High Energy Studies of
Collaborators:
D. Castro
S. Funk
J. Gelfand
T. Temim
D. Foight
J.P. Hughes
M. Lemoine-Goumard
R. Rousseau
B. Gaensler
and others…
Evolved Pulsar Wind Nebulae
Patrick Slane (CfA)
2011 AAS Summer Meeting, Boston, MA
Evolution of PWN Structure
• PWN expands within SNR as it
sweeps up ejecta
- eventually, SNR reverse shock
reaches PWN and halts expansion
• X-ray observations provide
ambient density estimates
- connect to age, energetics
• Magnetic field in PWN decreases
dramatically during adiabatic
expansion
• Upon RS interaction, PWN is
compressed and magnetic field
is increased
- high energy particles burn off
rapidly
- PWN is disrupted, often dramatically
CMB
synchrotron
Patrick Slane (CfA)
inverse
Compton
2011 AAS Summer Meeting, Boston, MA
Evolution of PWN Emission
Spitkovsky 2008
1000 yr
2000 yr
5000 yr
• Injected spectrum is expected to be
Maxwellian w/ nonthermal tail
- note that Maxwellian has never been
definitively detected
• Emax and fraction of energy in PL
likely to vary within PWN
Patrick Slane (CfA)
• Energetic electrons produce synchrotron
emission in X-ray band, and IC emission
in g-ray band
• Note that X-ray emission decreases
with time, while g-ray emission increases
CMB
synchrotron
inverse
Compton
2011 AAS Summer Meeting, Boston, MA
From Young to Old
Patrick Slane (CfA)
2011 AAS Summer Meeting, Boston, MA
HESS J1640-465
Slane et al. 2010
• Composite SNR in late evolution
• PWN model with evolved power
law electron spectrum fits X-ray
and TeV emission, but not GeV
Patrick Slane (CfA)
2011 AAS Summer Meeting, Boston, MA
HESS J1640-465
Slane et al. 2010
• Composite SNR in late evolution
• PWN model with evolved power
law electron spectrum fits X-ray
and TeV emission, but not GeV
• Modifying low-energy electron
spectrum by adding Maxwellian
produces GeV IC emission
- similar to results from Vela X
- possible evidence of long-sought
Maxwellian component expected from
shock acceleration models
Patrick Slane (CfA)
2011 AAS Summer Meeting, Boston, MA
MSH 11-62
• Radio observations reveal shell with
bright, flat-spectrum nebula in center
- no pulsar known, but surely a PWN
• Distance not well known, but ≈5 kpc
- R ≈ 10.6 pc
Patrick Slane (CfA)
2011 AAS Summer Meeting, Boston, MA
MSH 11-62
CXO
• X-ray studies show thermal shell with a
central PWN
- pulsar candidate seen as hard point source
in center of PWN (offset from radio center)
Patrick Slane (CfA)
• X-ray spectrum gives n0 ≈ 0.6 cm-3
• SNR/PWN modeling gives t ≈ 5 kyr
- SNR reverse shock has begun to interact
with PWN
2011 AAS Summer Meeting, Boston, MA
MSH 11-62
Fermi LAT
• 1FGL J1112.1-6041 is spatially associated
with MSH 11-62
- F(>100 MeV) ≈ 1 x 10-10 erg cm-2 s-1
• Two nearby pulsars w/ Ė >
1033
erg/s
- neither can yield more than 3% of the flux
Patrick Slane (CfA)
• Spectrum well-described by cut-off PL
- Ecut ≈ 5 GeV, consistent w/ pulsar spectra
• Pion model gives acceptable fit
- requires n0 = 7 cm-3 and Ecut = 70 GeV
- these values are too high and too low,
respectively, for a typical SNR scenario
2011 AAS Summer Meeting, Boston, MA
MSH 11-62
• PWN model with PL injection cannot fit
broadband spectrum
- either over-predicts TeV flux or underpredicts GeV flux
- similar to Vela X and HESS J1640-465
• Model w/ Maxwellian + PL gives good
approximation to data
- ge ≈ 106, G ≈ 2.7; EPL = 0.01 EMaxwellian
- B ≈ 2 mG, typical of evolved PWN
• Fermi observations of MSH 11-62 are
consistent with emission arising from
an evolved PWN
- if correct, broadband modeling appears to
provide additional support for presence of
Maxwellian electron component
- cannot rule out pulsar as origin of GeV
