46:08 | MASTER-Tunka | (15h 31m 17.49s , +16d 30m 25.9s) | C | 180 | 20.3 | Coadd 21678 | 2025-03-02 19:47:20 | MASTER-Tunka | (15h 39m 40.44s , +16d 31m 15.0s) | C | 60 | 19.8 | 21738 | 2025-03-02 19:47:20 | MASTER-Tunka | (15h 39m 40.44s , +16d 31m 14.9s) | C | 180 | 20.3 | Coadd 22064 | 2025-03-02 19:53:47 | MASTER-Tunka | (15h 41m 02.12s , +18d 25m 27.9s) | C | 60 | 19.8 | 22124 | 2025-03-02 19:53:47 | MASTER-Tunka | (15h 41m 02.11s , +18d 25m 27.9s) | C | 180 | 20.4 | Coadd 22137 | 2025-03-02 19:55:00 | MASTER-Tunka | (15h 49m 28.20s , +18d 23m 04.7s) | C | 60 | 19.7 | 22197 | 2025-03-02 19:55:00 | MASTER-Tunka | (15h 49m 28.20s , +18d 23m 04.6s) | C | 180 | 20.3 | Coadd 22210 | 2025-03-02 19:56:13 | MASTER-Tunka | (15h 31m 19.81s , +16d 32m 30.0s) | C | 60 | 19.9 | 22283 | 2025-03-02 19:57:25 | MASTER-Tunka | (15h 39m 34.02s , +16d 30m 56.3s) | C | 60 | 19.9 | 22586 | 2025-03-02 20:02:28 | MASTER-Tunka | (15h 23m 46.12s , +16d 31m 47.0s) | C | 60 | 20.0 | 22646 | 2025-03-02 20:02:28 | MASTER-Tunka | (15h 23m 46.12s , +16d 31m 47.0s) | C | 180 | 20.3 | Coadd 22744 | 2025-03-02 20:05:06 | MASTER-Kislovodsk | (15h 31m 05.90s , +18d 24m 03.2s) | C | 60 | 13.6 | 22820 | 2025-03-02 20:06:23 | MASTER-Tunka | (15h 40m 59.24s , +18d 26m 16.1s) | C | 60 | 19.8 | 22823 | 2025-03-02 20:06:26 | MASTER-Kislovodsk | (15h 20m 24.78s , +14d 35m 08.1s) | C | 60 | 14.4 | 22893 | 2025-03-02 20:07:36 | MASTER-Tunka | (15h 49m 30.08s , +18d 24m 37.9s) | C | 60 | 19.8 | 22904 | 2025-03-02 20:07:46 | MASTER-Kislovodsk | (15h 28m 43.31s , +14d 36m 18.2s) | C | 60 | 13.6 | 22967 | 2025-03-02 20:08:49 | MASTER-Tunka | (15h 31m 14.39s , +16d 31m 14.0s) | C | 60 | 19.8 | 23042 | 2025-03-02 20:10:04 | MASTER-Tunka | (15h 39m 39.86s , +16d 31m 01.5s) | C | 60 | 19.7 | 23160 | 2025-03-02 20:12:03 | MASTER-Kislovodsk | (15h 36m 12.34s , +14d 34m 34.1s) | C | 60 | 15.6 | 23240 | 2025-03-02 20:13:23 | MASTER-Kislovodsk | (15h 44m 23.73s , +14d 35m 43.7s) | C | 60 | 14.7 | 23337 | 2025-03-02 20:14:59 | MASTER-Tunka | (15h 23m 42.86s , +16d 33m 11.8s) | C | 60 | 19.9 | 23413 | 2025-03-02 20:16:15 | MASTER-Tunka | (15h 30m 58.44s , +12d 44m 41.7s) | C | 60 | 19.8 | 23473 | 2025-03-02 20:16:15 | MASTER-Tunka | (15h 30m 58.44s , +12d 44m 41.7s) | C | 180 | 20.1 | Coadd 23480 | 2025-03-02 20:17:22 | MASTER-Kislovodsk | (15h 31m 02.91s , +18d 23m 56.7s) | C | 60 | 16.9 | 23486 | 2025-03-02 20:17:29 | MASTER-Tunka | (15h 39m 05.45s , +12d 43m 05.6s) | C | 60 | 19.7 | 23546 | 2025-03-02 20:17:29 | MASTER-Tunka | (15h 39m 05.45s , +12d 43m 05.5s) | C | 180 | 20.1 | Coadd 23560 | 2025-03-02 20:18:42 | MASTER-Kislovodsk | (15h 20m 23.76s , +14d 37m 26.2s) | C | 60 | 17.0 | 23561 | 2025-03-02 20:18:43 | MASTER-Tunka | (15h 41m 05.86s , +18d 25m 13.1s) | C | 60 | 19.8 | 23637 | 2025-03-02 20:19:59 | MASTER-Tunka | (15h 49m 27.79s , +18d 25m 54.4s) | C | 60 | 19.7 | 23639 | 2025-03-02 20:20:02 | MASTER-Kislovodsk | (15h 28m 43.11s , +14d 36m 08.7s) | C | 60 | 16.8 | 23712 | 2025-03-02 20:21:15 | MASTER-Tunka | (15h 31m 16.75s , +16d 31m 55.3s) | C | 60 | 19.9 | 23772 | 2025-03-02 20:21:15 | MASTER-Tunka | (15h 31m 16.75s , +16d 31m 55.1s) | C | 180 | 19.8 | Coadd 23785 | 2025-03-02 20:22:27 | MASTER-Tunka | (15h 39m 40.80s , +16d 32m 51.7s) | C | 60 | 19.8 | 23799 | 2025-03-02 20:22:42 | MASTER-Kislovodsk | (15h 21m 17.81s , +12d 41m 36.6s) | C | 60 | 17.1 | 23959 | 2025-03-02 20:25:22 | MASTER-Kislovodsk | (15h 36m 07.19s , +14d 35m 28.8s) | C | 60 | 17.1 | 24039 | 2025-03-02 20:26:41 | MASTER-Kislovodsk | (15h 44m 26.50s , +14d 36m 37.5s) | C | 60 | 17.0 | 24080 | 2025-03-02 20:27:23 | MASTER-Tunka | (15h 23m 42.84s , +16d 32m 51.8s) | C | 60 | 19.9 | 24154 | 2025-03-02 20:28:37 | MASTER-Tunka | (15h 30m 58.25s , +12d 44m 31.8s) | C | 60 | 19.7 | 24230 | 2025-03-02 20:29:53 | MASTER-Tunka | (15h 39m 07.48s , +12d 45m 31.1s) | C | 60 | 19.7 | 24278 | 2025-03-02 20:30:40 | MASTER-Kislovodsk | (15h 31m 07.61s , +18d 24m 25.8s) | C | 60 | 17.4 | 24305 | 2025-03-02 20:31:07 | MASTER-Tunka | (15h 41m 01.62s , +18d 25m 42.8s) | C | 60 | 19.8 | 24365 | 2025-03-02 20:31:07 | MASTER-Tunka | (15h 41m 01.62s , +18d 25m 42.8s) | C | 180 | 20.2 | Coadd 