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Title: DISCOVERY OF VARIABILITY IN THE VERY HIGH ENERGY {gamma}-RAY EMISSION OF 1ES 1218+304 WITH VERITAS

Abstract

We present results from an intensive VERITAS monitoring campaign of the high-frequency peaked BL Lac object 1ES 1218+304 in 2008/2009. Although 1ES 1218+304 was detected previously by MAGIC and VERITAS at a persistent level of {approx}6% of the Crab Nebula flux, the new VERITAS data reveal a prominent flare reaching {approx}20% of the Crab. While very high energy (VHE) flares are quite common in many nearby blazars, the case of 1ES 1218+304 (redshift z = 0.182) is particularly interesting since it belongs to a group of blazars that exhibit unusually hard VHE spectra considering their redshifts. When correcting the measured spectra for absorption by the extragalactic background light, 1ES 1218+304 and a number of other blazars are found to have differential photon indices {gamma}{<=} 1.5. The difficulty in modeling these hard spectral energy distributions in blazar jets has led to a range of theoretical {gamma}-ray emission scenarios, one of which is strongly constrained by these new VERITAS observations. We consider the implications of the observed light curve of 1ES 1218+304, which shows day scale flux variations, for shock acceleration scenarios in relativistic jets, and in particular for the viability of kiloparsec-scale jet emission scenarios.

Authors:
;  [1];  [2]; ; ;  [3];  [4];  [5];  [6];  [7];  [8]; ;  [9];  [10]; ;  [11];  [12];  [13];  [14]
+ Show Author Affiliations
  1. Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645 (United States)
  2. Department of Physics and Astronomy, Barnard College, Columbia University, NY 10027 (United States)
  3. Department of Physics, Washington University, St. Louis, MO 63130 (United States)
  4. Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716 (United States)
  5. Astrophysical Institute, Department of Physics and Astronomy, Ohio University, Athens, OH 45701 (United States)
  6. School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT (United Kingdom)
  7. Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439 (United States)
  8. School of Physics, National University of Ireland Galway, University Road, Galway (Ireland)
  9. Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605 (United States)
  10. Physics Department, McGill University, Montreal, QC H3A 2T8 (Canada)
  11. Department of Physics, Purdue University, West Lafayette, IN 47907 (United States)
  12. Department of Physics, Grinnell College, Grinnell, IA 50112-1690 (United States)
  13. Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802 (United States)
  14. Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112 (United States)
Publication Date:
OSTI Identifier:
21301349
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal Letters
Additional Journal Information:
Journal Volume: 709; Journal Issue: 2; Other Information: DOI: 10.1088/2041-8205/709/2/L163; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 2041-8205
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; 99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE; ABSORPTION; ACCELERATION; BL LACERTAE OBJECTS; CRAB NEBULA; EMISSION; ENERGY SPECTRA; GALAXIES; GAMMA RADIATION; JETS; PHOTONS; RED SHIFT; RELATIVISTIC RANGE; SIMULATION

Citation Formats

Acciari, V A, Benbow, W, Aliu, E, Beilicke, M, Bugaev, V, Dickherber, R, Boltuch, D, Boettcher, M, Bradbury, S M, Byrum, K, Cesarini, A, Ciupik, L, Fortson, L, Cogan, P, Cui, W, Finley, J P, Duke, C, Falcone, A, Finnegan, G, and Furniss, A. DISCOVERY OF VARIABILITY IN THE VERY HIGH ENERGY {gamma}-RAY EMISSION OF 1ES 1218+304 WITH VERITAS. United States: N. p., 2010. Web. doi:10.1088/2041-8205/709/2/L163; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
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Acciari, V A, Benbow, W, Aliu, E, Beilicke, M, Bugaev, V, Dickherber, R, Boltuch, D, Boettcher, M, Bradbury, S M, Byrum, K, Cesarini, A, Ciupik, L, Fortson, L, Cogan, P, Cui, W, Finley, J P, Duke, C, Falcone, A, Finnegan, G, & Furniss, A. DISCOVERY OF VARIABILITY IN THE VERY HIGH ENERGY {gamma}-RAY EMISSION OF 1ES 1218+304 WITH VERITAS. United States. https://doi.org/10.1088/2041-8205/709/2/L163; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)
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Acciari, V A, Benbow, W, Aliu, E, Beilicke, M, Bugaev, V, Dickherber, R, Boltuch, D, Boettcher, M, Bradbury, S M, Byrum, K, Cesarini, A, Ciupik, L, Fortson, L, Cogan, P, Cui, W, Finley, J P, Duke, C, Falcone, A, Finnegan, G, and Furniss, A. 2010. "DISCOVERY OF VARIABILITY IN THE VERY HIGH ENERGY {gamma}-RAY EMISSION OF 1ES 1218+304 WITH VERITAS". United States. https://doi.org/10.1088/2041-8205/709/2/L163; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
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@article{osti_21301349,
title = {DISCOVERY OF VARIABILITY IN THE VERY HIGH ENERGY {gamma}-RAY EMISSION OF 1ES 1218+304 WITH VERITAS},
author = {Acciari, V A and Benbow, W and Aliu, E and Beilicke, M and Bugaev, V and Dickherber, R and Boltuch, D and Boettcher, M and Bradbury, S M and Byrum, K and Cesarini, A and Ciupik, L and Fortson, L and Cogan, P and Cui, W and Finley, J P and Duke, C and Falcone, A and Finnegan, G and Furniss, A.},
abstractNote = {We present results from an intensive VERITAS monitoring campaign of the high-frequency peaked BL Lac object 1ES 1218+304 in 2008/2009. Although 1ES 1218+304 was detected previously by MAGIC and VERITAS at a persistent level of {approx}6% of the Crab Nebula flux, the new VERITAS data reveal a prominent flare reaching {approx}20% of the Crab. While very high energy (VHE) flares are quite common in many nearby blazars, the case of 1ES 1218+304 (redshift z = 0.182) is particularly interesting since it belongs to a group of blazars that exhibit unusually hard VHE spectra considering their redshifts. When correcting the measured spectra for absorption by the extragalactic background light, 1ES 1218+304 and a number of other blazars are found to have differential photon indices {gamma}{<=} 1.5. The difficulty in modeling these hard spectral energy distributions in blazar jets has led to a range of theoretical {gamma}-ray emission scenarios, one of which is strongly constrained by these new VERITAS observations. We consider the implications of the observed light curve of 1ES 1218+304, which shows day scale flux variations, for shock acceleration scenarios in relativistic jets, and in particular for the viability of kiloparsec-scale jet emission scenarios.},
doi = {10.1088/2041-8205/709/2/L163; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)},
url = {https://www.osti.gov/biblio/21301349}, journal = {Astrophysical Journal Letters},
issn = {2041-8205},
number = 2,
volume = 709,
place = {United States},
year = {Mon Feb 01 00:00:00 EST 2010},
month = {Mon Feb 01 00:00:00 EST 2010}
}
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Journal Article:
https://doi.org/10.1088/2041-8205/709/2/L163; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)
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