Archival Chandra observations of M22
ATel #8035; Killian Long, Paul Callanan (University College Cork)
on 10 Sep 2015; 15:53 UT
Credential Certification: Paul Callanan (paulc@ucc.ie)
Subjects: Black Hole, Globular Cluster
We report on a 86 ksec archival Chandra ACIS observation of the globular cluster M22 (obtained 2014-05-22). These data have been used to search for X-ray counterparts to the two black hole candidates, M22 VLA1 and M22 VLA2, identified by Strader et al (2012, Nature 490 71), and are considerably deeper than the 16 ksec ACIS exposure used for this previous work. We set upper limits of ~2e30 ergs/s (0.5-10 keV) on any X-ray counterparts in these new data, ~3 times lower than previously published. This is comparable to, or fainter than, the lowest X-ray luminosity of any detected Galactic quiescent black hole system, despite these two objects being 10-100 times brighter in the radio (e.g. Gallo et al 2014 MNRAS 445 290). These results also appear to be inconsistent with M22 VLA1 and VLA2 containing more massive black hole (M~15-20 Mo), as these should also have been detected in these deeper observations (Strader et al 2012).
