Table Of ContentRICAP-07: SummaryComments
T.K. Gaissera
aBartol Research Institute and Dept.Physics& Astronomy, Universityof Delaware, Newark DE, 19716, U.S.A.
8
0
0
2
n
a
JAbstract
9
2TheRomaInternationalConferenceonAstroparticlePhysicscoveredgamma-rayastronomy,airshowerexperimentsandneutrino
astronomyonthreesuccessivedays.Iorganizemybriefsummarycommentsintofourtopicsthatcutacrossthesethreetechniques.
]They aredetector calibration, galactic sources, extra-galactic sources andcosmology.
h
p
-
Keywords: Cosmicrays, gamma-rayastronomy, neutrino astronomy
o
PACS: 96.50S-, 95.55Ka, 95.85Ry
r
t
s
a
[
1. Introduction Table1
Contents of LAT data challenge sky [2].
1
v
6 Amainthemeoftheconferencewasthemulti-messenger Galactic Sources Number Extra-galactic SourcesNumber
4approachtotheoriginofcosmicrays.Theconferencehada
MilkyWay 1 DiffuseExtra-galactic 1
5localflavorthatillustratesthestrongItaliancontributions
4tomajorexperimentalactivitiesinallthreefields,gamma- Moon 1
.
1ray astronomy, cosmic-ray experiments and neutrino as- Pulsars 414 BrightvariableAGN 204
0tronomy.InthesebriefremarksIwillpointoutsomecom-
Plerions 7 Faint steady AGN 900
8montechniquesandapproachesandfocusonafewimpor-
0 SNR 11 GRB 134
tant questions being addressed by current experiments in
:
vparticleastrophysics.Imakenoattempttogiveabalanced XRB 5 GRB afterglow 9
Xiandsystematicreviewofthe fieldhere [1]. OB associations 4 PBH 1
r Small mol.cloud 40 Galaxy clusters 4
a2. Calibration
DarkMatter ∼2 Galaxies 5
‘Other 3EG’ 120
Onecandistinguishtwoaspectsofcalibration.Oneisto
determine the response of a detector to a given beam or Solar flare 1
spectrumofparticles.The other is to evaluatethe levelat
sky has been created consisting of various likely sources
which a source can be seen above background and make
superimposedonthebackgroundoftheMilkyWayandan
sure the searchalgorithms would find a sufficiently strong
extra-galacticdiffuse flux,as showninTable1 [2].
sourceifitispresent.Computersimulationsandtestbeams
Pointing accuracy and angular resolution can be deter-
play a central role in both cases. For example, the Large
mined with data from a known source. Gamma-ray tele-
Area Telescope (LAT) team on GLAST uses GEANT 4
scopes typically use the Crab Nebula (e.g. VERITAS [3])
to simulate the full detector based on exposure of each
as a calibration source. The shadow of the Moon can also
component to accelerator beams. The simulation is tuned
beused,particularlyforgroundarraysoperatingathigher
to data from further exposures of prototype assemblies to
energy and with smaller statistics (e.g. ARGO-YBJ [4]).
acceleratorbeams.Toaddresstheotheraspect,asimulated
Angular resolution can also be determined by measuring
Email address: [email protected] (T.K. Gaisser). the same events with two different detectors. An example
Preprintsubmitted toElsevier 3February 2008
1]
-r
-2-1m s s1100--33 HBoarnrd aat mat.m n .m +n mn–+m n–m AatMmA. Nn mD+A n–-mI Id, uatnaf ofrldoemd
2000 - 2003
c
eV 1100--44
G
[ 2
En
--55
1100
F
--66
1100
--77
1100
--88
1100
Fig.2. Angular distributionof events inAntares [12].
