Star formation history and X-ray binary populations: the case of the Small Magellanic Cloud

TL;DR

This study investigates the relationship between star formation history and the distribution of X-ray binary populations in the Small Magellanic Cloud, revealing insights into their formation timescales and supernova kick velocities.

Contribution

It provides new empirical evidence linking star formation bursts to Be/X-ray binary occurrences and constrains neutron star kick velocities in the SMC.

Findings

Be/X-ray binaries are associated with star formation bursts 25-60 Myr ago.

Regions with recent star formation are deficient in Be-XRBs.

Estimated Be-XRB production rate is approximately 1 system per 3 x 10^-3 solar masses per year.

Abstract

Using Chandra, XMM-Newton, and optical photometric catalogs we study the young X-ray binary (XRB) populations of the Small Magellanic Cloud. We find that the Be/X-ray binaries (Be-XRBs) are observed in regions with star formation rate bursts ~25-60 Myr ago. The similarity of this age with the age of maximum occurrence of the Be phenomenon (~40 Myr) indicates that the presence of a circumstellar decretion disk plays a significant role in the number of observed XRBs in the 10-100 Myr age range. We also find that regions with strong but more recent star formation (e.g., the Wing) are deficient in Be-XRBs. By correlating the number of observed Be-XRBs with the formation rate of their parent populations, we measure a Be-XRB production rate of ~1 system per 3 x 10^(-3) M$_{\odot}$/yr. Finally, we use the strong localization of the Be-XRB systems in order to set limits on the kicks imparted on the neutron star during the supernova explosion.