DPG Tagung, March 2003Nadia Tonello, MPI für Physik (Werner- Heisenberg-Institut), München 1 Observations of 1ES1959+650 with the HEGRA CT1 Cherenkov Telescope

DPG Tagung, March 2003 Nadia Tonello, MPI für Physik (Werner-Heisenberg-Institut), München

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Observations of 1ES1959+650 with the HEGRA CT1 Cherenkov Telescope

(2000, 2001, 2002)

Nadia Tonello and Daniel Kranich, Max-Planck-Institut für Physik for the HEGRA Collaboration


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The Active Galactic Nucleus 1ES1959+650

• Discovered in 1993 by comparing X-ray/radio/optical fluxes of objects in the Einstein IPC Slew Survey.

• First emission detected in 1998 by the Seven Telescope Array in Utah (Nishiyama et al., OG.2.1.21).

• Not seen by EGRET.• Studied in 2000-2001 by the HEGRA System of Telescopes: weak signal

seen (5.4 8% Crab).• Short flare seen by the VERITAS collaboration in spring 2002 (IAU Circ.

7903).

• Observed with HEGRA CT1 Telescope (2000, 2001, 2002).

z 0.047 (= 718·106 ly)

RA 19h59m59.8s (2000)

Dec +65d08´54 (2000)


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Physics Motivation•Study the physics processes in AGNs, responsible for the production of high energy gamma rays

• Measure energy spectrum of gamma rays• Study time variability of source emission• Multi-wavelength (radio, optical, X-ray) studies

•Study the absorption by the Extragalactic Background Light

•Cut-off of energy spectrum•comparison with AGNs at different distances

Mkn421 (z = 0.031), Mkn501 (z = 0.034)


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The HEGRA CT1 Telescope

ORM, La Palma (Canary Islands)

Mirror area 10.3 m2

Camera 127 pixels

FOV ~3°Ø

threshold 750 GeV(small ZA)

sensitivity on CRAB

€

3.3σ t[h ]


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Observation statistics

year 2000 2001 2002

No moon (nom) 58 h 86 h 176 h

With moon (reduced hv)

hv00 -- 24 h 8.1 h

hv04 -- 12 h 16.1 h

hv08 -- 8 h 6.1 h

hv12 -- 7 h 2.9 h

2002 data: 180h preliminary analysis

Zenith angle range: between 36.4 ° and 54.2 °Data needed correction for slight mispointing (~0.1º). Correction determined from a 2d-plot, higher probability to have the source.


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Analysis method gamma/hadron

separation using dynamical cuts

(determined from real on and off data ):

DIST(SIZE, )WIDTH(SIZE, DIST, )LENGTH(SIZE, DIST, )

N of events before cuts: 1 661 840N of events after cuts: 7565

Center of the camera


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OFF data

ON data (2002)

signal region

Alpha distribution

• Peaked at 0 deg for point like sources

• Flat distribution expected for cosmic ray background

• Estimation of the excesses: Gaussian fit in the signal region.

• Estimation of the background: fit the ON data with a pol.2nd order between 20 and 80 deg, extended into the signal region.


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ON data (2002)

signal region

backgroundfit region

Alpha distribution

Significance for ALPHA≤13.1º

11.1

Excesses: 664 ± 40 Background: 1672 ± 37


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2000 and 2001 light curves

Source at low state.

Signal: not significant.

Average estimated flux:~ 6 % Crab

average flux6% Crab

average flux5% Crab

HEGRA CT1


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TeV and X-ray emission, 2002

HEGRA CT1En. range 1- 10 TeV

All-Sky Mon.En.range:1.5-12 keV

May July


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TeV and X-ray emission, 2002

HEGRA CT1En. range 1- 10 TeV

All-Sky Mon.En.range:1.5-12 keV

May July


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Flares of 2002

Maximum activity: CRAB flux (above 1 TeV) reached in May.In July a less strong flare has been seen.

combining nom and hv00 data


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Spectrum preliminary resultof all the data taken in 2002

(151 h, max ZA: 45°)

Fitted with a power low function

= 3.49 ± 0.19/d.o.f. = 9.1/6


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Spectrum preliminary resultof all the data taken in 2002

(151 h, max ZA: 45°)

Fitted with a power low function with a fixed cutoff at Ec = 2.4 TeV

= 2.54 ± 0.21/d.o.f. = 7.1/6

Mkn421 z = 0.031 2.41 ± 0.10 Ec3.24±0.50

Mkn501 z = 0.034 2.03 ± 0.19 Ec 6.12 ±1.31

1ES1959 z = 0.048 1.5 (fixed) Ec 2.4 ± 0.4HEGRA System results for the source at high state


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Conclusions

• CT1 observed 1ES1959+650 in 2000 and 2001 at a low flux level (no significant signal).

• In 2002 two periods of increased flux have been seen (0.5 -1 times the Crab flux above 1 TeV).

• The preliminary results of the analysis reveal a spectrum compatible with a power law.

• Further analysis will be done: optimization for weak source at high zenith angles.

Documents

DPG Tagung, March 2003Nadia Tonello, MPI für Physik (Werner- Heisenberg-Institut), München 1 Observations of 1ES1959+650 with the HEGRA CT1 Cherenkov Telescope