VERITAS OBSERVATIONS OF THE TeV BINARY LS I +61{sup 0} 303 DURING 2008-2010
- 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 and Astronomy, University of California, Los Angeles, CA 90095 (United States)
- Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064 (United States)
- Department of Physics, Washington University, St. Louis, MO 63130 (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, University College Dublin, Belfield, Dublin 4 (Ireland)
- School of Physics, National University of Ireland Galway, University Road, Galway (Ireland)
- Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605 (United States)
- 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)
We present the results of observations of the TeV binary LS I +61{sup 0} 303 with the VERITAS telescope array between 2008 and 2010, at energies above 300 GeV. In the past, both ground-based gamma-ray telescopes VERITAS and MAGIC have reported detections of TeV emission near the apastron phases of the binary orbit. The observations presented here show no strong evidence for TeV emission during these orbital phases; however, during observations taken in late 2010, significant emission was detected from the source close to the phase of superior conjunction (much closer to periastron passage) at a 5.6 standard deviation (5.6{sigma}) post-trials significance. In total, between 2008 October and 2010 December a total exposure of 64.5 hr was accumulated with VERITAS on LS I +61{sup 0} 303, resulting in an excess at the 3.3{sigma} significance level for constant emission over the entire integrated data set. The flux upper limits derived for emission during the previously reliably active TeV phases (i.e., close to apastron) are less than 5% of the Crab Nebula flux in the same energy range. This result stands in apparent contrast to previous observations by both MAGIC and VERITAS which detected the source during these phases at 10% of the Crab Nebula flux. During the two year span of observations, a large amount of X-ray data were also accrued on LS I +61{sup 0} 303 by the Swift X-ray Telescope and the Rossi X-ray Timing Explorer Proportional Counter Array. We find no evidence for a correlation between emission in the X-ray and TeV regimes during 20 directly overlapping observations. We also comment on data obtained contemporaneously by the Fermi Large Area Telescope.
- OSTI ID:
- 21582991
- Journal Information:
- Astrophysical Journal, Vol. 738, Issue 1; Other Information: DOI: 10.1088/0004-637X/738/1/3; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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