Electron heating, magnetic field amplification, and cosmic-ray precursor length at supernova remnant shocks

Journal Article · Sun Jul 20 04:00:00 EDT 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/790/1/11· OSTI ID:22365615

Laming, J. Martin ^[1]; Hwang, Una ^[2]; Ghavamian, Parviz ^[3]; Rakowski, Cara

---

1. Space Science Division, Naval Research Laboratory, Code 7684, Washington, DC 20375 (United States)
2. Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
3. Department of Physics, Astronomy and Geosciences, Towson University, Towson, MD 21252 (United States)

We investigate the observability, by direct and indirect means, of a shock precursor arising from magnetic field amplification by cosmic rays. We estimate the depth of such a precursor under conditions of nonresonant amplification, which can provide magnetic field strengths comparable to those inferred for supernova remnants. Magnetic field generation occurs as the streaming cosmic rays induce a plasma return current, and it may be quenched by either nonresonant or resonant channels. In the case of nonresonant saturation, the cosmic rays become magnetized and amplification saturates at higher magnetic fields. The precursor can extend out to 10{sup 17}-10{sup 18} cm and is potentially detectable. If resonant saturation occurs, the cosmic rays are scattered by turbulence and the precursor length will likely be much smaller. The dependence of precursor length on shock velocity has implications for electron heating. In the case of resonant saturation, this dependence is similar to that in the more familiar resonantly generated shock precursor, which when expressed in terms of the cosmic-ray diffusion coefficient kappav and shock velocity v{sub s} is kappav/v{sub s} . In the nonresonantly saturated case, the precursor length declines less quickly with increasing v{sub s} . Where precursor length proportional to 1/v{sub s} gives constant electron heating, this increased precursor length could be expected to lead to higher electron temperatures for nonresonant amplification. This should be expected at faster supernova remnant shocks than studied by previous works. Existing results and new data analysis of SN 1006 and Cas A suggest some observational support for this idea.

• OSTI ID: 22365615
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 790; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCELERATION
AMPLIFICATION
COSMIC RADIATION
DATA ANALYSIS
DIFFUSION
ELECTRON TEMPERATURE
HEATING
INSTABILITY
MAGNETIC FIELDS
PLASMA
SATURATION
SHOCK WAVES
SUPERNOVA REMNANTS
TURBULENCE
VELOCITY