M87 hosts a 3-6 billion solar mass black hole with a remarkable relativistic jet that has been regularly monitored in radio to TeV bands. However, hard X-ray emission \gtrsim 10keV, which would be expected to primarily come from the jet or the accretion flow, had never been detected from its unresolved X-ray core. We report NuSTAR detection up to 40 keV from the the central regions of M87. Together with simultaneous Chandra observations, we have constrained the dominant hard X-ray emission to be from its unresolved X-ray core, presumably in its quiescent state. The core spectrum is well fitted by a power law with photon index Gamma=2.11 (+0.15 -0.11). The measured flux density at 40 keV is consistent with a jet origin, although emission from the advection-dominated accretion flow cannot be completely ruled out. The detected hard X-ray emission is significantly lower than that predicted by synchrotron self-Compton models introduced to explain emission above a GeV.
@article{arxiv.1710.05031,
title = {Hard X-ray Emission from the M87 AGN Detected with NuSTAR},
author = {Ka-Wah Wong and Rodrigo S. Nemmen and Jimmy A. Irwin and Dacheng Lin},
journal= {arXiv preprint arXiv:1710.05031},
year = {2017}
}
Comments
5 pages, 4 figures, updated to better match the published version in the Astrophysical Journal Letters. A minor typo in the published version (angular scale should be 1 arcsec = 78 pc instead, no result of the paper is affected) is fixed here