Diffuse Galactic Emission
Jean-Marc Casandjian, CEA Saclay
For 90% of you: a nuisance
For the rest: a great tool to study the ISM, CRs and ISRF
Thursday, March 26, 2015
counts per 0.25 degree pixel
sqrt color scaling
E > 50 MeV
x19
E > 50 MeV
x17
1972
1975
11,762 events
E > 50 MeV
x6
198,327 events
E > 50 MeV
x37
1991
E > 50 MeV
2008
1,151,662 events
E > 50 MeV
E > 360 MeV
43,109,003 events
E > 50 MeV
diffuse ~60%
NASA High Energy Astrophysics Science Archive Research Center (HEASARC)
Gamma 2012
Thursday, March 26, 2015
2
Jean-Marc Casandjian
All that glitters is not gold !
Comptel
E = 1-30 MeV
RXTE-PCA E=3-20 keV
http://www.mpe.mpg.de/~aws/comptel/aws/skymos/skymos.html
INTEGRAL-SPI
E = 27-600 keV
Revnivtsev et al., 2004, A&A 418, 927-936
DIRBE, 1.25, 2.2, 3.5 μm
27-49 keV
49-90 keV
L. Bouchet et al., ApJ. 2011, 739,29
Diffuse emission similar to near-IR distribution, X-ray emission of
unresolved sources, not from interstellar origin.
100-200 keV
Thursday, March 26, 2015
200-600 keV
Processes for HE γ production
Thursday, March 26, 2015
Thursday, March 26, 2015
CR flux
HI emissivity
pi0
bremss
Electron
Helium
Proton
preliminary
pc
E
Thursday, March 26, 2015
preliminary
Thursday, March 26, 2015
The shape of the structures
within 10o of the GC depends on
inner gas emissivity within 1.5
kpc of the center and on the
model for the intensity.
residuals in
E > 1.7 GeV
residuals in
with sources
and
An enhanced emission within
few degrees to the GC, possibly
linked to the bubbles, is
observed
residuals in
with sources
The Fermi bubbles seem to have
a catenary shape approximately
pointing toward the GC
residuals in %
residuals with and without
preliminary
Catenary shape :
(South)
(North)
Thursday, March 26, 2015
Fermi vs ROSAT
casandjian arXiv:1502.07210
Thursday, March 26, 2015
At LAT energies ..
Bremsstrahlung cross-section
Hadronic Interaction cross-section
IC cross-section
E2 x Ncr x sigma
E2 x Ncr x sigma
proton
range
electron
range
electron
range
LAT range
Thursday, March 26, 2015
LAT range
LAT range
At ASTROGAM energies ..
Bremsstrahlung cross-section
Hadronic Interaction cross-section
E2 x Ncr x sigma
E2 x Ncr x sigma
IC cross-section
electron
range
proton
range
electron
range
ASTROGAM range
Thursday, March 26, 2015
ASTROGAM range
ASTROGAM range
Spectrum of low energy diffuse emission
Galprop
Fermi-LAT
Comptel
SPI
IC
pi0
total diffuse
diffuse emission
diffuse continuum
SPI
positronium
unresolved sources
bremsstrahlung
A. Strong, Cosmic Rays for Particle and Astroparticle 2011
Physics. arXiv:1101.1381
Thursday, March 26, 2015
L. Bouchet et al., ApJ. 2011, 739,29
Comptel vs Fermi
Comptel 1- 30 MeV, linear scaling
http://www.mpe.mpg.de/~aws/comptel/aws/skymos/skymos.html
Fermi-LAT counts, E=30-50 MeV, sqrt scaling
Thursday, March 26, 2015
Fermi-LAT counts minus sources
E=30-50 MeV, sqrt scaling
p and He flux from a fit to emissivities and PAMELA
proton spectral index
p spectral index
Systematics are not included in the error bars
-2.2
Proton spectral index
-2.3
preliminary
-2.4
-2.5
-2.6
Galprop
-2.7
-2.8
-2.9
-3
-3.1
0
5
10
15
20
25
30
Galactocentric distance (kpc)
p density above 10 GeV
Galactocentric distance (kpc)
preliminary
Integrated proton flux above 10 GeV
preliminary
Galprop
Galactocentric distance (kpc)
Thursday, March 26, 2015
Tentative of diffuse model at ~40 MeV
(possibly wrong !!)
Diffuse after 6 years of ASTROGAM survey
Fermi
Aeff = 65 cm2, PSF 68% = 9 deg
Estimated diffuse (interstellar+iso)
counts map for 0.25 deg pixel
30-50 MeV, 6 years
ASTROGAM “pair”
Aeff = 302 cm2, PSF FWHM = 4 deg
Thursday, March 26, 2015
ASTROGAM “Compton”
Aeff = 302 cm2, PSF FWHM = 0.7 deg
Conclusions
For 90% of you: diffuse emission is a great tool to study the
ISM, CRs and ISRF.
We did learn a lot about ISM and CRs with Fermi.
ASTROGAM should give us access to the electrons
and positions density in the local and outer Galaxy
and clouds.
It should be possible to model the diffuse emission
for point-source extraction.
Observation of extended structure toward the
inner Galaxy will be strongly affected by a strong IC
that is very difficult to model.
Thursday, March 26, 2015