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[vsnet-grb-info 38641] GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
by GCN Circulars 02 Jun '25

02 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40605 SUBJECT: GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry DATE: 25/06/02 15:01:40 GMT FROM: James Gillanders at University of Oxford <jhgillanders.astro(a)gmail.com> J. H. Gillanders (Oxford), M. Huber, K. C. Chambers (IfA, Univ. Hawaii), S. J. Smartt, K. W. Smith, (Oxford/QUB), S. Srivastav (Oxford), M. Nicholl, D. Young, M. Fulton (QUB), T.-W. Chen (NCU, Taiwan) A. S. B. Schultz, T. de Boer, J. Fairlamb, G. Paek, C. C. Lin, T. Lowe, E. Magnier, P. Minguez, I. A. Smith, R. J. Wainscoat (IfA, Univ. Hawaii). We observed the fast-fading transient AT2025mgj (Andreoni et al., GCN 40566), tentatively associated with the short-GRB 250521C (Fermi GBM Team, GCN 40515) using the Pan-STARRS telescope system (Chambers et al., 2016, arXiv e-prints, 1612.05560) on MJDs 60825.26 and 60827.26 (approximately 8.7 and 10.7 days post-GRB, respectively). The Pan-STARRS system consists of two 1.8m telescope units located at the summit of Haleakala on the Hawaiian island of Maui, employing an SDSS-like filter system denoted as grizy, and a broad w-filter, which is a composite of the gri-filters. Our observations consisted of 120s (MJD 60825.26) and 200s exposures (MJD 60827.26) in grizy-bands. All images were processed with the Pan-STARRS pipeline. After astrometric and photometric calibration, reference images were subtracted from the target images (Magnier et al., 2020a, ApJS, 251, 3; Magnier et al., 2020b, ApJS, 251, 6; Waters et al., 2020, ApJS, 251, 4). From these difference images, we recover the following photometry measurements: MJD Filter AB mag 60825.26 g 18.97 +/- 0.06 60825.26 r 19.18 +/- 0.08 60825.26 i 19.29 +/- 0.08 60825.26 z 19.5 +/- 0.2 60827.26 g 19.29 +/- 0.05 60827.26 r 19.39 +/- 0.06 60827.26 i 19.62 +/- 0.06 60827.26 z 19.57 +/- 0.08 From our multi-band Pan-STARRS photometry, we estimate a fade rate of ~0.1 mag/day in r-band. Our rate of fading across our photometric bands match those reported previously by Martin-Carrillo et al. (GCN 40584), Becerra et al. (GCN 40590), and Busmann et al. (GCN 40597). The rate of fading and persistent blue colour, with some indication of cooling, are all reminiscent of typical CV behaviour. While the connection to GRB 250521C cannot be definitively ruled out, the data match the lightcurve behaviour of CVs. Late-time, deep imaging is required to unambiguously uncover the nature of AT2025mgj. A point source would confirm AT2025mgj is indeed a CV, whereas an extended source in its vicinity would indicate that it was the afterglow of GRB 250521C. View this GCN Circular online at https://gcn.nasa.gov/circulars/40605. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38640] GRB 250601A: Swift-XRT observations
by GCN Circulars 02 Jun '25

02 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40604 SUBJECT: GRB 250601A: Swift-XRT observations DATE: 25/06/02 08:18:00 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Swift/BAT-detected burst GRB 250601A, collecting 4.6 ks of Photon Counting (PC) mode data between T0+17.2 ks and T0+35.3 ks. Two uncatalogued X-ray sources have been detected within the estimated 3-sigma Swift/BAT error region (493 arcsec), however none of them is above the RASS limit or shows definitive signs of fading. Therefore, at the present time we cannot identify which, if any, is the afterglow. Details of these sources are given below: Source 2: RA (J2000.0): 90.2023 = 06:00:48.56 Dec (J2000.0): -57.2379 = -57:14:16.6 Error: 7.3 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: (7.8 +/- 1.9)e-3 ct s^-1 Distance: 315 arcsec from Swift/BAT position. Flux: (4.2 +/- 1.0)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 3: RA (J2000.0): 90.0936 = 06:00:22.47 Dec (J2000.0): -57.2778 = -57:16:40.0 Error: 5.7 arcsec (radius, 90% conf.) Count-rate: (3.6 [+1.6, -1.3])e-3 ct s^-1 Distance: 60 arcsec from Swift/BAT position. Flux: (1.00 [+0.45, -0.35])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Another uncatalogued source was also detected, however this was too far from the GRB position to be the afterglow. 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/ToO_GRBs/00021844. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40604. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38639] Fermi GRB 250601A: Global MASTER-Net observations report
by GCN Circulars 02 Jun '25

