Ultraluminous X-ray sources in seven edge-on spiral galaxies

Abstract

We investigate a sample of seven edge-on spiral galaxies using Chandra observations. Edge-on spiral galaxies allow us to clearly separate source associated with their star-forming regions versus the outer edges of the system; offering a clear advantage over other systems. We uncover a number of X-ray point sources across these galaxies, and after eliminating contaminating foreground and background sources, we identify 12 candidate ultraluminous X-ray sources. All of these sources are projected on to the central regions, implying that the majority of ULXs in this sample of spiral galaxies are disk/bulge, and thus not halo sources. This also includes two transient ULXs, which may be long-duration transients and low mass X-ray binaries. This finding illustrates the need for further studies of transient ULXs.

A Long-Term Study of Ultraluminous X-ray Sources in NGC 891

“…At the distance of 9 Mpc used in our work, their result corresponds to a luminosity of 8.4 × 10 39 erg s −1 , consistent with our derived values. Our flux values are also in agreement with those quoted by Dage et al [41] for the 2000 observation. The long-term stability of the light curve suggests that the source is not a highly variable object over these timescales (Figure 4).…”

“…Of the 3 ULXs investigated in this work, ULX-2 appears to have been relatively well studied in the past [39][40][41]. However, spectral fits to the 2016 Chandra data were not previously reported.…”

“…ULX-1, although visible for over three decades, has not been investigated as thoroughly. While flux measurements from the Chandra 2000 and 2011 data were reported [37,41,42], spectral fits using other Chandra and XMM datasets are not found in the literature. Except HK12, other authors generally used only 1 or 2 spectral models to fit the data.…”

A Long-term Study of Ultraluminous X-ray Sources in NGC 891

“…Of the 3 ULXs investigated in this work, ULX-2 appears to have been relatively well studied in the past [39][40][41]. However, spectral fits to the 2016 Chandra data have not been previously reported.…”

“…ULX-1, although having been visible for over 3 decades, does not seem to have been investigated as thoroughly. While flux measurements from the Chandra 2000 and 2011 data have been reported [41][42][43], spectral fits using other Chandra and XMM datasets are not found in the literature. Except HK12, other authors generally used only 1 or 2 spectral models to fit the data.…”