--99
1100 Apart from coincident events, the energy spectrum and
33 33..55 44 44..55 55 55..55 66
log(E /GeV) angular distribution of atmospheric muons and neutrinos
n
are now rather well known in the TeV range. Measuring
andreconstructingboththesedistributionsisanimportant
Fig. 1. Unfolded spectrum of atmospheric neutrinos by AMAN-
benchmarkforneutrinotelescopes.Thespectrumofdiffuse
DA-II [8] compared to calculations of Refs. [9,10]. Shaded bands
neutrinosinAMANDA[7]hasbeenmeasuredtoapproach-
show the range between the horizontal (upper border) and vertical
flux (lower border). ing 100 TeV [8] and agrees reasonably well with expecta-
tion.Someatmosphericneutrinoshavebeenidentifiedwith
of this is a sub-array analysis with an air shower detec- 9-stringIceCubeduring2006[11].Thefirstphysics-quality
tor suchas IceTop[5]. The “checkerboard”analysisof the datawith IceCube is expected fromthe 22-stringdetector
ARGO-YBJcarpetisanotherexample. currently operating in 2007 and in early 2008. The next
ForIceCube,thesameprinciplecanbeusedtocheckthe version of IceCube, including the new strings of IceCube
pointing and angular resolution of the neutrino telescope, detectors to be deployed during the 2007/2008 season, is
to the extent that high-energy muons in air shower cores scheduledtostartanewruninApril,2008.Antareshasre-
tagged by IceTop are similar in the detector to upward- portedapreliminarymeasurementofthe zenithangledis-
movingneutrino-inducedmuons.Forairshowersabovethe tributionofmuonsasshowninFig.2[12].Althoughthere
thresholdforIceTop,onecancomparethedirectionrecon- is not yet a comparison with the expected angular distri-
structed with the surface array with the direction of the bution of atmospheric muons and neutrinos, the apparent
same event reconstructed independently by the deep ar- emergence of neutrino-induced muons slightly above the
ray. Since the surface array can be surveyed directly, this horizon is impressive. If this interpretation of the plot is
comparison checks pointing as well as angular resolution. correct, it indicates good angular resolution at the depth
Limitations are that showers above the threshold for Ice- of2050-2400meters inthe MediterraneanSea.
Toptypically haveseveralmuons atthe depthof the deep Theessentialproblemforcalibrationoflargeairshower
detectors of IceCube and that coincident events that pass arraysisthatreconstructionoftheenergyandmassofthe
throughboth detectors arenearly vertical.To addressthe primarycosmic-raystheyaredesignedtomeasuredepends
multiplicity problem,onecanalsouse lower-energyevents onextrapolationofpropertiesofhadronicinteractionsinto
that triggeronly a single,inner IceTopstationonthe sur- regions inaccessible at accelerators. Calibration of the in-
faceandcomparethelinefromthatstationtothecenterof dividualdetectorsonthegroundisstraightforward,either
thedeepeventwiththedirectionreconstructedbytheIce- by exposing them to accelerator beams or by using abun-
Cube reconstruction algorithm. In her talk on KM3NeT, dant GeV cosmic-ray muons in situ. The real problem is
the projectto buildacubic kilometerneutrino detectorin that reconstructing the properties of the primary cosmic
theMediterranean[6],ElsdeWolfpointedoutthepossibil- radiationfromwhatismeasuredonthegrounddependson
ityofdeploying,perhapstemporarily,afloatingair-shower comparison to simulations made with models of hadronic
detectorabovethedeep-seaneutrinotelescope.Suchade- interactions extrapolated orders of magnitude beyond the
tector could have a variable spacing tuned to be able to regions of energy and phase space measured at accelera-
reconstruct small showers likely to produce a single muon tors. Use of fluorescence detectors has the advantage that
that penetrates to the deep array. It could also be moved the measurement of shower energy is more nearly calori-
to expandthe rangeofanglesexplored. metricprovidedcomplicationsofviewingangle,Cherenkov
2
light background and variable atmospheric properties can KASCADE[22],J¨orgHo¨randelshowedevidenceforanin-
beovercome(forexamplewithlasercalibrationshots).But crease in the relative proportion of heavy nuclei with in-
eveninthis case,thereisasurprisinglylargerangeofpre- creasingenergythroughthekneeregion.Thisanalysisalso
dictions for the correction that has to be made for dark bringsupagainthe problemofhow toextrapolatemodels
energyinairshowers(i.e.energylostto neutrinosanden- of hadronic interactions correctly. The quantitative result
ergy carried into the ground by muons). In his talk on of the analysisdepends stronglyon which eventgenerator
Auger, [13] Alan Watson showed a 6-7% contribution to isusedtointerprettheKASCADEmeasurementofthera-
the 24% systematic uncertainty in the Auger flourescence tio of ∼GeV muons to electrons in the shower front. Two
detectorfromthis source. event generators are compared (SIBYLL 2.1 and QGSjet
01). In both cases helium is apparently more abundant
above 1015 eV than protons. However, the analysis with
3. Galactic sources
SIBYLL 2.1 shows the CNO group as the most abundant
component,whereaswithQGSjet01heliumissignificantly
Perhaps the most remarkable discovery in particle as- moreabundantthatthe othercomponents.
