X-ray Observations of

X-ray Observations of Supernova Remnant Shocks

What Do SNR Shocks Tells Us? • SNR Shocks: • Trace SNR dynamical evolution through heated CSM/ISM and ejecta, and reveal • nature and environment of their progenitors • Compress and amplify ambient magnetic fields, leading to particle acceleration • Mitigate electron heating through plasma or collisional processes • Major Uncertainties Include: • Electron-ion temperature equilibration processes and timescales • Approach to ionization equilibrium, and the effects of heating and particle acceleration • The strength of magnetic fields at the forward and reverse shock • Particle injection in the acceleration process • The roll of turbulence in ejecta mixing, field amplification, and other dynamical • processes • I.e., just about everything… • Here we touch on what X-ray observations of SNR shocks bring to some of these issues

Reverse Shock PWN Shock Forward Shock Pulsar Termination Shock Pulsar Wind Unshocked Ejecta Shocked Ejecta Shocked ISM PWN ISM SNRs: The (very) Basic Structure • Pulsar Wind • - sweeps up ejecta; shock decelerates • flow, accelerates particles; PWN forms • Supernova Remnant • - sweeps up ISM; reverse shock heats • ejecta; ultimately compresses PWN; particles accelerated at forward shock generate • magnetic turbulence; other particles scatter off this and receive additional acceleration

Shocks in SNRs: Thermal Spectra r v shock • Expanding blast wave moves supersonically • through CSM/ISM; creates shock • - mass, momentum, and energy conservation • across shock give (with=5/3) X-ray emitting temperatures

Tracking the Ejecta • Type Ia: • Complete burning of 1.4 Mo C-O white dwarf • Produces mostly Fe-peak nuclei (Ni, Fe, Co) • - very low O/Fe ratio • Si-C/Fe sensitive to transition from deflagration • to detonation; probes density structure • - X-ray spectra constrain burning models • Products stratified; preserve burning structure

Tracking the Ejecta • Type Ia: • Complete burning of 1.4 Mo C-O white dwarf • Produces mostly Fe-peak nuclei (Ni, Fe, Co) • - very low O/Fe ratio • Si-C/Fe sensitive to transition from deflagration • to detonation; probes density structure • - X-ray spectra constrain burning models • Products stratified; preserve burning structure • Core Collapse: • Explosive nucleosynthesis builds up light elements • - very high O/Fe ratio • Fe mass probes mass cut • O, Ne, Mg, Fe very sensitive to progenitor mass • Ejecta distribution probes mixing by instabilities

DEM L71: a Type Ia Hughes et al. 2003 • ~5000 yr old LMC SNR • Outer shell consistent with swept-up ISM • - LMC-like abundances • Central emission evident at E > 0.7 keV • - primarily Fe-L • - Fe/O > 5 times solar;typical of Type Ia • Total ejecta mass is ~1.5 solar masses • - reverse shock has heated all ejecta • Spectral fits give MFe ~ 0.8-1.5 Mo and • MSi ~ 0.12-0.24 Mo • - consistent w/ Type Ia progenitor

SNR 0509-67.5 • SNR 0509-67.5 is a young SNR • in the LMC • - identified as Type Ia based on • ASCA spectrum (Hughes et al. 1995) • Observations of optical light echoes • establish age as ~400 yr • - spectra of light echoes indicate • that SNR is result of an SN 1991T- • like (bright, highly energetic, Type • Ia) SN (Rest et al. 2008) • Comparison of hydrodynamic and • non-equilibrium ionization models • for emission from Type Ia events • with X-ray image and spectrum • indicates E = 1.4 x 1051 erg s-1 and • M(56Ni)=0.97 Mo (i.e. energetic, • high-luminosity, 1991T-like event) • - X-ray analysis can be used to infer type and details of SNe! Rest et al. 2005 Badenes et al. 2008

Shocks in SNRs: Dynamics r v shock Ellison et al. 2007 • Expanding blast wave moves supersonically • through CSM/ISM; creates shock • - mass, momentum, and energy conservation • across shock give (with=5/3) X-ray emitting temperatures • Shock velocity gives temperature of gas • - can get from X-rays (modulo NEI effects) • If cosmic-ray pressure is present the • temperature will be lower than this • - radius of forward shock affected as well =.63 =0

Ellison et al. 2007 Aside: Evidence for CR Ion Acceleration Tycho Forward Shock (nonthermal electrons) Warren et al. 2005 • Efficient particle acceleration in SNRs • affects dynamics of shock • - for given age, FS is closer to CD and • RS with efficient CR production • This is observed in Tycho’s SNR • - “direct” evidence of CR ion acceleration

Ellison et al. 2007 Aside: Evidence for CR Ion Acceleration Tycho Reverse Shock (ejecta - here Fe-K) Warren et al. 2005 • Efficient particle acceleration in SNRs • affects dynamics of shock • - for given age, FS is closer to CD and • RS with efficient CR production • This is observed in Tycho’s SNR • - “direct” evidence of CR ion acceleration

Ellison et al. 2007 Aside: Evidence for CR Ion Acceleration Tycho Contact Discontinuity Warren et al. 2005 • Efficient particle acceleration in SNRs • affects dynamics of shock • - for given age, FS is closer to CD and • RS with efficient CR production • This is observed in Tycho’s SNR • - “direct” evidence of CR ion acceleration Warren et al. 2005

