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[vsnet-grb-info 42068] GRB 260307B: Mephisto optical upper limits
by GCN Circulars 08 Mar '26

08 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43947 SUBJECT: GRB 260307B: Mephisto optical upper limits DATE: 26/03/08 13:15:21 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn> Guowang Du, Weikang Lin, Xueling Du, Donglin Gao, Xueteng Zhang, Yu Pan, Xingzhu Zou, Xinlei Chen, Brajesh Kumar, Yuan Fang, Jinghua Zhang, Xufeng Zhu, Tao Wang, Xinzhong Er, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team: The 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at the Lijiang Observatory, was triggered at 2026-03-07T13:48:27 (~181 seconds after the SVOM/ECLAIRs trigger) to observe the field of SVOM GRB 260307B (Magnani et al., GCN 43940). A set of simultaneous multi-band (ugi and vrz) images was collected. In our stacked frames, no optical candidate was detected within the SVOM/ECLAIRs localization and at the position reported by Corcoran et al. (GCN 43946). The upper limits (3 sigma) are listed below, which are consistent with the non-detection previously reported in Kang. et al., GCN 43941, Palmerio. et al., GCN 43942, Vijaykumar et al., GCN 43943 and Ma et al., GCN 43945. ----------------------------------------------------------------------------- Start_Time(UT) | Band | Exp(s) | LimMag (AB) ----------------------------------------------------------------------------- 2026-03-07T13:48:27 | u | 45.0*7,300.0*2 | >21.67 2026-03-07T13:51:28 | v | 45.0*8,300.0*2 | >21.94 2026-03-07T13:48:29 | g | 45.0*6,300.0*2 | >22.23 2026-03-07T13:51:30 | r | 45.0*8,300.0*2 | >22.54 2026-03-07T13:48:29 | i | 45.0*6,300.0*2 | >22.15 2026-03-07T13:51:30 | z | 45.0*8,300.0*2 | >21.31 ----------------------------------------------------------------------------- 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. The facility is operated by the South-Western Institute for Astronomy Research (SWIFAR), Yunnan University. It provides real-time, high-quality colors of stellar objects. The Mephisto mosaic cameras were installed in October 2025. The first light was achieved in all three channels on 10 October 2025, and presently, these are under the commissioning phase. All the data have been reduced by the Mephisto data processing pipeline. We note that the current data-processing pipeline is still at a preliminary stage, with flux calibration precision of ~2% in the u and v bands, ~1% in the g and r bands, and better than 1% in the i and z bands. View this GCN Circular online at https://gcn.nasa.gov/circulars/43947. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42067] GRB 260307B: possible NOT optical counterpart
by GCN Circulars 08 Mar '26

08 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43946 SUBJECT: GRB 260307B: possible NOT optical counterpart DATE: 26/03/08 12:01:24 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), S. Bijavara Seshashayana (NOT and Malmo Univ.), report on behalf of a larger collaboration: We observed the field of the SVOM GRB 260307B (Magnani et al., GCN 43940) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC instrument. Observations consisted of 6x200 s in the SDSS-z band and started at 22:29:21 UT on March 7 2026 (about 8.7 hr after the SVOM trigger). The sky conditions were modest, with mediocre and variable seeing (1.6" in our stack), and the imaging sequence had to be interrupted. The mid-time of our combined observation was 9.46 hr after the SVOM trigger. Within the SVOM/MXT localisation region reported by Magnani et al. (GCN 43940), we detect a faint source which visually is brighter than its archival counterpart in the Legacy survey. Its coordinates are: RA (J2000) = 10:22:02.65 Dec (J2000) = -21:00:02.6 with an estimated error of ~0.5". In our stacked images we measure a magnitude (AB) of: z = 22.47 +/- 0.33 This magnitude is calibrated using nearby objects from the Pan-STARRS catalog and is not corrected for Galactic extinction. Photometry of this object on the Legacy survey images yields z = 23.27 +/- 0.22 AB. The source was thus brighter in the NOT images at the 2-sigma level (by 0.8 +/- 0.4 mag). Given the low significance of the detection, we cannot securely claim the counterpart identification, and we invite to double-check the presence of this candidate in other data sets. View this GCN Circular online at https://gcn.nasa.gov/circulars/43946. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42066] GRB 260307B: SVOM/VT upper limit with X band data analysis
by GCN Circulars 08 Mar '26

