Gamma-ray Burst 240911A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #37462
  SVOM/ECLAIRs commissioning team: St=C3=A9phane Schanne, Herv=C3=A9 Le Provo= st, Nicolas Dagoneau, Fr=C3=A9d=C3=A9ric Chateau (CEA), Olivier Godet, Laur= ent Bouchet, Sebastien Guillot, Juliette Alaux (IRAP), Fr=C3=A9d=C3=A9ric P= iron (LUPM), Floriane Cangemi (APC), Karine Mercier, Marie-Claire Charmeau,= Stefano Crepaldi (CNES)
  SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (I= HEP), St=C3=A9phane Basa (LAM), Jean-Luc Atteia (IRAP), Arnaud Claret (CEA)= , Zi-Gao Dai (USTC), Fr=C3=A9d=C3=A9ric Daigne (IAP), Jin-Song Deng (NAOC),= Andrea Goldwurm (APC), Diego G=C3=B6tz (CEA), Xu-Hui Han (NAOC), Cyril Lac= haud (APC), En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna Vergani (Obs.Par= is), Jing Wang (NAOC), Chao Wu (NAOC), Li-Ping Xin (NAOC), Bing Zhang (UNLV= )
  report on behalf of the SVOM team:
  During the commissioning phase, the SVOM/ECLAIRs telescope triggered and lo= cated a weak GRB at 2024-09-11T20:38:48 (TtimeTb), called GRB 240911A. The = burst was detected by the Count-Rate Trigger (CRT) onboard ECLAIRs. The sig= nal to noise ratio in the reconstructed image was 6.8 in the 20-120 keV ene= rgy band during a single time window of 10.24 s starting at TimeTb. The ima= ge transmitted in real-time over the SVOM VHF network is clean and shows a = point-like source.
  The GRB location is RA, Dec =3D 351.30, 21.33 (J2000). This is about 41 deg= rees from the ECLAIRs optical axis. The statistical uncertainty on this pos= ition is 13 arcminutes, to which we recommend to add 10 arcminutes of syste= matic uncertainty.
  SVOM did not slew to the burst since automated slewing is not yet enabled.
  The Space Variable Objects Monitor (SVOM) is a China-France joint mission l= ed by the Chinese National Space Administration (CNSA, China), French Space= Agency (CNES, France) and the Chinese Academy of Sciences (CAS, China), wh= ich is dedicated to observing gamma-ray bursts and other transient phenomen= a in the energetic universe. ECLAIRs was developed jointly by APC, CEA, CNE= S and IRAP.
  The SVOM point of contact for this burst is: s.schanne AT cea.fr
• GCN Circular #37475
  P. A. Evans (U. Leicester) reports on behalf of the Swift team:
  Swift has initiated a series of observations, tiled on the sky, of the SVOM/ECLAIRs GRB 240911A. Automated analysis of the XRT data will be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00128
  Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. The probability of finding serendipitous sources, unrelated to the SVOM/ECLAIRs event is high: 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.
• GCN Circular #37483
  M. A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), J.A. Kennea (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
  Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected burst GRB 240911A in a series of observations tiled on the sky. The total exposure time is 2.9 ks, distributed over 3 tiles; the maximum exposure at a single sky location was 1.6 ks. The data were collected between T0+73.0 ks and T0+79.5 ks, and are entirely in Photon Counting (PC) mode.
  Two uncatalogued X-ray sources have been detected, 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 1:

    RA (J2000.0):  351.4579  =  23:25:49.91
    Dec (J2000.0): +21.3760  =  +21:22:33.6
    Error: 13.5 arcsec (radius, 90% conf.)
    Count-rate: (3.7 [+2.3, -1.6])e-3 ct s^-1   
    Distance: 554 arcsec from SVOM/ECLAIRs position.
  

  Source 2:

    RA (J2000.0):  351.5268  =  23:26:6.43
    Dec (J2000.0): +21.2944  =  +21:17:39.8
    Error: 8.2 arcsec (radius, 90% conf.)
    Count-rate: (5.5 [+3.6, -2.6])e-3 ct s^-1   
    Distance: 771 arcsec from SVOM/ECLAIRs position.
  

  The results of the XRT-team automatic analysis of the tiled XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00128.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #37486
  A. Kumar, Y. Julakanti, B. P. Gompertz, J. Lyman, R. Starling, K. Ackley, M. J. Dyer, K. Ulaczyk, F. Jimenez-Ibarra, D. O'Neill, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Palle and D. Pollacco report on behalf of the GOTO collaboration:
  The Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022) serendipitously covered part of the localisation region of the SVOM/ECLAIRs-detected and Swift/XRT followed-up GRB 240911A (Schanne et al. GCN 37462; Williams et al. GCN 37483) in survey mode at 2024-09-12 04:40:43 UT (8.03 hours after trigger). Each observation consisted of 4x45s exposures in the GOTO L-band (400-700 nm).
  Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same paintings.
  No candidate optical counterpart is detected at the positions of the 2 uncatalogued Swift/XRT detected sources (Williams et al. GCN 37483) to a 5-sigma limiting magnitude of L > 19.3.
  Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and were not corrected for Galactic extinction.
  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).
• GCN Circular #37489
  S.Y. Fu, S.Q. Jiang, J. An, Z.P. Zhu, X. Liu, D. Xu (NAOC), J.Z. Liu (XAO) report on behalf of a large collaboration:
  We observed the field of GRB 240911A detected by SVOM/ECLAIRs (Schanne et al., GCN 37462), using the 50cm-A/B telescopes (50A, 50B) of the JinShan project, located at Altay, Xinjiang, China. Observations started at 16:27:18 UT on 2024-09-12, i.e., 19.8 hr after the trigger, and a series of frames were obtained in the Sloan g-, r-, i- and z-bands.
  No new optical source is detected within the error circles of two uncatalogued Swift/XRT candidates (Williams et al., GCN 37483), down to the following 5-sigma upper limits:

  T_mid (UT) | T_mid (hr) | filter | 5-sigma U.L. (AB) 
  ----------------------------------------------------
  2024-09-12T17:18:03.5 | 20.65 | g | 21.1
  2024-09-12T16:42:30.0 | 20.06 | r | 21.1
  2024-09-12T16:49:22.0 | 20.18 | i | 20.1
  2024-09-12T17:24:54.0 | 20.77 | z | 18.8
  

  calibrated with nearby PanSTARRS stars and not corrected for Galactic extinction.
  We acknowledge the excellent support from X. Yao, S.W. Luo, and Z.K. Feng for enabling these observations.
• GCN Circular #37490
  L. Izzo (INAF-OACn and DARK/NBI) and D. B. Malesani (DAWN/NBI and Radboud Univ.) report:
  We observed the field of GRB 240911A (Schanne et al., GCN #37462) with the Sinistro instrument mounted on the 1-m telescope of the LCO network, located in Sutherland, South Africa. Observations started on 2024 September 11 at 22:30 UT (1.87 hr after the GRB trigger). We obtained a series of 3x180 s images in the SDSS-r filter, and of 5x120 s in the PS1-z filter.
  We did not detect any source consistent with the position of either of the two X-ray sources reported by Swift-XRT (Williams et al., GCN #37483) up to a limit of r = 21.0 mag and z = 19.5 mag.
  This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 101004719.