24749 | 2025-03-02 20:38:31 | MASTER-Tunka | (15h 30m 53.25s , +16d 35m 14.6s) | C | 60 | 19.9 | 24939 | 2025-03-02 20:41:41 | MASTER-Kislovodsk | (15h 21m 11.94s , +12d 41m 22.0s) | C | 60 | 17.7 | 25098 | 2025-03-02 20:44:21 | MASTER-Kislovodsk | (15h 36m 07.54s , +14d 36m 59.1s) | C | 60 | 17.5 | 25178 | 2025-03-02 20:45:41 | MASTER-Kislovodsk | (15h 44m 23.92s , +14d 35m 10.2s) | C | 60 | 17.4 | 25423 | 2025-03-02 20:49:46 | MASTER-Tunka | (15h 23m 44.45s , +16d 35m 47.7s) | C | 60 | 20.0 | 25497 | 2025-03-02 20:50:59 | MASTER-Tunka | (15h 30m 54.18s , +12d 45m 40.7s) | C | 60 | 19.9 | 25569 | 2025-03-02 20:52:11 | MASTER-Tunka | (15h 39m 10.58s , +12d 46m 23.3s) | C | 60 | 19.8 | 25643 | 2025-03-02 20:53:25 | MASTER-Tunka | (15h 40m 57.76s , +18d 27m 42.0s) | C | 60 | 20.0 | 25715 | 2025-03-02 20:54:38 | MASTER-Tunka | (15h 49m 22.96s , +18d 28m 04.2s) | C | 60 | 19.8 | 25788 | 2025-03-02 20:55:51 | MASTER-Tunka | (15h 31m 18.68s , +16d 34m 38.3s) | C | 60 | 19.8 | 25861 | 2025-03-02 20:57:04 | MASTER-Tunka | (15h 39m 32.28s , +16d 33m 01.3s) | C | 60 | 19.8 | 26164 | 2025-03-02 21:02:06 | MASTER-Tunka | (15h 23m 47.97s , +16d 36m 20.0s) | C | 60 | 19.7 | 26237 | 2025-03-02 21:03:20 | MASTER-Tunka | (15h 30m 50.25s , +12d 47m 05.1s) | C | 60 | 19.6 | 26311 | 2025-03-02 21:04:33 | MASTER-Tunka | (15h 39m 02.80s , +12d 47m 29.2s) | C | 60 | 19.5 | 26385 | 2025-03-02 21:05:48 | MASTER-Tunka | (15h 41m 03.56s , +18d 28m 19.9s) | C | 60 | 18.6 | 26460 | 2025-03-02 21:07:03 | MASTER-Tunka | (15h 46m 29.50s , +12d 46m 38.1s) | C | 60 | 19.8 | 26537 | 2025-03-02 21:08:19 | MASTER-Tunka | (15h 54m 41.53s , +12d 44m 47.4s) | C | 60 | 19.8 | 26838 | 2025-03-02 21:13:21 | MASTER-Tunka | (15h 23m 46.02s , +16d 36m 09.2s) | C | 60 | 20.1 | 26914 | 2025-03-02 21:14:37 | MASTER-Tunka | (15h 30m 49.86s , +12d 46m 41.0s) | C | 60 | 20.0 | 27078 | 2025-03-02 21:17:20 | MASTER-Tunka | (15h 39m 08.10s , +12d 47m 46.3s) | C | 60 | 20.0 | 27150 | 2025-03-02 21:18:33 | MASTER-Tunka | (15h 46m 26.15s , +12d 46m 38.9s) | C | 60 | 20.0 | 27222 | 2025-03-02 21:19:44 | MASTER-Tunka | (15h 54m 37.57s , +12d 47m 02.5s) | C | 60 | 20.0 | 27300 | 2025-03-02 21:21:02 | MASTER-Tunka | (15h 38m 21.62s , +14d 40m 25.5s) | C | 60 | 20.1 | 27373 | 2025-03-02 21:22:15 | MASTER-Tunka | (15h 46m 43.50s , +14d 39m 54.8s) | C | 60 | 20.1 | 27442 | 2025-03-02 21:23:24 | MASTER-Tunka | (15h 55m 28.03s , +10d 51m 13.2s) | C | 60 | 20.0 | 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/39552. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37565] EP250302a: FTW optical and NIR detection
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39551 SUBJECT: EP250302a: FTW optical and NIR detection DATE: 25/03/02 20:56:16 GMT FROM: Brendan O'Connor at Carnegie Mellon University <boconno2(a)andrew.cmu.edu> Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU) and Antonella Palmese (Carnegie Mellon U.) report: We observed location of EP250302a (Trigger ID: 01709132186; Zhu et al., GCN 39550) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously. Observations started at 19:28:31 UT on 2025-03-02, corresponding to ~3.87 hr after the EP-WXT trigger. At the location of the optical counterpart reported by Zhu et al. (GCN 39550) we detect a clear source with brightness r~20.3 AB mag. This confirms the fading of the source and its relation to EP250302a. We note the presence of a GLADE+ galaxy (~570 Mpc; photometric) at an offset of ~20" (Dalya et al. 2022). There is no underlying source at the position of this optical transient in Legacy Survey imaging. Further observations are encouraged. We thank Michael Schmidt from the staff of the Wendelstein Observatory for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39551. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37564] EP250302a: Nanshan/HMT optical counterpart detection
