Variability Timescales in the M87 Jet: Signatures of E Squared Losses, Discovery of a Quasi-period in HST-1, and the Site of TeV Flaring
We investigate the variability timescales in the jet of M87 with two goals. The first is to use the rise times and decay times in the radio, ultraviolet and X-ray lightcurves of HST-1 to constrain the source size and the energy loss mechanisms affecting the relativistic electron distributions. We find clear evidence for a frequency-dependent decrease in the synchrotron flux being consistent with E squared energy losses (i.e. synchrotron and inverse Compton). Assuming that these result predominantly from synchrotron cooling, we derive a value of 1 mG for the average magnetic field strength of the HST-1 emission region, a value consistent with previous estimates of the equipartition field. In the process of analyzing the first derivative of the X-ray light curve of HST-1, we discovered a quasi-periodic oscillation which was most obvious in 2003 and 2004 prior to the major flare. The four cycles observed have a period of order 6 months. The second goal is to search for evidence of differences in the X-ray variability timescales of the unresolved nuclear region (diameter < 0.6") and of HST-1, the first jet knot clearly resolved by Chandra. These features, separated by more than 60 pc, are the two chief contenders for the origin of the TeV variable emissions observed by HESS in 2005 and by MAGIC and VERITAS in 2008. The X-ray variability of the nucleus appears to be at least twice more rapid than that of HST-1. However, the shortest nuclear ariability timescale we can claim from the Chandra data (<=20 days) is still significantly longer than the shortest TeV variability of M87 reported by the HESS and MAGIC telescopes (1-2 days). Work at SAO was supported by NASA grants GO7-8119X and GO8-9116X.
American Astronomical Society Meeting Abstracts #213
- Pub Date:
- January 2009