large scale cosmic ray anisotropy and possible...

Paolo DesiatiRasha Abbasi and Juan Carlos Díaz-Vélez

May 1st, 2009University of Wisconsin - Madison

large scale cosmic ray anisotropyand possible interpretations

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cosmic ray isotropy

• cosmic rays below the knee are originated in the Galaxy

• cosmic rays below 1018 eV are predominantly galactic

• cosmic rays are expected to be isotropic

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5⋅10-5 pc10 AU

5⋅10-4 pc100 AU

5⋅10-2 pc104 AU

5 pc106 AU

500 pc108 AU

2⋅104 pc4⋅109 AU

0.05 TeV 0.5TeV 50 TeV 5 PeV 500 PeV 20 EeV

in 1 μG

Size of the Galaxy

cosmic ray anisotropy• Compton-Getting effect : relative motion of observer wrt CR plasma

• local structure of interstellar magnetic field

• helio-magnetic sphere and helio-magnetic tail

• nearby young sources of high energy cosmic rays

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Heliospheric termination shock

Heliospheric magnetic tail

Boundary to Local Interstellar Cloud

Nearby sources of CR ?

5⋅10-5 pc10 AU

5⋅10-4 pc100 AU

5⋅10-2 pc104 AU

5 pc106 AU

500 pc108 AU

2⋅104 pc4⋅109 AU

0.05 TeV 0.5TeV 50 TeV 5 PeV 500 PeV 20 EeV

in 1 μG

anisotropy discovered

• anisotropy of arrival direction of cosmic rays observed since 80’s

• 10’s GeV-100’s TeV in μ detector, surface arrays and ν detectors

• observed anisotropy of about 10-3

‣ originally measured as solar diurnal variation ofmuon count rate with a seasonal modulation

‣ atmospheric daily/seasonal temperature variation‣ Compton-Getting effect due to Earth’s motion

around the Sun

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compton-getting effect• apparent anisotropy due to relative motion of observer wrt

cosmic ray plasma

• motion of solar system around GC: v ~ 220 • 103 m/s

➡ maximum effect ~ 3.5 • 10-3

➡ sidereal diurnal variation of arrival directions with (~10%) yearly modulation

Compton and Getting, Phys. Rev. Vol. 47 (11) pp. 817 (1935)

!I

< I >= (2 + !)

v

ccos"

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compton-getting effect• apparent anisotropy due to relative motion of observer wrt

cosmic ray plasma

• motion of Earth around the Sun: v ~ 29.78 • 103 m/s

➡ maximum effect ~ 5 • 10-4

➡ solar diurnal variation of arrival directions (with yearly modulation)

!I

< I >= (2 + !)

v

ccos"

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temperature effects• the average atmospheric temperature changes during the day :

day-night (solar diurnal) variations

➡ ~ O(1) % ≫ GC effect

➡ null at the South Pole : SP-day = SP-year

• seasonal modulation over the year

➡ ~ O(1) %

➡ ~ 20 % at the South Pole

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IC22 IC40

measuring the anisotropy• measure sidereal variations @ sparse latitudes

• cosmic rays energy ~ 60-400 GeV (≲ 90 AU, if 1 μG)

• amplitude and phase change with latitude

• North-South asymmetry

Nagashima et al., Journ. Geophys. Res., Vol 103, No. A8, Pag. 17,429 (1998)

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measuring the anisotropy• measure sidereal variations @ sparse latitudes

• cosmic rays energy ~ 60-400 GeV



➡ tail-in modulated in time : max in Dec and min in Jun➡ from heliomagnetic tail

Nagashima et al., Journ. Geophys. Res., Vol 103, No. A8, Pag. 17,429 (1998)

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measuring the anisotropyNagashima et al., Journ. Geophys. Res., Vol 103, No. A8, Pag. 17,429 (1998)

proper motion of solar system

relative motion to ISM

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measuring anisotropy

• measure sidereal variations @ different latitudes (THN - two hemisphere network)

• cosmic rays energy ~ 140-1700 GeV (≲ 380 AU, if 1 μG)



Hall et al., Journ. Geophys. Res., Vol 103, No. A1, Pag. 367 (1998)

Tail-In max. shifts earlier in the south!

