Probing the TeV Emission and Jet Collimation Regions in M87
Abstract
During a 2008 cooperative program by the atmospheric Cerenkov telescopes VERITAS, MAGIC, and H.E.S.S., strong flaring activity was seen in M87 at TeV energies in February. VLBA monitoring observations during the same period showed that the 43 GHz radio flux density of the unresolved core began to rise at the time of the TeV flares and eventually reached levels above any previously seen with VLBI. New jet components appeared during the flare. The localization accuracy of the TeV instruments of many arcseconds, even for strong sources, is inadequate to constrain the origin of the emission in the inner jets of AGNs. The VLBA has far higher resolution. For M87, with a 6 billion solar mass black hole and a distance of 16.7 Mpc, the VLBA resolution (0.21 x 0.43 milliarcseconds) corresponds 30 by 60 Schwarzschild radii (Rs). This is starting to resolve the jet collimation region. The temporal coincidence of the TeV and radio flares indicates that they are related and provides the first direct evidence that the TeV radiation from this source is produced within a few tens of Rs of the radio core (Acciari et al. 2009, Science, 325, 444). For M87, the radio core is thought to be coincident to within the VLBA resolution with the black hole.
In terms of the ability to resolve jet structures on small gravitational scales, M87 is the best available source because of its high black hole mass, strong jet, and relative proximity. The VLBA monitoring observations show the structure and dynamics in and near the jet collimation region while astrometric results constrain any motions of the radio core. These observations provide constraints on the jet formation process and on the environment in which the high energy gamma-rays and the radio waves are emitted.- Publication:
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American Astronomical Society Meeting Abstracts #215
- Pub Date:
- January 2010
- Bibcode:
- 2010AAS...21522504W