Hard X-ray diffuse emission from the Galactic Center seen by INTEGRAL

TL;DR

This study analyzes the variability and origin of diffuse hard X-ray emission from the Galactic Center using INTEGRAL data, finding non-variable emission likely from synchrotron radiation of high-energy electrons.

Contribution

It provides the first constraints on the variability of hard X-ray sources in the Galactic Center and identifies synchrotron emission from TeV electrons as the likely origin of diffuse X-ray flux.

Findings

Three sources are non-variable on 1000 s timescale.

Upper limit on Sgr A*'s variable emission is 5 x 10^{-12} erg/(cm^2 sec).

Diffuse emission region size is about 20 pc.

Abstract

We study the hard X-ray (20-100 keV) variability of the Galactic Center (GC) and of the nearby sources on the time scale of 1000 s. We find that 3 of the 6 hard X-ray sources detected by INTEGRAL within the central 1 degree of the Galaxy are not variable on this time scale: the GC itself (the source IGR J1745.6-2901) as well as the source 1E 1743.1-2843 and the molecular cloud Sgr B2. We put an upper limit of 5 x 10^{-12} erg/(cm^2 sec) (in 20 to 60 keV band) on the variable emission form the supermassive black hole (the source Sgr A*) which powers the activity of the GC(although we can not exclude the possibility of rare stronger flares). The non-variable 20-100 keV emission from the GC turns out to be the high-energy non-thermal tail of the diffuse hard ``8 keV'' component of emission from Sgr A region. Combining the XMM-Newton and INTEGRAL data we find that the size of the extended hard X-ray emission region is about 20 pc. The only physical mechanism of production of diffuse non-thermal hard X-ray flux, which does not contradict the multi-wavelength data on the GC, is the synchrotron emission from electrons of energies 10-100 TeV.