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Pulsars:Pulsars: The Unexplored The Unexplored GeVGeV--TeV TeV Energy BandEnergy Band
Alice K. Harding NASA Goddard Space Flight Center
• CGRO pulsars: • High-energy cutoffs• No pulsed TeV emission detected
• Millisecond pulsars: • Only one detected (PSR J0218+4232)• Where are the nearby sources?
• AXPs: Where do the hard components end?
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• Power peaked in γ-rays
• No pulsed emission detected above 20 GeV
• High-energy turnover
• Increase in hardness with age
Broad-band spectra
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Changes in profile at highest energies (> 5 Changes in profile at highest energies (> 5 GeVGeV))Thompson 2001
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Pulsar highPulsar high--energy emission modelsenergy emission models
ΩBαLight
Cylinder
closed fieldregion
polarcap
null charge surfaceΩ . B = 0
outergap
|| 41/ 20c sin coss
2olowE θ η α φκ α
η−∝ +
3
IR
κ ∝
slot gap
Pair plasma
µ
slot
gap
Pairformation
front
∆ ξSG
Closed field region
|| 0E =
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Pair attenuation cutoff for normal pulsarsPair attenuation cutoff for normal pulsars7 / 2
1/ 2 1max 122esc
rE E GeV P BR
− ⎛ ⎞= ≈ ⎜ ⎟⎝ ⎠
1011 1012 1013 1014
B0 (Gauss)
10-3
10-2
10-1
100
101
102
103H
igh
Ene
rgy
Cut
off (
GeV
)
P =
0.1
- 5 s
3R019
51+3
2
20 GeV
2R0
R0
1055
-52
Vel
aC
rab
1509
-58
Gem
inga
1706
-44
0656
+14
100 GeV
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Sensitivity of H.E.S.S. to pulsar emissionSensitivity of H.E.S.S. to pulsar emission
De De Jager Jager et al. 2000et al. 2000( )exp / b
n
g
o
dN Ek EdE
EE
γ−
⎛ ⎞ ⎡ ⎤= −⎜ ⎟ ⎣ ⎦⎝ ⎠b ~ 2
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PSR B1951+32: How sharp is the cutoff?PSR B1951+32: How sharp is the cutoff?
10-4 10-3 10-2 10-1 100 101 102 103 104 105
Energy (GeV)
10-12
10-11
10-10
10-9
10-8
10-7
10-6
10-5
GeV
/(cm
2 s)
PSR1951+32
VERITAS
GLAST
EGRET
MAGIC
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PSR B1706PSR B1706--44: Where is the cutoff?44: Where is the cutoff?
10-4 10-3 10-2 10-1 100 101 102 103 104 105
Energy (GeV)
10-12
10-11
10-10
10-9
10-8
10-7
10-6
10-5G
eV/(c
m2
s)PSR1706-44
H.E.S.S.GLAST
EGRET
MAGIC
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10-2 10-1 100 101 102 103 104 105 106 107
10-9
10-8
10-7
10-6
10-5
10-4
10-3
Energy (MeV)
MeV
cm
-2 s
-1
EGRETCOMPTELOSSERXTE CANGAROOOPTICALROSAT
VELA PULSAR
101 102 103 104 105 106 107
10-9
10-8
10-7
10-6
10-5
10-4
10-3
Energy (MeV)
MeV
cm
-2 s
-1
CRAB PULSAR
The mystery of the missing The mystery of the missing TeVTeV emissionemission
Potchefstrom 1990
CANGAROO 1997
Hirotani et al. 2003Outer gap model Cheng, Ho & Ruderman 1986
Outer gap model Cheng, Ho & Ruderman 1986
Whipple 1990
Outer gap model Romani 1996
Hirotani et al. 2003
CANGAROO 1998
Whipple 2000
HEGRA 1999
W
Smaller outer gap size
less TeV emission
But what will happen to predicted pulse shapes??MAGIC VERITAS
H.E.S.S.MAGIC
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Detections of Detections of MSPs MSPs at high energyat high energy
1206>100Millisecond pulsars
812161400Normal pulsars
γ-raysteady
X-raypulsed
Radio
Why are so few seen at γ-ray energy?
