Supernova Remnants and Pulsar Wind Nebulae Collaborators: D. - - PowerPoint PPT Presentation

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

Supernova Remnants and Pulsar Wind Nebulae in the Fermi Era

Collaborators:

• D. Castro
• S. Funk

Y . Uchiyama

• S. LaMassa

O.C. de Jager

• A. Lemiere

and others…

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

PWNe and SNRs

• Pulsar Wind
• sweeps up ejecta; shock decelerates

flow, accelerates particles; PWN forms

• Supernova Remnant
• sweeps up ISM; reverse shock heats

ejecta; ultimately compresses PWN

• self-generated turbulence by streaming

particles, along with magnetic field amplification, promote diffusive shock acceleration

• f electrons and ions to energies exceeding 10-100 TeV

Gaensler & Slane 2006

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

• Neutral pion decay
• ions accelerated by shock collide w/ ambient

protons, producing pions in process: π0 → γγ

• flux proportional to ambient density; SNR-cloud

interactions particularly likely sites

• Inverse-Compton emission
• energetic electrons upscatter ambient photons

to γ-ray energies

• CMB, plus local emission from dust and starlight,

provide seed photons

• Fermi observations, in combination with multi-λ

data, will help differentiate between the two different mechanisms

Gamma-Ray Emission from SNRs

Ellison et al. 2007

.01 cm

• 3

0.1 cm

• 3

1 cm -3 B=15mG 60 µG 15 µG 3 µG

t=500y, ε=36%

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

• SNR age (need time to accumulate particles)
• acceleration efficiency (can be extremely high)
• electron-proton ratio in injection
• magnetic field (evidence suggests large amplification)
• ambient density (large density increases π0-decay emission)
• maximum energy limits (age, escape, radiative losses)

Gamma-Ray Emission from SNRs

Gamma-ray emission depends on (and thus constrains):

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

Young SNRs

• Young SNRs have fast shocks that clearly accelerate particles to high energies
• X-ray observations reveal multi-TeV electrons, and dynamical measurements imply

efficient acceleration of ions as well

• But…
• young SNRs generally haven’

t encountered high densities

• maximum energies may be age-limited
• Thus, while very young SNRs should be γ-ray sources, they are not likely to

be exceptionally bright See talk by Stefan Funk

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

G347.3-0.5/RX J1713.7-3946

• X-ray observations reveal a nonthermal

spectrum everywhere in G347 .3-0.5

• evidence for cosmic-ray acceleration
• based on X-ray synchrotron emission,

infer electron energies of >50 TeV

• SNR detected directly in TeV γ-rays
• γ-ray morphology very similar to

X-rays; suggests I-C emission

• spectrum suggests π0-decay, but lack
• f thermal X-rays is problematic

Acero et al. 2009 XMM MOS

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

G347.3-0.5/RX J1713.7-3946

• X-ray observations reveal a nonthermal

spectrum everywhere in G347 .3-0.5

• evidence for cosmic-ray acceleration
• based on X-ray synchrotron emission,

infer electron energies of >50 TeV

• SNR detected directly in TeV γ-rays
• γ-ray morphology very similar to

X-rays; suggests I-C emission

• spectrum suggests π0-decay, but lack
• f thermal X-rays is problematic
• Spectrum in Fermi band very different

for leptonic and hadronic scenarios

• if the γ-rays are hadronic in origin,

the emission in the Fermi LAT should be bright; weak or non-detection will favor a leptonic origin

See talk by Stefan Funk

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

SNRs in Dense Environments

F(> 100MeV) ≈ 4.4 × 10−7θE51dkpc

−2 n phot cm−2 s−1

• The expected π0 → γγ flux for an SNR is

where θ is a slow function of age (Drury et al. 1994)

• this leads to fluxes near sensitivity limit
• f EGRET, but only for large n
• Efficient acceleration can result in higher

values for I-C γ-rays

• SNRs should be detectable w/ Fermi for

sufficiently high density; favor SNRs in dense environments or highly efficient acceleration

• expect good sensitivity to SNR-cloud

interaction sites (e.g. W44, W28, IC 443)

1 yr sensitivity for high latitude point source W28, W44, γ Cygni, IC 443…

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

SNRs in Dense Environments

F(> 100MeV) ≈ 4.4 × 10−7θE51dkpc

−2 n phot cm−2 s−1

• The expected π0 → γγ flux for an SNR is

where θ is a slow function of age (Drury et al. 1994)

