Title: First detection of >100 MeV gamma-rays associated with a behind-the-limb solar flare

Abstract

Here, we report the first detection of >100 MeV gamma-rays associated with a behind-the-limb solar flare, which presents a unique opportunity to probe the underlying physics of high-energy flare emission and particle acceleration. On 2013 October 11 a GOES M1.5 class solar flare occurred ~9°.9 behind the solar limb as observed by STEREO-B. RHESSI observed hard X-ray (HXR) emission above the limb, most likely from the flare loop-top, as the footpoints were occulted. Surprisingly, the Fermi Large Area Telescope (LAT) detected >100 MeV gamma-rays for ~30 minutes with energies up to 3 GeV. The LAT emission centroid is consistent with the RHESSI HXR source, but its uncertainty does not constrain the source to be located there. The gamma-ray spectra can be adequately described by bremsstrahlung radiation from relativistic electrons having a relatively hard power-law (PL) spectrum with a high-energy exponential cutoff, or by the decay of pions produced by accelerated protons and ions with an isotropic pitch-angle distribution and a PL spectrum with a number index of ~3.8. Furthermore, we show that high optical depths rule out the gamma-rays originating from the flare site and a high-corona trap model requires very unusual conditions, so a scenario in which some ofmore » the particles accelerated by the CME shock travel to the visible side of the Sun to produce the observed gamma-rays may be at work.« less

Authors:

Pesce-Rollins, Melissa  ^[1];

• Search DOE PAGES for author "Pesce-Rollins, Melissa"
• Search DOE PAGES for ORCID "0000-0003-1790-8018"

Omodei, Nicola  ^[2];

• Search DOE PAGES for author "Omodei, Nicola"
• Search DOE PAGES for ORCID "0000-0002-5448-7577"

Petrosian, V.  ^[2];

• Search DOE PAGES for author "Petrosian, V."
• Search DOE PAGES for ORCID "0000-0002-2670-8942"

Liu, Wei  ^[2];

• Search DOE PAGES for author "Liu, Wei"
• Search DOE PAGES for ORCID "0000-0001-8794-3420"

Costa, Fatima Rubio da  ^[2];

• Search DOE PAGES for author "Costa, Fatima Rubio da"
• Search DOE PAGES for ORCID "0000-0002-8322-7141"

Allafort, A. ^[2]; Chen, Qingrong ^[2]

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+ Show Author Affiliations

1. Istituto Nazionale di Fisica Nucleare, Pisa (Italy); Stanford Univ., Stanford, CA (United States). SLAC National Accelerator Lab.
2. Stanford Univ., Stanford, CA (United States). SLAC National Accelerator Lab.

Publication Date:

Thu May 28 00:00:00 EDT 2015

Research Org.:

SLAC National Accelerator Lab., Menlo Park, CA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1355159

Grant/Contract Number:  

AC02-76SF00515

Resource Type:

Accepted Manuscript

Journal Name:

The Astrophysical Journal. Letters (Online)

Additional Journal Information:

Journal Name: The Astrophysical Journal. Letters (Online); Journal Volume: 805; Journal Issue: 2; Journal ID: ISSN 2041-8213

Publisher:

Institute of Physics (IOP)

Country of Publication:

United States

Language:

English

Subject:

79 ASTRONOMY AND ASTROPHYSICS; Sun: flares; Sun: X-rays; gamma rays