02 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40603 SUBJECT: Fermi GRB 250601A: Global MASTER-Net observations report DATE: 25/06/02 04:45:45 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 250601A ( Fermi GBM team, GCN 40596) errorbox 31266 sec after notice time and 31297 sec after trigger time at 2025-06-02 02:11:13 UT, with upper limit up to 18.8 mag. The observations began at zenith distance = 80 deg. The sun altitude is -41.7 deg. The galactic latitude b = -31 deg., longitude l = 264 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2888853 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 31328 | 2025-06-02 02:11:13 | MASTER-SAAO | (05h 23m 33.62s , -61d 25m 21.7s) | C | 60 | 18.1 | 31328 | 2025-06-02 02:11:13 | MASTER-SAAO | (05h 27m 12.25s , -61d 40m 47.0s) | C | 60 | 16.8 | 32079 | 2025-06-02 02:23:44 | MASTER-SAAO | (05h 23m 32.93s , -61d 25m 26.3s) | C | 60 | 18.2 | 32079 | 2025-06-02 02:23:44 | MASTER-SAAO | (05h 27m 11.81s , -61d 40m 51.9s) | C | 60 | 16.9 | 32832 | 2025-06-02 02:36:17 | MASTER-SAAO | (05h 23m 35.76s , -61d 24m 34.2s) | C | 60 | 18.2 | 32832 | 2025-06-02 02:36:17 | MASTER-SAAO | (05h 27m 14.94s , -61d 39m 58.9s) | C | 60 | 16.9 | 32926 | 2025-06-02 02:37:51 | MASTER-SAAO | (05h 01m 57.98s , -57d 37m 48.3s) | C | 60 | 18.3 | 32926 | 2025-06-02 02:37:51 | MASTER-SAAO | (05h 05m 13.56s , -57d 53m 13.1s) | C | 60 | 16.9 | 33492 | 2025-06-02 02:47:17 | MASTER-SAAO | (05h 23m 29.69s , -61d 25m 33.6s) | C | 60 | 18.3 | 33492 | 2025-06-02 02:47:17 | MASTER-SAAO | (05h 27m 09.27s , -61d 40m 57.8s) | C | 60 | 16.9 | 33586 | 2025-06-02 02:48:51 | MASTER-SAAO | (05h 01m 58.51s , -57d 38m 06.3s) | C | 60 | 18.6 | 33586 | 2025-06-02 02:48:51 | MASTER-SAAO | (05h 05m 14.44s , -57d 53m 30.3s) | C | 60 | 17.1 | 33679 | 2025-06-02 02:50:24 | MASTER-SAAO | (05h 17m 04.95s , -57d 38m 12.0s) | C | 60 | 18.3 | 33679 | 2025-06-02 02:50:24 | MASTER-SAAO | (05h 20m 20.73s , -57d 53m 36.1s) | C | 60 | 17.0 | 34244 | 2025-06-02 02:59:49 | MASTER-SAAO | (05h 23m 26.94s , -61d 25m 56.2s) | C | 60 | 18.2 | 34348 | 2025-06-02 03:01:33 | MASTER-SAAO | (05h 01m 56.88s , -57d 38m 26.6s) | C | 60 | 18.6 | 34348 | 2025-06-02 03:01:33 | MASTER-SAAO | (05h 05m 13.07s , -57d 53m 50.3s) | C | 60 | 17.2 | 34441 | 2025-06-02 03:03:06 | MASTER-SAAO | (05h 17m 02.63s , -57d 38m 31.9s) | C | 60 | 18.3 | 34441 | 2025-06-02 03:03:06 | MASTER-SAAO | (05h 20m 18.63s , -57d 53m 56.0s) | C | 60 | 17.0 | 35007 | 2025-06-02 03:12:32 | MASTER-SAAO | (05h 23m 27.32s , -61d 26m 18.0s) | C | 60 | 18.4 | 35101 | 2025-06-02 03:14:06 | MASTER-SAAO | (05h 01m 55.99s , -57d 38m 46.4s) | C | 60 | 18.6 | 35101 | 2025-06-02 03:14:06 | MASTER-SAAO | (05h 05m 12.55s , -57d 54m 10.0s) | C | 60 | 17.2 | 35194 | 2025-06-02 03:15:39 | MASTER-SAAO | (05h 17m 02.39s , -57d 38m 