Folie 1 - uhecr 2014

Report
Testing the origin of the UHECRs
with neutrinos
Walter Winter
DESY, Zeuthen, Germany
Kavli Institute for Theoretical Physics
(KITP), Santa Barbara, CA, USA
UHECR 2014,Springdale, UT, USA
Oct. 12-15, 2014
Contents
> Introduction
> Can the observed neutrinos come from the same sources as the
UHECRs?
> GRBs as test case for the UHECR-neutrino connection
> Summary
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 2
Cosmic messengers
Physics of astrophysical
neutrino sources = physics of
cosmic ray sources
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 3
3
2014: 37 neutrinos in the TeV-PeV range
Where do these come from?
Prompt atmospherics?
Directional information: Clustering?
Isotropic/from Galactic plane/Galactic center?
Why no events > few PeV?
Can these come from the sources of the ultra-high
energy cosmic rays?
Which source class? More than one?
Flavor composition?
 Requires more statistics
Science 342 (2013) 1242856; update by Gary Hill @ Neutrino 2014
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 4
Connection with primary nuclei?
> In pp and pg interactions, the secondary pions take about 20% of the
proton energy, the neutrinos about 5% (per flavor)
> PeV neutrinos must come from 20-500 PeV nuclei (depending on comp.)
> Observed cosmic ray composition
non-trivial function of energy (at Earth!)
> Simple
example:
Neutrinos from
cosmic ray
interactions
with hydrogen
in the
Milky Way
[O(0.1-1) event]
Joshi, Winter, Gupta,
MNRAS, 2014
n
primaries UHECRs
Gaisser, Stanev, Tilav, 2013
> Connection with UHECR sources requires extrapolation over
several orders of magnitude both in spectrum and composition
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 5
Fitting the observed neutrino spectrum
> Simplest possible
model: Ap (or AA)
interactions in sources;
SFR evolution
> Possible fits to data:
Protons, a=2.5
[Problem:
Fermi diffuse
g-ray bound
Murase, Ahlers,
Lacki, PRD 2013]
Protons
a=2
B ~ 104 G
(magnetic field effects on
sec. pions, muons, kaons)
Nuclei
a=2, Emax=1010.1 GeV
Composition at source
Protons
a=2
Emax=107.5 GeV
with b=0.4
WW, arXiv:1407.7536
(PRD, accepted)
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 6
Connection to UHECRs?
Yes, but: Energy input per decade very different
in neutrino-relevant and UHECR energy ranges
(Energetics seem to favor a~2, see e.g.
B. Katz, E. Waxman, T. Thompson, and A. Loeb (2013),
1311.0287)  will come up again later!
Protons, a=2.5
[Problem:
Fermi diffuse
g-ray bound
Protons
a=2
B ~ 104 G
Murase, Ahlers,
Lacki, PRD 2013]
Nuclei
a=2, Emax=1010.1 GeV
Composition at source
Protons
a=2
Emax=107.5 GeV
Yes, but: Need energydependent escape timescale
leading to break/cutoff within
source (diff. from ejection!)
see e.g. Liu et al, PRD, 2004;
arXiv:1310.1263
Yes, but: Synchrotron losses
limit maximal proton energies
as well. Need large Doppler
factors (e. g. GRBs)
with b=0.4
WW, arXiv:1407.7536
(PRD, accepted)
Yes, but: A(E) change somewhat too
shallow to match observation;
difference source-observation from
propagation?
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 7
GRBs as a test case
> Idea: Use timing and directional information to suppress atm. BGs
Coincidence!
Neutrino
observations
(e.g. IceCube, …)
(Source: IceCube)
(Source: NASA)
GRB gamma-ray observations
(e.g. Fermi, Swift, etc)
> Stacking limit exceeds
observed neutrino flux
(~10-8) by one order of
magnitude; interesting to
test specific models
Nature 484 (2012) 351
> Prediction (One zone model.
based on fixed collision radius
models) almost reached
(some recent corrections!)
(Hümmer,
Baerwald, Winter,
PRL 108 (2012)
231101;
method based on
Guetta et al, 2004;
Waxman, Bahcall
1997)
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 8
GRB - Internal shock model
(Source: SWIFT)
Engine
(intermittent)
G ~ 200-1000
“Isotropic
equivalent
energy“
Observable:
Light curves
(Simulation by
M. Bustamante)
Prompt phase
Collision of
shells
 Shocks
 Particle acc.
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 9
UHECR-neutrino connection: escape mechanisms?
