Post on 14-Jun-2020
Gamma ray emission from supernova remnant/molecular
cloud associations
Stefano GabiciAPC, Paris
stefano.gabici@apc.univ-paris7.fr
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
RX J1713 probably WAS a PeVatron!
THIS IS A SNR
We need to know a bit of shock acceleration theory...
Diffusion length:
Confinement condition:
ldiff ∼D(E)ush
∝ E
Bshush
D(E)ush(t)
< Rsh(t) → Emax ∼ Bsh ush(t) Rsh(t)
ush
Rsh
RX J1713 probably WAS a PeVatron!
THIS IS A SNR
We need to know a bit of shock acceleration theory...
Diffusion length:
Confinement condition:
ldiff ∼D(E)ush
∝ E
Bshush
D(E)ush(t)
< Rsh(t) → Emax ∼ Bsh ush(t) Rsh(t)
Sedov phase:
Rsh(t) ∝ t2/5
ush(t) ∝ t−3/5
ush
Rsh
RX J1713 probably WAS a PeVatron!
THIS IS A SNR
We need to know a bit of shock acceleration theory...
Diffusion length:
Confinement condition:
ldiff ∼D(E)ush
∝ E
Bshush
D(E)ush(t)
< Rsh(t) → Emax ∼ Bsh ush(t) Rsh(t)
Sedov phase:
Rsh(t) ∝ t2/5
ush(t) ∝ t−3/5
Emax ∝ Bsht−1/5
ush
Rsh
RX J1713 probably WAS a PeVatron!
THIS IS A SNR
We need to know a bit of shock acceleration theory...
Diffusion length:
Confinement condition:
ldiff ∼D(E)ush
∝ E
Bshush
D(E)ush(t)
< Rsh(t) → Emax ∼ Bsh ush(t) Rsh(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]
Particle escape from SNRsPtuskin & Zirakashvili, 2003
ush [km/s]
t [yr]Emax [GeV]
200 yrs
~ PeV
Particle escape from SNRsPtuskin & Zirakashvili, 2003
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
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
Particle escape from SNRs
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!
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
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!
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
Particle escape from SNRs
vs
Particle escape from SNRs
vs
γ
Both SNR and surrounding molecular clouds emit gammas
γ
Particle escape from SNRs
vs
γ
Both SNR and surrounding molecular clouds emit gammas
γ
Particle escape from SNRs
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)
Gamma rays from MCs illuminated by CRsd = 1 kpc
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!
Gabici&Aharonian(2007)
NO ICS -> Klein-Nishina
Gamma rays from MCs illuminated by CRsd = 1 kpc
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!
t = 8000 yr1 TeV 100 TeV
GLAST remnant? HESS and MILAGRO unidentified sources?
Gabici&Aharonian(2007)
Gamma rays from MCs illuminated by CRsd = 1 kpc
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!
t = 8000 yr1 TeV 100 TeV
GLAST remnant? HESS and MILAGRO unidentified sources?
Gabici&Aharonian(2007)
t = 32000 yr
no emission
100 GeV 10 TeV
Gamma rays from MCs illuminated by CRsd = 1 kpc
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!
t = 8000 yr1 TeV 100 TeV
GLAST remnant? HESS and MILAGRO unidentified sources?
Gabici&Aharonian(2007)
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
MultiWaveLength implications
<- 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
MultiWaveLength implications
<- 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
V-shaped spectra
MultiWaveLength implications
<- 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
V-shaped spectra
steep spectra
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
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
NANTEN 12CO(J=1-0) 10-20 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
)
NANTEN data - CO line
HESS - TeV emission
Aharonian et al, 2008
The W28 region in gammas, CO, & radio
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
NANTEN 12CO(J=1-0) 10-20 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
)
NANTEN data - CO line
HESS - TeV emission
Radio (Dubner et al 2000)
Aharonian et al, 2008
The W28 region in gammas, CO, & radio
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
NANTEN 12CO(J=1-0) 10-20 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
)
NANTEN data - CO line
HESS - TeV emission
Radio (Dubner et al 2000)
Aharonian et al, 2008
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?
W28 as seen by a theoretician
SNR shell
radio emission
-> GeV electrons
-> ongoing (re)acceleration?
