DISCOVERY OF VARIABILITY IN THE VERY HIGH ENERGY {gamma}-RAY EMISSION OF 1ES 1218+304 WITH VERITAS
- Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645 (United States)
- Department of Physics and Astronomy, Barnard College, Columbia University, NY 10027 (United States)
- Department of Physics, Washington University, St. Louis, MO 63130 (United States)
- Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716 (United States)
- Astrophysical Institute, Department of Physics and Astronomy, Ohio University, Athens, OH 45701 (United States)
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT (United Kingdom)
- Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439 (United States)
- School of Physics, National University of Ireland Galway, University Road, Galway (Ireland)
- Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605 (United States)
- Physics Department, McGill University, Montreal, QC H3A 2T8 (Canada)
- Department of Physics, Purdue University, West Lafayette, IN 47907 (United States)
- Department of Physics, Grinnell College, Grinnell, IA 50112-1690 (United States)
- Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802 (United States)
- Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112 (United States)
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.
- OSTI ID:
- 21301349
- Journal Information:
- Astrophysical Journal Letters, Vol. 709, Issue 2; Other Information: DOI: 10.1088/2041-8205/709/2/L163; Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
Similar Records
VERITAS Blazar Observations - Recent Results
VERITAS detection of γ-ray flaring activity from the BL LAC object 1ES 1727+502 during bright moonlight observations