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CosmicRayAnisotropywithMilagro
JohnPretzFortheMilagroCollabora;on
TeVPar;cleAstrophysicsConference–May15,2009
MilagroCollabora+on
A. Abdo, B. Allen, D. Berley, G. Christopher, T. DeYoung, B.L. Dingus, R.W. Ellsworth, M.M. Gonzalez, J.A. Goodman, C.M. Ho f fman ,P. Hun temeye r, B . Kolterman, C.P. Lansdell, J.T. Linnemann, J.E. McEnery, A.I. Mincer, P. Nemethy, J. Pretz, J.M. Ryan, P.M. Saz Parkinson, A. Shoup, G. Sinnis, A.J. Smith, G.W. Su l l i van , D .A . W i l l i ams , V. Vasileiou, G.B. Yodh
MilagroDetector• CentralWaterPond(80x60meter)
• 450PMTsunder1.5mwater• 273PMTsunder6mwater
• Outriggers• 2.4meterdiameter• 1.4metertall• 175PMTsinoutriggertanks
• WaterCherenkovDetector• 2600metersal+tude• 4000m2pond/40000m2outrigger
coverage• 1700HzTriggerRate• 0.4o–1.0oangularresolu+on• Sensi+vity100GeV–100TeV
Medianenergy10–40TeV(dependingoncuts,weightsetc)
• Operatedfrom2000‐2008.
Gamma/HadronDiscrimina+on• Penetra+ngcomponentofHadronicairshowersilluminatestheboWomlayer.
Gamma/HadronDiscrimina+on• Penetra+ngcomponentofHadronicairshowersilluminatestheboWomlayer.
Large‐ScaleAnisotropySeenbyManyExperiments
Anisotropy in Tibet Air Shower array data
M. Amenomori, et al. Science 314, 439 (2006)
Nagashima, K., K. Fujimoto, and R. M. Jacklyn (1998) J.Geophys. Res., 103(A8), 17,429–17,440.
LargeScaleAnisotropyasMeasuredbyMilagro
Abdo et al. ApJ. 698. 2121-2130 (2009)
MilagroMeasurementofLarge‐ScaleAnisotropy
Abdo et al. ApJ. 698. 2121-2130 (2009)
FB Asymmetry
LargeScaleAnisotropy
• Frac+onalstrengthof~10‐3.• Observedinsidereal+me.
SolarCompton‐Ge]ngeffectobservedinUT.– “Bugsonthewindshield”effect
asmemovearoundthesun• Consistentwithobserva+ons
byTibet,SuperK,IceCube,andothers.
• Indica+onsof+medependence.– Tibetsawno+medependence
between1997‐2001and2001‐2005(M. Amenomori, et al. Science 314, 439 (2006))
Abdo et al. ApJ. 698. 2121-2130 (2009)
LocalizedAnisotropy
• Discoveredserendipitouslywhencross‐checkinggamma‐raysearchresults.
• Normalgamma‐raypointsourcesearch,neglec+nggamma‐raycuts,appliedlookingforlargesources.
TechniqueforPointSourceSearches
• Backgroundes+ma+onconfinedtolocaldeclina+onstrip.
• Backgroundmethodusedtoes+matebackgroundforgamma‐raysourceanalysis.
• Assume:Localcoordinatedistribu+onisstableonshort+mescale.
• Neednotassumethattherateisconstantin+me.
• Integra+on+meis30o(2hr)
• Effec+velythisisaHigh‐Passfilter
LocalizedAnisotropyObserva+ons
• Noweigh+ngorcu]ng.Mapdominatedbycosmicrays.• Backgroundsubtrac+onservesasahigh‐passfilter.• 10osmoothinglooksforlargeishfeatures.• Tworegionsofexcess15.0σand12.7σ.Frac+onalexcessof
6x10‐4(4x10‐4)forregionA(B).• SeenalsobyTibetASγ
PRL 101, 221101 (2008)
MilagroCosmicRayObserva+ons
• ClearsimilaritybetweenMilagroobserva+onsandARGO‐YBJresults.
• AlsoseeninTibet‐ASγdata
S. Vernetto for ARGO-YBJ Collaboration RICAP 2009
MilagroCosmicRayObserva+ons
• Gamma‐rayoriginexcludedtohighconfidence.Cosmic‐rayhypothesisfitswell.
• Appearharderthanbackgroundcosmic‐rayswithacutoffat~10TeV.• RegionAcoincidentwiththeheliotail
PRL 101, 221101 (2008)
MilagroCosmicRayObserva+ons
• Gamma‐rayoriginexcludedtohighconfidence.Cosmic‐rayhypothesisfitswell.
• Appearharderthanbackgroundcosmic‐rayswithacutoffat~10TeV.• RegionAcoincidentwiththeheliotail
PRL 101, 221101 (2008)
Region A Region B
Whatarethesefeatures?
• Heliospheric?– ConsideredbySalva+andSaccoandfoundnotlikely.
• Neutronproduc+oninclumpofISMmaWergathredattheheliotail.– RejectedbyDruryandAharonian
• NearbySource– Gyroradiusof10TeVprotonisin>1µG<0.01pc.– 10TeVneutronwilllivefor0.1pc
• Aneffectresul+ngfromthesumma+onofsourcesnearEarth?
Salvati and Sacco. A&A 485, 527-529 (2008) Drury and Aharonian. Astropart. Phys. 29 420-423 (2008)
Poten+alNearbyCosmic‐RayAccelerator
• Consideredplausiblebythosewho’veconsideredit
• Requiresnon‐standardcosmic‐raydiffusionandanearbysource(Gemingasupernova?AsliWleas90pcaway.)
• Somecoherentmagne+cstructureconnec+ngustothesource.
• Needtounderstandcosmic‐raypropaga+onbeWer.
From: Salvati and Sacco. A&A 485, 527-529 (2008)
HAWC• Improvedgamma/hadron
discrimina+on• Improvedenergyresolu+on• Improveddetectorstability
– SeetheCrabeveryday• SeeB.DingustalkonFriday
Cosmic ray Gamma ray
Conclusions
• Large‐ScaleAnisotropyfirmlyestablished– ObservedbyanumberofexperimentsincludingMilagro
– Sugges+onsof+medependence• Localizedanisotropyat5x10‐4level
– Nocompellingexplana+on.– Nearbyaccelerator?GemingaSNR?– Non‐standardcosmic‐raydiffusion– Localmagne+cfields?
• CosmicRayAnisotropymaybequiterevealing.