IC 751: A NEW CHANGING LOOK AGN DISCOVERED by NUSTAR

C. Ricci, F. E. Bauer, P. Arevalo, S. Boggs, W. N. Brandt, F. E. Christensen, W. W. Craig, P. Gandhi, C. J. Hailey, F. A. Harrison, M. Koss, C. B. Markwardt, D. Stern, E. Treister, W. W. Zhang

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Abstract

We present results of five Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the type 2 active galactic nucleus (AGN) in IC 751, three of which were performed simultaneously with XMM-Newton or Swift/X-Ray Telescope. We find that the nuclear X-ray source underwent a clear transition from a Compton-thick () to a Compton-thin () state on timescales of months, which makes IC 751 the first changing look AGN discovered by NuSTAR. Changes of the line of sight column density at the ∼2σ level are also found on a timescale of ∼48 hr (). From the lack of spectral variability on timescales of ∼100 ks, we infer that the varying absorber is located beyond the emission-weighted average radius of the broad-line region (BLR), and could therefore be related either to the external part of the BLR or a clumpy molecular torus. By adopting a physical torus X-ray spectral model, we are able to disentangle the column density of the non-varying absorber () from that of the varying clouds , and to constrain that of the material responsible for the reprocessed X-ray radiation (). We find evidence of significant intrinsic X-ray variability, with the flux varying by a factor of five on timescales of a few months in the 2-10 and 10-50 keV band.

Original languageEnglish (US)
Article number5
JournalAstrophysical Journal
Volume820
Issue number1
DOIs
StatePublished - Mar 20 2016

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Ricci, C., Bauer, F. E., Arevalo, P., Boggs, S., Brandt, W. N., Christensen, F. E., Craig, W. W., Gandhi, P., Hailey, C. J., Harrison, F. A., Koss, M., Markwardt, C. B., Stern, D., Treister, E., & Zhang, W. W. (2016). IC 751: A NEW CHANGING LOOK AGN DISCOVERED by NUSTAR. Astrophysical Journal, 820(1), [5]. https://doi.org/10.3847/0004-637X/820/1/5