Gamma Ray Burst observations with the MAGIC
Telesope and a proposal for further improvement
Diplomarbeit
zur Erlangung des akademishen Grades
Dipl. Ing. Phys. (FH)
vorgelegt von
Ralf Kosyra
Fahbereih 06 Physikalishe Tehnik der
Fahhohshule Münhen (Munih University of Applied Sienes)
Betreuer: Prof. Dr. Sotier
Zweitbetreuer: Prof. Dr. Wondrazek
17th May 2006
MAGICisa17m Cherenkov-Telesopefor ground-based Very HighEnergy(VHE) Gamma
Ray-Astronomy. One of MAGIC's tasks is to searh for the so alled "Gamma Ray-Bursts"
(GRB),whihareshort(hundred miliseondsup tohundred seonds) outburstsofgammarays
with very high uxes. As the loation of the outbursts are a priory unknown, the MAGIC
Telesope has to be positioned as fast as possible after alert signals from wide-angle satellite
detetors.
The urrent maximum slewing speed of the telesope is about 180
o
50s
, whih often is not
enough for eetively reording the diret signalfrom GRBs.
I presenthere a study fora newoptimization forthe aeleration,respetively deeleration
and veloity ofthe 63ton MAGICTelesope,toredueonsiderably the repositioningtime, as
wellas ananalysis of the safety limitsof fast movements.
1 Introdution 5
1.1 HighEnergyAstropartilePhysisand VeryHighEnergyGammaRayAstronomy 5
1.1.1 Cosmi -rays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.1.2 Detetors for -rays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2 Some information on the relevant Astrophysial Proesses 12 2.1 The Imaging Air-Cherenkov Tehnique . . . . . . . . . . . . . . . . . . . . . . . 12
2.1.1 Gamma-HadronSeparation . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.2 Mehanisms for CosmiGammaRay Prodution. . . . . . . . . . . . . . . . . . 16
2.2.1 Inverse Compton Sattering . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.2.2 Synhrotron SelfCompton Sattering . . . . . . . . . . . . . . . . . . . . 17
2.2.3 Bremsstrahlung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.4 0 -deay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3 Soures of Cosmi GammaRays . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.3.1 Ative GalatiNulei (AGN) . . . . . . . . . . . . . . . . . . . . . . . . 19
2.3.2 Miroquasars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.3.3 SupernovaRemnants(SNR) . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.3.4 Pulsars and Pulsar Nebulae . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.3.5 GammaRay Bursts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3 Gamma Ray Bursts (GRB) 23 3.1 Afterglow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.2 Detetors for GRBs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.2.3 HETE 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.2.4 INTEGRAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.3 Detetion of GRBs with MAGIC . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4 Denition of the Problem 32 4.1 Current Situation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5 The MAGIC Telesope 36 5.1 Dierent types of telesopemounts . . . . . . . . . . . . . . . . . . . . . . . . . 39
5.1.1 Equatorial mounts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
5.1.2 Alt-azimuth mounts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
5.2 Dynamial range of trakingveloity . . . . . . . . . . . . . . . . . . . . . . . . 40
5.3 Neessary azimuthal slewingrange . . . . . . . . . . . . . . . . . . . . . . . . . 41
5.4 The Azimuth Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.5 The Elevation Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
6 The Drive System 56 6.1 Components of the Drive System . . . . . . . . . . . . . . . . . . . . . . . . . . 56
6.1.1 The Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
6.1.2 The Drive Controllers(DKC) . . . . . . . . . . . . . . . . . . . . . . . . 67
6.1.3 Miroontrollers (MACS). . . . . . . . . . . . . . . . . . . . . . . . . . . 69
6.2 The Endswithes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
7 Drive Tests 74 7.1 Tests onAeleration and Deeleration . . . . . . . . . . . . . . . . . . . . . . . 76
7.2 Endswith tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
8 Outlook 82
APPENDIX 86
List of Abbreviations 93
List of Tables 97
Bibliography 98
Aknowledgments 99
Introdution
1.1 High Energy Astropartile Physis and Very High En-
ergy Gamma Ray Astronomy
High energy astropartile physis (formerly alled Cosmi Ray Physis) is sine a few deades
a rapidly expanding eld of fundamental physis researh. It ombines partile physis with
astronomy and inawidersense withCosmology. Itdeals withrelativistiproessesinour uni-
verse(also alledthe "relativistiuniverse"orinthe languageofastronomersthe"non-thermal
universe"). One ofthe branhes of astropartilephysisdeals withthe observation ofenergeti
photons, ommonly alled gamma-rays (shortut ). Gamma-rays are eletromagneti parti-
les 1
with an energy of at least a few hundred keV. Of partiular interest are gammas of at
least a few 10 9
eV (GeV). These gammas are so-alled messengers of ultrarelativisti partile
proesses in the universe, mostly inor near stellarenvironments. The so-alledVery-High En-
ergy(VHE) -Astronomydeals withenergies of10GeVup to100TeVand allows onetolearn
therefore about stellar proesses atextreme onditions.