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measuring the anisotropy

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what’s the deal with the heliosphere ?

heliosphere• solar system moves wrt ISM at 26 km/sec

• solar wind (400-800 km/sec) diverts interstellar plasma

• when solar wind pressure ~ interstellar pressure the termination shock forms ~ 100 AU = 0.0005 pc (gyroradius @ 0.5 TeV)

• the heliopause separates solar from interstellar material and magnetic field ~ 150-200 AU ~0.001 pc (gyroradius @ 1 TeV)

• interstellar wind forms the heliotail that could extend to 20,000-40,000 AU ~ 0.1-0.2 pc (gyroradius @ 100-200 TeV)

Izmodenov et al., arXiv:astro-ph/0308211

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heliosphere

Lallement R. et al., Science Vol 307, page 144714

• solar system moves wrt ISM at 26 km/sec

• solar wind (400-800 km/sec) diverts interstellar plasma

• when solar wind pressure ~ interstellar pressure the termination shock forms ~ 100 AU = 0.0005 pc (gyroradius @ 0.5 TeV)

• the heliopause separates solar from interstellar material and magnetic field ~ 150-200 AU ~0.001 pc (gyroradius @ 1 TeV)

• interstellar wind forms the heliotail that could extend to 20,000-40,000 AU ~ 0.1-0.2 pc (gyroradius @ 100-200 TeV)

• cosmic compass

recent measurementsSuper-K

• data from 1996-2001• 1662 days• 2.1•108 events with res < 2º• median energy ~ 10 TeV (~2,200 AU)

Guillian et al., arXiv:astro-ph/0508468

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recent measurementsSuper-K

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recentmeasurementsTibet ASγ

• data from 1997-2005• 1874.8 days in total• 3.7•1010 events with res ~ 0.9º• modal energy ~ 3 TeV

Amenomori et al., Science Vol 314, Pag. 439 (2006)

Amenomori et al., arXiv:astro-ph/0505114

4 TeV0.004 pc880 AU

6.2 TeV0.007 pc1,400 AU

12 TeV0.01 pc

2,600 AU

50 TeV0.06 pc

11,000 AU

300 TeV0.3 pc

66,000 AU

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interstellar magnetic fieldLallement R. et al., Science Vol 307, page 1447 (2005)

26 km/sec

29 km/secVela

Geminga

Local Interstellar Cloudpartly ionized~6000 ºK ~ 0.5 eV

helio tail

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Priscilla Frisch, University of Chicago

interstellar magnetic fieldLallement R. et al., Science Vol 307, page 1447 (2005)

26 km/sec

29 km/secVela

Geminga

Local Interstellar Cloudpartly ionized~6000 ºK ~ 0.5 eV

helio tail

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19

+

+

=

+90o

-90o

0h 24h

Amenomori et al., ICRC 2007, Mérida, México (2007)

interstellar magnetic field


5 TeV0.006 pc1,000 AU

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residual skymap

interstellar magnetic field≲1 TeV≲0.01 pc≲200 AU

recent measurementsMILAGRO

• data from 2000-2007• 9.6•1010 events with res < 1º• median energy ~ 6 TeV (~ 1,300 AU)

Kolterman et al., ICRC 2007, Mérida, México (2007)Abdo et al., arXiv:0806.2293

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recent measurementsMILAGRO

• data from 2000-2007• 2.2•1011 events with res < 1º• median energy ~ 1 TeV (~ 200 AU)• resolve ≲10º structures

