(Abridged) Very high-energy (VHE, \(E>100\) GeV) observations of the blazar Mrk 501 with MAGIC in 2014 provided evidence for an unusual narrow spectral feature at about 3 TeV during an extreme X-ray ...flaring activity. The one-zone synchrotron-self Compton scenario, widely used in blazar broadband spectral modeling, fails to explain the narrow TeV component. Motivated by this rare observation, we propose an alternative model for the production of narrow features in the VHE spectra of flaring blazars. These spectral features may result from the decay of neutral pions (\(\pi^0\) bumps) that are in turn produced via interactions of protons (of tens of TeV energy) with energetic photons, whose density increases during hard X-ray flares. We explored the conditions needed for the emergence of narrow \(\pi^0\) bumps in VHE blazar spectra during X-ray flares reaching synchrotron energies \(\sim 100\) keV using time-dependent radiative transfer calculations. We focused on high-synchrotron peaked (HSP) blazars, which comprise the majority of VHE-detected extragalactic sources. We find that synchrotron-dominated flares with peak energies \(\gtrsim100\) keV can be ideal periods for the search of \(\pi^0\) bumps in the VHE spectra of HSP blazars. The flaring region is optically thin to photopion production, its energy content is dominated by the relativistic proton population, and the inferred jet power is highly super-Eddington. Application of the model to the spectral energy distribution of Mrk 501 on MJD 56857.98 shows that the VHE spectrum of the flare is described well by the sum of a synchrotron self-Compton (SSC) component and a distinct \(\pi^0\) bump centered at 3 TeV. Spectral fitting of simulated SSC+\(\pi^0\) spectra for the Cherenkov Telescope Array (CTA) show that a \(\pi^0\) bump could be detected at a 5\(\sigma\) significance level with a 30-min exposure.
The authors present the discovery of very high energy (VHE) ...-ray emission from the BL Lac object 1ES 1215+303 by the MAGIC telescopes and simultaneous multi-wavelength data in a broad energy range ...from radio to ...-rays. They study the VHE ...-ray emission from 1ES 1215+303 and its relation to the emissions in other wavelengths. Triggered by an optical outburst, MAGIC observed the source in 2011 January-February for 20.3 h. The target was monitored in the optical R-band by the KVA telescope that also performed optical polarization measurements. The MAGIC observations of 1ES 1215+303 carried out in 2011 January-February resulted in the first detection of the source at VHE with a statistical significance of 9.4 sigma . Simultaneously, the source was observed in a high optical and X-ray state. In 2010 the source was observed in a lower state in optical, X-ray, and VHE, while the GeV ...-ray flux and the radio flux were comparable in 2010 and 2011. (ProQuest: ... denotes formulae/symbols omitted.)
The high frequency peaked BL Lac PKS 2155-304 with a redshift of z = 0.116 was discovered in 1997 in the very high energy ...-ray range by the University of Durham Mark VI ...-ray Cherenkov telescope ...in Australia with a flux corresponding to 20% of the Crab Nebula flux. It was later observed and detected with high significance by the southern Cherenkov observatory HESS establishing this source as the best studied southern TeV blazar. The authors studied the behavior of the source after its extraordinary flare. Furthermore, they developed an analysis method in order to analyze these data taken under large zenith angles. With Their observations they increased the duty cycle of the source extending the light curve derived by HESS after the outburst. Finally, the authors find night-by-night variability with a maximal amplitude of a factor three to four and an intranight variability in one of the nights MJD 53 945 with a similar amplitude. (ProQuest: ... denotes formulae/symbols omitted.)
The W51 complex hosts the supernova remnant W51C which is known to interact with the molecular clouds in the star forming region W51B. In addition, a possible pulsar wind nebula CXO J192318.5+140305 ...was found likely associated with the supernova remnant. Gamma-ray emission from this region was discovered by Fermi/LAT (between 0.2 and 50 GeV) and H.E.S.S. (>1 TeV). The aim is to determine the morphology of the very-high-energy gamma-ray emission of W51 and measure its spectral properties. The researches detect an extended emission of very-high-energy gamma rays, with a significance of 11 standard deviations. They extend the spectrum from the highest Fermi/LAT energies to ...5 TeV and find that it follows a single power law with an index of 2.58 ... 0.07stat ... 0.22syst. The main part of the emission coincides with the shocked cloud region, while we find a feature extending towards the pulsar wind nebula. (ProQuest: ... denotes formulae/symbols omitted.)
The blazar Mrk 501 was observed at energies above 0.10 TeV with the MAGIC Telescope from 2005 May through July. The high sensitivity of the instrument enabled the determination of the flux and ...spectrum of the source on a night-by-night basis. Throughout our observational campaign, the flux from Mrk 501 was found to vary by an order of magnitude. Intranight flux variability with flux-doubling times down to 2 minutes was observed during the two most active nights, namely, June 30 and July 9. These are the fastest flux variations ever observed in Mrk 501. The similar to 20 minute long flare of July 9 showed an Indication of a 4 plus or minus 1 minute time delay between the peaks of F(<0.25 TeV) and F(>1.2 TeV), which may indicate a progressive acceleration of electrons in the emitting plasma blob. The flux variability was quantified for several energy ranges and found to Increase with the energy of the Y-ray photons. The spectra hardened significantly with Increasing flux, and during the two most active nights, a spectral peak was clearly detected at 0.43 plus or minus 0.06 and 0.25 plus or minus 0.07 TeV, respectively, for June 30 and July 9. There is no evidence of such a spectral feature for the other nights at energies down to 0.10 TeV, thus suggesting that the spectral peak is correlated with the source luminosity. These observed characteristics could be accommodated in a synchrotron self-Compton framework in which the increase in Y-ray flux is produced By a freshly injected (high energy) electron population.
In the first months of 2001 the AGN Mkn 421 showed highly variable, strong TeV activity at flux levels frequently exceeding 1 Crab. Here we present the light curve and energy spectrum of Mkn 421 as ...measured with the HEGRA stand alone telescope CT1. Around 30% of the data were taken under moonlight conditions. The spectrum shows a significant exponential energy cutoff at around 3.4 TeV. The results from the dark night- and the moon data are in excellent agreement with each other. A significant spectral shape variation depending on the flux level has been found. The TeV light curve is also found to be highly correlated with the X-ray light curve of the RXTE / ASM satellite, showing no significant time lag larger than 0.2 d. The derived correlation coefficient of 0.83 corresponds to a $5.2~\sigma$ significance.
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