GRB 241108A

SVOM/ECLAIRs Commissioning Team: Tatyana Sadibekova, Stéphane Schanne, Nicolas Dagoneau, Hervé Le Provost, Frédéric Chateau (CEA), Jean-Luc Atteia, Laurent Bouchet, Sebastien Guillot, Juliette Alaux, Hui Yang (IRAP), Tais Maiolino (LUPM), Wenjin Xie, Donghua Zhao (NAOC), Floriane Cangemi (APC), Karine Mercier, Marie-Claire Charmeau, Stefano Crepaldi (CNES)

SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (IHEP), Stéphane Basa (LAM), Olivier Godet (IRAP), Arnaud Claret (CEA), Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng (NAOC), Andrea Goldwurm (APC), Diego Götz (CEA), Xu-Hui Han (NAOC), Cyril Lachaud (APC), En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna Vergani (Obs.Paris), 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 detected and localized the likely weak long duration GRB 241108A (SVOM trigger reference: sb24110802) at 2024-11-08T07:09:55 UTC (Tb).

The following trigger information was received on the ground with low-latency by the SVOM VHF Alert Network. The burst was detected by the Image Trigger (IMT) which sent a single Alert message, with a signal-to-noise ratio of 7.1 in the 20-120 keV energy band over a time window of 20.48 s starting at Tb. The Alert was produced 75 s before the entry to SAA, such that the Alert sequence was interrupted. The on-ground data analysis confirms a weak point-like source in the reconstructed sky image.

The burst localization is RA, Dec = 123.72, -7.19 (J2000).

The statistical uncertainty on this position is 11.9 arcminutes, to which we recommend adding 2 arcminutes of systematic uncertainty in quadrature.

SVOM did not slew to the burst since the detection significance was below slew threshold.

The Space 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 APC, CEA, CNES, and IRAP.

The SVOM point of contact for this burst is: s.schanne AT cea.fr.

J.-G. Ducoin (CPPM), Francesco Magnani (CPPM), Alan M. Watson (UNAM),
S. Antier (OCA), Damien Dornic (CPPM), Stéphane Basa (UAR Pytheas),
William H. Lee (UNAM), D. Akl (AUS), Jean-Luc Atteia (IRAP), Nathaniel
R. Butler (ASU), Francis Fortin (IRAP), Simona Lombardo (LAM), and
Margarita Pereyra (UNAM)

SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan
Zhang (IHEP), Stéphane Basa (LAM), Jean-Luc Atteia (IRAP), Arnaud
Claret (CEA), Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng
(NAOC), Andrea Goldwurm (APC), Diego Götz (CEA), Xu-Hui Han (NAOC),
Cyril Lachaud (APC), En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna
Vergani (Obs.Paris), Jing Wang (NAOC), Chao Wu (NAOC), Li-Ping Xin
(NAOC), Bing Zhang (UNLV)

report:

We imaged the field of GRB 241108A detected by SVOM/ECLAIRs
(Sadibekova et al., GCN Circ. 38132
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 ) during the commissioning of the
COLIBRÍ (SVOM/F-GFT) telescope at the Observatorio Astronómico
Nacional on the Sierra de San Pedro Mártir in Mexico.

We observed with the engineering test camera in a red filter that
approximates SDSS r. The data were reduced using custom software and
then analysed and calibrated against the PS1 catalog using the STDWeb
service. Our field covers a 13 arcmin square region centered on the
ECLAIRS position and does not cover the whole uncertainty region.

In 9840 seconds of exposure from 2024-11-08 08:47 to 12:34 (1.63 to
5.41 hours after the trigger, we detect no sources other than those
previously identified in the PS1 or GAIA DR3 catalogs to a 5-sigma
limiting AB magnitude of:

r > 22.3

We warmly thank the COLIBRÍ engineering team and the staff of the
Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.
We warmly thank the GRANDMA IJCLAB team and S. Karpov for the access
of the STDWeb service for STDPipe.

P. A. Evans (U. Leicester) reports on behalf of the Swift team:

Swift has initiated a ToO observation of the SVOM/ECLAIRs GRB 241108A. 
Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021729

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 SVOM/ECLAIRs 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.

D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), C.
Salvaggio (INAF-OAB), M. A. Williams (PSU), S. Dichiara (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 241108A, collecting 2.9 ks of Photon
Counting (PC) mode data between T0+43.8 ks and T0+50.6 ks. 

One uncatalogued X-ray source has been detected, it is below the RASS
limit and shows no definitive signs of fading. Therefore, at the
present time we cannot confirm this as the afterglow. Details of this
source are given below:

Source 1:
  RA (J2000.0):  123.6378  =  08:14:33.07
  Dec (J2000.0): -7.0861  =  -07:05:09.9
  Error: 4.7 arcsec (radius, 90% conf.)
  Count-rate: (5.0 [+2.0, -1.6])e-3 ct s^-1   
  Distance: 494 arcsec from SVOM/ECLAIRs position.
  Flux: (2.99 [+1.17, -0.93])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

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/00021729.

This circular is an official product of the Swift-XRT team.

Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM),
D. Akl (AUS), S. Antier (OCA), Jean-Luc Atteia (IRAP), Nathaniel R. Butler
(ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), J.-G. Ducoin (CPPM),
Simona Lombardo (LAM), Francesco Magnani (CPPM), and Margarita Pereyra
(UNAM)

SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang
(IHEP), Stéphane Basa (LAM), Jean-Luc Atteia (IRAP), Arnaud Claret (CEA),
Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng (NAOC), Andrea
Goldwurm (APC), Diego Götz (CEA), Xu-Hui Han (NAOC), Cyril Lachaud (APC),
En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna Vergani (Obs.Paris), Jing
Wang (NAOC), Chao Wu (NAOC), Li-Ping Xin (NAOC), Bing Zhang (UNLV)

report:

We again imaged the field of GRB 241108A detected by SVOM/ECLAIRs
(Sadibekova et al., GCN Circ. 38132
Loading...
 
 ) during the commissioning of the
COLIBRÍ (SVOM/F-GFT) telescope at the Observatorio Astronómico Nacional on
the Sierra de San Pedro Mártir in Mexico.

We observed with the engineering test camera in a red filter that
approximates SDSS r. The data were reduced using custom software and then
analysed and calibrated against the PS1 catalog using the STDWeb service.
Our field is centered on the XRT source detected at 08:14:33.07 -07:05:09.9
J2000 (Burrows et al., GCN Circ. 38139
Loading...
 
 ).

In 7080 seconds of exposure from 2024-11-09 09:01 to 12:52 UTC (1.08 to
1.24 days after the trigger), we detect no new sources within the XRT
uncertainty region to a 3-sigma limiting AB magnitude of:

r > 23.6

We do detect a two point source within the uncertainty region and one just
outside it, but these are also present in the earlier PS1 image at a
similar magnitude and therefore are unlikely to be the optical counterpart
of the GRB.

We warmly thank the COLIBRÍ engineering team and the staff of the
Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. We
warmly thank the GRANDMA IJCLAB team and S. Karpov for the access of the
STDWeb service for STDPipe.