Transcript Propagation of Cosmic Rays & Diffuse Galactic Gamma Rays

Uncertainties in the determination of
the diffuse Galactic -ray emission
Igor V. Moskalenko (Stanford)
with
Seth Digel (SLAC)
Troy Porter (LSU)
Olaf Reimer (Stanford)
Andrew W. Strong (MPE)
GLAST LAT Project
Diffuse Galactic Gamma-ray Emission
~80% of total Milky Way luminosity at HE !!!
Tracer of CR (p, e−) interactions in the ISM (π0,IC,bremss):
o
o
o
o
Study of CR species in distant locations (spectra & intensities)
 CR acceleration (SNRs, pulsars etc.) and propagation
Emission from local clouds → local CR spectra
 CR variations, Solar modulation
May contain signatures of exotic physics (dark matter etc.)
 Cosmology, SUSY, hints for accelerator experiments
Background for point sources (positions, low latitude sources…)
Besides:
o
o
Foreground in studies of the extragalactic diffuse emission
Extragalactic diffuse emission (blazars ?) may contain signatures
of exotic physics (dark matter, BH evaporation etc.)
Calculation requires knowledge of CR (p,e) spectra in the entire Galaxy
Igor V. Moskalenko 2
February 23, 2006
DM’06/UCLA
Conventional model vs EGRET data
GLAST LAT Project
Conventional model
consistent with local
p,e spectra exhibits
the “GeV excess:” a
factor ~2
4a-f
Igor V. Moskalenko 3
February 23, 2006
DM’06/UCLA
Systematics of the Unknowns
GLAST LAT Project
Defense Secretary Donald Rumsfeld’s classification:
“…we know, there are known knowns; there are things we know we
know. We also know there are known unknowns; that is to say we
know there are some things we do not know. But there are also
unknown unknowns - the ones we don't know we don't know.”
• EGRET calibration & systematics

• Data handling
• Components of the Galactic propagation model
Igor V. Moskalenko 4
February 23, 2006
DM’06/UCLA
EGRET telescope
GLAST LAT Project
Mass : 1830 kg
Size
: 2.25m / 1.65m 
DE/E : ~ 25 %
Sensitivity
Apr 1991 – Jun 2000
(mainly off in the last years of CGRO)
Igor V. Moskalenko 5
: ~ 5 x 10-8 cm-2 s-1 (> 100 MeV, 106 s)
Time resolution: 0.1 ms
FoV
: ~ 0.5 sr (PSF: 6 above 100 MeV)
Source loc acc : 0.1° ... 1°, PSRs: arcmin
February 23, 2006
DM’06/UCLA
Exposure Map & Photon Counts (P1-4)
GLAST LAT Project
90
70
EGRET performed pointed
observations
30
10
-10
<- exposure: P1-4, <30° off-axis angle
-30
-50
-70
-90
180 160 140 120 100
80
60
40
20
0 340 320 300 280 260 240 220 200 180
90
Galactic Longitude
70
<- intensity:
exposure
corrected photons
50
Galactic Latitude
30
10
-10
-30
-50
-70
-90
180 160 140 120 100 80
60
40
90
20
0 340 320 300 280 260 240 220 200 180
70
Galactic Longitude
Diffuse emission model (GALDIF:
Hunter et al. 1997): dynamic balanceCR density ~ gas density
50
Galactic Latitude
Galactic Latitude
50
30
10
-10
-30
-50
-70
-90
180 160 140 120 100
Igor V. Moskalenko 6
February 23, 2006
80
60
40
20
0 340 320 300 280 260 240 220 200 180
Galactic Longitude
DM’06/UCLA
Spark chamber efficiency vs. time
GLAST LAT Project
Each pointed observation has been corrected for the varying spark
chamber performance (standard candles /diffuse emission !!!)
