The MAVERIC Survey: Chandra/ACIS Catalog of Faint X-Ray Sources in 38 Galactic Globular Clusters
Arash Bahramian, Jay Strader, James C. A. Miller-Jones, Laura Chomiuk, Craig O. Heinke, Thomas J. Maccarone, David Pooley, Laura Shishkovsky, Vlad Tudor, Yue Zhao, Kwan Lok Li, Gregory R. Sivakoff, Evangelia Tremou, Johannes Buchner
Abstract
Abstract Globular clusters host a variety of lower-luminosity ( L X < 10 35 erg s −1 ) X-ray sources, including accreting neutron stars (NSs) and black holes (BHs), millisecond pulsars (MSPs), cataclysmic variables, and chromospherically active binaries. In this paper, we provide a comprehensive catalog of more than 1100 X-ray sources in 38 Galactic globular clusters (GCs) observed by the Chandra X-ray Observatory’s Chandra/ACIS detector. The targets are selected to complement the MAVERIC survey’s deep radio continuum maps of Galactic GCs. We perform photometry and spectral analysis for each source, determine a best-fit model, and assess the possibility of it being a foreground or background source based on its spectral properties and location in the cluster. We also provide basic assessments of variability. We discuss the distribution of X-ray binaries in GCs and their X-ray luminosity function, and we carefully analyze systems with L X > 10 33 erg s −1 . Among these moderately bright systems, we discover a new source in NGC 6539 that may be a candidate accreting stellar-mass BH or a transitional MSP. We show that quiescent NS low-mass X-ray binaries in GCs may spend ∼2% of their lifetimes as transitional MSPs in their active ( L X > 10 33 erg s −1 ) state. Finally, we identify a substantial underabundance of bright ( L X > 10 33 erg s −1 ) intermediate polars in GCs compared to the Galactic field, in contrast with the literature of the past two decades.