supernova remnants @ he francesco giordano university and infn bari gamma 400 workshop
Post on 16-Dec-2015
212 Views
Preview:
TRANSCRIPT
Supernova Remnants
@ HE
Francesco GiordanoUniversity and INFN Bari
Gamma 400 Workshop
Outline
• Why @ HE (Emission Processes) • How Many @ HE (Towards the 1st Catalog)• How Good (Study of systematic errors)• Different Families?• Conclusions
3/5/2013 2F. Giordano @ Gamma 400
A “Typical” SNR SED
33/5/2013 F. Giordano @ Gamma 400
Sync
Fermi Range
Brem
IC on
CMB
0
Scaling the environment density we pass from a p-p dominated SED to a IC dominated
Kep=10-1
Eb=10TeV1=22=4.5B=100uG
nH=100cm-3
nH=1cm-3
Populations
F. Giordano @ Gamma 4003/5/2013 4
pe
pe
pepe
pe
pebr
pepepe
pe
pe
E
E
E
EA
dE
dN,;3
,;3
,;1,;2
,;1
,;
,
0
,,
,
, 1
Synchrotron radiation
F. Giordano @ Gamma 4003/5/2013 5
ece
e
e
dERdE
dN
ccm
BeQ
4
2
3)(
2
3
ωc = 1.5 Bp2/(mc)3
Zirakashvili and Aharonian (2007) A&A 465
IC Scattering
F. Giordano @ Gamma 4003/5/2013 6
sesNKsee
e dEEEEEndEdE
dNEQ ),,()()(
)1(2
)1(21log2
2),,(
222
2
20
q
qqqqqq
EE
rEEE e
esesNK
1exp)(
15)(
2
4
kT
EE
kT
UEn
s
ss
• U = 0.26 eV/cm3 • T = 2.73 K
Stuner et al. (1997) ApJ 490
Cosmic Microwave Background
We used the following expression for the number density of CMB photon as a function of energy (blackbody photon distribution):
1exp)(
15)(
2
4
kT
EE
kT
UEn
t
tt
][ 31 cmeV
where: • k is the Boltzmann
constant and T = 2.73 K;
• The parameter U represents the energy density of CMB photons and it is equal to 0.26 eV cm-3 .If we integrate over all values
of energy we obtain the value of the number density:
3411)( cmEdEnn tt
F. Giordano @ Gamma 4003/5/2013 7
F. Giordano @ Gamma 4003/5/2013 8
Bremsstrahlung yield
eHB
e
eH dE
d
d
dE
dNnQ
4)(
Bethe-Heitler ultra-relativistic Cross Section
2
12log
3
214
220
r
d
d f
Density of environment
𝜀=𝐸𝛾/𝑚𝑒𝑐2
Baring et al. (2000) ApJ 528
F. Giordano @ Gamma 4003/5/2013 9
Xpp 0
pp
p
pH dE
Ed
EEd
EdE
dNnc
EQ)log(
)/(14)(
p-p interactions via 0 decay
Parameterization proposed by Kamae et al 2006
Cygnus LoopVela JrTycho CTB37A
Fermi-Detected SNRs
13 identified SNRs: - 9 interacting - 4 young SNRs
counts3/5/2013 F. Giordano @ Gamma 400 10
Detection of the p0-decay bump in SNRs
IC 443 and W44 are the two brightest SNRs in the Fermi-LAT range
• The low energy break is very significant (~19σ and ~21σ for 60 MeV E 2 GeV);
•This gives unambiguous and robust detection of the pion decay bump
•and clear proof that these SNRs accelerate protons.
M. Ackermann et al. 2013
3/5/2013 11F. Giordano @ Gamma 400
+ 43 2FGL candidates, excluding spatial associations with PSRs, PWN, AGN
counts
Fermi-Detected SNRs
13 identified SNRs: - 9 interacting - 4 young SNRs
3/5/2013 F. Giordano @ Gamma 400 12
SNR Catalog:
To better understand SNRs in a statistically significant
manner within a MW context we:
● characterize the spatial and spectral morphology
of all regions containing known SNRs.● examine multi-wavelength (MW) correlation,
including spectrum + morphology for radio, X-ray,
and TeV and CO, maser, IR, … ● determine statistically significant SNR
classification(s) and perform spectral modeling
3/5/2013 13F. Giordano @ Gamma 400
Data Set:• 3 years of
P7SOURCE_V6 LAT data• E: 1-100 GeV• Region Of Interest: 10°
around each SNR
Green’s Catalog (2009):• 274+5 SNRs
Starting Model:
• 2FGL
Overlapping sources?• = None: Add a new extended source• = 1 source (not PSR): Replace w
extended source• > 1 source: Replace (non-PSR) source
closest to radio centroid w extended source. Delete all other (non-PSR) sources.
Localize source, fit extension• Disk extension seed = radio size• Spectral model: power law• Normalization of Galactic diffuse
and all sources w/in 5o of candidate are free during minimization procedure.
Output:• Position, extension, significance• Spectral energy distribution• Region and residual maps• Diagnostics
Characterize GeV Emission:Analysis Procedure
Identifying SNRs via extension:If a SNR’s spatial extension is larger than Fermi’s PSF, we can detect its size, helping to positively identify it.
