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

Title: Search for Magnetically Broadened Cascade Emission from Blazars with VERITAS

Abstract

We present a search for magnetically broadened gamma-ray emission around active galactic nuclei (AGNs), using VERITAS observations of seven hard-spectrum blazars. A cascade process occurs when multi-TeV gamma-rays from an AGN interact with extragalactic background light (EBL) photons to produce electron–positron pairs, which then interact with cosmic microwave background photons via inverse-Compton scattering to produce gamma-rays. Due to the deflection of the electron–positron pairs, a non-zero intergalactic magnetic field (IGMF) would potentially produce detectable effects on the angular distribution of the cascade emission. In particular, an angular broadening compared to the unscattered emission could occur. Through non-detection of angularly broadened emission from 1ES 1218+304, the source with the largest predicted cascade fraction, we exclude a range of IGMF strengths around 10{sup −14} G at the 95% confidence level. The extent of the exclusion range varies with the assumptions made about the intrinsic spectrum of 1ES 1218+304 and the EBL model used in the simulation of the cascade process. All of the sources are used to set limits on the flux due to extended emission.

Authors:
;  [1]; ;  [2]; ;  [3];  [4];  [5]; ;  [6];  [7];  [8]; ;  [9];  [10];  [11]; ;  [12];  [13];  [14] more »; « less
  1. Physics Department, McGill University, Montreal, QC H3A 2T8 (Canada)
  2. Department of Physics, Washington University, St. Louis, MO 63130 (United States)
  3. Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645 (United States)
  4. Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States)
  5. School of Physics, National University of Ireland Galway, University Road, Galway (Ireland)
  6. Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907 (United States)
  7. Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802 (United States)
  8. Instituto de Astronomía y Física del Espacio (IAFE, CONICET-UBA), CC 67—Suc. 28, (C1428ZAA) Ciudad Autónoma de Buenos Aires (Argentina)
  9. DESY, Platanenallee 6, D-15738 Zeuthen (Germany)
  10. School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455 (United States)
  11. Department of Physics, California State University—East Bay, Hayward, CA 94542 (United States)
  12. Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064 (United States)
  13. Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716 (United States)
  14. Physics Department, Columbia University, New York, NY 10027 (United States)
Publication Date:
OSTI Identifier:
22663913
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 835; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ANGULAR DISTRIBUTION; BL LACERTAE OBJECTS; COMPARATIVE EVALUATIONS; COMPTON EFFECT; DETECTION; ELECTRONS; EMISSION; GALAXIES; GALAXY NUCLEI; GAMMA RADIATION; MAGNETIC FIELDS; PHOTONS; POSITRONS; RELICT RADIATION; SIMULATION; SPECTRA; TEV RANGE; VISIBLE RADIATION

