Supernova remnants and molecular clouds
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Transcript of Supernova remnants and molecular clouds
Supernova remnants and molecular clouds
Armand FiassonLAPP - Annecy-le-vieux
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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?
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Hadronic or leptonic?
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Tycho - Fermi RX J1713.7-3946 - Fermi
Giordano et al. 2012 Abdo et al. 2011
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Hadronic or leptonic?
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TychoRX 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)
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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
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Aharonian & Atoyan 1996Gabici et al. 2009
Drury, Aharonian & Voelk 1994
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Molecular clouds
• The molecular clouds are major components of the ISM– Cold matter => T~10-20 K– Neutral molecular matter: mainly H2
– Density above a few 10 atoms/cm-3 up to 106 atoms/cm-3
When integrated over 10 pc scale = very massive target!!
• Visibility in the range radio – millimetric wavelengthThe H2 has no electric dipole => no rotationnal line=> detection through other lines CO, CS…
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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
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Montmerle, 1979
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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
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Wardle, 2002
Hewitt et al., 2009
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List of known associations
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34 confirmed+ 19 probable+ 11 possible
> 20 coincident γ-ray sources
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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
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4 years ago…
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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
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The picture now
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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, W51W44, W30, Kes41, G349.7+0.2, W41, W49, 3C391 …
Fermi-LAT
AGILE
HESS
VERITAS
MAGIC
…
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W28
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Fermi – Abdo et al. 2010AGILE – Giuliani et al. 2010HESS – 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
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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
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AGILE – Giuliani et al. 2010 Fermi – Abdo et al. 2010
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IC443
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Ackermann et al. 2013
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W44
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Ackermann et al. 2013
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GeV-TeV overview
A.Fiasson - Moriond 2013Li & 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
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Neutrino from these clouds?
• Soft hadron spectra above a few GeV low neutrino flux expected above 1 TeV ~0.1-0.5 neutrino/year
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Qiang et al. 2011
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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
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Indriolo et al. 2010 Ceccarelli et al. 2011
HESS-W51
MAGIC - IC443
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What to expect from CTA?
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• 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
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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
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