A new hard X-ray activity from XTE J1855-026 caught by INTEGRAL
ATel #16020; V. Sguera (INAF-OAS Bologna, Italy), L. Sidoli (INAF-IASF Milano, Italy)
on 28 Apr 2023; 14:38 UT
Credential Certification: Vito Sguera (vito.sguera@inaf.it)
XTE J1855-026 is classified as a classical, eclipsing, persistent supergiant high mass X-ray binary, although it is peculiarly characterized by sporadic bright and hard X-ray flares (Atel #2482, Atel #3964). Its enhanced level of hard X-ray activity makes it detectable with IBIS/ISGRI onboard INTEGRAL about 10% of the time (Sidoli & Paizis 2018).
The field region of XTE J1855-026 has been recently covered by
INTEGRAL observations from 21 April 2023 13:39 UTC to 22 April 2023 16:22 UTC.
The source was in the field of view of IBIS/ISGRI with an effective exposure time of about 3 ks. It was detected at about 8 sigma level (25-60 kev) with an average flux of 34.0+/-4.3 mCrab (3.2 x 10-10 erg cm-2 s-1). No significant emission was detected in the band 60-100 keV.
The source was again in the IBIS/ISGRI field of view during subsequent observations
from 26 April 2023 11:13 UTC to 27 April 2023 13:03 UTC. The effective exposure was about 2 ks.
This time the source was not significantly detected and the inferred 2 sigma upper limit is about 10 mCrab (25-60 keV).
The reported INTEGRAL observations provide evidence of a recent hard X-ray activity from the source, although it is not possible to constrain its beginning and duration since the source was not in the INTEGRAL field of view during the observations previous to the reported detection.
