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

[vsnet-grb-info 39913] GRB 250916A: GOTO optical counterpart candidate
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41847 SUBJECT: GRB 250916A: GOTO optical counterpart candidate DATE: 25/09/17 06:44:08 GMT FROM: Sergey Belkin at Monash University <sergey.belkin(a)monash.edu> S. Belkin, D. O'Neill, B. P. Gompertz, R. Starling, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, A. Kumar, M. Pursiainen, report on behalf of GOTO collaboration: We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to GRB 250916A (Fermi GBM team, GCN 41839; Arya et al., GCN 41843). Targeted observations were performed beginning at 2025-09-16 23:39:53 UT (+10.18h post trigger) and continued through to 2025-09-17 04:55:45 UT (+15.44h post trigger). 211 images were taken, across 10 unique pointings, covering 422.1 sq deg within the 90% localisation contour. ~68.1% of the total 2D localisation probability was covered, with an average 5-sigma depth of 20.0 mag. Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks. A new optical source, GOTO25hed, is identified within the GBM 90% localisation region with coordinates (J2000) RA = 26.570161, DEC = 36.16543. The source was initially detected with magnitude L = 18.90 ± 0.11 AB mag (+10.43h post trigger), before fading to L = 19.28 ± 0.12 AB mag (+14.47h post trigger). In total, the source was detected 3 times in our observations. The observed decay rate across the 4 hours our observations span is ~t^(-1.05±0.03). ATLAS forced photometry (Shingles et al. 2021) reveals a non-detection down to a 5-sigma upper limit of o > 19.6 AB mag at 2025-09-16 11:50:38 UT (-1.65h before trigger). We find no evidence of the source prior to the GRB trigger time in previous GOTO or ATLAS observations. A summary of our observations is presented below. +-----------------------------------------------------------------------------+ | Observation time (UT) | t-t0 | filter | AB mag | +-----------------------------------------------------------------------------+ | 2025-09-15 05:57:16 | -31.53h | L | >19.00 | | 2025-09-16 23:55:24 | +10.43h | L | 18.90 ± 0.11 | | 2025-09-17 02:49:13 | +13.33h | L | 19.17 ± 0.07 | | 2025-09-17 03:57:43 | +14.47h | L | 19.28 ± 0.12 | +-----------------------------------------------------------------------------+ 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/41847. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39912] GRB 250917B: Fermi GBM Final Real-time Localization
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41846 SUBJECT: GRB 250917B: Fermi GBM Final Real-time Localization DATE: 25/09/17 06:38:07 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 SHORT GRB At 06:27:44 UT on 17 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250917B (trigger 779783269.329994 / 250917269). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 275.0, Dec = 29.0 (J2000 degrees, equivalent to J2000 18h 19m, 29d 00'), with a statistical uncertainty of 6.2 degrees. The angle from the Fermi LAT boresight is 25.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250917269/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250917269/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250917269/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41846. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39911] GRB 250917A: Fermi GBM Final Real-time Localization
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41845 SUBJECT: GRB 250917A: Fermi GBM Final Real-time Localization DATE: 25/09/17 02:23:49 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 SHORT GRB At 02:13:13 UT on 17 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250917A (trigger 779767998.991126 / 250917093). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 14.5, Dec = -44.6 (J2000 degrees, equivalent to J2000 00h 58m, -44d 36'), with a statistical uncertainty of 21.8 degrees. The angle from the Fermi LAT boresight is 28.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250917093/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250917093/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250917093/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41845. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39910] The EP-WXT trigger 01709241037 is likely a flaring star
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41844 SUBJECT: The EP-WXT trigger 01709241037 is likely a flaring star DATE: 25/09/17 02:17:05 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> B.T. Wang (YNAO, CAS), S. Q . Jiang, W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709241037 at the time of 2025-09-16T23:34:38 (UTC), is likely a stellar flare associated with UPM J0113-5939. The estimated flux of the flare is around 6e-11 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 1.3e31 erg/s. 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/41844. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39909] GRB 250916A: AstroSat CZTI detection of a bright long burst