08 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43945 SUBJECT: GRB 260307B: SVOM/VT upper limit with X band data analysis DATE: 26/03/08 06:53:14 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, H. L. Li, Z. H. Yao, Y. L. Qiu, C. Wu, L. P. Xin, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), F. Magnani, A. Foisseau (CPPM) report on behalf of the SVOM/VT team. SVOM/VT performed an automatic slew on the burst GRB 260307B (sb26030704) triggered by SVOM/ECLAIRs (Magnani et al., GCN 43940). SVOM/VT began observing the field at 2026-03-07T13:50:41 UTC, 315.5 seconds after T0, in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. After quick analyzing the X band data avaliable, the VT-VHF candidate (Palmerio et al., GCN 43942) was not confirmed in either single or stacked X band images. Therefore, we conclude that the VT-VHF candidate is not a real source. Also, no any uncatalogued sources are detected within the error range of MXT (Magnani et al., GCN 43940) down to ~22.5 AB magnitude at the mid time of 10.25 minutes in both VT_B and VT_R. Considering the bright X-ray detection by MXT and non-detection by VT with auto slew, the GRB is an optically dark burst or a high-redshift candidate. Near infrared observations are encouraged. Further data analysis is ongoing. 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/43945. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42065] Fermi GRB 260307A: Global MASTER-Net observations report
by GCN Circulars 08 Mar '26

08 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43944 SUBJECT: Fermi GRB 260307A: Global MASTER-Net observations report DATE: 26/03/08 03:00:45 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-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260307A ( Fermi GBM team, GCN 43939) errorbox 52522 sec after notice time and 52542 sec after trigger time at 2026-03-08 02:03:41 UT, with upper limit up to 17.6 mag. The observations began at zenith distance = 27 deg. The sun altitude is -17.6 deg. The galactic latitude b = 75 deg., longitude l = 43 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3173784 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 52573 | 2026-03-08 02:03:41 | MASTER-Kislovodsk | (13h 56m 48.56s , +30d 11m 50.0s) | C | 60 | 17.5 | 52671 | 2026-03-08 02:05:19 | MASTER-Kislovodsk | (13h 55m 18.49s , +28d 17m 01.2s) | C | 60 | 17.3 | 52762 | 2026-03-08 02:06:51 | MASTER-Kislovodsk | (13h 41m 41.44s , +28d 16m 16.9s) | C | 60 | 17.1 | 52862 | 2026-03-08 02:08:30 | MASTER-Kislovodsk | (13h 42m 54.18s , +30d 11m 08.6s) | C | 60 | 17.4 | 53171 | 2026-03-08 02:13:40 | MASTER-Kislovodsk | (13h 54m 42.32s , +26d 22m 26.2s) | C | 60 | 17.4 | 53271 | 2026-03-08 02:15:20 | MASTER-Kislovodsk | (13h 41m 19.11s , +26d 22m 57.5s) | C | 60 | 17.6 | 53368 | 2026-03-08 02:16:57 | MASTER-Kislovodsk | (14h 08m 52.75s , +28d 17m 54.2s) | C | 60 | 17.2 | 53469 | 2026-03-08 02:18:38 | MASTER-Kislovodsk | (14h 09m 29.84s , +28d 17m 50.9s) | C | 60 | 12.1 | 53580 | 2026-03-08 02:20:28 | MASTER-Kislovodsk | (13h 48m 25.23s , +33d 57m 51.7s) | C | 60 | 17.3 | 54177 | 2026-03-08 02:30:26 | MASTER-Kislovodsk | (14h 08m 06.54s , +26d 23m 27.0s) | C | 60 | 17.3 | 54278 | 2026-03-08 02:32:07 | MASTER-Kislovodsk | (14h 13m 24.07s , +32d 04m 29.5s) | C | 60 | 17.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43944. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42064] GRB260307B: GROWTH-India Telescope optical upper limit
by GCN Circulars 07 Mar '26

