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Astrophysics and Astronomy

Physical Sciences Publications

2011

Articles 1 - 9 of 9

Full-Text Articles in Physical Sciences and Mathematics

Veritas Observations Of Gamma-Ray Bursts Detected By Swift, P. T. Reynolds, Et. Al. Dec 2011

Veritas Observations Of Gamma-Ray Bursts Detected By Swift, P. T. Reynolds, Et. Al.

Physical Sciences Publications

We present the results of 16 Swift-triggered Gamma-ray burst (GRB) follow-up observations taken with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) telescope array from 2007 January to 2009 June. The median energy threshold and response time of these observations were 260 GeV and 320 s, respectively. Observations had an average duration of 90 minutes. Each burst is analyzed independently in two modes: over the whole duration of the observations and again over a shorter timescale determined by the maximum VERITAS sensitivity to a burst with a t –1.5 time profile. This temporal model is characteristic of GRB afterglows …

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Multiwavelength Observations Of The Very High Energy Blazar 1es 2344+514, P. T. Reynolds, Et. Al. Sep 2011

Multiwavelength Observations Of The Very High Energy Blazar 1es 2344+514, P. T. Reynolds, Et. Al.

Physical Sciences Publications

Multiwavelength observations of the high-frequency-peaked blazar 1ES 2344+514 were performed from 2007 October to 2008 January. The campaign represents the first contemporaneous data on the object at very high energy (VHE, E >100 GeV) γ-ray, X-ray, and UV energies. Observations with VERITAS in VHE γ-rays yield a strong detection of 20σ with 633 excess events in a total exposure of 18.1 hr live time. A strong VHE γ-ray flare on 2007 December 7 is measured at F(>300 GeV) = (6.76 ± 0.62) × 10–11 photons cm–2 s–1, corresponding to 48% of the Crab Nebula flux. Excluding this flaring episode, …

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Tev And Multi-Wavelength Observations Of Mrk 421 In 2006-2008, P. T. Reynolds, Et. Al. Sep 2011

Tev And Multi-Wavelength Observations Of Mrk 421 In 2006-2008, P. T. Reynolds, Et. Al.

Physical Sciences Publications

We report on TeV γ-ray observations of the blazar Mrk 421 (redshift of 0.031) with the VERITAS observatory and the Whipple 10 m Cherenkov telescope. The excellent sensitivity of VERITAS allowed us to sample the TeV γ-ray fluxes and energy spectra with unprecedented accuracy where Mrk 421 was detected in each of the pointings. A total of 47.3 hr of VERITAS and 96 hr of Whipple 10 m data were acquired between 2006 January and 2008 June. We present the results of a study of the TeV γ-ray energy spectra as a function of time and for different flux levels. …

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Veritas Observations Of The Tev Binary Ls I+61 Degrees 303 During 2008-2010, P. T. Reynolds, Et. Al. Sep 2011

Veritas Observations Of The Tev Binary Ls I+61 Degrees 303 During 2008-2010, P. T. Reynolds, Et. Al.

Physical Sciences Publications

We present the results of observations of the TeV binary LS I +61° 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 (5.6σ) post-trials …

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Veritas Observations Of The Unusual Extragalactic Transient Swift J164449.3+573451, P. T. Reynolds, Et Al Aug 2011

Veritas Observations Of The Unusual Extragalactic Transient Swift J164449.3+573451, P. T. Reynolds, Et Al

Physical Sciences Publications

We report on very high energy (>100 GeV) gamma-ray observations of Swift J164449.3+573451, an unusual transient object first detected by the Swift Observatory and later detected by multiple radio, optical, and X-ray observatories. A total exposure of 28 hr was obtained on Swift J164449.3+573451 with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) during 2011 March 28-April 15. We do not detect the source and place a differential upper limit on the emission at 500 GeV during these observations of 1.4 × 10–12 erg cm–2 s–1 (99% confidence level). We also present time-resolved upper limits and use a …

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Discovery Of Tev Gamma Ray Emission From Tycho's Supernova Remnant, P. T. Reynolds, Et Al Mar 2011

Discovery Of Tev Gamma Ray Emission From Tycho's Supernova Remnant, P. T. Reynolds, Et Al

Physical Sciences Publications

We report the discovery of TeV gamma-ray emission from the Type Ia supernova remnant (SNR) G120.1+1.4, known as Tycho's SNR. Observations performed in the period 2008-2010 with the VERITAS ground-based gamma-ray observatory reveal weak emission coming from the direction of the remnant, compatible with a point source located at 00h25m270, + 64°10'50'' (J2000). The TeV photon spectrum measured by VERITAS can be described with a power law dN/dE = C(E/3.42 TeV)–Γ with Γ = 1.95 ± 0.51stat ± 0.30sys and C = (1.55 ± 0.43stat ± 0.47sys) × 10–14 cm–2 s–1 TeV–1. The integral …

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Spectral Energy Distribution Of Markarian 501: Quiescent State Versus Extreme Outburst, P. T. Reynolds, Veritas, Magic Mar 2011

Spectral Energy Distribution Of Markarian 501: Quiescent State Versus Extreme Outburst, P. T. Reynolds, Veritas, Magic

Physical Sciences Publications

The very high energy (VHE; E > 100 GeV) blazar Markarian 501 (Mrk 501) has a well-studied history of extreme spectral variability and is an excellent laboratory for studying the physical processes within the jets of active galactic nuclei. However, there are few detailed multiwavelength studies of Mrk 501 during its quiescent state, due to its low luminosity. A short-term multiwavelength study of Mrk 501 was coordinated in 2009 March, focusing around a multi-day observation with the Suzaku X-ray satellite and including γ-ray data from VERITAS, MAGIC, and the Fermi Gamma-ray Space Telescope with the goal of providing a well-sampled multiwavelength …

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Insights Into The High-Energy Gamma-Ray Emission Of Markarian 501 From Extensive Multifrequency Observations In The Fermi Era, P. T. Reynolds, Fermi-Lat, Magic, Veritas Feb 2011

Insights Into The High-Energy Gamma-Ray Emission Of Markarian 501 From Extensive Multifrequency Observations In The Fermi Era, P. T. Reynolds, Fermi-Lat, Magic, Veritas

Physical Sciences Publications

We report on the γ-ray activity of the blazar Mrk 501 during the first 480 days of Fermi operation. We find that the average Large Area Telescope (LAT) γ-ray spectrum of Mrk 501 can be well described by a single power-law function with a photon index of 1.78 ± 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of two), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 ± 0.14, and the softest one is 2.51 ± 0.20. These unexpected spectral changes do …

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Multi-Wavelength Observations Of The Flaring Gamma-Ray Blazar 3c 66a In 2008 October, P. T. Reynolds, Fermi-Lat, Veritas, Gasp-Webt Jan 2011

Multi-Wavelength Observations Of The Flaring Gamma-Ray Blazar 3c 66a In 2008 October, P. T. Reynolds, Fermi-Lat, Veritas, Gasp-Webt

Physical Sciences Publications

The BL Lacertae object 3C 66A was detected in a flaring state by the Fermi Large Area Telescope (LAT) and VERITAS in 2008 October. In addition to these gamma-ray observations, F-GAMMA, GASP-WEBT, PAIRITEL, MDM, ATOM, Swift, and Chandra provided radio to X-ray coverage. The available light curves show variability and, in particular, correlated flares are observed in the optical and Fermi-LAT gamma-ray band. The resulting spectral energy distribution can be well fitted using standard leptonic models with and without an external radiation field for inverse Compton scattering. It is found, however, that only the model with an external …

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