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41843 SUBJECT: GRB 250916A: AstroSat CZTI detection of a bright long burst DATE: 25/09/16 18:23:31 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Arya (IITB), A. Goyal (IITB), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a bright long-duration GRB 250916A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 41839), and CALET (Trig ID. 1442064382). Note that we detected the bright burst roughly 250 s after the initial fainter spike as seen in the GBM lightcurve. 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 2025-09-16 13:33:28.50 UTC. The measured peak count rate associated with the burst is 79 (+29, -4) counts/s above the background in the combined data of two quadrants (out of four), with a total of 1695 (+232, -241) counts. We caution that there is a 0.3 s readout dead time in CZT data during the burst which affects the calculated total counts. The local mean background count rate was 135 (+1, -2) counts/s. Using cumulative rates, we measure a T90 of 48 (+2, -6) 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 2025-09-16 13:33:26.00 UTC. The measured peak count rate associated with the burst is 556 (+80, -24) counts/s above the background in the combined data of all quadrants, with a total of 13048 (+742, -896) counts. The local mean background count rate was 1180 (+5, -4) counts/s. We measure a T90 of 50 (+2, -5) 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/41843. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39908] GRB 250910A: SVOM/ECLAIRs refined analysis
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41842 SUBJECT: GRB 250910A: SVOM/ECLAIRs refined analysis DATE: 25/09/16 16:03:05 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Baptiste Hubert, Nicolas Dagoneau, Stéphane Schanne (CEA), Jean-Luc Atteia (IRAP), Frédéric Piron (LUPM), Yinuo Ma, Donghua Zhao, Wenjin Xie (NAOC) Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250910A (SVOM burst-id sb25091001). The burst that triggered ECLAIRs (GCN 41769) consists of a broad structure with a duration of T90 = 22 -2/+3 s in the 4-20 keV energy band. The time-averaged spectrum from T0-15.5 s to T0+6.7 s (T0 = 2025-09-10T03:16:30) in the energy range 4-120 keV is best fitted by a power-law model with photon index 1.7 +/-0.2. With this model, the 4-120 keV flux is (2.2 -0.4/+0.2)e-08 erg/cm^2/s. All the quoted errors are at the 68% confidence level. 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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Nicolas Dagoneau (CEA) (nicolas.dagoneau at cea.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/41842. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39907] EP250916a: Einstein Probe detection of an X-ray transient
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41841 SUBJECT: EP250916a: Einstein Probe detection of an X-ray transient DATE: 25/09/16 16:02:54 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. Y. Wu (NAO, CAS), C. Y. Dai (NJU), D. Y. Li, H. W. Pan (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 through ground data analysis, designated EP250916a. The WXT position of the source is R.A. = 268.279 deg, DEC = -35.317 deg (J2000) with an uncertainty of 2.4 arcmin in radius (90% C.L. statistical and systematic), located at low Galactic latitude (l = 355.331, b = -4.634). The source was detected in three consecutive observations: the first started at 2025-09-16T03:33:13 (UTC) with a flux of ~3e-11 erg/s/cm^2; two subsequent observations, approximately 2 h and 6 h later, also detected the source with slightly higher fluxes of ~5e-11 erg/s/cm^2. As of the latest observation, the transient has persisted for ~7 hours. A preliminary spectral analysis shows that the 0.5-4 keV spectrum can be fitted by an absorbed power-law model with Galactic hydrogen column density fixed at 3.76 x 10^21 cm^-2 and a photon index of 1.1 (-/+0.8). No known X-ray sources have been found previously within the EP-WXT error circle. A stellar flare origin cannot be excluded at this stage. Follow-up observations with the Follow-up X-ray Telescope (FXT) on board EP have been scheduled, and further information will be updated when the telemetry data are 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/41841. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39906] Fermi GRB 250916A: Global MASTER-Net observations report
