Gamma ray emission from supernova remnant/molecular cloud ... · Gamma ray emission from supernova...

Gamma ray emission from supernova remnant/molecular

cloud associations

Stefano GabiciAPC, Paris

[email protected]

The Origin of galactic Cosmic Rays

CR knee

Facts: the spectrum is (ALMOST) a single power law -> CR knee at few PeVs extremely isotropic, up to very high energies energy density -> ωCR = 1 eV/cm3

δ = 2.7δ = 3.0

extragalactic

The Origin of galactic Cosmic Rays

CR knee

Most popular explanation:

acceleration in SuperNovaRemnants -> CR energy density if efficiency ≥10% diffusive shock acceleration -> roughly the required spectrum... propagation in the Galaxy -> isotropy

Facts: the spectrum is (ALMOST) a single power law -> CR knee at few PeVs extremely isotropic, up to very high energies energy density -> ωCR = 1 eV/cm3

δ = 2.7δ = 3.0

extragalactic

Gamma rays from SNRs:a test for CR origin

Drury, Aharonian & Volk, 1994

CR observations -> CR power of the Galaxy

Supernova rate in the Galaxy (≈3 per century)} ≳10% of SNR energy MUST be converted into CRs➩

➩ SNRs visible in TeV gamma rays ISM density n ≈ 0.1 ÷ 1 cm-3

proton-proton interactions }

SNRs detected @TeVs ➜ TEST PASSED!SNRs detected @TeVs ➜ TEST PASSED!

Gamma rays from SNRs:a test for CR origin

Drury, Aharonian & Volk, 1994

CR observations -> CR power of the Galaxy

Supernova rate in the Galaxy (≈3 per century)} ≳10% of SNR energy MUST be converted into CRs➩

➩ SNRs visible in TeV gamma rays ISM density n ≈ 0.1 ÷ 1 cm-3

proton-proton interactions }RXJ1713 as seen by HESS

SNRs detected @TeVs ➜ TEST PASSED!

hadronic or leptonic???

SNRs detected @TeVs ➜ TEST PASSED!SNRs detected @TeVs ➜ TEST PASSED!

BUT

CR knee @few PeV’sSomething must happen here...

We’d like CR sources to accelerate (at least) up

to that energy

Are SuperNova Remnants CR PeVatrons?

RXJ1713 does not look like a PeVatron...

RXJ1713 data from HESS

ν 's

Underlying proton spectrum E-2 with exponential cutoff

@150 TeV

We would like SNRs to be CR PeVatrons...

...but RXJ1713 is NOT!!!

Gabici, 2008

?

ush

Rsh

RX J1713 probably WAS a PeVatron!

THIS IS A SNR

We need to know a bit of shock acceleration theory...

Diffusion length: ldiff ∼D(E)ush

∝ E

Bshush

ush

Rsh


THIS IS A SNR


Diffusion length:

Confinement condition:

ldiff ∼D(E)ush

∝ E

Bshush

D(E)ush(t)

< Rsh(t) → Emax ∼ Bsh ush(t) Rsh(t)

ush

Rsh


THIS IS A SNR


Diffusion length:


ldiff ∼D(E)ush

∝ E

Bshush

D(E)ush(t)


Sedov phase:

Rsh(t) ∝ t2/5

ush(t) ∝ t−3/5

ush

Rsh


THIS IS A SNR


Diffusion length:


ldiff ∼D(E)ush

∝ E

Bshush

D(E)ush(t)


Sedov phase:

Rsh(t) ∝ t2/5

ush(t) ∝ t−3/5

Emax ∝ Bsht−1/5

ush

Rsh


THIS IS A SNR


Diffusion length:


ldiff ∼D(E)ush

∝ E

Bshush

D(E)ush(t)


Sedov phase:

Rsh(t) ∝ t2/5

ush(t) ∝ t−3/5

Emax ∝ Bsht−1/5

Emax decreases with timeParticles with E > Emax escape the SNR

Bsh also depends on

time

Particle escape from SNRsPtuskin & Zirakashvili, 2003

ush [km/s]

t [yr]Emax [GeV]


ush [km/s]

t [yr]Emax [GeV]

200 yrs

~ PeV


ush [km/s]

t [yr]Emax [GeV]

~10 GeV

~105 yrs

vs

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!

