TY - JOUR
T1 - Synchrotron Firehose Instability
AU - Zhdankin, Vladimir
AU - Kunz, Matthew W.
AU - Uzdensky, Dmitri A.
N1 - Funding Information:
The authors are grateful to Archie Bott, Per Helander, Bart Ripperda, Charles Gammie, and Luís Oliveira e Silva for useful conversations and comments. The authors also thank the anonymous referee for suggestions that improved the manuscript. V.Z. is supported by a Flatiron Research Fellowship at the Flatiron Institute, Simons Foundation. Research at the Flatiron Institute is supported by the Simons Foundation. This work was performed in part at the Aspen Center for Physics, which is supported by National Science Foundation grant PHY-1607611. M.W.K. acknowledges support from the NSF/DOE Partnership in Basic Plasma Science and Engineering through award DE-SC0019047, and thanks the Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) for its hospitality and visitor support while this work was in progress. D.A.U. gratefully acknowledges support from NASA grants 80NSSC20K0545 and 80NSSC22K0828 and from NSF grants AST-1806084 and AST-1903335. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1548562. This work used the XSEDE supercomputer Stampede2 at the Texas Advanced Computer Center (TACC) through allocation TG-PHY160032 (Towns et al. ).
Funding Information:
The authors are grateful to Archie Bott, Per Helander, Bart Ripperda, Charles Gammie, and Luís Oliveira e Silva for useful conversations and comments. The authors also thank the anonymous referee for suggestions that improved the manuscript. V.Z. is supported by a Flatiron Research Fellowship at the Flatiron Institute, Simons Foundation. Research at the Flatiron Institute is supported by the Simons Foundation. This work was performed in part at the Aspen Center for Physics, which is supported by National Science Foundation grant PHY-1607611. M.W.K. acknowledges support from the NSF/DOE Partnership in Basic Plasma Science and Engineering through award DE-SC0019047, and thanks the Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) for its hospitality and visitor support while this work was in progress. D.A.U. gratefully acknowledges support from NASA grants 80NSSC20K0545 and 80NSSC22K0828 and from NSF grants AST-1806084 and AST-1903335. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1548562. This work used the XSEDE supercomputer Stampede2 at the Texas Advanced Computer Center (TACC) through allocation TG-PHY160032 (Towns et al. 2014).
Publisher Copyright:
© 2023. The Author(s). Published by the American Astronomical Society.
PY - 2023/2/1
Y1 - 2023/2/1
N2 - We demonstrate using linear theory and particle-in-cell (PIC) simulations that a synchrotron-cooling collisionless plasma acquires pressure anisotropy and, if the plasma beta is sufficiently high, becomes unstable to the firehose instability, in a process that we dub the synchrotron firehose instability (SFHI). The SFHI channels free energy from the pressure anisotropy of the radiating, relativistic electrons (and/or positrons) into small-amplitude, kinetic-scale, magnetic-field fluctuations, which pitch-angle scatter the particles and bring the plasma to a near-thermal state of marginal instability. The PIC simulations reveal a nonlinear cyclic evolution of firehose bursts interspersed by periods of stable cooling. We compare the SFHI for electron-positron and electron-ion plasmas. As a byproduct of the growing electron-firehose magnetic-field fluctuations, magnetized ions gain a pressure anisotropy opposite to that of the electrons. If these ions are relativistically hot, we find that they also experience cooling due to collisionless thermal coupling with the electrons, which we argue is mediated by a secondary ion-cyclotron instability. We suggest that the SFHI may be activated in a number of astrophysical scenarios, such as within ejecta from black hole accretion flows and relativistic jets, where the redistribution of energetic electrons from low to high pitch angles may cause transient bursts of radiation.
AB - We demonstrate using linear theory and particle-in-cell (PIC) simulations that a synchrotron-cooling collisionless plasma acquires pressure anisotropy and, if the plasma beta is sufficiently high, becomes unstable to the firehose instability, in a process that we dub the synchrotron firehose instability (SFHI). The SFHI channels free energy from the pressure anisotropy of the radiating, relativistic electrons (and/or positrons) into small-amplitude, kinetic-scale, magnetic-field fluctuations, which pitch-angle scatter the particles and bring the plasma to a near-thermal state of marginal instability. The PIC simulations reveal a nonlinear cyclic evolution of firehose bursts interspersed by periods of stable cooling. We compare the SFHI for electron-positron and electron-ion plasmas. As a byproduct of the growing electron-firehose magnetic-field fluctuations, magnetized ions gain a pressure anisotropy opposite to that of the electrons. If these ions are relativistically hot, we find that they also experience cooling due to collisionless thermal coupling with the electrons, which we argue is mediated by a secondary ion-cyclotron instability. We suggest that the SFHI may be activated in a number of astrophysical scenarios, such as within ejecta from black hole accretion flows and relativistic jets, where the redistribution of energetic electrons from low to high pitch angles may cause transient bursts of radiation.
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U2 - 10.3847/1538-4357/acaf54
DO - 10.3847/1538-4357/acaf54
M3 - Article
AN - SCOPUS:85147805257
SN - 0004-637X
VL - 944
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 24
ER -