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Multiwavelength Observations of Markarian 421 in March 2001 |
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Science Publications
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Written by G. Fossati et. al.
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Thursday, 18 October 2007 |
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The Astrophysical Journal, Volume 677, p. 906 arXiv:0710.4138 Full Text We present a detailed analysis of week-long simultaneous observations of the blazar Mrk 421 at 2-60 keV X-rays (RossiXTE) and TeV gamma-rays (Whipple andHEGRA) in 2001. Accompanying optical monitoring was performed with the Mt. Hopkins 48" telescope. The unprecedented quality of this dataset enables us not only to establish the existence of the correlation between the TeV and X-ray luminosities, but also to start unveiling some of its more detailed characteristics, in particular its energy dependence, and time variability. The source shows strong variations in both X-ray and gamma-ray bands, which are highly correlated. No evidence of a non-zero X-ray/gamma-ray interband lag is found on the full week dataset. The upper limit on a delay is approximately 3 ks. A more detailed analysis focused on the March 19 flare, however, reveals that data are not consistent with the peak of the outburst in the 2-4 keV X-ray and TeV band being simultaneous. For this event we estimate a 2.1 +- 0.7 ks lag of the TeV flare with respect to the 2-4 keV X-ray band. The correlation with a higher X-ray energy band, namely 9-15 keV is consistent with coordinated variations, i.e. the gamma-ray rate is better correlated with the harder X-ray rate. The amplitudes of the X-ray and gamma-ray variations are also highly correlated, and the TeV luminosity increases more than linearly with respect to the X-ray one. The high degree of correlation lends further support to the standard model in which a unique electrons population produces the Xrays by synchrotron radiation and the gamma-ray component by inverse Compton scattering. However, the finding that for the individual best observed flares (March 18/19 and 22/23) the gamma-ray flux scales approximately quadratically with respect to the X-ray flux, poses a serious challenge to emission models for TeV blazars. Rather special conditions and/or ne tuning of the temporal evolution of the physical parameters of the emission region are required in order to reproduce the quadratic correlation. We briefly discuss the astrophysical consequences of these new findings in the context of the competing models for the jet emission in blazars. |
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Last Updated ( Monday, 14 April 2008 )
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VHE Emission from TeV J2032+4130 and Iterative Deconvolution in Ground Based Gamma-ray Astronomy |
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Theses and Dissertations
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Written by Gary Kenny
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Saturday, 01 September 2007 |
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VHE Emission from TeV J2032+4130 and Iterative Deconvolution in Ground Based Gamma-ray Astronomy Gary E. Kenny Supervisor: Dr. M. Lang Co-Supervisor: Dr. G. Gillanders Department of Physics National University of Ireland, Galway September 2007 |
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Last Updated ( Tuesday, 19 February 2008 )
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Observation of M87 with VERITAS |
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Conference Proceedings
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Written by P. Colin for the VERITAS Collaboration
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Tuesday, 10 July 2007 |
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Contribution to the 30th International Cosmic Ray Conference, Merida, Mexico, July 2007
arXiv:astro-ph/0709.3663 The giant radio galaxy M87 is the only extragalactic non-blazar object which has been detected as a source of very high energy gamma-rays. It represents a unique opportunity to study the phenomena of gamma-ray emission from a nearby AGN. In this paper we report preliminary results from the observations of M87 taken with the imaging atmospheric Cherenkov telescope array VERITAS in February, March and April 2007. An excess of photons above an energy threshold of 250 GeV is measured with a sta tistical significance of more than five standard deviations. |
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Last Updated ( Monday, 15 October 2007 )
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Very High Energy Observations of Gamma-ray Bursts with VERITAS and Whipple |
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Conference Proceedings
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Written by Deirdre Horan for the VERITAS Collaboration
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Tuesday, 10 July 2007 |
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Contribution to the 30th International Cosmic Ray Conference, Merida, Mexico, July 2007
abs/0709.3830v1 Many authors have predicted very-high-energy (VHE; E > 100 GeV) emission from gamma-ray bursts (GRBs) both during the prompt phase and during the multi-component afterglow. To date, however, there has been no definitive detection of such emission. Recently, the Swift Satellite made the exciting discovery that almost 50% of GRBs are accompanied by one or more X-ray flares, which are found to occur from several seconds to many hours after the prompt emission. The discovery of this phenomenon and the many predictions that VHE emission should accompany these flares increases the already strong motivation for making immediate follow-up VHE observations of GRBs. Observations of GRBs have high priority at VERITAS, preempting any observations that may be in progress. GRB alerts are received from the GCN via a socket connection. This is interfaced to the VERITAS Tracking Software to minimize the time between a notification arriving and the telescope being slewed to the GRB. We report here on GRB observations with VERITAS and with the Whipple Telescope from 2005 through 2007. |
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Last Updated ( Thursday, 29 November 2007 )
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Observations of Shell-Type Supernova Remnants with VERITAS |
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Conference Proceedings
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Written by Brian Humensky for the VERITAS Collaboration
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Tuesday, 10 July 2007 |
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Contribution to the 30th International Cosmic Ray Conference, Merida, Mexico, July 2007 abs/0709.4298v1 Shell-type supernova remnants (SNRs) accelerate particles at the shock front between the expanding remnant and the swept-up interstellar medium. If these particles include protons and nuclei, very-high-energy gamma-ray emission may result from the decay of pions produced in interactions between cosmic rays and the local insterstellar medium. For SNRs that are interacting with a nearby molecular cloud, such as IC 443, the enhanced matter density provides a target medium that can amplify the gamma-ray emission. IC 443 also contains the pulsar wind nebula (PWN) CXOU J061705.3+222127. PWNe are the most plentiful galactic sources of very-high-energy gamma rays, which are produced in the shock formed at the collision of the pulsar wind with the ambient medium.
VERITAS is an array of four 12-m telescopes dedicated to gamma-ray astronomy in the energy band above 100 GeV. Located on Mt. Hopkins in southern Arizona, VERITAS operated during the 2006-2007 season in 2-, 3-, and 4-telescope observation modes. In this talk, results from three-telescope observations of the composite supernova remnant IC 443 during the 2006-2007 season are discussed. |
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Last Updated ( Thursday, 29 November 2007 )
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