Particle escape from SNRs

vs




they quickly escape as the shock slows down


vs





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


vs





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


vs


vs

γ

Both SNR and surrounding molecular clouds emit gammas

γ


vs

γ

Both SNR and surrounding molecular clouds emit gammas

γ


Survey is a good strategy!

ϑ

ϑ ≈ 6◦�

D

1 kpc

�−1 �dcl

100 pc

�

Montmerle’s SNOBsadapted 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 CRsd = 1 kpc

dsnr/cl = 100 pc

Mcl = 104M⊙

DPeV = 3 1029cm2/s

SNR Cloud

PeVatron!!!but for short time!

1 PeV

t = 400 yr

Gabici&Aharonian(2007)


dsnr/cl = 100 pc

Mcl = 104M⊙

DPeV = 3 1029cm2/s

SNR Cloud

1 PeV

t = 400 yr

hard spectr

um!

100 TeV 1 PeVt = 2000 yr

HESS remnant Indirect detection of a PeVatron! Emission lasts longer!


NO ICS -> Klein-Nishina


dsnr/cl = 100 pc

Mcl = 104M⊙

DPeV = 3 1029cm2/s

SNR Cloud

1 PeV

t = 400 yr

hard spectr

um!

100 TeV 1 PeVt = 2000 yr


t = 8000 yr1 TeV 100 TeV

GLAST remnant? HESS and MILAGRO unidentified sources?



dsnr/cl = 100 pc

Mcl = 104M⊙

DPeV = 3 1029cm2/s

SNR Cloud

1 PeV

t = 400 yr

hard spectr

um!

100 TeV 1 PeVt = 2000 yr


t = 8000 yr1 TeV 100 TeV

GLAST remnant? HESS and MILAGRO unidentified sources?


t = 32000 yr

no emission

100 GeV 10 TeV

Naive statisticsd = 1 kpc

dsnr/cl = 100 pc

Mcl = 104M⊙

DPeV = 3 1029cm2/s

t = 32000 yr

t = 8000 yr

hard spectr

um!t = 2000 yr

soft spectrum

= 0.1×Dgal

Soft sources dominate the

total number of sources

Naive statisticsd = 1 kpc

dsnr/cl = 100 pc

Mcl = 104M⊙

DPeV = 3 1029cm2/s

t = 32000 yr

t = 8000 yr

hard spectr

um!t = 2000 yr

soft spectrum

= 0.1×Dgal

Soft sources dominate the

total number of sources

Cloud sta

tistics

-> diffu

sion co

efficient a

t specifi

c locat

ions in

the Galax

y

MultiWaveLength implications

<- time

M=105 M⊙ ; D=1kpc ; D10=1028cm2/s ; d = 100 pc

Cosmic Rays

CR “sea”

t = 328

2 kyr


<- time

M=105 M⊙ ; D=1kpc ; D10=1028cm2/s ; d = 100 pc

Cosmic Rays Gamma Rays

Peak from CR background (steady)

Peak from CRs from SNR (time

dependent)CR “sea”

t = 328

2 kyr


<- time

M=105 M⊙ ; D=1kpc ; D10=1028cm2/s ; d = 100 pc





t = 328

2 kyr

V-shaped spectra


<- time

M=105 M⊙ ; D=1kpc ; D10=1028cm2/s ; d = 100 pc





t = 328

2 kyr

V-shaped spectra

steep spectra

The W28 region in gammas, CO, & radio

W28

HESS - TeV emission


W28

HESS - TeV emission

Aharonian et al, 2008


W28

18h18h03m

-24o

-23o 30

´-2

3o

0

20

40

60

80

100

NANTEN 12CO(J=1-0) 0-10 km/s

l=+6.0o

l=+7.0o

b=-1.0o

b=0.0o

W 28 (Radio Boundary)

W 28A2

G6.1-0.6

6.225-0.569

GRO J1801-2320

HESS J1801-233

HESS J1800-240A B

C

RA J2000.0 (hrs)

Dec

J20

00.0

(deg

)

18h18h03m

-24o

-23o 30

´-2

3o

0

20

40

60

80

100


l=+6.0o

l=+7.0o

b=-1.0o

b=0.0o


W 28A2

G6.1-0.6

6.225-0.569

GRO J1801-2320

HESS J1801-233

HESS J1800-240A B

C

RA J2000.0 (hrs)

Dec

J20

00.0

(deg

)

