Einstein Probe detection of a new outburst from XRB IGR J17331-2406
ATel #17751; A. Li (BNU), C. Y. Wang (THU), X. H. Tang (THU), Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe team
on 12 Apr 2026; 10:07 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)
Subjects: X-ray, Transient
We report the detection of a new outburst from XRB IGR J17331-2406 with the Wide-field X-ray Telescope (WXT) onboard the Einstein Probe (EP). The source was discovered in 2004 (Atel #328) and has exhibited multiple outbursts in gamma-ray band since then. EP/WXT first detected the current outburst at 2026-04-02T02:52:30 (UTC), with a flux of about 1.1e-11 erg/cm^2/s.
Since then, the source was detected as follows,
UTC flux [1e10^-11 erg/cm^2/s]
2026-04-02T23:09:39 1.7
2026-04-07T02:36:27 2.3
2026-04-07T10:09:54 2.2
2026-04-08T21:42:58 1.8
The latest FXT observation started at 2026-04-11T19:32:48 and has an exposure time of 2995 s, its spectrum can be fitted with an absorbed power-law model, with a photon index of 1.0 +/- 0.1, with a column density fixed at the Galactic value of 3.02e21 cm^-2. The current unabsorbed flux in 0.5-10.0 keV is 6.9(+3.1,-3.2)e-11 erg/cm^2/s (68% confidence level). Further follow-up observations are encouraged.
Launched on January 9, 2024, EP is a space X-ray observatory designed to monitor the soft X-ray sky with rapid X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE, and CNES.
