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

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 2...

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Bibliographic Details
Published in:The Astrophysical journal 2013-05, Vol.768 (2), p.1-7
Main Authors: Steeghs, D, McClintock, J E, Parsons, S G, Reid, M J, Littlefair, S, Dhillon, V S
Format: Article
Language:English
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
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Summary: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.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/768/2/185