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

[vsnet-grb-info 39556] LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
by GCN Circulars 22 Aug '25

22 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41492 SUBJECT: LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz DATE: 25/08/22 11:30:51 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), A. Boye (DTU Space), L. Izzo (INAF/OAC and DARK/NBI), G. Leloudas (DTU Space), J. An (NAOC), X. Liu (NAOC), D. Xu (NAOC), M. Fraser (UCD), S. J. Brennan (MPE), J. Broe Bendsten (SDU), I. A. Koch (SDU), S. Lund Wagner (SDU), J. Magaard Knudsen (SDU), J. Hein Pedersen (SDU), J. P. U. Fynbo (DAWN/NBI), R. Holmberg Rasmussen (NOT and Aarhus), K. Valeckas (NOT and NBI), M. De Pasquale (U. Messina) report on behalf of a larger collaboration: We observed the optical transient AT2025ulz (Stein et al., GCN 41414; Busmann et al., GCN 41421; Hall et al., GCN 41433; Karambelkar et al., GCN 41436; O’Connor et al., GCN 41452; Gillanders et al., GCN 41454; Liu et al., GCN 41461; Banerjee et al., GCN 41476; Perley et al., GCN 41480), possibly connected with the GW event S250818k (LVK Collaboration, GCNs 41437, 41440), using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were started on 2025 Aug 20.875 UT (2.82 days after the GW trigger time). We adopted the filters r, i, and z (exposure times of 1200, 1200, and 1500 s, respectively). Image subtraction using the Legacy sky survey as reference reveals a transient at coordinates (J2000): RA = 15:51:54.19 Dec = +30:54:08.3 with an estimated error of < 0.5". These are consistent with the ZTF position (Stein et al., GCN 41414). The transient is located 1" southwest of the nucleus of its host galaxy, at a projected distance of 1.6 kpc (z = 0.0848; Karambelkar et al., GCN 41436; Banerjee et al., GCN 41476). Using nearby calibrators from the Legacy Survey, we obtained a provisional magnitude measurement of r = 23.2 ± 0.2 (AB), at a mean time of 2025 August 20.883 UT. We caution that we expect to refine our results after securing a deep template with the same instrument and filter. View this GCN Circular online at https://gcn.nasa.gov/circulars/41492. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39555] EP250821a: Swift/UVOT further observations.
by GCN Circulars 22 Aug '25

22 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41491 SUBJECT: EP250821a: Swift/UVOT further observations. DATE: 25/08/22 09:44:34 GMT FROM: Samantha Oates at University of Birmingham <samantha.oates(a)alumni.ucl.ac.uk> S. R. Oates (Lancaster U.) and S. Dichiara (PSU) report on behalf of the Swift-XRT and Swift-UVOT team: Swift/UVOT has performed further follow-up observations of the Einstein Probe/WXT-detected source EP250821a (Hu et al., GCN 41459). The UVOT optical counterpart reported in (Dichiara et al., GCN 41469) has faded, consistent with the behaviour reported by Li et al. (GCN 41470) and Yao et al. (GCN 41485). The refined UVOT position is RA (J2000) 19:19:32.56 Dec (J2000) -43:22:52.3 with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence). We note that this position supersedes that reported in Dichiara et al. (GCN 41469), which is incorrect. We apologise for any confusion. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag/3sigUL v 61584 72904 799 >19.9 u 5186 11029 1897 18.88+\-0.08 (reported in GCN 41469) u 68377 68575 195 >19.8 uvw1 67966 68372 399 >20.0 uvm2 67555 67961 399 >19.8 uvw2 61180 72857 1168 >20.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.07 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41491. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39554] EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
by GCN Circulars 22 Aug '25

