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

[vsnet-grb-info 38490] GRB 250502A: TESS observations
by GCN Circulars 14 May '25

14 May '25

TITLE: GCN CIRCULAR NUMBER: 40459 SUBJECT: GRB 250502A: TESS observations DATE: 25/05/14 20:02:36 GMT FROM: Rahul Jayaraman at MIT <rjayaram(a)mit.edu> R. Jayaraman (MIT), M.M. Fausnaugh (TTU), S. Chastain (TTU), R. Vanderspek (MIT), and G.R. Ricker (MIT) report: The Transiting Exoplanet Survey Satellite (TESS; Ricker et al., JATIS 1 2015) observed GRB 250502A (Wang et al., GCN 40313) during Sector 91 of its scheduled sky survey. We performed forced difference-imaging photometry at the location of the confirmed X-ray afterglow (Dichiara et al., GCN 40336) using the full-frame images from the publicly-available TICA data archived at MAST (https://archive.stsci.edu/hlsp/tica) Our data reduction routine is described in Fausnaugh et al. 2023 (ApJ 956(2):108). The light curve shows a rapidly rising afterglow in the three 200s exposures from after the trigger. The light curve peaks roughly ~700 s after the burst at a magnitude of 16.44 ± 0.14 (uncorrected for Galactic extinction), followed by a decay to the detection limit of 17.6 (3-sigma) over ~4 x 10^3 s. These results are consistent with measurements of the early afterglow from Rakotondrainibe et al. (GCN 40315), Xu et al. (GCN 40319), and Li et al. (GCN 40320). This circular includes data collected with the TESS mission, obtained from the MAST data archive at the Space Telescope Science Institute (STScI). Funding for the TESS mission is provided by the NASA Explorer Program. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. View this GCN Circular online at https://gcn.nasa.gov/circulars/40459. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38489] Fermi trigger No 768922089: Global MASTER-Net observations report
by GCN Circulars 14 May '25

14 May '25

TITLE: GCN CIRCULAR NUMBER: 40458 SUBJECT: Fermi trigger No 768922089: Global MASTER-Net observations report DATE: 25/05/14 19:46:06 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 (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB250514.56 (trigger No 768922089,16h 41m 45.60s , +29d 45m 00.0s, R=11.68) errorbox 21929 sec after notice time and 21974 sec after trigger time at 2025-05-14 19:34:19 UT, with upper limit up to 16.9 mag. The observations began at zenith distance = 79 deg. The sun altitude is -47.5 deg. The galactic latitude b = 39 deg., longitude l = 50 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2870382 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 22004 | 2025-05-14 19:34:19 | MASTER-SAAO | (15h 59m 51.82s , +28d 44m 08.0s) | C | 60 | 16.9 | 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/40458. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38488] GRB 250511A: GECAM-A detection of a short burst
by GCN Circulars 14 May '25

14 May '25

TITLE: GCN CIRCULAR NUMBER: 40457 SUBJECT: GRB 250511A: GECAM-A detection of a short burst DATE: 25/05/14 04:36:21 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Shao-Lin Xiong, Yue Huang (IHEP) report on behalf of GECAM team: GECAM-A detected a short burst GRB 250511A at 2025-05-11T00:52:17 UTC (denoted as T0). According to the GECAM-A light curves in about 40-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 1.9 +0.7/-0.7 s. The GECAM-A light curve can be found here: https://www.bursthub.cn//admin/static/gecamgrb250511A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (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/40457. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38487] GRB 250509A: Swift-BAT refined analysis
by GCN Circulars 14 May '25

14 May '25

TITLE: GCN CIRCULAR NUMBER: 40456 SUBJECT: GRB 250509A: Swift-BAT refined analysis DATE: 25/05/14 02:57:21 GMT FROM: Rahul Gupta at NASA GSFC <rahul.gupta(a)nasa.gov> T. Parsotan (GSFC), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU), M. H. Siegel (PSU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250509A (trigger #1311764) (Siegel, et al., GCN Circ. 40407). The BAT ground-calculated position is RA, Dec = 46.451, -38.854 deg which is RA(J2000) = 03h 05m 48.3s Dec(J2000) = -38d 51' 15.1" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 96%. The mask-weighted BAT light curve shows a sharp rise and exponential decay profile. T90 (15-350 keV) is 55.43 +- 10.47 sec (estimated error including systematics). The time-averaged spectrum from T-2.85 to T+71.46 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.54 +- 0.08. The fluence in the 15-150 keV band is 2.4 +- 0.1 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+0.42 sec in the 15-150 keV band is 1.9 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1311764 View this GCN Circular online at https://gcn.nasa.gov/circulars/40456. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38486] LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Final Epochs)
by GCN Circulars 13 May '25

