skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Local H i emissivity measured with FERMI-LAT and implications for Cosmic-ray spectra

Abstract

Cosmic-ray (CR) electrons and nuclei interact with the Galactic interstellar gas and produce high-energy γ-rays. The γ-ray emission rate per hydrogen atom, called emissivity, provides a unique indirect probe of the CR flux. We present the measurement and the interpretation of the emissivity in the solar neighborhood for γ-ray energy from 50 MeV to 50 GeV. We analyzed a subset of 4 yr of observations from the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope ( Fermi) restricted to absolute latitudes $$10^\circ \lt | b| \lt 70^\circ $$. From a fit to the LAT data including atomic, molecular, and ionized hydrogen column density templates, as well as a dust optical depth map, we derived the emissivities, the molecular hydrogen–to–CO conversion factor $${X}_{\mathrm{CO}}=(0.902\pm 0.007)\times {10}^{20}$$ cm–2 (K km s–1)–1, and the dust-to-gas ratio $${X}_{\mathrm{DUST}}=(41.4\pm 0.3)\times {10}^{20}$$ cm–2 mag–1. Moreover, we detected for the first time γ-ray emission from ionized hydrogen. We compared the extracted emissivities to those calculated from γ-ray production cross sections and to CR spectra measured in the heliosphere. We observed that the experimental emissivities are reproduced only if the solar modulation is accounted for. This provides a direct detection of solar modulation observed previously through themore » anticorrelation between CR fluxes and solar activity. Lastly, we fitted a parameterized spectral form to the heliospheric CR observations and to the Fermi-LAT emissivity and obtained compatible local interstellar spectra for proton and helium kinetic energy per nucleon between between 1 and 100 GeV and for electron–positrons between 0.1 and 100 GeV.« less

Authors:
 [1]
  1. CEA-IRFU/CNRS/Univ. Paris Diderot, Gif-sur-Yvette (France)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1355151
Grant/Contract Number:  
AC02-76SF00515
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Volume: 806; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; cosmic rays; gamma rays: diffuse background; gamma rays: ISM

Citation Formats

Casandjian, Jean -Marc. Local H i emissivity measured with FERMI-LAT and implications for Cosmic-ray spectra. United States: N. p., 2015. Web. doi:10.1088/0004-637X/806/2/240.
Casandjian, Jean -Marc. Local H i emissivity measured with FERMI-LAT and implications for Cosmic-ray spectra. United States. https://doi.org/10.1088/0004-637X/806/2/240
Casandjian, Jean -Marc. Sat . "Local H i emissivity measured with FERMI-LAT and implications for Cosmic-ray spectra". United States. https://doi.org/10.1088/0004-637X/806/2/240. https://www.osti.gov/servlets/purl/1355151.
@article{osti_1355151,
title = {Local H i emissivity measured with FERMI-LAT and implications for Cosmic-ray spectra},
author = {Casandjian, Jean -Marc},
abstractNote = {Cosmic-ray (CR) electrons and nuclei interact with the Galactic interstellar gas and produce high-energy γ-rays. The γ-ray emission rate per hydrogen atom, called emissivity, provides a unique indirect probe of the CR flux. We present the measurement and the interpretation of the emissivity in the solar neighborhood for γ-ray energy from 50 MeV to 50 GeV. We analyzed a subset of 4 yr of observations from the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope (Fermi) restricted to absolute latitudes $10^\circ \lt | b| \lt 70^\circ $. From a fit to the LAT data including atomic, molecular, and ionized hydrogen column density templates, as well as a dust optical depth map, we derived the emissivities, the molecular hydrogen–to–CO conversion factor ${X}_{\mathrm{CO}}=(0.902\pm 0.007)\times {10}^{20}$ cm–2 (K km s–1)–1, and the dust-to-gas ratio ${X}_{\mathrm{DUST}}=(41.4\pm 0.3)\times {10}^{20}$ cm–2 mag–1. Moreover, we detected for the first time γ-ray emission from ionized hydrogen. We compared the extracted emissivities to those calculated from γ-ray production cross sections and to CR spectra measured in the heliosphere. We observed that the experimental emissivities are reproduced only if the solar modulation is accounted for. This provides a direct detection of solar modulation observed previously through the anticorrelation between CR fluxes and solar activity. Lastly, we fitted a parameterized spectral form to the heliospheric CR observations and to the Fermi-LAT emissivity and obtained compatible local interstellar spectra for proton and helium kinetic energy per nucleon between between 1 and 100 GeV and for electron–positrons between 0.1 and 100 GeV.},
doi = {10.1088/0004-637X/806/2/240},
url = {https://www.osti.gov/biblio/1355151}, journal = {The Astrophysical Journal (Online)},
issn = {1538-4357},
number = 2,
volume = 806,
place = {United States},
year = {2015},
month = {6}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Citation Metrics:
Cited by: 12 works
Citation information provided by
Web of Science

Save / Share:

Works referenced in this record:

FERMI OBSERVATIONS OF CASSIOPEIA AND CEPHEUS: DIFFUSE GAMMA-RAY EMISSION IN THE OUTER GALAXY
journal, January 2010


FERMI LARGE AREA TELESCOPE OBSERVATIONS OF TWO GAMMA-RAY EMISSION COMPONENTS FROM THE QUIESCENT SUN
journal, June 2011


FERMI OBSERVATIONS OF γ-RAY EMISSION FROM THE MOON
journal, October 2012


THE FERMI LARGE AREA TELESCOPE ON ORBIT: EVENT CLASSIFICATION, INSTRUMENT RESPONSE FUNCTIONS, AND CALIBRATION
journal, October 2012


The cosmic-ray and gas content of the Cygnus region as measured in γ -rays by the Fermi Large Area Telescope
journal, February 2012


