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dc.contributor.authorBall, David
dc.contributor.authorSironi, Lorenzo
dc.contributor.authorÖzel, Feryal
dc.date.accessioned2018-12-03T23:40:46Z
dc.date.available2018-12-03T23:40:46Z
dc.date.issued2018-07-20
dc.identifier.citationDavid Ball et al 2018 ApJ 862 80en_US
dc.identifier.issn1538-4357
dc.identifier.doi10.3847/1538-4357/aac820
dc.identifier.urihttp://hdl.handle.net/10150/631095
dc.description.abstractNonthermal electron acceleration via magnetic reconnection is thought to play an important role in powering the variable X-ray emission from radiatively inefficient accretion flows around black holes. The trans-relativistic regime of magnetic reconnection-where the magnetization sigma, defined as the ratio of magnetic energy density to enthalpy density, is similar to 1-is frequently encountered in such flows. By means of a large suite of two-dimensional particle-in-cell simulations, we investigate electron and proton acceleration in the trans-relativistic regime. We focus on the dependence of the electron energy spectrum on sigma and the proton beta (the ratio of proton thermal pressure to mio agnetic pressure). We find that the electron spectrum in the reconnection region is nonthermal and can be modeled as a power law. At low beta, the slope, p, is independent of beta and hardens with increasing sigma as p similar or equal to 1.8 + 0.7/root sigma. Electrons are primarily accelerated by the nonideal electric field at X-points, either in the initial current layer or in current sheets generated between merging magnetic islands. At higher values of beta, the electron power law steepens, and the electron spectrum eventually approaches a Maxwellian distribution for all values of sigma. At values of beta near beta(max) approximate to 1/4 sigma, when both electrons and protons are relativistically hot prior to reconnection, the spectra of both species display an additional component at high energies, containing a few percent of particles. These particles are accelerated via a Fermi-like process by bouncing between the reconnection outflow and a stationary magnetic islanden_US
dc.description.sponsorshipNSF [AST-1715061, ACI-1657507, AST1716567]; Chandra Award [TM6-17006X]; John Simon Guggenheim Memorial Foundation; DoE [DE-SC0016542]; NASA [Fermi NNX-16AR75G, ATP NNX-17AG21G]en_US
dc.language.isoenen_US
dc.publisherIOP PUBLISHING LTDen_US
dc.relation.urlhttp://stacks.iop.org/0004-637X/862/i=1/a=80?key=crossref.4d6cf38312083f563656e5d76948123aen_US
dc.rights© 2018. The American Astronomical Society. All rights reserved.en_US
dc.subjectaccretion, accretion disksen_US
dc.subjectgalaxies: jetsen_US
dc.subjectmagnetic reconnectionen_US
dc.subjectradiation mechanisms: nonthermalen_US
dc.subjectX-rays: binariesen_US
dc.titleElectron and Proton Acceleration in Trans-relativistic Magnetic Reconnection: Dependence on Plasma Beta and Magnetizationen_US
dc.typeArticleen_US
dc.contributor.departmentUniv Arizona, Dept Astronen_US
dc.contributor.departmentUniv Arizona, Steward Observen_US
dc.identifier.journalASTROPHYSICAL JOURNALen_US
dc.description.collectioninformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.en_US
dc.eprint.versionFinal published versionen_US
dc.source.journaltitleThe Astrophysical Journal
dc.source.volume862
dc.source.issue1
dc.source.beginpage80
refterms.dateFOA2018-12-03T23:40:47Z


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