A MODEL FOR THE ORIGIN OF HIGH DENSITY IN LOOPTOP X-RAY SOURCES

Journal Article · Thu Oct 20 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/740/2/73; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21587385

Longcope, D W; Guidoni, S E ^[1]

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1. Department of Physics, Montana State University, Bozeman, MT 59717 (United States)

Super-hot (SH) looptop sources, detected in some large solar flares, are compact sources of HXR emission with spectra matching thermal electron populations exceeding 30 MK. High observed emission measure (EM) and inference of electron thermalization within the small source region both provide evidence of high densities at the looptop, typically more than an order of magnitude above ambient. Where some investigators have suggested such density enhancement results from a rapid enhancement in the magnetic field strength, we propose an alternative model, based on Petschek reconnection, whereby looptop plasma is heated and compressed by slow magnetosonic shocks generated self-consistently through flux retraction following reconnection. Under steady conditions such shocks can enhance density by no more than a factor of four. These steady shock relations (Rankine-Hugoniot relations) turn out to be inapplicable to Petschek's model owing to transient effects of thermal conduction. The actual density enhancement can in fact exceed a factor of 10 over the entire reconnection outflow. An ensemble of flux tubes retracting following reconnection at an ensemble of distinct sites will have a collective EM proportional to the rate of flux tube production. This rate, distinct from the local reconnection rate within a single tube, can be measured separately through flare ribbon motion. Typical flux transfer rates and loop parameters yield EMs comparable to those observed in SH sources.

• OSTI ID: 21587385
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 740; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
DENSITY
ELECTRONS
ELEMENTARY PARTICLES
EMISSION
ENERGY TRANSFER
FERMIONS
FLUID MECHANICS
HEAT TRANSFER
HYDRODYNAMICS
LEPTONS
MAGNETIC FIELDS
MAGNETIC RECONNECTION
MAGNETOHYDRODYNAMICS
MECHANICS
PHYSICAL PROPERTIES
SHOCK WAVES
SLOWING-DOWN
SOLAR ACTIVITY
SOLAR FLARES
STELLAR ACTIVITY
STELLAR FLARES
THERMAL CONDUCTION
THERMALIZATION