Shocks in SNRs: Nonthermal Spectra r v shock • Expanding blast wave moves supersonically • through CSM/ISM; creates shock • - mass, momentum, and energy conservation • across shock give (with=5/3) • Shock velocity gives temperature of gas • - can get from X-rays (modulo NEI effects) • If cosmic-ray pressure is present the • temperature will be lower than this • - radius of forward shock affected as well Ellison et al. 2007

Ellison, Slane, & Gaensler (2001) • inverse-Comptonscattering probes • same electron population; need self- • consistent model w/ synchrotron • pion production depends on density • - thermal X-ray emission provides • constraints Broadband Emission from SNRs • synchrotron emission dominates • spectrum from radio to x-rays • - shock acceleration of electrons • (and protons) to > 1013 eV • - Emax set by age or energy losses • - observed as spectral turnover

-rays from G347.3-0.5 (RX J1713.7-3946) ROSAT PSPC HESS Slane et al. 1999 Aharonian et al. 2006 • 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 • This SNR is detected directly in TeV • gamma-rays, by HESS • - -ray morphology very similar to • x-rays; suggests I-C emission • - spectrum seems to suggest 0 -decay • WHAT IS EMISSION MECHANISM?

Modeling the Emission Moraitis & Mastichiadis 2007 • Joint analysis of radio, X-ray, and -ray • data allow us to investigate the broad • band spectrum • - data can be accommodated by synch. • emission in radio/X-ray and pion decay • (with some IC) in -ray • - however, two-zone model for electrons • fits -rays as well, without pion-decay • component • Pion model requires dense ambient • material • - but, implied densities appear in • conflict with thermal X-ray upper • limits • Origin of emission NOT YET CLEAR

1d 1m 1y Modeling the Emission Moraitis & Mastichiadis 2007 • Joint analysis of radio, X-ray, and -ray • data allow us to investigate the broad • band spectrum • - data can be accommodated by synch. • emission in radio/X-ray and pion decay • (with some IC) in -ray • - however, two-zone model for electrons • fits -rays as well, without pion-decay • component • Pion model requires dense ambient • material • - but, implied densities appear in • conflict with thermal X-ray upper • limits • Origin of emission NOT YET CLEAR • - GLAST MAY SETTLE ISSUE Slane et al. 1999 For kT > 0.25 keV, while hadronic models require n0 > 0.8 cm-3

Diffusive Shock Acceleration • Particles scatter from MHD • waves in background plasma • - pre-existing, or generated • by streaming ions themselves • - scattering mean-free-path • (i.e., most energetic particles • have very large  and escape) see Reynolds 2008 • Maximum energies determined by either: • age – finite age of SNR (and thus of acceleration) • radiative losses (synchrotron) • escape – scattering efficiency decreases w/ energy High B => High Emax magnetic field amplification important! High B => Low Emax for e+- High B => High Emax

Diffusive Shock Acceleration • Particles scatter from MHD • waves in background plasma • - pre-existing, or generated • by streaming ions themselves • - scattering mean-free-path • (i.e., most energetic particles • have very large  and escape) see Reynolds 2008 Electrons: - large B lowers max energy due to synch. losses Ions: - small B lowers max energy due to inability to confine energetic particles Current observations suggest high B fields • Maximum energies determined by either: • age – finite age of SNR (and thus of acceleration) • radiative losses (synchrotron) • escape – scattering efficiency decreases w/ energy

Thin Filaments: B Amplification? • Thin nonthermal X-ray filaments are now observed in • many SNRs, including SN 1006, Cas A, Kepler, Tycho, • RX J1713, and others • - observed drop in synchrotron emissivity is too rapid • to be the result of adiabatic expansion • Vink & Laming (2003) and others argue that this • suggests large radiative losses in a strong magnetic field: • Diffusion length upstream appears to be very small as • well (Bamba et al. 2003) • - we don’t see a “halo” of synchrotron emission in the • upstream region • Alternatively, Pohl et al (2005) argue that field itself is • confined to small filaments due to small damping scale

Rapid Time Variability: B Amplification? Lazendic et al. 2004 Uchiyama et al. 2008 • Along NW rim of G347.3-0.5, brightness variations observed on timescales of ~1 yr • - if interpreted as synchrotron-loss or acceleration timescales, B is huge: B ~ 1 mG • This, along with earlier measurements of the nonthermal spectrum in Cas A, • may support the notion of magnetic field amplification => potential high energies for ions • Notion still in question; there are other ways of getting such variations (e.g. motion • across compact magnetic filaments); more investigation needed

Time Variations in Cas A • Cas A is expanding rapidly • Significant brightness • variations are seen on • timescales of years • - ejecta knots seen lighting • up as reverse shock • crosses • Variability seen in high • energy continuum as well • - similar to results from • RX J1713.7-3946 • Uchiyma & Aharonian (2008) • identify variations along region • of inner shell, suggesting particle • accelerations at reverse shock • - many more observations needed to understand this!

Summary • X-ray observations of SNRs provide spectra that probe the composition • and thermodynamic state of ejecta • - provides constraints on progenitor types and explosion physics • X-ray imaging and spectroscopy trace position of FS/CD/RS • - provides dynamical information about evolutionary state as well • as evidence for particle acceleration •  X-ray dynamics indicated strong hadronic component • - X-ray spectra (thermal and nonthermal) place constraints on nature • of VHE g-ray emission • Several lines of argument lead to conclusion that the magnetic • field is amplified to large values in shock • - thin filaments; rapid variability •  this could allow acceleration of hadrons to ~knee • - other explanations for above exist, without large B; further study needed

X-ray Observations of