Citation Formats

Archambault, S., Griffin, S., Archer, A., Bugaev, V., Benbow, W., Cerruti, M., Buchovecky, M., Connolly, M. P., Cui, W., Finley, J. P., Falcone, A., Alonso, M. Fernández, Fleischhack, H., Hütten, M., Fortson, L., Furniss, A., Hervet, O., Johnson, C. A., Holder, J., Humensky, T. B., E-mail: elisa.pueschel@ucd.ie, E-mail: weisgarber@physics.wisc.edu, and and others. Search for Magnetically Broadened Cascade Emission from Blazars with VERITAS. United States: N. p., 2017. Web. doi:10.3847/1538-4357/835/2/288.
Archambault, S., Griffin, S., Archer, A., Bugaev, V., Benbow, W., Cerruti, M., Buchovecky, M., Connolly, M. P., Cui, W., Finley, J. P., Falcone, A., Alonso, M. Fernández, Fleischhack, H., Hütten, M., Fortson, L., Furniss, A., Hervet, O., Johnson, C. A., Holder, J., Humensky, T. B., E-mail: elisa.pueschel@ucd.ie, E-mail: weisgarber@physics.wisc.edu, & and others. Search for Magnetically Broadened Cascade Emission from Blazars with VERITAS. United States. doi:10.3847/1538-4357/835/2/288.
Archambault, S., Griffin, S., Archer, A., Bugaev, V., Benbow, W., Cerruti, M., Buchovecky, M., Connolly, M. P., Cui, W., Finley, J. P., Falcone, A., Alonso, M. Fernández, Fleischhack, H., Hütten, M., Fortson, L., Furniss, A., Hervet, O., Johnson, C. A., Holder, J., Humensky, T. B., E-mail: elisa.pueschel@ucd.ie, E-mail: weisgarber@physics.wisc.edu, and and others. Wed . "Search for Magnetically Broadened Cascade Emission from Blazars with VERITAS". United States. doi:10.3847/1538-4357/835/2/288.
@article{osti_22663913,
title = {Search for Magnetically Broadened Cascade Emission from Blazars with VERITAS},
author = {Archambault, S. and Griffin, S. and Archer, A. and Bugaev, V. and Benbow, W. and Cerruti, M. and Buchovecky, M. and Connolly, M. P. and Cui, W. and Finley, J. P. and Falcone, A. and Alonso, M. Fernández and Fleischhack, H. and Hütten, M. and Fortson, L. and Furniss, A. and Hervet, O. and Johnson, C. A. and Holder, J. and Humensky, T. B., E-mail: elisa.pueschel@ucd.ie, E-mail: weisgarber@physics.wisc.edu and and others},
abstractNote = {We present a search for magnetically broadened gamma-ray emission around active galactic nuclei (AGNs), using VERITAS observations of seven hard-spectrum blazars. A cascade process occurs when multi-TeV gamma-rays from an AGN interact with extragalactic background light (EBL) photons to produce electron–positron pairs, which then interact with cosmic microwave background photons via inverse-Compton scattering to produce gamma-rays. Due to the deflection of the electron–positron pairs, a non-zero intergalactic magnetic field (IGMF) would potentially produce detectable effects on the angular distribution of the cascade emission. In particular, an angular broadening compared to the unscattered emission could occur. Through non-detection of angularly broadened emission from 1ES 1218+304, the source with the largest predicted cascade fraction, we exclude a range of IGMF strengths around 10{sup −14} G at the 95% confidence level. The extent of the exclusion range varies with the assumptions made about the intrinsic spectrum of 1ES 1218+304 and the EBL model used in the simulation of the cascade process. All of the sources are used to set limits on the flux due to extended emission.},
doi = {10.3847/1538-4357/835/2/288},
journal = {Astrophysical Journal},
number = 2,
volume = 835,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}
  • Indirect dark matter searches with ground-based gamma-ray observatories provide an alternative for identifying the particle nature of dark matter that is complementary to that of direct search or accelerator production experiments. We present the results of observations of the dwarf spheroidal galaxies Draco, Ursa Minor, Bootes 1, and Willman 1 conducted by the Very Energetic Radiation Imaging Telescope Array System (VERITAS). These galaxies are nearby dark matter dominated objects located at a typical distance of several tens of kiloparsecs for which there are good measurements of the dark matter density profile from stellar velocity measurements. Since the conventional astrophysical backgroundmore » of very high energy gamma rays from these objects appears to be negligible, they are good targets to search for the secondary gamma-ray photons produced by interacting or decaying dark matter particles. No significant gamma-ray flux above 200 GeV was detected from these four dwarf galaxies for a typical exposure of {approx}20 hr. The 95% confidence upper limits on the integral gamma-ray flux are in the range (0.4-2.2) x 10{sup -12} photons cm{sup -2} s{sup -1}. We interpret this limiting flux in the context of pair annihilation of weakly interacting massive particles (WIMPs) and derive constraints on the thermally averaged product of the total self-annihilation cross section and the relative velocity of the WIMPs (<{sigma}{nu}> {approx}< 10{sup -23} cm{sup 3} s{sup -1} for m{sub x} {approx}> 300 GeV c{sup -2}). This limit is obtained under conservative assumptions regarding the dark matter distribution in dwarf galaxies and is approximately 3 orders of magnitude above the generic theoretical prediction for WIMPs in the minimal supersymmetric standard model framework. However, significant uncertainty exists in the dark matter distribution as well as the neutralino cross sections which under favorable assumptions could further lower this limit.« less
