paper

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

arXiv:0806.4824 · doi:10.1111/j.1365-2966.2008.13657.x

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.

7 pages, 5 figures; corrected text in section 3, accepted for publication in MNRAS

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