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[vsnet-grb-info 41003] Swift GRB 251201B: Global MASTER-Net observations report
by GCN Circulars 01 Dec '25

01 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42928 SUBJECT: Swift GRB 251201B: Global MASTER-Net observations report DATE: 25/12/01 22:31:04 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, 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.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope [1] located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 251201B ( M. J. Moss et al., GCN 42924) errorbox 20045 sec after notice time and 20067 sec after trigger time at 2025-12-01 22:00:57 UT, with upper limit up to 17.9 mag. The observations began at zenith distance = 45 deg. The sun altitude is -35.7 deg. The galactic latitude b = -73 deg., longitude l = 317 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3057197 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 20158 | MASTER-SAAO | C | 180 | 17.9 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/42928. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41002] GRB 251201B: Enhanced Swift-XRT position
by GCN Circulars 01 Dec '25

01 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42927 SUBJECT: GRB 251201B: Enhanced Swift-XRT position DATE: 25/12/01 21:24:42 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 1078 s of XRT Photon Counting mode data and 3 UVOT images for GRB 251201B, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 6.39463, -44.23233 which is equivalent to: RA (J2000): 00h 25m 34.71s Dec (J2000): -44d 13' 56.4" with an uncertainty of 3.8 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at https://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42927. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41001] EP251118a: Mondy, CrAO, Assy and SAO RAS/Zeiss-1000 optical observations
by GCN Circulars 01 Dec '25

01 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42926 SUBJECT: EP251118a: Mondy, CrAO, Assy and SAO RAS/Zeiss-1000 optical observations DATE: 25/12/01 18:59:42 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. A. Volnova (IKI), A. S. Pozanenko (IKI), A. S. Moskvitin (SAO RAS), E. Klunko (ISTP), V. Rumyantsev (CrAO), M. Krugov (FAI), O. I. Spiridonnova (SAO RAS), N. S. Pankov (IKI) report on behalf of IKI-GRB-FuN: We observed the field of the transient EP251118a (Jiang et al., GCN 42749) detected by the Einstein Probe Wide-field X-ray Telescope (EP WXT), with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) on Nov. 20 and 24 in R filter, with the ZTSH telescope of CrAO on Nov. 20 and 22 in B and R bands, with the AZT-20 1.5m telescope of Assy-Turgen observatory on Nov. 21 in Sloan r filter and Zeiss-1000 of SAO RAS on Nov. 30 in Rc-filter. The optical counterpart (Malesani et al., GCN 42751; Lipunov et al., GCN 42755; An et al., GCN 42756; Belkin et al., GCN 42758; Yadav et al., GCN 42760; Busmann et al., GCN 42763; Francile et al., GCN 42767; Urquijo-Rodríguez et al., GCN 42773; Li et al., GCN 42776; Lee et al., GCN 42780; Moskvitin and Spiridonova, GCN 42785; Gupta et al., GCN 42787; Liu et al., GCN 42793; Aryan et al, GCN 42798; Gupta et al., GCN 42810) is detected in the stacked frame of each epoch. However the flux of the optical transient might be affected by the nearby red star SDSS J081239.57+105619.8 (r_SDSS = 21.911+/-0.178, g-r ~ 3 mag) located in 2.5 arcsec to the East. Some of our preliminary PSF photometry and observational details are the following: Date UT start t-T0 Exp. Filter OT Err. UL Site/Instrum (mid,days) (n*s) (3sigma) 2025-11-20 18:58:01 2.12539 45*120 R 21.45 0.11 22.4 Mondy/AZT-33IK 2025-11-20 21:40:22 2.23886 42*120 R 21.29 0.10 23.2 CrAO/ZTSh 2025-11-20 23:13:01 2.31556 51*120 B 21.02 0.11 23.1 CrAO/ZTSh 2025-11-21 19:57:19 3.16164 57*60 r 22.39 0.08 23.8 Assy/AZT-20 2025-11-22 22:55:20 4.29925 48*120 R 21.62 0.17 22.5 CrAO/ZTSh 2025-11-24 19:51:39 6.15840 36*120 R 23.1 0.4 22.5 Mondy/AZT-33IK 2025-11-30 01:49:42 11.40863 12*300 Rc 22.90 0.15 24.0 SAO/Zeiss-1000 The photometry is calibrated using several nearby stars, USNO-B1.0 B2, R2 magnitudes for AZT-33IK, ZTSh and Zeiss-1000 data, and SDSS r magnitudes for AZT-20 data, all magnitudes are not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42926. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41000] GRB 251130B: AstroSat CZTI detection
by GCN Circulars 01 Dec '25

