The mass of the black hole in GRS 1915+105: new constraints from IR spectroscopy

TL;DR

This study refines the black hole mass estimate in GRS 1915+105 using IR spectroscopy, addressing spectral contamination issues and proposing new methods to improve radial velocity measurements.

Contribution

It provides updated system parameters and introduces a novel approach to measure radial velocity despite phase-dependent spectral contamination.

Findings

Refined ephemeris for GRS 1915+105.

Identification of phase-dependent CO emission affecting spectra.

Proposed use of H-band atomic features for radial velocity measurement.

Abstract

GRS 1915+105 has the largest mass function of any Galactic black hole system, although the error is relatively large. Here we present spectroscopic analysis of medium-resolution IR VLT archival data of GRS 1915+105 in the K-band. We find an updated ephemeris, and report on attempts to improve the mass function by a refinement of the radial velocity estimate. We show that the spectra are significantly affected by the presence of phase-dependent CO bandhead emission, possibly originating from the accretion disc: we discuss the impact this has on efforts to better constrain the black hole mass. We report on a possible way to measure the radial velocity utilising apparent H-band atomic absorption features and also discuss the general uncertainty of the system parameters of this well-studied object