Using the Chandra and XMM-Newton spacecraft, astronomers from the Nicolaus Copernicus Astronomical Center in Warsaw, Poland, have investigated an ultraluminous X-ray source (ULX) in the galaxy NGC 5055.
ULXs are point sources in the sky that are so bright in X-rays that each emits more radiation than 1 million suns emit at all wavelengths. They are less luminous than active galactic nuclei, but more consistently luminous than any known stellar process. Although numerous studies of ULXs have been conducted, the basic nature of these sources remains unsolved.
NGC 5055 (also known as Messier 63, or the Sunflower galaxy) is a spiral galaxy located some 29 million light years away. It hosts an ultraluminous X-ray source designated NGC 5055 X-1. A team of astronomers led by Samaresh Mondal has now conducted timing and spectral analysis of observational data regarding NGC 5055 X-1.
In general, the observations found that NGC 5055 X-1 does not show much variability. Based on the hardness ratios (3-10 keV/0.3-3 keV flux), the astronomers concluded that the source is not spectrally variable.
According to the study, NGC 5055 X-1 mostly emits in soft X-rays in the range of 0.3-3 keV. Its hard X-ray band flux is only a fraction of the soft X-ray emission. This points to a dominant thermal component.