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

[vsnet-grb-info 38186] EP250416a: Gemini South-GMOS optical counterpart
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40160 SUBJECT: EP250416a: Gemini South-GMOS optical counterpart DATE: 25/04/17 10:42:52 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> Andrew J. Levan (Radboud), Jonathan Quirola-Vásquez (Radboud), Peter G. Jonker (Radboud), Franz E. Bauer (UTA), Antonio Martin-Carrillo (UCD), Daniele B. Malesani (DAWN/ NBI and Radboud), Javi Sánchez-Sierras (Radboud), Agnes van Hoof (Radboud), Jennifer Chacon (PUC), Joyce van Dalen (Radboud), Gregory Corcoran (UCD) report on behalf of a larger collaboration: We observed the field of the Einstein Probe (EP) transient EP250416a (Zhao et al., GCN 40154) using the Gemini South-GMOS in imaging mode located on Cerro Pachón, Chile. Photometric observations started at 2025-04-17 06:51:03 UTC (i.e., ~0.54 days after the EP detection), consisting of 4 exposures of 60 s each, carried out using filter r'. Consistent with the position of the X-ray source detected by XRT (target ID 19721, PI J. Kennea; https://www.swift.ac.uk/EP/) and the EP/FXT localization, we notice a source at coordinates measured from the WCS-calibrated Gemini image: RA = 17:05:40.83 Dec = +25:46:31.5 This source had magnitude r = 22.8 +/- 0.1 (AB), calibrated against the Pan-STARRS objects in the field. An underlying, fainter source is catalogued in the Legacy Survey (DR10; Dey et al. 2019), with a quoted magnitude of r = 23.16 and photometric redshift of 0.72+-0.24 (Zhou et al. 2021). Based on the position and brighter magnitude relative to the previously catalogued object, we conclude that the source is very likely the optical counterpart of EP250416a. We acknowledge excellent support from the Gemini South staff. View this GCN Circular online at https://gcn.nasa.gov/circulars/40160. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38185] EP250225a: SVOM/VT optical brightening
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40159 SUBJECT: EP250225a: SVOM/VT optical brightening DATE: 25/04/17 07:50:33 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> X. H. Han(NAOC), L. Zhang(IHEP), X. L. Chen(YNU), Y. D. Hu(GXU), L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. Xu, P. P. Zhang, W. J. Xie, J. Wang, Y. J. Xiao, H. B. Cai, L. Lan, J. Y. Wei (NAOC) report on behalf of the SVOM mission team. SVOM/VT conducted ToO follow-up observations of the fast X-ray transient EP250225a (Jiang et al., GCN 39475). The observation started on 2025 Feb 26 09:37:03 UT in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. The candidate (Malesani et al., GCN 39516; Malesani et al., GCN 39573) was clearly detected in stacked images of both channels. The brightness in AB magnitude was estimated to be: Mid time (hour) | Band | Exposure Time (second) | Magnitude | Magnitude error 21.80 | VT_B | 3000 | 22.31 | 0.13 21.80 | VT_R | 3000 | 21.50 | 0.10 The source was brightening with about 0.4 mag within 3.3 hours in both channels during our observations. This result is consistent with the report of the brightening compared with the archival brightness in the Legacy survey (Malesani et al., GCN 39516). The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/40159. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38184] SVOM/sb25041603 is not a GRB
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40158 SUBJECT: SVOM/sb25041603 is not a GRB DATE: 25/04/17 07:50:32 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> P. Maggi (ObAS), D. Götz (CEA), H. Goto (Kanazawa University/CEA), M. Moita (CEA), C. Plasse (CEA), F. Robinet (IJCLab), C. Van Hove (IJCLab) report of behalf of the SVOM/MXT Team: SVOM/ECLAIRs triggered on the X-ray transient labelled sb25041603 (SVOM burst-id sb25041603, Wang et al. GCN 40147). The field was observed by SVOM/MXT starting at T0 = 2025-04-16T08:57:43 (2.5 hour after trigger time Tb). MXT observed during 3 orbits for 3.0 ks effective exposure. Using the full X-band dataset, we find a source located at RA=183.889, Dec=52.6534 RA (J2000) = 12h15m33 Dec (J2000) = +52d39m12.3 with a statistical 90% C.L. radius of 39", to which a 35” systematic uncertainty