• this leads to fluxes near sensitivity limit
• f EGRET, but only for large n
• Efficient acceleration can result in higher

values for I-C γ-rays

• SNRs should be detectable w/ Fermi for

sufficiently high density; favor SNRs in dense environments or highly efficient acceleration

• expect good sensitivity to SNR-cloud

interaction sites (e.g. W44, W28, IC 443)

See talk by Takaaki Tanaka

Abdo et al. 2009

Example: W51C

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

G349.7+0.2

1 arcmin ATCA Chandra

• G349.7+0.2 is a small-diameter SNR

with high radio surface brightness

• HI absorption measurements indicate

a distance of 22 kpc

• one of the most luminous SNRs in

the Galaxy

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

G349.7+0.2

• G349.7+0.2 is a small-diameter SNR

with high radio surface brightness

• HI absorption measurements indicate

a distance of 22 kpc

• one of the most luminous SNRs in

the Galaxy

• CO emission reveals nearby MC
• OH masers at v = 16 km s-1 confirm

SNR shock-cloud interactions

• X-ray spectrum is dominated by bright thermal emission (Lazendic et al. 2005)
• consistent with interaction with high density surroundings
• high temperature suggestions fast shocks ⇒ efficient particle acceleration

Lazendic et al. 2005

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

G349.7+0.2

Castro et al. – in prep.

• Fermi LAT detects emission associated with G349.7+0.2 (Castro et al. – in prep)
• likely evidence of π0-decay γ-rays from p-p collisions in molecular cloud

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

Gamma-Ray Emission from PWNe

• PWN age
• maximum particle energy (depends on properties of both pulsar

and nebula)

• magnetic field (decreases with time, allowing high-E particles

injected at late phases to persist; also introduces loss breaks)

• ambient photon field (synchrotron self-Compton can be important)
• breaks in injection spectrum

Gamma-ray emission depends on (and thus constrains):

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

Broadband Emission from PWNe

• Spin-down power is injected into PWN

at time-dependent rate

• results in spectral break that propagate

to lower energy with time

• Based on studies of Crab Nebula, there

may be two distinct particle populations

• relic radio-emitting electrons and those

electrons injected in wind

Zhang et al. 2008

• Get synchrotron and IC emission from

electron population & evolved B field

synchrotron inverse- Compton cooling break

• Fermi observations can provide constraints on maximum particle energies via

synchrotron radiation, and on lower energy particles via IC emission

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

Connecting the Synchrotron and IC Emission

εkeV

s

≈ 2×10−4 ETeV

2 B−5

εTeV

ic

≈ 3×10−3ETeV

2

εkeV

s

≈ 0.06εTeV

ic B−5

• Energetic electrons in PWNe produce both

synchrotron and inverse-Compton emission

• for electrons with energy ETeV,
• synchrotron
• inverse-Compton
• Magnetic field strength links IC photons with

synchrotron photons from same electrons

• For low B, γ-ray emission probes electrons with

lower energies than those that produce X-rays

• γ-ray studies fill crucial gap in broadband

spectra of PWNe

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

Fermi Studies of 3C 58

• Lo

Low-fr frequenc equency br y brea eak sug k suggests p ts possibl ssible br brea eak in inje k in injectio ion sp n spectr trum

• Torus sp

s spectr trum r m requir equires c s chan hange in e in sl slope be e between IR an tween IR and X d X-r

• ray b

y ban ands ds

• challenges assumptions for single power

law for injection spectrum

• F

Fermi LA i LAT b T ban and p d probe

• bes CMB IC

s CMB IC em emissio ission fr n from ~0 m ~0.6 6 TeV el electr trons ns

• this probes electrons from the unseen

synchrotron region around Esyn = 0.4 eV where injection is particularly complex

Slane et al. 2004

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

• Vel

ela X is the PWN p a X is the PWN produc duced b d by the y the Vel ela pu a pulsa lsar

• a
• appa

pparen entl tly the r y the resu sult of r t of rel elic PWN bein c PWN being dis g distu turbe rbed b d by a y asym symmetr tric pa c passa ssage of the e of the SNR r SNR reverse sho se shock

• El

Elongated d “c “cocoon-l n-lik ike” ha hard X d X-r

• ray s

y str truc uctu ture e e ext xten ends so ds southwa thward of pu d of pulsa lsar

• c
• clea

early i y iden dentifie ified b d by HESS a y HESS as an e s an ext xten ende ded d VHE s VHE str truc uctu ture