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39550 SUBJECT: EP250302a: Nanshan/HMT optical counterpart detection DATE: 25/03/02 18:16:00 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> Z.P. Zhu, S.Q. Jiang, X. Liu, J. An, S.Y. Fu, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report on behalf of a large collaboration: We observed the field of EP250302a detected by Einstein Probe (Trigger ID: 01709132186), using the HMT-0.5m telescope located at Nanshan, Xinjiang, China. Observations started at 15:47:09 on 2025-03-02, i.e., 11.08 min after the EP trigger, and a series of unfiltered frames with different exposures were obtained. An uncatalogued and varying optical source is detected within the EP/WXT error circle at coordinates R.A.(J2000) = 11:18:03.58 Dec.(J2000) = +33:35:09.06 with an uncertainty of ~0.5 arcsec. The source has R ~ 18.3 mag at a median time of 11.58 min after the EP trigger, calibrated with Legacy Survey DR10 and not corrected for Galactic extinction. We conclude that the source is the optical counterpart of EP250302a. Observations are still ongoing, and spectroscopy is encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/39550. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37563] IceCube-250302A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39549 SUBJECT: IceCube-250302A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/03/02 16:04:00 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 2025-03-02 at 03:20:52.90 UT IceCube detected a track-like event with a high probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_GOLD alert stream. The average astrophysical neutrino purity for Gold alerts is 50%. This alert has an estimated false alarm rate of 0.1579 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/140601_60511904.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 2025-03-02 Time: 03:20:52.90 UT RA: 348.05 (+0.38 -0.43 deg 90% PSF containment) J2000 Dec: 3.77 (+0.42 -0.41 deg 90% PSF containment) J2000 No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of the event. However, given the particularly high signalness (~97%) and energy (~1.5 PeV) of this event, we strongly encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/39549. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37562] GRB 250302A: Fermi GBM Final Real-time Localization
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39548 SUBJECT: GRB 250302A: Fermi GBM Final Real-time Localization DATE: 25/03/02 13:57:01 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 13:46:32 UT on 2 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250302A (trigger 762615997.991246 / 250302574). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 236.4, Dec = 12.2 (J2000 degrees, equivalent to J2000 15h 45m, 12d 11'), with a statistical uncertainty of 5.4 degrees. The angle from the Fermi LAT boresight is 67.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250302574/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250302574/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250302574/… View this GCN Circular online at https://gcn.nasa.gov/circulars/39548. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37561] GRB 250228A: Fermi GBM Final Localization
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39547 SUBJECT: GRB 250228A: Fermi GBM Final Localization DATE: 25/03/02 09:43:31 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> The Fermi GBM team reports the detection of a likely SHORT GRB "At 07:23:46.16 UT on 28 February 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250228A (trigger 762420231/250228308). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 94.90, Dec = -46.81 (J2000 degrees, equivalent to J2000 6h 19m, -46d 48'), with a statistical uncertainty of 11.91 degrees. The angle from the Fermi LAT boresight is 27 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250228308/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250228308/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250228308/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/39547. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37560] The EP-WXT trigger 01709132140 is likely a flaring star
