Continued INTEGRAL observations of Swift J1658.2-4242: brighter and softer?
ATel #11318; V. Grinberg (ESA/ESTEC), W. Eikmann (Remeis/ECAP/FAU), I. Kreykenbohm (Remeis/ECAP/FAU), J. Wilms (Remeis/ECAP/FAU)
on 18 Feb 2018; 15:55 UT
Credential Certification: Victoria Grinberg (firstname.lastname@example.org)
Subjects: X-ray, Binary, Transient
INTEGRAL continued its observations of the new X-ray transient Swift J1658.2-4242 (GCN #22416 and #22417). The source was originally interpreted as a black hole X-ray binary due to its spectral shape (ATel #11306) but the detection of a pulsation with Swift (ATel #11311) points towards an accreting X-ray pulsar interpretation. Previous INTEGRAL observations of the source (ATel #11306) indicated a possible decrease in X-ray flux above 20 keV.
The source was at the edge of the IBIS field of view and could thus not be reliably analyzed during the Galactic Bulge Monitoring campaign (PI Kuulkers) from 2018-02-16 13:03:15 to 2018-02-16 16:44:50 during INTEGRAL revolution 1920, i.e., directly following the previous detections.
From 2018-02-16 17:00:39 to 2018-02-17 07:42:29 during the Galactic Center monitoring programme (PI Wilms) in INTEGRAL revolution 1920, we detect the source at:
15.3\pm0.7 cps or 153 mCrab in 20-40 keV band
7.1\pm0.6 cps or 130 mCrab in 40-80 keV band
We use source position for Swift J1658.2-4242 as reported in ATel #11310. We further use the newest observations of the Crab taken during revolution 1921 (2018-02-17/18) as reference values to convert detected counts to Crab values. The source thus appears to have brightened and slightly softened above 20 keV. However, we caution that inconsistent Crab conversions may be the reason for some or even most of the difference in reported flux values.
On timescales of individual INTEGRAL science windows (~30 min), the source shows a flux variability of 20-30% in the 20-40 keV band.
Currently next INTEGRAL observations of the Galactic center region are scheduled for 2018-02-20-22. We encourage further observations of this source with other instruments, especially simultaneous to upcoming INTEGRAL Galactic Center monitoring observations.