Particle acceleration & supernova remnants

Transcription

1 Particle acceleration & supernova remnants Tony Bell, Brian Reville, Klara Schure University of Oxford HESS SN1006: A supernova remnant 7,000 light years from Earth X-ray (blue): NASA/CXC/Rutgers/G.Cassam-Chenai, J.Hughes et al; Radio (red): NRAO/AUI/GBT/VLA/Dyer, Maddalena & Cornwell; Optical (yellow/orange): Middlebury College/F.Winkler. NOAO/AURA/NSF/CTIO Schmidt & DSS

2 Basic Physics 1) shock acceleration 2) magnetic field generation (scatters cosmic rays near shock)

3 Diffusive shock acceleration B 1 CR track B 2 High velocity plasma Low velocity plasma Due to scattering, CR recrosses shock many times Gains energy on each crossing

4 Magnetic field amplification Lucek & Bell 2000 CR Cavities and walls in B & ρ

5 Observations of CR acceleration

6 CR acceleration SN1006 (Chandra) CR electrons (10-100TeV) CR arriving at earth Nagano & Watson 2000 RX J (HESS) γ-rays (up to 80TeV) produced by CR

7 Observations of magnetic field amplification

8 Evidence for magnetic field amplification at shock (Vink & Laming, 2003; Völk, Berezhko, Ksenofontov, 2005) Tycho 1572AD Kepler 1604AD SN1006 Chandra observations Cas A 1680AD NASA/CXC/Rutgers/ J.Hughes et al. NASA/CXC/Rutgers/ J.Warren & J.Hughes et al. NASA/CXC/NCSU/ S.Reynolds et al. NASA/CXC/MIT/UMass Amherst/ M.D.Stage et al.

9 Shocks in radio jets Centaurus A (Croston et al 2008) CHANDRA + VLA (contours, 1.4GHz) Shocks on Mpc scale Merging galaxy cluster, radio (van Weeren et al 2010) B ~ 1.7 μg B ~ 5-7 μg

10 Observations Spectrum

11 Cosmic Ray spectrum arriving at earth Nagano & Watson 2000 ~ E -2.7 Theory: E -2 Leakage from galaxy accounts for some of difference (Hillas 2005)

12 Spectrum at source: RX J (HESS) Photon spectrum (Berge et al 2007) CR energy ~ 6x photon energy E -2 Photons up to 80TeV But turnover begins at 10TeV

13 SN1006 (HESS) Acero et al 2010 Lepton model, cut-off at 10TeV CR model: E -2 Hadron model, cut-off at 80TeV Leptonic or hadronic source of gamma-rays? Can middle aged SNR Accelerate CR to knee?

14 Spectrum at source: SN1006 (HESS) Photon spectrum (Acero 2010) CR energy ~ 6x photon energy E -2 E -2.5 Radio spectral index: 2.1/2.2

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16 CR spectrum deviations from standard diffusive shock acceleration observational signatures

17 Historical SNR (Glushak 1985) Cas A (0.76/0.77), Kepler(0.66/0.64), Tycho(0.67/0.61), SN1006(0.55/0.6), RCW86(0.45/0.6), RCW103(0.5/0.5), G349.7(0.54/0.5), 3C391(0.55/0.49), (0.60) o x + SN1993J: α = 0.81 (Weiler et al 2007) SN1987A: α = 0.9, flattening to 0.8 (Manchester et al 2005), recently to 0.5 (Zanardo 2010) G : α = 0.62 (Green et al 2008) x o Radio spectral index vs. age + Diffusive shock acceleration

18 Young SNR: radio spectral index vs magnetic field 0.8 Cas A synchrotron spectral index Kepler SN1006 RCW Magnetic field μg (Vink 2008) Tycho

19 Explanation A: CR-dominated shocks Non-linear effects: concave spectrum Low post-shock temperature RCW86 (CHANDRA/VLT Helder et al 2009) RCW86 (Vink et al 2006) CR pressure changes shock structure Drury & Völk 1981

20 Explanation B: non-diffusive behaviour walls B cavities B Magnetic barriers Perpendicular shocks B into screen CR CR escape through cavities shock P cr shock Super-diffusion & sub-diffusion due to wandering field lines (Duffy, Kirk, Gallant, Dendy 1995)

21 Need observations of SNR at other stages of evolution

22 Aharonian (2008): table of galactic γ-ray sources red for SNR, green for SNR?

23 SN1006 & Tycho now included RX J identified with G Where is Kepler? Can we see very young SNR?

24 SN interaction with dense circumstellar plasma Supernova 2006jc Pastorello et al 2007, Immler et al 2008 Dec 2001 Oct 2004 Sept 2006 Oct 2006 Pre-ejection >0.01M o Supernova inside pre-ejected shell Shells >1M o SN2005ap (Quimby et al 2007) SN2006gy (Smith & McCray 2007) Connection with gamma-ray bursts (GRB/XRF) eg GRB060218/SN2006aj Nova V407Cygni detected by FERMI

25 TeV-PeV spectrum Structure in spectrum? (Balloon expts) Multiple sources? Zatsepin & Sokolskaya (2006)

26 Please can we have more on Cas A! Cas A MAGIC Cas A VERITAS E -2 E -2.5 E -2 E -2.5 MAGIC

27 Can we observe shock acceleration in action?

28 Estimate shock structure scale δl R h j cr shock j cr xb moves upstream plasma a distance CR precursor v shock δl 1 2 j CR ρ B t 2 Using scaling arguments for j CR, B, ρ & t δl R 100

29 RX J HESS, Aharonian et al 2007 Cas A CHANDRA NASA/CXC/MIT/UMass Amherst/Stage et al. CHANDRA (0.1-10keV) Uchiyama et al 2007 CHANDRA (Patnaude et al 2008)

30 Can CR escape upstream of shock? How do CR get released from SNR?

31 CR interacting with dense clouds outside SNR? HESS: J

32 The future Aharonian 2008 Spectra: turnover - accelerated to knee in SNR? Spectra: concave? non-linear acceleration Spectra: slope is acceleration diffusive Spectra: spectrum below turnover - hadrons or leptons See young SNR: when are CR accelerated? Dense clouds near SNR: do CR escape ahead of shock? Angular resolution: where are CR accelerated in SNR