Hard X-ray Emission from the M87 AGN Detected with NuSTAR

TL;DR

This paper reports the first detection of hard X-ray emission up to 40 keV from the unresolved core of M87 using NuSTAR, providing new insights into the high-energy processes near its supermassive black hole.

Contribution

It presents the first detection of hard X-ray emission from M87's core with NuSTAR, constraining the emission origin and challenging existing models.

Findings

Hard X-ray emission detected up to 40 keV from M87's core.

Core spectrum fits a power law with photon index ~2.11.

Measured flux is consistent with jet origin, but accretion flow cannot be ruled out.

Abstract

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.