On the optical extinction and distance of GRS 1915+105

Abstract

Based on new millimeter and radio observations, we reevaluate the total hydrogen column density along the line of sight to the microquasar GRS 1915+105 to NH=(3.5 +/- 0.3) 10^22 cm^-2. Our value is consistent with the one derived from X-ray measurements, namely (3.8 +/- 0.3) 10^22 cm^-2 (Ebisawa et al. 1998). Using the empirical law between the visual extinction and the total column density of hydrogen, Av is found to 19.6 +/- 1.7 mag. This result is 7 mag lower than previously thought, and therefore, a reevaluation of infrared fluxes after derredening is needed. The revisited kinematic study allows to give a lower limit to the distance of GRS 1915+105, namely 6.0 kpc. Taking into account the most accurate upper limit of distance inferred from radio data (11.2 +/- 0.8 kpc; Fender et al. 1999) as well as this lower limit, this implies a distance of 9.0 +/- 3.0 kpc .