VHE g -ray observations of the AGN 1ES1959+650 with the HEGRA CT1 Cherenkov Telescope

VHE -ray observations of theAGN 1ES1959+650with the HEGRA CT1Cherenkov Telescope

Nadia TonelloMax Planck Institute for Physics (Werner-Heisenberg-

Institut),Munich, Germany

for the HEGRA Collaboration

28th ICRC, Tsukuba

•1ES1959+650 •CT1•Data, obs.time•ALPHA distr.•Light Curve•Spectrum•Summary

Overview

The AGN 1ES1959 +650

Nadia Tonello MPI for Physics, Munich

28th ICRC, Tsukuba

HEGRA CT1 observations of 1ES1959+650

1ES1959+650CT1Data, obs.timeALPHA distrib.Light curveEn. SpectrumSummary

Elliptical galaxyActive Galactic NucleusBL Lac objectz = 0.047RA =19h59m59.8sDec = +65d08'54''

1993: identified from the radio, optical and X-ray emissions(Einstein IPC Slew Survey) .

1998: First -ray emissionSeven Telescope Array in Utah (Nishiyama et al., 26th ICRC, OG.2.1)

2000: observations by the HEGRA Cherenkov Telescopes

2002: Short flare seen by the VERITAS collaboration(Dowdall et al., IAU Circ. 7903)

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HEGRA CT1 Cherenkov Telescope for -ray detection


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Camera

Reflecting surface

ORM, La Palma, .Canary Islands

10.3 m2 areaaluminum mirrors

127 pixels FOV 3° diam.

Energy threshold 750 GeV at small ZA

Sensitivity3.3 x

for a Crab-like source

28.75°N17.89°W2200 asl

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t h

Data and observation time


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2000 2001 2002Good dark nights, nom hv 58 h 86 h 174.2 hWeak moonlight no hv red. 24 h 8.1 hMoonlight 4%hv reduction 12 h 16.1 hMoonlight 8%hv reduction 8 h 6.1 hMoonlight 12%hv reduction 7 h 2.9 h

Dynamical cuts applied on the image parameter distributions of the showers: ZA, SIZE and DIST dependent

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ALPHA distribution


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MJD: 52412 - 52584ZA range: 36.4°- 54.2°obs.time: 174.2 hnom data

Cut in ALPHA= 13.1 degSignificance: 11.1

Excess: 691 ± 42off: 1826 ± 38

Comparison of the fit result with a normalized sample of off-data

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Light curve


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Periods of high activity: 20 May (MJD52414) 2 June(MJD52427)14-15 July (MJD52469-70)

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May June July Aug. Sept. Nov.

Correlation study


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HEGRA CT1 En.range 1 -10 TeVAll-Sky-mon. En.range 2 -12 keV

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Energy spectrum


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MJD: 52412 - 52584ZA range: 36.4°- 54.2° obs.time: 174.2 hnom data

/d.o.f. = 6.3 / 5f0 = (1.17± 0.27) 10 -11 cm -2 s-1 TeV-1

= 2.3 (fixed)E0 = (1.79 ± 0.31) TeV

Fit: power law function and exponential cut-off (solid line)

Fit: pure power law(dashed line)

/d.o.f. = 9.9 / 5f0 = (0.78± 0.13) 10 -11 cm -2 s-1 TeV-1

= 3.52 ± 0.18

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dF/dE = f0 (E/TeV) -

dF/dE = f0 (E/TeV) -e -(E/E0)

Summary and Conclusions


28th ICRC, Tsukuba8

We observed 1ES1959+650 in 2000, 2001 and 2002. Low flux recorded in 2000, 2001 (no significant signal in CT1).

In 2002, three periods of increased flux have been seen, one of them recorded during moonlight conditions.

No clear correlation between flares in the X-ray and -ray regions. Study in progress.

Spectrum compatible with a power law, well described also adding a cut-off. Due to lack of statistics, no decisive discrimination possible.



VHE g -ray observations of the AGN 1ES1959+650 with the HEGRA CT1 Cherenkov Telescope

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