I would like to mention that the rst studies of the universe outside optial astronomy
started inthe year1911. Firstexperimentswerearriedout by ViktorFranzHess, who disov-
eredtheexisteneofahargedradiationomingfromouterspae. Thisradiationwasoriginally
1
Intheeletromagnetispetrumoneusesommonlythenamewaveforlowenergyarriersandpartilefor
high energyeletromagneti arriers
Atthat timeitwas unlearwhyharged eletrometerswere losingtheir hargeovertime, even
if they were isolatedfromthe Earth. It wasthoughtthat this eet was ausedby ions, but it
was not known by what kind ofradiation these ions were generated.
One theory laimedthat this ionizingradiationwasomingfromradioativesubstanes inthe
Earth. In the years 1911 through 1913 Hess did measurements with eletrometersduring high
altitude balloon ights, and found out that the ionizing rate was at rst dereasing with in-
reasing height, asexpeted, and onrmed the originaltheory.
However, Hessfound that thedishargespeed, respetivelythe ionizingrate wasagaininreas-
ing with inreasing altitude. He interpreted this phenomenon as a onsequene of ionizing
radiationomingfromouter spae,while this radiationispartiallyshieldedlose togroundby
the Earth'satmosphere.
Histheorywasonrmedinthefollowingyearsandtheionizingpartileshavebeenidentiedas
seondary produts of interations between highlyenergeti partileswith the nulei of atoms
of the Earth's atmosphere.
Initially osmi rays were identied as harged nulei. At energies above 1 TeV
nuleus , the
CR are omposed of Protons (41%), Helium nulei (27%), Carbon (4%), Oxygen (6%) and
Iron (7%). The remaining 15% are omposed of heavier elements up to Uranium as well as
Eletrons, Positronsand Antiprotons.
Above a few GeV the energy spetrum of the CRs is desribed by a steeply falling power
lawwith anaverage exponent of -2.7. CRs up to 310 20
eV have been observed up to now.
SomeCRsoriginatefromthe sun. Theenergyofpartilesanonlybemeasured diretlyup
toenergiesofabout100 TeV
nuleus
bysatelliteorballoonbornedetetors. Higherenergypartiles
an only be deteted indiretly by airshowers that are initializedby the partiles.
The trajetories of partiles with energies below 10 9
eV
nuleon
are strongly inuened by the
galati,respetivelyextragalati(iftheseenergetipartilesoriginatefromoutsideourGalaxy)
magneti elds while partilesat the lowerend of the spetrum,i.e. a few GeV are alsoinu-
bak totheir soures of origin. Therefore they annot be used asmessengers .
Besides the originally disovered harged CRs there exist also omponents of CR whih
have no eletrial harge: -rays, neutrinos and may be neutrons (whih, due to their limited
lifetime an only originate from rather lose stars). These neutral partiles are not deeted
and are therefore useful messengers of highenergy proesses inthe universe. While-rays will
bedisussed inthe next hapter, I willgivehere a briefsummary onneutrino astronomy.
Sineneutrinoshaveaverysmallross-setionforallkindsofinterations,andtheyarenotar-
ryinganeletrialharge,they are inprinipleveryuseful forlookingdeeperintothe universe.
However, to detet neutrinos, a detetor with a very high mass is needed, whih is impossible
to install on satellites. For ground based experiments at the Earth's surfae, the bakground
whih isaused by the CRis very high, so itis very diulttomeasure neutrinos.
1.1.1 Cosmi -rays
Sinephotonsdonotarryaneletrialharge,theirtrajetoriesarenotinuenedbymagneti
elds. WhenaphotonhitstheEarth'satmosphere,thediretionofitssoureanbedetermined
if the diretionof arrivalofthe photon isknown. This allows astronomialobservationsover a
large partof the eletromagneti spetrum.
