Effects of the variability of the nucleus of NGC1275 on X-ray observations of the surrounding intracluster medium

TL;DR

This paper analyzes the long-term variability of NGC1275's nucleus and its impact on X-ray observations of the surrounding intracluster medium, highlighting how nuclear activity influences the visibility of X-ray features.

Contribution

It provides a 40-year X-ray lightcurve of NGC1275 and links nuclear variability to the detection of X-ray bubbles in the Perseus cluster.

Findings

The nucleus was in a bright phase around 1980, obscuring X-ray bubbles.

X-ray flux dropped by 1992, enabling bubble detection.

The nucleus shows a slow rise since 2000, affecting future spectroscopic studies.

Abstract

The active galaxy NGC1275 lies at the centre of the Perseus cluster of galaxies, which is the X-ray brightest cluster in the Sky. The nucleus shows large variability over the past few decades. We compile a lightcurve of its X-ray emission covering about 40 years and show that the bright phase around 1980 explains why the inner X-ray bubbles were not seen in the images taken with the Einstein Observatory. The flux had dropped considerably by 1992 when images with the ROSAT HRI led to their discovery. The nucleus is showing a slow X-ray rise since the first Chandra images in 2000. If it brightens back to the pre-1990 level, then X-ray absorption spectroscopy by ASTRO-H can reveal the velocity structure of the shocked gas surrounding the inner bubbles.