Gamma-Ray Emission from Core-Collapse SNRsDon Ellison, NCSU

SNR RX J1713

Abdo et al 2011

Co-workers for cr-hydro-NEI code: Andrei Bykov, Herman Lee (poster), Hiro Nagataki, Dan

Patnaude, John Raymond, Pat Slane

SNR RX J1713

Fermi LAT

HESS

Discuss Nonlinear Diffusive Shock Acceleration (DSA)

Fukui et al 2012

Origin of GeV-TeV emission:

Pion-decay from protons or inverse-Compton (IC) from electrons ?

We discuss a uniform wind model with no non-spherical density inhomogeneities.

Our fit to broad-band spectrum from radio to TeV gives strong indication that IC dominates the high-energy emission

In contrast, Fukui & Sano et al (2012) investigate clumpy structure of gas density and photon emission

They conclude that pion-decay dominates the GeV-TeV emission.

Homogeneous Model of Thermal & Non-thermal Emission in SNR RX J1713

► Suzaku X-ray observations smooth continuum well fit by synchrotron from TeV electrons

► No discernable line emission from shock-heated heavy elements

► Strong constraint on Non-thermal emission at GeV-TeV energies

Look at X-ray energies

Important to consider broad-band emission including thermal X-rays In nonlinear Diffusive Shock Acceleration (DSA) the production of gamma rays is coupled to thermal X-ray emission

Nonlinear Diffusive Shock Acceleration (DSA) with cr-hydro-NEI code (Ellison et al. 2012 and earlier papers) :

Generalized cr-hydro-NEI code (Lee et al. 2012) couples together:1) 1-D, spherically symmetric hydro simulation of SNR based on VH-1

2) NL DSA model largely following published, semi-analytic solutions of Blasi, Amato, Caprioli, Gabici & co-workers some differences and additions

3) Non-equilibrium ionization (NEI) calculation of X-ray line emission

4) Broad-band continuum emission from trapped CRs within SNR and forward shock precursor

5) Continuum emission from escaping CRs

Explicit calculation of upstream, cosmic-ray precursor

Momentum and space dependent CR diffusion coefficient

Explicit calculation of resonant, quasi-linear magnetic field amplification (MFA)

Calculation of Emax using amplified B-field

Finite Alfven speed for CR scattering centers

Line-of-sight projections of individual X-ray lines

CD

Forward Shock

Reverse Shock

Shocked Ejecta material :

Shocked ISM material : Calculate X-ray emission from this region

1-D core-collapse model: Pre-SN wind density: ∝ 1/r2

Here, we ignore emission from reverse shock and ejecta material

1) CR electrons and ions accelerated at FS

a) Protons give pion-decay -rays

b) Electrons give synchrotron, IC, & non-thermal brems.

c) High-energy CRs escape from shock precursor & interact with external mass

2) Follow evolution of shock-heated plasma between FS and contact discontinuity (CD)

a) Calculate electron temperature, density, charge states of heavy elements, and X-ray line emission

b) Include adiabatic losses & radiation losses

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Extent of shock precursor

Escaping CRs

Spherically symmetric: We do not model clumpy structure

1/r2 pre-SN wind density profile

Pressure precursor from shock accelerated CRs

Modified shock speed from CR pressure

Low B-field in pre-SN wind: <10-7 G at forward shock at 1600 yr

L

og

Pre

s.F

low

Sp

eed

B

[G]

Radial structure for core-collapse model for J1713

Radius [pc]

340 yr990 yr

1630 yr

FS

FS

Can include shell

FS radius

FS compression

Magnetic field amplification (MFA)

in precursor x40Total CRs

escaping CRs

Fra

c.

of

ES

N

in C

Rs

proton pmax

B

[G

]

proton pmax nearly

constant for J1713

B-field compression at subshock

4

~17% of SN explosion energy put into CRs at 1630 yr

SNR evolution

SNR Age [yr]

Forward shock of SNR produces 3 particle distributions that will contribute to the photon emission

1) Ions accelerated and trapped within SNR and precursor2) Electrons accelerated and trapped within SNR and precursor3) CRs escaping upstream (mainly ions)

trapped

Escaping CRsEllison & Bykov 2011

See T. Bell’s & M. Malkov’s talks concerning escaping CRs

FS protons

FS electrons

p-p

IC

brems

Results from generalized cr-hydro-NEI code (Lee, Ellison & Nagataki 2012, also Ellison, Slane, Patnaude, Bykov 2012 & previous work)

Core-collapse SN explodes in a 1/r2 pre-SN wind.

Excellent fit to broad-band (integrated) emission

IC dominates GeV-TeV emission

Pre-SN wind magnetic field much lower than ISM Strong Magnetic field amplification occurs but still have B-field low enough to have high electron energy to match HESS pointsFor J1713, we predict average shocked B ~ 10 µG ! (Amplification factor ~40)

Most CR energy is still in ions even with IC dominating the radiation

Most CR energy is still in ions even with IC dominating the radiation

synch

Note: p-p from escaping CRs small

unless external mass > 104 Msun

SNR RX J1713

L

og

p4

f(p

) CR spectra calculated between forward shock (FS) and contact discontinuity (CD) over 1630 yr age of SNR RX J1713

Photons produced by CR spectra with different evolutionary histories and in different B-fields

