sb25043004

Y. Liang (PMO), W. Zheng (Berkeley), O. Godet, S. Guillot (IRAP), C. Plasse, J. T. Palmerio (CEA)
on behalf of the SVOM mission team.


SVOM/ECLAIRs triggered and located the X-ray transient sb25043004 (SVOM burst-id sb25043004) starting at 2025-04-30T10:40:57.1 UTC (Tb).

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

The source was only detected by the Image Trigger (IMT), which produced a sequence of 3 alerts. IMT provided the alert with the best signal-to-noise-ratio (SNR) of 8.96 in the [5-8] keV energy band over a time window of 327.68 seconds starting at Tb.

The localization of the best alert is R.A., Dec. 272.104, -38.6635 degrees:
R.A. (J2000) = 18h08m25.13s
Dec. (J2000) = -38d39m48.60s
with a 90% confidence level (C.L.) radius of 8.82 arcmin (including systematic error of 2 arcmin added in quadrature).

SVOM slewed to the source.

MXT began observing the field after the slew. The analysis of the recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments.

VT began observing the field after the slew. The analysis of the recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments.

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 burst is Weikang Zheng: weikang@berkeley.edu.
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.

S.Q. Jiang, H.Y. Liu, R.D. Liang, H.W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team:

EP-FXT performed a follow-up observation on SVOM/sb25043004 at 2025-04-30T17:26:25 (UTC), about 7 hours after the SVOM/ECLAIRs trigger (Liang et al. GCN # 40287). Two previously known X-ray sources and an uncatalogued X-ray source are detected within the ECLAIRs error circle.

Preliminary analysis on these source are automatically conducted, and details are listed as follows. 

Source 1: EPF_J180814.9-384246 (1eRASS J180815.0-384254) 
RA (J2000): 272.0610 
Dec (J2000): -38.7126
Flux: 1.77 x 10^-13 erg/cm^2/s (observed, 0.5-10 keV)
Flux_error: 3.7 x 10^-14 erg/cm^2/s (1 sigma)
Note: The source is spatially consistent with 1eRASS J180815.0-384254, which has a flux of 
8.34 (+4.22/-3.17, 1 sigma) x 10^-14 erg/cm^2/s (0.2-2.3 keV).

Source 2: EPF_J180840.1-384205 (1eRASS J180840.7-384211)
RA (J2000): 272.1683
Dec (J2000): -38.7025
Flux: 4.88 x 10^-13 erg/cm^2/s (observed, 0.5-10 keV)
Flux_error: 5.9 x 10^-14 erg/cm^2/s (1 sigma)
Note: The source is spatially consistent with 1eRASS J180840.7-384211, which has a flux of
1.41 (+0.52/-0.41, 1sigma) x 10^-13 erg/cm^2/s (0.2-2.3 keV).

Source 3: EPF_J180801.1-384501 (uncataloged)
RA (J2000): 272.0057
Dec (J2000): -38.7511
Flux:  2.44 x 10^-13 erg/cm^2/s (observed, 0.5-10 keV)
Flux_error: 4.6 x 10^-14 erg/cm^2/s (1 sigma)
Note: The upper limit given by eROSITA DR1 is 1.71 x 10^-13 erg/cm^2/s (0.2-2.3 keV).

The position uncertainties of the above sources are about 10 arcsec in radius (90% C.L. statistical and systematic). 

Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).