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The structure of the X-ray absorber in Mrk 915 revealed by Swift

Journal
Date Issued
2015
Author(s)
•
Ballo, L.
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•
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Vignali, C.
DOI
Description
This work is based on observations obtained with the Swift satellite and it made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. We thank Neil Gehrels, Boris Sbarufatti, Gianpiero Tagliaferri and the Swift Mission Operation Center to make every effort to get our ToO request scheduled. This research has made use both of the Palermo BAT Catalogue and database operated at INAF - IASF Palermo and of the 70 month Swift -BAT Catalogue. We, moreover, thank Miguel Perez-Torres for the analysis of archival VLA data. Part of this work was supported by the European Commission Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 267251 Astronomy Fellowships in Italy (AstroFIt). The authors acknowledge financial support from the Italian Ministry of Education, Universities and Research (PRIN2010-2011, grant no. 2010NHBSBE). Support from the Italian Space Agency is acknowledged (contract ASI INAF I/037/12/0). Finally, we you would like to thank the anonymous referee for the useful and constructive comments which improved the quality of the paper.
Abstract
In this paper, we present the results obtained with a monitoring programme (23 days long) performed with Swift-XRT on the local Seyfert galaxy Mrk 915. The light-curve analysis shows a significant count rate variation (about a factor of 2-3) on a time-scale of a few days, while the X-ray colours show a change in the spectral curvature below 2 keV and the presence of two main spectral states. From the spectral analysis we find that the observed variations can be explained by the change of the intrinsic nuclear power (about a factor of 1.5) coupled with a change of the properties of an ionized absorber. The quality of the data prevents us from firmly establishing if the spectral variation is due to a change in the ionization state and/or in the covering factor of the absorbing medium. The latter scenario would imply a clumpy structure of the ionized medium. By combining the information provided by the light curve and the spectral analyses, we can derive some constraints on the location of the absorber under the hypotheses of either homogeneous or clumpy medium. In both cases, we find that the absorber should be located inside the outer edge of an extended torus and, in particular, under the clumpy hypothesis, it should be located near, or just outside, to the broad emission line region.
Volume
453
Issue
4
Start page
3611
Uri
Url
Issn Identifier
0035-8711
Ads BibCode
2015MNRAS.453.3611S
Rights
open.access
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