Ultraluminous X-ray sources in NGC 891 studied by researchers

Ultraluminous X-ray sources in NGC 891 studied by researchers

January 27, 2017 EPIC-pn observations of NGC 891 in the 0.3-10.0 keV band. Credit: Earley et al., 2021.

Researchers from the University of Chicago and Fordham University have conducted long-term monitoring of three ultraluminous X-ray sources (ULXs) in the spiral galaxy NGC 891. The results of the research, presented in a paper published on December 22 on arXiv.org, provide more insight into the properties of these sources. and could help us better understand the nature of the host galaxy.

ULXs are point sources in the sky that are so bright in X-rays that each of them emits more radiation than 1 million suns emit at all wavelengths. They are less luminous than active galactic nuclei (AGNs), but more consistently luminous than any known stellar process. Although several studies of ULXs have been conducted, the basic nature of these sources is still a jigsaw puzzle.

Long-term monitoring using a wide range of spectral models is required to fully determine and understand the nature of ULXs. Now, a team of astronomers led by Nicholas M. Earley has analyzed the data collected from 2000 to 2017 with NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton spacecraft. By combing the data sets, they focused on the observations of NGC 891 (a spiral galaxy with barrier edges about 30 million light-years away) and its ultraluminous X-ray sources, designated ULX-1, ULX-2 and ULX-3.

“We are making empirical adaptations to the Chandra and XMM-Newton spectra of three ultraluminous X-ray sources in the spiral galaxy NGC 891 on the edge and monitoring the area over a 17-year time window,” the researchers wrote in the paper.

According to the study, ULX-1 shows some spectral development of this source from 2003 to 2016, and its light curve shows a possible slight decrease in flux over time, especially from 2000 to 2003. However, the long-term stability curve of light indicates that the source is not a very variable object across these time scales. The luminosity of ULX-1 was measured to be about 8.4 duodecilion erg / s, while its column density was estimated to be about 8 sextillion cm-2.

ULX-2 has a remarkably constant flux that appears to be between 20 and 50 percent higher than ULX-1, which is expected from the count rates. The source has a column density of about 0.2 sextillion cm−2. with some variations. This value is lower than that found for ULX-1 by a factor of a few and turns out to be lower than any of the column densities calculated for the other known ULXs.

ULX-3 is the weakest of the three sources studied with a brightness at a level of 2 duodecilion erg / s, which places it in the lower brightness range of detected ULXs. The derived column density was found to be approx. 2 sextillion cm-2. The research revealed that flux and column density around this source both turn out to decrease by a factor of seven from November 2016 to January 2017. Astronomers added that ULX-3 currently no longer qualifies as ‘ultraluminous’ as its lower brightness value is more consistent with other high energy sources such as X-ray binary.


Inspects an ultraluminous X-ray source in the galaxy NGC 55


More information:
A long-term study of ultraluminous X-ray sources in NGC 891, arXiv: 2112.12212 [astro-ph.HE] arxiv.org/abs/2112.12212

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Citation: Ultraluminous X-Ray Sources in NGC 891 Examined by Researchers (2021, December 30) Retrieved December 30, 2021 from https://phys.org/news/2021-12-ultraluminous-x-ray-sources-ngc.html

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