Correlated Radio:X‐Ray Emission in the Hard States of Galactic Microquasars

Abstract

We present results of our study of correlated radio and X-ray emission in two black hole candidates and Galactic microquasars GRS 1915+105 and Cyg X-1 in their steady long term hard states, along with Cyg X-3 (using data obtained from Rossi X-Ray Timing Explorer all-sky monitor [RXTE-ASM], Compton Gamma Ray Observatory Burst and Transient Source Experiment [CGRO-BATSE], and Green Bank Intereferometer [GBI]). We detect a pivotal behavior in the X-ray spectrum of GRS 1915+105, correlated to the radio emission. Similar to the results obtained for Cyg X-3, the flux of X-rays softer than the pivoting point correlates with the radio emission, while the corresponding harder X-ray flux anti-correlates with both the radio and the softer X-ray emission, in this state. We examine all the previously reported correlations of X-ray properties with the radio emission in Galactic microquasars and argue that these are consistent with a general picture where a spectral pivoting is a common feature in these sources with the shape of the spectrum determining the flux of radio emission, during the hard states. We also detect a general monotonic increase in the radio emission of these sources with the soft X-ray emission spanning about 5 orders of magnitude. We qualitatively explain these findings with a Two Component Advective Flow model where the location of a boundary layer between the thin disk and the Comptonizing region determines the spectral shape and also the amount of outflow.

Binary corrected X-ray light curve of Cygnus X-3: Implications for the timing properties of the compact binary system

“…Choudhury et al (2003) point out that correlation between the X-ray and radio emission and the anti-correlation between the soft and hard X-rays are directly related to a causal connection between the spectral shape in the X-rays and the radio emission. They have shown that such a picture consistently explains the observed behaviors of three bright Galactic X-ray binary sources Cygnus X-3, Cygnus X-1 and GRS 1915+105.…”

“…This signifies a definite connection between the inflow of matter via accretion disk emission and the outflow via jet emission (Choudhury et al 2003).…”

“…We have folded the RXTE ASM data using the quadratic ephemeris of Singh et al (2002) from MJD 50 410 to MJD 51 400 (P = 0.19968443 d;Ṗ = 5.76 × 10 −10 ; time of zero phase T 0 = 2 440 949.892 JD). The time span chosen for the folding corresponds to the data used by Choudhury et al (2003) for the detailed X-ray, radio and hard X-ray correlation analysis. The folded light curve is shown in Fig.…”

“…At frequencies below 10 −5 Hz it was found that the PDS is consistent with an index of ∼−1 and the rms power below 10 −5 Hz is 21−27%, for these two sources. Recently we had argued that Cyg X-3 is an archetypical black hole binary and have compared its X-ray/ radio emission properties with the other known black hole binaries (Choudhury et al 2003) and hence it is instructive to compare the PDS of Cyg X-3 at very low frequencies. We have derived the PDS of Cyg X-3 at very low frequencies using RXTE-ASM data using a method similar to that followed by Reig et al(2002).…”

Relativistic Jets in the RXTE Era

“…The correlation between radio and Xray emission may also be interpreted within the framework of the Two Component Advective Flow (TCAF) model [47], in which the location of a boundary layer between the thin disk and the Comptonizing region determines the spectral shape and also the amount of outflow [48].…”