THE NOT-SO-MASSIVE BLACK HOLE IN THE MICROQUASAR GRS1915+105

• Published in: The Astrophysical journal Vol. 768; no. 2; pp. 1 - 7
• Main Authors: Steeghs, D, McClintock, J E, Parsons, S G, Reid, M J, Littlefair, S, Dhillon, V S
• Format: Journal Article
• Language: English
• Published: United States 10.05.2013
• Subjects: ABSORPTION; ABSORPTION SPECTROSCOPY; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BLACK HOLES; Black holes (astronomy); DISTANCE; EMISSION; Estimates; INCLINATION; INFRARED SPECTRA; LIMITING VALUES; MASS; Microquasars; Orbitals; QUASARS; RADIAL VELOCITY; RESOLUTION; SIMULATION; Spectra; STARS; TELESCOPES; TRANSIENTS; Very Large Telescope; Wavelengths; X RADIATION
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/768/2/185

We present a new dynamical study of the black hole X-ray transient GRS1915+105 making use of near-infrared spectroscopy obtained with X-shooter at the Very Large Telescope. We detect a large number of donor star absorption features across a wide range of wavelengths spanning the H and K bands. Our 24 epochs covering a baseline of over 1 yr permit us to determine a new binary ephemeris including a refined orbital period of P = 33.85 + or - 0.16 days. The donor star radial velocity curves deliver a significantly improved determination of the donor semi-amplitude which is both accurate (K sub(2) = 126 + or - 1 km s super(-1)) and robust against choice of donor star template and spectral features used. We furthermore constrain the donor star's rotational broadening to v sin i = 21 + or - 4 km s super(-1), delivering a binary mass ratio of q = 0.042 + or - 0.024. If we combine these new constraints with distance and inclination estimates derived from modeling the radio emission, a black hole mass of M sub(BH) = 10.1 + or - 0.6 M sub(+ or -) is inferred, paired with an evolved mass donor of M sub(2) = 0.47 + or - 0.27 M sub([middot in circle]). Our analysis suggests a more typical black hole mass for GRS 1915+105 rather than the unusually high values derived in the pioneering dynamical study by Greiner et al. Our data demonstrate that high-resolution infrared spectroscopy of obscured accreting binaries can deliver dynamical mass determinations with a precision on par with optical studies.