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39546 SUBJECT: The EP-WXT trigger 01709132140 is likely a flaring star DATE: 25/03/02 04:53:52 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> X. Mao, S. X. Wen (NAOC, CAS), Y. Q. Zhao (USTC, PRIC), C. Y. Dai (NJU), W. Yuan (NAOC, CAS) report on behalf of the Einstein Probe team: The EP-WXT trigger (ID: 001709132140) on 2025-03-02 01:37:56(UTC) is likely a stellar flare associated with a High Proper Motion Star LP 378-313. 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/39546. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37559] LIGO/Virgo/KAGRA S250206dm: early X-ray upper limits from Einstein Probe WXT and preliminary results of FXT observations
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39545 SUBJECT: LIGO/Virgo/KAGRA S250206dm: early X-ray upper limits from Einstein Probe WXT and preliminary results of FXT observations DATE: 25/03/02 03:55:41 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> D. Y. Li, J. W. Hu, Q. Y. Wu, M. J. Liu, R. D. Liang, H. Sun (NAOC, CAS), A. Li (BNU), C. Q. Shui (IHEP, CAS), M. H. Zhang, X. P. Xu, W. X. Wang, H. Q. Cheng, H. N. Yang, D. H. Zhao, X. Pan, Y. F. Xu, M. Zhang (NAOC, CAS), X. Y. Zhou (PRIC), Y. C. Fu (BNU), S. F. Zhu (CSTU), Y. J. Zhang (THU), H. L. Peng (NJNU), G. Y. Zhao (SYU), C. Zhou (HUST), T. C. Zheng (PMO, CAS), Y. Chen, J. Guan, C. K. Li, S. M. Jia, H. S. Zhao, J. Zhang, M. Y. Ge, W. W. Cui, H. Feng, W. Li, C. Z. Liu, F. J. Lu, L. M. Song, J. Wang, J. J. Xu, D. W. Han, S. N. Zhang, X. F. Zhao (IHEP, CAS), Y. Liu, W. D. Zhang, Z. X. Ling, C. C. Jin, H. W. Pan, C. Zhang, W. Yuan (NAOC), B. Zhang (UNLV), L. Piro (INAF), V. Burwitz, P. Friedrich, N. Meidinger, K. Nandra, A. Rau (MPE), E. Kuulkers, A. Santovincenzo (ESA), P. O'Brien (Univ. of Leicester), B. Cordier (CEA) report on behalf of the Einstein Probe team: We report on preliminary results of the observations targeting the sky regions of the LIGO/Virgo/KAGRA NS-BH gravitational-wave event S250206dm (The LIGO-Virgo-KAGRA Collaboration, GCN 39175) to search for any potentially associated X-ray source with the Einstein Probe (EP). Two rounds of observations were carried out with the Wide-field X-ray Telescope (WXT) and Follow-up X-ray Telescope (FXT) on board EP between Feb. 7th and 18th 2025. No promising X-ray transient candidates have been found. The information on the sky coverage and observations can be found at the web page https://ep.bao.ac.cn/ep/cms/article/view?id=185. First, two early WXT observations were performed, starting at 2025-02-07T02:55:12.000Z and 2025-02-07T03:40:22.000Z, about 4.5 hours and 6 hours after the GW event, respectively, each with an exposure time of 2400s. These observations covered 302 square degrees within (55% of) the 90% credible region of the updated LVK sky localization (The LIGO-Virgo-KAGRA Collaboration, GCN 39231). No new X-ray sources were detected. The 0.5-4 keV flux limits over the covered regions are set to be approximately 1.0 x 10^-11 erg/s/cm2 at the 90% confidence level in general. Then, 100 pointed FXT observations were carried out during Feb. 7th and 8th, each with a 300s-exposure, targeting galaxies located within the 90% credible region and the distance uncertainty range of S250206dm. The targets are among the top 500 galaxies that were selected from the GLADE+ catalog and prioritized based on their location, mass, and visibility to FXT. These observations covered 32 (24) square degree in the 90% (50%) credible region, setting 0.5-10 keV flux limits of generally 3e-13 erg/s/cm2 at the 90% confidence level. From Feb. 11th to 18th, 2025, the second round of observations consisted of tiling observations with FXT, covering 34 square degrees in (89% of) the 50% credible region of S250206dm. There were 59 observations performed, each with an exposure of 2000s, setting the average flux limits of approximately 5e-14 erg/s/cm2 at the 90% confidence level. We searched for transient or variable candidates in the FXT data which are apparently associated with the galaxies in the NED-LVS sample in the credible region and distance range of S250206dm (Cook et al. GCN 39235) within a radius of 30 arcsec. Two uncatalogued sources were found to exhibit significant flux decay from the FXT observations, whose details are listed in the table below. The fluxes are in the 0.5-10 keV band and estimated from spectral fitting with an