Accurate classification of 29 objects detected in the 39 months Palermo Swift/BAT hard X-ray catalogue

Abstract

Through an optical campaign performed at 4 telescopes located in the northern and the southern hemispheres, plus archival data from two on-line sky surveys, we have obtained optical spectroscopy for 29 counterparts of unclassified or poorly studied hard X-ray emitting objects detected with Swift/BAT and listed in the 39 months Palermo catalogue. All these objects have also observations taken with Swift/XRT or XMM-EPIC which not only allow us to pinpoint their optical counterpart, but also to study their X-ray spectral properties (column density, power law photon index and F2-10 keV flux). We find that 28 sources in our sample are AGN; 7 are classified as type 1 while 21 are of type 2; the remaining object is a galactic cataclysmic variable. Among our type 1 AGN, we find 5 objects of intermediate Seyfert type (1.2-1.9) and one Narrow Line Seyfert 1 galaxy; for 4 out of 7 sources, we have been able to estimate the central black hole mass. Three of the type 2 AGN of our sample display optical features typical of the LINER class and one is a likely Compton thick AGN. All galaxies classified in this work are relatively nearby objects since their redshifts lie in the range 0.008-0.075; the only galactic object found lies at an estimated distance of 90 pc. We have also investigated the optical versus X-ray emission ratio of the galaxies of our sample to test the AGN unified model. For them, we have also compared the X-ray absorption (due to gas) with the optical reddening (due to dust): we find that for most of our sources, specifically those of type 1.9-2.0 the former is higher than the latter confirming early results by Maiolino et al. (2001); this is possibly due to the properties of dust in the circumnuclear obscuring torus of the AGN.

15 pages, 4 figures, 8 tables, accepted for publication on Astronomy and Astrophysics

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• BAT AGN Spectroscopic Survey I: Spectral Measurements, Derived Quantities, and AGN Demographics
• The distribution of interstellar dust in CALIFA edge-on galaxies via oligochromatic radiative transfer fitting
• Unveiling the nature of the unidentified gamma-ray sources IV: the $\text{Swift}$ catalog of potential X-ray counterparts
• Restarting activity in the nucleus of PBC J2333.9-2343: an extreme case of jet realignment
• The INTEGRAL/IBIS AGN catalogue: an update
• Accurate classification of 75 counterparts of objects detected in the 54 month Palermo Swift/BAT hard X-ray catalogue
• Hard X-ray selected giant radio galaxies -- II. Morphological evidence of restarted radio activity
• Detection of faint broad emission lines in type 2 AGN: I. Near infrared observations and spectral fitting
• The nature of fifty Palermo Swift-BAT hard X-ray objects through optical spectroscopy
• Low-luminosity X-ray sources and the Galactic ridge X-ray emission
• Hard X-ray selected giant radio galaxies - I. The X-ray properties and radio connection
• Hard X-ray luminosity functions of cataclysmic variables: Joint Swift/BAT and Gaia data
• A New Sample of Obscured AGNs Selected from the XMM-Newton and AKARI Surveys
• Stellar population properties for a sample of hard X-ray AGNs
• Variable broad lines and outflow in the weak blazar PBC J2333.9-2343
• Optical spectroscopic classification of 35 hard X-ray sources from the Swift-BAT 70-month catalogue
• Indications of magnetic accretion in Swift J0826.2-7033
• A new panchromatic classification of unclassified Burst Alert Telescope active galactic nuclei
• SRG/ART-XC all-sky X-ray survey: Catalog of sources detected during the first year