Gamma-Ray Emission from Core-Collapse SNRs Don Ellison, NCSU

1. Gamma-Ray Emission from Core-Collapse SNRs Don Ellison, NCSU Co-workers for cr-hydro-NEI code: Andrei Bykov, Herman Lee (poster), Hiro Nagataki, Dan Patnaude, John Raymond, Pat Slane SNR RX J1713 SNR RX J1713 Abdo et al 2011 Fukui et al 2012 HESS Fermi LAT Discuss Nonlinear Diffusive Shock Acceleration (DSA)

2. 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.

3. 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

4. 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-D, spherically symmetric hydro simulation of SNR based on VH-1 • NL DSA model largely following published, semi-analytic solutions of Blasi, Amato, Caprioli, Gabici & co-workers  some differences and additions • Non-equilibrium ionization (NEI) calculation of X-ray line emission • Broad-band continuum emission from trapped CRs within SNR and forward shock precursor • 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

5. Shocked ISM material : Calculate X-ray emission from this region 1-D core-collapse model: Pre-SN wind density:  ∝ 1/r2 • CR electrons and ions accelerated at FS • Protons give pion-decay -rays • Electrons give synchrotron, IC, & non-thermal brems. • High-energy CRs escape from shock precursor & interact with external mass • Follow evolution of shock-heated plasma between FS and contact discontinuity (CD) • Calculate electron temperature, density, charge states of heavy elements, and X-ray line emission • Include adiabatic losses & radiation losses Forward Shock CD Reverse Shock Escaping CRs Shocked Ejecta material : Here, we ignore emission from reverse shock and ejecta material Extent of shock precursor Spherically symmetric: We do not model clumpy structure

6. Radial structure for core-collapse model for J1713 340 yr 1/r2 pre-SN wind density profile 990 yr 1630 yr FS Pressure precursor from shock accelerated CRs Log Pres. Modified shock speed from CR pressure FS Flow Speed Low B-field in pre-SN wind: <10-7 G at forward shock at 1600 yr Can include shell B [G] Radius [pc]

7. SNR evolution FS radius  4 FS compression B-field compression at subshock B [G] Magnetic field amplification (MFA) in precursor x40 Total CRs Frac. of ESN in CRs escaping CRs ~17% of SN explosion energy put into CRs at 1630 yr proton pmax proton pmax nearly constant for J1713 SNR Age [yr]

8. Forward shock of SNR produces 3 particle distributions that will contribute to the photon emission Ions accelerated and trapped within SNR and precursor Electrons accelerated and trapped within SNR and precursor CRs escaping upstream (mainly ions) Ellison & Bykov 2011 Escaping CRs FS protons trapped FS electrons See T. Bell’s & M. Malkov’s talks concerning escaping CRs

9. 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 SNR RX J1713 synch IC p-p • Most CR energy is still in ions even with IC dominating the radiation brems Note: p-p from escaping CRs small unless external mass > 104 Msun 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 points For J1713, we predict average shocked B ~ 10 µG ! (Amplification factor ~40)

10. CRs accelerated by FS and trapped within SNR • 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 Log p4 f(p) electrons 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)

11. Before Fermi data, possible to get good fit to J1713 continuum with pion-decay dominating GeV-TeV. For example: Zirakashvili & Aharonian 2010 My apologies to the many papers on modeling young SNRs that I don’t mention 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

12. NEI calculation of Thermal X-ray emission p-p Don Ellison, NCSU

13. NEI calculation of heavy element ionization and X-ray line emission ne [cm-3] Electrons reach X-ray emitting temperatures rapidly even if DSA highly efficient and shocked temperature is reduced Not easy to suppress thermal X-rays Te [K] np = 1 cm-3 Ionization fraction np = 0.1 cm-3 Ionization fraction Forward shock overtakes this gas at 100 yr General calculations: Patnaude et al. , ApJ 2009 Applied to J1713: Ellison et al. ApJ 2010 R [arcsec] Forward shock

14. 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 Coulomb Eq. Suzaku Hadron Instant equilibration 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 Coulomb Eq. Lepton model Thermal X-ray constraint  IC dominates GeV-TeV emission in J1713 Ellison, Patnaude, Slane & Raymond ApJ (2007, 2010)

15. Note: Fukui et al (2012) reach conclusion that pion-decay from protons dominates emission in J1713 based on spatial correlation of gas and -rays Contours: HESS TeV -rays Color: Np(H2 + H1) column density Fukui et al. 2012 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

16. 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 Inoue et al (2012) High densities needed for pion-decay may be in cold clumps that don’t radiate thermal X-ray emission

17. 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: • Shape and normalization of CR ions from particular SNRs • Kep, electron/proton injection ratio • Acceleration efficiency • Magnetic Field Amplification • Properties of escaping CRs • Geometry effects in SNRs such as SN1006

19. Extra slides

20. Forward shock of SNR produces 3 particle distributions that will contribute to the photon emission Ions accelerated and trapped within SNR and precursor Electrons accelerated and trapped within SNR and precursor CRs escaping upstream (mainly ions) Ellison & Bykov 2011 Escaping CRs Some fraction of the highest energy CRs will always escape upstream in DSA trapped Vsk Qesc CRs need self-generated turbulence to diffuse. This B/B will be lacking far upstream Shock wave T. Bell & M. Malkov’s talks

21. Word on observations of rapid time variability in SNR synchrotron emission RX J1713 Nature 2007 1-2.5 keV X-rays Interpreted by Uchiyama et al. as time-scale for synchrotron losses in B > 1 mG fields ! We predict much lower (integrated) B-fields

22. 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 50 keV 5 keV 20 keV High 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 Low B Log Ne Log Electron Energy

23. SNR J1713: Tanaka et al 2008 Hadronic model XIS spectrum Leptonic model Simulated Suzaku XIS spectra (nH = 7.9 1021 cm-2) Lines produced by Hadronic model would have been seen ! 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