Prospects for gamma-ray observations of narrow-line Seyfert 1 galaxies with the Cherenkov Telescope Array

TL;DR

This paper assesses the potential of the Cherenkov Telescope Array to detect gamma-ray narrow-line Seyfert 1 galaxies, showing promising prospects especially during high or flaring states, and emphasizing the importance of low-energy thresholds.

Contribution

It provides the first extensive simulation-based analysis of CTA's ability to observe gamma-ray NLSy1 galaxies, considering various intrinsic and extragalactic absorption effects.

Findings

Brightest sources can be detected during flaring states.

Detection is possible even with internal absorption in the central regions.

CTA's low-energy threshold is crucial for observing sources within opaque regions.

Abstract

Gamma-ray emitting narrow-line Seyfert 1 ($\gamma$-NLSy1) galaxies are thought to harbour relatively low-mass black holes (10$^6$-10$^8$ M$_{\odot}$) accreting close to the Eddington limit. They show characteristics similar to those of blazars, such as flux and spectral variability in the gamma-ray energy band and radio properties which point toward the presence of a relativistic jet. These characteristics make them an intriguing class of sources to be investigated with the Cherenkov Telescope Array (CTA), the next-generation ground-based gamma-ray observatory. We present our extensive set of simulations of all currently known $\gamma$-ray emitters identified as NLS1s (20 sources),investigating their detections and spectral properties, taking into account the effect of both the extra-galactic background light in the propagation of gamma-rays and intrinsic absorption components.We find that the prospects for observations of $\gamma$-NLSy1 with CTA are promising. In particular, the brightest sources of our sample, SBS 0846+513, PMN J0948+0022, and PKS 1502+036 can be detected during high/flaring states, the former two even in the case in which the emission occurs within the highly opaque central regions, which prevent $\gamma$ rays above few tens of GeV to escape. In this case the low-energy threshold of CTA will play a key role. If, on the other hand, high-energy emission occurs outside the broad line region, we can detect the sources up to several hundreds of GeV-depending on the intrinsic shape of the emitted spectrum. Therefore, CTA observations will provide valuable information on the physical conditions and emission properties of their jets.