52.0s) | C | 60 | 18.4 | 35194 | 2025-06-02 03:15:39 | MASTER-SAAO | (05h 20m 18.72s , -57d 54m 16.2s) | C | 60 | 17.0 | 35288 | 2025-06-02 03:17:13 | MASTER-SAAO | (05h 02m 24.56s , -54d 08m 10.8s) | C | 60 | 17.0 | 35381 | 2025-06-02 03:18:46 | MASTER-SAAO | (05h 12m 59.55s , -53d 50m 37.6s) | C | 60 | 18.5 | 35381 | 2025-06-02 03:18:46 | MASTER-SAAO | (05h 15m 57.34s , -54d 06m 02.3s) | C | 60 | 16.7 | 35661 | 2025-06-02 03:23:26 | MASTER-SAAO | (05h 11m 01.98s , -51d 56m 40.6s) | C | 60 | 18.5 | 35661 | 2025-06-02 03:23:26 | MASTER-SAAO | (05h 13m 52.04s , -52d 12m 05.7s) | C | 60 | 16.8 | 35757 | 2025-06-02 03:25:02 | MASTER-SAAO | (05h 01m 55.75s , -57d 41m 01.1s) | C | 60 | 18.6 | 35757 | 2025-06-02 03:25:02 | MASTER-SAAO | (05h 05m 12.76s , -57d 56m 25.1s) | C | 60 | 17.3 | 35851 | 2025-06-02 03:26:36 | MASTER-SAAO | (05h 17m 02.21s , -57d 39m 55.6s) | C | 60 | 18.5 | 35851 | 2025-06-02 03:26:36 | MASTER-SAAO | (05h 20m 18.88s , -57d 55m 20.0s) | C | 60 | 17.2 | 36038 | 2025-06-02 03:29:43 | MASTER-SAAO | (05h 12m 58.98s , -53d 52m 22.2s) | C | 60 | 18.4 | 36038 | 2025-06-02 03:29:43 | MASTER-SAAO | (05h 15m 56.70s , -54d 07m 48.0s) | C | 60 | 17.0 | 36318 | 2025-06-02 03:34:23 | MASTER-SAAO | (05h 11m 01.70s , -51d 56m 54.3s) | C | 60 | 18.7 | 36318 | 2025-06-02 03:34:23 | MASTER-SAAO | (05h 13m 51.53s , -52d 12m 20.2s) | C | 60 | 17.0 | 36411 | 2025-06-02 03:35:56 | MASTER-SAAO | (05h 24m 08.15s , -51d 57m 10.8s) | C | 60 | 18.4 | 36411 | 2025-06-02 03:35:56 | MASTER-SAAO | (05h 26m 57.92s , -52d 12m 36.4s) | C | 60 | 17.0 | 36504 | 2025-06-02 03:37:29 | MASTER-SAAO | (05h 05m 10.11s , -57d 56m 43.4s) | C | 60 | 17.4 | 36504 | 2025-06-02 03:37:29 | MASTER-SAAO | (05h 01m 53.17s , -57d 41m 19.2s) | C | 60 | 18.7 | 36597 | 2025-06-02 03:39:02 | MASTER-SAAO | (05h 20m 17.51s , -57d 55m 46.9s) | C | 60 | 17.3 | 36597 | 2025-06-02 03:39:02 | MASTER-SAAO | (05h 17m 00.88s , -57d 40m 22.3s) | C | 60 | 18.6 | 36784 | 2025-06-02 03:42:09 | MASTER-SAAO | (05h 15m 55.94s , -54d 07m 49.4s) | C | 60 | 17.0 | 36784 | 2025-06-02 03:42:09 | MASTER-SAAO | (05h 12m 57.97s , -53d 52m 23.8s) | C | 60 | 18.6 | 36973 | 2025-06-02 03:45:18 | MASTER-SAAO | (05h 04m 12.35s , -56d 01m 02.3s) | C | 60 | 17.5 | 36973 | 2025-06-02 03:45:18 | MASTER-SAAO | (05h 01m 05.36s , -55d 45m 37.7s) | C | 60 | 18.8 | 37066 | 2025-06-02 03:46:51 | MASTER-SAAO | (05h 13m 57.11s , -52d 13m 36.4s) | C | 60 | 17.2 | 37066 | 2025-06-02 03:46:51 | MASTER-SAAO | (05h 11m 06.80s , -51d 58m 10.9s) | C | 60 | 18.7 | 37159 | 2025-06-02 03:48:24 | MASTER-SAAO | (05h 26m 51.17s , -52d 13m 53.2s) | C | 60 | 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/40603. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38638] GRB 250602A: Fermi GBM Final Real-time Localization
by GCN Circulars 02 Jun '25