absorbed powerlaw model. EPF J022731.1+551813 was not detected in the second observation, and an upper limit at the 90% confidence level is provided. We note that, however, a stellar flare origin of these two sources cannot be ruled out. ------------------------------------------------------------------------------------------------------ | Source Name | Obs_Time (UTC) | RA | DEC | Flux(erg/s/cm2) | Flux_err | ------------------------------------------------------------------------------------------------------ |EPF J022731.1+551813| 2025-02-13 08:35:07 | 36.8797 | 55.3037 | 5.28e-13 | 2.27e-14 | | | 2025-02-15 13:24:47 | | | <7.0e-14 | | ------------------------------------------------------------------------------------------------------ |EPF J022842.7+542051| 2025-02-08 07:59:43 | 37.1780 | 54.3475 | 6.61e-13 | 1.94e-14 | | | 2025-02-11 18:44:27 | 37.1839 | 54.3466 | 1.09e-13 | 4.27e-14 | | | 2025-02-15 10:12:36 | 37.1795 | 54.3469 | 1.07e-13 | 2.81e-14 | ------------------------------------------------------------------------------------------------------ Follow-up observations are encouraged to identify the nature of these two variable sources. 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/39545. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37558] GRB 250225B: VLT near-infrared afterglow confirmation
by GCN Circulars 01 Mar '25

01 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39544 SUBJECT: GRB 250225B: VLT near-infrared afterglow confirmation DATE: 25/03/01 18:56:01 GMT FROM: Yu-Han Yang at University of Rome Tor Vergata <yyang(a)roma2.infn.it> Yu-Han Yang (U Rome), Muskan Yadav (U Rome), Eleonora Troja (U Rome) on behalf of the ERC BHianca team: We re-observed the field of GRB 250225B (Williams et al., GCN 39473) with the HAWKI imager on the ESO VLT UT4 (Yepun). Observations began at T+3.6 d days and were carried out at an average airmass of about 2.4 in the J filter. In comparison to our first epoch of observations, the candidate counterpart (Schneider et al. GCN 39494, Yang et al. GCN 39495, Rayson et al. GCN 39535) appears to have substantially faded by about 1 mag. Image subtraction between the two epochs, reveals no other credible counterpart within the BAT error circle. We therefore confirm that this is the GRB afterglow. 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/39544. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37557] EP250228a: Optical observations with Kinder and Swift/UVOT
by GCN Circulars 01 Mar '25

01 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39543 SUBJECT: EP250228a: Optical observations with Kinder and Swift/UVOT DATE: 25/03/01 13:45:29 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> A. Aryan, Y. J. Yang (both 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), 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 EP250228a (Liu et al., GCN 39525; Liu et al., GCN39531) 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 10:54 UT on the 28th of February 2025 (MJD = 60734.454), ~6.91 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 frame, we did not detect any uncataloged optical counterpart candidate within the EP-FXT localization error circle of radius 20 arcseconds. Moreover, we employed the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction utilizing the "sfft" (Hu, 2022, ApJ, 936, 157) and "hotpants" (Becker A., 2015, ascl.soft. ascl:1504.004) algorithms using templates from SkyMapper DR4 (Onken et., 2024, PASA, 41, e061). We found no evidence of any prominent candidate optical counterpart in the difference images as well. We further employed AutoPhOT to perform the PSF photometry. The details of the observations and measured 3-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 | 60734.454 | 6.91 | 300 * 12 | >20.2 | 1".20 | 2.44 SLT | r | 60734.503 | 8.08 | 300 * 24 | >19.9 | 1".43 | 2.53 The X-ray transient was also detected in Swift-XRT (Page et al., GCN39527). The Swift-XRT position coincided with a star (Gaia DR3 5563280076339409920; as updated by Liu et al., GCN39531), but we probably missed the flaring stage as we did not see any credible excess flux in the difference image. For this