The Long-Term Variability of the X-Ray Sources in NGC 6946 and NGC 4485/4490
We analyze data from five Chandra observations of the spiral galaxy NGC 6946 and from three Chandra observations of the irregular/spiral interacting galaxy pair NGC 4485/4490, with an emphasis on investigating the long-term variability exhibited by the source populations. We detect 90 point sources...
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Published in | The Astrophysical journal. Supplement series Vol. 177; no. 2; pp. 465 - 492 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
IOP Publishing
01.08.2008
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Online Access | Get full text |
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Summary: | We analyze data from five Chandra observations of the spiral galaxy NGC 6946 and from three Chandra observations of the irregular/spiral interacting galaxy pair NGC 4485/4490, with an emphasis on investigating the long-term variability exhibited by the source populations. We detect 90 point sources coincident with NGC 6946 down to luminosities of a few times 10 super(36) ergs s super(-1), and 38 sources coincident with NGC 4485/90 down to a luminosity of [image]1 x 10 super(37) ergs s super(-1). Twenty-five (15) sources in NGC 6946 (NGC 4485/90) exhibit long-term (i.e., weeks to years) variability in luminosity; 11 (4) are transient candidates. The single ultraluminous X-ray source (ULX) in NGC 6946 and all but one of the eight ULXs in NGC 4485/90 exhibit long-term flux variability. Two of the ULXs in NGC 4485/90 have not been identified before as ultraluminous sources. The widespread variability in both systems is indicative of the populations being dominated by X-ray binaries, and this is supported by the X-ray colors of the sources. The distribution of colors among the sources indicates a large fraction of high- mass X-ray binaries in both systems. The shapes of the X-ray luminosity functions of the galaxies do not change significantly between observations and can be described by power laws with cumulative slopes [image]0.6-0.7 (NGC 6946) and [image]0.4 (NGC 4485/90). |
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Bibliography: | ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 |
ISSN: | 0067-0049 1538-4365 |
DOI: | 10.1086/588817 |