3/5/2013 F. Giordano @ Gamma 400 14
SNR Catalog:
● Fermi-LAT has the ability to spatially resolve a large number of the 279 known SNRs assuming their GeV and radio sizes are similar.
3/5/2013 15F. Giordano @ Gamma 400
SNR Catalog:
● Fermi-LAT has the ability to spatially resolve a large number of the 279 known SNRs assuming their GeV and radio sizes are similar.
● Spatial extension measured for 15 SNRs, 6 of which are new candidates, permitting clear identification.
3/5/2013 16F. Giordano @ Gamma 400
Systematic Error Study
To explore systematic uncertainties related to the choice of the Interstellar Emission Model (IEM), we localized and fit 8 representative candidate SNRs using alternative IEMs.The eight remnants are a combination of hard and soft and point-like (x) and extended (o) sources and they are located in regions with different intensities of the IEM.
3/5/2013 17F. Giordano @ Gamma 400
Alternative IEMs
They are build using GALPROP with input parameters set as:
• HI spin temperature =[150K and optically thin],
• CR source distribution =[SNR and Lorimer],
• Halo height = [4 kpc and 10 kpc],
and then fit to the data.
The HI and CO emission split into 4 Galactocentric rings and the inverse Compton emission are fit simultaneously with the source of interest.
Warning:
• these 8 models do not span the complete uncertainty of the systematics.
• the method for creating this model differs from that used to create the official Fermi-LAT interstellar emission model, so these 8 models do not bracket the official model. 3/5/2013 18F. Giordano @ Gamma 400
Systematic Error Study
Our automated analysis finds a softer index and a much larger flux for SNR347.3-0.5 (RX J1713) than that obtained in a dedicated analysis. [Abdo et al. 2010] Since the best fit radius (0.8o ) is larger than the dedicated analysis’ (0.55o ), the disk encompasses nearby sources that are not in the model. This make it softer than the more accurate analysis.
SNR candidates' flux and index averaged over the alternative IEMs' solutions, compared to the standard (STD) model result.
PRELIMINARY PRELIMINARY
Flux: Index:
SNRs:
3/5/2013 19F. Giordano @ Gamma 400
End of slide show
Radio synchrotron emission indicates the presence of relativistic leptons.LAT-detected SNRs tend to be radio-bright:
● Interacting SNRs: general correlation suggests a physical link
● Young SNRs show more scatter
Radio-GeV Correlation?
upper limits (i=2.5, 99%)
3/5/2013 20F. Giordano @ Gamma 400
p0 decay or e+/- brem.
inverse Compton
● Young SNRs: seem consistent
● Others, including interacting SNRs: softer than expected
Data now challenge model assumptions!
● Underlying particle populations may have different indices.
● Emitting particle populations may not follow a power law: breaks?
● Multiple emission zones?
Radio-GeV Index
If radio and GeV emission arise from the same particle population(s), under simple assumptions, the GeV and radio indices should be correlated:
=2a+1
=a+1
213/5/2013 F. Giordano @ Gamma 400
Break region
Fermi IACT
EE
2dN
/dE
IC 443
IC 443 SED
1 TeV1 GeV
GeV-TeV Index
• Indication of break at TeV energies• Caveat: TeV sources are not uniformly surveyed.3/5/2013 22F. Giordano @ Gamma 400
E
RX J1713-3946
RX J1713-3946 SED
1 TeV1 GeV
Fermi IACT
GeV-TeV Index
E2dN
/dE
Break region
• Indication of break at TeV energies• Caveat: TeV sources are not uniformly surveyed.3/5/2013 23F. Giordano @ Gamma 400
Interacting SNRs tend to be more luminous than young SNRs.
Young SNRs:• Low Lg evolving
into low density medium?
Interacting SNRs:• Higher Lg
encountering higher densities?
Environment?
3/5/2013 24F. Giordano @ Gamma 400
Young SNRs tend to be harder than older, interacting SNRs.
Or Evolution?
Due to• decreasing shock
speed allowing greater particle escape?
• decreasing maximum acceleration energy as SNRs age?
3/5/2013 25F. Giordano @ Gamma 400
May a simple simulation help???
F. Giordano @ Gamma 4003/5/2013 26
=4.5
Particle injection
F. Giordano @ Gamma 400 273/5/2013
=4.5
Particle injection
0 -> SEDs
F. Giordano @ Gamma 4003/5/2013 28
=4.5
Particle injection
1
Conclusions
• Our systematic study has identified a statistically significant population of Galactic SNRs, including:
– 6 new extended and >25 pointlike SNR candidates,– evidence for at least 2 SNRs’ classes: young and interacting.
• Combining GeV and MW observations suggests that:– some SNRs' emitting particle populations may be linked,– simple model assumptions are no longer sufficient, allowing
more complex models to be tested.• Improved observations and modeling will give us greater
insight into SNRs, their acceleration mechanisms and their accelerated particles.
• Accurately estimating SNRs’ aggregate particle acceleration mechanisms will also allow us to better quantify SNRs’ capability to produce the observed CRs.
3/5/2013 29F. Giordano @ Gamma 400
top related