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Hard emission from millisecond pulsarsHard emission from millisecond pulsars
2 4
|| 2
1/ 42|| 7 1/ 4 1/ 4 3/ 4
8
3/ 4 5/ 4 3/ 4 11/ 48 0.15
4536
23
3 102
10 GeV
0.15
CRc
cCRR ms
CRpeak ms
eeE
EB P
e
B P
IR
γγρ
ργ η
ε κ η
κ
− −
− −
= =
⎛ ⎞= ≈⎜ ⎟⎜ ⎟
⎝ ⎠
≈
≈
&
Radiation reaction-limited acceleration
Curvature radiation peak energy:
PSR P (ms) B (G) d (kpc) ε CRpeak (GeV)
J0437-4715 5.75 6.95E+08 0.18 4.8B1821-24 3.05 4.47E+09 5.5 42.9J0218-4232 2.32 8.44E+08 5.85 17.3B1937+21 1.60 8.10E+08 3.60 26.7J0030+0451 4.86 4.46E+08 0.23 4.3J2124-3358 4.93 1.47E+09 0.25 10.2B1957+20 1.61 3.33E+08 1.6 13.6
Dependent on NS equation-of-state
Dependent on emission radius r/R
Usov 1983
Bulik, Rudak & Dyks 2000
Luo, Shibata & Melrose 2000
Harding, Muslimov & Zhang 2002
Harding, Usov & Muslimov 2004
1/ 2c Pρ ∝
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108 109 1010 1011
B0 (Gauss)
100
101
102
103
104
105
106H
igh
Ene
rgy
Cut
off (
GeV
)
P = 1 - 10 ms
20 GeV
2R0
R0
100 GeV
Pair attenuation cutoff for ms pulsarsPair attenuation cutoff for ms pulsars
CR
Peak E
nergy (GeV
)
Maximum peak energy < 100 GeV
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Curvature radiation from J0437Curvature radiation from J0437--4715 4715 ––can we constrain the NS equationcan we constrain the NS equation--ofof--state?state?
10-4 10-3 10-2 10-1 100 101 102 103 104 105
Energy (GeV)
10-13
10-12
10-11
10-10
10-9
10-8
10-7
10-6
10-5
10-4G
eV/(c
m2
s)J0437-4715
H.E.S.S.
BPS: R6=0.8, I45=0.6FP: R6=1.0, I45=1.0PS: R6=1.6, I45=2.2
ICS
MAGIC
GLAST
EGRET
CR
Venter & De Jager 2004
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But effect of altitude/viewing angle is strongerBut effect of altitude/viewing angle is stronger……
10-4 10-3 10-2 10-1 100 101 102 103 104 105
Energy (GeV)
10-12
10-11
10-10
10-9
10-8
10-7
10-6
10-5
GeV
/(cm
2 s)
J0437-4715
H.E.S.S.
R3R1R2R5
GLAST
EGRET
MAGIC
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B1821-24: acceleration limited to low altitude
10-4 10-2 100 102 104 106
Energy (MeV)
10-10
10-8
10-6
10-4
MeV
/(cm
2 s)
B0 = 4.4 x 109 GP = 3 msχ = 1.0
PCAHRIEGRETHEXTEOSSE
GLAST
PSR B1821-24
H.E.S.S.
MAGIC
SR
ICS
CR
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J0218+4232: unscreened acceleration
10-4 10-2 100 102 104 106
Energy (MeV)
10-9
10-7
10-5
10-3
MeV
/(cm
2 s)
MECSPCAHRIHEXTECOMPTELEGRET
GLAST
VERITASSR
CR
PSR J0218+4232
MAGIC
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Predicted CR flux from millisecond pulsarsPredicted CR flux from millisecond pulsars
B182
1-24
B193
7+21
B195
7+20
J003
0+04
51
J021
8-42
32
J043
7-47
15
J212
4-33
58
47Tu
c10-1
100
101
102
103
Flux
(>10
0 M
eV) (
10-8
cm-2
s-1)
GLAST
EGRET
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Outer gap model predictions for ms pulsarsOuter gap model predictions for ms pulsarsZhang & Cheng 2003Zhang & Cheng 2003
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Hidden population of millisecond pulsars?Hidden population of millisecond pulsars?
10-3 10-2 10-1 100 101
Pdo
t (s
s-1)
10-22
10-20
10-18
10-16
10-14
10-12
P (s)
B1821-24
radiogamma-rayX-ray
Pair death lineJ0218+4232 J0437-4715
???
?
