Using ESA’s XMM-Newton and NASA’s NuSTAR space telescopes, astronomers have noticed a close-by lively galaxy referred to as NGC 7582. Results of the observational marketing campaign, revealed March 30 on the arXiv pre-print server, shed extra mild on the X-ray spectral variability of NGC 7582’s lively galactic nucleus (AGN).
An AGN is a compact area on the middle of a galaxy, extra luminous than the encircling galaxy mild. Studies present that AGNs are very energetic due both to the presence of a black hole or star formation exercise on the core of the galaxy.
Astronomers typically divide AGNs into two teams primarily based on emission line options. Type 1 AGNs present broad and slender emission traces, whereas solely slender emission traces are current in Type 2 AGNs. However, observations revealed that some AGNs transition between completely different spectral varieties; due to this fact, they had been dubbed changing-look (CL) AGNs.
At a distance of some 73 million mild years away from the Earth, NGC 7582 is a Type 2 Seyfert galaxy with a changing-look AGN. The galaxy has a diameter of about 100,000 mild years and a supermassive black hole at its core with a mass of about 55 million solar plenty.
Now, a group of astronomers led by Mehdy Lefkir of the University of Leicester, U.Ok., have analyzed the obtainable observational information of NGC 7582 obtained with XMM-Newton and NuSTAR between 2001 and 2018. The primary purpose of their examine was to elucidate the short- and long-term X-ray conduct of this supply.
“To study the variability, we perform a time-resolved spectral analysis using a phenomenological model and a physically-motivated model (uxclumpy). The spectral fitting is achieved using a nested sampling Monte Carlo method. Uxclumpy enables testing various geometries of the absorber that may fit AGN spectra,” the researchers defined.
It turned out that NGC 7582 reveals a long-term variability between observations carried out by Lefkir’s group but additionally a short-term variability in two observations that has not been studied earlier than. The astronomers discovered that the long-term and short-term variability are attributable to intrinsic modifications within the X-ray luminosity of the supply, and modifications within the absorption within the line of sight.
According to the paper, this absorption is greatest described by a totally protecting clumpy absorber. The researchers famous that the short-term variability of NGC 7582 may very well be defined by a spherical clump with a density profile peaking within the core and slowly reducing in the direction of the floor of the clump.
The outcomes counsel that the absorber is positioned at a distance not bigger than 1.95 mild years from the X-ray supply, shifting with a transverse velocity exceeding roughly 700 km/s. Assuming that the absorber is a single cloud within the line of sight, the dimensions of this cloud is estimated to be bigger than 100 million kilometers.
All in all, the observations point out the presence of quite a lot of cloud densities, or perhaps a gradient within the density inside a single cloud. This, in accordance with the authors of the paper, favors a comet-shaped cloud situation or at the very least a non-uniform cloud.
More data:
Mehdy Lefkir et al, A tough take a look at the X-ray spectral variability of NGC 7582, arXiv (2023). DOI: 10.48550/arxiv.2303.17473
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