The absence of a thin disc in M81*

Andrew Young, Ian McHardy, D Emmanoulopoulos, S Connolly

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Abstract

We present the results of simultaneous Suzaku and NuSTAR observations of the nearest Low-Luminosity Active Galactic Nucleus (LLAGN), M81*. The spectrum is well described by a cut-off power law plus narrow emission lines from Fe Kα, Fe XXV and Fe XXVI. There is no evidence of Compton reflection from an optically thick disc, and we obtain the strongest constraint on the reflection fraction in M81* to date, with a best-fit value of R=0.0 with an upper limit of R<0.1. The Fe Kα line may be produced in optically thin, N_H=1×10^23 cm^−2, gas located in the equatorial plane that could be the broad line region. The ionized iron lines may originate in the hot, inner accretion flow. The X-ray continuum shows significant variability on ∼40 ks timescales suggesting that the primary X-ray source is ∼100s of gravitational radii in size. If this X-ray source illuminates any putative optically thick disc, the weakness of reflection implies that such a disc lies outside a few ×10^3 gravitational radii. An optically thin accretion flow inside a truncated optically thick disc appears to be a common feature of LLAGN that are accreting at only a tiny fraction of the Eddington limit.
Original languageEnglish
Pages (from-to)5698–5703
Number of pages6
JournalMonthly Notices of the Royal Astronomical Society
Volume476
Issue number4
Early online date13 Mar 2018
DOIs
Publication statusPublished - 1 Jun 2018

Keywords

  • Astrophysics - High Energy Astrophysical Phenomena

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