emission
- timing and sub-mm observations important
Patrick Slane (CfA)
2011 AAS Summer Meeting, Boston, MA
MOST
MSH 15-56
• Prototypical composite SNR
• Radio observations reveal shell with
bright, flat-spectrum nebula in center
- no pulsar known, but surely a PWN
- nebula significantly displaced from SNR
center
• Kinematic distance ≈4 kpc based on
Ha radial velocity measurements
- R ≈ 20 pc
Patrick Slane (CfA)
2011 AAS Summer Meeting, Boston, MA
ROSAT
MSH 15-56
CXO
• X-ray studies show thermal shell w/
very faint hard emission near PWN
- pulsar candidate seen as hard point source
w/ faint X-ray trail extending to PWN
Patrick Slane (CfA)
• X-ray spectrum gives n0 ≈ 0.1 cm-3
• SNR/PWN modeling gives t ≈ 12 kyr
- SNR reverse shock has completely
disrupted PWN
2011 AAS Summer Meeting, Boston, MA
MSH 15-56
Fermi LAT
• 1FGL J1552.4-5609 is spatially associated
with MSH 15-56
- F(> 100 MeV) ≈ 3.3 x 10-10 erg cm-2 s-1
• One nearby pulsar w/ Ė >
1033
erg/s
- can not yield more than 5% of the flux
Patrick Slane (CfA)
• PL spectrum provides reasonable fit
- any cutoff much harder than for pulsars
• Pion model gives acceptable fit
- requires n0 = 1.5 cm-3 and Ecut = 300 GeV
- these values are too high and a bit low,
respectively, for a typical SNR scenario
2011 AAS Summer Meeting, Boston, MA
MSH 15-56
• PWN model with PL injection cannot fit
broadband spectrum
- either over-predicts TeV flux or underpredicts GeV flux
• Broken PL reproduced general behavior,
but misses radio index, X-ray flux, and
TeV upper limit
- low X-ray to radio flux ratio consistent
with post-compression PWN phase
• Fermi observations of MSH 15-56 may
be consistent with emission from an
evolved PWN
- if correct, pulsar has essentially departed
relic PWN and is injecting particles into
newly-forming nebula
- additional modeling required to consider
possible evidence for low-energy electron
component
Patrick Slane (CfA)
2011 AAS Summer Meeting, Boston, MA
Missing Cousins?
G272.2-3.2
d ~ 5 kpc, R ~ 12 pc, t ~ 6-15 kyr
Kes 73
• Do other SNRs with ages similar to the
detected composite SNRs also show GeV
emission?
- Certainly not all. Little or no evidence from
G272.2-3.2, Kes 73, or G299.2-2.9
- no strong evidence of emission from magnetar
in Kes 73 either…
• Not exactly a “control sample”
- distance from Galactic Plane is large for
G272.2-3.2 and G299.2-2.9 (density low,
but confusion from Plane also low…)
- small number statistics…
d ~ 7.5 kpc, R ~ 4 pc, t ~ 1 kyr
G299.2-2.9
Patrick
Slane
d ~ 5 kpc,
R ~ 7 pc,
t ~ 4.5(CfA)
kyr
• Need to carry out further Fermi studies
to establish whether or not composite
SNRs are more prevalent GeV emitters
(which would point to either PWN or
pulsar as origin of emission
2011 AAS Summer Meeting, Boston, MA
Conclusions
• Both X-ray and g-ray emission are produced in composite SNRs
- GeV emission is expected to increase as PWN evolves; X-ray
emission decreases
• Broadband modeling places strong constraints on evolution of
composite SNRs
- provide probe of underlying electron spectrum
• MSH 11-62 may provide additional evidence of a Maxwellian electron
component accompanying the power law tail
- spectrum could also be produced by pulsar; pulsation searches
and studies of spatial extent needed
- sub-mm observations to confirm or refute presence of Maxwellian
electron distribution are crucial for this and other systems
• MSH 15-56 appears to be in late phase of evolution
- GeV emission provides unique probe of evolved electron population
• Continued X-ray and g-ray studies of composite SNRs hold promise
Patrick Slane (CfA)
2011 AAS Summer Meeting, Boston, MA