The MAGIC Telescope, now taking data with an energy threshold well below 100
GeV, will soon be able to take full advantage of the fast slewing capability of
its altazimuthal mount. Exploiting the link with the GCN network, the MAGIC
Telescope could be one of the first ground-based experiments able to see the
prompt emission of Gamma Ray Bursts in the few tens of GeV region.Comment: 4 pages, 1 figure (-> 3 subfigures), class file (cimento.cls)
  included. To appear in: "Gamma-Ray Bursts in the Afterglow Era: 4rd
  Workshop", Rome 200

.  Collaboration

D.  Bastieri

F.  Longo

L.  Peruzzo

M.  Garczarczyk

M.  Gaug

N.  Galante

S.  Mizobuchi

English

arXiv

D. Bastieri

N. Galante

M. Gaug

M. Garczarczyk

S. Mizobuchi

L. Peruzzo

. Collaboration

LONGO, FRANCESCO

Archivio istituzionale della ricerca - Università di Trieste

The MAGIC Telescope and the observation of Gamma Ray Bursts

The MAGIC Telescope, now taking data with an energy threshold well below 100 GeV, will soon be able to take full advantage of the fast slewing capability of its altazimuthal mount. Exploiting the link with the GCN network, the MAGIC Telescope could be one of the first ground-based experiments able to see the prompt emission of Gamma Ray Bursts in the few tens of GeV region

Bastieri, D.

Galante, N.

Gaug, M.

Garczarczyk, M.

Longo, F.

Mizobuchi, S.

Peruzzo, L.

