High Energy Emission in Extragalactic Nonblazar Sources Chuck Dermer U.S. Naval Research Laboratory...
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Transcript of High Energy Emission in Extragalactic Nonblazar Sources Chuck Dermer U.S. Naval Research Laboratory...
High Energy Emission in Extragalactic Nonblazar Sources
Chuck Dermer U.S. Naval Research Laboratory
July 4, 2006Multi-Messenger Approach to Unidentified Gamma-Ray Sources
Barcelona, Spain
Armen Atoyan U. de Montréal
Markus Böttcher Ohio University
Jim Chiang UMBC/GSFC
Bob Berrington University of Wyoming
Solar System:
1. Sun/Solar Flares (1)
Galaxy:
1. Pulsars (~8)
2. SNRs/Diffuse cosmic-ray induced radiations (~10)
3. High-mass microquasars (2)
4. Pulsar Wind Nebulae and X-ray Binaries (~dozen)
Extragalactic:
1. Diffuse CR emissions (LMC)
2. Blazars + Radio Galaxies (Cen A, M87) (~100 + 2)
3. GRBs (~8)
3. Clusters of Galaxies?
4. Dark Matter Emission??
Catalog of Established High Energy (> 100 MeV) Gamma-Ray Sources
EGRET Unidentified Sources (~170)
HESS/TeV Unidentified Sources (>15)
GLAST Unidentified Sources (tbd)
Outline
Gamma Ray Bursts:1. Observations
Evidence for Multiple Components: Results from EGRET and BATSERapid X-ray Declines Discovered with Swift
2. Blast Wave Model: Leptonic Processes3. Blast Wave Model: Hadronic Processes4. GRB/Cosmic Ray/-ray/Neutrino Connection5. SGRBs Clusters of Galaxies:1. Merger and Accretion Shocks2. Spectral Analysis3. Predictions
subsecond variability
1. Gamma Ray Bursts
GRB 940217GRB 940217
Long (>90 min) -ray emission
(Hurley et al. 1994)
GRB 940217GRB 940217
Nonthermal processes
Two components seen in two epochs
MeV synchrotron and GeV/TeV SSC
lower limit to the bulk Lorentz factor of the outflow
How to explain the two components?
Two components seen in two separate epochs
How to explain the two components?
Anomalous High-Energy Emission Components in GRBs
Evidence for Second Component from BATSE/TASC Analysis
Hard (-1 photon spectral index) spectrum during
delayed phase
−18 s – 14 s
14 s – 47 s
47 s – 80 s
80 s – 113 s
113 s – 211 s
100 MeV
1 MeV
(González et al. 2003)
GRB 941017
Second Gamma-ray Component in GRBs: Other EvidenceSecond Gamma-ray Component in GRBs: Other Evidence
(Requires low-redshift GRB to avoid attenuation by diffuse IR background)
Delayed high-energy -ray emission from superbowl burst
Seven GRBs detected with EGRET either during prompt MeV burst emission or after MeV emission has decayed away (Dingus et al. 1998)
Average spectrum of 4 GRBs detected over 200 s time interval from start of BATSE emission with photon index 1.95(0.25) (> 30 MeV)
Atkins et al. 2002Bromm & Schaefer 1999
O’Brien et al. (2006)
Swift Observations of Rapid X-Ray Temporal Decays
Tagliaferri et al. (2005)
GRB 940217GRB 940217
Nonthermal processes
Two components seen in two epochs
MeV synchrotron and GeV/TeV SSC
lower limit to the bulk Lorentz factor of the outflow
How to explain the two components?
