Measuring The Soft Excess Region Size Relative to the Corona in AGN With NICER

TL;DR

This study uses NICER observations to measure and compare the sizes of the soft excess emission regions and the corona in different AGN, revealing variability in their relative sizes without relying on spectral model assumptions.

Contribution

It provides the first independent quantification of the soft excess region size relative to the corona in AGN, based on variability time scales.

Findings

The soft excess region size varies among AGN.

In TON S180, the soft excess is comparable to the corona.

In MRK 335 and 1H0707-495, the soft excess is 2-4 times larger.

Abstract

The soft excess is a significant emission component in the Soft (<1 keV) X-ray spectra of many AGN. It has been explained by disk reflection, a warm corona and other models. Understanding its origin is crucial for the energy budget of AGN emission, and for using it to study the inner accretion disk. Here, we track the weeks-to-months variability of several AGN that show different levels of soft excess strength with NICER. We use the variability time scales to compare the relative size of the soft excess emission region to the corona producing the hard X-ray emission above 1 keV. We find that the size of the soft excess emission region relative to the corona is not the same for the three sources studied. For TON S180, the soft excess region is comparable in size to the hard corona. While for MRK 335 and 1H0707-495, the soft excess region is larger than the corona by a factor of 2-4. This is the first time the relative sizes are quantified independently of the assumptions of the spectral models.