The black hole in NGC 1313 X-2: constraints on the mass from optical observations

TL;DR

This study constrains the mass of the black hole in NGC 1313 X-2 using optical observations and binary evolution models, suggesting it is likely a 50-100 solar mass black hole based on orbital period data.

Contribution

The paper provides the first detailed binary evolution modeling combined with optical constraints to estimate the black hole mass in NGC 1313 X-2, highlighting the importance of orbital period confirmation.

Findings

Black hole mass likely 50-100 M_Sun if orbital period is confirmed.

Alternative model with a ~20 M_Sun black hole is less probable.

Optical observations effectively constrain the nature of the binary system.

Abstract

We present a theoretical study on the nature of the ultra-luminous X-ray source NGC 1313 X-2. We evolved a set of binaries with high mass donor stars orbiting a 20 M_Sun or a 50-100 M_Sun black hole. Using constraints from optical observations we restricted the candidate binary system for NGC 1313 X-2 to be either a 50-100 M_Sun black hole accreting from a 12-15 M_Sun main sequence star or a ~20 M_Sun black hole with a 12-15 M_Sun giant donor. If the modulation of ~6.12 days recently identified as the orbital period of the system is confirmed, a ~20 M_Sun black hole model becomes unlikely and we are left with the only possibility that the compact accretor in NGC 1313 X-2 is a massive black hole of ~50-100 M_Sun.