Shock Speed, Cosmic Ray Pressure, and Gas Temperature in the Cygnus Loop

Details Shock Speed, Cosmic Ray Pressure, and Gas Temperature in the Cygnus Loop Shock Speed, Cosmic Ray Pressure, and Gas Temperature in the Cygnus Loop

Jan 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21348803s&link_type=abstract

American Astronomical Society, AAS Meeting #213, #488.03; Bulletin of the American Astronomical Society, Vol. 41, p.462

Astronomy and Astrophysics

Astronomy

Scientific paper

Upper limits on the shock speeds can be combined with post-shock temperatures to obtain upper limits on the ratio of cosmic ray to gas pressure (PCR / PG) behind the shocks. We constrain shock speed limits from proper motions and distance estimates, and we derive temperatures from X-ray spectra. The Palomar Observatory Sky Survey (POSS) observed faint Hα emission stretching around the Cygnus Loop supernova remnant over epochs separated by 39.1 years. We measured proper motions of 18 non-radiative filaments and derived shock velocity limits based on a limit to the Cygnus Loop distance of 576 ± 61 pc given by Blair et al. for a background star. The PSPC instrument on-board ROSAT observed the X-ray emission of the post-shock gas along the perimeter of the Cygnus Loop, and we measure post-shock electron temperatures from spectral fits. Proper motions range from 2.7 - 5.4 arcseconds over the POSS epochs and post-shock temperatures range from kT 100-200 eV. Our preliminary analysis suggests a cosmic ray to post-shock gas pressure consistent with zero, and in some positions PCR is formally smaller than zero. We conclude that the distance to the Cygnus Loop is close to the upper limit given by the distance to the background star and that either the electron temperatures are lower than those measured from ROSAT PSPC X-ray spectral fits or an additional heat input for the electrons, possibly due to thermal conduction, is required.
This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 0754568 and by the Smithsonian Institution.

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