friday, april 23, 2004university udine, italy razmick mirzoyan mpi munich where do we stay after...

Friday, April 23, 2004 University Udine, Italy

Razmick MirzoyanMPI Munich

Where do we stay after having seen the first signals from Crab and Mrk-421 ?

how should we proceed further ?


Recent Successful Detections

• Due to the strong efforts of most people attending now this working meeting we have succeeded to measure strong signals with MAGIC from Crab Nebula and from Mrk-421! Many thanks to all of you!

• Now we shall start to understand the performance of our instrument.


Questions which we shall ask ourselves :

• What were the thresholds of recent detections of Crab and Mrk What -421 ?

• What about the agreement between the data and the Monte Carlo ?

• Why could we see signal/s for showers of size above 3000 ADC counts (or photons) and no signal for lower lower energies ?


More questions:

• For example, what is the REAL Sensitivity of MAGIC for Crab Nebula above the threshold of 3000 ADC counts ?

• Can we improve that sensitivity and, if the answer is yes, then – how – by how much ?


The situation with competitors• Recently during the annual meeting of the German

Physical Society (DPG) in Mainz our competitors from HESS have shown impressive results. They have shown a sensitivity to Crab of:

26.5 /hour ½

measured with 3 telescopes in the zenith angle range ~ 45°- 50°

Obviously for lower zenith angle range their sensitivity will go and also the 4th telescope will slightly their sensitivity.


The situation with competitors

• There is a heavy competition and sometime soon everybody will try to understand the situation with the sensitivites and compare the performances of different instruments.

• So already now we shall start to think about how and up to what level our current

7-9 /hour ½ from Crab can be boosted up ?


Short excursion into stereo and background determination

• From the past experience with the HEGRA system of telescopes one would conclude that by operating N telescopes one can enhance the significance of a measurement by N ½ times. That means that if we are going to compare MAGIC with one telescope of HESS above the same given energy then one should normalize the HESS result to the number of telescopes.


Wide field of view camera and determination of OFF

• A wide field of view camera has the advantages that – one can determine the OFF-data simultaneously

with the ON data; HEGRA has accumulated quite some experience on it and there are few publications (G. Rowell,...).

– One can measure extended sources or perform source search in a relatively large field of view.


The wide field of view camera can provide many

advantages like:

+ One can use the observation time only for ON measurements; gain in ON time > 2 X (no Off, no switching time between On and Off)

+ Sky brightness region is very similar

+ Weather conditions are identical

+ One can define many OFF regions and therefore provide much more OFF data compared to the source region; the significance of a measurement will go up. Let me dwell a bit on that. In the ‚classical‘ Li&Ma formula for the significance calculation for equal time measured On and Off one has:

offon

offon

NN

NN


Non can be presented as Nh

Noff can be presented as Nh

The Li&Ma formula can be re-written as

hh NNN

N

)(

Given M measurements of Nh are available the error on Nh = h² will be reduced by 1/M times. This means that under the condition of Nh

one may obtain a times higher upper limit2


Trying to understand

When trying to understand the results of our competitors one shall separate the two mentioned boosters :

• While x N ½ improvement is due to the multiple telescopes, the improvement is due to the wide field of view. The latter can be achieved also by a single telescope and has nothing to do with stereo.

• So for example: the 10-11 /hour ½ signal from Crab with a single HESS telescope will go up to – ~19 because of 3 telescopes (x 3 ½) and up to the– ~26 because of multiple Off measurements.

2


Now let us turn to MAGIC:• Our camera is not too large. But if we could keep the

known source position on ~ 0.4° from the camera centre then

• on the one hand

– We will lose collection area (~ 20 % ? M-C necessary)• and on the other hand

+ We will gain a factor slightly > 2 because we could save the Off runs and measure instead only in On mode.

+ We can obtain multiple Off‘s for better sensitivity+ We would deal with just one star-field (alternatively the Off

run position would have its own star-field pattern).So we may provide multiple Off‘s and 1.6 x more data.


What sensitivity should one expect from MAGIC for Size > 3000 ?

• If one would compare the sensitivity of MAGIC with HESS for a given fixed energy (sometime in future) I guess a single MAGIC will have somewhat better sensitivity than a single HESS because of– Larger light collection area, higher collected charge– Higher pixel resolution (0.16° Hess; 0.10° MAGIC)But as long as we will not be able to use the multiple

Off‘s the single MAGIC would provide less sensitivity than full HESS. The single MAGIC can further increase the sensitivity by lowering the threshold much below the energies accessable to HESS.


Next realistic measures for increased sensitivity with MAGIC:

• To improve the pointing of the telescope• To improve the analysis methods; use dynamical

cuts, ...• To lower the threshold: check and improve the

trigger, coincidence of low amplitude pulses– Mask the rotating bright stars in pixels either by

• Flexible pre-programmed trigger tables or by• Dynamic variation of the HV for pixels

• To construct & operate MAGIC-II and later on more, MAGIC-X

friday, april 23, 2004university udine, italy razmick mirzoyan mpi munich where do we stay after...

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