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Search for an Enhanced TeV Gamma-Ray Flux from the Crab Nebula with VERITAS

ATel #2968; Rene A. Ong (UCLA) for the VERITAS Collaboration
on 23 Oct 2010; 19:25 UT
Credential Certification: Rene Ong (rene@astro.ucla.edu)

Subjects: Gamma Ray, >GeV, TeV, VHE, Neutron Star, Supernova Remnant, Pulsar

Both the AGILE (ATEL #2855) and Fermi-LAT (ATEL #2861) teams have reported an increased >100 MeV gamma-ray flux from a source positionally coincident with the Crab Nebula over the time period from September 19 to September 21, 2010. The ARGO-YBJ air shower detector has reported a gamma-ray excess from the region at the 4 standard deviation level, corresponding to a flux about 3-4 times higher than usual. The ARGO-YBJ result covers the period from September 17 to September 22, at a median energy of about 1 TeV (ATEL #2921).

VERITAS observations of the Crab Nebula in the energy range from 200 GeV to 3 TeV were made on the four nights of September 17, 18, 19, and 20, 2010, totaling 120 minutes. We detect a strong gamma-ray signal corresponding to 40 standard deviations above background. The measured flux level is consistent with VERITAS observations of the Crab Nebula from the previous year (the 2009-2010 observing season). There is no evidence for enhanced emission during the period of time that VERITAS observed the source region; the VERITAS observation times are given in the table below. Statistical errors (one standard deviation) on the average and nightly fluxes above 1 TeV are at the 9% and 20% level, respectively.

Table of VERITAS Observations of the Crab Nebula between Sept 17 and Sept 20, 2010:
| Start (MJD) | End (MJD) | Duration (secs)
| 55456.4471 | 55456.4610 | 1202.14
| 55456.4717 | 55456.4856 | 1202.12
| 55457.4790 | 55457.4929 | 1202.15
| 55458.4529 | 55458.4669 | 1202.13
| 55458.4710 | 55458.4849 | 1202.14
| 55459.4729 | 55459.4868 | 1202.11

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