02 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40602 SUBJECT: GRB 250602A: Fermi GBM Final Real-time Localization DATE: 25/06/02 03:14:49 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 LONG GRB At 03:04:31 UT on 2 Jun 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250602A (trigger 770526276.307432 / 250602128). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 111.7, Dec = 67.8 (J2000 degrees, equivalent to J2000 07h 26m, 67d 47'), with a statistical uncertainty of 4.9 degrees. The angle from the Fermi LAT boresight is 111.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250602128/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250602128/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250602128/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40602. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38637] Fermi trigger No 770470765: Global MASTER-Net observations report
by GCN Circulars 02 Jun '25

02 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40601 SUBJECT: Fermi trigger No 770470765: Global MASTER-Net observations report DATE: 25/06/02 00:48:11 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB250601.49 (trigger No 770470765,03h 02m 00.00s , -51d 57m 00.0s, R=11.63) errorbox 43681 sec after notice time and 43715 sec after trigger time at 2025-06-01 23:47:55 UT, with upper limit up to 19.0 mag. The observations began at zenith distance = 80 deg. The sun altitude is -71.3 deg. The galactic latitude b = -55 deg., longitude l = 267 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2888592 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 43745 | 2025-06-01 23:47:55 | MASTER-SAAO | (01h 44m 18.74s , -52d 18m 33.7s) | C | 60 | 16.4 | 43745 | 2025-06-01 23:47:55 | MASTER-SAAO | (01h 41m 30.62s , -52d 03m 14.0s) | C | 60 | 18.7 | 44762 | 2025-06-02 00:04:51 | MASTER-SAAO | (01h 44m 12.09s , -52d 18m 24.7s) | C | 60 | 16.8 | 44762 | 2025-06-02 00:04:51 | MASTER-SAAO | (01h 41m 22.46s , -52d 02m 58.5s) | C | 60 | 18.8 | 45994 | 2025-06-02 00:25:24 | MASTER-SAAO | (01h 44m 18.84s , -52d 18m 56.3s) | C | 60 | 17.2 | 45994 | 2025-06-02 00:25:24 | MASTER-SAAO | (01h 41m 28.06s , -52d 03m 32.4s) | C | 60 | 19.0 | 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/40601. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38636] GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
by GCN Circulars 01 Jun '25

01 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40600 SUBJECT: GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst DATE: 25/06/01 22:21:42 GMT FROM: Samuele Ronchini at PSU <sjs8171(a)psu.edu> James DeLaunay (PSU), Samuele Ronchini (PSU), Aaron Tohuvavohu (Caltech), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report: Swift/BAT did not localize GRB 250601A onboard (T0: 2025-06-01T17:29:35.54 UTC, Fermi GCN 40596). The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground. The position is found with standard imaging, with an SNR = 8.7. The duration of the burst is ~1 sec. The BAT position is RA, Dec = 90.0709, -57.2892 deg which is RA(J2000) = 06h 00m 17.02s Dec(J2000) = -57d 17’ 21.1″ with an estimated uncertainty of 3 arcmin radius. More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=770491811 XRT and UVOT follow-up has been requested. Results of follow-up observations will be reported in future circulars. GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/ View this GCN Circular online at https://gcn.nasa.gov/circulars/40600. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38635] GRB 250601A: Swift ToO observations
by GCN Circulars 01 Jun '25

01 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40599 SUBJECT: GRB 250601A: Swift ToO observations DATE: 25/06/01 22:17:16 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a ToO observation of the Swift/BAT-detected event GRB 250601A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021844 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Swift/BAT event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration. Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40599. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38634] GRB 250530A: VLT/HAWK-I NIR counterpart fading
by GCN Circulars 01 Jun '25

