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Comptonization and reflection of X-ray radiation and the X-ray-radio correlation in the chi

a r X i v :a s t r o -p h /0207474v 2 6 O c t 2002

Astronomy &Astrophysics manuscript no.(will be inserted by hand later)

Comptonization and re?ection of X-ray radiation and the X-ray-radio correlation in the χ-states of GRS 1915+105?

A.Rau 1,2&J.Greiner 1,2

1Astrophysical Institute Potsdam,An der Sternwarte 16,14482Potsdam,Germany

2

Max-Planck-Institute for extraterrestrial Physics,Giessenbachstrasse,85748Garching,Germany

Received 8March 2002;accepted ????

Abstract.We present a comprehensive X-ray study of four years of pointed RXTE observations of GRS 1915+105in the χ-state.We interpret the behavior of the hard power law tail spectrum as coming from inverse Compton scattering of soft disk photons on a thermally dominated hybrid corona above the accretion disk.GRS 1915+105shows a strong,variable re?ection amplitude.As in other BHC and in Seyfert galaxies,a correlation between the power law slope and the re?ection was found.Also,the radio ?uxes at 2.25GHz and 15GHz correlate with the power law slope,thus revealing a connection between the out?owing matter and the comptonizing region in the χ-states.

Key words.X-ray:stars –binaries:close –sources:individual:GRS 1915+105

1.Introduction

With the discovery of superluminal ejections (Mirabel &Rodriguez 1994)from the galactic transient source GRS 1915+105and GRO J1655-40,much observational and theoretical attention has been directed to the ?eld of mi-croquasars.Microquasars are thought to be downscaled analogs to quasars exhibiting much smaller time scales and are therefore potential laboratories for studying ac-cretion and relativistic jets near black holes (Mirabel et al.1992).The most prominent object of this type is the galac-tic X-ray binary system GRS 1915+105which shows dra-matic variability (Greiner et al.1996)in light curve,quasi-periodic oscillations,phase lags and coherence behavior (Morgan et al.1997,Muno et al.2001).GRS 1915+105is the most energetic object known in our galaxy with a luminosity of ~1038erg/s in the low state.

GRS 1915+105harbors a black hole of 14M ⊙(Greiner et al.2001b)making it the most massive stellar black hole known.Being in the galactic plane and at a distance of ~12kpc the source su?ers a very high extinction in the optical band of the order of 25-30mag (Greiner et al.1994,Chaty et al.1996).Greiner et al.(2001a)found the donor to be an K-M III late type giant as determined from ab-sorption line measurements in the near infrared.