COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) X-ray Observations of Supernova Remnant Shocks

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) 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

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) SNRs: The (very) Basic Structure ISM Shocked ISM Shocked EjectaUnshocked Ejecta PWN Pulsar Wind Forward Shock Reverse Shock PWN Shock Pulsar Termination Shock 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

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) 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  v Shocks in SNRs: Thermal Spectra

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) Tracking the Ejecta Type Ia: Complete burning of 1.4 M o 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

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) Tracking the Ejecta Type Ia: Complete burning of 1.4 M o 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

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) DEM L71: a Type Ia ~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 Hughes et al Total ejecta mass is ~1.5 solar masses - reverse shock has heated all ejecta Spectral fits give M Fe ~ M o and M Si ~ M o - consistent w/ Type Ia progenitor

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) SNR SNR 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 erg s -1 and M( 56 Ni)=0.97 M o (i.e. energetic, high-luminosity, 1991T-like event) - X-ray analysis can be used to infer type and details of SNe! Rest et al Badenes et al. 2008

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) 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 X-ray emitting temperatures shock  v Shocks in SNRs: Dynamics Ellison et al  =0  =.63

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) Aside: Evidence for CR Ion Acceleration Tycho Ellison et al Warren et al 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 Forward Shock (nonthermal electrons)

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) Aside: Evidence for CR Ion Acceleration Ellison et al Tycho Warren et al 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 Reverse Shock (ejecta - here Fe-K)

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) Aside: Evidence for CR Ion Acceleration Ellison et al Tycho Warren et al 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 Contact Discontinuity

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) 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 shock  v Shocks in SNRs: Nonthermal Spectra Ellison et al. 2007

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) Broadband Emission from SNRs Ellison, Slane, & Gaensler (2001) synchrotron emission dominates spectrum from radio to x-rays - shock acceleration of electrons (and protons) to > eV - E max set by age or energy losses - observed as spectral turnover inverse-Compton scattering probes same electron population; need self- consistent model w/ synchrotron pion production depends on density - thermal X-ray emission provides constraints

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA)  -rays from G (RX J ) X-ray observations reveal a nonthermal spectrum everywhere in G 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   -decay WHAT IS EMISSION MECHANISM? ROSAT PSPC HESS Slane et al Aharonian et al. 2006

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) 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

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) Modeling the Emission 1d 1m 1y 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 Moraitis & Mastichiadis 2007 For kT > 0.25 keV, while hadronic models require n0 > 0.8 cm -3 Slane et al. 1999

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) 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) Maximum energies determined by either: age – finite age of SNR (and thus of acceleration) radiative losses (synchrotron) escape – scattering efficiency decreases w/ energy Diffusive Shock Acceleration see Reynolds 2008 High B => High E max High B => Low E max for e +- High B => High E max magnetic field amplification important!

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) 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) Maximum energies determined by either: age – finite age of SNR (and thus of acceleration) radiative losses (synchrotron) escape – scattering efficiency decreases w/ energy Diffusive Shock Acceleration 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

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) 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

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) Rapid Time Variability: B Amplification? Along NW rim of G , 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 Lazendic et al Uchiyama et al. 2008

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) 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 J Uchiyma & Aharonian (2008) identify variations along region of inner shell, suggesting particle accelerations at reverse shock - many more observations needed to understand this!

COSPAR 2008, Montreal, 13 July Patrick Slane (CfA) 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  -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