Baerwald, Bustamante, Winter, Astrophys. J. 768 (2013) 186
Optically thin
(to neutron escape)
n
Optically thick
(to neutron escape)
n
n
n
p
n
n
n
n
 One neutrino per
cosmic ray
 Protons magnetically
confined
p
n
n
n
p
n
p
n
p
n
p
n
n
p
Direct proton escape
(UHECR leakage)
n
p
p
l‘ ~ c t‘pg
 Neutron escape limited
to edge of shells
 Neutrino prod.
relatively enhanced
l‘ ~ R‘L
 pg interaction rate
relatively low
 Protons leaking from
edges dominate
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 10
An example (before propagation)
(only adiabatic energy losses)
 For high enough acceleration
efficiencies:
R‘L can reach shell thickness
at highest energies
(if E‘p,max determined by t‘dyn)
 Hard spectrum, aka “high pass
filter“ (Globus et al, 2014)
 Relative importance depends
on optical thickness to pg
interactions
Neutron spectrum
harder than E-2
proton spectrum
(from: Baerwald, Bustamante, Winter,
Astrophys. J. 768 (2013) 186)
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 11
Combined source-propagation model: Ankle transition
(ap=2, fit range 1010 ... 1012 GeV)
> Neutron-dominated cases can be constrained by neutrino emission
> Baryonic loading fe-1 (energy protons to photons) typically somewhat larger
than IceCube assume, to fit UHECR data (here Liso=1052 erg s-1, Eiso=3 1052 erg)
G=300
G=800
(Baerwald, Bustamante, Winter, Astropart. Phys. 62 (2015) 66; figures with TA data)
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 12
Combined source-propagation model: Dip transition
(ap=2.5 with SFR evolution, fit range 109 ... 1012 GeV)
> Neutron-dominated cases even more extreme
> Required baryonic loading fe-1 extremely large; implication of unequal
energy output per decade (bolometric correction)
G=300
G=600 1050.5 erg/s
(Baerwald, Bustamante, Winter, Astropart. Phys. 62 (2015) 66; figures with TA data)
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 13
Parameter space constraints (ankle model, fit to TA data)
Example:
Moderate acc.
efficiency, escape
by Bohm-like
diffusion, SFR
evolution of
sources,
ankle transition
log10 fe-1
(baryonic loading)
obtained from fit
Direct
escape
Optically
thick pg
IceCube
expectation
(15yr)
Current
IceCube
limit
Best-fit (shaded
contours: TA
UHECR fit)
(Baerwald, Bustamante, Winter, Astropart. Phys. 62 (2015) 66; figures with TA data)
… but - maybe - assigning one parameter set
to all shells is too simple?
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 14
The future: more dynamical collision models
> Set out a number of shells with a
Lorentz factor distribution
> Shells collide, merge and cool by
radiation of energy
> Light curve predictable (see below)
> Efficient energy dissipation (e. g.
into gamma-rays) requires broad
Lorentz factor distribution
(Bustamante, Baerwald, Murase, Winter, 2014;
based on collision model Kobayashi, Piran, Sari,
1997; see Globus et al, 2014 for a similar approach)
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 15
Consequences for different messengers
> Collision radii reach from below
photosphere to circumburst medium
> UHECR escape as neutrons (red) and
directly (blue) at intermediate radii
> Energy output ~ no of collsions x energy
per collision (counting important!)
> The burst looks different in different
messengers!
(Bustamante, Baerwald, Murase, Winter, 2014)
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 16
Consequences for neutrino production
> Neutrino flux comes from a
few collisions at photosphere
Eiso=1053 erg per GRB
> Photospheric radius and
photohadronic interactions
both depend on particle
densities (scale at same way)
> Super-photospheric
(minimal?) prediction hardly
depends on baryonic loading,
G (different from earlier works!)
> Testable in high-energy
extension of IceCube?
> Sub-photospheric
contribution could be much
larger. However: photons
from below photosphere not
observable
(Bustamante, Baerwald, Murase, Winter, 2014)
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 17
Summary
> Neutrino observations open new window to cosmic ray source
identification; data (discovery and constraints) become meaningful
> UHECR connection somewhat more challenging, as several orders of
magnitude in energy between UHECRs and primaries leading to
observed neutrino flux
> GRBs are an interesting test case, as
 The constraints are strongest on GRBs because of timing cuts
 Well-motivated models for gamma-ray emission exist
 IceCube data already test the parameter space
> Different messengers are produced in different regions of a GRB.
