Astronomers have recognized an ultraluminous X-ray source known as the NGC 925 ULX-3 by utilizing NASA’s Swift and NuSTAR spacecraft, as well as ESA’s XMM-Newton satellite. Outcomes of this observational campaign, announced on June 16th, provide essential insights into the erratic behavior of this source.
Ultraluminous X-ray sources (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 as compared to n active galactic nuclei. However, they are more brilliant than any known stellar process. Although several studies of ULXs have been performed, the fundamental nature of these sources is still unsolved.
NGC 925 ULX-3 is a volatile ultraluminous X-ray source serendipitously observed during NASA’s Chandra spacecraft studies of NGC 925. It is a spiral galaxy found roughly 31 million light-years away. Although some studies of this ULX have been performed, the nature of its variability is still inadequately understood.
Thus a team of astronomers directed by Caltech’s Hannah P. Earnshaw conducted a monitoring campaign of ULX-3 utilizing Swift, reinforced by target-of-opportunity observations with XMM-Newton and NuSTAR activated when this source was bright.
“We report the results of a 2019–2021 monitoring campaign with Swift and associated target-of-opportunity observations with XMM-Newton and NuSTAR, examining the spectral and timing behavior of the highly variable ultraluminous X-ray source (ULX) NGC 925 ULX-3,” the researchers said in the paper.
The study demonstrated that ULX-3 exhibits a 127–128-day periodicity over which it joins and leaves the ULX luminosity regime. This is probably a supraorbital fluctuation typical in ULXs enclosing neutron star accretors. Also, the source demonstrates flux variation of around an order of magnitude, which is typical for ULXs found so far.