Opacity Constraints: Lower Limits to Opacity Constraints: Lower Limits to
Nonthermal Nonthermal -Ray Emission: -Ray Emission: Transparency Argument for Transparency Argument for
Bulk Relativistic MotionBulk Relativistic Motion
In comoving frame, avoiding threshold condition for interactions requires
126
61 10:;1
scmergsfFluxPeak
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,)2
()2
(3 '
1
''1 z
ctrrn vbbph
T
6/163/128 ]
)(
)([])1[(200
st
GeVEfdz
v
Requirement that optical depth be less than unity:
Dermer, astro-ph/0402438Baring 2006
Blast Wave Physics with Leptons
Electrons
• Acceleration by Fermi Processes• Power in electrons and magnetic field determined by e and B parameters• Radiation and cooling by synchrotron and Compton Processes
Structured jetStructured jet
Colliding ShellsColliding Shells
External MediumUnshocked shell
GRB source
Shocked shell
*
Cloud Forward Shock
Reverse Shock
0
Captured particle
GeV/TeV Component from Leptonic Processes
Observed properties sensitive to initial Lorentz factor of outflow (or baryon loading)
Dominant SSC component in some cases
Dermer, Chiang, and Böttcher (2000)
Blast Wave Physics with Leptons and Hadrons
Protons • Acceleration by Fermi processes• Energy content in protons determined by e, B parameters: p =1- e - B
• Radiative cooling by
• Escape from blast wave shell
1. Proton synchrotron
2. Photopair production
3. Photopion production
pBp eepp
Np
Photopion Production
Threshold m 150 MeV
1. Resonance Production+(1232), N+(1440),…
2. Direct Production
pn+, p ++- , p0+
3. Multi-pion productionQCD fragmentation models
4. DiffractionCouples photons with 0,
2.0,500200,340)( 1 KMeVEMeVbE rr
Mücke et al. 1999
r
Two-Step Function Approximation for Photopion Cross SectionAtoyan and Dermer 2003
6.0,500,120 2 KMeVEb rMeVEbEK rrin 200,70ˆ)( (useful for energy-
loss rate estimates)
Er
Photopion Processes in a GRB Blast Wave
400: mThreshold p
Fast cooling
s = 2
c
= c
= min
abs
4/3
a= 1/2 b = (2-p)/2 -0.5
3
pkf
Ff
pk
min
Threshold energy of protons interacting with photons with energy pk (as measured by outside observer)
2/ cmh e
ppp cmE 2
pE
Describe F spectrum as a brokenpower law
Protons with E > interact with photons with < pk, and vice versa
pE
Photopion Energy Loss Rate in a GRB Blast Wave
Relate F spectrum to comoving photon density nph(´) for blast-wave geometry (´2nph(´)dL
2f/x22) Calculate comoving rate t´-1
(Ep) = r in comoving frame using photopion () cross-section approximation
pEpE
r
bpE 1
apE 1
)10( aK
All factors can be easily derivedfrom blast-wave physics (in the external shock model)
Choose Blast-Wave Physics Model
Adiabatic blast wave with apparent total isotropic energy release 1054 E54 ergs (cf. Friedman and Bloom 2004)
Assume uniform surrounding medium with density 100 n2 cm-3
Relativistic adiabatic blast wave decelerates according to the relation
Deceleration length
Deceleration timescale
Why these parameters?(see Dermer, Chiang, and Mitman 2000)
(Böttcher and Dermer 2000)
1 s 10 s
3 5 7
(Chiang and Dermer 1999)
(Mészáros and Rees 1993)
10-9
10-7
10-5
10-3
10-1
101
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
101
102
103
1 10 100 1000
Standard Parameters
Com
ovi
ng R
ate
s (s
-1) E
ne
rgies a
nd
fluxes
Observer time t(s)
racc
1/t'ava
r
resc
Epk
(MeV)
Ep(1018eV)
rp,syn
f-6
Energies and Fluxes for Standard ParametersStandard parameter set: z = 1
F flux ~ 10-6 ergs cm-2 s-1
Epk ~ 200 keV at start of GRB
Characteristic hard-to-soft evolution
Duration ~ 30 s
Requires very energetic protons (> 1015 eV) to interact with peak of the synchrotron spectrum
Photopion Rate vs. Available Time for Standard ParametersStandard parameter set: z = 1
Photopion rate increases with time for protons with energy Ep that have photopion interactions with photons with pk
Unless the rate is greater than the inverse of the available time, then no significant losses
10-9
10-7
10-5
10-3
10-1
101
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
101
102
103
1 10 100 1000
Standard Parameters
Com
ovi
ng R
ate
s (s
-1) E
ne
rgies a
nd
fluxes
Observer time t(s)
racc
1/t'ava
r
resc
Epk
(MeV)
Ep(1018eV)
rp,syn
f-6
Acceleration Rate vs. Available Time for Standard ParametersStandard parameter set: z = 1
Assume Fermi acceleration mechanism; acceleration timescale = factor acc greater than the Larmor timescale t´L = mc´p/eB
Take acc = 10: no problem to accelerate protons to Ep
Implicitly assumes Type 2 Fermi acceleration, through gyroresonant interactions in blast wave shell
Makes very hard proton spectrum n´(´p) 1/´p
10-9
10-7
10-5
10-3
10-1
101
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
101
102
103
1 10 100 1000
Standard Parameters
Com
ovi
ng R
ate
s (s
-1) E
ne
rgies a
nd
fluxes
Observer time t(s)
racc
1/t'ava
r
resc
Epk
(MeV)
Ep(1018eV)
rp,syn
f-6
Dermer and Humi 2001
Escape Rate vs. Available Time for Standard ParametersStandard parameter set: z = 1
Diffusive escape from blast wave with comoving width <x> = x/(12).