is to be added in quadrature. That position matches the M4V star [StKM 2-809](https://simbad.cds.unistra.fr/simbad/sim-id?Ident=%40568434&Name=StKM%202-809), and exclude the potential counterparts V* EG UMa and 2MASS J12161363+5242459 mentioned in GCN 40147. The spectrum is modelled by an absorbed thermal component with a Gaussian distribution of emission measure (`Tbabs*gadem` in xspec). The absorption column is NH = 5 (<10) x 1e20 /cm2 (90% C.L. uncertainties) and a broad distribution of temperature with a mean value of 2.7 (+/- 0.8) keV. The observed average flux in the 0.3-5 keV band is 2.2 (+/-0.4) x1e-11 erg/cm2/s. At the parallactic distance of 25 pc of StKM 2-809, this translates to a luminosity of 1.6e30 erg/s, consistent with a flare from a low-mass main sequence star. Over the 3 orbits the source was fading, from 3.1e-11 erg/cm2/s in the first half to 0.3e-11 erg/cm2/s in the second half. We conclude that SVOM/sb25041603 is likely not a GRB but a flare from the M4V star StKM 2-809. The Space 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. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE. The SVOM point of contact for this trigger is Ziqi Wang (zq.wang(a)st.gxu.edu.cn). Please contact the BA by email if you require additional information regarding the SVOM follow-up of this trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40158. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38183] EP250416a: GSP optical upper limit
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40157 SUBJECT: EP250416a: GSP optical upper limit DATE: 25/04/17 06:06:13 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> W. X. Li, S. J. Xue (NAOC), M. Andrews, J. Farah, D. A. Howell, M. Newsome, E. Padilla Gonzalez, C. McCully, and G. Terreran (Las Cumbres Observatory), on behalf of a larger collaboration, report: Following the detection of the fast X-ray transient EP250416a by the Einstein Probe (Zhao et al., GCN 40154), we initiated observations of its location starting on 2025 April 17th at 01:43 UT (~8 hours after the EP/WXT trigger) in the i band. These observations were conducted using the 1-meter telescope at the Las Cumbres Observatory node located at Siding Spring Observatory in Australia. No new optical source was detected in the co-added images within the EP/FXT error box down to ~20 mag. These observations were taken as part of the Global Supernova Project. View this GCN Circular online at https://gcn.nasa.gov/circulars/40157. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38182] EP250416a: Global MASTER-Net observations report
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40156 SUBJECT: EP250416a: Global MASTER-Net observations report DATE: 25/04/17 05:18:32 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 EP250416a ( EP Team et al., GCN 40154) errorbox 3581 sec after notice time and 37096 sec after trigger time at 2025-04-17 04:12:15 UT, with upper limit up to 18.2 mag. The observations began at zenith distance = 79 deg. The sun altitude is -68.8 deg. The galactic latitude b = 33 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=2845513 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 37127 | 2025-04-17 04:12:15 | MASTER-OAFA | (17h 05m 52.87s , +25d 40m 55.7s) | C | 60 | 16.5 | 37187 | 2025-04-17 04:12:15 | MASTER-OAFA | (17h 05m 52.85s , +25d 40m 55.5s) | C | 180 | 17.7 | Coadd 37590 | 2025-04-17 04:19:58 | MASTER-OAFA | (17h 05m 56.72s , +25d 41m 13.9s) | C | 60 | 17.3 | 38093 | 2025-04-17 04:28:21 | MASTER-OAFA | (17h 06m 00.04s , +25d 40m 57.5s) | C | 60 | 17.5 | 38511 | 2025-04-17 04:35:20 | MASTER-OAFA | (17h 05m 58.06s , +25d 40m 40.2s) | C | 60 | 17.7 | 39442 | 2025-04-17 04:50:50 | MASTER-OAFA | (17h 06m 00.53s , +25d 42m 42.8s) | C | 60 | 18.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40156. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38181] Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40155 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB DATE: 25/04/17 04:59:28 GMT FROM: Lorenzo Scotton at UAH <lscottongcn(a)outlook.com> L. Scotton (UAH) and O. Mukherjee (USRA) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 766505186/250416588 at 14:06:21.40 UT on 16 April 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to distant particles." View this GCN Circular online at https://gcn.nasa.gov/circulars/40155. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38180] EP250416a: Einstein Probe detection of an X-ray transient
