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Particle acceleration in Supernova Remnants from X-ray observations. Anne Decourchelle Service d’Astrophysique, CEA Saclay. I- Ejecta dominated SNRs: Cas A, Tycho and Kepler II- Synchrotron-dominated SNRs: SN 1006, G347.3-0.5. Shell SNRs and plerions. =>Restriction to shell SNRs.
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Particle acceleration in Supernova Remnants from X-ray observations Anne Decourchelle Service d’Astrophysique, CEA Saclay I- Ejecta dominated SNRs: Cas A, Tycho and Kepler II- Synchrotron-dominated SNRs: SN 1006, G347.3-0.5
Shell SNRs and plerions =>Restriction to shell SNRs PWN in G0.9+0.1 (XMM-Newton) Tycho (XMM-Newton) -> talk of Sidoli
Particle acceleration in SNRs SNRs : main source of cosmic-rays with E ≤ 1015 eV ? ► SNRs have enough total power ► Strong shocks in SNRs: First-order Fermi shock acceleration (radio emission → relativistic GeVelectrons) ► Composition of bulk of CRs, typical of mixed ISM → acceleration of ISM gas and dust by shocks in SNRs ► X-ray observations of synchrotron emission → TeVelectrons Pending questions: • How efficient is cosmic-ray acceleration in SNRs ? • What is the maximum energy of accelerated particles ? • How large is the magnetic field ? Is it very turbulent ? • Is it amplified ? • No unambiguous evidence for ion acceleration in SNRs
Interstellar medium <---Ejecta ---> Efficient particle acceleration in young supernova remnants 2 shocks =>Modification of the X-ray morphology and temperature of the gas RADIUS Decourchelle, Ellison, Ballet 2000, ApJ 543, L57 Blondin and Ellison 2001, ApJ 560, 244
Morphology of the X-ray continuum in young SNRs • Strong radio emission “associated” with the ejecta=> amplified magnetic field due to R-T instabilities at the interface ejecta/ambient medium • Strong X-ray emission “associated” with the ejecta and weaker plateau in X-rays associated with the blast wave=> inconsistent with synchrotron: non-thermal bremstrahlung ? Particle acceleration at secondary shocks ?(Vink & Laming 2003, pJ 584, 758) ? Allen et al. 1997, ApJ 487, L97 Cas A Cas A XMM-Newton 8-15 keV XMM-Newton 8-15 keV Radio Radio Bleeker et al. 2001, A&A 365 Bleeker et al. 2001, A&A 365
Spectrum of the forward shock in Cas A Vink and Laming 2003, ApJ 584, 758 X-ray continuum Chandra VLA radio (x 10) Thermal component: kT ~ 3.5 keV and net ~ 4 1010 cm-3s Non-thermal component: RIM: 84 % of the 4-6 keV continuum, power law a ~ 2.2 INSIDE: 11% of the 4-6 keV continuum, power law a > 4.5 =>width of the rim inconsistent with thermal emission
XMM-NewtonSi K XMM-Newton4-6 keV Radio VLA Shocked ambient medium Shocked ejecta DeLaney et al., 2002, ApJ 580, 914 Kepler (1604) Cassam-Chenai et al., 2003, A&A in press Cassam-Chenai et al., 2003 • Continuum associated with the forward shock: • synchrotron emission ? • Forward shock very close to the interface ejecta/ambient medium: RFS/RCD = 11/10: • morphology expected when particle acceleration is nonlinear ! XMM spectrum of the forward shock Shocked ejecta => thermal non ionization equilibrium emission Shocked ambient medium => synchrotron emission using radio constraints: Maximum energy of accelerated electrons ~ 60 TeV
Chandra spectrum of the forward shock continuum Radio 22cm Broad band Chandra Chandra Hwang et al, 2002, ApJ 4-6 keV Decourchelle et al. 2001, A&A 365, L218 No emission line features ! Thermal interpretation: kT = 2.1 keV and net = 108 cm-3s => strong ionization delay but problem with the morphology Non-thermal interpretation: synchrotron X-ray power law: a ~ 2.8 Rolloff frequency: n ~7 1016 Hz => maximum electron energies ~ 1-12 TeV • Tycho (1572) • Continuum associated with the forward shock: • synchrotron emission ? • Forward shock very close to the interface ejecta/ambient medium: RFS/RCD = 11/10: • morphology expected when particle acceleration is nonlinear !