Calculate escape timescale using Bohm diffusion approximation
No significant escape for protons with energy Ep until >>103 s
10-9
10-7
10-5
10-3
10-1
101
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
101
102
103
1 10 100 1000
Standard Parameters
Com
ovi
ng R
ate
s (s
-1) E
ne
rgies a
nd
fluxes
Observer time t(s)
racc
1/t'ava
r
resc
Epk
(MeV)
Ep(1018eV)
rp,syn
f-6
Proton Synchrotron Loss Rate vs. Available TimeStandard parameter set: z = 1
Proton synchrotron energy-loss rate:
No significant proton sychrotron energy loss for protons with energy Ep
10-9
10-7
10-5
10-3
10-1
101
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
101
102
103
1 10 100 1000
Standard Parameters
Com
ovi
ng R
ate
s (s
-1) E
ne
rgies a
nd
fluxes
Observer time t(s)
racc
1/t'ava
r
resc
Epk
(MeV)
Ep(1018eV)
rp,syn
f-6
Gamma-Ray Bursts as Sources of High-Energy Cosmic Rays
Solution to Problem of the Origin of Ultra-High Energy Cosmic Rays
(Wick, Dermer, and Atoyan 2004)
(Waxman 1995, Vietri 1995, Dermer 2002)
Hypothesis requires that GRBs can accelerate cosmic rays to energies > 1020 eV
Injection rate density determined by GRB formation rate (= SFR?)
GZK cutoff from photopion processes with CMBR
Pair production effects for ankle
(Berezinsky and Grigoreva 1988,Berezinsky, Gazizov, and Grigoreva 2005)
Rates for 1020 eV ProtonsStandard parameter set: z = 1
For these parameters, it takes too long to accelerate particles before undergoing photopion losses or escaping.
10-7
10-6
10-5
10-4
10-3
10-2
1 10 100 1000 104
Observer time t(s)
Com
ovi
n R
ate
s (s
-1)
racc
1/t'ava
r
rp,syn
resc
Calculated at Ep=1020 eV
Rates for 1020 eV Protons with Equipartition Parameters
Equipartition parameter set with density = 1000 cm-3, z = 1
Within the available time, photopion losses and escape cause a discharge of the proton energy several hundred seconds after GRB
10-5
10-4
10-3
10-2
1 10 100 1000
Observer time t(s)
Com
ovi
n R
ate
s (s
-1)
racc 1/t'
ava
r
rp,syn
resc
Calculated at Ep=1020 eV
Rates for 1020 eV Protons with Different Parameter Set
New parameter set with density = 1000 cm-3, z = 1
Escape from the blast wave also allows internal energy to be rapidly lost (if more diffusive, more escape)
10-5
10-4
10-3
10-2
1 10 100 1000
Observer time t(s)
Com
ovi
ng R
ate
s (s
-1)
racc
1/t'ava
r
rp,syn
resc
Calculated at Ep=1020 eV
Blast Wave Evolution with Loss of Hadronic Internal Energy
Assume blast wave loses 0, 25, 50, 75, 90, and 95% of its energy at x = 6x1016 cm.
