Abstract Details
| Name: Savithri H. Ezhikode Affiliation: St. Thomas College, Kozhencherry, Kerala Conference ID: ASI2015_607 Title : UV and X-ray Correlations of the NLS1 galaxy Ark 564 Authors and Co-Authors : Gulab Chand Dewangan, IUCAA, Pune Ranjeev Misra, IUCAA, Pune, Shruti Tripathi, IUCAA, Pune and Ninan Sajeeth Philip, St. Thomas College, Kozhencherry, Kerala Abstract Type : Poster Abstract Category : Extragalactic astronomy Abstract : The optical/UV and X-ray variability in AGNs and their interrelationship is an unclear issue till date. It is debatable that the X-ray variability arises due to the optical/UV flux variations or the latter originates from the reprocessing of X-rays. In the first case, the disc flux is expected to vary with variations in the accretion rate ($\dot{M}$) and so does the X-ray spectrum. We address this problem by studying the UV and X-ray correlation of Arakelian 564 (Ark 564) using the simultaneous X-ray and UV data available from XMM-Newton. Ark 564 is one of the brightest sources among Narrow-Line Seyfert 1 (NLS1) galaxies which accretes at Super-Eddington rate. We describe the soft and hard X-ray spectra of this source by Comptonization models, assuming a geometry of `two-component corona' coupled to the accretion disc. The geometry suggests a steepening of high energy spectrum with an increase in the soft X-ray flux and therefore due to an increase in the accretion rate. We confirm this by finding that the high energy photon index ($\Gamma$) and the scattered fraction ($f_{sc}$) of photons from the cool, optically thick corona to the optically thin, hot corona are well correlated with the Eddington ratio ($\dot{m}=\dot{M}/\dot{M_{Edd}}$) and soft and hard X-ray luminosities relative to the Eddington value ($L_{soft}/L_{Edd}$ and $L_{hard}/L_{Edd}$ respectively). We also find positive correlations between $\Gamma$ and $f_{sc}$, $L_{hard}/L_{Edd}$ and $L_{soft}/L_{Edd}$ and $L_{soft}/L_{Edd}$ and $\dot{m}$, whereas $L_{hard}/L_{Edd}$ and $\dot{m}$ show poor correlation. |