NANTEN data - CO line

HESS - TeV emission



W28

18h18h03m

-24o

-23o 30

´-2

3o

0

20

40

60

80

100


l=+6.0o

l=+7.0o

b=-1.0o

b=0.0o


W 28A2

G6.1-0.6

6.225-0.569

GRO J1801-2320

HESS J1801-233

HESS J1800-240A B

C

RA J2000.0 (hrs)

Dec

J20

00.0

(deg

)

18h18h03m

-24o

-23o 30

´-2

3o

0

20

40

60

80

100


l=+6.0o

l=+7.0o

b=-1.0o

b=0.0o


W 28A2

G6.1-0.6

6.225-0.569

GRO J1801-2320

HESS J1801-233

HESS J1800-240A B

C

RA J2000.0 (hrs)

Dec

J20

00.0

(deg

)


HESS - TeV emission

Radio (Dubner et al 2000)



W28

18h18h03m

-24o

-23o 30

´-2

3o

0

20

40

60

80

100


l=+6.0o

l=+7.0o

b=-1.0o

b=0.0o


W 28A2

G6.1-0.6

6.225-0.569

GRO J1801-2320

HESS J1801-233

HESS J1800-240A B

C

RA J2000.0 (hrs)

Dec

J20

00.0

(deg

)

18h18h03m

-24o

-23o 30

´-2

3o

0

20

40

60

80

100


l=+6.0o

l=+7.0o

b=-1.0o

b=0.0o


W 28A2

G6.1-0.6

6.225-0.569

GRO J1801-2320

HESS J1801-233

HESS J1800-240A B

C

RA J2000.0 (hrs)

Dec

J20

00.0

(deg

)


HESS - TeV emission

Radio (Dubner et al 2000)


FERMI and AGILE - GeV emission

AGILE -> Giuliani et al, 2010

–23:00:00

–24:00:00

18:04:00 18:00:00

Right Ascension (J2000)

Dec

linat

ion

(J20

00)

0.1 0.2 0.3 0.4 0.5 0.6 0.7

HESS J1800-240

Source N

Source S

A B C

(a)

[counts/pixel]FERMI -> Abdo et al, 2010

W28 as seen by a theoretician

SNR shell

radio emission

-> GeV electrons

-> ongoing (re)acceleration?


SNR shell

radio emission

-> GeV electrons


Molecular clouds


SNR shell

radio emission

-> GeV electrons


Molecular clouds

gamma rays + gas

-> CR protons?

γ

γ


SNR shell

radio emission

-> GeV electrons


Molecular clouds

gamma rays + gas

-> CR protons?

-> coming from the SNR?

γ

γ

CR

CR


SNR shell

radio emission

-> GeV electrons


Molecular clouds

gamma rays + gas

-> CR protons?


-> projection effects?

γ

γ

~12 pc

~ 20 pcCR

CR

?


SNR shell

radio emission

-> GeV electrons


Molecular clouds

gamma rays + gas

-> CR protons?



+ masers

γ

γ

~12 pc

~ 20 pcCR

CR

?


SNR shell

radio emission

-> GeV electrons


Molecular clouds

gamma rays + gas

-> CR protons?



+ masers

-> most of the protons

already escaped (> GeV?)

γ

γ

~12 pc

~ 20 pcCR

CR

Escaping particles assumptions

-> point like explosion

-> (isotropic) diffusion coefficient independent on position

-> particles with energy E escape after a time: tout ∝ E−δ





this is just a parametrization





higher energy particles are released first

when the SNR is smaller









ld ≈ (D t)1/2

t = tage − tout

diffusion length

? model dependent...








ld ≈ (D t)1/2

t = tage − tout

diffusion length


≈ (D tage)1/2

high energy particles

✘

✘








ld ≈ (D t)1/2

t = tage − tout

diffusion length


≈ (D tage)1/2

high energy particles

✘

✘

lower energies -> point-like approx not so good + model dependent (tout ~ tage)

Escaping particles: CR spectrumtage -> ld = 10, 30, 100 pc

ld ≈ (D tage)1/2


const ∝ ηCR ESN

l3d

ld ≈ (D tage)1/2


const ∝ ηCR ESN

l3d

∝ e−�

Rld

�2

ld ≈ (D tage)1/2


const ∝ ηCR ESN

l3d

∝ e−�

Rld

�2

γ

ld ≈ (D tage)1/2


const ∝ ηCR ESN

l3d

∝ e−�

Rld

�2

γ

ld ≈ (D tage)1/2

0.1 � ηCR � 1

tage ≈ 3× 104 ÷ 105yr

ESN � 2÷ 4× 1050erg

estimate D?