Sharp rims at the forward shock. Radiative ? X-ray continuum Chandra Sharp filaments observed all along the periphery of these young SNRs => synchrotron emission, width determined by synchrotron losses of ultrarelativistic electrons Time to move out t = r / ugas with ugas = 1/R*Vsh , R: compression ratio Equating tloss and t gives B. Cas A:D = 3.4 kpc, Vsh~ 5200 km/s, <4", t < 1.56109 s=> B 60-100 G Vink and Laming 2003, ApJ 584, 758 Tycho:D = 3.2 kpc, Vsh~ 4600 km/s, 4”, t = 1.65109 s=> B 60 G Kepler:D = 4.8 kpc, Vsh~ 5400 km/s, 3”, t = 1.59109 s=> B 60 G Requires magnetic field amplification (Lucek and Bell 2000, MNRAS 314,65) or nonlinear particle acceleration and large compression ratio at the shock (~8)
Summary on particle acceleration in young SNRs • Morphology of the high energy X-ray continuum • Bright emission associated with the ejecta in Cas A: nonthermal bremsstrahlung. • Particle acceleration at secondary shocks ? • Ejecta interface close to the forward shock in Kepler and Tycho => nonlinear particle acceleration with shock modification • Sharp filaments all along the rim => magnetic field randomly oriented around the 3 remnants (unlike in SN 1006) • Forward shock: nature of the spectrum and width of the rim • Synchrotron emission at the forward shock • => First order Fermi acceleration with electrons up to energies of 1-60 TeV • Sharp rims due to the limited lifetime of the ultrarelativistic electrons in the SNR • =>large magnetic field values ~ 60-100 G derived for Cas A, Tycho, Kepler • Amplification of the magnetic field or nonlinear particle acceleration with large compression ratio (>>4) ?
SN 1006: first evidence of electrons acceleration up to TeV energies (Koyama et al. 1995, Nature 378, 255) • X-ray thermal emission in the faint areas • X-ray synchrotron emission in the bright rims • Power-law distribution of electrons, cut-off at high energy • νcut = 240 eV (Dyer et al. 2001, ApJ 551, 439)
γ-ray emission Synchrotron νFν IC Radio SN 1006, CANGAROO (Tanimori et al. 1998, ApJ 497, L33) or large B small B • 0 decayfollowing nuclear reactions by the accelerated ions on the thermal gas • Only spectral range where the protons may be directly detected (electrons make up only a few % of the energy density of CRs) • Inverse Compton on 3 K CMB (or local photons) by the same TeV electrons emitting the X-rays by synchrotron
SN 1006 with XMM-Newton : Geometry of the acceleration R. Rothenflug et al. MOS images (square root scaling), 4 pointings GT Oxygen band (0.5 – 0.8 keV) : thermal emission 2 – 4.5 keV band : Non-thermal emission
φ = π/3 Out In Transverse profile: principle How is the magnetic field oriented ? A symmetry axis seems to be running from south-east to north-west, BUT if the bright limbs were an equatorial belt, non-thermal emission should also be seen in the interior => Polar caps If equatorial belt:Fin/Fout > 0.5 Observed: 0.8-2 keV: 0.300 ± 0.014 2-4.5 keV: 0.127 ± 0.074 Fin/Fout > π/2φ– 1 = 0.5
Radio/X-ray comparison XMM-Newton: 2 – 4.5 keV band RADIO Combined Molonglo + Parkes radio image at 843 MHz with 44" x 66" (FWHM) spatial resolution (Roger et al., ApJ 332, 940). Extract spectra in boxes just behind the shock all around the remnant, and as a function of radius toward the North-East
NorthEast Spectral modelling • Fit the spectra with a two-component model: • synchrotron emission from a cut-off electron power law (SRCUT). • thermal emission from a plasma out of ionisation equilibrium behind a shock (VPSHOCK) with variable abundances. • Interstellar absorption fixed: NH = 7 1020 cm-2. • Slope of the e- power-law fixed: 2.2. • (α = 0.6 in the radio) • Normalisationof the synchrotron component fixedusing theradio data • => only the cut-off frequency was left free. SouthEast
Cut-off frequency Center - Spatial variations of the cut-off frequency of the synchrotron emission exist in SN 1006. - The very strong radial variationsconfirm that the bright limbs look like polar caps. Shock - Very strong azimuthal variations,cannot be explained byvariations of themagneticcompressionalone. => Maximum energyof accelerated particles higher at the bright limbsthan elsewhere. - If B ~ 50 μG, the maximum energy reached by the electrons at the bright limb is around 100 TeV. νcut(eV) ~ 0.02 B(μG) E2cut (TeV) The X-ray geometry of SN 1006 favors cosmic-ray acceleration where the magnetic field was originally parallel to the shock speed (polar caps)
An extreme case of synchrotron-dominated SNR: G347.3-0.5 ASCA XMM-Newton results => talk of G. Cassam-Chenai Uchiyama et al. 2002, PASJ 54, L73 TeV emission (CANGAROO) in the NW: Inverse compton or p0 decay process ? Muraishi et al. 2000, A&A, 365, L57, Enomoto et al. 2002, Nature, 416, 25, Reimer & Pohl 2002, A&A, 390, L43 GeV emission (EGRET) associated with cloud A ? Butt et al. 2001, ApJ, 562, L167