As already mentioned, photons with energies above 100keV are alled -rays.
2
Only at energies above a few times 10 19
eV harged partiles are not anymore deeted by the gala-
ti, respetively extragalati magneti elds and an be traed bak to their origin and at as messengers
of partile proesses of at least their energy. Unfortunately the ux of these partiles is very low, below 1
partile/year/100km 2
area.
universe". Three dierent parameters an be measured diretly by experiments and thus an
giveinformationon the mehanismof -rayprodution:
1. The ux froma soure,whihis the numberof photons pertime and area that arriveat
the Earth's atmosphere.
2. The energy spetrum, whih is the ux depending onthe photonenergy.
3. The time dependane of the ux, alsooften referredto asthe so-alledlighturve.
In table 1.1 I show the onditional splitting of the energy bands for -rays. There is no
sharp border between the shown dierent energy bands,that iswhy it isalled onditional.
Low Energy LE 100keV -10MeV
Medium Energy ME 10MeV - 1GeV
HighEnergy HE 1GeV - 100GeV
VeryHigh Energy VHE 100GeV -100TeV
UltraHigh Energy UHE >100TeV
Table 1.1: Splittingof energy bandsof -radiation
Thereexist many dierent types of souresof osmi -rays aswellas dierent prodution
mehanisms. Iwillpresentashortintrodutionontheminhapter2. Onespeiphenomenon
of osmi -radiationare the so alled GammaRay Bursts(GRB), whih are haraterizedby
veryhigh outburstsof energyoveraveryshortperiodof time(afewhundred mse uptoafew
hundreds of se). These willbe presented in hapter 3.
VHE Gamma Sources (E > 100 GeV)
(Status August 2005)
= Radio galaxy = Undetermined
= AGN (BL Lac)
= Pulsar/Plerion
Galactic Coordinates
+180 -180
-90 +90
Vela Mkn 501
Galactic center
1ES 2344+514
SN 1006
Cen X-3 M87
Mkn 421
PSR 1706-44
Crab Nebula RXJ 1713
= Starburst galaxy = SNR
H1426+428
1ES1959+650 Cygnus OB2 CasA
NGC 253 PKS2155-304
PSR B1259-63 VHE J1303-63
= XRB
= OB association
3C66A BL Lacertae
TeV 2032
H2356 PKS2005 LS5039 SNRG0.9
1ES1218
HessJ1303 RXJ0852 1ES1101
Figure1.1: The VHE-Gamma sky (Courtesy: NadiaTonello)
In Figure1.1are presented the known ray souresand their types.
1.1.2 Detetors for -rays
Therearetwotypesofdetetorsforosmi-raysommonlyused: satelleite-basedandground-
based detetors.
Sine the ux of the gammas isdereasing steeply with energy, one needs detetors with very
large areas toobserve osmi -rays of very high energies. Satelliteswith suh large detetors
would beome too heavy and too expensive. That is the reason why satellite-based detetors
are onlyused to measure -rays up to10 12
eV.
instruments. WithdetetorsontheEarth'ssurfaeitisnotpossibletodetetprimaryphotons,
beause they interat with the atoms high up in the atmosphere and reate an avalanhe of
seondary partiles, mostlyeletrons positronsand -rays(this willbeexplainedinhapter2).
This avalanhe of seondary partiles isalled "airshower". The harged shower partiles,
provided that they move faster than the speed of light in the atmosphere, generate so-alled
Cherenkov light, whih an be measured by the above mentioned Cherenkov telesopes. One
of thesetelesopes,atually theworld'slargestone, isthereently installedMAGICTelesope.
MAGIC (Major AtmospheriGamma ImagingCherenkov Telesope)isanimagingatmo-
spheri Cherenkov Telesope (IACT), for Gamma astronomy between 30GeV and 30TeV.
The photograph below shows the 17m diameter MAGIC Telesope with its 238m 2
mirror
area.
MAGIC isloatedat the "Roquede losMuhahos" onthe Canarianisland LaPalma ata
geographial latitude of 28 o
north and a geographial longitude of 17 o
west, atapproximately
2200m above sea level.
OneoftheaimsofMAGICistodetetthepreviouslymentionedGammaRayBursts(GRB).