trophysics of the last few years is the large number of
galacticsourcesobservedindetail(includingspatialstruc-
ture) by H.E.S.S. and described in this meeting in [14]. 4. Extra-galactic sources
The MILAGRO experiment reports structure reflecting
several sources in the Cygnus region as well as a diffuse A major recentresult is the observationof a steepening
TeV gamma-ray background that is higher than expected ofthe ultra-highenergy cosmicrayspectrum aboveabout
from cosmic-ray propagation [15]. Some of the H.E.S.S. 3−5×1019eVbyHi-Res[23]andAuger[13].Onequestion
sourcesaresupernovaremnantsforwhichhadronicmodels thatarisesiswhetherthespectrumsteepensbecauseaccel-
seem likely [16] in view of measurements of strong mag- erators are reaching their maximum energy or because of
neticfields,whichmaketheelectromagneticinterpretation the effectofpropagationandenergylossinthe microwave
more difficult, in particular RX J1713-3946, in which the background, the Greisen-Kuz’min-Zatsepin (GZK) effect.
gamma-rayspectrumis observedto 100TeV[17]. OnewaytoconfirmthatitistheGZKeffectistomeasure
The mostdirectsignalofaccelerationofprotonsas well theintensityofneutrinosintheEeVenergyrange.Predic-
as electrons in SNR would be observation of neutrinos. If tionsfortheintensityofGZKneutrinosthatwouldbepro-
the >TeV gamma-rays are decay products of neutral pi- ducedby∼1020eVprotonsduringpropagationdependon
ons produced in hadronic interactions (p → π0 → γ+γ), the cosmologicalevolutionof the sourcesand their energy
then one can calculate from kinematics the corresponding spectra,asdiscussedherebyTodorStanev[24].Theques-
spectrum of neutrinos from p → π+ → µ+ + ν . This tion arises how precisely and over what energy region it
µ
hasbeendoneforseveralH.E.S.S.TeVgamma-raysources wouldbe necessaryto measurethe spectrumofGZK neu-
in Ref. [18]. Optimistically, one expects to observe only a trinos in order to unfold information about the history of
few neutrino-induced muons per year in a cubic kilometer cosmic-ray sources at large red shift and the source spec-
detector, and atmospheric backgroundsin the searchwin- trum.TheexpectedintensityofGZKneutrinosissuchthat
dow arecomparableorsomewhatlarger.In this situation, akilometer-scaledetectormightbeexpectedtodetectone
strategies such as source stacking can be helpful. Further or two per year. For this reason there is strong interest in
referencesanddiscussionaregiveninRef. [19]. using other techniques, such as radio [25] or acoustic [26],
Inhistalkonoriginandaccelerationofcosmicrays[20], toachieveasignificantlylargereffective detectorvolume.
Pasquale Blasi emphasized the role of magnetic field am- The most frequently mentioned possibilities for the
plificationandnon-lineareffectsatstrongshocks.Thereis sources of ultra-high energy cosmic rays are Gamma Ray
evidencefromX-rayobservationsofyoungsupernovarem- Bursts and Active Galaxies. In either case, depending on
nants for magnetic fields as high as 100 µGauss,which al- the environment of the accelerator, a fraction of the en-
lowsaccelerationofprotonsto>1015eV.Non-lineareffects ergy could be lost in interactions of accelerated hadrons
lead to differential spectra harder than −2 at the source. in or near their sources. If so, there could be correlated
The galactic spectrum with its observeddifferential index hadronic production of both >TeV gamma-rays and neu-
of −2.7 must then be explained by a combination of sev- trinos[27,28].
eral effects, including propagation and time evolution of The recentAMANDA limit on neutrino-inducedmuons
the sources[21]. from Northern Hemisphere GRBs [29] is close to the
Developing a full model of galactic cosmic rays is a job benchmark Waxman-Bahcallprediction [28],and IceCube
that remains to be completed, but there is a growingcon- is poised to extend the sensitivity significantly [30]. With
sensus that the knee of the cosmic-ray spectrum must be AGILE already in orbit [31] and sensitive to GRBs on
associatedwiththebeginningoftheendofthespectrumof a range of time scales, and particularly next year when
cosmicraysfromsourcesintheGalaxy.Ifso,thespectrum GLAST begins operation,there will be an increasednum-
is expected to become increasingly dominated by heavy ber of tagged GRBs to define a time window in which to
primaries as the transition is approached. In his talk on look for neutrinos. With time and direction windows de-
3
finedbyanobservedGRB,thebackgroundofatmospheric The branching ratio for this mode is likely to be small,
neutrinosis reducedtoa verylow level. butthesignatureisdistinctive.Ingeneral,anygamma-ray
LeptonicmodelsofTeVgamma-rayproductioninAGN productofdarkmatterinteractionsshouldpointtoregions
are generally favored over hadronic models, in which case ofhighmassconcentrationinthe Galaxy.
