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Sachindra Naik, Main Pal & Neeraj Kumari

Short-term variabilities in X-ray/Optical/UV emission from Seyfert 1 galaxy NGC 4593

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Mots-clés : accrétion, disque, noyau galactique actif, NGC 4593, rayons X, galaxies


We present results obtained from a detailed multi-band analysis of the Seyfert 1 galaxy NGC 4593. Publicly available Swift monitoring observations in optical, ultraviolet and X-ray bands were used in the present work. A total of 185 pointings over a duration of about a month were used to understand the variabilities in emission in optical, ultraviolet, soft and hard X-ray bands. It was found that the source emission in the hard X-ray band (1.5-10 keV range) was highly variable compared to that at longer wavelengths. The variability amplitude decreased gradually from hard X-ray to optical bands. A cross-correlation analysis between light curves in different bands inferred that the observed variation in ultraviolet and optical bands is strongly correlated with the hard X-ray emission. Observed time lag for changes in emission in longer wavelength bands with respect to the hard X-ray emission suggests X-ray reprocessing as the cause of variation. Though the observed lag spectrum follows a 4/3rd power of wavelength, as predicted by the standard disk model, the estimated lags are found to be larger than the lags predicted from the standard disk model. This suggests that the actual disk in NGC 4593 is possibly larger than the standard thin disk. Though similar findings have been reported in NGC 5548 and Fairall 9, simultaneous near-infrared, ultraviolet, soft X-ray and hard X-ray band observations of a sample of AGNs with the 1.2 m telescope of Physical Research Laboratory at Mount Abu, India and first space-based multiwavelength observatory of India - AstroSat will provide significant information on the actual and model predicted sizes of the accretion disk.

Keywords : accretion, accretion disks, active galactic nuclei, NGC 4593, X-rays, galaxies

To cite this article

Sachindra Naik, Main Pal & Neeraj Kumari, «Short-term variabilities in X-ray/Optical/UV emission from Seyfert 1 galaxy NGC 4593», Bulletin de la Société Royale des Sciences de Liège [En ligne], Volume 88 - Année 2019, Actes de colloques, 2nd Belgo-Indian Network for Astronomy & Astrophysics (BINA) workshop - October 2018 - Brussels, Belgium, 143-151 URL :

About: Sachindra Naik

Physical Research Laboratory, Navrangpura, Ahmedabad - 380009, India,   

About: Main Pal

Physical Research Laboratory, Navrangpura, Ahmedabad - 380009, India and Centre for Theoretical Physics, Jamia Millia Islamia University, New Delhi - 110025, India,

About: Neeraj Kumari

Physical Research Laboratory, Navrangpura, Ahmedabad - 380009, India,