Here, the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes observed S2 0109+22 in 2015 July during its flaring activity in high-energy gamma-rays observed by Fermi-Large Area ...Telescope. We analyse the MAGIC data to characterize the very high energy (VHE) gamma-ray emission of S2 0109+22, which belongs to the subclass of intermediate synchrotron peak (ISP) BL Lacertae (BL Lac) objects. We study the multifrequency emission in order to investigate the source classification. Finally, we compare the source long-term behaviour to other VHE gamma-ray emitting (TeV) blazars. We performed a temporal and spectral analysis of the data centred around the MAGIC interval of observation (MJD 57225–57231). Long-term radio and optical data have also been investigated using the discrete correlation function. The redshift of the source is estimated through optical host-galaxy imaging and also using the amount of VHE gamma-ray absorption. The quasi-simultaneous multifrequency spectral energy distribution (SED) is modelled with the conventional one-zone synchrotron self-Compton (SSC) model. MAGIC observations resulted in the detection of the source at a significance level of 5.3σ. The VHE gamma-ray emission of S2 0109+22 is variable on a daily time scale. VHE gamma-ray luminosity of the source is lower than the average of TeV BL Lacs. The optical polarization and long-term optical/radio behaviour of the source are different from the general population of TeV blazars. All these findings agree with the classification of the source as an ISP BL Lac object. As a result, we estimate the source redshift as z = 0.36 ± 0.07. The SSC parameters describing the SED are rather typical for blazars.
A 17-m-diameter air Cherenkov telescope, dubbed MAGIC, for ground-based gamma-ray astronomy above 30 GeV is under construction on the Canary Island of La Palma. The 577-pixel photomultiplier camera ...requires precise and regular calibration over a large dynamic range. A system for the optical calibration consisting of a number of very fast and powerful light emitting diode light pulsers is presented. We intend to calibrate each individual pixel up to 2000-3000 photoelectrons with different wavelengths, e.g. 370, 460, and 520 nm. We aim to achieve an absolute calibration at these three wavelengths by comparing the signal of the pixels with the one of specially prepared and calibrated photomultipliers and, at a later stage, hybrid photon detectors operated in single photon counting mode and with the use of well-calibrated attenuation filters ("blind pixels"). The light flux of the pulser is cross calibrated by a 1 cm/sup 2/ PIN diode (Hamamatsu), read out via a charge sensitive preamplifier. The PIN diode is calibrated with 60-keV gammas (from an Am 241 source) producing a precise signal of 16 570 electron-hole pairs. In addition, there will be a computer adjustable continuous light source to simulate and calibrate the response of the PMTs in the camera to the moon and the light of the night sky. This will also help to handle starlight in the field of view of the camera during analysis. Special attention is paid toward building a robust field usable device complying with IP 65 standards (sealed against heavy jet spray and dust).
A study of the new hemispherical 6-dynodes PMT from electron tubes Ostankov, A.; Paneque, D.; Lorenz, E. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2000, Letnik:
442, Številka:
1-3
Journal Article
Recenzirano
The main electro-optical properties of the new fast and low-gain hemispherical PMT from Electron Tubes Ltd. have been studied. This PMT is considered as photosensor for the camera of the 17m diameter ...air Cherenkov telescope MAGIC to be installed in two years at Canary Island La Palma. The dependence of the single-electron resolution and afterpulse rates as well as linearity on the interdynode voltages have been studied in detail.
