IC 751: a new changing-look AGN discovered by NuSTAR

Abstract

We present the results of five NuSTAR observations of the type 2 active galactic nucleus (AGN) in IC 751, three of which were performed simultaneously with XMM-Newton or Swift/XRT. We find that the nuclear X-ray source underwent a clear transition from a Compton-thick ($N_{\mathrm{H}}\simeq 2\times 10^{24}\mathrm{c}{\mathrm{m}}^{-2}$) to a Compton-thin ($N_{\mathrm{H}}\simeq 4\times 10^{23}\mathrm{c}{\mathrm{m}}^{-2}$) state on timescales of $\lesssim 3$ months, which makes IC 751 the first changing-look AGN discovered by NuSTAR. Changes of the line-of-sight column density at a $\sim 2\sigma$ level are also found on a time-scale of $\sim 48$ hours ($\Delta N_{\mathrm{H}}\sim 10^{23}\mathrm{c}{\mathrm{m}}^{-2}$). From the lack of spectral variability on timescales of $\sim 100$ ks we infer that the varying absorber is located beyond the emission-weighted average radius of the broad-line region, and could therefore be related either to the external part of the broad-line region 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 ($N_{\mathrm{H}}\sim 3.8\times 10^{23}\mathrm{c}{\mathrm{m}}^{-2}$) from that of the varying clouds [$N_{\mathrm{H}}\sim (1-150)\times 10^{22}\mathrm{c}{\mathrm{m}}^{-2}$], and to constrain that of the material responsible for the reprocessed X-ray radiation ($N_{\mathrm{H}}\sim 6\times 10^{24}\mathrm{c}{\mathrm{m}}^{-2}$). 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.

Accepted for publication in ApJ, 11 pages, 6 figures

Cited by in corpus (60)

• BAT AGN Spectroscopic Survey - V. X-ray properties of the Swift/BAT 70-month AGN catalog
• BAT AGN Spectroscopic Survey I: Spectral Measurements, Derived Quantities, and AGN Demographics
• New Spectral Model for Constraining Torus Covering Factors from Broadband X-ray Spectra of Active Galactic Nuclei
• Discovery of 21 New Changing-look AGNs in Northern Sky
• 1ES 1927+654: An AGN Caught Changing Look on a Timescale of Months
• A Mid-IR Selected Changing-Look Quasar and Physical Scenarios for Abrupt AGN Fading
• The Close AGN Reference Survey (CARS) - Mrk 1018 returns to the shadows after 30 years as a Seyfert 1
• A new class of flares from accreting supermassive black holes
• BAT AGN Spectroscopic Survey - XI. The Covering Factor of Dust and Gas in Swift/BAT Active Galactic Nuclei
• X-Ray Spectral Model from Clumpy Torus and Its Application to Circinus Galaxy
• New changing look case in NGC 1566
• X-ray spectral and eclipsing model of the clumpy obscurer in active galactic nuclei
• Long-Term X-ray Variability of Typical Active Galactic Nuclei in the Distant Universe
• NuSTAR observations of WISE J1036+0449, a Galaxy at z$\sim 1$ obscured by hot dust
• The detection and X-ray view of the changing look AGN HE 1136-2304
• The 450 days X-ray monitoring of the changing-look AGN 1ES 1927+654
• The Chandra Deep Fields: Lifting the Veil on Distant Active Galactic Nuclei and X-Ray Emitting Galaxies
• Distinguishing Tidal Disruption Events from Impostors
• The Hunt for Intermediate Mass Black Holes in the JWST Era
• The Host Galaxy and Rapidly Evolving Broad-line Region in the Changing-look Active Galactic Nucleus 1ES 1927+654
• Near Infrared Variability of obscured and unobscured X-ray selected AGN in the COSMOS field
• Compton Thick AGN in the 70 Month Swift-BAT All-Sky Hard X-ray Survey: a Bayesian approach
• The NuSTAR Extragalactic Surveys: X-ray spectroscopic analysis of the bright hard-band selected sample
• BASS XXXIX: Swift-BAT AGN with changing-look optical spectra
• The weak neutral Fe fluorescence line and long-term X-ray evolution of the Compton-thick AGN in NGC 7674
• Modified viscosity in accretion disks. Application to Galactic black hole binaries, intermediate mass black holes and AGN
• BASS XXIX: The near-infrared view of the BLR: the effects of obscuration in BLR characterisation
• Hard X-ray selected AGNs in low-mass galaxies from the NuSTAR serendipitous survey
• Probing the Origin of Changing-look Quasar Transitions with Chandra
• Two New "Turn-off" Changing-look Active Galactic nuclei and Implication on "Partially Obscured" AGNs
• WISE view of changing-look AGNs: evidence for a transitional stage of AGNs
• Insight Into "Changing-Look" AGN Mrk 1018 from the Fe K$\alpha$ Line: The Reprocessing Gas Has Yet to Fully Respond to the Fading of the AGN
• Broadband X-Ray Observations of the 2018 Outburst of the Changing-Look Active Galactic Nucleus NGC 1566
• IC 3639 - A new bona fide Compton thick AGN unveiled by NuSTAR
• An Iwasawa-Taniguchi Effect for Compton-thick Active Galactic Nuclei
• A forward modelling approach to AGN variability -- Method description and early applications
• The RapidXMM Upper Limit Server: X-ray aperture photometry of the XMM-Newton archival observations
• Investigating Changing-Look Active Galactic Nuclei with Long-term Optical and X-Ray Observations
• Unveiling the physics behind the spectral variations of "changing-look" quasars with optical polarimetry
• A Low Incidence of Mid-Infrared Variability in Dwarf Galaxies
• Searching for fast extragalactic X-ray transients in Chandra surveys
• Joint NuSTAR and Chandra analysis of the obscured quasar in IC 2497 - Hanny's Voorwerp system
• Variable mass accretion and failed wind explain changing look phenomena in NGC 1365
• Coevolution of broad emission lines and X-ray spectrum in changing-look AGNs
• The Fermi-LAT view of the changing-look blazar OQ 334
• Hard X-ray View of HCG 16 (Arp 318)
• Highly Variable Active Galactic Nuclei in the SRG/eROSITA All-Sky Survey: I. Constructing Sample and Catalog of Sources Detected in Low State
• NuSTAR observations of the unidentified INTEGRAL sources: constraints on the Galactic population of HMXBs
• The NuSTAR view of the changing look AGN ESO 323-G77
• The Luminosity and Stellar Mass Functions of Red W1-W2 Galaxies
• XMM-Newton and NuSTAR Observations of an Optically Quiescent Quasar
• Multi-epoch hard X-ray view of Compton-thick AGN Circinus Galaxy
• The Awakening Beast in the Seyfert 1 Galaxy KUG 1141+371 I
• The Complex X-ray Obscuration Environment in the Radio Loud Type 2 Quasar 3C 223
• Absorption Variability of the Highly Obscured Active Galactic Nucleus NGC 4507
• X-ray Unveiling Events in a z~1.6 Active Galactic Nucleus in the 7 Ms Chandra Deep Field-South
• Time Domain Astronomy with the THESEUS Satellite
• Selection of Compton-thick AGN from a hard photometric sample using XMM-Newton observations
• Automatic detection of tidal disruption events and other long duration transients in XMM-Newton data
• Evidence of Heavy Obscuration in the Low-Luminosity AGN NGC 4941