07 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43943 SUBJECT: GRB260307B: GROWTH-India Telescope optical upper limit DATE: 26/03/07 17:57:41 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> V. Vijaykumar, A. Khade, V. Swain, S. Patil, A.P. Saikia, T. Mohan, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of GRB260307B detected by SVOM/ECLAIRs (SVOM, GCN 43940), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-03-07 15:51:15 (UTC), i.e., 2.1 hours after the trigger, and obtained 5x300 exposures in the r' filter. We did not detect any transient in our image. The photometric upper limit is as follows: | MJD (mid) | Filter | tmid-t0 (hours) | Exposure Time (sec) | Upper limit (AB) | | ------------ | ------ | --------------- | ------------------- | ---------------- | | 61106.6694 | r' | 2.26 | 5x300 | 20.4 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our magnitude is consistent with other optical observations (Kang. et al., GCN 43941, Palmerio. et al., GCN 43942). The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/43943. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42063] GRB 260307B: SVOM/VT optical candidate
by GCN Circulars 07 Mar '26

07 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43942 SUBJECT: GRB 260307B: SVOM/VT optical candidate DATE: 26/03/07 16:41:03 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> J. T. Palmerio (CEA/Irfu), H. L. Li, L. P. Xin, Y. N. Ma, Y. L. Qiu, C. Wu (NAOC), A. Saccardi (CEA/Irfu), F. Magnani, A. Foisseau (CPPM) on behalf of the SVOM/VT team. After the trigger by SVOM/ECLAIRs at 2026-03-07T13:45:26 UTC (T0), SVOM performed an automatic slew on the burst location (Magnani et al., GCN 43940). SVOM/VT began observing the field at 2026-03-07T13:51:31, 364.31 seconds after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. From a preliminary analysis of the 1-bit subimage and source list downloaded via VHF network, at least one credible candidate is identified, the details of which are presented below. VT_ID 245: This candidate was flagged as an uncatalogued fading source. The position of this candidate is R.A., Dec. 155.5129, -21.0067 degrees, corresponding to: R.A. (J2000) = 10h22m03.1s Dec. (J2000) = -21d00m24.1s with an uncertainty of 0.5 arcsec. This location is within the R90 uncertainty region of the SVOM/MXT onboard localization. The source was detected only in VT_R and faded beyond detection in the third sequence. The candidate's magnitudes are: | date-obs (UTC) | mid-time | exposure | band | mag(AB) | | ------------------- | -------- | -------- | ---- | ---------- | | 2026-03-07T13:51:31 | 6.1 min | 6*50 sec | VT_R | 21.3 ± 0.1 | | 2026-03-07T13:56:31 | 11.1 min | 6*50 sec | VT_R | 21.8 ± 0.1 | Magnitudes were not corrected for Galactic extinction. 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. SVOM/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/43942. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42062] GRB 260307B: SVOM/C-GFT upper limit
by GCN Circulars 07 Mar '26

07 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43941 SUBJECT: GRB 260307B: SVOM/C-GFT upper limit DATE: 26/03/07 15:46:50 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Z. Kang(CHO), C. Wu (NAOC), L.P. Xin, X.H. Han, P.P. Zhang, X.M. Lu (NAOC), Z.W. Li, Y. Lv (CHO), R.S. Zhang, Y.J. Xiao, Y.L. Qiu, J. Wang, J.S. Deng, L. Huang, J.Y. Wei (NAOC), F. Mag-nani, A. Foisseau (CPPM) report on behalf of the SVOM/C-GFT team: We observed the field of GRB 260307B detected by SVOM/ECLAIRs (Magnani et al. GCN 43940) with LATIOS on SVOM/C-GFT. Observations started at 2026-03-07T13:47:15 UTC, ~109 seconds after the trigger. We obtained i-band follow-up imaging. The target had a very low elevation. After preliminary analysis, no credible candidate was detected within the error box provided by SVOM/MXT (Magnani et al., GCN 43940) in our images. The 5-sigma upper limits are: i > 19.7 mag (AB) (5-sigma, mid-time 7.7 min after the trigger) The photometry was calibrated against the UCAC4 catalogue, and no correction for Galactic dust extinction was applied. Further observations and analyses are ongoing. We thank the observation assistants Chun-Lei Guo and Ying-Huai Hao at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/43941. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42061] GRB 260307B: SVOM detection of a burst
by GCN Circulars 07 Mar '26

