Gamma ray emission from supernova remnant/molecular cloud associations

Gamma ray emission from supernova remnant/molecular cloud associations Stefano Gabici APC, Paris stefano.gabici@apc.univ-paris7.fr

The Origin of galactic Cosmic Rays Facts: the spectrum is (ALMOST) a single power law -> CR knee at few PeVs extremely isotropic, up to very high energies energy density -> ω CR = 1 ev/cm 3 Most popular explanation: acceleration in SuperNovaRemnants -> CR energy density if efficiency 10% diffusive shock acceleration -> roughly the required spectrum... propagation in the Galaxy -> isotropy δ = 2.7 CR knee δ = 3.0 extragalactic

Gamma rays from SNRs: a test for CR origin Drury, Aharonian & Volk, 1994 CR observations -> CR power of the Galaxy 10% of SNR energy MUST Supernova rate in the Galaxy ( 3 per century)} be converted into CRs ISM density n 0.1 1 cm -3 } proton-proton interactions SNRs visible in TeV gamma rays

Are SuperNova Remnants CR PeVatrons? We d like CR sources to accelerate (at least) up to that energy CR knee @few PeV s Something must happen here...

RXJ1713 does not look like a PeVatron... We would like SNRs to be CR PeVatrons... RXJ1713 data from HESS Underlying proton spectrum E -2 with exponential cutoff @150 TeV...but RXJ1713 is NOT!!!? ν 's Gabici, 2008

RX J1713 probably WAS a PeVatron! We need to know a bit of shock acceleration theory... THIS IS A SNR u sh Diffusion length: l diff D(E) u sh E B sh u sh R sh

RX J1713 probably WAS a PeVatron! We need to know a bit of shock acceleration theory... THIS IS A SNR u sh Diffusion length: l diff D(E) u sh E B sh u sh R sh Confinement condition: D(E) u sh (t) < R sh(t) E max B sh u sh (t) R sh (t) Sedov phase: R sh (t) t 2/5 u sh (t) t 3/5

Particle escape from SNRs Ptuskin & Zirakashvili, 2003 E max [GeV] t [yr] u sh [km/s]

Particle escape from SNRs ~ PeV Ptuskin & Zirakashvili, 2003 E max [GeV] t [yr] 200 yrs u sh [km/s]

Particle escape from SNRs Ptuskin & Zirakashvili, 2003 E max [GeV] t [yr] ~10 5 yrs ~10 GeV u sh [km/s]

Particle escape from SNRs v s RXJ1713 WAS a CR PeVatron PeV particles are accelerated at the beginning of Sedov phase (~200yrs), when the shock speed is high! This is a supernova remnant

Particle escape from SNRs v s RXJ1713 WAS a CR PeVatron PeV particles are accelerated at the beginning of Sedov phase (~200yrs), when the shock speed is high! they quickly escape as the shock slows down This is a supernova remnant

Particle escape from SNRs v s This is a supernova remnant RXJ1713 WAS a CR PeVatron PeV particles are accelerated at the beginning of Sedov phase (~200yrs), when the shock speed is high! they quickly escape as the shock slows down Highest energy particles are released first, and particles with lower and lower energy are progressively released later a SNR is a PeVatron for a very short time

Particle escape from SNRs v s

Particle escape from SNRs v s γ γ Both SNR and surrounding molecular clouds emit gammas

Particle escape from SNRs Survey is a good strategy! v s γ ϑ 6 1 D 1 kpc dcl 100 pc γ ϑ Both SNR and surrounding molecular clouds emit gammas

Montmerle s SNOBs adapted from Montmerle, 1979 ; Casse & Paul, 1980 Massive (OB) stars form in dense regions -> molecular cloud complexes OB stars evolve rapidly and eventually explode forming SNRs SNR shocks accelerate COSMIC RAYS CRs escape from their sources and diffuse away in the DENSE circumstellar material -> molecular cloud complex and produce there gamma rays! An association between cosmic ray sources and molecular clouds is expected

