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Published February 21, 2018 | Published + Submitted
Journal Article Open

Joint NuSTAR and Chandra analysis of the obscured quasar in IC 2497 - Hanny's Voorwerp system


We present new Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the core of IC 2497, the galaxy associated with Hanny's Voorwerp. The combined fits of the Chandra  (0.5–8 keV) and NuSTAR  (3–24 keV) X-ray spectra, together with WISE mid-IR photometry, optical longslit spectroscopy and optical narrow-band imaging, suggest that the galaxy hosts a Compton-thick active galactic nucleus (AGN) (N_H ∼ 2 × 10^(24) cm^(−2), current intrinsic luminosity Lbol ∼ 2–5 × 10^(44) erg s^(−1)) whose luminosity dropped by a factor of ∼50 within the last ∼100 kyr. This corresponds to a change in Eddington ratio (ER) from ^λEdd ∼ 0.35 to ^λEdd ∼ 0.007. We argue that the AGN in IC 2497 should not be classified as a changing-look AGN, but rather we favour the interpretation where the AGN is undergoing a change in accretion state (from radiatively efficient to radiatively inefficient). In this scenario, the observed drop in luminosity and ER corresponds to the final stage of an AGN accretion phase. Our results are consistent with previous studies in the optical, X-ray and radio although the magnitude of the drop is lower than previously suggested. In addition, we discuss a possible analogy between X-ray binaries and an AGN.

Additional Information

© 2017 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2017 November 14. Received 2017 November 14; in original form 2017 March 31. We thank the anonymous referee for helpful comments which improved the quality of the manuscript. We also thank the NuSTAR Cycle 2 TAC for the NuSTAR data on which this paper is based. LFS and KS gratefully acknowledge support from Swiss National Science Foundation Grants PP00P2_138979 and PP00P2_166159. MJK acknowledges support from the Swiss National Science Foundation through the Ambizione fellowship grant PZ00P2_154799/1. MJK acknowledges support from NASA through ADAP award NNH16CT03C. ET acknowledges support from: CONICYT-Chile grants Basal-CATA PFB-06/2007 and FONDECYT Regular 1160999. CR acknowledges the China-CONICYT fund, FONDECYT 1141218 and Basal-CATA PFB–06/2007. WPM acknowledges partial support by HST guest observer program #14271 under NASA contract NAS 5-26555 (HST) and Chandra Award GO5-16101X under NASA contract NAS8-03060 (CXC). GL acknowledges support from a Herchel Smith Research Fellowship of the University of Cambridge. This work is based on observations with the Chandra  satellite and has made use of software provided by the CXC in the application package CIAO. This work has made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NUSTARDAS) jointly developed by the ASI Science DataCenter (ASDC, Italy) and the California Institute of Technology (USA). The research has made use of NASA's Astrophysics Data System Bibliographic Service.

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Submitted - 1711.06270.pdf


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