10966(  1) - 04/03/06 11:14  - [  1]

                  HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 10966

Version: 1    Check-in Time: 03-Apr-2006 15:13:49

Title
Simulation Study of Diffusive Synchrotron Radiation from Hot Spots in Relativistic
Jets such as M87
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Type             Cycle     Parallel Pointing Tolerance
AR               15        <none>
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Investigators
                                                                                     Contact?
    PI: Dr. Ken-Ichi Nishikawa            University of Alabama in Huntsville
   CoI: Prof. Philip E. Hardee            University of Alabama                         N
   CoI: Dr. Gerald J. Fishman             NASA Marshall Space Flight Center             N

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Abstract

We propose to apply numerical simulations and modeling to obtain emission spectrum
from relativistic shocks and to compare the emission spectrum with observed optical-
X-ray spectra from the M87 jet and 3C273. In particular, the project involves the
study of relativistic collisionless shocks associated with knots and other optical
structures (synchrotron spectrum models and break frequencies) observed in the kpc
scale jet from knot HST-1 to knot A. Recent PIC simulations have revealed that in
collisionless shocks, plasma waves and their associated instabilities (e.g., the
Weibel, Buneman and other two-stream instabilities) are responsible for particle
(electron, positron, and ion) acceleration and magnetic field generation. A 3-D
relativistic electromagnetic particle (REMP) code will be used to investigate the
shock processes in unmagnetized and magnetized electron-ion and electron-positron
plasmas in order to obtain self-consistent spectra based on the trajectories of
electrons in inhomogeneous magnetic fields. The diffusive synchrotron radiation
(DSR) (jitter radiation) theory (Fleishman 2006; Medvedev 2006) shows that the
synchrotron radiation spectrum produced by relativistic electrons in the jet is
modified by the presence of small-scale random magnetic fields assumed to be
generated by the Weibel instability. A high-frequency power-law component to the
spectrum is yielded by taking account of the perturbations to the electron
trajectories as a result of small-scale magnetic fields, which deviate from the
standard synchrotron spectrum, especially at the high frequency. In our
investigations, the density of the plasmas, the ambient magnetic field strength and
direction, and jet Lorentz factor will be varied in order to evaluate the effect of
changes in macroscopic properties (deceleration in jet velocity) that might be
expected along the M87 jet. Emission spectra calculated based on electron
trajectories in collisionless relativistic shocks (hot spots) generated by the
Weibel instability in our simulations and its comparison with observations will
enable us to address the radio-optical-X-ray spectra and its variability in M87 and
other relativistic sources.
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