Gamma rays from MCs illuminated by CRs t = 400 yr 1 PeV d = 1 kpc d snr/cl = 100 pc M cl = 10 4 M D P ev = 3 10 29 cm 2 /s SNR Cloud PeVatron!!! but for short time! Gabici&Aharonian(2007)

Gamma rays from MCs illuminated by CRs t = 400 2000 yr yr 100 1 PeV TeV 1 PeV d = 1 kpc d snr/cl = 100 pc M cl = 10 4 M D P ev = 3 10 29 cm 2 /s SNR Cloud hard spectrum! Gabici&Aharonian(2007) HESS remnant Indirect detection of a PeVatron! Emission lasts longer! NO ICS -> Klein-Nishina

Gamma rays from MCs illuminated by CRs t 400 2000 yr t = 8000 yr yr 100 1 TeV PeV 100 1 PeV TeV d = 1 kpc d snr/cl = 100 pc M cl = 10 4 M D P ev = 3 10 29 cm 2 /s SNR Cloud hard spectrum! Gabici&Aharonian(2007) GLAST HESS remnant? Indirect HESS and detection MILAGRO of a PeVatron! unidentified Emission sources? lasts longer!

Gamma rays from MCs illuminated by CRs t 400 2000 yr 8000 yr t = 32000 yr yr 100 100 1 TeV PeV GeV 100 1 PeV TeV d = 1 kpc d snr/cl = 100 pc M cl = 10 4 M D P ev = 3 10 29 cm 2 /s SNR Cloud hard spectrum! Gabici&Aharonian(2007) GLAST HESS no emission remnant? Indirect HESS and detection MILAGRO of a PeVatron! unidentified Emission sources? lasts longer!

Naive statistics hard spectrum! t = 2000 yr d = 1 kpc d snr/cl = 100 pc M cl = 10 4 M D P ev = 3 10 29 cm 2 /s = 0.1 D gal t = 8000 yr soft spectrum t = 32000 yr Soft sources dominate the total number of sources

Naive statistics hard spectrum! soft spectrum t = 2000 yr t = 8000 yr t = 32000 yr d = 1 kpc d snr/cl = 100 pc M cl = 10 4 M D P ev = 3 10 29 cm 2 /s = 0.1 D gal Soft sources dominate the total number of sources Cloud statistics -> diffusion coefficient at specific locations in the Galaxy

MultiWaveLength implications M=10 5 M ; D=1kpc ; D 10 =10 28 cm 2 /s ; d = 100 pc CR sea <- time t = 32 Cosmic Rays 8 2 kyr

MultiWaveLength implications M=10 5 M ; D=1kpc ; D 10 =10 28 cm 2 /s ; d = 100 pc CR sea Peak from CR background (steady) Peak from CRs from SNR (time dependent) <- time t = 32 Cosmic Rays 8 2 kyr Gamma Rays

The W28 region in gammas, CO, & radio W28 HESS - TeV emission

The W28 region in gammas, CO, & radio W28 HESS - TeV emission Aharonian et al, 2008

The W28 region in gammas, CO, & radio NANTEN data - CO line W28-24 o -23 o 30-23 o Dec J2000.0 (deg) NANTEN 12 CO(J=1-0) 0-10 km/s HESS J1801-233 l=+7.0 o GRO J1801-2320 6.225-0.569 G6.1-0.6 W 28 (Radio Boundary) l=+6.0 o b=0.0 o 100 80 60 40 20-24 o -23 o 30-23 o Dec J2000.0 (deg) NANTEN 12 CO(J=1-0) 10-20 km/s HESS J1801-233 l=+7.0 o GRO J1801-2320 6.225-0.569 G6.1-0.6 W 28 (Radio Boundary) l=+6.0 o b=0.0 o 100 80 60 40 20 b=-1.0 o A HESS J1800-240 18h03m W 28A2 C B RA J2000.0 (hrs) 18h 0 b=-1.0 o A HESS J1800-240 18h03m W 28A2 C B RA J2000.0 (hrs) 18h 0 HESS - TeV emission Aharonian et al, 2008

