INTEGRAL upper limit on the short hard X-ray transient IGR J17533-2928
ATel #14470; V. Sguera (INAF-OAS Bologna, Italy), L. Sidoli (INAF-IASF MIlano, Italy), E. Kuulkers on behalf of the Galactic bulge monitoring team (ESA/ESTEC, Noordwijk, Netherlands)
on 18 Mar 2021; 12:22 UT
Credential Certification: Vito Sguera (sguera@iasfbo.inaf.it)
Subjects: X-ray, Transient
Recent INTEGRAL observations of the Galactic Center, from 13 to 23 February 2021, detected transient hard X-ray activity from the newly discovered source IGR J17533-2928 (ATel #14425) at a flux level of about 12 mCrab (20-80 keV). Subsequent Swift/XRT and NICER follow-up in the softer X-ray band (0.5-10 keV) detected the soft X-ray counterpart with a low X-ray flux state of about 4 x 10-11 erg cm-2 s-1 (ATels #14430, #14442).
The sky region of IGR J17533-2928 was covered by further INTEGRAL observations of the Galactic Center region (PI J. Wilms, E. Kuulkers) carried out from 25 February 2021 at 10:09 to 8 March 2021 at 22:56 UTC (revolutions from 2336 to 2340) for a total on source exposure time of about 23 ks. IGR J17533-2928 was not detected in the energy band of the original discovery (20-80 kev), we inferred a constrained 3 sigma upper limit of about 3 mCrab. We note that no detection was achieved in the alternative energy band 25-60 keV as well.
In the light of the reported upper limit, we can firmly constrain the duration of the hard X-ray outburst (above 20 keV) to no longer than about 10 days (the duration could possibly be even shorter). This makes IGR J17533-2928 an interesting short hard X-ray transient. Further multi-wavelength observations are strongly encouraged.