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41840 SUBJECT: Fermi GRB 250916A: Global MASTER-Net observations report DATE: 25/09/16 15:30:58 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 250916A ( Fermi GBM team, GCN 41839) errorbox 2134 sec after notice time and 2165 sec after trigger time at 2025-09-16 14:05:26 UT, with upper limit up to 20.8 mag. The observations began at zenith distance = 44 deg. The sun altitude is -24.7 deg. The galactic latitude b = -20 deg., longitude l = 137 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2992979 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 2196 | 2025-09-16 14:05:26 | MASTER-Tunka | (01h 01m 35.41s , +42d 32m 50.5s) | C | 60 | 20.7 | 2196 | 2025-09-16 14:05:26 | MASTER- | (01h 02m 07.93s , +42d 25m 57.0s) | C | 60 | 20.5 | 2271 | 2025-09-16 14:06:42 | MASTER-Tunka | (01h 31m 07.38s , +48d 15m 08.4s) | C | 60 | 19.6 | 2271 | 2025-09-16 14:06:42 | MASTER- | (01h 31m 43.29s , +48d 08m 17.2s) | C | 60 | 19.5 | 2825 | 2025-09-16 14:15:56 | MASTER-Tunka | (01h 01m 37.13s , +42d 32m 44.7s) | C | 60 | 20.6 | 2825 | 2025-09-16 14:15:56 | MASTER- | (01h 02m 10.56s , +42d 25m 34.6s) | C | 60 | 20.6 | 2900 | 2025-09-16 14:17:11 | MASTER-Tunka | (01h 31m 06.83s , +48d 15m 06.1s) | C | 60 | 20.2 | 2900 | 2025-09-16 14:17:11 | MASTER- | (01h 31m 43.65s , +48d 07m 58.6s) | C | 60 | 19.8 | 4244 | 2025-09-16 14:39:34 | MASTER-Tunka | (01h 17m 38.67s , +38d 43m 55.2s) | C | 60 | 19.8 | 4244 | 2025-09-16 14:39:34 | MASTER- | (01h 18m 09.42s , +38d 37m 35.4s) | C | 60 | 19.7 | 4985 | 2025-09-16 14:51:56 | MASTER-Tunka | (01h 01m 35.37s , +42d 30m 26.2s) | C | 60 | 20.7 | 4985 | 2025-09-16 14:51:56 | MASTER- | (01h 02m 11.14s , +42d 22m 49.2s) | C | 60 | 20.6 | 5059 | 2025-09-16 14:53:10 | MASTER-Tunka | (01h 31m 07.69s , +48d 15m 07.8s) | C | 60 | 20.2 | 5059 | 2025-09-16 14:53:10 | MASTER- | (01h 31m 47.54s , +48d 07m 33.5s) | C | 60 | 19.9 | 5553 | 2025-09-16 15:01:23 | MASTER-Tunka | (01h 17m 43.01s , +38d 42m 15.8s) | C | 60 | 19.8 | 5553 | 2025-09-16 15:01:23 | MASTER- | (01h 18m 15.41s , +38d 35m 49.9s) | C | 60 | 19.7 | 5775 | 2025-09-16 15:05:05 | MASTER-Tunka | (01h 01m 31.47s , +42d 30m 13.1s) | C | 60 | 20.8 | 5775 | 2025-09-16 15:05:06 | MASTER- | (01h 02m 08.39s , +42d 23m 51.2s) | C | 60 | 20.6 | 5852 | 2025-09-16 15:06:22 | MASTER-Tunka | (01h 31m 05.98s , +48d 12m 03.1s) | C | 60 | 20.3 | 5852 | 2025-09-16 15:06:22 | MASTER- | (01h 31m 46.96s , +48d 05m 44.0s) | C | 60 | 19.9 | 6285 | 2025-09-16 15:13:36 | MASTER-Tunka | (01h 17m 33.49s , +38d 39m 54.6s) | C | 60 | 19.9 | 6285 | 2025-09-16 15:13:36 | MASTER- | (01h 18m 04.22s , +38d 34m 21.2s) | C | 60 | 19.7 | 6508 | 2025-09-16 15:17:18 | MASTER-Tunka | (01h 01m 28.89s , +42d 27m 40.0s) | C | 60 | 20.7 | 6508 | 2025-09-16 15:17:18 | MASTER- | (01h 02m 05.60s , +42d 21m 48.9s) | C | 60 | 20.7 | 6582 | 2025-09-16 15:18:33 | MASTER-Tunka | (01h 31m 05.87s , +48d 12m 44.6s) | C | 60 | 19.7 | 6582 | 2025-09-16 15:18:33 | MASTER- | (01h 31m 46.70s , +48d 06m 57.1s) | C | 60 | 19.6 | 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/41840. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39905] GRB 250916A: Fermi GBM Final Real-time Localization
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41839 SUBJECT: GRB 250916A: Fermi GBM Final Real-time Localization DATE: 25/09/16 13:40:16 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 13:29:21 UT on 16 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250916A (trigger 779722166.007904 / 250916562). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 29.3, Dec = 40.3 (J2000 degrees, equivalent to J2000 01h 57m, 40d 17'), with a statistical uncertainty of 9.8 degrees. The angle from the Fermi LAT boresight is 66.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250916562/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250916562/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250916562/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41839. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39904] EP250827b: VLA Observations
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41838 SUBJECT: EP250827b: VLA Observations DATE: 25/09/16 13:27:15 GMT FROM: Genevieve Schroeder at Cornell University <genevieveschroeder(a)u.northwestern.edu> G. Schroeder (Cornell), D. A. Perley (LJMU), X. J. Hall (CMU), A. Y. Q. Ho (Cornell), Gokul Srinivasaragavan (UMD) report: We observed the location of the optical transient AT2025wkm, associated with EP250827b (Schroeder et al., GCN 41635) with the NSF’s Karl G. Jansky Very Large Array under program 25B-363 (PI Perley) on 2025 September 13 at a mid time of 13:02 UT (~17.3 days post discovery) at a mid frequency of 10 GHz (4 GHz bandwidth). Based on preliminary analysis, we detect a ~6 sigma source with a flux density of ~28 microJy. At a redshift of z = 0.120 (Sevilla et al., GCN 41639), this corresponds to a luminosity of ~1e28 erg/s/Hz. This is a factor of ~6 less luminous than the radio emission associated with SN1998bw (Kulkarni et al. Nature, 395, 663), and a factor of ~5 more luminous than the radio emission associated with SN2006aj (Soderberg et al. 2006, Nature, 442, 1014) at a similar observing frequency and epoch. If the radio emission can be attributed solely to star formation, this would indicate a radio star formation rate of ~3 Msol/year. Additional followup is planned to determine variability of the source. We thank the VLA staff for quickly approving and executing these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41838. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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