Einstein Probe detection of a new outburst from IGR J20155+3827

ATel #17317; Q. C. Liu (THU), R. Z. Li (YNAO, CAS), B. B. Zhang, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team
on 1 Aug 2025; 06:06 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)

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We report on the detection of a possible new X-ray outburst from the High Mass X-ray Binary (HMXB) IGR J20155+3827, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The source exhibited a recent flux increase since 2025-07-31 17:25:35 (UTC). The position of the source is R.A. = 303.863 deg, DEC = 38.424 deg (J2000) with an uncertainty of 2.6 arcmin in radius (90% C.L. statistical and systematic), which is 99 arcsec from the HMXB IGR J20155+3827, indicating the possible association between the two. The WXT spectra around the detection time can be simultaneously fitted by an absorbed blackbody plus power-law with a blackbody temperature of 0.13 (+0.04/-0.03) keV and a neutral hydrogen column density of 1.2 (+0.7/-0.4)x 10^22 cm^-2. The derived unabsorbed flux in 0.5-4 keV is 0.9 (+2.5/-0.6) x 10^-9 erg/s/cm^2 in the latest observation and 0.4 (+1.2/-0.3) x 10^-10 erg/s/cm^2 in the first observation. The photon index cannot be well constrained.

We note that IGR J20155+3827 exhibited outbursts in 2024 (ATel #16730). The last observation was reported by EP team on July, 2024 with a flux of 1.0(+0.3/-0.2)x10^-10 erg/s/cm^2 in 0.5-4 keV (ATel #16730). Multi-wavelength follow-up observations are encouraged.

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).