sb25042207

Yifang Liang (PMO), Ziqi Wang (GXU), Wenjin Xie (NAOC), Stephane Schanne (CEA)  report on behalf of the SVOM mission team:


SVOM/ECLAIRs triggered on the X-ray transient labelled sb25042207 (SVOM burst-id sb25042207) starting at 2025-04-22T22:36:17 UTC (Tb).

The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.

The burst was only detected by the Image Trigger (IMT), which produced a sequence of 1 alert. IMT provided the alert with the best signal-to-noise ratio (SNR) of 7.01 in the 5-8 keV energy band over a time window of 1310.72 seconds starting at Tb.

The localization of the best alert is R.A., Dec 194.9273, 27.7745 degrees:
RA (J2000) = 12h59m42.56s
Dec (J2000) = 27d46m28.13s
with a 90% C.L. radius of 11.17 arcmin (including systematic error of 2 arcmin added in quadrature).

We notice the presence of many X-ray candidate sources inside the error region, including 2 QSOs, as well as 2 nearby AGNs including Mrk 60.

SVOM did not slew to this transient because it did not exceed the slew threshold. SVOM follow-up observations will be scheduled.

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.

The Burst Advocate (BA) on shift for this transient is Yifang Liang: yfliang@pmo.ac.cn
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.

S. Belkin, A. Kumar, G. Ramsay, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, D. O'Neill, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration:

We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO, Steeghs et al. 2022; Dyer et al. 2024) in response to the SVOM/ECLAIRs alert sb25042207 (Liang et al., GCN 40213
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 ). Targeted observations were performed on April 22 2025 23:39:55 UT (+1.06 h post trigger) and on April 23 2025 01:20:48 UT (+2.74 h post trigger). The first epoch of observations consisted of 4x90 s exposures, while the second epoch was obtained in survey mode with 4x45 s exposures. All images were taken 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. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks.

No new transients that could be credibly associated with SVOM/ECLAIRs sb25042207 were detected down to a 5-sigma L-band limiting magnitude of 20.4.

Additionally, no source is detected prior to the GRB trigger time in archival GOTO observations (4x45 s; in survey mode) taken 1.347 h before the trigger, down to a 5-sigma L-band upper limit of 19.7 mag.

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).

M. Gritsevich (Univ. of Helsinki), I. Perez-Garcia, M.D. Caballero-Garcia, E. J. Fernandez-Garcia, R. Sanchez-Ramirez, S.-Y. Wu, S. Guziy, and A. J. Castro-Tirado (IAA-CSIC, Granada), Y.-D. Hu (GXU), C. Perez del Pulgar and A. Reina (Univ. of Malaga), R. Fernandez-Munoz (IHSM/UMA-CSIC), and M. Jelinek (ASU-CAS, Ondrejov Obs.), on behalf of a larger collaboration, report:

Following the detection of the X-ray transient sb25042207 by SVOM (Liang et al. GCNC [40213](https://gcn.nasa.gov/circulars/40213
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 )), the 0.6m BOOTES-2/TELMA robotic telescope at IHSM UMA “La Mayora” (Malaga, Spain) automatically responded to this high-energy event starting on Apr 22, 23:38:10 UT (i.e. 2 min after alert). On a coadd (20) of images at 00:00:50 UT (mid exposure time; i.e. 24 min post detection), nothing is detected down to 18.1 mag (clear filter), in agreement with the deeper observations taken later on (Belkin et al., GCNC [40215](https://gcn.nasa.gov/circulars/40215
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 )).

We would like to thank the staff at IHSM-/UMA-CSIC “La Mayora” for their excellent support.

Antonino D'Aì (INAF/IASFPA), J. A. Kennea (PSU), Elena Ambrosi (INAF/IASFPA), Valerio D'Elia (SSDC & INAF-OAR), Andrea Melandri (INAF-OAR) reports on behalf of the Swift-XRT team:

We have analysed 1.8 ks of XRT data for the SVOM/ECLAIRs-detected X-ray transient sb25042207 
(Liang et al., GCN Circ. 40213
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 ), from T0+3.8 ks to T0+5.6 ks after the SVOM/ECLAIRs trigger. 
The data are entirely in Photon Counting (PC) mode.

We detect two previously known X-ray sources and two uncatalogued X-ray sources within the ECLAIRs error circle. We note that the ECLAIRs error region overlaps with the Coma cluster region, a well-known galaxy cluster that exhibits significant diffuse X-ray emission.

Details of the uncatalogued sources:

Source 2:
RA (J2000): 194.93972 = 12:59:45.53
Dec (J2000): +27.8781 = +27:52:41.0
Error: 6.0 arcsec (radius, 90% confidence)
Count rate: 8 (+5, -4) x 10^-3 ct/s
Flux: [3.5 (+2.1, -1.9)] x 10^-13 erg/cm^2/s (observed, 0.3–10 keV)

Source 4:
RA (J2000): 195.13942 = 13:00:33.46
Dec (J2000): +27.7478 = +27:44:52.0
Error: 7.5 arcsec (radius, 90% confidence)
Count rate: 0.011 (+0.005, -0.004) ct/s
Flux: [4.8 (+2.1, -1.8)] x 10^-13 erg/cm^2/s (observed, 0.3–10 keV)

Both sources are below the RASS limit and show no definitive signs of fading.

The results of the XRT team's automatic analysis of the tiled XRT observations, 
including a position-specific upper limit calculator, are available at:
https://www.swift.ac.uk/SVOM/SVOM_FIELD00013/

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