First high energy observations of Narrow Line Seyfert 1s with INTEGRAL/IBIS

TL;DR

This study presents the first high-energy (17-100 keV) observations of Narrow Line Seyfert 1 galaxies using INTEGRAL/IBIS, revealing distinct spectral features such as a steeper spectrum and lower energy cutoff compared to classical Seyfert 1s, indicating different nuclear conditions.

Contribution

First high-energy observations of NLS1 galaxies with INTEGRAL/IBIS, providing new spectral insights and highlighting differences from classical Seyfert 1 galaxies.

Findings

Steeper spectrum (Gamma=2.6) than classical Seyfert 1s

High energy cutoff below 60 keV in NLS1s

No soft excess detected in individual objects

Abstract

Narrow Line Seyfert 1 galaxies (NLS1) are very interesting objects which display peculiar properties when compared to their broad line analogues (BLS1). Although well studied in many wavebands, their behaviour at >10 keV is poorly studied and yet important to discriminate between models invoked to explain the complexity observed in the X-ray band. Here we present for the first time high energy observations (17-100 keV) of five NLS1 galaxies (3 bona fide and 2 candidates) detected by INTEGRAL/IBIS and provide for all of them a broad band spectral analysis using data obtained by Swift/XRT below 10 keV. The combined INTEGRAL spectrum is found to be steeper (Gamma=2.6 +/- 0.3) than those of classical Seyfert 1 objects. This is due to a high energy cutoff, which is required in some individual fits as in the average broad band spectrum. The location of this high energy cutoff is at lower energies (E < 60 keV) than typically seen in classical type 1 AGNs; a reflection component may also be present but its value (R < 0.8) is compatible with those seen in standard Seyfert 1s. We do not detect a soft excess in individual objects but only in their cumulative spectrum. Our results suggest a lower plasma temperature for the accreting plasma which combined to the high accretion rates (close to the Eddington rate) point to different nuclear conditions in broad and narrow line Seyfert 1 galaxies, likely related to different evolutionary stages.