Parameters for J1713 at 1630 yr: e/p = Kep =0.01

EffDSA ~ 40%,

ESN put into CRs ~17%

B2 ~ 10 G

protons

electrons

CRs accelerated by FS and trapped within SNR

Shape of turnover is important. Controls X-ray synch. & TeV match. Turnover from escaping CRs not yet modeled self-consistently. Warning: Cannot take simple power law prediction from DSA and match only GeV-TeV emission.(see M. Malkov’s talk for more on problem of escape)

Before Fermi data, possible to get good fit to J1713 continuum with pion-decay dominating GeV-TeV. For example: Zirakashvili & Aharonian 2010

Even with Fermi data, shape of spectrum at GeV-TeV may not be enough to discriminate between IC and pion-decay (Fukui & Sano et al. 2012;

Zirakashvili & Aharonian 2010 )

Essential to consider X-ray line emission

My apologies to the many papers on modeling young SNRs that I don’t mention

p-p

Don Ellison, NCSU

NEI calculation of Thermal X-ray emissionNEI calculation of Thermal X-ray emission

Ion

izat

ion

fr

acti

on

Electrons reach X-ray emitting temperatures rapidly even if DSA highly efficient and shocked temperature is reducedNot easy to suppress thermal X-rays

ne [

cm-3

]T

e [

K]

General calculations: Patnaude et al. , ApJ 2009 Applied to J1713: Ellison et al. ApJ 2010

Ion

izat

ion

fra

ctio

n

Forward shockR [arcsec]

np = 1 cm-3

np = 0.1 cm-3

NEI calculation of heavy element ionization and X-ray line emissionNEI calculation of heavy element ionization and X-ray line emission

Forward shock overtakes this gas at 100 yr

Coulomb Eq.

Instant equilibration

Lepton model

► Compare Hadronic & Leptonic fits

► Range of electron temperature equilibration models

► The high ambient densities needed for pion-decay to dominate at TeV energies result in strong X-ray lines

Hadron

Hadron

Ellison, Patnaude, Slane & Raymond ApJ (2007, 2010)

Suzaku

Coulomb Eq.

To be consistent with Suzaku observations with lines weaker than synchrotron continuum, must have low density and high accelerated e/p ratio (Kep ~ 0.01)

This impacts GeV-TeV emission

Best fit models have low shocked B-field B2

~ 10 G

Thermal X-ray constraint IC dominates GeV-TeV emission in J1713

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Note: Fukui et al (2012) reach conclusion that pion-decay from protons dominates emission in J1713 based on spatial correlation of gas and -rays

Also, high resolution Suzaku images may show that spatial correlation between X-ray and TeV gamma-ray emission may not be as good as thought from low-resolution images

Contours: HESS TeV -raysColor: Np(H2 + H1) column density

Fukui et al. 2012

High densities needed for pion-decay may be in cold clumps that don’t radiate thermal X-ray emission

Inoue et al (2012)

Mult-component model (Inoue et al 2012; Fukui et al 2012):

Average density of ISM protons: ~130 cm-3

Total mass ~2 104 Msun over SNR radius

~0.1% of supernova explosion energy in CR protons !!

This may be a problem for CR origin

Warning: many parameters and uncertainties in model, but :

For homogeneous model of SNR RX J1713 :

Inverse-Compton is best explanation for GeV-TeV (Note: other remnants can certainly be Hadronic, e.g. Tycho’s SNR see G. Morlino’s talk)

Note: For DSA most CR energy (~17% of ESN) is still in ions even

with IC dominating the radiation SNRs produce CR ions !

Beyond CR question: Careful modeling of SNRs provides constraints on critical parameters for shock acceleration:

a) Shape and normalization of CR ions from particular SNRsb) Kep, electron/proton injection ratioc) Acceleration efficiencyd) Magnetic Field Amplificatione) Properties of escaping CRsf) Geometry effects in SNRs such as SN1006

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19

Extra slides

Forward shock of SNR produces 3 particle distributions that will contribute to the photon emission

1) Ions accelerated and trapped within SNR and precursor2) Electrons accelerated and trapped within SNR and precursor3) CRs escaping upstream (mainly ions)

trapped

Escaping CRsEllison & Bykov 2011

Shock wave

Vsk

Some fraction of the highest energy CRs will always escape upstream in DSA

CRs need self-generated turbulence to diffuse. This B/B will be lacking far upstream

Qesc

T. Bell & M. Malkov’s talks

RX J1713 Nature 2007

Word on observations of rapid time variability in SNR synchrotron emission

1-2.5 keV X-rays

Interpreted by Uchiyama et al. as time-scale for synchrotron lossesin B > 1 mG fields !

We predict much lower (integrated) B-fields

Alternative explanation that doesn’t set time scale of variations by radiation losses (Bykov, Uvarov & Ellison 2008)

Combine turbulent magnetic field with steep electron distribution

For given synchrotron emission energy, local regions with high B have many more electrons to radiate than regions of low B

Local high-B regions dominate line-of-sight projection Varying magnetic turbulence produces intermittent, clumpy emission Time scales consistent with SNR observations No need for ~ 1000 µG magnetic fields

5 keV 20 keV 50 keV

High B

Low BLog Ne

Log Electron Energy

SNR J1713: Tanaka et al 2008

Simulated Suzaku XIS spectra (nH = 7.9 1021 cm-2)Lines produced by Hadronic model would have been seen !

Leptonic model

Hadronic model

XIS spectrum

To be consistent with Suzaku observations. That is, to have lines weaker than synchrotron continuum, must have low ISM density and accelerated e/p ratio, Kep~ 10-2

This determines GeV-TeV emission mechanism