MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes located in the Canary island of La Palma, Spain. During summer 2011 and 2012 it underwent a series of upgrades, involving the ...exchange of the MAGIC-I camera and its trigger system, as well as the upgrade of the readout system of both telescopes. We use observations of the Crab Nebula taken at low and medium zenith angles to assess the key performance parameters of the MAGIC stereo system. For low zenith angle observations, the standard trigger threshold of the MAGIC telescopes is ∼ 50GeV. The integral sensitivity for point-like sources with Crab Nebula-like spectrum above 220GeV is (0.66 ± 0.03)% of Crab Nebula flux in 50h of observations. The angular resolution, defined as the σ of a 2-dimensional Gaussian distribution, at those energies is ≲ 0.07°, while the energy resolution is 16%. We also re-evaluate the effect of the systematic uncertainty on the data taken with the MAGIC telescopes after the upgrade. We estimate that the systematic uncertainties can be divided in the following components: < 15% in energy scale, 11%–18% in flux normalization and ± 0.15 for the energy spectrum power-law slope.
We present time-resolved broad-band observations of the quasar 3C 279 obtained from multi-wavelength campaigns conducted during the first two years of the Fermi Gamma-ray Space Telescope mission. ...While investigating the previously reported gamma-ray/optical flare accompanied by a change in optical polarization, we found that the optical emission appears delayed with respect to the gamma-ray emission by about 10 days. X-ray observations reveal a pair of `isolated' flares separated by ~90 days, with only weak gamma-ray/optical counterparts. The spectral structure measured by Spitzer reveals a synchrotron component peaking in the mid-infrared band with a sharp break at the far-infrared band during the gamma-ray flare, while the peak appears in the mm/sub-mm band in the low state. Selected spectral energy distributions are fitted with leptonic models including Comptonization of external radiation produced in a dusty torus or the broad-line region. Adopting the interpretation of the polarization swing involving propagation of the emitting region along a curved trajectory, we can explain the evolution of the broad-band spectra during the gamma-ray flaring event by a shift of its location from ~ 1 pc to ~ 4 pc from the central black hole. On the other hand, if the gamma-ray flare is generated instead at sub-pc distance from the central black hole, the far-infrared break can be explained by synchrotron self-absorption. We also model the low spectral state, dominated by the mm/sub-mm peaking synchrotron component, and suggest that the corresponding inverse-Compton component explains the steady X-ray emission.
Precursor flares in OJ 287 Pihajoki, P; Valtonen, M; Zola, S ...
arXiv.org,
12/2012
Paper, Journal Article
Odprti dostop
We have studied three most recent precursor flares in the light curve of the blazar OJ 287 while invoking the presence of a precessing binary black hole in the system to explain the nature of these ...flares. Precursor flare timings from the historical light curves are compared with theoretical predictions from our model that incorporate effects of an accretion disk and post-Newtonian description for the binary black hole orbit. We find that the precursor flares coincide with the secondary black hole descending towards the accretion disk of the primary black hole from the observed side, with a mean z-component of approximately z_c = 4000 AU. We use this model of precursor flares to predict that precursor flare of similar nature should happen around 2020.96 before the next major outburst in 2022.
The flare behavior of OJ 287 during the years 1983 and 1984 is studied on the basis of all the available data in the different wavebands from these years. A strong correlation between the flux and ...the spectral index is found in the optical wavebands. At the same time there is weak evidence for a 9.3 days periodicity in the same waveband. Time lags of the flares and sharp drops are studied between different wavebands. The sharp events seem to be simultaneous in the region ultraviolet (0.25 microns)-infrared (25 micron) but between these and millimeter wavelengths there seem to be a timelag of 40-60 days so that the short wavelength variations precede the radio ones. At longer wavelengths (greater than 3 cm) the variations are much slower and it is very difficult to find the exact delay times. (Author)
Photopolarimetry of BL Lac SILLANPAÄ, A; TAKALO, L. O; NILSSON, K ...
Astrophysics and space science,
08/1993, Letnik:
206, Številka:
1
Journal Article
Recenzirano
This paper presents results of our monitoring of BL Lac at the 2.56 m Nordic Optical Telescope in La Palma and at the 0.91 m telescope at National Astronomical Observatory in Dodaira, Japan. On La ...Palma we used a UBVRI-photopolarimeter which gives truly simultaneous observations in all five color bands. At Dodaira we used a photopolarimeter which gives, simultaneously, photometry at B, V and R-bands and polarimetry at V-band. We have observations of BL Lac during flare behavior, and, during these times, we have observed a clear rotation of the polarization position angle. During these flares the polarization level has also been strongly variable, and the object has lost its preferred direction of the polarization position angle. The reason for this behavior still remains unclear, but there are two possible explanations: shocks in the helical magnetic field in the jet pointing nearly towards us or polarized synchrotron flares rotating within the accretion disk (seen nearly face on) of the supermassive central black hole.
We perform simulations for future Cherenkov Telescope Array (CTA) observations of RX J1713.7−3946, a young supernova remnant (SNR) and one of the brightest sources ever discovered in very high energy ...(VHE) gamma rays. Special attention is paid to exploring possible spatial (anti)correlations of gamma rays with emission at other wavelengths, in particular X-rays and CO/H i emission. We present a series of simulated images of RX J1713.7−3946 for CTA based on a set of observationally motivated models for the gamma-ray emission. In these models, VHE gamma rays produced by high-energy electrons are assumed to trace the nonthermal X-ray emission observed by XMM-Newton, whereas those originating from relativistic protons delineate the local gas distributions. The local atomic and molecular gas distributions are deduced by the NANTEN team from CO and H i observations. Our primary goal is to show how one can distinguish the emission mechanism(s) of the gamma rays (i.e., hadronic versus leptonic, or a mixture of the two) through information provided by their spatial distribution, spectra, and time variation. This work is the first attempt to quantitatively evaluate the capabilities of CTA to achieve various proposed scientific goals by observing this important cosmic particle accelerator.
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