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

[vsnet-grb-info 38226] EP250421a: Global MASTER-Net observations report
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40200 SUBJECT: EP250421a: Global MASTER-Net observations report DATE: 25/04/22 05:36:49 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 EP250421a ( EP Team et al., GCN 40198) errorbox 2313 sec after notice time and 46767 sec after trigger time at 2025-04-22 05:15:55 UT, with upper limit up to 20.0 mag. The observations began at zenith distance = 43 deg. The sun altitude is -68.7 deg. The galactic latitude b = 35 deg., longitude l = 281 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2849886 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 46798 | 2025-04-22 05:15:55 | MASTER-OAFA | (11h 29m 43.36s , -24d 18m 41.7s) | 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/40200. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38225] GRB 250421B: AstroSat CZTI detection of a bright long burst
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40199 SUBJECT: GRB 250421B: AstroSat CZTI detection of a bright long burst DATE: 25/04/22 05:05:30 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 a bright long-duration GRB 250421B. 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 2025-04-21 21:59:57.50 UTC. The measured peak count rate associated with the burst is 586 (+45, -49) counts/s above the background in the combined data of three quadrants (out of four), with a total of 3514 (+233, -248) counts. The local mean background count rate was 209 (+3, -4) counts/s. Using cumulative rates, we measure a T90 of 17 (+1, -1) 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 2025-04-21 21:59:57.06 UTC. The measured peak count rate associated with the burst is 1713 (+87, -96) counts/s above the background in the combined data of all quadrants, with a total of 9802 (+468, -504) counts. The local mean background count rate was 1168 (+7, -8) counts/s. We measure a T90 of 17 (+1, -1) 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/40199. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38224] EP250421a: Einstein Probe detection of an X-ray transient
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40198 SUBJECT: EP250421a: Einstein Probe detection of an X-ray transient DATE: 25/04/22 04:36:14 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> G. Y. Zhao (SYSU), C. Zhou (HUST), R.-Z. Li (YNAO, CAS), W. Chen, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) 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 EP250421a. The transient triggered EP-WXT (ID: 01709135179) at 2025-04-21T16:16:28 (UTC) and WXT detected a rise of about 70 s. The WXT position of the source is R.A. = 172.4130 deg, DEC = -24.6830 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 about 245 s after the EP/WXT trigger. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 172.4201 deg, DEC = -24.6758 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The WXT spectrum can be fitted by an absorbed power law model with a photon index of 2.91(+2.76, -1.72) and an absorbing column density of 4.1e21 cm^-2. The unabsorbed 0.5-4 keV flux is about 1.3 (+14.7,-0.81) e-9 erg/cm^2/s. The FXT spectrum can be fitted by an absorbed power law model with a photon index of 2.11 (+0.15, -0.14) and an absorbing column density of 8.3e20 cm^-2. The unabsorbed 0.5-10 keV flux is about 1.39 (+0.07, -1.39) e-11 erg/cm^2/s. The contact TA of EP250421a is Chang Zhou. Please contact her via email d202180110(a)hust.edu.cn if needed. 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/40198. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38223] EP250421a: Mephisto optical counterpart confirmation
