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Register a new userVery high energy gamma-ray observations during moonlight and twilight with the MAGIC telescope
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Emma de Ona Wilhelmi
Publication date
2007
fields
Physics
and research's language is
English
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We study the capability of the MAGIC telescope to observe under moderate moonlight. TeV gamma-ray signals from the Crab nebula were detected with the MAGIC telescope during periods when the Moon was above the horizon and during twilight. This was accomplished by increasing the trigger discriminator thresholds. No change is necessary in the high voltage settings since the camera PMTs were especially designed to avoid high currents. We characterize the telescope performance by studying the effect of the moonlight on the gamma-ray detection efficiency and sensitivity, as well as on the energy threshold.
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Context. In the last five years the Fermi Large Area Telescope (LAT) instrument detected GeV {gamma}-ray emission from five novae. The GeV emission can be interpreted in terms of an inverse Compton process of electrons accelerated in a shock. In this case it is expected that protons in the same conditions can be accelerated to much higher energies. Consequently they may produce a second component in the {gamma}-ray spectrum at TeV energies. Aims. We aim to explore the very-high-energy domain to search for {gamma}-ray emission above 50 GeV and to shed light on the acceleration process of leptons and hadrons in nova explosions. Methods. We have performed observations with the MAGIC telescopes of the classical nova V339 Del shortly after the 2013 outburst, triggered by optical and subsequent GeV {gamma}-ray detec- tions. We also briefly report on VHE observations of the symbiotic nova YY Her and the dwarf nova ASASSN-13ax. We complement the TeV MAGIC observations with the analysis of con- temporaneous Fermi-LAT data of the sources. The TeV and GeV observations are compared in order to evaluate the acceleration parameters for leptons and hadrons. Results. No significant TeV emission was found from the studied sources. We computed upper limits on the spectrum and night-by-night flux. The combined GeV and TeV observations of V339 Del limit the ratio of proton to electron luminosities to Lp<~0.15 Le.
In this paper we report on the Markarian 501 results obtained during our TeV $gamma$-ray observations from March 11 to May 12, 2005 and February 28 to May 7, 2006 for 112.5 hours with the TACTIC $gamma$-ray telescope. During 2005 observations for 45.7 hours, the source was found to be in a low state and we have placed an upper limit of 4.62 $times$ 10$^{-12}$ photons cm$^{-2}$ s$^{-1}$ at 3$sigma$ level on the integrated TeV $gamma$-ray flux above 1 TeV from the source direction. However, during the 2006 observations for 66.8h, detailed data analysis revealed the presence of a TeV $gamma$-ray signal from the source with a statistical significance of 7.5$sigma$ above $E_{gamma}geq$ 1 TeV. The time averaged differential energy spectrum of the source in the energy range 1-11 TeV is found to match well with the power law function of the form ($dPhi/dE=f_0 E^{-Gamma}$) with $f_0=(1.66pm0.52)times 10^{-11}cm^{-2}s^{-1}TeV^{-1}$ and $Gamma=2.80pm0.27$.
Gamma-ray burst (GRB) observations at very high energies (VHE, E > 100 GeV) can impose tight constraints on some GRB emission models. Many GRB afterglow models predict a VHE component similar to that seen in blazars and plerions, in which the GRB spectral energy distribution has a double-peaked shape extending into the VHE regime. VHE emission coincident with delayed X-ray flare emission has also been predicted. GRB follow-up observations have had high priority in the observing program at the Whipple 10m Gamma-ray Telescope and GRBs will continue to be high priority targets as the next generation observatory, VERITAS, comes on-line. Upper limits on the VHE emission, at late times (>~4 hours), from seven GRBs observed with the Whipple Telescope are reported here.
The H.E.S.S. Imaging Atmospheric Cherenkov Telescope Array is currently the most sensitive instrument for Very High Energy (VHE) gamma-ray observations in the energy range of about 0.1-10 TeV. During more than two years of operation with the complete 4-telescope array, many galactic and extragalactic VHE gamma-ray sources have been discovered. With its superior sensitivity and its large field-of-view camera, H.E.S.S. is particularly suited for surveys and detailed studies of extended sources. A selection of recent H.E.S.S. results is presented in this proceeding.
In the last few years the Fermi-LAT instrument has detected GeV gamma-ray emission from several novae. Such GeV emission can be interpreted in terms of inverse Compton emission from electrons accelerated in the shock or in terms of emission from hadrons accelerated in the same conditions. The latter might reach much higher energies and could produce a second component in the gamma-ray spectrum at TeV energies. We perform follow-up observations of selected novae and dwarf novae in search of the second component in TeV energy gamma rays. This can shed light on the acceleration process of leptons and hadrons in nova explosions. We have performed observations with the MAGIC telescopes of 3 sources, a symbiotic nova YY Her, a dwarf nova ASASSN-13ax and a classical nova V339 Del, shortly after their outbursts. We did not detect TeV gamma-ray emission from any of the objects observed. The TeV upper limits from MAGIC observations and the GeV detection by Fermi constrain the acceleration parameters for electrons and hadrons.
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