An Experiment to Locate the Site of TeV Flaring in M87

TL;DR

This study uses Chandra X-ray observations to investigate the location of TeV flaring in M87, finding elevated X-ray activity in the nucleus associated with past TeV flares and estimating the size of the emission region.

Contribution

First X-ray monitoring campaign aimed at pinpointing TeV flare sites in M87, providing insights into the size and spectral evolution of the emission region.

Findings

Elevated X-ray activity in the nucleus correlates with TeV flares.

Estimated emission region size is a few light days, similar to TeV region.

Spectral evolution suggests radiative losses in the electron population.

Abstract

We describe a Chandra X-ray ToO project designed to isolate the site of TeV flaring in the radio galaxy M87. To date, we have triggered the Chandra observations only once (2010 April) and by the time of the first of our 9 observations, the TeV flare had ended. However, we found that the X-ray intensity of the unresolved nucleus was at an elevated level for our first observation. Of the more than 60 Chandra observations we have made of the M87 jet covering 9 years, the nucleus was measured at a comparably high level only 3 times. Two of these occasions can be associated with TeV flaring, and at the time of the third event, there were no TeV monitoring activities. From the rapidity of the intensity drop of the nucleus, we infer that the size of the emitting region is of order a few light days times the unknown beaming factor; comparable to the same sort of estimate for the TeV emitting region. We also find evidence of spectral evolution in the X-ray band which seems consistent with radiative losses affecting the non-thermal population of the emitting electrons within the unresolved nucleus.