SineaGRBlastsonlyseveralseonds anditspositionisnot knownbeforehand,itisneessary
tomovethe telesopeveryfast tothe positionofthe GRB(goal: <20s). The aimof thiswork
wastodetermine thesafety limitsand theneessary driveparametersforthe fastmovementof
the MAGIC Telesope. Notethat MAGIChas amass of 63t and a mass momentum of inertia
of approximately4000tm 2
. Toprepare this, Idid several alulationsonaelerationand mass
momentum (hapter 5), haraterized the motors and the ontrol loop and nally performed
many driving tests (presented inhapter7).
Some information on the relevant
Astrophysial Proesses
The eletromagneti waves observable fromosmos range fromradio waves of less than 1meV
energyuptoultra-highenergygammaraysofseveral TeV.Astronomialobservationsatvisible
wavelengths have a history of enturies, while gammaastronomy using satellites (keV up toa
few GeV) and ground-based telesopes (above300GeV) ame up in the late 20 th
entury.
2.1 The Imaging Air-Cherenkov Tehnique
VHE -rays annot be observed diretly by ground-based instruments, beause they are ab-
sorbed in the atmosphere. In the initialabsorption proess (eletromagnetiinteration of the
with a nuleus of the moleules of the atmosphere) harged partiles are reated, usually
an eletron positron pair (pair prodution mehanism), eah arrying half of the -energy on
average. These seondary partiles have normally suh high energies, that they reate addi-
tionalenergeti-raysviaBremstrahlungwhiletheypropagatethroughtheatmosphere. These
-rays produe further eletron-positron pairs, againwith onaverage halfthe energy eah and
so on...
TheseproessesalternateandontinueuntiltheenergylossduetopairprodutionorBremsstrahlung
In summarythe primary initial-ray produes ashower ofhargedpartiles. Beause nor-
mallyonlyeletromagnetipartilesareinvolvedin-rayshowersonenamesthistypeofshower
"eletromagnetishower". Theshowerreahesitsmaximumsizeinnumberofhargedpartiles
at the pointwhenthe probability forenergy lossdue topair produtionperunit lengtheqauls
that due to the ionization loss per unit length (at 81MeV). The eletrons and positrons in
a shower have suh high energies that their veloity is higher than the speed of light in the
atmosphere. While propagating through the atmosphere, the eletrons and positrons polarize
moleules beauseof their eletriharge. Inthis proess the atmospherimoleules emit low-
energy photons (visible to near UV, wavelengths down to 300nm, the spetral ut-o due to
the Ozoneontentofthe atmosphere)inaharateristionewithanopeningangledependent
on the veloity of the partile and the refrative index of the atmosphere and is in the range
of 0.4 - 1.2 o
(analogous to asupersoni bang). This emissionis alled "Cherenkov Radiation"
after the Russian sientist Pavel Cherenkov, who disovered it in 1934 and was later honored
by the Nobel prie for this disovery.
In an IACT, the Cherenkov-Photons passing down to the ground are olleted by a large
mirror and foused onto a ne pixelized matrix of photomultipliers in the foal plane of the
telsope (for telesope details see later). It is ovious that as lower the energy of the initial
-rayis,aslowerthe lightintensity ongroundwillbe. Therefore telesopesforthe observation
of lower energy -rays need normally larger light olleting mirrors. MAGIC is urrently the
world'slargestIACTandonseutivelyithasthelowest energythreshold. TheCherenkov light
ash is extremelyshort intime, inthe orderof afew nse. Byusing ultrafastphotomultipliers
and readout eletronisone anreordanimage(with aomplexstruture)of theshowereven
in the presene of a sizeable night sky bakground. As an example I would like to mention
that a typial vertial inidene 100GeV -ray shower produes on average a light ux in the
wavelength rangeof 300-600nmof about100
photons
m 2
onthe groundwhenever theshoweraxis
is within 120m radius from the telesope. After taking reetivity losses and the quantum
eieny of the amera PMT's into aount, one reords normallyimages of 100GeV showers
of typially1000 photoeletons.
e+
e+
e- primary
e- e+
e+
e- e+
e- e-
e-
e-
e + e + +
π+ π−
K , etc.+−
nucleons,
K , etc.+−
nucleons,
γ
π0
π+ π0
µ− _ γ
γ
µ
γ γ νµ
νµ cosmic ray (p, alpha,...)
γ γ
γ γ
atmospheric nucleus atmospheric nucleus
EM cascades EM cascade
EM cascade
Figure 2.2: Examples of an eletromagneti and hadroni air Shower (Courtesy: Markus Gar-