22 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41490 SUBJECT: EP250821a: VLT X-shooter spectroscopic redshift z = 0.577 DATE: 25/08/22 09:01:58 GMT FROM: nrt3(a)le.ac.uk J. An (NAOC), V. Abril-Melgarejo (LUX-Paris Obs.), R. A. J. Eyles-Ferris (U. Leicester), D. Xu (NAOC), A. L. Thakur (INAF-IAPS), A. J. Levan (Radboud U.), P. G. Jonker (Radboud U.), D. B. Malesani (DAWN/NBI and Radboud), S. R. Oates (U. Lancaster), G. Corcoran (UCD), A. Martin-Carrillo (UCD), V. D’Elia (ASI/SSDC), N. R. Tanvir (U. Leicester) report on behalf of the Stargate collaboration: We observed the location of the optical counterpart and coincident likely host galaxy (Dichiara et al., GCN 41469; Li et al. GCN 41470; Yao et al. GCN 41485) of the X-ray transient EP250821a detected by Einstein Probe (Hu et al. GCN 41459; Liang et al., GCN 41467), using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 AA, and consist of 4 exposures of 600 s each. Observations started on 2025-08-22 at approximately 04:10 UT (20.9 hr after the EP trigger). In a preliminary reduction of the spectra, we detect absorption lines of Fe II (fine structure), Mg II, Ca II, Na I, and emission lines of [O II], [O III], H alpha, H beta, H gamma, [N II], [S II], from which we infer a redshift of z = 0.577. We note that our spectroscopic redshift measurement is roughly consistent with the photometric redshift value of 0.64 +/- 0.06 provided for the catalogued object in Legacy Survey that was noted by Li et al. (GCN 41470). From the X-shooter acquisition imaging we estimate a magnitude of r = 20.9 at 2025-08-22 03:41 UT, approximately 20.4 hr post-trigger. Given the Legacy Survey host magnitude of r = 21.79 +/- 0.02, this suggests a significant transient contribution at this epoch. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Celia Desgrange, Lorena Faundez, Camila de Sa Freitas. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) View this GCN Circular online at https://gcn.nasa.gov/circulars/41490. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39553] LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
by GCN Circulars 22 Aug '25

22 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41489 SUBJECT: LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz DATE: 25/08/22 08:32:41 GMT FROM: Paolo D'Avanzo at INAF - OAB <paolo.davanzo(a)inaf.it> P. D'Avanzo, (INAF-OAB), M.T. Botticella (INAF - OACn), E. Cappellaro (INAF-OAPd), L. Izzo (INAF - OACn), A. Rossi (INAF-OAS), V. D’Elia (ASI-SSDC), S. Piranomonte (INAF-OAR), G. Greco (INFN), M.G. Bernardini (INAF-OAB), S. Ronchini (GSSI), B. Patricelli (Univ. Pisa), O. S. Salafia, G. Ghirlanda (INAF-OAB), N. Elias-Rosa (INAF-OAPd), Fabio Ragosta (Università degli studi di Napoli “Federico II”), R. Salvaterra (INAF-IASF Milano), E. Brocato (INAF-OAR), V. Lorenzi, A. Garcia De Gurtubai Escudero (INAF-TNG), on behalf of GRAWITA report: We observed the optical transient AT2025ulz (Stein et al., GCN Circ. 41414; Busmann et al., GCN Circ. 41421; Hall et al., GCN Circ. 41433; Karambelkar et al., GCN Circ. 41436; O’Connor et al., GCN Circ. 41452; Gillanders et al., GCN Circ. 41454; Liu et al., GCN Circ. 41461; Perley et al., GCN Circ. 41480) possibly connected to the GW candidate event S280818k (LVK collaboration, GCN Circ. 41437 & GCN Circ. 41440) with the Italian 3.6m TNG telescope, located in Canary Islands (Spain), equipped with the near-infrared camera NICS in imaging mode. A series of images were obtained with the J filter starting on 2025-08-20T20:27:00 UT (i.e. 2.80 days post the GW T0), with the H filter starting on 2025-08-20T21:42:37 UT (i.e. 2.85 days post the GW T0) and with the K filter starting on 2025-08-20T23:00:15 UT (i.e. 2.90 days post the GW T0). The exposure time for each filter was 50 minutes. The transient host galaxy is clearly detected in all our images, while no source is detected at the position of AT2025ulz down to the following 3sigma upper limits (AB magnitudes, calibrated against the 2MASS catalogue and obtained after subtracting a 2D galaxy model obtained with galfit, Peng et al., 2010, AJ, 139, 2097): J > 21.7 mag H > 21.3 mag K > 20.5 mag View this GCN Circular online at https://gcn.nasa.gov/circulars/41489. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39552] GRB 250821A: VLT/FORS2 Optical Observation
by GCN Circulars 22 Aug '25

