Search for Nonthermal X-ray Emission in the Ophiuchus Galaxy Cluster

TL;DR

This study analyzes INTEGRAL/IBIS data to search for nonthermal X-ray emission in the Ophiuchus galaxy cluster, finding a possible excess above 60 keV but no definitive detection due to spectral uncertainties.

Contribution

First detailed analysis of the Ophiuchus cluster in the 20-120 keV range using INTEGRAL data, exploring potential nonthermal emission components.

Findings

Extended hard X-ray emission with an angular size of 4.9 arcmins.

Possible nonthermal X-ray component detected at 5.5 sigma significance.

No definitive nonthermal emission confirmed due to spectral uncertainties.

Abstract

We present the results of our study of the X-ray emission from the Ophiuchus galaxy cluster based on INTEGRAL/IBIS data in the energy range 20-120 keV. Our goal is the search for a nonthermal emission component from the cluster. Using the INTEGRAL data over the period of observations 2003-2009, we have constructed the images of the Ophiuchus galaxy cluster in different energy bands from 20 to 120 keV with the extraction of spectral information. We show that in the hard X-ray energy band the source is an extended one with an angular size of 4.9 +/- 0.1 arcmins. Assuming a fixed intracluster gas temperature of 8.5 keV, a power-law component of the possible nonthermal X-ray emission is observed at a 5.5 sigma significance level, the flux from which is consistent with previous studies. However, in view of the uncertainty in constraining the thermal emission component in the X-ray spectrum at energies above 20 keV, we cannot assert that the nonthermal emission of the cluster has been significantly detected. Based on the fact of a confident detection of the cluster up to 70 keV, we can draw the conclusion only about the possible presence of a nonthermal excess at energies above 60 keV.