AstroSat/UVIT observations of IC4329A: Constraining the accretion disc inner radius

TL;DR

This study uses high-resolution UV imaging from AstroSat to analyze the accretion disk in IC4329A, revealing that the UV emission aligns with standard models only if the disk's inner radius is significantly larger than the innermost stable orbit.

Contribution

First high-resolution UV imaging of IC4329A's accretion disk enabling precise separation of AGN and host galaxy emissions, constraining the disk's inner radius.

Findings

UV emission consistent with standard disk models at larger radii

Inner disk radius estimated to be 80-150 gravitational radii

High-resolution UV data improves understanding of accretion disk structure

Abstract

We present a study of far and near-ultraviolet emission from the accretion disk in a powerful Seyfert 1 galaxy IC4329A using observations performed with the Ultraviolet Imaging Telescope (UVIT) onboard AstroSat. These data provide the highest spatial resolution and deepest images of IC4329A in the far and near UV bands acquired to date. The excellent spatial resolution of the UVIT data has allowed us to accurately separate the extended emission from the host galaxy and the AGN emission in the far and near UV bands. We derive the intrinsic AGN flux after correcting for the Galactic and internal reddening, as well as for the contribution of emission lines from the broad and narrow-line regions. The intrinsic UV continuum emission shows a marked deficit compared to that expected from the "standard" models of the accretion disk around an estimated black hole mass of 1-2x10^8Msun when the disk extends to the innermost stable circular orbit. We find that the intrinsic UV continuum is fully consistent with the standard disk models, but only if the disk emits from distances larger than 80-150 gravitational radii.