We report the first hard X-ray observations with NuSTAR of the BL Lac-type blazar PKS 2155-304, augmented with soft X-ray data from XMM-Newton and γ-ray data from the Fermi Large Area Telescope, ...obtained in 2013 April when the source was in a very low flux state. A joint NuSTAR and XMM spectrum, covering the energy range 0.5–60 keV, is best described by a model consisting of a log-parabola component with curvature β=0.3{sub −0.1}{sup +0.2} and a (local) photon index 3.04 ± 0.15 at photon energy of 2 keV, and a hard power-law tail with photon index 2.2 ± 0.4. The hard X-ray tail can be smoothly joined to the quasi-simultaneous γ-ray spectrum by a synchrotron self-Compton component produced by an electron distribution with index p = 2.2. Assuming that the power-law electron distribution extends down to γ {sub min} = 1 and that there is one proton per electron, an unrealistically high total jet power of L {sub p} ∼ 10{sup 47} erg s{sup −1} is inferred. This can be reduced by two orders of magnitude either by considering a significant presence of electron–positron pairs with lepton-to-proton ratio n{sub e+e−}/n{sub p}∼30, or by introducing an additional, low-energy break in the electron energy distribution at the electron Lorentz factor γ {sub br1} ∼ 100. In either case, the jet composition is expected to be strongly matter-dominated.
The first statistically significant detection of the cosmic {gamma}-ray horizon (CGRH) that is independent of any extragalactic background light (EBL) model is presented. The CGRH is a fundamental ...quantity in cosmology. It gives an estimate of the opacity of the universe to very high energy (VHE) {gamma}-ray photons due to photon-photon pair production with the EBL. The only estimations of the CGRH to date are predictions from EBL models and lower limits from {gamma}-ray observations of cosmological blazars and {gamma}-ray bursts. Here, we present homogeneous synchrotron/synchrotron self-Compton (SSC) models of the spectral energy distributions of 15 blazars based on (almost) simultaneous observations from radio up to the highest energy {gamma}-rays taken with the Fermi satellite. These synchrotron/SSC models predict the unattenuated VHE fluxes, which are compared with the observations by imaging atmospheric Cherenkov telescopes. This comparison provides an estimate of the optical depth of the EBL, which allows us a derivation of the CGRH through a maximum likelihood analysis that is EBL-model independent. We find that the observed CGRH is compatible with the current knowledge of the EBL.
We present coordinated multiwavelength observations of the bright, nearby BL Lacertae object Markarian 421 (Mrk 421) taken in 2013 January-March, involving GASP-WEBT, Swift, NuSTAR, Fermi-LAT, MAGIC, ...VERITAS, and other collaborations and instruments, providing data from radio to very high energy„ (VHE) gamma-ray bands. NuSTAR yielded previously unattainable sensitivity in the 3-79 kiloelectronvolt range, revealing that the spectrum softens when the source is dimmer until the X-ray spectral shape saturates into a steep Gamma approximating 3 power law, with no evidence for an exponential cutoff or additional hard components up to 80 kiloelectronvolts. For the first time, we observed both the synchrotron and the inverse-Compton peaks of the spectral energy distribution (SED) simultaneously shifted to frequencies below the typical quiescent state by an order of magnitude. The fractional variability as a function of photon energy shows a double-bump structure that relates to the two bumps of the broadband SED. In each bump, the variability increases with energy, which, in the framework of the synchrotron self-Compton model, implies that the electrons with higher energies are more variable. The measured multi band variability, the significant X-ray-to-VHE correlation down to some of the lowest fluxes ever observed in both bands, the lack of correlation between optical/UV and X-ray flux, the low degree of polarization and its significant (random) variations, the short estimated electron cooling time, and the significantly longer variability timescale observed in the NuSTAR light curves point toward in situ electron acceleration and suggest that there are multiple compact regions contributing to the broadband emission of Mrk 421 during low-activity states.
Ultrafast Flash amplitude-to-digital converters (FADCs) are still very expensive. Here we propose a multiplexing scheme allowing one in common trigger mode to read out multiple signal sources by ...using a single FADC channel. Usual coaxial cables can be used in the multiplexer as analog signal delay elements. The limited bandwidth of the coaxial cable, depending on its type and length will set an upper limit to the number of multiplexed channels. Better bandwidth and the correspondingly higher number of multiplexed channels one can obtain when using the technique of transmission of analog signals via optical fibers. Low-cost vertical cavity surface emitting laser (VCSEL) diodes can be used as converters of fast electrical signals into near infrared light. Multiplexing can be an economically priced solution when one needs ultrafast digitization of hundreds of fast signal channels.
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