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 00h25m27.s0, + 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)-- Delta *G with Delta *G = 1.95 ? 0.51stat ? 0.30sys and C = (1.55 ? 0.43stat ? 0.47sys) X 10--14 cm--2 s--1 TeV--1. The integral flux above 1 TeV corresponds to ~0.9% of the steady Crab Nebula emission above the same energy, making it one of the weakest sources yet detected in TeV gamma rays. We present both leptonic and hadronic models that can describe the data. The lowest magnetic field allowed in these models is ~80 Delta *mG, which may be interpreted as evidence for magnetic field amplification.
The short gamma-ray front air-cherenkov experiment (SGARFACE) uses the Whipple 10
m telescope to search for bursts of
γ-rays. SGARFACE is sensitive to bursts with duration from a few ns to ∼20
μs and ...with
γ-ray energy above 100
MeV. SGARFACE began operating in March 2003 and has collected 2.2 million events during an exposure time of 2267
h. A search for bursts of
γ-rays from explosions of primordial black holes (PBH) was carried out. A Hagedorn-type PBH explosion is predicted to be visible within 60
pc of Earth. Background events were caused by cosmic rays and by atmospheric phenomena and their rejection was accomplished to a large extent using the time-resolved images. No unambiguous detection of bursts of
γ-rays could be made as the remaining background events mimic the expected shape and time-development of bursts. Upper limits on the PBH explosion rate were derived from the SGARFACE data and are compared to previous and future experiments. We note that a future array of large wide-field air-Cherenkov telescopes equipped with a SGARFACE-like trigger would be able to operate background-free with a 20–30 times higher sensitivity for PBH explosions.
The VERITAS array of Cherenkov telescopes has carried out a deep observational program on the nearby dwarf spheroidal galaxy Segue 1. We report on the results of nearly 48 hours of good quality ...selected data, taken between January 2010 and May 2011. No significant gamma -ray emission is detected at the nominal position of Segue 1, and upper limits on the integrated flux are derived. According to recent studies, Segue 1 is the most dark matter-dominated dwarf spheroidal galaxy currently known. We derive stringent bounds on various annihilating and decaying dark matter particle models. The upper limits on the velocity-weighted annihilation cross-section are (sigmav) super(95% CL) <, ~ 10 super(-23) cm super(3) s super(-1), improving our limits from previous observations of dwarf spheroidal galaxies by at least a factor of 2 for dark matter particle masses m sub( chi ) > ~ 300 GeV. The lower limits on the decay lifetime are at the level of tau super(95% CL) > ~ 10 super(24) s. Finally, we address the interpretation of the cosmic ray lepton anomalies measured by ATIC and PAMELA in terms of dark matter annihilation, and show that the VERITAS observations of Segue 1 disfavor such a scenario.
Very High Energy Gamma‐Ray Astronomy Catanese, Michael; Weekes, Trevor C.
Publications of the Astronomical Society of the Pacific,
10/1999, Letnik:
111, Številka:
764
Journal Article
Recenzirano
Odprti dostop
We present a review of the current status of very high energy γ‐ray astronomy. The development of the atmospheric Cerenkov imaging technique for ground‐based γ‐ray astronomy has led to a rapid growth ...in the number of observatories. The detection of TeV γ‐rays from active galactic nuclei was unexpected and is providing new insights into the emission mechanisms in the jets. Next‐generation telescopes are under construction and will increase dramatically the knowledge available at this extreme end of the cosmic electromagnetic spectrum.
We report on TeV Delta *g-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 Delta *g-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 Delta *g-ray energy spectra as a function of time and for different flux levels. On 2008 May 2 and 3, bright TeV Delta *g-ray flares were detected with fluxes reaching the level of 10 Crab. The TeV Delta *g-ray data were complemented with radio, optical, and X-ray observations, with flux variability found in all bands except for the radio wave band. The combination of the Rossi X-ray Timing Explorer and Swift X-ray data reveal spectral hardening with increasing flux levels, often correlated with an increase of the source activity in TeV Delta *g-rays. Contemporaneous spectral energy distributions were generated for 18 nights, each of which are reasonably described by a one-zone synchrotron self-Compton model.
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