Correlations between the arrival time and the energy of photons emitted in outbursts of astrophysical objects are predicted in quantum and classical gravity scenarios and can appear as well as a ...result of complex acceleration mechanisms responsible for the photon emission at the source. This paper presents a robust method to study such correlations that overcomes some limitations encountered in previous analysis, and is based on a likelihood function built from the physical picture assumed for the emission, propagation and detection of the photons. The results of the application of this method to a flare of Markarian 501 observed by the MAGIC telescope are presented. The method is also applied to a simulated dataset based on the flare of PKS 2155-304 recorded by the H.E.S.S. observatory to proof its applicability to complex photon arrival time distributions.
•We search for TeV gamma-ray emission from blazar 1ES 1218+304 with TACTIC telescope.•No activity in TeV energy regime is observed from the source.•We present 99% confidence level upper limit on ...integral flux as 23% of Crab Nebula flux.•Simultaneous data from Fermi-LAT, Swift-XRT/UVOT, and OVRO are used to study the emission in low energy regime.
In this paper, we present results of TeV γ-ray observations of the high synchrotron peaked BL Lac object 1ES 1218+304 (z=0.182) with the TACTIC (TeV Atmospheric Cherenkov Telescope with Imaging Camera). The observations are primarily motivated by the unusually hard GeV–TeV spectrum of the source despite its relatively large redshift. The source is observed in the TeV energy range with the TACTIC from March 1, 2013 to April 15, 2013 (MJD 56352–56397) for a total observation time of 39.62h and no evidence of TeV γ-ray activity is found from the source. The corresponding 99% confidence level upper limit on the integral flux above a threshold energy of 1.1TeV is estimated to be 3.41×10-12photonscm−2s−1 (i.e. <23% Crab Nebula flux) assuming a power law differential energy spectrum with photon index 3.0, as previously observed by the MAGIC and VERITAS telescopes. For the study of multi-wavelength emission from the source, we use nearly simultaneous optical, UV and X-ray data collected by the UVOT and XRT instruments on board the Swift satellite and high energy γ-ray data collected by the Large Area Telescope on board the Fermi satellite. We also use radio data at 15GHz from OVRO 40m telescope in the same period. No significant increase of activity is detected from radio to TeV γ-rays from 1ES1218+304 during the period from March 1, 2013 to April 15, 2013.
► We optimize the collection efficiency of a hexagonal light collector to be used for very-high-energy gamma-ray telescopes. ► Quadratic and cubic Bézier curves are used for the inner shape of a ...light collector instead of a Winston cone. ► The efficiency of the optimized design is higher for signal photons and lower for stray light compared to a Winston cone.
Reflective light collectors with hexagonal entrance and exit apertures are frequently used in front of the focal-plane camera of a very-high-energy gamma-ray telescope to increase the collection efficiency of atmospheric Cherenkov photons and reduce the night-sky background entering at large incident angles. The shape of a hexagonal light collector is usually based on Winston’s design, which is optimized for only two-dimensional optical systems. However, it is not known whether a hexagonal Winston cone is optimal for the real three-dimensional optical systems of gamma-ray telescopes. For the first time we optimize the shape of a hexagonal light collector using quadratic and cubic Bézier curves. We demonstrate that our optimized designs simultaneously achieve a higher collection efficiency and background reduction rate than traditional designs.
Blazars like Markarian 421 or Markarian 501 are active galactic nuclei (AGN), with their jets orientated towards the observer. They are among the brightest objects in the very high energy (VHE) gamma ...ray regime (>100 GeV). Their emitted gamma-ray fluxes are extremely variable, with changing activity levels on timescales between minutes, months, and even years. Several questions are part of the current research, such as the question of the emission regions or the engine of the AGN and the particle acceleration. A dedicated longterm monitoring program is necessary to investigate the properties of blazars in detail. A densely sampled and unbiased light curve allows for observation of both high and low states of the sources, and the combination with multi-wavelength observation could contribute to the answer of several questions mentioned above. FACT (First G-APD Cherenkov Telescope) is the first operational telescope using silicon photomultiplier (SiPM, also known as Geigermode—Avalanche Photo Diode, G-APD) as photon detectors. SiPM have a very homogenous and stable longterm performance, and allow operation even during full moon without any filter, leading to a maximal duty cycle for an Imaging Air Cherenkov Telescope (IACT). Hence, FACT is an ideal device for such a longterm monitoring of bright blazars. A small set of sources (e.g., Markarian 421, Markarian 501, 1ES 1959+650, and 1ES 2344+51.4) is currently being monitored. In this contribution, the FACT telescope and the concept of longterm monitoring of bright blazars will be introduced. The results of the monitoring program will be shown, and the advantages of densely sampled and unbiased light curves will be discussed.
We present results of very-high-energy gamma-ray observations (
E
γ
>
160
GeV) of two high-frequency-peaked BL Lac (HBL) objects, 1ES 1218
+
304 and H 1426
+
428, with the Solar Tower Atmospheric ...Cherenkov Effect Experiment (STACEE). Both sources are very-high-energy gamma-ray emitters above 100
GeV, detected using ground-based Cherenkov telescopes. STACEE observations of 1ES 1218
+
304 and H 1426
+
428 did not produce detections; we present 99% CL flux upper limits for both sources, assuming spectral indices measured mostly at higher energies.
Active galactic nuclei, hosting supermassive black holes and launching relativistic jets, are the most numerous objects on the gamma-ray sky. At the other end of the mass scale, phenomena related to ...stellar mass black holes, in particular gamma-ray bursts and microquasars, are also seen on the gamma-ray sky. While all of them are thought to launch relativistic jets, the diversity even within each of these classes is enormous. In this review, I will discuss recent very high energy gamma-ray results that underline both the similarity of the black hole systems, as well as their diversity.
Very high-energy gamma rays from gamma-ray bursts Chadwick, Paula M
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
05/2007, Letnik:
365, Številka:
1854
Journal Article
Recenzirano
Very high-energy (VHE) gamma-ray astronomy has undergone a transformation in the last few years, with telescopes of unprecedented sensitivity having greatly expanded the source catalogue. Such ...progress makes the detection of a gamma-ray burst at the highest energies much more likely than previously. This paper describes the facilities currently operating and their chances for detecting gamma-ray bursts, and reviews predictions for VHE gamma-ray emission from gamma-ray bursts. Results to date are summarized.
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