A Parallax Distance to the Microquasar GRS 1915+105 and a Revised Estimate of its Black Hole Mass

TL;DR

This study measures the distance to the microquasar GRS 1915+105 using VLBA parallax, revises its black hole mass, and analyzes jet properties and black hole spin, providing new insights into its astrophysical characteristics.

Contribution

It provides the first direct parallax distance measurement to GRS 1915+105 and refines the black hole mass and jet parameters, improving understanding of its nature.

Findings

Distance to GRS 1915+105 is 8.6 kpc.

Black hole mass is estimated at 12.4 solar masses.

Jet inclination is about 60 degrees with speeds up to 0.81c.

Abstract

Using the Very Long Baseline Array, we have measured a trigonometric parallax for the micro quasar GRS 1915+105, which contains a black hole and a K-giant companion. This yields a direct distance estimate of 8.6 (+2.0,-1.6) kpc and a revised estimate for the mass of the black hole of 12.4 (+2.0,-1.8) Msun. GRS 1915+105 is at about the same distance as some HII regions and water masers associated with high-mass star formation in the Sagittarius spiral arm of the Galaxy. The absolute proper motion of GRS 1915+105 is -3.19 +/- 0.03 mas/y and -6.24 +/- 0.05 mas/y toward the east and north, respectively, which corresponds to a modest peculiar speed of 22 +/-24 km/s at the parallax distance, suggesting that the binary did not receive a large velocity kick when the black hole formed. On one observational epoch, GRS 1915+105 displayed superluminal motion along the direction of its approaching jet. Considering previous observations of jet motions, the jet in GRS 1915+105 can be modeled with a jet inclination to the line of sight of 60 +/- 5 deg and a variable flow speed between 0.65c and 0.81c, which possibly indicates deceleration of the jet at distances from the black hole >2000 AU. Finally, using our measurements of distance and estimates of black hole mass and inclination, we provisionally confirm our earlier result that the black hole is spinning very rapidly.