INTEGRAL detects transient activity from IGR J00370+6122

ATel #14295; M. Fiocchi (INAF-IAPS Roma, Italy), A. Bazzano (INAF-IAPS Roma, Italy), A. J. Bird (Univ. of Southampton, UK), V. A. Lepingwell (Univ. of Southampton, UK), L. Natalucci (INAF-IAPS Roma, Italy), V. Sguera (INAF-IASF Bologna, Italy), P. Ubertini (INAF-IAPS Roma, Italy),
on 29 Dec 2020; 18:26 UT
Credential Certification: mariateresa fiocchi (mariateresa.fiocchi@iaps.inaf.it)

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During a recent INTEGRAL public observation of the Galactic Plane (revolution 2311), performed between 2020-12-20 20:21:51 and 2020-12-23 02:44:03 UTC, a transient activity from supergiant High Mass X-ray Binary IGR J00370+6122 has been detected. The 22-60 keV IBIS/ISGRI flux corresponds to (29.2+/-2.5) mCrab with an effective exposure time of 12.5 ks. This field was also observed during the previous revolution 2310 (start time 2020-12-18 04:30:36 UTC, end time 2020-12-20 10:59:40 UTC) for an effective exposure time of 10.7 ks. IGR J00370+6122 was not detected and an upper limit of 5 mCrab (2sigma) in the 22-60 keV energy range has been derived.
This source is a periodic system with an orbital period P=15.6627d and a claimed spin period of 346s (Gonzalez-Galan et al 2014). It shows a peculiar X-ray behaviour, characteristic of either a persistent HMXB or an intermediate SFXT (Hainich et al. 2020, Gonzalez-Galan et al 2014). During the INTEGRAL observation, it showed a transient behaviour on short time scales resembling that of an SFXT: it was detected during a short time interval, from MJD 59204.595 to MJD 59204.616 (effective exposure time of 325s) with an intensity of 95+/-16 mCrab. We note that the time of this detection is consistent with the epoch of expected maximum flux (59204.13+/-1.67) assuming the ephemeris information reported in Gonzalez-Galan et al 2014. It was not detected either before or after this time interval. The upper limits for the short time periods selected (MJD 59204.573-59204.594 and MJD 59204.617-59204.638) are about 30 mCrab (2sigma) in 22-60 keV during both time intervals . The spectrum at the peak of the emission is well fitted with a power law model with a spectral index of 3.0+/-0.5 and a flux of 3.1e-10 ergs cm-2 s-1 in 22-60 keV energy range (Reduced chi-squared = 1.1).
All the data have been analyzed using the Offline Software Analysis version 11.0 (OSA11).
Results from the Galactic Plane Scanning are publicly available at: http://gps.iaps.inaf.it