The Study of X-Ray Flux Variability of M87

TL;DR

This study investigates short-term X-ray flux variability in M87's core and jet, revealing minute-scale emission regions and insights into particle acceleration and emission mechanisms near the supermassive black hole.

Contribution

It provides the first detection of intraday X-ray variability in M87's core and jet, constraining emission region sizes and magnetic fields, and distinguishing between emission models.

Findings

Detected intraday variability in Suzaku and Chandra data.

Estimated emission region size to be comparable to the Schwarzschild radius.

Suggested particle acceleration occurs far from the core, likely in the HST-1 region.

Abstract

We searched for a short-term X-ray variability of the M87 core and jet from archival X-ray data with long exposure data taken by the Suzaku, Chandra, and NuSTAR telescopes. We found the intraday variability for the Suzaku data obtained in 2006, and for the Chandra core obtained in 2017. The intraday variability suggested a minute emission region of about the size of Schwartzshild radius of the M87 supermassive black hole. Suzaku could not resolve a core and HST-1; however, in 2006, HST-1 was much brighter than the core, and thus, the variability is likely due to the HST-1. Since the photon index in 2006 was 2.38, the emission was possibly synchrotron emission from the local shock region in the HST-1, indicating that the particle acceleration of TeV electrons occurred far away (~100 pc) from the core. Assuming the fading time to be equal to the synchrotron cooling time, the magnetic field is constrained to be B ~1.94 ${\delta}^{1/3}$ mG. Moreover, the photon index of the core in 2017 was approximately 1.96; thus, the possible emission was from the radiative inefficiency accretion flow of the core or inverse Compton scattering in the jet. Intraday time variability prefers the latter possibility.