The first look at Narrow-Line Seyfert 1 Galaxies with eROSITA

TL;DR

This study provides the first spectral and timing analysis of nearly 1,200 Narrow-Line Seyfert 1 Galaxies using eROSITA data, revealing their X-ray spectral properties, potential ionised outflows, and variability characteristics.

Contribution

It presents the first large-scale X-ray spectral analysis of NLS1s with eROSITA, highlighting extreme spectral steepness and possible outflows, expanding understanding of these galaxies.

Findings

Photon index mean ~2.81 with positive skewness.

About 10% have super-soft photon indices >4.

No significant variability detected in the sample.

Abstract

We present the first look at the spectral and timing analysis of Narrow-Line Seyfert 1 Galaxies (NLS1s) with the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) on board the Spectrum-Roentgen-Gamma (SRG) mission. The sample of about 1,200 NLS1s was obtained via cross-match of the first eROSITA All-Sky Survey (eRASS1) catalogue with the catalogue of spectroscopically selected NLS1s from the Sloan Digital Sky Survey (SDSS) DR12 by Rakshit et al. [ApJS, 229, 39 (2017)]. The X-ray spectral analysis is based on a simple power-law fit. The photon index distribution has a mean value of about 2.81+-0.03, as expected from previous X-ray studies of NLS1s. Interestingly, it is positively skewed, and about 10 percent of the sources are located in the super-soft tail of photon indices larger than 4. These sources are of further interest as their source counts run into the X-ray background at values at around 1 keV. We argue that ionised outflows have been detected by eROSITA and may account for some of the extreme spectral steepness, which is supported by correlations found between the photon index and optical outflows parameters. We analysed the intrinsic X-ray variability of the eRASS1 to eRASS3 light curves of the sample but do not find significant variability neither during the individual survey scans nor between them.