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  1. OA@INAF
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  3. 1 CONTRIBUTI IN RIVISTE (Journal articles)
  4. 1.01 Articoli in rivista
Please use this identifier to cite or link to this item: http://hdl.handle.net/20.500.12386/23335
Title: Spectral variability in Swift and Chandra observations of the ultraluminous source NGC 55 ULX1
Authors: Pintore, Fabio 
ESPOSITO, PAOLO
ZAMPIERI, Luca 
Motta, Sara
WOLTER, Anna Luisa Maria 
Issue Date: 2015
Journal: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 
Number: 448
Issue: 2
First Page: 1153
Abstract: NGC 55 ULX1 is a bright Ultraluminous X-ray source located 1.78 Mpc away. We analysed a sample of 20 Swift observations, taken between 2013 April and August, and two Chandra observations taken in 2001 September and 2004 June. We found only marginal hints of a limited number of dips in the light curve, previously reported to occur in this source, although the uncertainties due to the low counting statistics of the data are large. The Chandra and Swift spectra showed clearly spectral variability which resembles those observed in other ULXs. We can account for this spectral variability in terms of changes in both the normalization and intrinsic column density of a two-component model consisting of a blackbody (for the soft component) and a multicolour accretion disc (for the hard component). We discuss the possibility that strong outflows ejected by the disc are in part responsible for such spectral changes.
Acknowledgments: We thank the anonymous referee for the useful comments and suggestions. FP, PE, LZ, and AW acknowledge financial support from the INAF research grant PRIN-2011-1 (‘Challenging Ultraluminous X-ray sources: chasing their BHs and formation pathways’) and the ASI/INAF contract I/004/11/0 and ASI/INAF n. I/037/12/0. PE acknowledges a Fulbright Research Scholar grant administered by the U.S.–Italy Fulbright Commission and is grateful to the Harvard–Smithsonian Center for Astrophysics for hosting him during his Fulbright exchange. This research is based on observations made by the Chandra X-ray Observatory and has made use of software provided by the Chandra X-ray Center (CXC, operated for NASA by SAO) in the application packages ciao and ChIPS . This research is based on observations with the NASA/UKSA/ASI mission Swift .
URI: http://hdl.handle.net/20.500.12386/23335
URL: https://academic.oup.com/mnras/article/448/2/1153/1050404
ISSN: 0035-8711
DOI: 10.1093/mnras/stv028
Bibcode ADS: 2015MNRAS.448.1153P
Fulltext: open
Appears in Collections:1.01 Articoli in rivista

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