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

[vsnet-grb-info 38056] Fermi GRB 250403A: Global MASTER-Net observations report
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40035 SUBJECT: Fermi GRB 250403A: Global MASTER-Net observations report DATE: 25/04/03 21:47:38 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 250403A ( Fermi GBM team, GCN 40025) errorbox 22256 sec after notice time and 22291 sec after trigger time at 2025-04-03 21:26:53 UT, with upper limit up to 18.5 mag. The observations began at zenith distance = 27 deg. The sun altitude is -58.3 deg. The galactic latitude b = 36 deg., longitude l = 316 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2832003 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 22321 | 2025-04-03 21:26:53 | MASTER-SAAO | (13h 38m 33.90s , -25d 30m 56.0s) | C | 60 | 18.5 | 22400 | 2025-04-03 21:28:13 | MASTER-SAAO | (13h 47m 18.63s , -25d 31m 56.8s) | C | 60 | 18.4 | 22559 | 2025-04-03 21:30:51 | MASTER-SAAO | (13h 34m 56.63s , -27d 26m 34.6s) | C | 60 | 18.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40035. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38055] GRB 250403A: GOTO optical counterpart follow-up observations
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40034 SUBJECT: GRB 250403A: GOTO optical counterpart follow-up observations DATE: 25/04/03 19:34:36 GMT FROM: Yashaswi Julakanti at University of Leicester <skyj1(a)leicester.ac.uk> Y. Julakanti, A. Kumar, B. P. Gompertz, D. O'Neill, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on further observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) on GRB 250403A (Julakanti et al. 2025, GCN 40026; Fermi GBM team, GCN 40025). Images were processed immediately after acquisition using the GOTO pipeline. Observations consisted of 4x90s exposures in the GOTO L-band (400-700 nm). We continue to detect the optical counterpart (Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032) with the following AB magnitudes: +-------------------------------------------------------------------+ | Observation time (UT) | t-t0 | filter | mag (AB) | +-------------------------------------------------------------------+ | 2025-04-03 16:20:24 | +1.08h | L | 18.99 ± 0.07 | | 2025-04-03 16:27:28 | +1.2h | L | 19.10 ± 0.07 | | 2025-04-03 16:34:48 | +1.32h | L | 19.30 ± 0.08 | | 2025-04-03 17:41:22 | +2.44h | L | 19.35 ± 0.08 | | 2025-04-03 17:51:00 | +2.60h | L | 19.47 ± 0.12 | +-------------------------------------------------------------------+ Our observations can be fit with a broken power-law model with slopes of t^-0.90 and t^-0.44 on either side of a break at 1.32 hours. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/40034. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38054] GRB 250402A: NUTTelA-TAO Early Optical Limits
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40033 SUBJECT: GRB 250402A: NUTTelA-TAO Early Optical Limits DATE: 25/04/03 19:02:42 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 GRB250402A on receipt of an automated GCN / SVOM 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 23:10:30 UT on 2025-04-02, 154 seconds after the SVOM/ECLAIRs trigger (X. Chen et al., GCN 40014). Observations were made in partially cloudy conditions. No source consistent with the SVOM/VT (L. P. Xin et al., GCN 40015) was detected. We report the following results: start time t-t0(s) end time UL g' UL r' exposure_time (s) -------------------------------------------------------------- 23:10:30 154 23:11:30 18.01 18.35 60 23:12:13 257 23:22:13 18.58 18.67 600 t is the middle time, t0 is the SVOM/ECLAIRs trigger time, t-t0 is given in seconds. UL gives the 5 sigma upper limit sensitivity in magnitudes, for images of the given exposure time. Calibration was done with 4 Pan-STARRS catalog stars on our images. No color or other corrections were applied to the values above. ---------------------------------- 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/40033. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38053] GRB 250403A: GMG Optical Observation
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40032 SUBJECT: GRB 250403A: GMG Optical Observation DATE: 25/04/03 17:52:32 GMT FROM: Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi(a)ynao.ac.cn> R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, H.-C. Feng and J.-M. Bai (YNAO, CAS) report: We observed the field of GRB 250403A (Fermi/GBM team, GCN 40025, T0 at 2025-04-03T15:15:22; Julakanti et al., GCN 40026) using the GMG-2.4m telescope at the Lijiang Observatory. The observation began at 2025-04-03 17:24:07, about 2.15 hours after the trigger. The optical counterpart of GRB 250403A (Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031) was clearly detected in the r-band image with an exposure of 600 s. The preliminary analysis results are shown as follows: +---------------+------------+----------+--------------+----------------+ | Tmid-T0 [h] | Exp. [s] | Filter | Mag | 5-sigma U.L. | +===============+============+==========+==============+================+ | 2.23 | 600 | r | 19.23 ± 0.03 | 21.6 | +---------------+------------+----------+--------------+----------------+ The given magnitudes are derived based on calibration against Pan-STARRS1 field stars, and are not corrected for the expected Galactic foreground extinction, corresponding to a reddening of E(B-V) = 0.1110 mag in the direction of the optical counterpart (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/40032. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38052] GRB 250403A: 1.6m Mephisto multi-band optical detection