CO(J=1-0) 0-10 km/s NANTEN data - CO line FERMI and HESS J1801-233 AGILE - GeV emission 100 W 28 (Radio Boundary) 80 12 CO(J=1-0) 10-20 km/s 100 W 28 (Radio Boundary) HESS J1801-233 80 o o -23o30 W28 60 GRO J1801-2320 60 GRO J1801-2320 l=+6.0o l=+6.0o 40 6.225-0.569 G6.1-0.6 o G6.1-0.6 40 6.225-0.569-24 Source N 23:00:00-24o Declination (J2000) (a) NANTEN l=+7.0-23 30 o l=+7.0 Dec J2000.0 (deg) 12 o NANTEN -23-23o Dec J2000.0 (deg) The W28 region in gammas, CO, & radio o b=0.0 b=0.0o 20 o b=-1.0 A HESS J1800-240 18h03m A 24:00:00 B C Source S 18:04:00 18:00:00 Right Ascension (J2000) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 HESS - TeV emission [counts/pixel] FERMI -> Abdo et al, 2010 Aharonian et al, 2008 C o b=-1.0 B RA J2000.0 (hrs) 18h 0 A HESS J1800-240 18h03m W 28A2 B C RA J2000.0 (hrs) 0 18h Radio (Dubner et al 2000) HESS J1800-240 W 28A2 20 AGILE -> Giuliani et al, 2010

W28 as seen by a theoretician SNR shell radio emission -> GeV electrons -> ongoing (re)acceleration?

W28 as seen by a theoretician SNR shell radio emission Molecular clouds -> GeV electrons -> ongoing (re)acceleration?

W28 as seen by a theoretician γ SNR shell radio emission Molecular clouds gamma rays + gas -> GeV electrons -> ongoing (re)acceleration? -> CR protons? γ

W28 as seen by a theoretician γ CR SNR shell radio emission Molecular clouds gamma rays + gas -> GeV electrons -> ongoing (re)acceleration? -> CR protons? -> coming from the SNR? CR γ

W28 as seen by a theoretician γ CR SNR shell Molecular clouds gamma rays + gas ~12 pc radio emission -> GeV electrons -> ongoing (re)acceleration? -> CR protons? -> coming from the SNR? CR ~ 20 pc -> projection effects? γ

Escaping particles assumptions -> point like explosion -> (isotropic) diffusion coefficient independent on position -> particles with energy E escape after a time: t out E δ

Escaping particles assumptions -> point like explosion -> (isotropic) diffusion coefficient independent on position -> particles with energy E escape after a time: t out E δ this is just a parametrization

assumptions -> point like explosion Escaping particles when the SNR higher energy is smaller particles are released first -> (isotropic) diffusion coefficient independent on position -> particles with energy E escape after a time: t out E δ this is just a parametrization diffusion length l d (D t) 1/2 t = t age t out? model dependent...

Escaping particles: CR spectrum t age -> l d = 10, 30, 100 pc l d (D t age ) 1/2

Escaping particles: CR spectrum t age -> l d = 10, 30, 100 pc const η CR E SN l 3 d l d (D t age ) 1/2

Escaping particles: CR spectrum t age -> l d = 10, 30, 100 pc const η CR E SN l 3 d e 2 R l d l d (D t age ) 1/2

Escaping particles: CR spectrum t age -> l d = 10, 30, 100 pc const η CR E SN l 3 d γ e 2 R l d l d (D t age ) 1/2

Escaping particles: CR spectrum if we want SNRs to be the sources of CRs... t age -> l d = 10, 30, 100 pc 0.1 η CR 1 t age 3 10 4 10 5 yr const η CR E SN l 3 d E SN 2 4 10 50 erg M N cl 5 10 4 M γ e 2 R l d estimate D? l d (D t age ) 1/2

Escaping particles: W28 Fγ Fγ M cl North M cl South North South

Escaping particles: W28 Fγ Fγ M cl North M cl South North ld both clouds within a distance l d South

Escaping particles: W28 Fγ Fγ M cl North M cl South North ld both clouds within a distance l d South F γ f CR M cl d 2