FERMI LARGE AREA TELESCOPE STUDY OF COSMIC RAYS AND THE INTERSTELLAR MEDIUM IN NEARBY MOLECULAR CLOUDS
journal, July 2012


GAMMA-RAY OBSERVATIONS OF THE ORION MOLECULAR CLOUDS WITH THE FERMI LARGE AREA TELESCOPE
journal, August 2012


FERMI -LAT OBSERVATIONS OF THE DIFFUSE γ-RAY EMISSION: IMPLICATIONS FOR COSMIC RAYS AND THE INTERSTELLAR MEDIUM
journal, April 2012


THE SPECTRUM AND MORPHOLOGY OF THE FERMI BUBBLES
journal, September 2014


PAMELA Measurements of Cosmic-Ray Proton and Helium Spectra
journal, March 2011


Inclusive particle production in 400 GeV/c pp-interactions
journal, September 1991


NINE-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE ( WMAP ) OBSERVATIONS: FINAL MAPS AND RESULTS
journal, September 2013


The Milky Way in Molecular Clouds: A New Complete CO Survey
journal, February 2001


Towards a free-free template for CMB foregrounds
journal, May 2003


EGRET Observations of the Diffuse Gamma‐Ray Emission in Orion: Analysis through Cycle 6
journal, July 1999


High-energy gamma-ray results from the second small astronomy satellite
journal, May 1975


The Vertical Structure of Warm Ionised Gas in the Milky Way
journal, January 2008


Solar Modulation of Galactic Cosmic Rays
journal, November 1968


HEALPix: A Framework for High‐Resolution Discretization and Fast Analysis of Data Distributed on the Sphere
journal, April 2005


Unveiling Extensive Clouds of Dark Gas in the Solar Neighborhood
journal, February 2005


The Correlation Between Dispersion Measure and X-Ray Column Density from Radio Pulsars
journal, April 2013


The Millennium Arecibo 21 Centimeter Absorption‐Line Survey. II. Properties of the Warm and Cold Neutral Media
journal, April 2003


EGRET Observations of the Diffuse Gamma‐Ray Emission from the Galactic Plane
journal, May 1997


Nuclear Enhancement of the Photon Yield in Cosmic ray Interactions
journal, June 2014


Diffractive Interaction and Scaling Violation in pp  →π  0 Interaction and GeV Excess in Galactic Diffuse Gamma‐Ray Spectrum of EGRET
journal, February 2005


Parameterization of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $\gamma ,\, e^{\pm }$ \end{document} , and Neutrino Spectra Produced by p‐p Interaction in Astronomical Environments
journal, August 2006


An h i Column Density Threshold for cold gas Formation in the Galaxy
journal, August 2011


The relationship between the galactic matter distribution, cosmic-ray dynamics, and gamma-ray production
journal, August 1977


High-Energy Cosmic Gamma-Ray Observations from the OSO-3 Satellite
journal, October 1972


The Likelihood Analysis of EGRET Data
journal, April 1996


Solar-stellar outer atmospheres and energetic particles, and galactic cosmic rays
journal, January 1985


A broadband study of galactic dust emission
journal, January 2007


Dark gas in the solar neighborhood from extinction data
journal, July 2012


Inverse Compton Origin of the Hard X‐Ray and Soft Gamma‐Ray Emission from the Galactic Ridge
journal, July 2008


Maps of Dust Infrared Emission for Use in Estimation of Reddening and Cosmic Microwave Background Radiation Foregrounds
journal, June 1998


Modelling the Galactic distribution of free electrons: The Galactic distribution of free electrons
journal, November 2012


On the Origins of the Diffuse hα Emission: Ionized gas or Dust-Scattered hα Halos?
journal, October 2012


PYTHIA 6.4 physics and manual
journal, May 2006


A Three‐dimensional Decomposition of the Infrared Emission from Dust in the Milky Way
journal, May 1997


The cosmic ?-ray spectrum from secondary particle production in cosmic-ray interactions
journal, March 1970


Production spectrum of gamma rays in interstellar space through neutral pion decay
journal, January 1981


GIANT GAMMA-RAY BUBBLES FROM FERMI -LAT: ACTIVE GALACTIC NUCLEUS ACTIVITY OR BIPOLAR GALACTIC WIND?
journal, November 2010


Radio observational constraints on Galactic 3D-emission models
journal, November 2007


Calibration of the Energetic Gamma-Ray Experiment Telescope (EGRET) for the Compton Gamma-Ray Observatory
journal, May 1993


Solar modulation parameter for cosmic rays since 1936 reconstructed from ground-based neutron monitors and ionization chambers: COSMIC RAY MODULATION
journal, February 2011


On the Origins of the High-Latitude hα Background
journal, November 2010


Revisiting the radial distribution of pulsars in the Galaxy
journal, July 2004


    Works referencing / citing this record:

    Galactic bulge preferred over dark matter for the Galactic centre gamma-ray excess
    journal, March 2018


    Cosmic rays, gas and dust in nearby anticentre clouds: I. CO-to-H
    journal, May 2017


    Exploring the shape of the γ -ray spectrum around the “ π 0 -bump”
    journal, July 2018


    Hard and bright gamma-ray emission at the base of the Fermi bubbles
    journal, May 2019


    The cosmic-ray content of the Orion-Eridanus superbubble
    journal, March 2020


    On the progressive hardening of the cosmic-ray proton spectrum in the inner Galaxy
    journal, October 2018


    Imprints of cosmic rays in multifrequency observations of the interstellar emission
    journal, December 2017


    Gamma-Ray Emission from Molecular Clouds Generated by Penetrating Cosmic Rays
    journal, November 2018


    Fermi -LAT Observations of γ -Ray Emission toward the Outer Halo of M31
    journal, July 2019