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Long-term wind-driven X-ray spectral variability of NGC 1365 with Swift

Long-term wind-driven X-ray spectral variability of NGC 1365 with Swift
Long-term wind-driven X-ray spectral variability of NGC 1365 with Swift
We present long-term (months–years) X-ray spectral variability of the Seyfert 1.8 galaxy NGC 1365 as observed by Swift, which provides well-sampled observations over a much longer time-scale (six years) and a much larger flux range than is afforded by other observatories. At very low luminosities, the spectrum is very soft, becoming rapidly harder as the luminosity increases and then, above a particular luminosity, softening again. At a given flux level, the scatter in hardness ratio is not very large, meaning that the spectral shape is largely determined by the luminosity. The spectra were therefore summed in luminosity bins and fitted with a variety of models. The best-fitting model consists of two power laws, one unabsorbed and another, more luminous, which is absorbed. In this model, we find a range of intrinsic 0.5–10.0 keV luminosities of approximately 1.1–3.5 erg s?1, and a very large range of absorbing columns, of approximately 1022–1024 cm?2. Interestingly, we find that the absorbing column decreases with increasing luminosity, but that this result is not due to changes in ionization. We suggest that these observations might be interpreted in terms of a wind model in which the launch radius varies as a function of ionizing flux and disc temperature and therefore moves out with increasing accretion rate, i.e. increasing X-ray luminosity. Thus, depending on the inclination angle of the disc relative to the observer, the absorbing column may decrease as the accretion rate goes up. The weaker, unabsorbed, component may be a scattered component from the wind.
galaxies: active, galaxies: individual NGC 1365, galaxies: nuclei, galaxies: Seyfert, X-rays: galaxies
1365-2966
3503-3510
Connolly, S. D.
6067c40f-49e1-4d57-be94-b8753eee8230
McHardy, I. M.
4f215137-9cc4-4a08-982e-772a0b24c17e
Dwelly, T.
c4368952-92c1-45c1-b3c5-5a2a4f18fa60
Connolly, S. D.
6067c40f-49e1-4d57-be94-b8753eee8230
McHardy, I. M.
4f215137-9cc4-4a08-982e-772a0b24c17e
Dwelly, T.
c4368952-92c1-45c1-b3c5-5a2a4f18fa60

Connolly, S. D., McHardy, I. M. and Dwelly, T. (2014) Long-term wind-driven X-ray spectral variability of NGC 1365 with Swift. Monthly Notices of the Royal Astronomical Society, 440 (4), 3503-3510. (doi:10.1093/mnras/stu546).

Record type: Article

Abstract

We present long-term (months–years) X-ray spectral variability of the Seyfert 1.8 galaxy NGC 1365 as observed by Swift, which provides well-sampled observations over a much longer time-scale (six years) and a much larger flux range than is afforded by other observatories. At very low luminosities, the spectrum is very soft, becoming rapidly harder as the luminosity increases and then, above a particular luminosity, softening again. At a given flux level, the scatter in hardness ratio is not very large, meaning that the spectral shape is largely determined by the luminosity. The spectra were therefore summed in luminosity bins and fitted with a variety of models. The best-fitting model consists of two power laws, one unabsorbed and another, more luminous, which is absorbed. In this model, we find a range of intrinsic 0.5–10.0 keV luminosities of approximately 1.1–3.5 erg s?1, and a very large range of absorbing columns, of approximately 1022–1024 cm?2. Interestingly, we find that the absorbing column decreases with increasing luminosity, but that this result is not due to changes in ionization. We suggest that these observations might be interpreted in terms of a wind model in which the launch radius varies as a function of ionizing flux and disc temperature and therefore moves out with increasing accretion rate, i.e. increasing X-ray luminosity. Thus, depending on the inclination angle of the disc relative to the observer, the absorbing column may decrease as the accretion rate goes up. The weaker, unabsorbed, component may be a scattered component from the wind.

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e-pub ahead of print date: 17 April 2014
Published date: 1 June 2014
Keywords: galaxies: active, galaxies: individual NGC 1365, galaxies: nuclei, galaxies: Seyfert, X-rays: galaxies
Organisations: Physics & Astronomy

Identifiers

Local EPrints ID: 369399
URI: http://eprints.soton.ac.uk/id/eprint/369399
ISSN: 1365-2966
PURE UUID: ccc3510c-1c53-487c-9c30-67e9d49e39a4

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Date deposited: 25 Sep 2014 11:43
Last modified: 14 Mar 2024 18:02

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Contributors

Author: S. D. Connolly
Author: I. M. McHardy
Author: T. Dwelly

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