title: Evidence of nonthermal particles in coronal loops heated impulsively by nanoflares.
abstract: The physical processes causing energy exchange between the Sun's hot corona and its cool lower atmosphere remain poorly understood. The chromosphere and transition region (TR) form an interface region between the surface and the corona that is highly sensitive to the coronal heating mechanism. High-resolution observations with the Interface Region Imaging Spectrograph (IRIS) reveal rapid variability (~20 to 60 seconds) of intensity and velocity on small spatial scales (≲500 kilometers) at the footpoints of hot and dynamic coronal loops. The observations are consistent with numerical simulations of heating by beams of nonthermal electrons, which are generated in small impulsive (≲30 seconds) heating events called "coronal nanoflares." The accelerated electrons deposit a sizable fraction of their energy (≲10(25) erg) in the chromosphere and TR. Our analysis provides tight constraints on the properties of such electron beams and new diagnostics for their presence in the nonflaring corona.
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA. ptesta@cfa.harvard.edu.
authors.forename: P
authors.initials: P
authors.lastname: Testa
authors.affiliation: Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA. Institute of Theoretical Astrophysics, University of Oslo, Post Office Box 1029, Blindern, N-0315, Oslo, Norway.
authors.forename: B
authors.initials: B
authors.lastname: De Pontieu
authors.affiliation: NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
authors.forename: J
authors.initials: J
authors.lastname: Allred
authors.affiliation: Institute of Theoretical Astrophysics, University of Oslo, Post Office Box 1029, Blindern, N-0315, Oslo, Norway.
authors.forename: M
authors.initials: M
authors.lastname: Carlsson
authors.affiliation: Dipartimento di Fisica e Chimica, Universita' di Palermo and Istituto Nazionale di Astrofisica (INAF)/Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Reale
authors.affiliation: NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
authors.forename: A
authors.initials: A
authors.lastname: Daw
authors.affiliation: Institute of Theoretical Astrophysics, University of Oslo, Post Office Box 1029, Blindern, N-0315, Oslo, Norway.
authors.forename: V
authors.initials: V
authors.lastname: Hansteen
authors.affiliation: Bay Area Environmental Research Institute 596 1st Street West, Sonoma, CA 95476, USA.
authors.forename: J
authors.initials: J
authors.lastname: Martinez-Sykora
authors.affiliation: Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA. W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA.
authors.forename: W
authors.initials: W
authors.lastname: Liu
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
authors.forename: E E
authors.initials: EE
authors.lastname: DeLuca
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
authors.forename: L
authors.initials: L
authors.lastname: Golub
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
authors.forename: S
authors.initials: S
authors.lastname: McKillop
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
authors.forename: K
authors.initials: K
authors.lastname: Reeves
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
authors.forename: S
authors.initials: S
authors.lastname: Saar
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
authors.forename: H
authors.initials: H
authors.lastname: Tian
authors.affiliation: Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA.
authors.forename: J
authors.initials: J
authors.lastname: Lemen
authors.affiliation: Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA.
authors.forename: A
authors.initials: A
authors.lastname: Title
authors.affiliation: Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA.
authors.forename: P
authors.initials: P
authors.lastname: Boerner
authors.affiliation: Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA.
authors.forename: N
authors.initials: N
authors.lastname: Hurlburt
authors.affiliation: Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA.
authors.forename: T D
authors.initials: TD
authors.lastname: Tarbell
authors.affiliation: Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Wuelser
authors.affiliation: Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA. Bay Area Environmental Research Institute 596 1st Street West, Sonoma, CA 95476, USA.
authors.forename: L
authors.initials: L
authors.lastname: Kleint
authors.affiliation: Department of Physics, Montana State University, Bozeman, Post Office Box 173840, Bozeman, MT 59717, USA.
authors.forename: C
authors.initials: C
authors.lastname: Kankelborg
authors.affiliation: Department of Physics, Montana State University, Bozeman, Post Office Box 173840, Bozeman, MT 59717, USA.
authors.forename: S
authors.initials: S
authors.lastname: Jaeggli