the connection between the observed intensity of TeV Finally,Iconcludewithareminderthatthe particlede-
gamma-raysand possible neutrino fluxes would be lost. A tectors PAMELA and AMS will make measurements of
recent additionto the arguments againsthadronic models spectra of galactic cosmic rays with unprecedented preci-
ofAGNscomesfromthe observationbyMAGIC ofaflare sion. They will also map the effects of the Sun on cosmic
from Mrk-501 in which the higher energy photons arrive rays and observe solar energetic particles. A nice example
a few minutes after lower energy ones [32]. If the time shownherewasthespectrumoftheDecember13,2006so-
delay reflects the time history of the accelerated charged larflareobservedwithPAMELA[36].
particles, it has a natural explanation in the context of
the electromagnetic, Synchrotron-Self-Compton Model;
namely, that it may take longer to accelerate electrons to
higherenergy,sothe higherenergyComptonup-scattered
AcknowledgmentsThisworkissupportedinpartbythe
photonswouldarrivelater[33].
U.S.DepartmentofEnergyunder DE-FG0291ER40626.
5. Cosmology
OnemotivationforthestudyofAGNspectra,apartfrom
References
their intrinsic interest as compact, energetic astrophysical
sources,is that they have the potential to probe the spec- [1] For a current reviews of gamma-ray astronomy, high-energy
cosmic rays and neutrinos and muons see the rapporteur
trum of extra-galactic background light in the infra-red
talksofthe30thInternationalCosmic-RayConference,Merida,
whichreflectsthehistoryofstarformationinearlyepochs
Yucatan, Mexico, July (2007). The talks are accessible at
oftheUniverse[34].Thehigh-energypartofthespectrum http://www.icrc2007.unam.mx/ by clicking on ”Conference
is cutoff in the TeV rangeby γγ →e+e− for sourceswith Timetable” and then selecting ”Rapporteurs”. The relevant
z ∼ 0.1 and at lower energy for sources at larger redshift. talks are, Gamma-ray astronomy: J. Hinton, G. Rowell; High-
energycosmicrays:P.Blasi,M.Teshima;NeutrinosandMuons:
Thepossibilityofsuchasystematicstudywasemphasized
T. Gaisser.
here as one motivating factor in the proposal for a next
[2] A. Moiseev, GLAST, RICAP07.
generation gamma-ray telescope, CTA [35]. In his review [3] D. Hanna, VERITAS, RICAP07.
of the subject [34], Stecker points out that cutoffs in the [4] G. D’Ali-Staiti,ARGO-YBJ, RICAP07.
range oftens of GeV areexpected in the spectra of AGNs [5] T. Waldenmaier, IceTop, RICAP07.
withz ∼2,arangeaccessibletoGLAST. [6] E. deWolf, KM3NeT,RICAP07.
[7] T. DeYoung, IceCube, RICAP07.
Indirect detection of dark matter is a major goal of the
[8] K.Mu¨nich&J.Lu¨nemann,Proc.30thICRC,Merida,Yucatan,
satelliteexperimentsdiscussedatthisconference.Thepar- Mexico (2007); arXiv:0711.0353v1 [astro-ph]pp. 71-74.
ticle detectors (PAMELA [36], AMS [37]) will be search- [9] G.D. Barret al.,Phys.Rev. D 70 (2004) 023006.
ingforanexcessofanti-matteroverwhatisexpectedfrom [10]M. Hondaet al.,Phys. Rev. D 70(2004) 043008.
[11]J. Pretz for the IceCube Collaboration, Proc. 30th ICRC,
cosmic-ray propagation through the interstellar medium.
