Tomasz Nowakowski is a writer for Phys.org.
Analyzing the data from four space observatories, European astronomer presented a complete and thorough X-ray view of an active galactic nucleus in a nearby spiral galaxy. The results of the study were published on arXiv.org.
The AGNs emit high-energy radiation as they accrete gas and dust at the centers of some galaxies. Even on megaparsec scales, these nuclei can form jets, having mostly cylindrical, conical or parabolic shapes.
One of the closest AGNs is located at a distance of 24.7 million light years away from the Earth. Water masers were found around the AGN in 1984, making it the cleanest evidence for the existence of black holes. Further investigation of these masers revealed a dusty disk around a central mass of 40 million solar mass.
Astronomers are interested in the low bolometric luminosity of AGN. They assumed that it could be due to either a low accretion rate or a radiatively inefficient accretion flow. The nature of the accretion flow in NGC 4258 is still puzzling despite several previous studies examining it.
In order to shed new light on its accretion flow and long term evolution, a team of astronomer led by Alberto Masini of the International School for Advanced Studies in Trieste, Italy reviewed the X-ray properties of NGC 4258. They analyzed archival observations made with Chandra, Swift, NuSTAR and XMM-Newton space telescopes.
The obtained results are complemented with others from the literature to obtain a complete and thorough X-ray view of a nearby AGN.
The X-ray properties of the AGN have changed over time. The results suggest that the change was due to two variations of the absorbing column density and a change in the emission from the central engine.
Changes in the accretion rate and the rate of energy deposition in the corona may be related to the short variability timescale seen in the NuSTAR. The long term decrease in intrinsic luminosity observed for this AGN is explained by the accretion rate variability.
The variations in photon index and luminosity seem to follow two behaviors. The first one is observed when the source is brighter than a certain critical value. There appears to be an anti-correlation between the two quantities, which suggests a transition between hot and cold accretion states.
The authors of the paper concluded that the average spectral properties of NGC 4258 are typical of a low luminosity obscured type II Seyfert galaxy, with a photon index within the range of 1.6 to 2.2.
More information: Alberto Masini, J. V. Wijesekera, Annalisa Celotti, Peter G. Boorman, A comprehensive X-ray view of the active nucleus in NGC 4258. arXiv:2205.07899v1 [astro-ph.HE], arxiv.org/abs/2205.07899The Science X Network will be launched in 2022.
Citation: Study provides a comprehensive X-ray view of an active galactic nucleus in NGC 4258 (2022, May 24) retrieved 24 May 2022 from https://phys.org/news/2022-05-comprehensive-x-ray-view-galactic-nucleus.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
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