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40197 SUBJECT: EP250421a: Mephisto optical counterpart confirmation DATE: 25/04/22 04:28:53 GMT FROM: liuxk(a)ynu.edu.cn Xiangkun Liu, Xinlei Chen, Yi Zhang, Runnan Jiang, Brajesh Kumar, Guowang Du, Yuan Fang, Jinghua Zhang, Xingzhu Zou, Yu Pan, Yuanpei Yang, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team: The field of EP250421a (EP-WXT trigger ID: 01709135179) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Simultaneous uvgriz band photometric observations were conducted starting from 16:26:55 2025-04-21 UT (~5 mins after the trigger) and 7 frames with 45s exposure time for ugi bands and 6 frames with 45s exposure times for vrz bands were taken, followed by another 2 frames with 300s exposure time for all ugi/vrz bands. We detected an optical transient candidate (Lee et al., GCN 40192; Fu et al., GCN 40193) in the stacked riz band images in both sets of observations but no detection in uvg bands. In our priliminary photometry there is clear indication of the decay of the source as listed below. Start_Time(UT) | Band | Exp(s) | Mag/LimMag (AB) ---------------------------|--------|---------|------------ 2025-04-21T16:26:55 | u | 45*7 | >21.15 2025-04-21T16:38:05 | v | 45*6 | >21.39 2025-04-21T16:26:55 | g | 45*7 | >22.02 2025-04-21T16:38:05 | r | 45*6 | 20.47 +/- 0.10 2025-04-21T16:26:55 | i | 45*7 | 19.07 +/- 0.07 2025-04-21T16:38:05 | z | 45*6 | 18.62 +/- 0.13 Start_Time(UT) | Band | Exp(s) | Mag/LimMag (AB) ---------------------------|--------|---------|------------ 2025-04-21T17:12:15 | u | 300*2 | >21.41 2025-04-21T16:59:53 | v | 300*2 | >21.64 2025-04-21T17:12:15 | g | 300*2 | >22.27 2025-04-21T16:59:53 | r | 300*2 | 21.21 +/- 0.16 2025-04-21T17:12:15 | i | 300*2 | 20.28 +/- 0.12 2025-04-21T16:59:53 | z | 300*2 | 19.15 +/- 0.14 ------------------------------------------------------------------------------------------------- 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/40197. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38222] IceCube Alert 250421.71: Global MASTER-Net observations report
by GCN Circulars 22 Apr '25

22 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40196 SUBJECT: IceCube Alert 250421.71: Global MASTER-Net observations report DATE: 25/04/22 00:39:39 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-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 inspect of the IceCube Alert 250421.71 (trigger No 2517159,16h 02m 52.80s , +28d 41m 24.0s, R=1.29) errorbox 21082 sec after notice time and 21147 sec after trigger time at 2025-04-21 22:58:35 UT, with upper limit up to 18.5 mag. The observations began at zenith distance = 15 deg. The sun altitude is -29.5 deg. The galactic latitude b = 48 deg., longitude l = 47 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2849038 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 21177 | 2025-04-21 22:58:35 | MASTER-Kislovodsk | (15h 56m 30.81s , +28d 05m 01.6s) | C | 60 | 18.3 | 21275 | 2025-04-21 23:00:13 | MASTER-Kislovodsk | (16h 05m 26.91s , +28d 03m 52.9s) | C | 60 | 18.5 | 21369 | 2025-04-21 23:01:47 | MASTER-Kislovodsk | (15h 56m 32.92s , +29d 59m 34.7s) | C | 60 | 18.4 | 21452 | 2025-04-21 23:03:10 | MASTER-Kislovodsk | (16h 01m 36.09s , +28d 57m 32.8s) | C | 60 | 18.5 | 21535 | 2025-04-21 23:04:32 | MASTER-Kislovodsk | (16h 05m 49.55s , +29d 59m 23.6s) | C | 60 | 18.3 | 21618 | 2025-04-21 23:05:55 | MASTER-Kislovodsk | (16h 00m 56.86s , +28d 56m 50.7s) | C | 60 | 18.5 | 21701 | 2025-04-21 23:07:19 | MASTER-Kislovodsk | (15h 57m 26.75s , +26d 09m 30.2s) | C | 60 | 18.5 | 21784 | 2025-04-21 23:08:42 | MASTER-Kislovodsk | (16h 06m 15.13s , +26d 08m 27.7s) | C | 60 | 18.3 | 21872 | 2025-04-21 23:10:10 | MASTER-Kislovodsk | (15h 57m 30.28s , +27d 55m 28.7s) | C | 60 | 18.4 | 21962 | 2025-04-21 23:11:40 | MASTER-Kislovodsk | (16h 05m 31.54s , +28d 05m 04.3s) | C | 60 | 18.5 | 22051 | 2025-04-21 23:13:08 | MASTER-Kislovodsk | (15h 57m 31.03s , +29d 48m 52.4s) | C | 60 | 18.4 | 22134 | 2025-04-21 23:14:31 | MASTER-Kislovodsk | (16h 03m 33.66s , +28d 48m 15.9s) | C | 60 | 18.2 | 22225 | 2025-04-21 23:16:02 | MASTER-Kislovodsk | (16h 05m 42.85s , +29d 58m 37.8s) | C | 60 | 18.5 | 22313 | 2025-04-21 23:17:31 | MASTER-Kislovodsk | (15h 58m 22.90s , +26d 02m 50.4s) | C | 60 | 18.5 | 22396 | 2025-04-21 23:18:53 | MASTER-Kislovodsk | (16h 07m 20.08s , +26d 01m 46.7s) | C | 60 | 18.4 | 22480 | 2025-04-21 23:20:17 | MASTER-Kislovodsk | (15h 57m 23.52s , +27d 54m 39.6s) | C | 60 | 18.3 | 22561 | 2025-04-21 23:21:39 | MASTER-Kislovodsk | (16h 06m 31.84s , +27d 54m 51.5s) | C | 60 | 18.4 | 22645 | 2025-04-21 23:23:02 | MASTER-Kislovodsk | (16h 03m 47.65s , +28d 48m 03.3s) | C | 60 | 18.4 | 22729 | 2025-04-21 23:24:27 | MASTER-Kislovodsk | (15h 57m 30.40s , +29d 47m 32.2s) | C | 60 | 18.5 | 22821 | 2025-04-21 23:25:59 | MASTER-Kislovodsk | (16h 06m 46.00s , +29d 49m 01.6s) | C | 60 | 18.3 | 22905 | 2025-04-21 23:27:23 | MASTER-Kislovodsk | (16h 02m 59.34s , +28d 47m 13.7s) | C | 60 | 18.4 | 22989 | 2025-04-21 23:28:46 | MASTER-Kislovodsk | (15h 58m 20.68s , +26d 01m 13.8s) | C | 60 | 18.4 | 23079 | 2025-04-21 23:30:17 | MASTER-Kislovodsk | (16h 07m 19.99s , +26d 00m 16.2s) | C | 60 | 18.4 | 23168 | 2025-04-21 23:31:46 | MASTER-Kislovodsk | (15h 57m 22.17s , +27d 53m 08.2s) | C | 60 | 18.2 | 23249 | 2025-04-21 23:33:07 | MASTER-Kislovodsk | (16h 06m 30.59s , +27d 53m 33.5s) | C | 60 | 18.4 | 23332 | 2025-04-21 23:34:30 | MASTER-Kislovodsk | (15h 57m 29.74s , +29d 49m 01.8s) | C | 60 | 18.3 | 23416 | 2025-04-21 23:35:53 | MASTER-Kislovodsk | (16h 02m 59.31s , +28d 46m 20.5s) | C | 60 | 18.4 | 23500 | 2025-04-21 23:37:17 | MASTER-Kislovodsk | (16h 06m 46.26s , +29d 48m 42.9s) | C | 60 | 18.5 | 23582 | 2025-04-21 23:38:40 | MASTER-Kislovodsk | (15h 58m 38.21s , +31d 42m 59.5s) | C | 60 | 18.3 | 23675 | 2025-04-21 23:40:13 | MASTER-Kislovodsk | (16h 08m 06.89s , +31d 42m 00.6s) | C | 60 | 18.3 | 23758 | 2025-04-21 23:41:36 | MASTER-Kislovodsk | (15h 58m 20.02s , +25d 59m 10.7s) | C | 60 | 18.3 | 23841 | 2025-04-21 23:42:59 | MASTER-Kislovodsk | (16h 07m 19.25s , +25d 59m 29.4s) | C | 60 | 18.3 | 23923 | 2025-04-21 23:44:21 | MASTER-Kislovodsk | (15h 57m 24.42s , +27d 55m 01.1s) | C | 60 | 18.4 | 24006 | 2025-04-21 23:45:44 | MASTER-Kislovodsk | (16h 06m 29.06s , +27d 53m 16.7s) | C | 60 | 18.4 | 24089 | 2025-04-21 23:47:06 | MASTER-Kislovodsk | (15h 57m 31.86s , +29d 48m 38.3s) | C | 60 | 18.4 | 24171 | 2025-04-21 23:48:29 | MASTER-Kislovodsk | (16h 06m 39.44s , +29d 48m 02.0s) | C | 60 | 18.5 | 24253 | 2025-04-21 23:49:51 | MASTER-Kislovodsk | (15h 58m 34.34s , +31d 42m 56.4s) | C | 60 | 18.3 | 24337 | 2025-04-21 23:51:15 | MASTER-Kislovodsk | (16h 08m 07.18s , +31d 42m 00.6s) | C | 60 | 18.2 | 24419 | 2025-04-21 23:52:37 | MASTER-Kislovodsk | (15h 58m 19.75s , +25d 59m 08.0s) | C | 60 | 18.5 | 24503 | 2025-04-21 23:54:00 | MASTER-Kislovodsk | (16h 07m 17.89s , +25d 59m 14.5s) | C | 60 | 18.3 | 24586 | 2025-04-21 23:55:24 | MASTER-Kislovodsk | (15h 57m 24.98s , +27d 54m 39.2s) | C | 60 | 18.4 | 24671 | 2025-04-21 23:56:48 | MASTER-Kislovodsk | (16h 06m 27.62s , +27d 53m 20.7s) | C | 60 | 18.4 | 24754 | 2025-04-21 23:58:11 | MASTER-Kislovodsk | (15h 57m 31.26s , +29d 48m 28.6s) | C | 60 | 18.5 | 24836 | 2025-04-21 23:59:34 | MASTER-Kislovodsk | (16h 06m 39.93s , +29d 48m 02.0s) | C | 60 | 18.1 | 24918 | 2025-04-22 00:00:56 | MASTER-Kislovodsk | (15h 58m 34.74s , +31d 42m 54.9s) | C | 60 | 18.3 | 25011 | 2025-04-22 00:02:29 | MASTER-Kislovodsk | (16h 08m 04.50s , +31d 41m 58.9s) | C | 60 | 18.3 | 25095 | 2025-04-22 00:03:52 | MASTER-Kislovodsk | (15h 58m 19.27s , +25d 59m 06.6s) | C | 60 | 18.5 | 25178 | 2025-04-22 00:05:15 | MASTER-Kislovodsk | (16h 07m 18.60s , +25d 59m 18.3s) | C | 60 | 18.4 | 25260 | 2025-04-22 00:06:37 | MASTER-Kislovodsk | (16h 14m 35.48s , +27d 53m 24.2s) | C | 60 | 18.4 | 25423 | 2025-04-22 00:09:20 | MASTER-Kislovodsk | (16h 14m 55.83s , +29d 49m 02.3s) | C | 60 | 18.5 | 25591 | 2025-04-22 00:12:08 | MASTER-Kislovodsk | (15h 58m 33.07s , +31d 40m 48.1s) | C | 60 | 18.4 | 25673 | 2025-04-22 00:13:31 | MASTER-Kislovodsk | (16h 08m 05.94s , +31d 41m 04.6s) | C | 60 | 18.4 | 25838 | 2025-04-22 00:16:16 | MASTER-Kislovodsk | (15h 49m 17.53s , +27d 54m 38.2s) | C | 60 | 18.3 | 25922 | 2025-04-22 00:17:39 | MASTER-Kislovodsk | (16h 14m 33.10s , +27d 54m 04.7s) | C | 60 | 18.4 | 26099 | 2025-04-22 00:20:37 | MASTER-Kislovodsk | (16h 15m 02.20s , +29d 47m 57.2s) | C | 60 | 18.0 | 26268 | 2025-04-22 00:23:25 | MASTER-Kislovodsk | (15h 58m 40.47s , +31d 41m 07.7s) | C | 60 | 18.4 | 26350 | 2025-04-22 00:24:47 | MASTER-Kislovodsk | (16h 08m 00.84s , +31d 42m 25.0s) | C | 60 | 18.4 | 26517 | 2025-04-22 00:27:34 | MASTER-Kislovodsk | (15h 49m 16.89s , +27d 54m 28.4s) | C | 60 | 18.3 | 26600 | 2025-04-22 00:28:57 | MASTER-Kislovodsk | (16h 14m 31.40s , +27d 53m 55.4s) | C | 60 | 18.5 | 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/40196. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38221] IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 21 Apr '25

21 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40195 SUBJECT: IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/04/21 21:07:00 GMT FROM: Giacomo Sommani at Ruhr-Universität Bochum <gsommani(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 25-04-21 at 17:06:08.07 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_BRONZE alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 1.0254 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/140824_2517159.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 25-04-21 Time: 17:06:08.07 UT RA: 240.91 (+2.62/-4.44 deg 90% PSF containment) J2000 Dec: 28.67 (+1.70/-1.70 deg 90% PSF containment) J2000 This neutrino candidate event traversed through the corner of the instrumented IceCube volume, yielding an event direction reconstruction with larger than average uncertainties. We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. There are four Fermi 4FGL-DR4 or 3FHL catalog sources in the 90% uncertainty region: 4FGL J1606.5+2717 at RA: 241.64 deg, Dec: 27.30 deg J2000 (1.51 deg away from the best-fit event position); 4FGL J1556.1+2812 at RA: 239.05 deg, Dec: 28.21 deg J2000 (1.70 deg away from the best-fit event position); and 4FGL J1555.3+2903 at RA: 238.83 deg, Dec: 29.06 deg J2000 (1.86 deg away from the best-fit event position); and 4FGL J1612.2+2828 at RA: 243.06 deg, Dec: 28.47 deg J2000 (1.90 deg away from the best-fit event position). 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/40195. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38220] IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 21 Apr '25

21 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40194 SUBJECT: IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/04/21 20:59:33 GMT FROM: Sam Hori at IceCube/U Wisc-Madison <sahori(a)wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-Cascade 250414A (https://gcn.gsfc.nasa.gov/notices_amon_icecube_cascade/140790_14362468.amon) in a time range of 1000 seconds centered on the alert event time (2025-04-14 07:38:53.610 UTC to 2025-04-14 07:55:33.610 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-Cascade 250414A. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-Cascade 250414A ranges from 1.3e-01 to 1.4e-01GeV cm^-2 in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 2e+05 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-04-13 07:47:13.610 UTC to 2025-04-15 07:47:13.610 UTC). In this case, we report a p-value of 0.41, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-Cascade 250414A ranges from 1.5e-01 to 1.6e-01 GeV cm^-2 in a 2 day time window. 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] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/40194. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38219] EP250421a: JinShan likely optical counterpart
by GCN Circulars 21 Apr '25