13 May '25

TITLE: GCN CIRCULAR NUMBER: 40455 SUBJECT: LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Final Epochs) DATE: 25/05/13 17:45:36 GMT FROM: Isaac McMahon at University of Zürich <isaac.mcmahon(a)ligo.org> Isaac McMahon, Sean MacBride, Marcelle Soares-Santos (UZH), Simran Kaur (U. of Michigan/UZH), Lillian Joseph (Benedictine U.), Ken Herner, Tom Diehl (Fermilab), Haibin Zhang, Mitsuru Kokubo, Nozomu Tominaga, Yousuke Utsumi, Michitoshi Yoshida (NAOJ), Tomoki Morokuma (Chiba Tech), Akira Arai, Wanqui He, Yuki Moritani, Masato Onodera, Vera Maria Passegger, Ichi Tanaka, Kiyoto Yabe (NAOJ) report on behalf of the Dark Energy Survey Gravitational Wave (DESGW) Team, the Japanese Collaboration for Gravitational-Wave Electro-Magnetic Follow-up (J-GEM), and Subaru Telescope: At 01:20 UTC April 6th and 00:14 UTC April 25th, the Dark Energy Camera (DECam) began the third and fourth epochs of observations in final response to the LVK alert issued for the candidate gravitational-wave event S250328ae (GCN 39898). The pointings of these observations were identical to the first epoch observations from March 29th, 2025 (GCN 39934). All fields were observed in DECam r, i, and z filters with 90-second exposures. The limiting magnitude achieved is ~21.3 in r-band, ~21.2 in i-band, and ~21.0 in z-band for the third epoch and ~22.3 in r-band, ~22.1 in i-band, and ~21.6 in z-band for the fourth. We process the images with our difference imaging pipeline (Herner et al. 2020) using DES and public DECam images as templates. We employ the autoscan machine learning code (Goldstein et al 2015) to reject subtraction artifacts, requiring an autoscan score of at least 0.7 on at least 3 nights of observations. We also match our candidates against the ALLWISE, Milliquas, Quaia, and LQAC-6 AGN catalogs (Secrest et al 2015, Flesch 2023, Storey-Fisher et al 2024, Souchay et al 2024) within the LVK localization volume. Of the 88 AGNs which exhibited transient variability in our observations, none lay within the localization volume. Of the 25 high confidence candidates reported previously (GCN 39992), 15 were observed by the J-GEM collaboration, using the Subaru Telescope Prime Focus Spectrograph (PFS), and ruled out by spectral identification and redshift (GCN 40221). Another 8 candidates either did not exhibit any further transient activity after the first two epochs or were determined to be likely stellar in origin. The final 2 candidates were not within the footprint observed by J-GEM and thus could not be determined. We report these two candidates and one last candidate which was observed only in the most recent epochs below, all likely of supernova origin. | TYPE | ID | ATNAME | RA | DEC | MAG_R | MAG_R_ERR | MAG_I | MAG_I_ERR | MAG_Z | MAG_Z_ERR | | -------- | ------- | --------- | ---------- | ---------- | ----- | ---- | ----- | ---- | ----- | ---- | | SN_LIKE | 2290001 | AT2025avp | 144.806008 | 10.632223 | 20.36 | 0.02 | 20.19 | 0.02 | 20.22 | 0.06 | | SN_LIKE | 2291473 | AT2025gem | 144.706509 | 11.560317 | 20.92 | 0.03 | 21.03 | 0.15 | 21.22 | 0.10 | | SN_LIKE | 2295351 | AT2025kjv | 143.077064 | 7.385021 | 22.3 | 0.10 | 21.81 | 0.07 | 22.86 | 0.44 | Additionally, J-GEM reported 5 QSOs which had a redshift consistent with the localization volume. We do not find any evidence of any transient variability for any of these QSOs in our observations after the detection of S250328ae. We also do not recover any of the X-ray source candidates reported by Swift XRT (GCN 39972) within their reported error bounds. Thus, apart from the possibility that the three supernova-like candidates reported above are related to S250328ae, we find no suitable optical counterpart candidate for this binary black hole gravitational wave event. The DECam Search & Discovery Program for Optical Signatures of Gravitational Wave Events (DESGW) is carried out by the Dark Energy Survey (DES) collaboration in partnership with wide-ranging groups in the community. DESGW uses data obtained with the Dark Energy Camera (DECam), which was constructed by the DES collaboration with support from the Department of Energy and member institutions, and utilizes data as distributed by the Science Data Archive at NOIRLAB. NOIRLAB is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. We thank the Cerro Tololo observatory staff for their support in acquiring these observations. We also thank the J-GEM and Swift XRT teams for their contribution and support. We are grateful to the staff at NAOJ and Subaru Telescope for their contributions to the deployments of PFS hardware and software, and the preparations of PFS system integration, engineering observations, and various other engineering works. Our thanks should also be propagated to the administrative staffs at Kavli IPMU, NAOJ, Subaru Telescope, and all the PFS institutes for kind support in such aspects as finances, contracts, asset managements, and so on. This research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has cultural, historical, and natural significance in Hawaii. View this GCN Circular online at https://gcn.nasa.gov/circulars/40455. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38485] Fermi GRB 250512A: Global MASTER-Net observations report
by GCN Circulars 13 May '25

