Cosmic Ray Anisotropy with Milagro

Cosmic Ray Anisotropy with Milagro John Pretz For the Milagro Collabora;on TeV Par;cle Astrophysics Conference May 15, 2009

Milagro Collabora+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. H o f f m a n, P. H u n t e m e y e 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. S u l l i v a n, D. A. W i l l i a m s, V. Vasileiou, G.B. Yodh

Milagro Detector Central Water Pond (80x60 meter) 450 PMTs under 1.5 m water 273 PMTs under 6 m water Outriggers 2.4 meter diameter 1.4 meter tall 175 PMTs in outrigger tanks Water Cherenkov Detector 2600 meters al+tude 4000 m2 pond / 40000 m2 outrigger coverage 1700 Hz Trigger Rate 0.4o 1.0o angular resolu+on Sensi+vity 100 GeV 100 TeV Median energy 10 40 TeV (depending on cuts, weights etc) Operated from 2000 2008.

Gamma/Hadron Discrimina+on Penetra+ng component of Hadronic air showers illuminates the bowom layer.

Large Scale Anisotropy Seen by Many Experiments 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.

Large Scale Anisotropy as Measured by Milagro Abdo et al. ApJ. 698. 2121-2130 (2009)

Milagro Measurement of Large Scale Anisotropy FB Asymmetry Abdo et al. ApJ. 698. 2121-2130 (2009)

Large Scale Anisotropy Frac+onal strength of ~10 3. Observed in sidereal +me. Solar Compton Ge]ng effect observed in UT. Bugs on the windshield effect as me move around the sun Consistent with observa+ons by Tibet, SuperK, IceCube, and others. Indica+ons of +me dependence. Tibet saw no +me dependence between 1997 2001 and 2001 2005 (M. Amenomori, et al. Science 314, 439 (2006)) Abdo et al. ApJ. 698. 2121-2130 (2009)

Localized Anisotropy Discovered serendipitously when cross checking gammaray search results. Normal gamma ray point source search, neglec+ng gamma ray cuts, applied looking for large sources.

Technique for Point Source Searches Background es+ma+on confined to local declina+on strip. Background method used to es+mate background for gammaray source analysis. Assume: Local coordinate distribu+on is stable on short +me scale. Need not assume that the rate is constant in +me. Integra+on +me is 30 o (2hr) Effec+vely this is a High Pass filter

Localized Anisotropy Observa+ons No weigh+ng or cu]ng. Map dominated by cosmic rays. Background subtrac+on serves as a high pass filter. 10 o smoothing looks for largeish features. Two regions of excess 15.0σ and 12.7σ. Frac+onal excess of 6x10 4 (4x10 4 ) for region A(B). Seen also by Tibet ASγ PRL 101, 221101 (2008)

Milagro Cosmic Ray Observa+ons Clear similarity between Milagro observa+ons and ARGO YBJ results. Also seen in Tibet ASγ data S. Vernetto for ARGO-YBJ Collaboration RICAP 2009

Milagro Cosmic Ray Observa+ons Gamma ray origin excluded to high confidence. Cosmic ray hypothesis fits well. Appear harder than background cosmic rays with a cutoff at ~10 TeV. Region A coincident with the heliotail PRL 101, 221101 (2008)

Milagro Cosmic Ray Observa+ons Region A Region B Gamma ray origin excluded to high confidence. Cosmic ray hypothesis fits well. Appear harder than background cosmic rays with a cutoff at ~10 TeV. Region A coincident with the heliotail PRL 101, 221101 (2008)

What are these features? Heliospheric? Considered by Salva+ and Sacco and found not likely. Neutron produc+on in clump of ISM mawer gathred at the heliotail. Rejected by Drury and Aharonian Nearby Source Gyroradius of 10 TeV proton is in >1µG <0.01 pc. 10 TeV neutron will live for 0.1 pc An effect resul+ng from the summa+on of sources near Earth? Salvati and Sacco. A&A 485, 527-529 (2008) Drury and Aharonian. Astropart. Phys. 29 420-423 (2008)

Poten+al Nearby Cosmic Ray Considered plausible by those who ve considered it Requires non standard cosmic ray diffusion and a nearby source (Geminga supernova? As liwle as 90 pc away.) Some coherent magne+c structure connec+ng us to the source. Need to understand cosmicray propaga+on bewer. Accelerator From: Salvati and Sacco. A&A 485, 527-529 (2008)

HAWC Improved gamma/hadron discrimina+on Improved energy resolu+on Improved detector stability See the Crab every day See B. Dingus talk on Friday Cosmic ray Gamma ray

Conclusions Large Scale Anisotropy firmly established Observed by a number of experiments including Milagro Sugges+ons of +me dependence Localized anisotropy at 5x10 4 level No compelling explana+on. Nearby accelerator? Geminga SNR? Non standard cosmic ray diffusion Local magne+c fields? Cosmic Ray Anisotropy may be quite revealing.