SVOM/ECLAIRs detection of an X-ray flare from the high-mass X-ray binary 4U 2206+54

ATel #17288; F. Cangemi (APC, France), S. Guillot (IRAP, F), A. Coleiro (APC, F), N. Dagoneau (CEA, F), J. Rodriguez (CEA, F), L. Zhang (IHEP, China)
on 18 Jul 2025; 07:34 UT
Credential Certification: Floriane Cangemi (cangemi@apc.in2p3.fr)

Tweet

On Wednesday, July 16th 2025, at Tb=12:35:54.823 UTC, the SVOM/ECLAIRs (4-150 keV) coded-mask telescope detected, via its onboard trigger, an X-ray flare of around 200 s at a position compatible with that of the high-mass X-ray binary 4U 2206+54.

The 4-50 keV spectrum extracted between Tb and Tb+220 s is well fitted (chi2_red = 5.61/4) with a powerlaw with a photon index of gamma = 1.7 +/-0.3 (90% confidence) and a normalisation of phi_0 = 0.2 +0.2/-0.1 ph/keV/s/cm2 @1 keV (90% confidence). The integrated 4-50 keV and 20-40 keV fluxes are 1.6(+0.1/-0.4)e-09 erg/s/cm^2 (68% confidence) and 5.1(-2.7/+0.4)e-10 ergs/cm^2/s (68% confidence) respectively. They correspond to a luminosity of about 2.0e36 erg/s and 6.3e35 erg/s assuming a distance of 3.2 kpc (Hambaryan et al. 2022).

Previous X-ray flaring activity of 4U 2206+54 has been reported by MAXI in October 2009 (ATel #2271) with a 2-20 keV flux of about 3.7e-9 erg/cm2/s, and by INTEGRAL in June 2017 (ATel #10519). During the latter event, the flare reached a peak flux of 1.34e-09 ergs/s/cm^2 in the INTEGRAL/IBIS 20-40 keV band, making it the brightest hard X-ray flare ever observed from this high-mass X-ray binary. It exhibited a power-law like spectrum, with a luminosity roughly ten times higher than usual.

The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), 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. MXT has been developed jointly by CNES, CEA, IJCLab, University of Leicester and MPE.