MNcl ≈ 5× 104M⊙

if we want SNRs to be the sources of CRs...

North

South

�Fγ

Mcl

�

North

≈�

Fγ

Mcl

�

South

Escaping particles: W28

North

South

�Fγ

Mcl

�

North

≈�

Fγ

Mcl

�

South

ld both clouds within a distance ld


North

South

�Fγ

Mcl

�

North

≈�

Fγ

Mcl

�

South


Fγ ∝ fCR Mcl

d2


North

South

�Fγ

Mcl

�

North

≈�

Fγ

Mcl

�

South


Fγ ∝ fCR Mcl

d2∝ ηCR ESN

(D tage)3/2

�Mcl

d2

�


North

South

�Fγ

Mcl

�

North

≈�

Fγ

Mcl

�

South


Fγ ∝ fCR Mcl

d2∝ ηCR ESN

(D tage)3/2

�Mcl

d2

�


D ∝�ηCRESN Mcl

Fγd2

�2/3

t−1ageand we get... ->

W28: numbers

Measured quantities:

apparent size: ~ 45’-50’, distance ~ 2 kpc -> Rs ~ 12 pc ratio OIII/Hβ -> vs = 80 km/s

Assumptions:

mass of ejecta -> Mej ~ 1.4 Msun

ambient density -> n ~ 5 cm-3

Derived quantities (Cioffi et al 1989 model):

explosion energy -> ESN ~ 0.4 x 1051 erg initial velocity -> v0 ~ 5500 km/s SNR age -> 4.4 x 104 yr (radiative phase)

W28: TeV emission

North

South

A B

~ 5 104 Msun

~ 6 104 Msun

~ 4 104 Msun

W28: TeV emission

North

South

A B

~ 5 104 Msun

~ 6 104 Msun

~ 4 104 Msun

North

South A

South B

virtually the same curves for:

(η,χ) = (10%, 0.028); (30%, 0.06); (50%, 0.085)

acceleration efficiency

diffusion coefficient in units of the galactic one

W28: TeV emission

North

South

A B

~ 5 104 Msun

~ 6 104 Msun

~ 4 104 Msun

North

South A

South B


(η,χ) = (10%, 0.028); (30%, 0.06); (50%, 0.085)



diffusion

coe

ffici

ent is

supp

ressed

!

W28: TeV emission

North

South

A B

~ 5 104 Msun

~ 6 104 Msun

~ 4 104 Msun

North

South A

South B


(η,χ) = (10%, 0.028); (30%, 0.06); (50%, 0.085)



size of “CR bubble” @3 TeV

ld ≈ 70 pc → χ = 0.028

≈ 95 pc → χ = 0.06

≈ 115 pc → χ = 0.085diffusion

coe

ffici

ent is

supp

ressed

!

W28: GeV emission

Energy (GeV)110 1 10 210 310

) 1 s2

dF/d

E (e

V cm

2 E

110

1

10

210(b) W28 South (Source S)

Energy (GeV)110 1 10 210 310

) 1 s2

dF/d

E (e

V cm

2 E

110

1

10

(a) HESS J1800 240A

Energy (GeV)110 1 10 210 310

) 1 s2

dF/d

E (e

V cm

2 E110

1

10

210(a) W28 North (Source N)

FERM

I ->

Abd

o et

al,

2010

if the cloud is within the “CR bubble” [d < ld(E)]

if cloud A and B are at the same distance -> same spectrum

AB

cloud A might not be physically associated with the

W28 system

W28: GeV emission

W28: GeV emission

~ TeV

W28: GeV emission

~ TeV

~ GeV

W28: GeV emission

d = 12 pc d = 32 pc d = 65 pc

η = 30%

χ = 0.06

North South B South A

W28: GeV emission

d = 12 pc d = 32 pc d = 65 pc

η = 30%

χ = 0.06this peak is removed as background


W28: GeV emission

d = 12 pc d = 32 pc d = 65 pc

η = 30%

χ = 0.06this peak is removed as background

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?


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...




...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...

-> more data from HESS, Fermi, and CTA

Gamma ray emission from supernova remnant/molecular cloud ... · Gamma ray emission from supernova...

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