Geometry of acceleration in the bipolar remnant of SN1006 with XMM-Newton

1. Irfu Saclay Geometry of acceleration in the bipolar remnant of SN1006 with XMM-Newton Gilles Maurin, Service d’Astrophysique/AIM - CEA Saclay, France First results from the XMM-Newton LP on SN 1006 Co-Is: A. Decourchelle, M. Miceli, F. Bocchino, G. Dubner, E. Giacani, J. Ballet, S. Orlando, J. Vink, E. Helder, D. Kosenko, Acero F., Cassam Chenai G.

2. SN1006 : Why study SN 1006 ? • SN 1006 is a historical SN: age and distance (2.2 kpc) are well-known • Synchrotron emission from radio to X-rays: first evidence of electron acceleration up to TeV energies in this source (Koyama et al. 1995, Nature 378, 255). Nonthermal rims Thermal interior

3. SN1006 : Why study SN 1006 ? • SN 1006 is a historical SN: age and distance (2.2 kpc) are well-known • Synchrotron emission from radio to X-rays: first evidence of electron acceleration up to TeV energies in this source (Koyama et al. 1995, Nature 378, 255). • Thermal emission : uniform ambient medium around the source • The interstellar absorption towards it, is low • Observed in optic, radio, x-rays and recently in γ-rays CTIO optic ATCA Dyer et al. 09 Chandra Cassam-Chenaï et al. 08 HESS Naumann-Godo et al. 09 • For all these reasons, SN1006 is a good target to study particle acceleration

4. Particle acceleration in SN1006: a number of pending questions • Where particle acceleration occurs ? Polar caps vs equatorial belt (Berezhko et al. 02, Rothenflug et al. 04) • Fraction of shock energy tapped by cosmic rays? • Curvature of the particle spectra (Berezhko & Ellison 99, Ellison & Reynolds 91, Allen et al. 08) • Lower post-shock temperature (Ellison et al. 00, Decourchelle et al. 00) • Shrinking of the post-shock region (Decourchelle et al. 00, Cassam-Chenaï et al. 08, Miceli et al. 09) • What is the maximum energy Emax of accelerated particles ? • Electrons are a few % of cosmic rays but can reveal a lot on the mechanism of diffusive shock acceleration => accelerated like protons, so their spectrum is expected to be the same. • How does Emax and hence particle acceleration change with ambient B orientation ? • High latitude SNRs evolving in a uniform interstellar magnetic field, like SN 1006, offer the possibility to investigate this dependence (Völk et al. 03)  We requested a XMM-Newton large project to bring new elements of answers to these questions.

5. XMM-Newton Large program on SN 1006 Objectives: particle acceleration, magnetic field amplification, heating of the electrons and ions at the shock, abundances and distribution of the chemical elements in the ejecta Large project : • New observations: 7 • Total observation time: 642 ks • Status: all observations performed Exposure • Data: all XMM data available (LP + previous shallow observations) • 955 ks -> 656 ks after flare rejection • New analysis: instrumental background subtraction based on ‘close’ rather than blank sky observations • = Better control of systematic errors G. Maurin et al. in prep. • Spatially resolved spectroscopy of the synchrotron emission • Measurement of the azimuthal variation of the cut-off frequency and the spectral index • along the shock

6. New XMM-Newton images of SN1006 3-6 keV 0.5-0.8 keV Dominated by synchrotron emission

7. New XMM-Newton image of SN1006 1.5-3 keV Dominated by synchrotron emission

8. New XMM-Newton image of SN1006 1.5-3 keV The inner filaments Dominated by synchrotron emission

9. New XMM-Newton image of SN1006 1.5-3 keV We defined ‘’seven’’ filaments Dominated by synchrotron emission

10. Spectral modelling of the X-ray and radio emission Spectral modelling: • thermal plane-parallel non-equilibrium model (VPSHOCK, Borkowski et al. 01) • interstellar absorption (WABS): NH ~7 1020 cm-2 (Dubner et al. 02) • exponential cut-off power law model (SRCUT, Reynolds & Keohane 99) we used radio flux to fix its normalization (expansion taken into account) Radio Maps XMM - Newton Box: 16’’ x 16’’ Rothenflug 2004 Petruk 2008 G. Maurin et al. in prep. Dyer 2009 Reynoso 2010

11. Azimuthal variation of the synchrotron cut-off frequency for the inner filament E W E W • Cut-off frequencies obtained with the 4 radio maps are compatible : •  Cut-off frequency depends mainly on the X-rays spectrum • Along these two extended filaments, cut-off frequency shows : • A rapid increase, followed by a plateau and a rapid decrease (same behaviour in each rim) • = this very strong variation (hνcut-off up to 5 keV) cannot be explained only by the variation of the magnetic compression •  Maximum energy of accelerated particles is higher at the bright limbs (?)

12. Azimuthal variation of the synchrotron cut-off frequency for each filaments (with Dyer’s map) E W E W • In the extended filaments, cut-off frequency shows : • Same Behaviour : a rapid increase, followed by a plateau and a rapid decrease • Amplitude depends on filaments (x 4 to 10) • The most outward filaments have a larger cut-off frequency (Vs ~ 5000 km/s, Katsuda et al. 09)

13. Synchrotron spectral index for the inner filament E W • Synchrotron spectral index depends mainly on the radio normalization •  Significant differences between the 4 radio maps (in particular with the Petruk’s map) • Along these two extended filaments, synchrotron spectral index shows : • a small increase towards the pole and a small decrease outwards (same behaviour in each rim)

14. Synchrotron spectral index for each filaments (with Dyer’s map) E W ≈ 0.52 • Along all filaments, same behavior of the spectral index: • Values vary from 0.4 to 0.55 • Increase slightly towards the pole and decrease outwards •  but it’s compatible with a constant: ≈ 0.52

15. Interpretations(?) and conclusion These data provide and will provide (size of filaments, magnetic field, thermal emission, density) strong constraints to the acceleration mechanism. But for the moment, we don’t explain the azimuthal dependences ! Possibilities : • The high cut-off frequency in the pole could mean a high energy reached by particles • The higher shock velocity must explainthe highest cut-off frequencyin the outermost filaments • The saturation of the cut-off frequency near the pole may be explained by an identical value of the post-shock magnetic field • The large spectral index could be explain by a high acceleration efficiency or injection In order to test these possibilities, we need a detailed modeling • And, of course, we must understand why radio maps present such differences.