Multi-messenger connections are more model-dependent than
previously anticipated
> Heavy nuclei are anticipated to escape from larger radii than protons,
as disintegration is to be avoided – but they can survive
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 18
BACKUP
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 19
Neutrino production
Dashed arrows: kinetic equations include cooling and escape
B‘
Input  Object-dependent:
Q(E) [GeV-1 cm-3 s-1]
per time frame
N(E) [GeV-1 cm-3]
steady spectrum
Optically
thin
to neutrons
from:
Baerwald, Hümmer, Winter,
Astropart. Phys. 35
(2012) 508
Walter Winter | UHECR 2014 |
Oct. 13-15, 2014 | Page 20
Kinetic equations (steady state, one zone)
> Energy losses in continuous limit:
Injection
Energy losses
Escape
b(E)=-E t-1loss
Q(E,t) [GeV-1 cm-3 s-1] injection per time frame (from sep. acc. zone)
N(E,t) [GeV-1 cm-3] particle spectrum including spectral effects
NB: Need N(E) to compute particle interactions
> Simple case: No energy losses b=0:
> Special cases:
 tesc ~ R/c (leaky box)
 tesc ~ E-a . Consequence: N(E) ~ Qinj(E) E-a, Escape: Qesc(E) = N(E)/tesc~ Qinj
(Neutrino spectrum from N(E) can have a break which is not present in
escaping primaries Qesc(E))
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 21
Peculiarity for neutrinos: Secondary cooling
> Secondary spectra (m, p, K) losssteepend above critical energy
Example: GRB
Decay/cooling: charged m, p, K
nm
Pile-up effect
 Flavor ratio!
E‘c depends on particle physics
only (m, t0), and B‘
E‘c
E‘c
Leads to characteristic flavor
composition and shape
E‘c
Spectral
split
Adiabatic
Decouples maximal neutrino and
proton energies
Baerwald, Hümmer, Winter, Astropart. Phys. 35 (2012) 508;
also: Kashti, Waxman, 2005; Lipari et al, 2007
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 22
22
From the source to the detector: UHECR transport
> Kinetic equation for co-moving number density:
Expansion of
Universe
Pair production
Blumenthal, 1970
[here b=-dE/dt=E t-1loss]
Photohadronics
Hümmer, Rüger,
Spanier, Winter, 2010
CR inj.
z-dep!
GZK cutoff
> Energy losses
 UHECR must from
from our local
environment
(~ 1 Gpc at 1010 GeV,
~ 50 Mpc at 1011 GeV)
(M. Bustamante)
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 23
Cosmogenic neutrinos
Cosmogenic neutrinos
EeV
> Prediction depends on
maximal proton energy,
spectral index g, source
evolution, composition
> Can test UHECR beyond the
local environment
Protons
> Can test UHECR injection
independent of CR
production model
 constraints on UHECR
escape
(courtesy M. Bustamante; see also Kotera, Allard, Olinto, JCAP 1010 (2010) 013)
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 24
UHECR transition models
> Transition between Galactic (?) and extragalactic cosmic rays at
different energies:
> Ankle model:
Extragalactic
 Injection index g ~ 2
possible
( Fermi shock acc.)
 Transition at > 4 EeV
> Dip model:
 Injection index
g ~ 2.5-2.7 (how?)
 Transition at ~ 1 EeV
 Characteristic shape
by pair production dip
Figure courtesy M. Bustamante; for a recent review, see Berezinsky, arXiv:1307.4043
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 25
More details: Gamma-ray observables?
> Redshift distribution
~
(1+z)a
> Can be integrated over.
SFR
Total number of bursts in the
observable universe
Threshold correction
 Can be directly determined
(counted)!
 Order 1000 yr-1
(Kistler et al, Astrophys.J. 705 (2009) L104)
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 26
26
Consequence: Local GRB rate
> The local GRB rate can be written as
where fz is a cosmological correction factor:
(for 1000
observable
GRBs per
year and 30%
of all bursts
seen)
(Baerwald, Bustamante, Winter, arXiv:1401.1820)
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 27
Required baryonic loading (analytical)
> Required energy ejected in UHECR per burst:
> In terms of
g-ray energy:
~1.5 to fit UHECR
observations
Fraction of energy
in CR production?
~5-25
How much energy
in UHECR?
Energy in protons
vs. electrons (IceCube def.)
> Baryonic loading fe-1~50-100 for E-2 inj. spectrum (fbol ~ 0.2),
Eg,iso ~ 1053 erg, neutron model (fCR ~ 0.4)
[IceCube standard assumption: fe-1~10]
Walter Winter | UHECR 2014 | Oct. 13-15, 2014 | Page 28

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