Recently the AGILE \(\gamma\)-ray telescope has reported the enhanced \(\gamma\)-ray emission above 100 MeV from the direction of the Crab Nebula during a period of a few days. This intriguing ...observation has been confirmed by the Fermi-LAT telescope. This emission does not show evidences of pulsations with the Crab pulsar. It seems that it originates at the shock region created as a result of the interaction of the pulsar wind with the nebula. We propose that such variable \(\gamma\)-ray emission originate in the region behind the shock when the electrons can be accelerated as a result of the reconnection of the magnetic field compressed by the decelerating pulsar wind. The natural consequence of such interpretation is the prediction that the Crab Nebula \(\gamma\)-ray spectrum produced by electrons as a result of the inverse Compton scattering of soft radiation to multi-TeV energies should also show synchronous variability on the time scales as observed at GeV energies by the AGILE and Fermi-LAT telescopes. We calculate how the end of the IC component of the Crab Nebula \(\gamma\)-ray spectrum should look like during the quiescent and the flare GeV \(\gamma\)-ray emission. We conclude that the variability of the multi-TeV \(\gamma\)-ray spectrum from the Crab Nebula might in principle be responsible for the differences between the spectral features reported by the HEGRA and HESS Collaborations at the multi-TeV energies.
We have studied the wisps to the northwest of the Crab pulsar as part of a multi-wavelength campaign in the visible and in X-rays. Optical observations were obtained using the Nordic Optical ...Telescope in La Palma and X-ray observations were made with the Chandra X-ray Observatory. The observing campaign took place from October 2010 until September 2012. About once per year we observe wisps forming and peeling off from (or near) the region commonly associated with the termination shock of the pulsar wind. We find that the exact locations of the northwestern wisps in the optical and in X-rays are similar but not coincident, with X-ray wisps preferentially located closer to the pulsar. This suggests that the optical and X-ray wisps are not produced by the same particle distribution. It is also interesting to note that the optical and radio wisps are also separated from each other (Bietenholz et al. 2004). Our measurements and their implications are interpreted in terms of a Doppler-boosted ring model that has its origin in MHD modeling. While the Doppler boosting factors inferred from the X-ray wisps are consistent with current MHD simulations of PWNe, the optical boosting factors are not, and typically exceed values from MHD simulations by about a factor of 4.
A&A 568, A109 (2014) It has been claimed that the nova-like cataclysmic variable (CV) AE Aquarii
(AE Aqr) is a very-high-energy (VHE, $E>$100 GeV) source both on observational
and theoretical ...grounds. We aim to search for VHE gamma-ray emission from AE
Aqr during different states of the source at several wavelengths to confirm or
rule out previous claims of detection of gamma-ray emission from this object.
We report on observations of AE Aqr performed by MAGIC. The source was observed
during 12 hours as part of a multiwavelength campaign carried out between May
and June 2012 covering the optical, X-ray, and gamma-ray ranges. Besides MAGIC,
the other facilities involved were the KVA, Skinakas, and Vidojevica telescopes
in the optical and Swift in X-rays. We calculated integral upper limits
coincident with different states of the source in the optical. We computed
upper limits to the pulsed emission limiting the signal region to 30% of the
phaseogram and we also searched for pulsed emission at different frequencies
applying the Rayleigh test. AE Aqr was not detected at VHE energies during the
multiwavelength campaign. We establish integral upper limits at the 95\%
confidence level for the steady emission assuming the differential flux
proportional to a power-law function d\phi/dE \propto E^{-Gamma}, with a
Crab-like photon spectral index of Gamma=2.6. The upper limit above 200 GeV is
6.4\times10^{-12} cm^{-2}s^{-1} and above 1 TeV is 7.4\times10^{-13}
cm^{-2}s^{-1}. We obtained an upper limit for the pulsed emission of
2.6\times10^{-12} cm^{-2}s^{-1} for energies above 200 GeV. Applying the
Rayleigh test for pulsed emission at different frequencies we did not find any
significant signal. Our results indicate that AE Aqr is not a VHE gamma-ray
emitter at the level of emission previously claimed. We have established the
most constraining upper limits for the VHE gamma-ray emission of AE Aqr.
JCAP 02 (2014) 008 We present the results of stereoscopic observations of the satellite galaxy
Segue 1 with the MAGIC Telescopes, carried out between 2011 and 2013. With
almost 160 hours of ...good-quality data, this is the deepest observational
campaign on any dwarf galaxy performed so far in the very high energy range of
the electromagnetic spectrum. We search this large data sample for signals of
dark matter particles in the mass range between 100 GeV and 20 TeV. For this we
use the full likelihood analysis method, which provides optimal sensitivity to
characteristic gamma-ray spectral features, like those expected from dark
matter annihilation or decay. In particular, we focus our search on gamma-rays
produced from different final state Standard Model particles, annihilation with
internal bremsstrahlung, monochromatic lines and box-shaped signals. Our
results represent the most stringent constraints to the annihilation
cross-section or decay lifetime obtained from observations of satellite
galaxies, for masses above few hundred GeV. In particular, our strongest limit
(95% confidence level) corresponds to a ~500 GeV dark matter particle
annihilating into tau+tau-, and is of order <sigma v> ~ 1.2x10^{-24} cm^3
s^{-1} - a factor ~40 above the <sigma v> thermal value.
It has been claimed that the nova-like cataclysmic variable (CV) AE Aquarii (AE Aqr) is a very-high-energy (VHE, \(E>\)100 GeV) source both on observational and theoretical grounds. We aim to search ...for VHE gamma-ray emission from AE Aqr during different states of the source at several wavelengths to confirm or rule out previous claims of detection of gamma-ray emission from this object. We report on observations of AE Aqr performed by MAGIC. The source was observed during 12 hours as part of a multiwavelength campaign carried out between May and June 2012 covering the optical, X-ray, and gamma-ray ranges. Besides MAGIC, the other facilities involved were the KVA, Skinakas, and Vidojevica telescopes in the optical and Swift in X-rays. We calculated integral upper limits coincident with different states of the source in the optical. We computed upper limits to the pulsed emission limiting the signal region to 30% of the phaseogram and we also searched for pulsed emission at different frequencies applying the Rayleigh test. AE Aqr was not detected at VHE energies during the multiwavelength campaign. We establish integral upper limits at the 95\% confidence level for the steady emission assuming the differential flux proportional to a power-law function d\phi/dE \propto E^{-Gamma}, with a Crab-like photon spectral index of Gamma=2.6. The upper limit above 200 GeV is 6.4\times10^{-12} cm^{-2}s^{-1} and above 1 TeV is 7.4\times10^{-13} cm^{-2}s^{-1}. We obtained an upper limit for the pulsed emission of 2.6\times10^{-12} cm^{-2}s^{-1} for energies above 200 GeV. Applying the Rayleigh test for pulsed emission at different frequencies we did not find any significant signal. Our results indicate that AE Aqr is not a VHE gamma-ray emitter at the level of emission previously claimed. We have established the most constraining upper limits for the VHE gamma-ray emission of AE Aqr.
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