MG13 - Talk detail

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Abstract

Generally, most of the transient black hole candidates (BHCs) show low and intermediate frequency quasi-periodic oscillations (QPOs) ranging between 0.01 to 30 Hz in their power density spectra (PDS). More precisely these QPOs are observed during hard and intermediate (hard-intermediate or soft-intermediate) spectral states. Our study during the outburst phases of few Galactic transient black hole candidates (for e.g., GX 339-4, H 1743-322, GRO J1655-40) show that during the rising phases (mainly during hard and hard-intermediate spectral states) QPO frequencies are observed to be increasing monotonically and during declining phases (during same spectral states as of rising) the sources show a monotonically decreasing nature of QPO frequencies. There are many models available in literature for explaining the origin of QPOs, but one satisfactory model, namely, shock oscillation model (SOM) by Chakrabarti and his collaborators in mid 90's shows that the oscillation of X-ray intensity is actually due to the oscillation of the post-shock (Comptonizing) region. According to this model the oscillations take place at a frequency equals to the inverse to the infall time in the post-shock region. Also the above mentioned evolving nature of the QPOs during the rising and declining phases of the outbursts, can be explained with Propagating Oscillatory Shock (POS) model, which is the special (propagating shock wave) case of SOM. According to this POS model solution, at rising phases of the outbursts, a shock wave moves toward the black hole and at declining phases it moves away from the black hole and as a result of that during the rising phases QPO frequency increases with time (day) and during the declining phases QPO frequency decreases with time (day). Here we present the results from 2005 outburst of GRO J1655-40, 2010-11 outburst of GX 339-4 and 2010 & 2011 outbursts of H 1743-322. Evolutions of QPO frequency during the rising and the declining phases of these outbursts are well fitted with POS model and physical parameters of the shock waves are extracted, will be discussed.

Session

Accepted

Yes

Order

Time

Talk

Title

Abstract

The Galactic black hole candidate H 1743-322 exhibited several X-ray outbursts in past decade. Recently, it showed two outbursts in August 2010 and April 2011 in a quick time period. The nature (outburst profile light curve, evolution of quasi-periodic oscillation frequency and spectral states, etc.) of these two successive outbursts, which continued for around two months each, are very similar. Similar to other transient black hole candidates, this source also exhibited quasi-periodic oscillations (QPOs) in power-density spectra (PDS). Also, similar to other outbursting black hole candidates (for e.g., GX 339-4, GRO J1655-40, XTE J155-564 etc.), this source showed the evolutions of the QPO frequencies during both the rising and declining phases of both the outbursts. During the outbursts four basic spectral states are observed: hard, hard-intermediate, soft-intermediate and soft; and these states make a hysteresis-loop in the sequence: hard -> hard-intermediate -> soft-intermediate -> soft -> soft-intermediate -> hard-intermediate -> hard. According to the two-component advective flow (TCAF) model (Chakrabarti & Titarchuk 1995) and as mentioned in Mandal and Chakrabarti (2010), we can show that this hysteresis behaviour cannot be achieved by changing a single parameter, namely the accretion disk of the Keplerian flow; requires the variation of the rates of both the low angular momentum halo (sub-Keplerian) and the high angular momentum, viscous disk (Keplerian) flows of matters.

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