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Supernova remnants and molecular clouds

Supernova remnants and molecular clouds. Armand Fiasson LAPP - Annecy-le-vieux. Where CRs originate ?. The usual suspects up to the knee are s upernova remnants ( SNRs ) Diffusive shock acceleration Conversion efficiency into CR ~10-30 % needed and expected

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Supernova remnants and molecular clouds

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  1. Supernova remnants and molecularclouds Armand Fiasson LAPP - Annecy-le-vieux

  2. WhereCRsoriginate? • The usual suspects up to the knee are supernova remnants (SNRs) • Diffusive shockacceleration • Conversion efficiencyinto CR ~10-30 % needed and expected • TeVγ-ray emitters (RX J1713, Vela Jr …) => particleacceleration up to 100 TeV • But… • Hadronic or leptonic? • PeVaccelerators? SNR/MC Associations

  3. Hadronic or leptonic? Tycho - Fermi RX J1713.7-3946 - Fermi Giordano et al. 2012 Abdo et al. 2011 SNR/MC Associations

  4. Hadronic or leptonic? RX J1713.7-3946 Tycho Giordano et al. ApJ744 L2 (2012) Bothleptonic and hadronicinterpretation come out fromthese observations Does RXJ1713.7-3946 accelerate hadrons? Not enoughmatter to detectthem? Abdo et al. ApJ734 28 (2011) SNR/MC Associations

  5. The key point: matter • When a leptonic scenario isfavoured: no hadrons or not enoughtarget? • A solution: dense matter concentration surrounding the remnant= molecularclouds • Enoughmatter to detect hadrons in the remnantwheninteractingwith the cloud • Clouds in the vicinity of the remnantmay help detecting the highestenergyparticlethatescaped the remant Drury, Aharonian& Voelk 1994 Aharonian & Atoyan 1996 Gabici et al. 2009 SNR/MC Associations

  6. Molecularclouds • The molecularclouds are major components of the ISM • Coldmatter => T~10-20 K • Neutralmolecularmatter: mainly H2 • Densityabove a few10 atoms/cm-3up to 106 atoms/cm-3 • Whenintegratedover 10 pc scale = verymassivetarget!! • Visibility in the range radio – millimetricwavelength The H2has no electricdipole => no rotationnalline => detectionthroughotherlines CO, CS… SNR/MC Associations

  7. SNR/MC associations Montmerle, 1979 Alreadysuggested as potential gamma-ray emitters in 1979 • Massive stars originate in dense regions => dense molecularclouds • These stars end rapidly in SNRs • TheseSNRsevolves in the vicinity of the parent cloud • The SNRsaccelerateCRs • The CRsinteractinto the cloud and produceγ-rays • Such associations should be frequent SNR/MC Associations

  8. OH masers • The distance to SNRs is not well known • association with MC difficult to assess • Physical interactions can be traced • Line broadening, OH masers … • OH masers are produced via collisions • shock propagating through a dense cloud • >10% of the known SNRs are OH emitting • Correlation between OH emission and gamma-ray emission Wardle, 2002 Hewitt et al., 2009 SNR/MC Associations

  9. List of known associations 34 confirmed + 19 probable + 11 possible > 20 coincidentγ-ray sources Jiang et al. 2010 SNR/MC Associations

  10. Caveats • SNR-MC associations seem to be good targetsto search for CR acceleration but … • Somecaveats to keep in mind: • OH masers indicatephysical SNR-MC association • The shock propagation isaffected by the dense matter • Whatabout the CR accelerationefficiency? • Unusual SNR morphology due to the inhomogeneousmedium • Probably not the best candidates for comparisonwiththeoreticalpredictions • Maser emittingSNRsappearto beratherevolvedSNRswithage ~ 10 kyr • Mostenergeticparticleshave escapedfrom the remnant • Not the best candidates to study the highestenergy in the shockregion SNR/MC Associations

  11. 4 yearsago… MAGIC VERITAS HESS A few TeV sources withstrong indication of hadronicorigin W28, IC443, CTB37A, G359.1-0.5, W51 Fermi & AGILE observations were in progress SNR/MC Associations

  12. The picturenow AGILE Fermi-LAT MAGIC VERITAS HESS All the TeV sources have been confirmedatGeVenergies by Fermi or AGILE + other candidates have been discovered (GeV and/or TeV) W28, IC443, CTB37A, G359.1-0.5, W51 W44, W30, Kes41, G349.7+0.2, W41, W49, 3C391 … … SNR/MC Associations

  13. W28 HESS – Aharonian et al. 2008 AGILE – Giuliani et al. 2010 Fermi – Abdo et al. 2010 • Severalcloudsdetected by HESS atTeVenergies • Molecularclouds in the vicinity of the shock (OH masers) • Plus giantclouds distant from the shock • Confirmation atlowerenergies by AGILE and Fermi • … but 2 hotspots over 4 visible SNR/MC Associations

  14. W28 - CR Diffusion AGILE – Giuliani et al. 2010 Fermi – Abdo et al. 2010 • Hadronicoriginof the γ-rays favoured • The brightest spot in TeVis the fainter in GeV • Different SNR-MC distance • Escaped CR from the shellhavingdiffusedtoward the clouds SNR/MC Associations

  15. IC443 Ackermann et al. 2013 SNR/MC Associations

  16. W44 Ackermann et al. 2013 SNR/MC Associations

  17. GeV-TeVoverview • Hadronicorigin of the γ-rays favored • Bright GeV sources • Faint TeV sources + soft spectra • Break in the CR spectra at GeV energies • Diffusion effects probably Ackermann et al. 2013 Li & Chen 2012 SNR/MC Associations

  18. Neutrino fromtheseclouds? • Soft hadron spectraabove a few GeV • low neutrino flux expectedabove 1 TeV • ~0.1-0.5 neutrino/year Qiang et al. 2011 SNR/MC Associations

  19. CR and cloud ionisation • Molecularclouds are composedmainly of neutral H2 • Ionised by the presence of CRs • Modifiedchemistery • The abundance ratio of severalspeciesis proportionnal to the ionisation rate • GHz observations have been ledtowards IC443 and W51 • Over-ionisation in the cloudassociatedwith IC443 and W51 • ~100 times the typical value HESS-W51 MAGIC - IC443 Indriolo et al. 2010 Ceccarelli et al. 2011 SNR/MC Associations

  20. What to expectfrom CTA? HESS 500h • Improvedsensitivityabove a few 10 GeV by a factor ~10 • Improvedangularresolution by a factor ~5 • Increasednumber of sources atTeVenergies • Increasedsensitivity to the highestenergies and propagation effects CTA 500h Hermann 2008 Acero et al. 2012 SNR/MC Associations

  21. Summary SNR/MC association: a class of sources in rapid expansion • A lot of new candidates atTeVenergies (HESS MAGIC VERITAS) • A lot of detectionatGeVenergies and precise spectral measurement by Fermi & Agile • Point to a hadronicorigin of gamma-rays • Common spectral features • Propagation effects visible (W28, IC443…) • Interesting class of sources for variouscommunity • CRs& ionisation intomolecularclouds and theirchemistery SNR/MC Associations

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