-> systematic uncertainties in high end data products
-> implicit dependencies in t and E introduced
1st gas refill
3rd gas
refill
2nd gas
refill
partial
refill
partial refill
Sc B failure
last partial
refill
100%
in-flight
100%
corrected
P1-4
Igor V. Moskalenko 7
February 23, 2006
DM’06/UCLA
GLAST LAT Project
Spark chamber efficiency vs. energy & time
- functional expressions
fitted in order to
describe the varying
performance of the
EGRET spark chamber
- assumed to be
qualitatively the same in
the 10 energy bands
-> implicit dependencies
resulting in systematic
uncertainties, here
particularly in source &
diffuse emission spectra
Igor V. Moskalenko 8
P1-4
February 23, 2006
DM’06/UCLA
GLAST LAT Project
Other Corrections
Other corrections resulting in systematic uncertainties
in EGRET measurements:
-> qualitative event classification (A, B, or C) during spark
chamber track reconstruction (different response functions)
-> corrections for distortions under large incident angles (fisheye)
-> earth albedo cut (contaminations) as function of energy and
vector to earth from instrumental pointing axis
-> point source detections (and removal):
-> non-gaussian tails in psf -> narrow/wide field psf
-> residuals/artefacts in the diffuse maps
-> different detection thresholds…
-> different operation modes (wide, narrow, strip modes)
DON’T FORGET: SATELLITE BASED GAMMA-RAY
ASTROMOMY IS (BESIDES ALL SYSTEMATICS)
PHOTON LIMITED !
Igor V. Moskalenko 9
February 23, 2006
DM’06/UCLA
Model comparison with data
GLAST LAT Project
Convolution with EGRET PSF:
 Important below 1 GeV
 A large effect at low energies especially in
latitude affecting the overall spectral shape
 Convolution itself is model dependent depends on spectrum, not fully accounted for
Spectral response: 10% effect
Igor V. Moskalenko 10
February 23, 2006
DM’06/UCLA
GLAST LAT Project
Effect of Convolution: 70-100 MeV
Longitude profile |b|<5
Unconvolved
Igor V. Moskalenko 11
February 23, 2006
Convolved
DM’06/UCLA
GLAST LAT Project
Effect of De-Convolution: Spectrum |l|<30 |b|<5
“Convolved data”
De-convolved
NB here the spatial convolution correction
is applied to the DATA based on the model.
Hence the DATA changes, not the model
(procedure appropriate for spectra)
Igor V. Moskalenko 12
February 23, 2006
DM’06/UCLA
GLAST LAT Project
Effect of the Energy Dispersion
Dispersion 40% → Effect ~10%
Beam calibration
% FWHM
~10%
<D>~25%
Corrected
EGRET Calibration
(Thompson etal 1993)
1 GeV
E, MeV
<D>~25% → ~5% effect
on spectrum, but it is
energy dependent !
Diffuse emission
Energy
Igor V. Moskalenko 13
February 23, 2006
DM’06/UCLA
GLAST LAT Project
CR Interactions in the Interstellar Medium
SNR RX J1713-3946
42 sigma (2003+2004 data)
ISM
X,γ
+
e-
B
P diffusion
He energy losses
CNO
reacceleration
+
convection e etc. π +-
IC
ISRF
gas
π0
GLAST
gas
_
P
+
π- p
LiBeB
He
CNO
+
e-
Flux
PSF
HESS
Preliminary
Chandra
20 GeV/n
BESS
PAMELA
Igor V. Moskalenko 14
AMS
helio-modulation
February 23, 2006
ACE
CR species:
 Only 1 location
 modulation
DM’06/UCLA
GLAST LAT Project
What it takes to model CR propagation in the Galaxy
 Gas distribution (energy losses, π0, brems)
 Interstellar radiation field (IC, e± energy losses)
 Nuclear & particle production cross sections
 Gamma-ray production: brems, IC, π0
 Energy losses: ionization, Coulomb, brems, IC, synch
 Assume propagation model (Dxx, Dp, Va)
 Source distribution & injection spectra
 Solve transport equations for all CR species
 Fix propagation parameters
Igor V. Moskalenko 15
February 23, 2006
DM’06/UCLA
GLAST LAT Project
How It Works: Fixing Propagation Parameters
E2 Flux
B/C
Carbon
Radioactive isotopes:
Galactic halo size Zh
Ek, GeV/nucleon
Be10/Be9
Ek, MeV/nucleon
Using secondary/primary nuclei ratio & flux:
•Diffusion coefficient and its index
•Propagation mode and its parameters (e.g.,
reacceleration VA, convection Vz)
Zh increase
Ek, MeV/nucleon
Igor V. Moskalenko 16
February 23, 2006
DM’06/UCLA
GLAST LAT Project
Effect of Cross Sections: Radioactive Secondaries
Different size from different ratios…
Has a direct impact on the propagation parameters
27Al+p26Al
T1/2=?
