Astrosat Observation of Class Variable Source GRS 1915+105: AN Analysis in the Light of Two Component Advective Flow Model
Abstract
he class variable source GRS 1915+105 is a well studied source. It also has been observed by Indian multi-wavelength satellite Astrosat over different variability classes. In its theta class of observation, the distinct concentration of power around the frequency $\sim$ 3-4 Hz is observed in the dynamic power density spectra (PDS). With the increase in the photon count rate, the dominant frequency increases slightly. The dynamic spectra show a gradual softening with the increase in the flux. This suggests a plausible transition from soft-intermediate state (SIMS) to soft state (SS). The photon index gradually increases as the source transits to softer states. The spectral and timing behaviours have a direct correlation with the variation of flow parameters which can be studied in the light of Two Component Advective Flow (TCAF) paradigm. As the photon count increases, the disk rate also increases and shock location moves in towards the black hole. The oscillation of the shock front is manifested as distinct peak in PDS. As a result, we observe an increase of this so-called QPO frequency with the reduction of shock location. As we observe the QPOs in different energy bands like 4-6 keV, 6-10 keV and 10-25 keV, the Q-factor decreases and integrated rms power contributions are also not the same. This implies different oscillation frequencies at different length scales of the accretion flow. In the dynamic PDS, we further observe high frequency (~$\sim$40 Hz) and low frequency ($\sim$2 Hz) oscillation. This provides us with further insights in probing the accretion flow at different length scales in different energy bands.
- Publication:
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43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E1711B