star, we measured an r-band magnitude of 15.33 +/- 0.03 mag and an i-band magnitude of 13.65 +/- 0.03 mag in our stacked frames. Our measured magnitudes for this source align perfectly with the archival values in the SkyMapper catalog. In addition, a preliminary U-band magnitude of 17.61 +/- 0.05 (stat) +/- 0.02 (sys) was measured from the quick-look Swift-UVOT observation. The presented measurements were calibrated using the field stars from the SkyMapper catalog and were not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_i = 0.20 mag, and A_r = 0.27 mag in the direction of the transient (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/39543. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37556] Konus-Wind detection of GRB 250226A
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39542 SUBJECT: Konus-Wind detection of GRB 250226A DATE: 25/02/28 22:10:03 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 250226A (Fermi-GBM detection: The Fermi GBM team, GCN 39479; Pathak and Meegan, GCN 39530; EP-WXT detection: Jiang et al., GCN 39482; INTEGRAL SPI-ACS and PICsIT detection: Thakur et al., GCN 39518) triggered Konus-Wind at T0=23700.486 s UT (06:35:00.486). The burst light curve shows a single emission episode which starts at ~T0-5 s and has a total duration of ~32 s. The emission is seen up to ~1 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250226_T23700/ As observed by Konus-Wind, the burst had a fluence of 1.17(-0.21,+0.28)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+0.438 s, of 3.45(-1.09,+1.18)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+24.832 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.16(-0.47,+0.68), the high energy photon index beta = -2.25(-0.38,+0.24), the peak energy Ep = 143(-28,+35) keV (chi2 = 64/97 dof). The spectrum near the maximum count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.60(-0.36,+0.54), the high energy photon index beta = -2.00(-8,+0.17), the peak energy Ep = 190(-53,+331) keV (chi2 = 86/97 dof). Assuming the redshift z=3.315 (Zhu et al. GCN 39487) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy release E_iso is 2.80(-0.51,+0.67)x10^53 erg, the peak luminosity L_iso is 3.56(-1.12,+1.22)x10^53 erg/s, the rest-frame peak energy of the time-averaged spectrum Ep,i,z is 616(-119,+151) keV and the spectrum near the maximum count rate Ep,p,z is 822(-229,+1427) keV. With the obtained estimates, GRB 250226A is inside 68% prediction bands for both the 'Amati' and the 'Yonetoku' relations derived for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB250226_T23700/GRB250226A_rest_frame.pdf All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/39542. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37555] GRB 250225B: EIRSAT-1 GMOD Detection
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39541 SUBJECT: GRB 250225B: EIRSAT-1 GMOD Detection DATE: 25/02/28 21:22:14 GMT FROM: Gabriel Finneran at School of Physics and Centre for Space Research, University College Dublin <gabriel.finneran(a)ucdconnect.ie> G. Finneran, C. McKenna, D. Murphy, C. de Barra, A. Ulyanov, P. McDermott, M. Doyle, R. Dunwoody, J. Mangan, G. Corcoran, L. Cotter, A. Empey, J. Fisher, F. Gibson Kiely, J. Thompson, D. McKeown, A. Martin-Carrillo, L. Hanlon, S. McBreen, on behalf of the EIRSAT-1 team: EIRSAT-1 reports the detection of the long gamma-ray burst GRB250225B by the Gamma-ray Module (GMOD) instrument, which was also detected by Swift BAT (GCN 39473), SVOM GRM (GCN 39493), Konus-Wind (GCN 39498), Fermi GBM (GCN 39502) and INTEGRAL SPI-ACS (GCN 39517). The GMOD detection was made starting at 2025-02-25 19:39:13.1 UTC. The GMOD light-curve for GRB250225B with 1.2s binning shows a peak consistent with the first peak seen by SVOM GRM, with a tentative detection of the second peak at around 60 seconds. The spacecraft location at the time of detection was 31.703 N, 135.873 W, at an altitude of 425.8km. The GMOD light curve for this event can be found here: https://grb.eirsat1.ie/250225B/250225B_LC_onboard_preliminary.png EIRSAT-1 is Ireland’s first satellite (Doyle et al. Proceedings of the 4th SSEA, 2022). It is a 2U CubeSat and carries onboard a number of experiments including the Gamma-Ray Module (GMOD), a novel, compact, gamma-ray detector (Murphy et al, Experimental Astronomy, 53, 961–990, 2022). GMOD consists of a 25 mm × 25 mm × 40 mm Cerium Bromide scintillator coupled to SiPMs and is designed to detect gamma-ray bursts in the ~ 60 keV - 1.5 MeV range. EIRSAT-1 was developed in University College Dublin with support from ESA’s Fly Your Satellite! programme and was launched on 1st December 2023. View this GCN Circular online at https://gcn.nasa.gov/circulars/39541. