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Title: CONSTRAINTS ON THE INTERGALACTIC MAGNETIC FIELD WITH GAMMA-RAY OBSERVATIONS OF BLAZARS

Abstract

Distant BL Lacertae objects emit γ rays which interact with the extragalactic background light (EBL), creating electron-positron pairs, and reducing the flux measured by ground-based imaging atmospheric Cherenkov telescopes (IACTs) at very-high energies (VHE). These pairs can Comptonscatter the cosmic microwave background, creating a γ-ray signature at slightly lower energies observable by the Fermi Large Area Telescope (LAT). This signal is strongly dependent on the intergalactic magnetic field (IGMF) strength (B) and its coherence length (LB). We use IACT spectra taken from the literature for 5 VHE-detected BL Lac objects, and combine it with LAT spectra for these sources to constrain these IGMF parameters. Low B values can be ruled out by the constraint that the cascade flux cannot exceed that observed by the LAT. High values of B can be ruled out from the constraint that the EBL-deabsorbed IACT spectrum cannot be greater than the LAT spectrum extrapolated into the VHE band, unless the cascade spectrum contributes a sizable fraction of the LAT flux. We rule out low B values (B . 10 -19 G for LB ≥ 1 Mpc) at > 5σ in all trials with different EBL models and data selection, except when

Authors:
 [1];  [2];  [3];  [2]; ORCiD logo [4];  [5];  [3]
  1. Naval Research Lab. (NRL), Washington, DC (United States)
  2. California Polytechnic State Univ. (CalPoly), San Luis Obispo, CA (United States)
  3. Univ. of Maryland Baltimore County (UMBC), Baltimore, MD (United States)
  4. Clemson Univ., SC (United States)
  5. Ecole Polytechnique, Palaiseau (France)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1354847
Grant/Contract Number:  
AC02-76SF00515
Resource Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 814; Journal Issue: 1; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS

Citation Formats

Finke, Justin D., Reyes, Luis C., Georganopoulos, Markos, Reynolds, Kaeleigh, Ajello, Marco, Fegan, Stephen J., and McCann, Kevin. CONSTRAINTS ON THE INTERGALACTIC MAGNETIC FIELD WITH GAMMA-RAY OBSERVATIONS OF BLAZARS. United States: N. p., 2015. Web. doi:10.1088/0004-637X/814/1/20.
Finke, Justin D., Reyes, Luis C., Georganopoulos, Markos, Reynolds, Kaeleigh, Ajello, Marco, Fegan, Stephen J., & McCann, Kevin. CONSTRAINTS ON THE INTERGALACTIC MAGNETIC FIELD WITH GAMMA-RAY OBSERVATIONS OF BLAZARS. United States. doi:10.1088/0004-637X/814/1/20.
Finke, Justin D., Reyes, Luis C., Georganopoulos, Markos, Reynolds, Kaeleigh, Ajello, Marco, Fegan, Stephen J., and McCann, Kevin. Thu . "CONSTRAINTS ON THE INTERGALACTIC MAGNETIC FIELD WITH GAMMA-RAY OBSERVATIONS OF BLAZARS". United States. doi:10.1088/0004-637X/814/1/20. https://www.osti.gov/servlets/purl/1354847.
@article{osti_1354847,
title = {CONSTRAINTS ON THE INTERGALACTIC MAGNETIC FIELD WITH GAMMA-RAY OBSERVATIONS OF BLAZARS},
author = {Finke, Justin D. and Reyes, Luis C. and Georganopoulos, Markos and Reynolds, Kaeleigh and Ajello, Marco and Fegan, Stephen J. and McCann, Kevin},
abstractNote = {Distant BL Lacertae objects emit γ rays which interact with the extragalactic background light (EBL), creating electron-positron pairs, and reducing the flux measured by ground-based imaging atmospheric Cherenkov telescopes (IACTs) at very-high energies (VHE). These pairs can Comptonscatter the cosmic microwave background, creating a γ-ray signature at slightly lower energies observable by the Fermi Large Area Telescope (LAT). This signal is strongly dependent on the intergalactic magnetic field (IGMF) strength (B) and its coherence length (LB). We use IACT spectra taken from the literature for 5 VHE-detected BL Lac objects, and combine it with LAT spectra for these sources to constrain these IGMF parameters. Low B values can be ruled out by the constraint that the cascade flux cannot exceed that observed by the LAT. High values of B can be ruled out from the constraint that the EBL-deabsorbed IACT spectrum cannot be greater than the LAT spectrum extrapolated into the VHE band, unless the cascade spectrum contributes a sizable fraction of the LAT flux. We rule out low B values (B . 10-19 G for LB ≥ 1 Mpc) at > 5σ in all trials with different EBL models and data selection, except when},
doi = {10.1088/0004-637X/814/1/20},
journal = {The Astrophysical Journal (Online)},
number = 1,
volume = 814,
place = {United States},
year = {2015},
month = {11}
}

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