07 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43940 SUBJECT: GRB 260307B: SVOM detection of a burst DATE: 26/03/07 14:09:39 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> F. Magnani, A. Foisseau (CPPM), M. Brunet, O. Godet (IRAP), report on behalf of the SVOM mission team: At 2026-03-07T13:45:26 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260307B (SVOM burst-id sb26030704). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 4 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 9.92 in the [8-120] keV energy band over a time window of 40.96 seconds starting at 2026-03-07T13:45:06. The localization of the best alert is R.A., Dec. 155.5760, -21.0620 degrees (J2000) with a 90% confidence level (C.L.) radius of 8.01 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM slewed to the burst. SVOM/MXT began observing the field at 2026-03-07T13:48:16 UTC, 170 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 155.5216, -20.9972 degrees: R.A. (J2000) = 10h22m05.19s Dec. (J2000) = -20d59m49.81s with a 90% C.L. radius of 43.83 arcseconds. This location is 4.94 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. No optical observation could be performed by SVOM/VT for the time being. 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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Francesco Magnani: magnani(a)cppm.in2p3.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/43940. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42060] GRB 260307A: Fermi GBM Final Localization
by GCN Circulars 07 Mar '26

07 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43939 SUBJECT: GRB 260307A: Fermi GBM Final Localization DATE: 26/03/07 13:08:25 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> The Fermi GBM team reports the detection of a likely LONG GRB "At 11:27:59.32 UT on 07 March 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260307A (trigger 794575684/260307478). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 209.07, Dec = 29.03 (J2000 degrees, equivalent to J2000 13h 56m, 29d 01'), with a statistical uncertainty of 2.88 degrees. The angle from the Fermi LAT boresight is 77 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260307478/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260307478/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260307478/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/43939. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42059] GRB 260211A: late-time NOT i-band observations consistent with archival flux
by GCN Circulars 07 Mar '26

07 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43938 SUBJECT: GRB 260211A: late-time NOT i-band observations consistent with archival flux DATE: 26/03/07 10:55:59 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), S. Bijavara Seshashayana (NOT and Malmo Univ.) report on behalf of a larger collaboration: We observed the optical counterpart (Li et al., GCN 43748) of GRB 260211A (Gotz et al., GCN 43705; Hamburg, GCN 43713) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC instrument. Observations (3x300 s) were conducted in the SDSS i band, in order to reduce the effect of the large Galactic extinction towards this line of sight (A_V = 2.1 mag). Our image quality was unfortunately degraded by poor seeing (2.1"). The optical counterpart is detected in our images (mid time 23.1 days after the SVOM trigger). We measure a magnitude i = 22.5 +/- 0.2 AB, calibrated against nearby objects from the Pan-STARRS catalog, and not corrected for Galactic extinction. The source is also detected in archival imaging from the DELVE survey (Drlica-Wagner et al., 2022, doi:10.3847/1538-4365/ac78eb), for which we find a consistent magnitude to within 0.2 mag. Imagine subtraction between the two data sets yields an upper limit of i > 22.9 for any excess component at the afterglow location. Li et al. (GCN 43923) report a rebrightening of this source between 2.7 and 19.4 days after trigger, possibly suggesting the emergence of a SN. Our data cannot confirm this trend, though the different filters and the large extinction may introduce a systematic difference. View this GCN Circular online at https://gcn.nasa.gov/circulars/43938. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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