Merida,Yucatan,Mexico(2007)and“Detectionofatmospheric
Such excesses would be a natural expectation, for exam-
muon neutrinos with the IceCube 9-string detector”, A.
plefromWIMPpairannihilationinconcentrationsofdark Achterberg et al.,Phys. Rev. D76(2007) 027101.
matter, because particles and antiparticles would be pro- [12]J. Carr,ANTARES,RICAP07.
ducedinequalabundance.AsemphasizedinRobertoBat- [13]A.A.Watson, AUGER, RICAP07.
tiston’stalk[37],notonlypositronsandanti-protonscould [14]G. Pu¨hlhofer, H.E.S.S.,RICAP07.
[15]G. Sinnis,MILAGRO, RICAP07.
beobserved,butalsoanti-deuterons.Thelatterwouldbea
[16]E.G.Berezhko&H.J.Vo¨lk,“Theoryofcosmicrayproductionin
particularlycleansignalofannihilation[38]becauseofthe
the supernova remnant RX J1713.7-3946”, Astron. Astrophys.
extremedifficultyofproducingananti-deuteronatlowen- 451 (2006) 981.
ergyinthecollisionofacosmicraywithaninterstellarnu- [17]F. Aharonian et al., “Primary particle acceleration above 100
cleusatrest.Becauseoftheveryhighenergythresholdfor TeVintheshell-typesupernovaremnantRXJ1713.7-3946with
the process, any d¯produced on a stationary target would deep HESS observations”, Astron.Astrophys. 464 (2007) 235.
[18]A. Kappes, J. Hinton, C. Stegmann, & F.A. Aharonian,
be quite energetic. “Potential neutrino signals from galactic γ-ray sources”, Ap.J.
Gamma-raysarealsoapotentialsignatureofdarkmat- 656 (2007) 870.
ter, particularly in the case where the signal produces a [19]T.K. Gaisser,“Muons and Neutrinos 2007”, rapporteur talk at
peakorlineinthespectrum.Thesearchforasignalofdark ICRC2007 (see Ref.1).
[20]P.Blasi,RICAP07.(See alsohisrapporteur talkatICRC2007,
matter is among the principal goals of GLAST [2]. In his
Ref. 1).
talkhere,LarsBergstrom[39]describedthelinesignature
[21]V.S. Ptuskin & V.N. Zirakashvili, “On the spectrum of high-
fromWIMPpairannihilationintoγγ withEγ =MWIMP. energy cosmic rays produced by supernova remnants in the
4
presence of strong cosmic-ray streaming instability and wave [31]M. Tavani, AGILE, RICAP07.
dissipation”, Astron.Astrophys. 429 (2005) 755. [32]D. Bastieri,MAGIC, RICAP07.
[22] Jo¨rgHo¨randel,KASCADE,RICAP07.SeealsoT.Antoni,etal., [33]J. Albertetal.,“VariableVHEγ-rayemissionfromMarkarian
Astropart. Phys.24 (2005) 1. 501”, astro-ph/0702008v3, 5Dec2007.
[23] Z.Cao, HiRes, RICAP07. [34]F. Stecker, “Stellar Photon and Blazar Archaeology with
[24] T.Stanev, RICAP07. Gamma-rays”,invitedtalk,30thInt.CosmicRayConf.,Merida,
[25] D.Besson, RICAP07. Yucatan, Mexico, arXiv:0709.0904v2[astro-ph]12 Sep 2007.
[26] L.Thompson, RICAP07. [35]M. Teshima,CTA, RICAP07.
[27] A. Mu¨cke et al., “BL Lac objects in the synchrotron proton [36]P. Papini,PAMELA,RICAP07.
blazar model”, Astropart. Phys. 18(2003) 593. [37]R. Battiston, AMS,RICAP07.
[28] E. Waxman & J. Bahcall, “High Energy Neutrinos from [38]H. Baer & S. Profumo, “Low energy antideuterons: shedding
CosmologicalGamma-RayBurstFireballs”,Phys.Rev.Letters lighton darkmatter”, JCAP 0512 (2005) 008.
78(1997) 2292. [39]L. Bergstrom,RICAP07.
[29] A. Achterberg et al., “The Search for Muon Neutrinos from
Northern Hemisphere Gamma-Ray Bursts with AMANDA”,
arXiv:0705.1186v1[astro-ph] 8May2007.
[30] A.Kappes, M.Kowalski,E.Strahler &I. Taboada, “Detecting
GRBs with IceCube and optical follow-upobservations”, Proc.
30thICRC,Merida,Yucatan,Mexico,arXiv:0711.0353v1[astro-
ph] 2Nov2007, pp127–130.
5
