Spectral analysis of χ class data of GRS 1915+105 using TCAF solution

The class variable source GRS 1915+105 exhibits a wide range of time variabilities on timescales of a few seconds to a few days. Depending on the count rates in different energy bands and the nature of the conventional color-color diagram, the variabilities were classified into sixteen classes that were later sequenced in ascending order of Comptonization Efficiency(CE), which is the ratio of power-law and blackbody photons. However, CE estimation is based on an empirical model which does not provide us with a comprehensive picture regarding accretion flow dynamics around the central source. In reality, the accretion flow is comprised of two components: the high angular momentum Keplerian flow in the form of a radiatively efficient disk and a low angular momentum radiatively inefficient sub-Keplerian halo enveloping the disk. These two components contribute differently to the overall flux due to the differences in their radiative efficiencies. Therefore, it is necessary to analyze the spectral behaviors and time variabilities in terms of accretion rates. In χ class, X-ray flux is steady with no significant variation, however various χsubclasses are observed at different X-ray fluxes and variations of count rates across different χ subclasses must be linked to the variation of flow parameters such as the accretion rates, be it the Keplerian disk rate and/or the low angular momentum halo rate. This motivated us to analyze the spectra of the χ class data implementing the physical Two Component Advective Flow(TCAF) solution which directly extracts these two rates from spectral fits. We find that in the χ2,4 classes, which are reportedly devoid of significant outflows, the spectra could be fitted well applying the TCAF solution alone. In the χ1,3 classes, which are always linked with outflows, a cutoff power-law model is needed in addition to the TCAF solution.At the same time, the normalization required by this model along with the variation of photon index and exponential roll-off factor provides us with information on the relative dominance of the outflow in the latter two classes. TCAF fit also supplies us with the size and location of the Compton cloud along with its optical depth. Thus by fitting with TCAF, a physical understanding of the flow geometry in different χclasses of GRS 1915+105 has been obtained.

Correlations of Active Galactic Nuclei with Microquasars

Correlations of active galactic nuclei （AGNs） with microquasars are discussed based on the coexistence of the Blandford-Znajek （BZ） and magnetic coupling （MC） processes （CEBZMC） in black hole （BH） accretion disk. The proportions of several quantities of BH systems for both AGNs and microquasars are derived by combining the observational data with CEBZMC. It is shown that the square of the magnetic field at the BH horizon is inversely proportional to the BH mass, while the accretion rate of the disk is proportional to the BH mass. In addition, the very steep emissivity indexes from the recent XMM-Newton observations of the nearby bright Seyfert 1 galaxy MCG-6-30-15 and the microquasars XTE J1650-500 are well fitted by considering the MC effects on the disk radiation. These results suggest strongly the correlations of A GNs with microquasars.

A magnetic reconnection model for quasi-periodic oscillations in black hole systems

The quasi-periodic oscillations （QPOs） in black hole （BH） systems with different scales are interpreted based on the magnetic reconnection of large-scale mag- netic fields generated by toroidal electric currents flowing in the inner region of the accretion disk, where the current density is assumed to be proportional to the mass density of the accreting plasma. The magnetic connection （MC） is taken into account in resolving dynamic equations describing the accretion disk, in which the MC be- tween the inner and outer disk regions, between the plunging region and the disk, and between the BH horizon and the disk are involved. It turns out that a single QPO frequency associated with several BH systems with different scales can be fitted by in- voking the magnetic reconnection due to the MC between the inner and outer regions of the disk, including the BH binaries XTE J1859＋226, XTE J1650-500 and GRS 1915＋105 and the massive BHs in NGC 5408 X-1 and RE J1034＋396. In addition, the X-ray spectra corresponding to the QPOs for these sources are fitted based on the typical disk-corona model.