Scientific Open-access Literature Archive and Repository

DOI 10.1393/ncc/i2005-10136-yIL NUOVO CIMENTO Vol. 28 C, N. 4-5 Luglio-Ottobre 2005The MAGIC Telescope and the observation ofGamma Ray Bursts(∗)D. Bastieri(1)(∗∗), N. Galante(2), M. Gaug(3), M. Garczarczyk(4)F. Longo(5), S. Mizobuchi(4)(6) and L. Peruzzo(1)for the MAGIC Collaboration(∗∗∗)(1) Universita` and INFN - Via Marzolo 8, 35131 Padova, Italy(2) Universita` di Siena and INFN - Via Buonarroti 2, 56127 Pisa, Italy(3) IFAE, Edifici Cn. Facultat Cie`ncies UAB - 08193 Bellaterra (Barcelona), Spain(4) Max Planck Institut fu¨r Physik - Fo¨hringer Ring 6, 80805 Mu¨nchen, Germany(5) Universita` and INFN - Via Valerio 2, 34100 Trieste, Italy(6) Ehime University 3 - Bunkyo-cho, Matsuyama 790-8577, Japan(ricevuto il 23 Maggio 2005; pubblicato online il 28 Ottobre 2005)Summary. — The MAGIC Telescope, now taking data with an energy thresholdwell below 100 GeV, will soon be able to take full advantage of the fast slewingcapability of its altazimuthal mount. Exploiting the link with the GCN network,the MAGIC Telescope could be one of the first ground-based experiments able tosee the prompt emission of Gamma Ray Bursts in the few tens of GeV region.PACS 95.55.Ka – X- and γ-ray telescopes and instrumentation.PACS 95.85.Pw – Astronomical observations: γ-ray.PACS 98.70.Rz – γ-ray sources; γ-ray bursts.PACS 01.30.Cc – Conference proceedings.1. – IntroductionThe MAGIC Collaboration started to build the Telescope since the beginning of 2001.The MAGIC Telescope entered the commissioning phase in October 2003 and had, sincethen, observed few different sources at different redshifts.The telescope is one of the so-called last generation Cherenkov telescopes and canexplore the electromagnetic spectrum starting well below ∼ 100 GeV.Besides MAGIC [1], built at 2200m a.s.l. in the island of La Palma, Canary Islands,there are three other Collaborations working with last generation Cherenkov telescopes:HESS [2] (Windhoek, Namibia), CANGAROO [3] (Woomera, Australia) and VERI-TAS [4] (Horseshoe Canyon, Arizona, USA). While these last three are actually an array(∗) Paper presented at the “4th Workshop on Gamma-Ray Burst in the Afterglow Era”, Rome,October 18-22, 2004.(∗∗) E-mail: bastieri@pd.infn.it (corresponding author)(∗∗∗) Updated collaborator list at http://magic.mppmu.mpg.de/collaboration/index.htmlc© Societa` Italiana di Fisica 711712 D. BASTIERI, N. GALANTE, M. GAUG, ETC.Fig. 1. – Data from 155-minutes of acquisition taken on April 22nd, 2004 with MAGIC pointingatMkn 421. The histogram of alpha for on- and off-source observations, are relative to differentbin in size: 800–1200 (left), 1200–2000 (middle) and more than 2000 photons (right).of telescopes (4 CANGAROO, 7 VERITAS and 4, at the beginning, also HESS), MAGICfavoured the construction of a single, although huge, telescope, featuring 241m2 of re-flecting surface instead of ∼ 100m2 as the other detectors do.Nevertheless, a second telescope, clone of the first one, with the same dimensions andimproven capabilities, is already foreseen for MAGIC and should be operating in 2007,by the time of the launch of the GLAST mission.The keystones of the single MAGIC are the huge reflecting area, capable to collecteven the few Cherenkov photons emitted by low energy gamma, and the trigger, ableto cope with the high rate of the Night Sky Background, filtering it and let the dataacquisition mostly deal with real atmospheric showers. In this way, MAGIC shouldreach the lowest energy threshold among the Cherenkov experiments.Additionally, the overall mechanical design of the telescope, based upon a carbon-fiberfiligree, allows the telescope to slew to a new position in less than 20 seconds, in orderto follow up the GRB since its early onset.For this reason, MAGIC is part of GCN, the GRB Coordinates Network [5].In this work, after a brief description of MAGIC first observations, we provide somequantitative predictions on GRB observation for MAGIC, but most of all we show thatMAGIC is working, and due to its low energy threshold and fast repositioning capabilitiescan be the ideal detector to follow the early development of GRB at high energies.2. – The MAGIC TelescopeMAGIC has been in a commissioning phase since October 2003. Beyond technicalruns, there was time also for some physics observations. Both kind of runs were necessaryto tune or improve the hardware of the detectors, and the first physics signals were readyin February 2004.The first sources observed were the Crab Nebula andMkn 421. Both of these sourcesare a sort of standard sources: the Crab has a steady flux that can be used to calibratedetectors, and Mkn 421, while not being steady, stays from time to time in a high statewith fluxes few times bigger than the Crab one.These two sources were observed in Winter 2003/2004 (the Crab Nebula) and duringSpring 2004 (Mkn 421) and both revealed signals well above the 5σ level.Special attention must be given to fig. 1. It represents the data collected on AprilTHE MAGIC TELESCOPE AND THE OBSERVATION OF GAMMA RAY BURSTS 71322nd, 2004 pointing at Mkn 421 that was in a high state. The so-called IACT (ImagingAtmospheric Cherenkov Technique) used by MAGIC, records for each event the direc-tions of the Cherenkov photons emitted during the shower development. The image isthen analysed using a well-established technique that exploits the so-called Hillas param-eters [6].Two Hillas parameters have a particular importance in the figure: alpha and size.Alpha is