21 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40193 SUBJECT: EP250421a: JinShan likely optical counterpart DATE: 25/04/21 18:54:51 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> S.Y. Fu (HUST), S.Q. Jiang, J. An, Z.P. Zhu, X. Liu, D. Xu (NAOC), J.Z. Liu (XAO) report on behalf of a large collaboration: We observed the field of EP250421a (ID: 01709135179) detected by EP/WXT, using the 100cm-C telescope (100C) of the JinShan project, located at Altay, Xinjiang, China. Observations started at 16:25:07.32 UT on 2025-04-21, i.e., 8.64 min after the EP/WXT trigger, and a series of frames were obtained in the Sloan r-bands. An uncatalogued optical source is detected within the EP/WXT error circle at coordinates R.A.(J2000) = 11:29:40.80 Dec.(J2000) = -24:40:31.84 with an uncertainty of ~0.6 arcsec. The source has r ~ 20.6 mag, calibrated with nearby PanSTARRS stars and not corrected for Galactic extinction. We think the source is likely the optical counterpart of EP250421a. We acknowledge the excellent support from T.Q. Chen and Z.K. Feng for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40193. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38218] The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
by GCN Circulars 21 Apr '25

21 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40192 SUBJECT: The EP-WXT trigger 01709135179: Kinder optical counterpart candidate DATE: 25/04/21 18:39:24 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> Y.-H. Lee, A. Aryan, T.-W. Chen, W.-J. Hou (all NCU), A. K. H. Kong (NTHU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), Y. J. Yang, M.-H. Lee, Y.-C. Pan, C.-C. Ngeow, A. Sankar. K, C.-H. Lai, C.-S. Lin, H.-Y. Hsiao, H.-C. 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 EP-WXT trigger 01709135179 at the time of 2025-04-21T16:16:28.949 using the Lulin One-meter Telescope (LOT) at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86). The first LOT epoch of observations started at 16:43:39 UT on 21st of April 2025 (MJD = 60786.697), 27 minutes after the EP trigger. We detected an optical transient in the stacked frame, at RA = 11:29:40.757, Dec = -24:40:31.98 (which is 22.3 arcsec east and 26.8 arcsec north away from the reported coordinate of the EP-WXT trigger 01709135179, and within the sky localisation error of 0.05 deg). We used the Kinder pipeline (Yang et al. A&A 646, A22) to stack the images, and utilised the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, 62) to perform PSF photometry on our stacked frames The details of the observations and measured PSF magnitude (in the AB system) of the proposed counterpart of the EP-WXT trigger 01709135179 (possibly EP250421a) are as follows: Telescope | Filter | MJD | t-t0 | Exposure | Magnitude | avg. Seeing | med. Airmass LOT | r | 60786.697| 0.45 hrs | 300 sec * 6 | 21.44 +/- 0.09 | 1".15 | 3.06 The multiband observations using 40cm SLT and 1m LOT are ongoing. We encourage further follow-up observations to identify the nature of this optical counterpart candidate. We also note that at this optical counterpart position, a very faint, uncatalogued, extended source is visible in the DESI Legacy Survey image. A visual comparison with nearby objects suggests it is likely fainter than r > 24 mag. This faint, extended source could be the host of the transient. The presented magnitudes are calibrated using the field stars from the Pan-STARRS1 catalog and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_r = 0.15 mag in the direction of the transient (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/40192. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38217] GRB 250421A: Fermi GBM Final Real-time Localization
by GCN Circulars 21 Apr '25

21 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40191 SUBJECT: GRB 250421A: Fermi GBM Final Real-time Localization DATE: 25/04/21 10:48:59 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 10:38:31 UT on 21 Apr 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250421A (trigger 766924716.344264 / 250421443). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 249.1, Dec = -59.9 (J2000 degrees, equivalent to J2000 16h 36m, -59d 53'), with a statistical uncertainty of 3.8 degrees. The angle from the Fermi LAT boresight is 103.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250421443/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250421443/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250421443/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40191. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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