• th
• this is n

is is not the pu t the pulsa lsar je r jet

Evolution in an SNR: Vela X

Blondin et al. 2001

t = 10,000 yr t = 20,000 yr t = 30,000 yr t = 56,000 yr

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

Understanding Vela X: Fermi

de Jager et al. 2008

• Br

Broadb dban and sp d spectr trum f m for PWN sug r PWN suggests tw ts two dis

• distinc

inct el t electr tron p n popu pulatio ions ns an and v d very l y low ma w magnetic field ( c field (∼5 5 µG) )

• r
• radio

dio-em

• emittin

ing p g popu pulatio ion w n wil ill g l gen enerate IC em e IC emissio ission in LA n in LAT b T ban and d

• sp
• spectr

tral f l fea eatu tures ma s may i y iden dentify dis fy distinc inct pho t photon p n popu pulatio ion an n and de d determin ine e cu cut-of

• off en

f energy f y for r r radio dio-em

• emittin

ing el g electr trons ns

LaMassa et al. 2008

See Talk by Marianne Lemoine-Goumard

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

HESS J1640-465

5 arcmin

• Extended source identified in HESS GPS
• no known pulsar associated with source
• may be associated with SNR G338.3-0.0
• XMM observations (Funk et al. 2007) identify extended X-ray PWN
• Chandra observations (Lemiere et al. 2009) reveal neutron star within extended nebula
• Lx ∼1033.1 erg s-1  Ė ~ 1036.7 erg s-1
• X-ray and TeV spectrum well-described by leptonic model with B ∼6 µG and t ∼15 kyr
• example of late-phase of PWN evolution: X-ray faint, but γ-ray bright

LAT 1 yr sensitivity Lemiere et al. 2009

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

HESS J1640-465

5 arcmin

Castro et al. – in prep.

• Extended source identified in HESS GPS
• no known pulsar associated with source
• may be associated with SNR G338.3-0.0
• XMM observations (Funk et al. 2007) identify extended X-ray PWN
• Chandra observations (Lemiere et al. 2009) reveal neutron star within extended nebula
• Lx ∼1033.1 erg s-1  Ė ~ 1036.7 erg s-1
• X-ray and TeV spectrum well-described by leptonic model with B ∼6 µG and t ∼15 kyr
• example of late-phase of PWN evolution: X-ray faint, but γ-ray bright
• Fermi LAT reveals extended emission associated with source (Castro et al. – in prep.)
• flux appears consistent with PWN model predictions

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

Conclusions

• SNRs are efficient particle accelerators, leading to γ-ray emission from

both hadronic and leptonic processes

• the associated spectra strongly constrain fundamental parameters
• f particle acceleration processes; Fermi LAT observations will help

differentiate between emission mechanisms

• SNRs interacting with dense clouds are particularly strong candidates

for γ-ray emission

• Fermi has already detected several, and more are being uncovered
• PWNe are reservoirs of energetic particles injected from pulsar
• synchrotron and inverse-Compton emission places strong constraints
• n the underlying particle spectrum and magnetic field
• Fermi LAT has sensitivity and resolution to probe underlying electron

spectrum in crucial energy regimes

• observations of PWNe will complement multi-λ studies to constrain the

structure and evolution of PWNe

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

Understanding Vela X: XMM

• Br

Broadb dban and sp d spectr trum f m for PWN sug r PWN suggests tw ts two dis

• distinc

inct el t electr tron p popu pulatio ions ns

• r
• radio

dio-em

• emittin

ing p g popu pulatio ion w n wil ill g l gen enerate IC em e IC emissio ission in LA n in LAT b T ban and d

• sp
• spectr

tral f l fea eatu tures w s wil ill i l iden dentify dis fy distinc inct pho t photon p n popu pulatio ion an n and de d determin ine e cu cut-of

• off en

f energy f y for r r radio dio-em

• emittin

ing el g electr trons ns

• XMM l

XMM large p e proje ject (40 t (400 0 ks ks) t ) to s

• stu

tudy y eje jecta an and d nonthe therma mal em emissio ission n n now u unde derwa way; ima images r s revea eal c l consi nside derabl ble s e str truc uctu ture an e and sp d spectr tral v l variatio ion

2009 Fermi Symposium, Washington, DC Patrick Slane (CfA)

The Surrounding Ejecta: 3C 58

• Chandra reveals complex structure
• f wind shock zone and surroundings
• Spectrum reveals ejecta shell with

enhanced Ne and Mg

• PWN expansion sweeps up and

heats cold ejecta

• Mass and temperature of swept-up

ejecta suggests an age of ~2400 yr and a Type IIp progenitor, similar to that for Crab (Chevalier 2005)

• Temperature appears lower than

expected based on radio/optical data