Selection Effects on the Orbital Period Distribution of Low Mass Black Hole X-ray Binaries

TL;DR

This study examines the observed scarcity of short-period low mass black hole X-ray binaries by correcting for observational biases and comparing distributions, predicting hundreds of such binaries exist in the galaxy.

Contribution

It introduces a method to account for observational effects and provides estimates of the true population of short-period black hole binaries.

Findings

Predicted >200 and <3000 binaries with 2-3 hour periods in the galaxy.

Estimated ~600 binaries with periods between 3 and 10 hours.

Identified observational biases affecting the detection of short-period systems.

Abstract

We investigate the lack of observed low mass black hole binary systems at short periods ( < 4 hours) by comparing the observed orbital period distribution of 17 confirmed low mass Black hole X-ray Binaries (BHXBs) with their implied period distribution after correcting for the effects of extinction of the optical counterpart, absorption of the X-ray outburst and the probability of detecting a source in outburst. We also draw samples from two simple orbital period distributions and compare the simulated and observed orbital period distributions. We predict that there are >200 and <3000 binaries in the Galaxy with periods between 2 and 3 hours, with an additional ~600 objects between 3 and 10 hours