•• No pairsNo pairs•• No radio No radio •• No XNo X--raysrays•• Detectable Detectable
only in highonly in high--energy energy γγ--raysrays
•• At d = 100 pc:At d = 100 pc:
32 33 -14 10 erg sSDE −≈ ×&
8 2 -1
( 1 GeV)2 10 ph cm sF
−
> ≈×
8 2 -1
( 100 MeV)5 10 ph cm sF
−
> ≈×
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10-4 10-3 10-2 10-1 100 101 102 103 104 105
Energy (GeV)
10-12
10-11
10-10
10-9
10-8
10-7
10-6
10-5
GeV
/(cm
2 s)
Vela
J0437-4715 VERITAS
MAGICGLAST
Radio-quiet MSP with P=3 ms, d=100 pc
Harding, Usov & Muslimov 2004
Detecting hidden millisecond pulsarsDetecting hidden millisecond pulsars
Number of Number of radioradio--quiet quiet MSPsMSPs::
MSP BirthrateMSP Birthrate
( )2
MSP MSPgal
dN d NR
τ⎛ ⎞
≤ = ⎜ ⎟⎜ ⎟⎝ ⎠
&
6 14 1040,000
MSPN yrtotal
− −≈ ×&
( ) 2400MSP kpcN d d≤ ≈
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Chandra Detection of Millisecond Pulsars in 47 Tuc
Grindlay et al. 2001
15 millisecond radio pulsars in 47 15 millisecond radio pulsars in 47 TucTuc
•• Total predicted flux > 100 Total predicted flux > 100 MeVMeV
EGRET limit ( )EGRET limit ( )
•• This and other globular clusters should This and other globular clusters should be detectable by GLASTbe detectable by GLAST
8 2 -16.5 10 ph cm s−×8 2 -15 10 ph cm s−×
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Hard Emission from Kes 73 and AXP 1E 1841-045
11
22
33
44
55
66
1) Total1) TotalXMMXMM--NewtonNewton
2) Total 2) Total 1E 18411E 1841--045;045;
ChandraChandra((MoriiMorii et al. 2003)et al. 2003)
3) Pulsed 3) Pulsed RXTE/PCARXTE/PCAγγ 1.931.93±±0.010.01
4) Pulsed 4) Pulsed RXTE/HEXTERXTE/HEXTEγγ 0.940.94±±0.160.16
5) Total 5) Total RXTE/HEXTERXTE/HEXTEγγ 1.471.47±±0.050.05
6) Total6) TotalINTEGRALINTEGRAL
((MolkovMolkov et al 2004)et al 2004)
KuiperKuiper,, HermsenHermsen, Mendez 2004, Mendez 2004
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Resonant Compton Resonant Compton UpscatteringUpscattering??
Baring 2004Baring 2004
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Polarization signature of photon splitting in Polarization signature of photon splitting in AXPsAXPs
10-3 10-2 10-1 100 101 102 103
E (MeV)
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
⊥II
MeV
/(cm
2 s)
Bo = 10 Bcr
EGRET
GLAST
Full polar cap
⊥ →Only permitted splitting mode
Photon splitting cutoff
Pair attenuation cutoff
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Outer gap model predictions for Outer gap model predictions for SGRsSGRsZhang & Cheng 2002Zhang & Cheng 2002
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What we can learn from coordinated What we can learn from coordinated observations with GLAST and observations with GLAST and ACTsACTs
• Where and how sharp are high-energy cutoffs?
• Is there an ICS TeV component from the outer gap ?
• CR component (1-50 GeV) from millisecond pulsars
• Radio (and X-ray) quiet MSPs
• Hard emission from AXPs
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Which pulsars have slot gaps?Which pulsars have slot gaps?
10-3 10-2 10-1 100 101
Pdot
(s s
-1)
10-22
10-20
10-18
10-16
10-14
10-12
P (s)
CR
ICS
Only the younger pulsars above the death line for production of curvature radiation pairs will have
SLOT GAPS
Harding, Muslimov & Zhang 2002
Older pulsars belowthe death line for production of curvature radiation pairs will have unscreened E|| and
NO SLOT GAPS
B1821-24
radiogamma-rayX-ray
J0437-4715
J0218+4232
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Slot gap modelSlot gap model
• Pair-free zone near last open field-lineSlower accelerationPair formation front at
higher altitudeSlot gap forms
between conducting walls
• E|| acceleration is not screened
e+e-
Pair plasma
µ
slot
gap
Pairformation
front
∆ ξSG
Closed field region
|| 0E =
(Muslimov & Harding 2003, 2004)
Slot gap width:∆ξ SG P B≈ −015 0 1 12
4 7. ./
Solid angle:2
SG o SGrθ ξΩ ∝ ∆Slot gap pair
cascade
Primary CR, IC
Closed fieldregion
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Crab NebulaCrab Nebula
From Rowell 2003