13 May '25

TITLE: GCN CIRCULAR NUMBER: 40454 SUBJECT: Fermi GRB 250512A: Global MASTER-Net observations report DATE: 25/05/13 16:16:08 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-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 250512A ( Fermi GBM team, GCN 40436) errorbox 1 days 10178 sec after notice time and 1 days 10229 sec after trigger time at 2025-05-13 14:52:05 UT, with upper limit up to 17.9 mag. Observations started at twilight. The observations began at zenith distance = 38 deg. The sun altitude is -14.8 deg. The galactic latitude b = 19 deg., longitude l = 112 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2868622 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 96660 | 2025-05-13 14:52:05 | MASTER-Tunka | (17h 57m 54.62s , +86d 24m 49.3s) | C | 60 | 14.5 | 96798 | 2025-05-13 14:54:24 | MASTER-Tunka | (20h 39m 40.13s , +76d 43m 27.8s) | C | 60 | 13.0 | 96962 | 2025-05-13 14:57:08 | MASTER-Tunka | (21h 30m 19.84s , +78d 37m 25.1s) | C | 60 | 13.4 | 100410 | 2025-05-13 15:54:36 | MASTER-Tunka | (18h 00m 35.78s , +86d 29m 00.2s) | C | 60 | 17.8 | 100410 | 2025-05-13 15:54:36 | MASTER- | (17h 52m 00.08s , +86d 24m 46.8s) | C | 60 | 17.5 | 100489 | 2025-05-13 15:55:55 | MASTER-Tunka | (20h 40m 09.79s , +76d 45m 49.8s) | C | 60 | 17.9 | 100489 | 2025-05-13 15:55:55 | MASTER- | (20h 37m 45.37s , +76d 40m 53.1s) | C | 60 | 17.4 | 100690 | 2025-05-13 15:59:16 | MASTER-Tunka | (21h 31m 11.48s , +78d 36m 43.9s) | C | 60 | 17.7 | 100871 | 2025-05-13 16:02:17 | MASTER-Tunka | (21h 47m 34.81s , +76d 42m 05.1s) | C | 60 | 17.1 | 100871 | 2025-05-13 16:02:17 | MASTER- | (21h 45m 01.87s , +76d 37m 00.9s) | C | 60 | 16.4 | Coadd 101045 | 2025-05-13 16:05:11 | MASTER-Tunka | (18h 00m 13.68s , +86d 28m 34.8s) | C | 60 | 17.0 | 101129 | 2025-05-13 16:06:35 | MASTER-Tunka | (20h 40m 08.00s , +76d 47m 07.4s) | C | 60 | 16.6 | 101209 | 2025-05-13 16:07:54 | MASTER-Tunka | (21h 02m 16.63s , +74d 50m 57.9s) | C | 60 | 17.0 | 101287 | 2025-05-13 16:09:13 | MASTER-Tunka | (21h 31m 11.49s , +78d 36m 46.3s) | C | 60 | 17.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40454. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38484] Konus-Wind detection of GRB 250506A
by GCN Circulars 13 May '25

13 May '25

TITLE: GCN CIRCULAR NUMBER: 40453 SUBJECT: Konus-Wind detection of GRB 250506A DATE: 25/05/13 10:36:33 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 250506A (Fermi-GBM detection: The Fermi GBM team, GCN 40355; SVOM detection: Wang et al., GCN 40358; GECAM-B detection: Wang et al., GCN 40396; GRBAlpha detection: Pal et al., GCN 40440;) triggered Konus-Wind at T0=08605.817 s UT (02:23:25.817). The burst light curve shows a multi-peaked structure which starts at ~T0-2.1 s and has a total duration of ~56 s. The emission is seen up to ~7 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250506_T08605 As observed by Konus-Wind, the burst had a fluence of 2.41(-0.16,+0.38)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+33.728 s, of 8.39(-0.74,+0.75)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+57.600 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 = -1.06(-0.04,+0.08), the high energy photon index beta = -3.51(-6.49,+0.91), the peak energy Ep = 284(-28,+28) keV (chi2 = 123/97 dof). The spectrum near the maximum count rate (measured from T0+33.024 to T0+41.216 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 = -1.02(-0.07,+0.08) and Ep = 278(-21,+25) keV (chi2 = 111/98 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.0 (chi2 = 111/97 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/40453. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38483] EP250512a/GRB 250512B: REM optical/NIR observations
by GCN Circulars 13 May '25

