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Register a new userVHE Spectral Properties of Mrk 501 with the CAT telescope
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J.-P. Tavernet
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We report here observations of the active galactic nucleus Mrk 501, at energies above 250 GeV carried out with the CAT atmospheric imaging telescope from March 1997 to Autumn 1998. This source was in a high state of activity at several different wavelengths in 1997, and the observed flux at TeV energies has been seen to change by a factor of ~ 20 from from 1995 and 1996 fluxes. CAT observations also indicate a curved spectrum at TeV energies, and a correlation between the gamma-ray intensity and the spectral hardness. The temporal variability and the TeV spectral properties are examined.
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The Very High Energy (VHE) gamma-ray emission of the BL Lacertae objects Markarian 501 and Markarian 421 has been observed by the CAT Imaging Atmospheric Cherenkov Telescope in 1997 and 1998. The spectrum extraction method is presented, and the spectral properties of both sources are compared in different activity states. Theoretical implications for jet astrophysics are discussed.
The blazar Markarian 501 (Mrk 501) was observed above 100 GeV with the MAGIC Telescope during May, June and July 2005. The high sensitivity of the instrument made possible the detection of the source with high significance in each of the observing nights. During this observational campaign, the emitted gamma-ray flux from Mkn 501 was found to vary by one order of magnitude, and showed a high correlation with spectral changes. Intra-night flux variability was also observed, with flux-doubling times of ~2 minutes. The data showed a clear evidence of a spectral peak (in the nuFnu representation) during the nights when the gamma-ray activity was highest. The location of this spectral feature was found to be correlated with the emitted gamma-ray flux. In these proceedings we discuss some of the results of this unprecedented spectral and temporal analysis of Mrk 501 observations in the very high energy range.
Since 1996, the CAT experiment, operating at the THEMIS site (French Pyrenees), has been collecting Very High Energy (VHE) gamma-ray data from the Crab. The temporal analysis of photon arrival times folded with the pulsar parameters did not reveal any significant pulsation. The upper limit of a steady pulsed flux over the 102.7 hours of observation is 1.5 10^-12 cm^-2.s^-1, 3.0 10^-13 cm^-2.s^-1 and 5.4 10^-14 cm^-2.s^-1 above 250 GeV, 1 TeV and 5 TeV, respectively. These results put stringent constraints on the models of high energy pulsar electrodynamics.
ANTARES is the largest high-energy neutrino telescope in the Northern Hemisphere. This contribution presents the results of a search, based on the ANTARES data collected over 17 months between November 2014 and April 2016, for high energy neutrino emission in coincidence with TeV $gamma$-ray flares from Markarian 421 and Markarian 501, two bright BL Lac extragalactic sources highly variable in flux, detected by the HAWC observatory. The analysis is based on an unbinned likelihood-ratio maximization method. The $gamma$-ray lightcurves (LC) for each source were used to search for temporally correlated neutrinos, that would be produced in pp or p-$gamma$ interactions. The impact of different flare selection criteria on the discovery neutrino flux is discussed. Plausible neutrino spectra derived from the observed $gamma$-ray spectra in addition to generic spectra $E^{-2}$ and $E^{-2.5}$ are tested.
Observations at Very High Energies (VHE, E > 100 GeV) of the BL Lac object Mrk 501 taken with the High Energy Stereoscopic System (H.E.S.S.) in four distinct periods between 2004 and 2014 are presented, with focus on the 2012 and 2014 flaring states. The source is detected with high significance above $sim$ 2 TeV in $sim$ 13.1 h livetime. The observations comprise low flux states and strong flaring events, which in 2014 show a flux level comparable to the 1997 historical maximum. Such high flux states enable spectral variability and flux variability studies down to a timescale of four minutes in the 2-20 TeV energy range. During the 2014 flare, the source is clearly detected in each of these bins. The intrinsic spectrum is well described by a power law of index $Gamma=2.15pm0.06$ and does not show curvature in this energy range. Flux dependent spectral analyses show a clear harder-when-brighter behaviour. The high flux levels and the high sensitivity of H.E.S.S. allow studies in the unprecedented combination of short timescales and an energy coverage that extends significantly above 20 TeV. The high energies allow us to probe the effect of EBL absorption at low redshifts, jet physics and LIV. The multiwavelength context of these VHE observations is presented as well.
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