01 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40598 SUBJECT: GRB 250530A: VLT/HAWK-I NIR counterpart fading DATE: 25/06/01 19:26:39 GMT FROM: Ben Rayson at University of Leicester <br155(a)leicester.ac.uk> B. C. Rayson (Leicester), B. Schneider (LAM), P. D'Avanzo (INAF-OAB), A. Saccardi (CEA/Irfu), G. Corcoran (UCD), B. P. Gompertz (U. Birmingham), N. Habeeb (Leicester), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), G. Pugliese (API), N. R. Tanvir (Leicester) report on behalf of the Stargate collaboration: We observed the near-infrared source reported by D'Avanzo et al. (GCN 40588), a candidate afterglow of GRB 250530A detected by SVOM/ECLAIRs (Wang et al., GCN 40576). We used the ESO VLT UT4 (Yepun) equipped with the HAWK-I near-infrared camera. We obtained a 20 min exposure in the J band, starting at 23:17:32 UT on 2025-05-31, i.e. 1.7 days after the SVOM trigger. The near-infrared source is well detected in our image and we measured J = 21.65 +/- 0.10 mag (Vega), calibrated against the 2MASS catalogue. Compared with the value reported by D'Avanzo et al. (GCN 40588), our measurement indicates fading of the counterpart with a power-law decay index of ~0.6. This confirms the source as the NIR afterglow of GRB 250530A. As noted by D'Avanzo et al. (GCN 40588), this source is consistent with a catalogued source reported in the Legacy Survey. This is the likely GRB host, therefore, the red colors and the optical faintness (Li et al., GCN 40582) are likely due to dust extinction rather than high redshift - as also confirmed by the large column density measured in the X-ray spectrum (Evans et al., GCN 40579; see also: https://www.swift.ac.uk/SVOM/SVOM_FIELD00017/Source1.php). We acknowledge excellent support from the ESO observing staff in Paranal, in particular Thallis Pessi, Israel Blanchard, Miguel Lopez & Aaron Labdon View this GCN Circular online at https://gcn.nasa.gov/circulars/40598. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38633] GRB 250521C/AT2025mgj: FTW optical and NIR observations
by GCN Circulars 01 Jun '25

01 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40597 SUBJECT: GRB 250521C/AT2025mgj: FTW optical and NIR observations DATE: 25/06/01 18:58:47 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU), and Antonella Palmese (Carnegie Mellon U.) report: We observed the candidate counterpart AT2025mgj (Andreoni et al., GCN 40566; Martin-Carrillo et al., GCN 40584; Becerra et al., GCN 40590) of GRB 250521C (Fermi GBM team, GCN 40515) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 10 x 180 s starting at 2025-05-30T20:31:19 UT (9.3 days after the GRB trigger). We detect the source at r = (19.28 +/- 0.01) mag i = (19.45 +/- 0.02) mag J = (20.03 +/- 0.07) mag. We note that the blue color is inconsistent with an afterglow origin, despite the similar power law temporal decay (Martin-Carrillo et al., GCN 40584; Becerra et al., GCN 40590). The source is therefore unlikely to be associated to GRB 250521C. The most likely origin in a Cataclysmic Variable (CV) as noted by Andreoni et al. (GCN 40566). However, given the coincidence with GRB 250521C, we encourage additional observations to conclusively determine the nature of this transient. The r and i band magnitudes are calibrated against the PS1 catalog and the J band is calibrated with the 2MASS Catalog. All magnitudes are provided in the AB system and are not corrected for Galactic extinction. We thank Michael Schmidt from the Wendelstein Observatory staff for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40597. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38632] GRB 250601A: Fermi GBM Final Real-time Localization
by GCN Circulars 01 Jun '25

01 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40596 SUBJECT: GRB 250601A: Fermi GBM Final Real-time Localization DATE: 25/06/01 17:40:08 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 17:29:35 UT on 1 Jun 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250601A (trigger 770491780.538054 / 250601729). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 86.5, Dec = -55.7 (J2000 degrees, equivalent to J2000 05h 46m, -55d 42'), with a statistical uncertainty of 4.5 degrees. The angle from the Fermi LAT boresight is 23.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250601729/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250601729/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250601729/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40596. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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