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Supernova remnants and molecular clouds Armand Fiasson LAPP - Annecy-le-vieux.

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Presentation on theme: "Supernova remnants and molecular clouds Armand Fiasson LAPP - Annecy-le-vieux."— Presentation transcript:

1 Supernova remnants and molecular clouds Armand Fiasson LAPP - Annecy-le-vieux

2 Where CRs originate? The usual suspects up to the knee are supernova remnants (SNRs) – Diffusive shock acceleration – Conversion efficiency into CR ~10-30 % needed and expected TeV γ-ray emitters (RX J1713, Vela Jr …) => particle acceleration up to 100 TeV But… – Hadronic or leptonic? – PeV accelerators? A.Fiasson - Moriond 2013SNR/MC Associations2

3 Hadronic or leptonic? A.Fiasson - Moriond 2013SNR/MC Associations3 Tycho - Fermi RX J1713.7-3946 - Fermi Giordano et al. 2012 Abdo et al. 2011

4 Hadronic or leptonic? A.Fiasson - Moriond 2013SNR/MC Associations4 Tycho RX J1713.7-3946 Both leptonic and hadronic interpretation come out from these observations Does RXJ1713.7-3946 accelerate hadrons? Not enough matter to detect them? Giordano et al. ApJ 744 L2 (2012) Abdo et al. ApJ 734 28 (2011)

5 The key point: matter When a leptonic scenario is favoured: no hadrons or not enough target? A solution: dense matter concentration surrounding the remnant = molecular clouds – Enough matter to detect hadrons in the remnant when interacting with the cloud – Clouds in the vicinity of the remnant may help detecting the highest energy particle that escaped the remant A.Fiasson - Moriond 2013SNR/MC Associations5 Aharonian & Atoyan 1996 Gabici et al. 2009 Drury, Aharonian & Voelk 1994

6 Molecular clouds The molecular clouds are major components of the ISM – Cold matter => T~10-20 K – Neutral molecular matter: mainly H 2 – Density above a few 10 atoms/cm -3 up to 10 6 atoms/cm -3  When integrated over 10 pc scale = very massive target!! Visibility in the range radio – millimetric wavelength The H 2 has no electric dipole => no rotationnal line => detection through other lines CO, CS… A.Fiasson - Moriond 2013SNR/MC Associations6

7 SNR/MC associations Already suggested as potential gamma-ray emitters in 1979 Massive stars originate in dense regions => dense molecular clouds These stars end rapidly in SNRs These SNRs evolves in the vicinity of the parent cloud The SNRs accelerate CRs The CRs interact into the cloud and produce γ-rays  Such associations should be frequent A.Fiasson - Moriond 2013SNR/MC Associations7 Montmerle, 1979

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 A.Fiasson - Moriond 2013SNR/MC Associations8 Wardle, 2002 Hewitt et al., 2009

9 List of known associations A.Fiasson - Moriond 2013SNR/MC Associations9 Jiang et al. 2010 34 confirmed + 19 probable + 11 possible > 20 coincident γ-ray sources

10 Caveats SNR-MC associations seem to be good targets to search for CR acceleration but … Some caveats to keep in mind: – OH masers indicate physical SNR-MC association  The shock propagation is affected by the dense matter  What about the CR acceleration efficiency? – Unusual SNR morphology due to the inhomogeneous medium  Probably not the best candidates for comparison with theoretical predictions – Maser emitting SNRs appear to be rather evolved SNRs with age ~ 10 kyr  Most energetic particles have escaped from the remnant  Not the best candidates to study the highest energy in the shock region A.Fiasson - Moriond 2013SNR/MC Associations10

11 4 years ago… A.Fiasson - Moriond 2013SNR/MC Associations11 A few TeV sources with strong indication of hadronic origin W28, IC443, CTB37A, G359.1-0.5, W51 Fermi & AGILE observations were in progress HESS VERITAS MAGIC

12 The picture now A.Fiasson - Moriond 2013SNR/MC Associations12 All the TeV sources have been confirmed at GeV energies 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 … Fermi-LAT AGILE HESS VERITAS MAGIC …

13 W28 A.Fiasson - Moriond 2013SNR/MC Associations13 Fermi – Abdo et al. 2010AGILE – Giuliani et al. 2010 HESS – Aharonian et al. 2008 Several clouds detected by HESS at TeV energies  Molecular clouds in the vicinity of the shock (OH masers)  Plus giant clouds distant from the shock Confirmation at lower energies by AGILE and Fermi … but 2 hotspots over 4 visible

14 W28 - CR Diffusion Hadronic origin of the γ-rays favoured The brightest spot in TeV is the fainter in GeV – Different SNR-MC distance  Escaped CR from the shell having diffused toward the clouds A.Fiasson - Moriond 2013SNR/MC Associations14 AGILE – Giuliani et al. 2010Fermi – Abdo et al. 2010

15 IC443 A.Fiasson - Moriond 2013SNR/MC Associations15 Ackermann et al. 2013

16 W44 A.Fiasson - Moriond 2013SNR/MC Associations16 Ackermann et al. 2013

17 GeV-TeV overview A.Fiasson - Moriond 2013SNR/MC Associations17 Li & Chen 2012 Hadronic origin 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

18 Neutrino from these clouds? Soft hadron spectra above a few GeV  low neutrino flux expected above 1 TeV  ~0.1-0.5 neutrino/year A.Fiasson - Moriond 2013SNR/MC Associations18 Qiang et al. 2011

19 CR and cloud ionisation Molecular clouds are composed mainly of neutral H2  Ionised by the presence of CRs  Modified chemistery The abundance ratio of several species is proportionnal to the ionisation rate GHz observations have been led towards IC443 and W51  Over-ionisation in the cloud associated with IC443 and W51  ~100 times the typical value A.Fiasson - Moriond 2013SNR/MC Associations19 Indriolo et al. 2010Ceccarelli et al. 2011 HESS-W51 MAGIC - IC443

20 What to expect from CTA? A.Fiasson - Moriond 2013SNR/MC Associations20 Improved sensitivity above a few 10 GeV by a factor ~10 Improved angular resolution by a factor ~5  Increased number of sources at TeV energies  Increased sensitivity to the highest energies and propagation effects Hermann 2008 HESS 500h CTA 500h Acero et al. 2012

21 Summary SNR/MC association: a class of sources in rapid expansion A lot of new candidates at TeV energies (HESS MAGIC VERITAS) A lot of detection at GeV energies and precise spectral measurement by Fermi & Agile  Point to a hadronic origin of gamma-rays  Common spectral features Propagation effects visible (W28, IC443…) Interesting class of sources for various community – CRs & ionisation into molecular clouds and their chemistery A.Fiasson - Moriond 2013SNR/MC Associations21

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