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40154 SUBJECT: EP250416a: Einstein Probe detection of an X-ray transient DATE: 25/04/17 03:08:20 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> G.Y. Zhao (SYSU), C. Zhou (HUST), X.L. Chen, K. Chatterjee (YNU), H. Zhou (PMO, CAS) and C.C. Jin (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 EP250416a. The transient triggered EP-WXT (ID: 01709135021) at 2025-04-16T17:53:59 (UTC). The WXT position of the source is R.A. = 256.402 deg, DEC = 25.768 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 256.4228 deg, DEC = 25.7755 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/40154. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38179] IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 16 Apr '25

16 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40153 SUBJECT: IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/04/16 20:17:54 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 25-04-16 at 18:32:14.97 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 2.3036 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/140799_37236133.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 25-04-16 Time: 18:32:14.97 UT RA: 83.1 (+0.57/-0.58 deg 90% PSF containment) J2000 Dec: 15.64 (+0.49/-0.5 deg 90% PSF containment) J2000 We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of the event. 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/40153. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38178] IceCube Alert 250416.77: Global MASTER-Net observations report
by GCN Circulars 16 Apr '25

16 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40152 SUBJECT: IceCube Alert 250416.77: Global MASTER-Net observations report DATE: 25/04/16 18:39:53 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-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) was pointed to the IceCube Alert 250416.77 (trigger No 37236133,05h 32m 21.84s , +15d 26m 27.6s, R=0.51) errorbox 18 sec after notice time and 81 sec after trigger time at 2025-04-16 18:33:36 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 75 deg. The sun altitude is -29.8 deg. The galactic latitude b = -9 deg., longitude l = 190 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2845236 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 92 | 2025-04-16 18:33:36 | MASTER-SAAO | (05h 31m 59.71s , +15d 20m 12.0s) | C | 20 | 17.0 | 131 | 2025-04-16 18:34:15 | MASTER-SAAO | (05h 32m 00.24s , +15d 20m 15.4s) | C | 20 | 17.0 | 175 | 2025-04-16 18:34:54 | MASTER-SAAO | (05h 32m 00.81s , +15d 20m 18.5s) | C | 30 | 17.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40152. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38177] IceCube Alert 250416.77: Global MASTER-Net observations report
by GCN Circulars 16 Apr '25

16 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40152 SUBJECT: IceCube Alert 250416.77: Global MASTER-Net observations report DATE: 25/04/16 18:39:53 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-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) was pointed to the IceCube Alert 250416.77 (trigger No 37236133,05h 32m 21.84s , +15d 26m 27.6s, R=0.51) errorbox 18 sec after notice time and 81 sec after trigger time at 2025-04-16 18:33:36 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 75 deg. The sun altitude is -29.8 deg. The galactic latitude b = -9 deg., longitude l = 190 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2845236 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 92 | 2025-04-16 18:33:36 | MASTER-SAAO | (05h 31m 59.71s , +15d 20m 12.0s) | C | 20 | 17.0 | 131 | 2025-04-16 18:34:15 | MASTER-SAAO | (05h 32m 00.24s , +15d 20m 15.4s) | C | 20 | 17.0 | 175 | 2025-04-16 18:34:54 | MASTER-SAAO | (05h 32m 00.81s , +15d 20m 18.5s) | C | 30 | 17.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40152. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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