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Title: Measuring the Local Diffusion Coefficient with H.E.S.S. Observations of Very High-Energy Electrons

Abstract

The HAWC Collaboration has recently reported the detection of bright and spatially extended multi-TeV gamma-ray emission from Geminga, Monogem, and a handful of other nearby, middle-aged pulsars. The angular profile of the emission observed from these pulsars is surprising, in that it implies that cosmic-ray diffusion is significantly inhibited within ~25 pc of these objects, compared to the expectations of standard Galactic diffusion models. This raises the important question of whether the diffusion coefficient in the local interstellar medium is also low, or whether it is instead better fit by the mean Galactic value. Here, we utilize recent observations of the cosmic-ray electron spectrum (extending up to ~20 TeV) by the H.E.S.S. Collaboration to show that the local diffusion coefficient cannot be as low as it is in the regions surrounding Geminga and Monogem. Instead, we conclude that cosmic rays efficiently diffuse through the bulk of the local interstellar medium. Among other implications, this further supports the conclusion that pulsars significantly contribute to the observed positron excess and provides strong evidence for spatially varying diffusion coefficients throughout the Milky Way.

Authors:
ORCiD logo [1]; ORCiD logo [2]
  1. Fermilab
  2. Ohio State U., CCAPP
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
1431584
Report Number(s):
arXiv:1711.07482; FERMILAB-PUB-17-530-A
1637327
DOE Contract Number:  
AC02-07CH11359
Resource Type:
Journal Article
Journal Name:
Phys.Rev.
Additional Journal Information:
Journal Volume: D98; Journal Issue: 8
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Citation Formats

Hooper, Dan, and Linden, Tim. Measuring the Local Diffusion Coefficient with H.E.S.S. Observations of Very High-Energy Electrons. United States: N. p., 2018. Web. doi:10.1103/PhysRevD.98.083009.
Hooper, Dan, & Linden, Tim. Measuring the Local Diffusion Coefficient with H.E.S.S. Observations of Very High-Energy Electrons. United States. doi:10.1103/PhysRevD.98.083009.
Hooper, Dan, and Linden, Tim. Sat . "Measuring the Local Diffusion Coefficient with H.E.S.S. Observations of Very High-Energy Electrons". United States. doi:10.1103/PhysRevD.98.083009. https://www.osti.gov/servlets/purl/1431584.
@article{osti_1431584,
title = {Measuring the Local Diffusion Coefficient with H.E.S.S. Observations of Very High-Energy Electrons},
author = {Hooper, Dan and Linden, Tim},
abstractNote = {The HAWC Collaboration has recently reported the detection of bright and spatially extended multi-TeV gamma-ray emission from Geminga, Monogem, and a handful of other nearby, middle-aged pulsars. The angular profile of the emission observed from these pulsars is surprising, in that it implies that cosmic-ray diffusion is significantly inhibited within ~25 pc of these objects, compared to the expectations of standard Galactic diffusion models. This raises the important question of whether the diffusion coefficient in the local interstellar medium is also low, or whether it is instead better fit by the mean Galactic value. Here, we utilize recent observations of the cosmic-ray electron spectrum (extending up to ~20 TeV) by the H.E.S.S. Collaboration to show that the local diffusion coefficient cannot be as low as it is in the regions surrounding Geminga and Monogem. Instead, we conclude that cosmic rays efficiently diffuse through the bulk of the local interstellar medium. Among other implications, this further supports the conclusion that pulsars significantly contribute to the observed positron excess and provides strong evidence for spatially varying diffusion coefficients throughout the Milky Way.},
doi = {10.1103/PhysRevD.98.083009},
journal = {Phys.Rev.},
number = 8,
volume = D98,
place = {United States},
year = {2018},
month = {10}
}

Journal Article:

Figures / Tables:

Figure 1 Figure 1: The secondary contribution to the cosmic-ray electron (plus positron) spectrum, as calculated using GALPROP, and adopting the default values for all propagation parameters. Comparing this to the spectrum as reported by the HESS Collaboration, it is clear that secondary production provides only a small fraction of this flux.more » At the highest measured energies, this result is largely independent of the value of the diffusion coefficient.« less

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Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.