13 May '25

TITLE: GCN CIRCULAR NUMBER: 40452 SUBJECT: EP250512a/GRB 250512B: REM optical/NIR observations DATE: 25/05/13 10:28:43 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 EP250512a/GRB 250512B detected by EP/WXT (Zhao et al., GCN 40437) and SVOM/ECLAIRs (Maggi et al., GCN 40439) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 May 12 at 22:52:55 UT (i.e. 11.5 hr after the burst), and lasted for about 1 hour. From preliminary inspection, we do not detect any possible counterpart consistent with the afterglow (Li et al., GCN 40443; Xin et al., GCN 40444; Busmann et al., GCN 40447) down to the following 3sigma limits: r > 18.9 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 12.0 hr after the trigger; H > 16.2 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 11.9 hr after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40452. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38482] EP250511a: Koshka Zeiss-1000 Optical Upper Limit
by GCN Circulars 13 May '25

13 May '25

TITLE: GCN CIRCULAR NUMBER: 40451 SUBJECT: EP250511a: Koshka Zeiss-1000 Optical Upper Limit DATE: 25/05/13 10:27:04 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Novichonok (Petrozavodsk State University, KIAM), I. Nikolenko (INASAN), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We performed optical observations of the field of EP250511a (Lian et. al, GCN 40429; Li et. al, GCN 40434) using the 1-meter Zeiss-1000 telescope of the Simeiz (Koshka) Observatory. The R-band observations began on 2025-05-11 19:37:13 UT, i.e. ~0.51 days since trigger at a low altitude (~40 deg) and in the presence of the full Moon. The optical counterpart (Schneider et. al, GCN 40431; Li et. al, GCN 40433; Sanchez-Sierras et. al, GCN 40449) is not detected in the stacked image of an exposure of 86*60 sec. The preliminary upper limit is given below: Date UT start t-T0 Exp. Filter OT Err. UL (mid, days) (n*s) (3sigma) 2025-05-11 19:37:13 0.51405 86*60 R n/d n/d 18.9 The photometry was calibrated using nearby stars from USNO-B1.0 and has not been corrected for the Galactic extinction. Our result is consistent with non-detections reported by (Lipunov et. al, GCN 40432; Brivio et. al, GCN 40435; Zhong et. al, GCN 40442; Busmann et. al, GCN 40445). Ref. stars USNO-B1.0 RA Dec R2 202.1106 -2.6632 15.94 202.0790 -2.7119 15.27 202.0868 -2.7163 15.00 View this GCN Circular online at https://gcn.nasa.gov/circulars/40451. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38481] GRB 250507B: AstroSat CZTI detection
by GCN Circulars 13 May '25

13 May '25

TITLE: GCN CIRCULAR NUMBER: 40450 SUBJECT: GRB 250507B: AstroSat CZTI detection DATE: 25/05/13 09:42:32 GMT FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in> M. Tembhurnikar (IUCAA), G. Waratkar (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 GRB 250507B which was also detected by SVOM/GRM (SVOM/GRM team, GCN Circ. 40438) and GRBAlpha (Pal et al., GCN Circ. 40441). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-05-07 09:31:33.55 UTC. The measured peak count rate associated with the burst is 158 (+90, -40) counts/s above the background in the combined data of two quadrants (out of four), with a total of 70 (+31, -29) counts. The local mean background count rate was 128 (+5, -8) counts/s. Using cumulative rates, we measure a T90 of 0.7 (+0.2, -0.3) s. We detect only the brighter part of the pulse detected by SVOM/GRM, likely because the source is at a sky position where our effective area is low. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-05-07 09:31:32.65 UTC. The measured peak count rate associated with the burst is 262 (+67, -44) counts/s above the background in the combined data of all quadrants, with a total of 613 (+161, -168) counts. The local mean background count rate was 1220 (+8, -8) counts/s. Due to the intrinsic 1 s binning of veto data, we cannot reliably estimate a T90 from it. 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/40450. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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