Astronomers investigate X-ray spectral variability of active galaxy NGC 7582

Utilizing ESA’s XMM-Newton and NASA’s NuSTAR space telescopes, astronomers have noticed a close-by energetic galaxy often known as NGC 7582. Outcomes 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 energetic galactic nucleus (AGN).

An AGN is a compact area on the heart of a galaxy, extra luminous than the encircling galaxy mild. Research 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 based mostly on emission line options. Kind 1 AGNs present broad and slim emission strains, whereas solely slim emission strains are current in Kind 2 AGNs. Nevertheless, observations revealed that some AGNs transition between completely different spectral varieties; subsequently, they have been dubbed changing-look (CL) AGNs.

At a distance of some 73 million mild years away from the Earth, NGC 7582 is a Kind 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 workforce of astronomers led by Mehdy Lefkir of the College of Leicester, U.Ok., have analyzed the accessible observational knowledge of NGC 7582 obtained with XMM-Newton and NuSTAR between 2001 and 2018. The primary purpose of their research was to clarify the short- and long-term X-ray conduct of this supply.

“To review the variability, we carry out a time-resolved spectral evaluation utilizing a phenomenological mannequin and a physically-motivated mannequin (uxclumpy). The spectral becoming is achieved utilizing a nested sampling Monte Carlo technique. Uxclumpy allows testing numerous geometries of the absorber that will match AGN spectra,” the researchers defined.

It turned out that NGC 7582 displays a long-term variability between observations carried out by Lefkir’s workforce 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 as a consequence of intrinsic modifications within the X-ray luminosity of the supply, and modifications within the absorption within the line of sight.

Based on the paper, this absorption is finest described by a totally overlaying clumpy absorber. The researchers famous that the short-term variability of NGC 7582 might 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 recommend that the absorber is positioned at a distance not bigger than 1.95 mild years from the X-ray supply, transferring with a transverse velocity exceeding roughly 700 km/s. Assuming that the absorber is a single cloud within the line of sight, the scale 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 not less than a non-uniform cloud.

© 2023 Science X Community