Gamma ray emission from supernova remnant/molecular cloud associations

Transcription

1 Gamma ray emission from supernova remnant/molecular cloud associations Stefano Gabici APC, Paris

2 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 δ = 2.7 CR knee δ = 3.0 extragalactic

3 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

4 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 cm -3 } proton-proton interactions SNRs visible in TeV gamma rays

5 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 cm -3 } proton-proton interactions SNRs visible in TeV gamma rays RXJ1713 as seen by HESS SNRs TEST PASSED! BUT hadronic or leptonic???

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

7 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 TeV...but RXJ1713 is NOT!!!? ν 's Gabici, 2008

8 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

9 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)

10 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

11 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 E max B sh t 1/5

12 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 E max B sh t 1/5 B sh also depends on time E max decreases with time Particles with E > E max escape the SNR

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

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

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

16 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

17 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

18 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

19 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 still no evidence for the existence of escaping CRs

20 Particle escape from SNRs v s

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

22 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

23 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

24 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 = cm 2 /s SNR Cloud PeVatron!!! but for short time! Gabici&Aharonian(2007)

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

26 Gamma rays from MCs illuminated by CRs t yr t = 8000 yr yr TeV PeV PeV TeV d = 1 kpc d snr/cl = 100 pc M cl = 10 4 M D P ev = 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!

27 Gamma rays from MCs illuminated by CRs t yr 8000 yr t = yr yr TeV PeV GeV PeV TeV d = 1 kpc d snr/cl = 100 pc M cl = 10 4 M D P ev = 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!

28 Gamma rays from MCs illuminated by CRs t yr 8000 yr t = yr yr TeV PeV GeV PeV TeV d = 1 kpc d snr/cl = 100 pc M cl = 10 4 M D P ev = 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!

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

30 Naive statistics hard spectrum! soft spectrum t = 2000 yr t = 8000 yr t = yr d = 1 kpc d snr/cl = 100 pc M cl = 10 4 M D P ev = 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

31 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

32 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

33 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 V-shaped spectra Gamma Rays

34 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 V-shaped spectra Gamma Rays steep spectra

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

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

37 The W28 region in gammas, CO, & radio NANTEN data - CO line W28-24 o -23 o o Dec J (deg) NANTEN 12 CO(J=1-0) 0-10 km/s HESS J l=+7.0 o GRO J G W 28 (Radio Boundary) l=+6.0 o b=0.0 o o -23 o o Dec J (deg) NANTEN 12 CO(J=1-0) km/s HESS J l=+7.0 o GRO J G W 28 (Radio Boundary) l=+6.0 o b=0.0 o b=-1.0 o A HESS J h03m W 28A2 C B RA J (hrs) 18h 0 b=-1.0 o A HESS J h03m W 28A2 C B RA J (hrs) 18h 0 HESS - TeV emission Aharonian et al, 2008

38 The W28 region in gammas, CO, & radio NANTEN data - CO line W28-24 o -23 o o Dec J (deg) NANTEN 12 CO(J=1-0) 0-10 km/s HESS J l=+7.0 o GRO J G W 28 (Radio Boundary) l=+6.0 o b=0.0 o o -23 o o Dec J (deg) NANTEN 12 CO(J=1-0) km/s HESS J l=+7.0 o GRO J G W 28 (Radio Boundary) l=+6.0 o b=0.0 o b=-1.0 o A HESS J h03m W 28A2 C B RA J (hrs) 18h 0 b=-1.0 o A HESS J h03m W 28A2 C B RA J (hrs) 18h 0 HESS - TeV emission Radio (Dubner et al 2000) Aharonian et al, 2008

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

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

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

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

43 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

44 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

45 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? + masers γ

46 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? + masers γ -> most of the protons already escaped (> GeV?)

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

48 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

49 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

50 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...

51 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 (D t age ) 1/2 t = t age t out? model dependent... high energy particles

52 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 (D t age ) 1/2 t = t age t out? model dependent... high energy particles lower energies -> point-like approx not so good + model dependent (t out ~ t age )

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

54 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

55 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

56 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

57 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 yr const η CR E SN l 3 d E SN erg M N cl M γ e 2 R l d estimate D? l d (D t age ) 1/2

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

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

60 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

61 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

62 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

63 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 erg initial velocity -> v 0 ~ 5500 km/s SNR age -> 4.4 x 10 4 yr (radiative phase)

64 W28: TeV emission ~ M sun North South ~ M sun A B ~ M sun

65 W28: TeV emission ~ 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 ~ M sun A B ~ M sun South A South B

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

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

68 W28: GeV emission if cloud A and B are at the same distance -> same spectrum s 1 ) 2 df/de (ev cm 2 E (a) W28 North (Source N) 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 (b) W28 South (Source S) B 10 Energy (GeV) s 1 ) 2 df/de (ev cm 2 E (a) HESS J A A 10 Energy (GeV) FERMI -> Abdo et al, 2010

69 W28: GeV emission

70 ~ TeV W28: GeV emission

71 W28: GeV emission ~ TeV ~ GeV

72 W28: GeV emission ~ TeV ~ GeV

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

74 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

75 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)

76 Conclusions (problems) Can we estimate the diffusion coefficient?

77 Conclusions (problems) Can we estimate the diffusion coefficient? The diffusion coefficient around W28 might be suppressed... by a factor of ~ ~TeV CRs fill a region of ~ 100 pc around W28 GeV emission more model dependent -> constrains on particle escape?

78 Conclusions (problems) Can we estimate the diffusion coefficient? The diffusion coefficient around W28 might be suppressed... by a factor of ~ ~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...

79 Conclusions (problems) Can we estimate the diffusion coefficient? The diffusion coefficient around W28 might be suppressed... by a factor of ~ ~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 W > more data from HESS, Fermi, and CTA