FERMI
Gamma-ray Space Telescope
Sources in the solar system
observed by the Fermi Large
Area Telescope
N.Giglietto
(INFN and Politecnico of Bari)
on behalf of the FERMI LAT Collaboration
Sources in Solar System



Sources:
• The Moon
• The Sun (quiet and/or flaring)
• The Earth
Potential Sources
Asteroids in different populations:
 Main Asteroid Belt (MBAs)
 Jovian and Neptunian Trojans (Trojans)
 Kuiper Belt Objects (KBOs)
Other planets

Debris (< few meter size, dust, grains) MBAs, Trojans,
KBOs Oort Cloud
2
N.Giglietto – TevPA 2009
Solar system objects observation interest
•
•
•
•
Moon gamma ray emission depends by the nuclei
CR flux intensity on surface
Quiet solar gamma ray emission depends mainly
by the electron flux interactions in the photosphere
(IC) and the nuclei CR interactions inside the Sun
Therefore the gamma ray emission studies are a
sensible probe for CR fluxes in the solar system
Gamma ray flux measurements during the entire
solar cycle will be very important!
3
N.Giglietto – TevPA 2009
Solar System observation
capabilities with Fermi


Solar Activity expected to peak around 2012
Fermi will operate for nearly the entire duration of
solar cycle 24
4
N.Giglietto – TevPA 2009
Solar System observation
capabilities with Fermi (2)





Fermi is the only satellite capable of making solar
observations >100 MeV
Coordinated mesurements between LAT gamma-ray and GBM
(10 keV-40 MeV)
Comparison with RHESSI (1 keV –20 MeV)
Comparison with energetic solar particle observations (ACE,
STEREO, SOHO, WIND) and ground based experiments
(Milagro) for flaring Sun alerts
About ten high-energy flares expected during the FERMI
operation period
5
N.Giglietto – TevPA 2009
Emission mechanism

“γ-ray albedo” due to CR interactions
with surface material:

Moon rock (solid)

Solar atmosphere (gaseous)
Moon g-ray emission:



CR
γ-rays produced by p0
decays produced in hadronic showers
γ
we expect lunar limb brighter then
central disk
γ-ray spectrum should be soft
Similar emission mechanism for any solid
object in solar system
6
N.Giglietto – TevPA 2009
Sun: second component
Inverse Compton Scattering
e
e
©UCAR
Inverse-Compton scattering of solar photons in the
heliosphere by Galactic CR electrons: the emission is
predicted to be extended and the spectrum hard
•Electrons are isotropic
Moskalenko ’06
•Photons have a radial angular distribution
N.Giglietto – TevPA 2009Orlando&Strong’08
7
Fermi: the Sun track in the sky
8
N.Giglietto – TevPA 2009
Variability: a 3 months look (north-south
galactic emisphere)
SUN
path
E>100MeV, poles view, 1day time interval,
extreme sensitivity to fluxN.Giglietto
variations
– TevPA 2009
9
Data selection

Data from Aug 2, 2008 until March 1, 2009

Analysis in celestial relative coordinates
(Moon and Sun centered data)








SUN is moving about 1°/day
MOON is moving about 15°/day
E > 100MeV
Zenith angle < 105° (to avoid the Earth limb)
Galactic Plane Cut (>30°)
Moon-Sun angular separation >20°
ROI: 10°
True/Fake source comparison
10
N.Giglietto – TevPA 2009
Background estimation approach
The “fake” source method:
 A fake source follow the path of the real source but 30 degrees away
(passes through the same areas on the sky but at different times)
N.Giglietto – Vulcano workshop
2009
N.Giglietto
– TevPA 2009
11
The Moon: first 7 months
Moon count map and
projections in RA and DEC
axes centered on Moon
position.
E>100MeV
0.2deg/bin
gaussian smothed
N.Giglietto – TevPA 2009
12
12
The Quiet Sun: first 7 months
Sun count map and projections
in RA and DEC axes centered
on Sun position.
E>100MeV
0.2deg/bin
gaussian smothed
N.Giglietto – Vulcano workshop
2009
N.Giglietto – TevPA 2009
13
13
Moon
Spectra
- lower solar activity
(upper solid line)
- hight solar activity
(lower solid line)
Data: EGRET
Pion decay
limb (outer 5’)
center (inner 20”)
of the Moon disk
Moskalenko
&Porter’07
Flux (E>100MeV) = (1.06 +/- 0.20) x 10-6 ph cm-2 s-1
(statistical + 20% systematic error)
N.Giglietto – TevPA 2009
14
The Sun: spectra
Sun Spectrum:
•Red Point from
Unfolding
(statistical error only)
•Fit with a PL
in the energy range
100MeV < E < 10GeV
Spectral Index: -2.25
+/- 0.03
Flux(E>100MeV)= (4.6 +/- 0.9) x 10-7 ph cm-2 s-1
(statistical + 20% systematic error)
15
N.Giglietto – TevPA 2009
Sun and Moon spectra:
a comparison
Moon and Sun
Spectra
Compared
16
N.Giglietto – TevPA 2009
Sun: the flux
P6V3 IRFs
Fermi
Expected (total disk+IC)
(Moskalenko ’06
Orlando&Strong ’07)
Flux
(x 10-7 ph cm-2 s-1)
(E>100MeV) = 4.59 +/- 0.89
F(E>100 MeV) = 4.30
(@ solar min)
not observed by EGRET
(Thompson ’97)
EGRET Flux
(>100MeV) = 4.44±2.03
Reanalysis by
Orlando&Strong’08
17
N.Giglietto – TevPA 2009
Conclusions





During the first months of data taking Fermi has
observed the quiet Sun and the Moon emission
Preliminary Spectra and Fluxes has been reported
for both sources
Fermi will follow both the Moon and Sun emission
during the entire solar cycle
The Fermi preliminary results are consistent with
predictions at solar minimum activity
Fermi ready to detect high energy Solar Flares!
18
N.Giglietto – TevPA 2009
Fermi/LAT performance
(update in progress)
Energy Resolution: ~10% (~5% off-axis)
PSF (68%) at 100 MeV ~ 5o
PSF (68%) at 1 GeV ~ 0.6°
PSF (68%) at 10 GeV ~ 0.1o
Field Of View: 2.4 sr
Point Source sens. (>100 MeV): 3x10-9 cm-2 s-1
19
N.Giglietto – TevPA 2009