Abstract Details
| Name: Prashanth Mohan Affiliation: ARIES, Nainital Conference ID: ASI2015_547 Title : Models of Observational Signatures of Black Holes Authors and Co-Authors : Arun Mangalam, Indian Institute of Astrophysics, Bangalore. Abstract Type : Oral Abstract Category : Thesis Abstract : Light curves from active galactic nuclei (AGN) indicate aperiodic variability over a wide range of timescales: $\sim$ 100 s to a few 100 s in the $\gamma$-rays; $\sim$ 1000 s to a few hours in the optical/UV and X-rays; less than a day to a few days in the optical and radio and months to years in the optical and radio depending on the type of AGN. The variability could be attributed to orbiting inhomogeneities in the vicinity of a supermassive black hole (SMBH) of mass $\sim$ $10^6 - 10^9 M_{\odot}$. Some key issues in this context include the cause for variability over this diverse range of timescales, the presence of quasi-periodic oscillations (QPOs) in this variable emission and how one can use this information to constrain the SMBH mass $M_{\bullet}$, spin $a$, emission region size $r$ and other physical quantities. To address these, we developed theoretical models of disk and jet based variability involving both geometrical and physical effects on emission from the vicinity of the SMBH. General relativistic effects including light bending, time delay, aberration, gravitational and Doppler shifts modulate the simulated light curve. In these models, there is a natural development of a power law shape with slopes in the range $\sim-1.5$ to $-3$ in the simulated power spectral density (PSD) along with a weak to strong QPO, attributable to orbital signatures; the strength of which depends on the number of orbital features - a single feature results in a strong QPO which becomes weaker for multiple emitters. These are supplemented by a timing analysis of the multi-wavelength AGN light curves. For this, we developed a suite of time series analysis techniques consisting of the periodogram, Lomb-Scargle periodogram, multi-harmonic analysis of variance periodogram and wavelet analysis. A data characterization and search strategy is applied to optical and X-ray light curves from AGN to infer the shape of the PSD and its parameters followed by the statistical identification of any characteristic break frequencies or QPOs. We thus used the disk and jet models of orbital signatures to place constraints on $M_{\bullet}$, $a$ and $r$ with inputs from the statistical analysis of observed light curves. |