Supernova remnants and molecular clouds

Supernova remnants and molecular clouds

Armand FiassonLAPP - Annecy-le-vieux

SNR/MC Associations 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 2013


Hadronic or leptonic?


Tycho - Fermi RX J1713.7-3946 - Fermi

Giordano et al. 2012 Abdo et al. 2011


Hadronic or leptonic?


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)


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


Aharonian & Atoyan 1996Gabici et al. 2009

Drury, Aharonian & Voelk 1994


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…



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


Montmerle, 1979


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


List of known associations

A.Fiasson - Moriond 2013Jiang et al. 2010

34 confirmed+ 19 probable+ 11 possible

> 20 coincident γ-ray sources


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



4 years ago…


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


The picture now


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

…


W28


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


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


AGILE – Giuliani et al. 2010 Fermi – Abdo et al. 2010


IC443


Ackermann et al. 2013


W44




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



Neutrino from these clouds?

• Soft hadron spectra above a few GeV low neutrino flux expected above 1 TeV ~0.1-0.5 neutrino/year


Qiang et al. 2011


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


Indriolo et al. 2010 Ceccarelli et al. 2011

HESS-W51

MAGIC - IC443


What to expect from CTA?


• 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


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


Supernova remnants and molecular clouds

Documents

Transcript of Supernova remnants and molecular clouds