Prospects of Identifying the Sources of

the Galactic Cosmic Rays with IceCube

Alexander KappesFrancis HalzenAongus O’Murchadha

University Wisconsin-Madison

3rd VLVnT Workshop

April 22. - 24. 2008, Toulon France

April 23, 2008 Alexander Kappes, 3rd VLVnT Workshop, Toulon France 2

Outline

Cosmic rays and gamma/neutrino production

Which are the accelerators of the Galactic cosmic rays?

Can we see them with neutrino telescopes (IceCube)?

April 23, 2008 Alexander Kappes, 3rd VLVnT Workshop, Toulon France 3

The Cosmic Ray Spectrum

Cosmic ray spectrum measured over more than 12 decades

Spectrum steepens at ~3 PeV Transition between Galactic

and extra-Galactic component at 1016 - 1018 eV

Form of spectrum requires Galactic accelerators up to 3 PeV (PeVatrons)

Not identifiable with cosmic ray experiments (magnetic fields)

extragalacticgalactic

April 23, 2008 Alexander Kappes, 3rd VLVnT Workshop, Toulon France 4

The Cosmic-Ray Gamma/Neutrino Connection

Relation / spectrum parameters (pp interactions)(at Earth mixing leads to (1 : 1 : 1))

Protons @ CR “knee” produce -rays of ~300 TeV

p + p() → + X + e + e +

p + p() → 0 + X

Hadronic neutrino and ray production:

( e :

Norm:

Index:

Cut-off:Kappes etal: ApJ,656:870-896,2007

April 23, 2008 Alexander Kappes, 3rd VLVnT Workshop, Toulon France 5

The Mystery of the Missing PeVatrons

SNRs best candidates for Galactic cosmic ray accelerators

But no SNR spectrum extends above a few 10 TeV

Possible reason: “Direct” high energy -ray emission only in first few hundred years

Detection still possible by observing secondary -rays produced in nearby clouds

Milagro better suited than Cherenkov telescopes

400 yr

2000 yr8000 yr

32000 yr

(104 solar masses)

at 1 Kpc

8000 yr2000 yr

Cherenkov telescopes(e.g. HESS, Magic)

Air shower arrays(Milagro)

Gabici, Aharonian: arXiv:0705.3011

April 23, 2008 Alexander Kappes, 3rd VLVnT Workshop, Toulon France 6

2007 Milagro Sky Survey At 12 TeV

MGRO J2019+37

MGRO J2032+37

MGRO J2031+41 MGRO J1852+01

MGRO J1908+06

MGRO J2043+36

MGRO 2019+37: not seen by VERITAS in first observation consistency requires < 2.2

MGRO J2031+41: Magic measures E-2 spectrum

Abdo thesis defense, March 2007

VERITAS observation

April 23, 2008 Alexander Kappes, 3rd VLVnT Workshop, Toulon France 7

Gamma-ray Spectrum of MGRO J1908+06

Again E-2 spectrum; extends up to 100 TeV ! Strong indicator of proton acceleration in this source

April 23, 2008 Alexander Kappes, 3rd VLVnT Workshop, Toulon France 8

The Role of Neutrino Telescopes

Air shower array currently only in Northern Hemisphere Photon production ambiguous Cherenkov telescopes have only small field of view (few deg2)

cover only small part of sky (at a time) large photon background in star forming region (e.g. Cygnus)

can hide sources

Neutrinos unambiguous sign for hadronic acceleration Neutrino telescope properties fit well to air shower arrays

“all sky” sensitivity increasing sensitivity with energy (small background) angular resolution O(1º)

April 23, 2008 Alexander Kappes, 3rd VLVnT Workshop, Toulon France 9

Gamma and Neutrino Spectra

Neutrino spectra for all sourcesSpectra for MGRO J1908+06

Assumed E-2 with Milagro normaliztion (MGRO J1908+06 index = 2.1)

spectrum cutoff @ 180 TeV

Halzen, Kappes, O’Murchadha: arXiv:0803.0314

neutrino flux

gamma flux

MGRO J1852+01MGRO J2019+37MGRO J1908+06MGRO J2031+41MGRO J2043+36MGRO J2032+37

1 10Ethresh (TeV)

1000100 1 10Ethresh (TeV)

100010010-13

10-12

10-11

10-10

E2

flu

x (T

eV s

-1 c

m-2)

E2

flu

x (T

eV s

-1 c

m-2)

10-13

10-12

10-11

April 23, 2008 Alexander Kappes, 3rd VLVnT Workshop, Toulon France 10

Significance for MGRO J1908+06 (5 years)

Milagro measurements favor lower sensitivity curve (dashed line) 2 - 2.5 after 5 years

IceCube (80 strings) effective area (with quality cuts)

Search window:

observed eventssignal + atm.

calculated signal events

€

1.6 × rsrc2 + rres

2

Halzen, Kappes, O’Murchadha: arXiv:0803.0314

1

2

3

1 10Ethresh (TeV)

1001 10Ethresh (TeV)

100

1

10

# ev

ents

p v

alu

e

April 23, 2008 Alexander Kappes, 3rd VLVnT Workshop, Toulon France 11

Significance for all 6 Milagro sources after 5 years

p-value = 10-4 after 5 years but large error band (not shown)

Optimal threshold @ 30 TeV (determined by loss of signal events)

Halzen, Kappes, O’Murchadha: arXiv:0803.0314

April 23, 2008 Alexander Kappes, 3rd VLVnT Workshop, Toulon France 12

Simulated Neutrino Skymaps IC80 (5 years)# events

(arb. units)Correlated Skymap

Not actual w

ay to analyse data !

April 23, 2008 Alexander Kappes, 3rd VLVnT Workshop, Toulon France 13

Summary

Cosmic ray sources (PeVatrons) should leave imprint on Milagro sky map

Milagro observes several hotspots with apparently hard spectra maybe first PeVatron(s) discovered (MGRO J1908+06)

If these are the cosmic ray sources IceCube will be able to see them with time (best sensitivity above several 10 TeV)

MGRO J1852+01 and MGRO J1908+06 also visible (50%)by Mediterranean detectors

More information in Halzen, Kappes, O’Murchadha: arXiv:0803.0314