  • Indirect dark matter searches with ground-based gamma-ray observatories provide an alternative for identifying the particle nature of dark matter that is complementary to that of direct search or accelerator production experiments. We present the results of observations of the dwarf spheroidal galaxies Draco, Ursa Minor, Booetes 1, and Willman 1 conducted by the Very Energetic Radiation Imaging Telescope Array System (VERITAS). These galaxies are nearby dark matter dominated objects located at a typical distance of several tens of kiloparsecs for which there are good measurements of the dark matter density profile from stellar velocity measurements. Since the conventional astrophysical backgroundmore » of very high energy gamma rays from these objects appears to be negligible, they are good targets to search for the secondary gamma-ray photons produced by interacting or decaying dark matter particles. No significant gamma-ray flux above 200 GeV was detected from these four dwarf galaxies for a typical exposure of {approx}20 hr. The 95% confidence upper limits on the integral gamma-ray flux are in the range (0.4-2.2) x 10{sup -12}photonscm{sup -2} s{sup -1}. We interpret this limiting flux in the context of pair annihilation of weakly interacting massive particles (WIMPs) and derive constraints on the thermally averaged product of the total self-annihilation cross section and the relative velocity of the WIMPs (({sigma}v) {approx}< 10{sup -23} cm{sup 3} s{sup -1} for m {sub {chi} {approx}}> 300 GeV c {sup -2}). This limit is obtained under conservative assumptions regarding the dark matter distribution in dwarf galaxies and is approximately 3 orders of magnitude above the generic theoretical prediction for WIMPs in the minimal supersymmetric standard model framework. However, significant uncertainty exists in the dark matter distribution as well as the neutralino cross sections which under favorable assumptions could further lower this limit.« less
  • Recent data from the Fermi Large Area Telescope have revealed about a dozen distant hard-spectrum blazars that have very-high-energy (VHE; {approx}> 100 GeV) photons associated with them, but most of them have not yet been detected by imaging atmospheric Cherenkov Telescopes. Most of these high-energy gamma-ray spectra, like those of other extreme high-frequency peaked BL Lac objects, can be well explained either by gamma rays emitted at the source or by cascades induced by ultra-high-energy cosmic rays, as we show specifically for KUV 00311-1938. We consider the prospects for detection of the VHE sources by the planned Cherenkov Telescope Arraymore » (CTA) and show how it can distinguish the two scenarios by measuring the integrated flux above {approx}500 GeV (depending on source redshift) for several luminous sources with z {approx}< 1 in the sample. Strong evidence for the origin of ultra-high-energy cosmic rays could be obtained from VHE observations with CTA. Depending on redshift, if the often quoted redshift of KUV 00311-1938 (z = 0.61) is believed, then preliminary H.E.S.S. data favor cascades induced by ultra-high-energy cosmic rays. Accurate redshift measurements of hard-spectrum blazars are essential for this study.« less
  • We show that recent data from the Fermi Large Area Telescope have revealed about a dozen distant hard-spectrum blazars that have very-high-energy (VHE; ≳ 100 eV) photons associated with them, but most of them have not yet been detected by imaging atmospheric Cherenkov Telescopes. Most of these high-energy gamma-ray spectra, like those of other extreme high-frequency peaked BL Lac objects, can be well explained either by gamma rays emitted at the source or by cascades induced by ultra-high-energy cosmic rays, as we show specifically for KUV 00311–1938. We consider the prospects for detection of the VHE sources by the plannedmore » Cherenkov Telescope Array (CTA) and show how it can distinguish the two scenarios by measuring the integrated flux above ~500 GeV (depending on source redshift) for several luminous sources with z ≲ 1 in the sample. Strong evidence for the origin of ultra-high-energy cosmic rays could be obtained from VHE observations with CTA. Depending on redshift, if the often quoted redshift of KUV 00311–1938 (z = 0.61) is believed, then preliminary H.E.S.S. data favor cascades induced by ultra-high-energy cosmic rays. Lastly, accurate redshift measurements of hard-spectrum blazars are essential for this study.« less
  • The ANTARES telescope is well-suited for detecting astrophysical transient neutrino sources as it can observe a full hemisphere of the sky at all times with a high duty cycle. The background due to atmospheric particles can be drastically reduced, and the point-source sensitivity improved, by selecting a narrow time window around possible neutrino production periods. Blazars, being radio-loud active galactic nuclei with their jets pointing almost directly towards the observer, are particularly attractive potential neutrino point sources, since they are among the most likely sources of the very high-energy cosmic rays. Neutrinos and gamma rays may be produced in hadronicmore » interactions with the surrounding medium. Moreover, blazars generally show high time variability in their light curves at different wavelengths and on various time scales. This paper presents a time-dependent analysis applied to a selection of flaring gamma-ray blazars observed by the FERMI/LAT experiment and by TeV Cherenkov telescopes using five years of ANTARES data taken from 2008 to 2012. The results are compatible with fluctuations of the background. Upper limits on the neutrino fluence have been produced and compared to the measured gamma-ray spectral energy distribution.« less