Mining the XRT archive to probe the X-ray absorber structure in the AGN population

Abstract

One of the key ingredients of the Unified Model of Active Galactic Nuclei (AGN) is the presence of a torus-like optically thick medium composed by dust and gas around the putative supermassive black hole. However, the structure, size and composition of this circumnuclear medium are still matter of debate. To this end, the search for column density variations through X-ray monitoring on different timescales (months, weeks and few days) is fundamental to constrain size, kinematics and location of the X-ray absorber(s). Here we describe our project of mining the Swift-XRT archive to assemble a sample of AGN with extreme column density variability and determining the physical properties of the X-ray absorber(s). We also present the results obtained from a daily-weekly Swift-XRT follow-up monitoring recently performed on one of the most interesting new candidates for variability discovered so far, Mrk 915.

6 pages, 3 figures. To appear in Proceedings of Science for the "Swift: 10 years of Discovery" meeting, held in Rome (2-5 December 2014)

References in corpus (4)

• Occultation measurement of the size of the X-ray emitting region in the Active Galactic Nucleus of NGC 1365
• Search for X-ray occultations in Active Galactic Nuclei
• NGC 1365: A low column density state unveiling a low ionization disk wind
• Scaling relations of the colour-detected cluster RzCS 052 at z=1.016 and of some other high redshift clusters