Research Projects

Active galactic nuclei (AGNs) at the center of galaxies are considered to be the primary contributors to the complex spectral and temporal behavior of these regions throughout the electromagnetic radiation spectrum. In a series of three key papers viz. Sriram et al. 2022; Nour and Sriram 2023a, Nour and Sriram 2023b we showed how important are such correlations. Sriram et al. (2022) suggested that a break in the relation between photon index and mass of the black hole as well as FWHM of Hβ and the breaks were found to be at ~10^8 solar mass and ~4000 km s-1. Based on relatively larger sample of AGNs, our studies revealed slightly different correlations and regressions between Balmer components and X-ray power-law index than what reported by Jin et al. (2012a). Nour and Sriram (2023a), Nour and Sriram (2023b) studied various correlation and determined different regression estimates in different energy bands. These relations were used to find that, how different emitting regions mutually control respective structures in the accretion disk. In one of the studies we showed that X-ray power-law index does not varied with any of the redshift and similar studies unveil similar correlations with other optical parameters (Nour & Sriram 2023b). Apart from the spectral domain, a study in the time domain also plays a key role in exploring the dynamics and geometry of the inner region of the accretion disk. Hard lags are quite common but soft lags has its important in order to confirm the reflection models in AGNs. Sriram et al. (2023) studied flux dependent energy-lag and frequency-lag spectra of an AGN source Mrk 704 and found that even though the flux varied by 50% there is no change in the estimated lag. This suggests that the presence of cloud during the low flux state plays a key role in producing the lag spectra. We estimated the size of the SMBH based on the estimated lag which is within uncertainty of the mass estimated from optical spectrum of the source. I would like to perform such studies in other AGNs which constrain the mass of SMBH, cloud size and comptonization region. Objective: study of correlations and regression of component dependent Balmer lines and their association with emission parameters in other wavelengths will be studied viz. Mg II, UV, soft X-ray and hard X-rays. Energy-lag and frequency-lag spectra in X-ray band using XMM-Newton and Chandra satellites at different flux emitted by AGNs will be studied. This will help to understand the nature of reflection model, whether corona is been varying or not and how it is shining the inner region of accretion disk. Significance: By studying frequency and energy dependent time lags, one can constrain the mass of the SMBH, size of the cloud and comptonization region in AGN.The correlation and regression studies in different wavelengths will help us to determine the production mechanism of various spectral lines, what is the dynamics of the clouds around the SMBH.