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37554] GRB 250226A: KAO Optical Upper Limit
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39540 SUBJECT: GRB 250226A: KAO Optical Upper Limit DATE: 25/02/28 20:48:07 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. M. Abdelaziz (NRIAG), M. Abdelkareem (NRIAG), E. Amin (NRIAG), A. Pozanenko (IKI) report on behalf of IKI GRB-FuN: We performed optical observations of the field of GRB 250226A (The Fermi GBM team, GCN 39479; V.Lipunov et. al, GCN 39481; Jiang et. al, GCN 39482; An et. al, GCN 39486; Zhu et. al, GCN 39487; Magnani et. al, GCN 39488; Li et. al, GCN 39489; Li et. al, GCN 39492; Aryan et. al, GCN 39509; Zou et. al, GCN 39511; Jiang et. al, GCN 39513; Li et. al, GCN 39514; Junjie-Jin et. al, GCN 39515; Thakur et. al, GCN 39518; Poidevin et. al, GCN 39524; Pathak et. al, GCN 39530; Pankov et. al, GCN 39539) in the R filter with the 1.88-meter telescope of the Kottamia Astronomical Observatory (KAO). The observations started on (UT) 2025-02-28 00:30:36, i.e. ~1.78 days since trigger and consists of 39x150 sec exposures. We do not detect the optical counterpart in the stacked image. The preliminary upper limit is as follows: Date UT start t-T0 Exp. Filter UL(3sigma) (mid, days) (s) 2025-02-28 00:30:36 1.78084 39*150 R 22.3 The photometry is based on nearby stars from the USNO-B1.0 catalog and has not been corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/39540. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37553] GRB 250226A: AbAO AS-32 Optical Upper Limit
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39539 SUBJECT: GRB 250226A: AbAO AS-32 Optical Upper Limit DATE: 25/02/28 20:42:33 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), R. Ya. Inasaridze (AbAO), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We performed optical observations of the field of GRB 250226A (The Fermi GBM team, GCN 39479; V.Lipunov et. al, GCN 39481; Jiang et. al, GCN 39482; An et. al, GCN 39486; Zhu et. al, GCN 39487; Magnani et. al, GCN 39488; Li et. al, GCN 39489; Li et. al, GCN 39492; Aryan et. al, GCN 39509; Zou et. al, GCN 39511; Jiang et. al, GCN 39513; Li et. al, GCN 39514; Junjie-Jin et. al, GCN 39515; Thakur et. al, GCN 39518; Poidevin et. al, GCN 39524; Pathak et. al, GCN 39530) in the R filter with the 0.7-meter AS-32 telescope of the Abastumani Astrophysical Observatory. The observations started on (UT) 2025-02-28 00:25:49, i.e. ~1.76 days since trigger and consists of 70*60 sec exposures. We do not detect the optical counterpart in the stacked image. The preliminary upper limit is as follows: Date UT start t-T0 Exp. Filter UL(3sigma) (mid, days) (s) 2025-02-28 00:25:49 1.76796 70*60 R 21.4 The photometry is based on nearby stars from the USNO-B1.0 catalog and has not been corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/39539. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37552] EP250227a: Global MASTER-Net observations report
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39538 SUBJECT: EP250227a: Global MASTER-Net observations report DATE: 25/02/28 17:54:50 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the EP250227a ( EP Team et al., GCN 39532) errorbox 5473 sec after notice time and 1 days 45921 sec after trigger time at 2025-02-28 17:25:01 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 74 deg. The sun altitude is -46.8 deg. The galactic latitude b = 47 deg., longitude l = 320 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2795063 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 132351 | 2025-02-28 17:25:01 | MASTER-Tunka | (13h 36m 31.38s , -13d 41m 08.1s) | C | 60 | 17.1 | 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/39538. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37551] EP250223A: Upper limits from Fermi-GBM Observations