Molecular clouds
W28 as seen by a theoretician
SNR shell
radio emission
-> GeV electrons
-> ongoing (re)acceleration?
Molecular clouds
gamma rays + gas
-> CR protons?
γ
γ
W28 as seen by a theoretician
SNR shell
radio emission
-> GeV electrons
-> ongoing (re)acceleration?
Molecular clouds
gamma rays + gas
-> CR protons?
-> coming from the SNR?
γ
γ
CR
CR
W28 as seen by a theoretician
SNR shell
radio emission
-> GeV electrons
-> ongoing (re)acceleration?
Molecular clouds
gamma rays + gas
-> CR protons?
-> coming from the SNR?
-> projection effects?
γ
γ
~12 pc
~ 20 pcCR
CR
?
W28 as seen by a theoretician
SNR shell
radio emission
-> GeV electrons
-> ongoing (re)acceleration?
Molecular clouds
gamma rays + gas
-> CR protons?
-> coming from the SNR?
-> projection effects?
+ masers
γ
γ
~12 pc
~ 20 pcCR
CR
?
W28 as seen by a theoretician
SNR shell
radio emission
-> GeV electrons
-> ongoing (re)acceleration?
Molecular clouds
gamma rays + gas
-> CR protons?
-> coming from the SNR?
-> projection effects?
+ 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
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
Escaping particles assumptions
-> point like explosion
-> (isotropic) diffusion coefficient independent on position
-> particles with energy E escape after a time: tout ∝ E−δ
higher energy particles are released first
when the SNR is smaller
this is just a parametrization
Escaping particles assumptions
-> point like explosion
-> (isotropic) diffusion coefficient independent on position
-> particles with energy E escape after a time: tout ∝ E−δ
higher energy particles are released first
when the SNR is smaller
this is just a parametrization
ld ≈ (D t)1/2
t = tage − tout
diffusion length
? model dependent...
Escaping particles assumptions
-> point like explosion
-> (isotropic) diffusion coefficient independent on position
-> particles with energy E escape after a time: tout ∝ E−δ
higher energy particles are released first
when the SNR is smaller
this is just a parametrization
ld ≈ (D t)1/2
t = tage − tout
diffusion length
? model dependent...
≈ (D tage)1/2
high energy particles
✘
✘
Escaping particles assumptions
-> point like explosion
-> (isotropic) diffusion coefficient independent on position
-> particles with energy E escape after a time: tout ∝ E−δ
higher energy particles are released first
when the SNR is smaller
this is just a parametrization
ld ≈ (D t)1/2
t = tage − tout
diffusion length
? model dependent...
≈ (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
Escaping particles: CR spectrumtage -> ld = 10, 30, 100 pc
const ∝ ηCR ESN
l3d
ld ≈ (D tage)1/2
Escaping particles: CR spectrumtage -> ld = 10, 30, 100 pc
const ∝ ηCR ESN
l3d
∝ e−�
Rld
�2
ld ≈ (D tage)1/2
Escaping particles: CR spectrumtage -> ld = 10, 30, 100 pc
const ∝ ηCR ESN
l3d
∝ e−�
Rld
�2
γ
ld ≈ (D tage)1/2
Escaping particles: CR spectrumtage -> ld = 10, 30, 100 pc
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
Escaping particles: W28
North
South
�Fγ
Mcl
�
North
≈�
Fγ
Mcl
�
South
ld both clouds within a distance ld
Fγ ∝ fCR Mcl
d2
Escaping particles: W28
North
South
�Fγ
Mcl
�
North
≈�
Fγ
Mcl
�
South
ld both clouds within a distance ld
Fγ ∝ fCR Mcl
d2∝ ηCR ESN
(D tage)3/2
�Mcl
d2
�
Escaping particles: W28
North
South
�Fγ
Mcl
�
North
≈�
Fγ
Mcl
�
South
ld both clouds within a distance ld
Fγ ∝ fCR Mcl
d2∝ ηCR ESN
(D tage)3/2
�Mcl
d2
�
Escaping particles: W28
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
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
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
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
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
~ 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
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
some problems here...+ some of the approximations are not very good at low energies
+ subtraction of the background?+ other contributions? (Bremsstrahlung)
North South B South A
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?
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...
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...
-> more data from HESS, Fermi, and CTA