22 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41488 SUBJECT: GRB 250821A: VLT/FORS2 Optical Observation DATE: 25/08/22 08:32:30 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Rome), Niccolò Passaleva (U Rome), Yu-Han Yang (U Rome) and Eleonora Troja (U Rome) report on behalf of the ERC BHianca team: We observed the field of GRB 250821A (Dichiara et al., GCN 41462) with the FORS2 imager on the ESO VLT UT1 (Antu). Observations began 18.4 hours after the trigger and were carried out in the R filter with an average airmass of ~1.0. We do not detect any new source at the enhanced Swift-XRT position (Beardmore et al. GCN 41472) down to the following 3-sigma limit R>26.1 AB mag calibrated with using nearby stars in the PanSTARRS PS1 DR2 catalogue (Flewelling et al. 2020) and without Galactic extinction correction. We thank the staff at the VLT for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41488. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39551] GRB 250821A: GECAM-B detection
by GCN Circulars 22 Aug '25

22 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41487 SUBJECT: GRB 250821A: GECAM-B detection DATE: 25/08/22 07:46:56 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Shao-Lin Xiong and Yue Huang (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 250821A at 2025-08-21T10:46:18.000 UTC (denoted as T0), which is also detected by Swift/BAT (S. Dichiara et al., GCN#41462). According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 1.5 +1.5/-0.5 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecamgrb250821A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/41487. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39550] GRB 250821B: SVOM/GRM observation
by GCN Circulars 22 Aug '25

22 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41486 SUBJECT: GRB 250821B: SVOM/GRM observation DATE: 25/08/22 06:53:40 GMT FROM: tanwj(a)ihep.ac.cn SVOM/GRM team: Wen-Jun Tan, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Daigne (IAP), Stéphane Schanne (CEA) and Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 250821B (SVOM burst-id sb25082109) at 2025-08-21T16:07:47.500 UTC (T0), which is also detected by FERMI/GBM (GBM team, GCN #41473 and GCN #41477). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 2.5 +0.3/-0.2 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250821B.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 39.95, Dec = -77.13, GCN #41473), is located at about 65 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. However, ECLAIRs detected this burst above 50 keV, through the shield. With this localization given by FERMI/GBM, the time-averaged spectrum from T0-0.5 to T0+3.5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.89 +/-0.05 and the cutoff energy, parameterized as Epeak, is 289 +37/-31 keV. The event fluence (10-1000 keV) in this time interval is (1.1 +/-0.1)E-05 erg/cm^2. The localization of GRB 250821B in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/grb250821B_amati.png 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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Wen-Jun Tan (IHEP)(tanwj(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41486. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39549] EP250821a: SVOM/VT optical observation
by GCN Circulars 22 Aug '25

22 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41485 SUBJECT: EP250821a: SVOM/VT optical observation DATE: 25/08/22 03:16:13 GMT FROM: zhyao(a)bao.ac.cn Z. H. Yao, Y. N. Ma, L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM performed a Target of Opportunity observation of EP250821a detected by EP/WXT (Hu et al., GCN 41459). SVOM/VT began observing the field at 2025-08-21T11:23:41.5 UTC, 4.087 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. An uncatalogued source is found using VT X-band data, within the error box of EP/FXT (Hu et al., GCN 41459; Liang et al., GCN 41467), Swift/XRT and UVOT (Dichiara et al., GCN 41469) and Las Cumbres (Li et al., GCN 41470) at R.A., Dec 289.88564, -43.38115 degrees: RA (J2000) = 19:19:32.55 Dec (J2000) = -43:22:52.14 with an uncertainty of 0.5 arcsec. The source is detected in both VT_R and VT_B and was fading by ~0.5 mag between the first 2 VT observing sequences, the magnitudes are: T-T0 (h) | Exposure Time (s) | Band | Mag (AB) | Mag err --------------------|-------------------|------|----------|-------- 4.087 | 70 | VT_B | 19.44 | 0.12 4.087 | 70 | VT_R | 18.49 | 0.05 6.363 | 70 | VT_B | 19.93 | 0.05 6.363 | 70 | VT_R | 19.02 | 0.03 Our photometry was not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre 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/41485. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39548] Fermi GRB 250821B: Global MASTER-Net observations report
by GCN Circulars 22 Aug '25

