The CAT imaging telescope for very-high-energy gamma-ray astronomy

Barrau, A.; Bazer‐Bachi, R.; Beyer, E.; Cabot, H.; Cerutti, M.; Chounet, L.‐M.; Debiais, G.; Degrange, B.; Delchini, H.; Denance, J.P.; Descotes, G.; Dezalay, J. P.; Djannati‐Ataï, A.; Dumora, D.; Espigat, P.; Fabre, B.; Fleury, P.; Fontaine, G.; George, R.; Ghesquière, C.; Gilly, J.; Goret, P.; Gouiffès, C.; Gouillaud, J.C.; Grégory, C.; Grenier, I. A.; Iacoucci, L.; Kalt, L.; Bohec, S. Le; Malet, Isabelle; Meynadier, C.; Mols, J. P.; Freitas, P. Mora de; Morano, R.; Morinaud, Gilles; Münz, F.; Palatka, M.; Palfrey, T.; Paré, E.; Pons, Y.; Punch, M.; Québert, J.; Ragan, K.; Renault, C.; Rivoal, M.; Rob, L.; Schovánek, Petr; Smith, D. A.; Tabary, A.; Tavernet, J.‐P.; Toussenel, F.; Vrána, J.

doi:10.1016/s0168-9002(98)00749-9

Cited by 68 publications

(40 citation statements)

References 12 publications

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“…This effect can be clearly seen on Figure 3, in which the difference between the two panels is hardly perceptible. Note that in fact the level of the curve depends implicitly also on the value of modified power-law index of the spectrum ( Pian et al 1998) and by the CAT imaging atmospheric Cerenkov telescope ( Djannati-Ataï et al 1999;Barrau et al 1998). Regarding high-energy data points, filled gray circles are the ones observed with CAT, while open squares are unabsorbed ones, corrected from our estimation of the DIrB attenuation.…”

Section: Application To Mrk 501mentioning

confidence: 95%

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The Bulk Lorentz Factor Crisis of TeV Blazars: Evidence for an Inhomogeneous Pileup Energy Distribution?

Henri

Saugé

2006

ApJ

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There is growing evidence that the estimations of the beaming Doppler factor in TeV BL Lac objects based on the synchrotron self-Compton (SSC) models are in strong disagreement with those deduced from the unification models between blazars and radio galaxies. When corrected from extragalactic absorption by the diffuse infrared background (DIrB), the SSC one-zone models require a very high Lorentz factor (around 50) to avoid strong -absorption. However, the statistics on beamed versus unbeamed objects, as well as the luminosity contrast, favors a much lower Lorentz factor, on the order of 3. In this paper, we show that for the special case of Markarian 501, the need for a very high Lorentz factor is unavoidable for all one-zone models in which all photons are assumed to be produced at the same location at the same time. Models assuming a double structure with two different beaming patterns can partially solve the problem of luminosity contrast, but we point out that they are inconsistent with the statistics on the number of detected TeV sources. The only way to solve the issue is to consider inhomogeneous models, in which low-energy and high-energy photons are not produced at the same place, allowing for much smaller Lorentz factors. This approach implies that the jet is stratified, but also that the particle energy distribution is close to a monoenergetic one and that pair production is likely to be significant. The implications for relativistic jet physics and the particle acceleration mechanism are discussed.

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Section: Application To Mrk 501mentioning

confidence: 95%

“…We apply this calculation to the case of the Mrk 501 object from 1997 April 16 when the BeppoSAX satellite ( Pian et al 1998) and the CAT imaging atmospheric Cerenkov telescope ( Djannati-Ataï et al 1999;Barrau et al 1998) recorded simultaneous data (see Fig. 2).…”

Section: Application To Mrk 501mentioning

confidence: 99%

The Bulk Lorentz Factor Crisis of TeV Blazars: Evidence for an Inhomogeneous Pileup Energy Distribution?

Henri

Saugé

2006

ApJ

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“…Located on the site of the former solar plant at Thémis in the French Pyrénées (2 • East, 42 • North, altitude 1650 m above sea level), the CAT telescope (Barrau et al 1998) uses the Cherenkov imaging technique. Its 17.8 m 2 mirror collects the Cherenkov light emitted by the secondary particles produced during the development of atmospheric showers and forms their image in its focal plane.…”

Section: Telescope Characteristicsmentioning

confidence: 99%

Temporal and spectral gamma-ray properties of Mkn 421 above 250 GeV from CAT observations between 1996 and 2000

Piron

Djannati‐Ataï

Punch

et al. 2001

A&A

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140

117

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Abstract. The γ-ray emission above 250 GeV from the BL Lac object Markarian 421 was observed by the CAT Cherenkov imaging telescope between December, 1996, and June, 2000. In 1998, the source produced a series of small flares, making it the second extragalactic source detected by CAT. The time-averaged differential spectrum has been measured from 0.3 to 5 TeV, which is well fitted with a power law: dφ dE _ E −2.88±0.12 stat ±0.06 syst TeV. In 2000, the source showed an unprecedented activity, with variability time-scales as short as one hour, as for instance observed during the night between 4 and 5 February. The 2000 time-averaged spectrum measured is compatible with that of 1998, but some indication of a spectral curvature is found between 0.3 and 5 TeV. The possibility of TeV spectral hardening during flares is also discussed, and the results are compared to those obtained on the other TeV BL Lac, Markarian 501.

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“…The fine grain of its camera, combined with fast electronics, allows a relatively low γ-ray detection threshold energy of 250GeV (at Zenith) as well as an accurate analysis of the resulting images. The experiment is fully described elsewhere [3]. The analysis method is based on the fit of each individual shower image with theoretical mean γ-ray images coming from a semi-analytical model [7].…”

Section: Spectral Analysis Methodsmentioning

confidence: 99%

VHE γ-ray spectral properties of the blazars Mrk 501 and Mrk 421 from CAT observations in 1997 and 1998

Piron¹

2000

AIP Conference Proceedings

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The CAT imaging telescope for very-high-energy gamma-ray astronomy

Cited by 68 publications

References 12 publications

The Bulk Lorentz Factor Crisis of TeV Blazars: Evidence for an Inhomogeneous Pileup Energy Distribution?

The Bulk Lorentz Factor Crisis of TeV Blazars: Evidence for an Inhomogeneous Pileup Energy Distribution?

Temporal and spectral gamma-ray properties of Mkn 421 above 250 GeV from CAT observations between 1996 and 2000

VHE γ-ray spectral properties of the blazars Mrk 501 and Mrk 421 from CAT observations in 1997 and 1998

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