W
ST
ST
natSi+p26Al
W
Zhalo,kp
c
Ek, MeV/nucleon
Igor V. Moskalenko 17
• Errors in CR measurements (HE & LE)
• Errors in production cross sections
• Errors in the lifetime estimates
• Different origin of elements (Local Bubble ?)
February 23, 2006
DM’06/UCLA
GLAST LAT Project
Peak in the Secondary/Primary Ratio
• Leaky-box model:
fitting path-length distribution -> free function
• Diffusion models:
 Diffusive reacceleration
 Convection
 Damping of interstellar turbulence
 Etc.
B/C
Ek, MeV/nucleon
too
sharp
max?
Igor V. Moskalenko 18
Accurate measurements in a wide energy range
may help to distinguish between the models
February 23, 2006
DM’06/UCLA
GLAST LAT Project
Distributed Stochastic Reacceleration
Simon et al. 1986
Seo & Ptuskin 1994
Scattering on
magnetic turbulences
Dpp~ p2Va2/D
D ~ vR1/3 - Kolmogorov spectrum
Icr
B
1/3
ΔE
Fermi 2-nd order mechanism
Dxx = 5.2x1028 (R/3 GV)1/3cm-2 s-1
Va = 36 km s-1
γ ~ R-δ, δ=1.8/2.4 below/above 4 GV
Igor V. Moskalenko 19
February 23, 2006
strong
reacceleration
weak
reacceleration
E
DM’06/UCLA
GLAST LAT Project
Convection
Galactic wind
Jones 1979
Escape length
Xe
v
wind or
turbulent
diffusion
D~R0.6
R-0.6
resonant
diffusion
E
problem: too broad sec/prim peak
Dxx = 2.5x1028 (R/4 GV)0.6cm-2 s-1
dV/dz = 10 km s-1 kpc-1
γ ~ R-δ, δ=2.46/2.16 below/above 20 GV
Igor V. Moskalenko 20
February 23, 2006
DM’06/UCLA
GLAST LAT Project
Distribution of interstellar gas
•
Neutral interstellar medium – most of the interstellar gas mass
– 21-cm H I spin flip & 2.6-mm CO (standing for H2)
(25°, 0°)
CO
Dame et al.
(1987)
G.C.
HI
outside
solar circle
within solar circle
Hartmann &
Burton (1997)
W. Keel
• Differential rotation of the Milky Way – plus random motions,
streaming, and internal velocity dispersions – is largely
responsible for the spectrum
• This is the best – but far from perfect – distance measure
available
• Self-absorption of HI (21cm) and optical depth effects…
Igor V. Moskalenko 21
February 23, 2006
DM’06/UCLA
GLAST LAT Project
Limitations of velocity as distance measure
• For Clemens (1985) rotation curve
V(R), the pattern of line-of-sight
velocities (shown from above with
dashed lines indicating different
Galactic longitudes viewed from the
sun)
– Contour interval is 20 km s-1
– This is ~ internal velocity
dispersion of a large interstellar
cloud
• In the inner Galaxy, the velocitydistance relation is double valued
• Near the center and anticenter, the
velocity is ~0 for all R
• In the outer Galaxy the gradient of
velocity with distance approaches 0 at
large R
Igor V. Moskalenko 22
February 23, 2006
Line of Sight Velocities from
Differential Rotation of the Milky Way
DM’06/UCLA
GLAST LAT Project
Overall distribution of interstellar gas
• No unique answer – owing to distance ambiguity,
choice of rotation curve, streaming motions,
radiative transfer, …
Hunter et al. (1997)
Two studies that
started with
essentially the
same data
disagree in
many details
Pohl & Esposito (1998)
Sun
Galactic Center
Igor V. Moskalenko 23
February 23, 2006
Strong & Moskalenko
DM’06/UCLA
GLAST LAT Project
Deriving the SNR distribution
Case & Bhattacharya
+
+
=
Milky Way
Igor V. Moskalenko 24
February 23, 2006
DM’06/UCLA
GLAST LAT Project
Injection Spectra (p, e)
HESS RX1713
|| 2
Hydro-simulation of particle
acceleration in SNRs
||>2
Ellison etal 2004
“Model dependent”
Igor V. Moskalenko 25
February 23, 2006
DM’06/UCLA
GLAST LAT Project
0-production cross section: Dermer’s 1986 recipe
Stecker’s Δ-isobar model @LE
SB scaling model @HE
Interpolation
in between
BUT:
The data of
1960’s have
large syst.