22 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41484 SUBJECT: Fermi GRB 250821B: Global MASTER-Net observations report DATE: 25/08/22 02:45:40 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-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) started inspect of the Fermi GRB 250821B ( Fermi GBM team, GCN 41473) errorbox 26834 sec after notice time and 35938 sec after trigger time at 2025-08-22 02:06:45 UT, with upper limit up to 18.8 mag. The observations began at zenith distance = 63 deg. The sun altitude is -50.3 deg. The galactic latitude b = -39 deg., longitude l = 295 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2974796 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 35953 | 2025-08-22 02:06:45 | MASTER-OAFA | (02h 39m 51.65s , -77d 15m 11.6s) | C | 30 | 18.2 | 36003 | 2025-08-22 02:07:35 | MASTER-OAFA | (02h 39m 51.48s , -77d 14m 09.1s) | C | 30 | 18.2 | 36081 | 2025-08-22 02:08:38 | MASTER-OAFA | (02h 39m 55.46s , -77d 15m 05.3s) | C | 60 | 18.5 | 36162 | 2025-08-22 02:09:59 | MASTER-OAFA | (02h 39m 48.90s , -77d 16m 01.7s) | C | 60 | 18.4 | 36246 | 2025-08-22 02:11:23 | MASTER-OAFA | (02h 39m 55.59s , -77d 15m 36.4s) | C | 60 | 18.4 | 36370 | 2025-08-22 02:13:27 | MASTER-OAFA | (02h 39m 50.79s , -77d 14m 15.1s) | C | 60 | 18.6 | 36494 | 2025-08-22 02:15:31 | MASTER-OAFA | (02h 39m 49.56s , -77d 15m 45.5s) | C | 60 | 18.2 | 36592 | 2025-08-22 02:17:09 | MASTER-OAFA | (02h 39m 51.22s , -77d 13m 46.7s) | C | 60 | 18.7 | 36673 | 2025-08-22 02:18:30 | MASTER-OAFA | (02h 39m 44.40s , -77d 14m 42.5s) | C | 60 | 18.8 | 36749 | 2025-08-22 02:19:46 | MASTER-OAFA | (02h 39m 43.93s , -77d 13m 40.2s) | C | 60 | 18.5 | 36829 | 2025-08-22 02:21:06 | MASTER-OAFA | (02h 39m 50.13s , -77d 14m 36.9s) | C | 60 | 18.8 | 36918 | 2025-08-22 02:22:34 | MASTER-OAFA | (02h 39m 43.66s , -77d 15m 33.3s) | C | 60 | 17.7 | 37024 | 2025-08-22 02:24:21 | MASTER-OAFA | (02h 39m 46.86s , -77d 15m 02.4s) | C | 60 | 17.9 | 37132 | 2025-08-22 02:26:09 | MASTER-OAFA | (02h 39m 43.59s , -77d 13m 42.4s) | C | 60 | 17.9 | 37229 | 2025-08-22 02:27:46 | MASTER-OAFA | (02h 39m 42.71s , -77d 15m 06.5s) | C | 60 | 17.9 | 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/41484. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39547] GRB 250821A: NOT z-band upper limit
by GCN Circulars 22 Aug '25

22 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41483 SUBJECT: GRB 250821A: NOT z-band upper limit DATE: 25/08/22 02:33:46 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> M. Beyer Stjerne (KU), K. A. Grimstrup (KU), W. K. Krarup Mirsal (KU), C. Lind-Thomsen (KU), F. Hjorth Gammelgaard (KU), I. L. Róbertsdóttir (KU), J. P. U. Fynbo (DAWN/NBI), K. Valeckas (NOT and KU), R. Holmberg Rasmussen (NOT and Aarhus), D. B. Malesani (DAWN/NBI) and Radboud), report on behalf of a larger collaboration: We observed the field of the Swift GRB 250821A (Dichiara et al., GCN 41462) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. A total of 45 min of imaging was secured using the SDSS z filter, with a mean epoch 2025 Aug 22.075 UT (15.0 hr after the Swift/BAT trigger). No new sources are detected consistent with the Swift/XRT position (Beardmore et al., GCN 41472), down to a 3-sigma limit of z > 22.8 (AB), calibrated against nearby stars from the Pan-STARRS catalog. Our result is consistent with, and extends to redder wavelengths, the non-detections reported by Strausbaugh & Cucchiara (GCN 41466) and Oates & Dichiara (GCN 41471). View this GCN Circular online at https://gcn.nasa.gov/circulars/41483. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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