Optical Astronomy with Cerenkov telescopes

E. Oña-Wilhelmi1,2, O.C. de Jager1, J. Cortina3, V. Fonseca2

1 NWU, Potchefstroom, South Africa.2 UCM, Madrid, Spain.3 IFAE, Barcelona, Spain.

Erice, July 10th, 2004

Erice, July 10th, 2004 2

Cerenkov telescopes

1. Huge reflectors, i.g. MAGIC has a 230 m2 mirror: ~3 times more light than a 10 m optical telescope.

2. Very fast light detectors: good for transients.

Advantages

Targets

Pulsar mv

Crab 17

PSR B0540-69 14

Vela 24

PSR B0656+14 25

Geminga 26

AGN mv

Mkn 421 14.0

Mkn 501 14.5

1ES 1959 12.0

1ES 1426 16.5

3C279 18.0

(ms time scale) (1 min-1 hour time scale)

Erice, July 10th, 2004 3

Cerenkov cameras

1. Digitization of pixel currents (PM).

2. Single Photo Counting (APD or HPD).

Erice, July 10th, 2004 4

The Optical Central PixelWhy using an optical central pixel?:Contemporary ephemeris for active pulsars

Monitoring of atmospheric conditions

Monitoring of transients (high variability of Active Galaxies)

Test the telescope data acquisition and analysis software

Light of the Night Sky Background

What to do in MAGIC?:

Test in HEGRA-CT1 to detect the Crab Optical Pulsation

HPD testing in progress

de Oña-Wilhelmi et al., astro-ph/0405088

Erice, July 10th, 2004 5

The HEGRA-CT1 Optical Central Pixel

Detection of the Crab optical pulsation:

- Cerenkov detectors:

Whipple (10 m reflector)

CELESTE (solar farm)

-HEGRA-CT1 (3.5 m diameter reflector)

- Future plan: MAGIC

Srinivisan et al. 1997

De Naurois et al. 2001

10 m2

127 pixels each one 0.25° FOV

Erice, July 10th, 2004 6

0.1°

0.25°

CT1 central pixel

The HEGRA-CT1 Optical Central Pixel

Pulsed Signal

LONS+Nebula

Erice, July 10th, 2004 7

• DAQ : PCI NI 6034 E card, 16 analogical inputs, 16 bits resolution

• High pass filter to reduce the background

R=2 M & C=100 pF -> 0.5 ms

The CT1 Central Pixel: PM base and data acquisition

Erice, July 10th, 2004 8

• Basic Transformations: Inertial Frame (SSB)

• Princeton monthly ephemeris: and derivates and T0

i(t) = (To) + (ti-To) + 1/2! d/dt (ti-To)2

• Periodicity search with statistical method (e.g. 2)

0 (15 Oct) 29.8 Hz

Data analysis

Erice, July 10th, 2004 9

30.9 Hz = 0

Crab light curve

Nov 8th 2002

Erice, July 10th, 2004 10

Nov 8th 2002

(Hz)

Crab optical signal in 2 hours

Erice, July 10th, 2004 11

Application: LONS around CrabCamera point run

LONSnebulapulsed

pulsed

RRR

Rp

Misspointing & PSF

-Tauri:

%69

),(

),(

0

2

0

0

2

0

ddrrG

ddrrGpixelr

1121210)4.06.4( srsmphdFI LONSLONS

Erice, July 10th, 2004 12

background

backgroundreds

2

Single Photon Count.:

Tx 57Npx

Log

(s)

CT1

MAGIC

MAGIC for single photon count. method

5

200s30s

Sensitivity of the method

Erice, July 10th, 2004 13

Conclusions

1. We detected the Crab Optical Pulsation in 200 s with a 3.5 m diameter telescope.

2. The detection allowed us to infer the LONS in the galactic anticenter: 2.5 times larger than previous measures done for an extragalactic zone.

3. Next steps: test the same procedure in MAGIC (DC currents)

use an Hybrid Photo Detector (HPD)