01 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42925 SUBJECT: GRB 251130B: AstroSat CZTI detection DATE: 25/12/01 18:20:31 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Goyal (IITB), A. Arya (IITB), M. Tembhurnikar (IUCAA), S. Salunke (IUCAA), Harsha K. H. (IUCAA), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long duration GRB 251130B which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 42905). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-11-30T15:34:35 UTC. The measured peak count rate associated with the burst is 122 (+26, -28) counts/s above the background in the combined data of two quadrants (out of four), with a total of 467 (+165, -180) counts. The local mean background count rate was 139 (+3, -3) counts/s. Using cumulative rates, we measure a T90 of 11 (+5, -4) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-11-30T15:34:32 UTC. The measured peak count rate associated with the burst is 244 (+68, -42) counts/s above the background in the combined data of all quadrants, with a total of 1517 (+308, -325) counts. The local mean background count rate was 1246 (+7, -8) counts/s. We measure a T90 of 12 (+2, -3) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/42925. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40999] GRB 251201B: Swift detection of a burst with an optical counterpart
by GCN Circulars 01 Dec '25

01 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42924 SUBJECT: GRB 251201B: Swift detection of a burst with an optical counterpart DATE: 25/12/01 16:38:08 GMT FROM: Tyler Parsotan at NASA GSFC <tyler.parsotan(a)nasa.gov> M. J. Moss (GSFC), S. Dichiara (PSU), R. Gupta (NASA GSFC), J. A. Kennea (PSU), K. L. Page (U Leicester) and T. M. Parsotan (GSFC) report on behalf of the Neil Gehrels Swift Observatory Team: At 16:26:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251201B (trigger=1418729). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 6.409, -44.237 which is RA(J2000) = 00h 25m 38s Dec(J2000) = -44d 14' 12" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 40 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 16:28:03.7 UT, 93.4 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 6.3925, -44.2312 which is equivalent to: RA(J2000) = 00h 25m 34.20s Dec(J2000) = -44d 13' 52.3" with an uncertainty of 7.0 arcseconds (radius, 90% containment). This location is 47 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 0.1 s image was 8.63e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 101 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 00:25:34.59 = 6.39413 DEC(J2000) = -44:14:01.1 = -44.23364 with a 90%-confidence error radius of about 0.75 arc sec. This position is 9.7 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.28 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.008. Burst Advocate for this burst is M. J. Moss (mikejmoss3 AT gmail.com) Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/42924. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40998] GRB 251201B: Fermi GBM Final Real-time Localization
by GCN Circulars 01 Dec '25

01 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42923 SUBJECT: GRB 251201B: Fermi GBM Final Real-time Localization DATE: 25/12/01 16:37:01 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 16:26:24 UT on 1 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251201B (trigger 786299189.217446 / 251201685). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 13.8, Dec = -40.0 (J2000 degrees, equivalent to J2000 00h 55m, -40d 00'), with a statistical uncertainty of 1.1 degrees. The angle from the Fermi LAT boresight is 118.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251201685/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251201685/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251201685/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42923. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40997] EP251130a: Mondy optical observations
by GCN Circulars 01 Dec '25

01 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42922 SUBJECT: EP251130a: Mondy optical observations DATE: 25/12/01 15:00:28 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. A. Volnova (IKI), A. S. Pozanenko (IKI), E. Klunko (ISTP), N. S. Pankov (HSE, IKI) report on behalf of IKI-GRB-FuN: We observed the field of the X-ray transient EP251130a (Wu et al., GCN 42903; Zhang et al., GCN 42915), also detected by Swift/XRT (Evans et al., GCN 42908) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) starting on 2025-11-30 (UT) 15:06:18 in R filter. The optical counterpart (Dornic et al., GCN 42904; He et al. GCN 42914; Gupta et al. GCN 42916; Zheng et al. GCN 42917; van Dalen et al., GCN 42918; Moskvitin and Spiridonova, GCN 42919; Aryan et al., GCN 42921) is detected in the stacked frame. Preliminary photometry is the following: Date UT start t-T0 Exp. Filter OT Err. UL Site/Instrum (mid,days) (n*s) (3sigma) 2025-11-30 15:06:18 0.18716 60*120 R 21.76 0.20 22.1 Mondy/AZT-33IK The photometry is calibrated using USNO-B1.0 stars from Moskvitin and Spiridonova, GCN 42919, and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42922. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40996] EP251130a: Optical detections with Kinder observations
by GCN Circulars 01 Dec '25