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39537 SUBJECT: EP250223A: Upper limits from Fermi-GBM Observations DATE: 25/02/28 17:47:57 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio (Radboud Univ.), E. Burns (LSU), and P.G. Jonker (Radboud Univ.) report on behalf of the Fermi-GBM Team: Fermi-GBM had full spatial coverage of the transient EP250223A detected by EP-WXT (Lian et al., GCN 39429). There was no Fermi-GBM onboard trigger around the EP starting time T0=2025-02-23T15:02:05.66 UTC (Wang et al., GCN 39448). The GBM targeted search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [T0-50;T0+500] s, seeking signals between 64 ms and 32.768 s in duration. No signal consistent with the EP transient both temporally and spatially is identified, as confirmed by visual inspection of the data. Assuming a “soft” spectral template (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7), and a duration of 8.192 s, we derive a sky-averaged flux upper limit of 3.1e-08 erg/cm2/s in the energy band 10-1000 keV. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/39537. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37550] EP250227a: TRT optical upper limit
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39536 SUBJECT: EP250227a: TRT optical upper limit DATE: 25/02/28 17:28:36 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), J. An, X. Liu, S.Y. Fu, Z.P. Zhu, D. Xu, Z. Fan, W.X. Li, Y.N. Wang, N.C. Sun (NAOC) report on behalf of a large collaboration: We observed the field of EP250227a detected by EP (Wen et al., GCN 39532), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. Observations started at 04:10:11.093 UT on 2025-02-28, i.e., 0.98 days after the EP trigger, and a series of 300 s frames were obtained in the R band. No uncatalogued optical source is detected in the stacked R-band image within the EP/FXT error circle (Wen et al., GCN 39532), down to the 5-sigma limiting magnitude of R ~ 22.1, calibrated with LS-DR10 stars and not corrected for Galactic extinction, being consistent with the non-detections by NOT (Malesani et al., GCN 39533) and SLT (Aryan et al., GCN 39534). View this GCN Circular online at https://gcn.nasa.gov/circulars/39536. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37549] GRB 250225B: VLT/HAWKI near-infrared observations
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39535 SUBJECT: GRB 250225B: VLT/HAWKI near-infrared observations DATE: 25/02/28 17:08:01 GMT FROM: Nusrin Habeeb at University of Leicester <nh312(a)leicester.ac.uk> B.C. Rayson (U. Leicester), N. Habeeb (U. Leicester), N. R. Tanvir (U. Leicester), R. A. J. Eyles-Ferris (U. Leicester), R. Brivio (INAF-OAB), M. Ferro (INAF-OAB), A J. Levan (Radboud and Warwick), D. B. Malesani (DAWN/NBI and Radboud) report on behalf of the Stargate collaboration: We observed the field of the GRB 250225B (Williams et al., GCN 39473) with the ESO Very Large Telescope UT4, equipped with the HAWK-I near-infrared camera. We obtained a 20 min exposure Ks band, starting at 09:12:18.45 UT on 2025-02-27, i.e. 1.56 days after the Swift trigger. The observations were obtained under good seeing conditions, with a measured seeing of 0.96″ in the Ks band. We detect the optical afterglow candidate reported by Schneider et al. (GCN 39494) and Yang et al. (GCN 39495) at coordinates: RA(J2000) = 20:24:33.81 DEC(J2000) = -41:28:25.4 Its Vega magnitude is Ks = 19.382 +- 0.057, calibrated using nearby stars in the 2MASS catalogue. From VISTA survey images, we measured a 2-sigma upper limit to be Ks(Vega) > 19.56. No other obviously variable sources are seen, to the depth of the VISTA comparison images. 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/39535. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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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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