Cosmic Ray Anisotropy with Milagro · Milagro Cosmic Ray Observaons • Gamma‐ray origin excluded...

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.