errors
Interpolation
may produce
error
Igor V. Moskalenko 26
February 23, 2006
DM’06/UCLA
GLAST LAT Project
Electron Fluctuations/SNR stochastic events
GeV electrons
100 TeV electrons
E(dE/dt)-1,yr
GALPROP/Credit S.Swordy
107 yr
6
10 yr
Electron energy loss timescale:
1 TeV: ~300 kyr
100 TeV: ~3 kyr
Energy losses
Bremsstrahlung
Ionization
IC, synchrotron
Coulomb
1
GeV
1 TeV
Ekin, GeV
Igor V. Moskalenko 27
February 23, 2006
DM’06/UCLA
GLAST LAT Project
Interstellar Radiation Field
• Target for CR leptons (IC)
• Energy losses
Local ISRF
Systematic uncertainty
Optical
IR
Model components:
 Geometrical: disk, ring, halo, bar, triaxial bulge,
arms
 87 stellar types (main sequence), AGB & exotics
 Dust: silicate, graphite, PAH (5Å – few m)
 Absorbed light gives mid-IR (small grains +PAH)
and FIR (~0.1-1 m grains)
Systematic errors:
Star distribution –star counts
Grain properties –lab measurements
Gas/dust proportion –extinction
curve
“Reasonable parameters”
Compare with ISRF data only at R
Igor V. Moskalenko 28
(PS05)
February 23, 2006
Scatt.opt.
R=0
PAH
SMR00
PS05
4 kpc
12 kpc
16kpc
DM’06/UCLA
GLAST LAT Project
Heliospheric Modulation & Charge Sign Effect
Bieber etal 1999
A<0
pbar
Parker’s Equation:
Convection, gradient &
curvature drifts, diffusion,
adiabatic energy changes +
diffusion tensor (K, Kr,
K)
pbar/p
pbar/p
p
M. etal 2002
pbar/p
e/p (2.5 GV)
A>0
Igor V. Moskalenko 29
February 23, 2006
Ferreira etal 2003
DM’06/UCLA
GLAST LAT Project
More Effects: Local Environment
Local Bubble:
A hole in the interstellar gas is formed in a
series of SN explosions; some shocks may still
exist there…
May be important for radioactive CR species,
but Dxx=?
Sun
Sun
~200pc
Regular Galactic magnetic field
may establish preferential
directions of CR propagation
GC
Igor V. Moskalenko 30
February 23, 2006
DM’06/UCLA
Consistency Check
GLAST LAT Project
Every model has to be checked
back to be consistent with all
kinds of data (CR, astrophysics,
nuclear physics)
 Finally gamma rays
Igor V. Moskalenko 31
February 23, 2006
DM’06/UCLA
Conventional model vs EGRET data
GLAST LAT Project
Taking into
account all the
uncertainties –
remarkable
agreement !!!
Conventional model
consistent with local
p,e spectra exhibits
the “GeV excess:” a
factor ~2
4a-f
Igor V. Moskalenko 32
February 23, 2006
DM’06/UCLA
Optimized Model (CR variations)
Inner Galaxy:
l=330°-30°,|b|<5°
l=40°-100°,|b|<5°
Intermediate latitudes:
l=0°-360°,10°<|b|<20°
GLAST LAT Project
Outer Galaxy:
l=90°-270°,|b|<10°
Intermediate latitudes:
l=0°-360°,20°<|b|<60°
Milagro
Igor V. Moskalenko 33
February 23, 2006
DM’06/UCLA
Conclusion
GLAST LAT Project
• The systematic effects are numerous
(data, astrophysical input, models)
• Not all of them are equally important
• May contain “unknown unknowns”
• Errors are hard to estimate
• The effects are energy-dependent &
intrinsically inseparable
• GLAST will do better!
What to do:
• Exercise caution and apply
consistency checks where possible
Igor V. Moskalenko 34
February 23, 2006
DM’06/UCLA
GLAST LAT Project
Thank you !
Igor V. Moskalenko 35
February 23, 2006
DM’06/UCLA