GRB 241009A

SVOM/ECLAIRs Commissioning Team: Jean-Luc Atteia, Laurent Bouchet, Sebastien Guillot, Juliette Alaux (IRAP), Stéphane Schanne, Frédéric Chateau, Nicolas Dagoneau, Hervé Le Provost (CEA), Wenjin Xie (NAOC),Floriane Cangemi (APC), Tais Maiolino (LUPM), 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 triggered and located GRB 241009A (sb24100915) at 2024-10-09T19:17:29 UT (Tb).

The following trigger information was received on the ground with low-latency by the SVOM VHF Alert Network.
The burst was detected by both the on-board Count-Rate Trigger (CRT) and Image Trigger (IMT) and 12 Alerts were received. The detection with the best signal-to-noise ratio of 15.3 sigma is obtained by CRT in the 8-50 keV energy band over a time window of 10.24 s starting at Tb.

This is a clear long duration GRB.

The median location of the event on all 12 Alerts is RA, Dec = 325.11, -35.63 (J2000).
The statistical uncertainty on this position is 5.6 arcminutes, to which we recommend adding 10 arcminutes of systematic uncertainty in quadrature.

The SVOM satellite did not slew onto this burst.

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: olivier.godet AT irap.omp.eu

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

Swift has initiated a ToO observation of the SVOM/ECLAIRs GRB 241009A. 
Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021722

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.

M. A. Williams (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P.
Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), R. Brivio
(INAF-OAB) 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 241009A, collecting 2.1 ks of Photon
Counting (PC) mode data between T0+14.7 ks and T0+106.0 ks. 

Seven uncatalogued X-ray sources are detected, of which one ("Source
1") is believed to be the afterglow. Using 433 s of PC mode data and 1
UVOT image, we find an enhanced XRT position (using the XRT-UVOT
alignment and matching UVOT field sources to the USNO-B1 catalogue):
RA, Dec = 325.00866, -35.65944 which is equivalent to:

RA (J2000): 21h 40m 02.08s
Dec(J2000): -35d 39' 34.0"

with an uncertainty of 4.2 arcsec (radius, 90% confidence). This
position is 6.3 arcmin from the SVOM/ECLAIRs position. The source has
faded from a count rate of 0.0441 [+0.013, -0.011] ct s^-1 at T0+14.9
ks to an upper limit of 0.0132 ct s^-1 at T0+100.9 ks.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00021722.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/00021722.

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

T. Hussenot-Desenonges (IJCLAB), Y. Rajabov (UBAI), A. Tanasan (NARIT), I. Abdi (AUS), R.Strasbaugh (EIU), M.Lamoureux (UCLouvain), S. Antier (OCA), S. Karpov (FZU), M. Coughlin (UMN), C. Andrade (UMN), I. Tosta e Melo (UniCT-DFA), P. Hello, N. Leroy (IJCLAB), P-A Duverne (APC), T. Pradier (Unistra/IPHC), N. Guessoum (AUS), A. Klotz (IRAP/OMP), C. Limonta, M .Boer (OCA), M. Masek, M. Prouza (FZU), D.Turpin (CEA-Saclay/Irfu), M. Freeberg, D. St-Gelais (KNC)
on behalf of the GRANDMA collaboration.

We observed the field of GRB 241009A, detected by SVOM/ECLAIRs (GCN 37749
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 ) with the GRANDMA network and its citizen science project Kilonova-catcher (KNC). Our observations started with TAROT-Reunion (TRE), 36 min after the trigger.

We did not detect any uncatalogued optical sources in the error region of SVOM/ECLAIRs, with the following 5-sigma upperlimits on the field:

| Tstart (UTC)  | Telescope | Exposure | Filter | U.L. |
	 	 	 	
| 2024-10-09T19:53:31 | TAROT-TRE | 32x60s | Clear (G) | 18.7 (Vega) |
| 2024-10-09T21:13:08 | FRAM-CTA-N | 17x120s | R | 18.4 (Vega) |
| 2024-10-09T22:25:02 | KNC-HakosRC360 | 19x180s | sdssr | 19.8 (AB) |
| 2024-10-09T23:39:34 | FRAM-Auger | 15x120s | R | 18.2 (Vega) |
| 2024-10-10T02:16:21 | KNC-Obs. Laurier | 41x60s | R | 19.1 (Vega) |

In particular, within these upperlimits, we do not detect any optical counterpart of the Swift-XRT afterglow position candidate (RA 21h 40m 02.08s DEC -35° 39′ 34.0″) (GCN 37772
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 ).

Images obtained in Johnson Cousin filters were calibrated using the Gaia DR3 Synphot catalog. Images obtained with Sloan filters were calibrated using the SkyMapper DR4 catalog. The unfiltered image taken by TAROT-TRE was calibrated as a Gaia G image using the Gaia eDR3 catalogue.

All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). We use the SkyPortal application (skyportal.io) to monitor our observational campaign.

We thank the SVOM collaboration for useful communication.

GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/).

D. Turpin (CEA/Irfu), J. T. Palmerio (CEA/Irfu, GEPI/Obs. de Paris), A. Saccardi (GEPI/Obs. de Paris, CEA/Irfu), S. Vergani (GEPI/Obs. de Paris), S. Basa (OSU Pytheas, LAM), E. Le Floc'h (CEA Paris-Saclay, DAp/AIM) on behalf of a larger collaboration.

We observed the field of GRB 241009A detected by SVOM/ECLAIRs (Dagoneau et al., GCN 37749
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 ) with the LCO 1m telescope at the Cerro Tololo Inter-American Observatory equipped with the Sinistro instrument. Our observation started at 2024-10-10 03:53:09 (T - TGRB = 8.6 h) with 4 x 180s exposure using the sdss-r filter.

We did not detect any uncatalogued optical source in the error region of SVOM/ECLAIRs (Dagoneau et al., GCN 37749
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 ) and at the position of the Swift/XRT afterglow source (Williams et al., GCN 37772
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 ). We derived the following upper limit (5 sigma, AB system) calibrated with the SkyMapper DR4 catalog and not corrected from the galactic extinction:

r > 20.9 (AB)

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101004719.