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40031 SUBJECT: GRB 250403A: 1.6m Mephisto multi-band optical detection DATE: 25/04/03 17:46:43 GMT FROM: Chenxu Liu at Mephisto Team <cxliu(a)ynu.edu.cn> Guowang Du (SWIFAR, YNU), Ziwei Li (SWIFAR, YNU), Dezi Liu (SWIFAR, YNU), Yaosong Yu (SWIFAR, YNU), Chenxi Shang (SWIFAR, YNU), Chenxu Liu (SWIFAR, YNU), Jinghua Zhang (SWIFAR, YNU), Yuan Fang (SWIFAR, YNU), Xufeng Zhu (SWIFAR, YNU), Tao Wang (SWIFAR, YNU), Xinlei Chen (SWIFAR, YNU), Xingzhu Zou (SWIFAR, YNU), Xuhui Han (NAOC), Pinpin Zhang (NAOC), Liping Xin (NAOC), Chao Wu (NAOC), Yu Pan (SWIFAR, YNU), Brajesh Kumar (SWIFAR, YNU), Yuanpei Yang (SWIFAR, YNU), Xiangkun Liu (SWIFAR, YNU), Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team: We performed simultaneous multi-band photometric observations of GRB 250403A (SVOM burst-id sb25040305) detected by SVOM/ECLAIRs (Y. Julakanti et. al. 2025, GCN 40026) and by Fermi (Fermi GBM team, GCN 40025) with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. The observations were initiated at 15:17:48UTC 2025-04-03 (i.e., 148s after the Swift/BAT trigger) and are still ongoing at the time of this report. Multiple frames were obtained in uvgriz- bands. The optical counterpart is clearly detected in all bands. The photometry of the initial frames is listed below: UT start |Band | Exp | Mag (AB) ---------------------------|-------|---------------- 2025/04/03T15:25:37 | u |180s |17.92 +/- 0.12 2025/04/03T15:17:48 | v |180s |16.51 +/- 0.03 2025/04/03T15:25:38 | g | 50s |17.16 +/- 0.05 2025/04/03T15:17:49 | r | 50s |15.64 +/- 0.01 2025/04/03T15:25:38 | i | 79s |16.68 +/- 0.04 2025/04/03T15:17:49 | z | 79s |15.27 +/- 0.02 Our results are consistent with the previously reported circulars (R. Starling et al., GCN 40028; Wu et al., GCN 40029). Further analysis of the additional images is ongoing. ---------------------------------------------------------- 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/40031. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38051] GRB 250402A: Fermi GBM Observation
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40030 SUBJECT: GRB 250402A: Fermi GBM Observation DATE: 25/04/03 17:29:10 GMT FROM: Matt Godwin <msg0028(a)uah.edu> Jacob Smith (UAH), Utkarsh Pathak(IIT Bombay), and Matt Godwin (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 23:08:09.09 UT on 02 April 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250402A (trigger 765328094/250402964). which was also detected by SVOM (Chen et al. 2025, GCN 40014). The Fermi GBM on-ground location is consistent with the SVOM position. The angle from the Fermi LAT boresight is 57 degrees. The GBM light curve consists of a double peak with a duration (T90) of about 44 s (50-300 keV). The time-averaged spectrum from T0-5.1 to T0+45.1 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.1 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 115 +/- 10 keV. The event fluence (10-1000 keV) in this time interval is (4.1 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+23 s in the 10-1000 keV band is 2.4 +/- 0.2 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 60 +/- 10 keV, alpha = -0.4 +/- 0.3 and beta = -2.1 +/- 0.1. 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/40030. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38050] GRB 250403A: SVOM/C-GFT optical observations
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40029 SUBJECT: GRB 250403A: SVOM/C-GFT optical observations DATE: 25/04/03 17:08:55 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Chao WU (NAOC), Liping Xin(NAOC), Zhe Kang (CHO), 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), Y. Julakanti, R. A. J. Eyles-Ferris (U. Leicester) report on behalf of the SVOM/C-GFT team: We observed the field of GRB 250403A detected by FERMI/GBM(FERMI team: GCN 40025) and SVOM/ECLAIRs/GRM (sb25040305, Julakanti et al., GCN 40026)with C-GFT. Our observations were started on 2025-04-03T15:16:17 UTC, ~57s after the trigger. The optical counterpart (reported by Starling et al., GCN 40028) was clearly detected in our images. Its brightness is 15.60 +/- 0.13 mag in i band at 62 sec after the burst. The photometry was calibrated with nearby Pan-STARRS1 stars. Further observation and analysis is on-going. We thank the observation assistants Shuai lui and Guangsheng Zhang 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/40029. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38049] GRB 250403A: GOTO detection of the optical afterglow