related to the actual direction of the primary particle that initiated the shower,thus an excess in alpha must be seen in the direction of a source. Size is the number ofphotons making up the image and is related to the energy of the primary particles (themore energetic is the particle, more photons appear in the image).The three figures show that the Mkn 421 flare was well detected by MAGIC atdifferent energies, and the excess seen in the first figure with size ranging from 800 to1200 photons is consistent with an energy well below 100GeV.3. – GRB observabilityHaving shown that MAGIC is effectively working, let us see what we expect fromGRBs. The main parameter influencing the GRB observability is the telescope duty-cycle [7]. The duty-cycle of the telescope was calculated as the fraction of sky areaaccessible to MAGIC per year, where, to be accessible, the following conditions must bemet:– the Sun must be below astronomical horizon or have a zenith angle > 108◦;– the minimum angular distance from the Moon must be 30◦;– the relative humidity of the air must be lower than 80%;– the wind speed must be lower than 10m/s.The calculation, using the weather data and ephemerides for year 2001, gives a valueslightly below 10%. This means that roughly 1/10 of all GRB alerts can be immediatelypursued.Once determined the fraction of GRB observable, it is possible to estimate how manyGRB can be actually observed, that is, if their significance is above 5σ. The number ofσ can be calculated using the Li-Ma formula:Nσ = Q(Ron −Roff)T√(Ron +Roff)T= QRγ√T√Ron +Roff,(1)where Q, the so-called quality factor, represents the efficiency of the analysis and is oforder unity at low energies, T is the actual acquisition time and the R’s represent therates. Each R takes into account the particle flux, Φ, and the detector sensitivity to theflux itself, expressed as the effective area of the telescope, Aeff(E, ϑ). For instance, wehave that the expected signal from the GRB is: Rγ =∫ΦGRB(E)Aγeff(E, ϑ)dE and thecosmic-ray background is: Roff =∫ΦCR(E, ϑ)ACReff (E, ϑ)dE.The effective area of a Cherenkov telescope is quite huge, reaching 105m2 around100GeV and dropping to 104m2 around 50GeV.The GRB flux is obtained extrapolating the power law spectrum found inside theBATSE catalogues, taking also into account the cosmological cutoff due to the absorptionof high-energy γ by the Metagalactic Radiation Field via γHEγMRF → e+e−.714 D. BASTIERI, N. GALANTE, M. GAUG, ETC.Of paramount importance for a good observation of GRBs is the delay between theGRB onset and the time when MAGIC can actually observe the GRB. This delay sumsup three different times:1. the time needed by the satellite to recognise that a GRB event may be going on;2. the time elapsing between the sending of the alert by the satellite, the broadcastvia GCN and the final acknowledgment by MAGIC (∼ 2 seconds);3. the slewing time needed by MAGIC to point to the GRB position (< 20 seconds).It can be calculated that reducing this total delay from 1 minute to 15 seconds in-creases of a factor 5 the number of observable GRBs.It should be noted also that the zenith angle, ϑ, enters the formulae for the rates. Thenumber of observable GRBs thus it is not obtained with a straightforward multiplicationof the duty-cycle (≈ 10%) times the number of GRBs expected to have a significanceNσ > 5, but it is better expressed with NGRB =∑ϑD(ϑ)η(ϑ) where D(ϑ) is the duty-cycle in a given bin of zenith angle, η(ϑ) is the number of GRBs (extrapolated fromBATSE catalogues) actually observable in a given bin of zenith angle and the sum isperformed over all zenith angle bins.Values of η(ϑ) range between 5 and 24, strongly depending upon the delays from theGRB onset to the actual observation of the GRB by MAGIC, and the final result is thatMAGIC should observe 0.5–2 GRBs per year.4. – ConclusionsThe results exposed in this work show that MAGIC is now operating and can be usedto follow the GRB events since its early onset. Observations with Cherenkov detectorsbelow 100GeV seem now attainable, even if the analysis of low-energy events is still achallenge and may require more work.∗ ∗ ∗The development and construction of the MAGIC Telescope was mainly supportedby the BMBF (Germany), CICYT (Spain), INFN and MURST (Italy). The authorswish to thank also the people from the Observatorio del Roque de Los Muchachos forthe excellent working conditions in La Palma.REFERENCES[1] Mart´ınez M. (MAGIC Coll.), in Proc. 28th ICRC, Japan 2003, pp. 2815-2818.http://www-rccn.icrr.u-tokyo.ac.jp/icrc2003/PROCEEDINGS/PDF/695.pdf[2] Hofmann W. (HESS Coll.), in Proc. 28th ICRC, Japan 2003, pp. 2811-2814. http://www-rccn.icrr.u-tokyo.ac.jp/icrc2003/PROCEEDINGS/PDF/694.pdf[3] Enomoto R. (CANGAROO Coll.), in Proc. 28th ICRC, Japan 2003, pp. 2807-2810.http://www-rccn.icrr.u-tokyo.ac.jp/icrc2003/PROCEEDINGS/PDF/693.pdf[4] Wakely S. P. (VERITAS Coll.), in Proc. 28th ICRC, Japan 2003, pp. 2803-2806.http://www-rccn.icrr.u-tokyo.ac.jp/icrc2003/PROCEEDINGS/PDF/692.pdf[5] See http://gcn.gsfc.nasa.gov/ and references therein.[6] Hillas A. M., in Proc. 19th ICRC, La Jolla, USA 1985, Vol. 3, pp. 445-448.[7] Galante N. (MAGIC Coll.), in Proc. 28th ICRC, Japan 2003, p. 2753-2756. http://www-rccn.icrr.u-tokyo.ac.jp/icrc2003/PROCEEDINGS/PDF/680.pdf.

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The MAGIC Telescope and the Observation of Gamma Ray Bursts

The MAGIC Telescope and the Observation of Gamma Ray Bursts

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