Escaping particles: W28 Fγ Fγ M cl North M cl South North ld both clouds within a distance l d South Mcl F γ f CR M cl d 2 η CR E SN (D t age ) 3/2 d 2

North Escaping particles: W28 Fγ M cl North Fγ M cl South ld both clouds within a distance l d South F γ f CR M cl d 2 η CR E SN (D t age ) 3/2 Mcl d 2 and we get... -> D ηcr E SN M cl F γ d 2 2/3 t 1 age

W28: numbers Measured quantities: apparent size: ~ 45-50, distance ~ 2 kpc -> R s ~ 12 pc ratio OIII/Hβ -> v s = 80 km/s Assumptions: mass of ejecta -> M ej ~ 1.4 M sun ambient density -> n ~ 5 cm -3 Derived quantities (Cioffi et al 1989 model): explosion energy -> E SN ~ 0.4 x 10 51 erg initial velocity -> v 0 ~ 5500 km/s SNR age -> 4.4 x 10 4 yr (radiative phase)

W28: TeV emission ~ 5 10 4 M sun North South ~ 6 10 4 M sun A B ~ 4 10 4 M sun

W28: TeV emission ~ 5 10 4 M sun virtually the same curves for: North South acceleration efficiency diffusion coefficient in units of the galactic one (η, χ) = (10%, 0.028); (30%, 0.06); (50%, 0.085) North ~ 6 10 4 M sun A B ~ 4 10 4 M sun South A South B

W28: TeV emission ~ 5 10 4 M sun virtually the same curves for: North South ~ 6 10 4 M sun A acceleration efficiency diffusion coefficient in units of the galactic one B ~ 4 10 4 M sun (η, χ) = (10%, 0.028); (30%, 0.06); (50%, 0.085) diffusion coefficient is suppressed! North South A South B

W28: TeV emission ~ 5 10 4 M sun virtually the same curves for: North South ~ 6 10 4 M sun A acceleration efficiency diffusion coefficient in units of the galactic one B ~ 4 10 4 M sun size of CR bubble @3 TeV l d 70 pc χ =0.028 95 pc χ =0.06 115 pc χ =0.085 (η, χ) = (10%, 0.028); (30%, 0.06); (50%, 0.085) diffusion coefficient is suppressed! North South A South B

W28: GeV emission if cloud A and B are at the same distance -> same spectrum s 1 ) 2 df/de (ev cm 2 E 2 10 10 1 1 10 (a) W28 North (Source N) 1 10 1 10 2 10 3 10 Energy (GeV) if the cloud is within the CR bubble [d < l d (E)] cloud A might not be physically associated with the W28 system s 1 ) 2 df/de (ev cm 2 E 2 10 10 1 1 10 (b) W28 South (Source S) 1 10 1 10 2 10 3 B 10 Energy (GeV) s 1 ) 2 df/de (ev cm 2 E 10 1 1 10 (a) HESS J1800 240A 1 10 1 10 2 10 3 A 10 Energy (GeV) FERMI -> Abdo et al, 2010

W28: GeV emission

~ TeV W28: GeV emission

W28: GeV emission ~ TeV ~ GeV

W28: GeV emission η = 30% χ =0.06 North South B South A d = 12 pc d = 32 pc d = 65 pc

W28: GeV emission η = 30% χ =0.06 this peak is removed as background North South B South A d = 12 pc d = 32 pc d = 65 pc

W28: GeV emission η = 30% χ =0.06 this peak is removed as background North South B South A d = 12 pc d = 32 pc d = 65 pc some problems here... + some of the approximations are not very good at low energies + subtraction of the background? + other contributions? (Bremsstrahlung)

Conclusions (problems) Can we estimate the diffusion coefficient?

Conclusions (problems) Can we estimate the diffusion coefficient? The diffusion coefficient around W28 might be suppressed... by a factor of ~ 10-100 ~TeV CRs fill a region of ~ 100 pc around W28 GeV emission more model dependent -> constrains on particle escape?...but... can CRs suppress D? -> non-linear diffusion (e.g. Ptuskin et al 2007) is D isotropic? -> or mostly // to field lines? we have only one W28...