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40028 SUBJECT: GRB 250403A: GOTO detection of the optical afterglow DATE: 25/04/03 16:26:51 GMT FROM: Rhaana Starling at U of Leicester <rlcs1(a)leicester.ac.uk> R. Starling, Y. Julakanti, A. Kumar, D. O'Neill, B. P. Gompertz, J. Lyman, G. Ramsay, M. Kennedy, K. Ackley, M. J. Dyer, K. Ulaczyk, F. Jimenez-Ibarra, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Palle and D. Pollacco report on behalf of the GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to GRB 250403A detected by SVOM (Julakanti et al. 2025, GCN 40026) and by Fermi (Fermi GBM team, GCN 40025). Targeted observations were performed using the GOTO-South starting at 15:25:31 UT on 2025-04-03 (10.12 minutes after the SVOM ECLAIRs trigger) to to 15:30:27 UT on 2025-04-03 (15.10 minutes after the SVOM ECLAIRs trigger). The images are 90s exposures in the GOTO L-band (400-700 nm). A new optical source within the SVOM localisation region (Julakanti et al., GCN 40026) is identified at the position: RA, Dec: 194.61570 -24.37950 deg. We report four epochs of observations, showing a clear power-law-like decay with t^-1.1. +------------------------------------------------------------------------------------------------+ | Observation time (UT) | t-t0 (min) | Mag (AB) | +------------------------------------------------------------------------------------------------+ | 2025-04-03 15:25:31.182 | 10.12 | 17.02 ± 0.02 | | 2025-04-03 15:27:09.645 | 11.82 | 17.16 ± 0.03 | | 2025-04-03 15:28:48.308 | 13.47 | 17.35 ± 0.03 | | 2025-04-03 15:30:26.677 | 15.10 | 17.50 ± 0.03 | +------------------------------------------------------------------------------------------------+ Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/40028. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38048] GRB 250402A: Swift-XRT observations
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40027 SUBJECT: GRB 250402A: Swift-XRT observations DATE: 25/04/03 16:01:19 GMT FROM: Simone Dichiara at Pennsylvania State University <sbd5667(a)psu.edu> S. Dichiara (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB), K.L. Page and P.A. Evans (U.Leicester) reports on behalf of the Swift-XRT team: We have analysed 2.4 ks of XRT data for the SVOM/ECLAIRs-detected burst GRB 250402A (SVOM trigger sb25040203; Chen et al., GCN circ. 40014), from T0+49.2 ks to T0+51.5 ks after the SVOM/ECLAIRs trigger. The data are entirely in Photon Counting (PC) mode. We find an uncatalogued X-ray source consistent with the X-ray counterpart identified by SVOM/MXT (Maggi et al., GCN circ. 40019) and the optical counterpart (Xin et al., GCN 40015, Pérez-Fournon et al., GCN 40020, Schneider et al., GCN 40022, Magnani et al., GCN 40023). We note that the source is fading compared to the flux reported by previous MXT observations (Maggi et al., GCN circ. 40019). Details of this source are given below: Source 1: RA (J2000.0): 213.4089 = 14:13:38.13 Dec (J2000.0): -5.9302 = -05:55:48.5 Error: 3.4 arcsec (radius, 90% conf. [Enhanced position]) Count-rate:0.045 (±0.012) ct s-1 Flux: 1.9 (±0.5) ×10-12 erg cm-2 s-1 (observed, 0.3-10 keV) This XRT position is 1.07 arcsec away from the optical position. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00009/. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40027. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38047] GRB 250403A : SVOM detection of a burst
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40026 SUBJECT: GRB 250403A : SVOM detection of a burst DATE: 25/04/03 15:58:17 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y. Julakanti, R. A. J. Eyles-Ferris (U. Leicester), S. Schanne, D. Turpin (CEA), M. Brunet (IRAP) report: SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250403A (SVOM burst-id sb25040305) starting at 2025-04-03T15:15:20 UTC (Tb), also detected by Fermi (GCN 40025). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT) which produced a sequence of 19 alerts. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 42.11 in the 8-120 keV energy band over a time window of 20.40 seconds starting at Tb. The downloaded light curve shows a single broad structure of duration of about 20 seconds. The localization of the best alert is R.A., Dec 194.5927, -24.3762 degrees: RA (J2000) = 12h58m22.24s Dec (J2000) = -24d22m34.36s with a 90% C.L. radius of 2.71 arcmin (including systematic error of 2 arcmin added in quadrature). The burst was also detected by GRM as SVOM burst-id sb25040306. No immediate slew was performed on this burst. A SVOM ToO has been programmed for follow-up. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. The Burst Advocate (BA) on shift for this burst is Y. Julakanti (skyj1(a)leicester.ac.uk) Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/40026. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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