• fractional excess highest in winter lowest in summer

Abdo et al., arXiv:0801.3827

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recent measurementsMILAGRO Abdo et al., Phys.Rev.Lett.101:221101,2008, arXiv:0801.3827


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5 TeV

1 TeV

direction of Geminga

• Salvati & Sacco (arXiv:0802.2181)

• heliospheric acceleration scenario excluded• Geminga SN (~340,000 yr old, ~170 pc, 0633+1746)• burst of CR injected with ~ 1049 erg (1% of SN output)• Geminga radial velocity ~ 160 km/sec

• Drury & Aharonian (Astrop.Phys.29:420-423,2008, arXiv:0802.4403)

• magnetic highway between Geminga and us !

nearby source of cosmic rays ?

10o

nearby sources of CR ?Chang et al., Nature, Vol. 456 Pag. 362 (2008)

* AMS△ HEAT

○ BETS╳ PPB-BETS◊ emulsion chambers

ATICelectron energy spectrum

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Adriani et al., arXiv:0810.4995

Profumo, arXiv:0812.4457

Vela SNR (0835-4510)

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• formed 10,000-13,000 years ago• ~250 pc away (~230 PeV)• associated to Vela Pulsar (PSR J0835-4510)

• embedded in the Gum Nebula• very bright in x-rays

• cosmic rays from SN exposion• either a faint dipole anisotropy• or totally isotropized

• eventually anisotropy embedded in the observed one

IceCube-22

26Rasha’s analysis

direction of Veladirection of LIMF

conclusions• large scale anisotropy could reveal the structure and intensity of the local IS

magnetic field

• ~1-10 TeV cosmic rays likely to be disturbed by the closer heliospheric structure : helio-tail as cosmic compass

• do HE cosmic ray co-rotate with the Galaxy ? Compton-Getting effect

• nearby sources of cosmic rays influence the anisotropy ?

• search for middle & smaller scale structure : how smaller ?

• correlation between anisotropy and spectral features ?

• how would a young nearby SNR show up ?

• measure anisotropy @ different energies and times of the year

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spare slides

diurnal variations

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diurnal variations• at any given time only a fraction of the sky is visible

• it takes 1 solar year to scan the entire visible sky @ given location (with different exposure)

• non uniform sky coverage• diurnal variations from anisotropy

• @ South Pole entire half sky uniformly visible @ any time

• diurnal variation from contingent effects only

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diurnal variations• @ South Pole entire half sky uniformly visible @ any time

• diurnal variation from contingent effects only

• uniform sky coverage

• no diurnal weather effect

• seasonal weather variation slow ≫ 1 day

• anisotropy visible in right ascension

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diurnal variationssolar diurnal variation can be represented as(*)

R(t) = 1 + [ A + 2B*cos2π ( t - ƒ2 ) ] * cos2π ( Nt - ƒ1 ) + C*cos2π [ (N+1)t - ƒ3 ]

R(t) = 1 + A*cos2π ( Nt - ƒ1 )

+ B*cos2π [ (N+1)t - (ƒ1 + ƒ2) ] + C*cos2π [ (N+1)t - ƒ3 ]

+ B*cos2π [ (N-1)t - (ƒ1-ƒ2) ]

(*) assume Compton-Getting effect is negligible or included in the solar/sidereal daily variation

solar daily variationseasonal yearly modulation sidereal daily variationatmospheric local effects extra-terrestrial effects

t = time in solar year (i.e. t=1 is one solar year)N = 365.24 cycles / year = solar diurnal frequency

solar diurnal variation

sidereal diurnal variation

spurious sidereal variation true sidereal variation

pseudo-sidereal diurnal variation

Farley and Storey, Proc. Phys. Soc. A67, 996(1954)


toward an interpretation

5 TeV

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toward an interpretation

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gyroradius3 µG

10 µG

2•105 AU

2•104 AU

2•103 AU

2•102 AU

20 AU

2 AU

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large scale cosmic ray anisotropy and possible...

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