01 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42921 SUBJECT: EP251130a: Optical detections with Kinder observations DATE: 25/12/01 14:51:58 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> A. Aryan, T.-W. Chen, H.-Y. Hsiao, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), J. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), Y.-H. Lee, A. Sankar.K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, C.-H. Lai, W.-J. Hou, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, 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 EP251130a (Wu et al., GCN 42903; Zhang et al., GCN 42915) using the 1m LOT and 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first epoch of r-band LOT observations began at 16:49 UTC on November 30, 2025 (MJD 61009.701), 5.70 hours after the EP-WXT 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 clearly detected the optical counterpart (Dornic et al., GCN 42904; He et al., GCN 42914; Gupta et al., GCN 42916; Zheng et al., GCN 42917; van Dalen et al., GCN 42918; Moskvitin et al., GCN 42919). The optical counterpart lies within the Swift-XRT (Evans et al., GCN 42908) and the refined EP-FXT (Zhang et al., GCN 42915) localizations. Moreover, we utilized AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform PSF photometry on stacked images. The details of the observations and the measured magnitudes (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass LOT | r | 61009.701 | 5.70 | 300 * 6 | 21.97 +/- 0.08 | 1".16 | 1.03 SLT | i | 61009.703 | 5.74 | 300 * 7 | 20.87 +/- 0.09 | 1".78 | 1.03 We plan to continue following the FXT on a few subsequent days. The presented magnitudes are calibrated using the field stars from the ATLAS-RefCat2 catalog from MAST (Tonry J. L. et al., 2018, ApJ, 867, 105) and are not corrected for the expected Galactic foreground extinction of A_r = 0.26 mag and A_i = 0.19 in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission can be found in Aryan et al., 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/42921. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40995] SVOM GRB251201.19: Global MASTER-Net observations report
by GCN Circulars 01 Dec '25

01 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42920 SUBJECT: SVOM GRB251201.19: Global MASTER-Net observations report DATE: 25/12/01 14:42:24 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, 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.Sosnovskij (CrAO), 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-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the SVOM GRB251201.19 (trigger No 1764563824,22h 55m 57.19s , +47d 49m 47.3s, R=1) errorbox 35398 sec after notice time and 35428 sec after trigger time at 2025-12-01 14:27:33 UT, with upper limit up to 15.8 mag. Observations started at twilight. The observations began at zenith distance = 11 deg. The sun altitude is -9.2 deg. The galactic latitude b = -11 deg., longitude l = 104 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3056585 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 35459 | 2025-12-01 14:27:33 | MASTER-Kislovodsk | (22h 53m 50.26s , +48d 11m 12.3s) | C | 60 | 15.8 | 35459 | 2025-12-01 14:27:33 | MASTER-Kislovodsk | (23h 00m 39.53s , +47d 47m 53.5s) | C | 60 | 13.6 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/42920. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40994] EP251130a: SAO RAS optical observations
by GCN Circulars 01 Dec '25

01 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42919 SUBJECT: EP251130a: SAO RAS optical observations DATE: 25/12/01 14:03:05 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. S. Moskvitin and O. I. Spiridonova (SAO RAS) report on behalf of GRB follow-up team. We observed the field of the X-ray transient EP251130a (Wu et al., GCN 42903; Zhang et al., GCN 42915), also detected by Swift-XRT (Evans et al., GCN 42908) with the Zeiss-1000 1m telescope of the SAO RAS on December 1, 01:29:21--03:08:47 UT (t_mid - T0 = 0.63281 days). We obtained 11 * 300 images in Rc band under mediocre weather conditions. The optical counterpart (Dornic et al., GCN 42904; He et al. GCN 42914; Gupta et al. GCN 42916; Zheng et al. GCN 42917; van Dalen et al., GCN 42918) is clearly detected in our stacked image with the brightness of R = 20.11 +/- 0.07 (R_lim = 21.8). This preliminary photometry is based on nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction. USNO-B1 star RA DEC R2 1173-00161316 101.000000 +27.372589 16.26 1173-00161485 101.071981 +27.375787 16.76 1173-00161417 101.045348 +27.394953 16.04 In comparison with the OT brightness from 1.3m DFOT data (Gupta et al., GCN 42916) we noted a brightening between two epochs (also reported by Zheng et al. GCN 42917 and van Dalen et al., GCN 42918). View this GCN Circular online at https://gcn.nasa.gov/circulars/42919. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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