Astrophys. J., Suppl. Ser., 177, 465-492 (2008/August-0)
The long-term variability of the X-ray sources in NGC 6946 and NGC 4485/4490.
FRIDRIKSSON J.K., HOMAN J., LEWIN W.H.G., KONG A.K.H. and POOLEY D.
Abstract (from CDS):
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 1036 ergs/s, and 38 sources coincident with NGC 4485/90 down to a luminosity of ∼1x1037 ergs/s. 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 ∼0.6-0.7 (NGC 6946) and ∼0.4 (NGC 4485/90).
Galaxies: Individual: NGC Number: NGC 6946 - Galaxies: Individual: NGC Number: NGC 4485 - Galaxies: Individual: NGC Number: NGC 4490 - X-Rays: Binaries - X-Rays: Galaxies
VizieR on-line data:
<Available at CDS (J/ApJS/177/465): table2.dat table6.dat table9.dat table10.dat spec.dat table13.dat>
Table 2: [FHL2008] NGC 6946 NN (Nos 1-90). Table 6, col(1): [FHL2008] NGC 4485-4490 NN (Nos 1-38). Table 6, col(11): [FHL2008] NGC 4485-4490 ULX-N (Nos ULX-1 to ULX-8).
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