Transition to radiative solution
Rapid reduction in blast wave Lorentz factor = (P2 +1)1/2
Rapid decay in emissionsfrom blast wave, limitedby curvature relation
Highly radiative phase---due to escape of UHECRs from GRB blast wave---proposed as explanation of Swift observations of rapid X-ray declines in GRB light curves
Photon and Neutrino Fluence during Prompt Phase
Hard -ray emission component from hadronic cascade radiation inside GRB blast wave Second component from outflowing high-energy neutral beam of neutrons, -rays, and neutrinos
e
pnep
2
),,(0
Nonthermal Baryon
Loading Factor fb = 1
Requires large baryon loadto explain GRB 941017
tot = 310-4 ergs cm-2
= 100
Photon attenuation strongly dependent on and tvar in collapsar model
Optical Depth
evolves in collapsar model due toevolving Doppler factor and internal radiation field
pulses
one
cmergs
tot
sec50
,
1032
4
Neutrinos from GRBs in the Collapsar Model
(~2/yr)
Nonthermal Baryon Loading Factor fb = 20
Dermer & Atoyan 2003
requires Large Baryon-Loading
Rapidly Declining X-ray Emission Observed with Swift
Zhang et al. 2006
F
Difficult for superposition of colliding-shell emissions to explain Swift observations of rapid X-ray decay
Rising phase of light curve shorter than declining phase in colliding shell emission
Rapid X-ray Decays in Short Hard Gamma-Ray Bursts
Loss of internal energy through ultra-high energy particle escape: UHECRs from SGRBs? High-energy -rays expected from SGRBs from leptonic and, possibly, hadronic components
Barthelmy et al. (2005)
GRB 050724
Implications and Predictions• Photopion production
Cascade radiation, including proton synchrotron radiation, forms a new -ray emission component: Explanation of GRB 940217, GRB 941017,…
Escaping neutrons and -rays form hyper-relativistic electrons; transient -ray/X-ray synchrotron halos, as in blazars (Coppi, Aharonian & Völk 1994)
• Unidentified -ray Flashes: Proton synchrotron radiation– Discover with GLAST or Milagro– Need rapid alert from GLAST to TeV telescopes
Decay lifetime 900 n seconds
2. Nonthermal Particles and Radiation Produced by Cluster Merger Shocks
Thermal bremsstrahlung X-ray Emission of galaxy clusters traces gravitational well
Rich clusters (thousands of Galaxies;
~1015 Msun; kT ~ 5-10 keV, LX ~ 1043 -
1045 ergs s-1)Velocity dispersions ~500-1000 km s-1
Poor clusters (hundreds of Galaxies;
~1014 Msun; kT ~ 1-5 keV, LX ~ 1041 -
1043 ergs s-1 )Velocity dispersions ~250-500 km s-1
~5-10% of total mass of cluster; Orbital motion dominated by distribution of dark matter
Which clusters are GLAST/TeV-bright?
Structure Formation• Density fluctuations cause region to
collapse.– Magnitude of the density fluctuation
determines the formation time– Larger structures form by accreting
smaller clumps--hierarchical merging– Lumpy, continuous accretion
Cluster Merger• Simulation of merging clusters of galaxies
Shocks in Merging Clusters
• (0, R, ) (mass, curvature, and dark energy)= (0.3, 0.0, 0.7)– Redshift of cluster:
– Cosmic Microwave Background (CMBR) dependence• UCMBR(z) = UCMBR(z=0) (1 + z)4
• Rich clusters form by accreting poor clusters
• Shocks in Merging Clusters
Particle Injection
• Power law distribution with exponential cutoff
– Occurs only if M 1.0– Occurs only during lifetime of shock
• Normalization
– Where e,p is an efficiency factor, and is set to 5%.– Typical values are Etot1063-64 ergs
)(exp
)(),(
max
0,, tE
EpcQtEQ pepe
ssspe
pe
E
E pepe vAvmndEtEQE
2
,,, 2
1,
max
minHeICM
Particle and Photon Energy Spectra: Coma Cluster
Fit to Data for the Coma Cluster
Galaxy Cluster Nonthermal Brightness
Nonthermal Emission from Cluster Merger Shocks
• Unidentified EGRET sources: Doubtful
• Diffuse Extragalactic -ray Background: Few % contribution
Summary
Clusters of Galaxies
Unidentified EGRET sources: Doubtful
Diffuse extragalactic -ray background: Few % contribution
Predictions: Handful (~ 5 – 10) detected with GLAST
(Merger vs. accretion shocks)
(Merger shock acceleration vs. turbulent acceleration)
GRBs Highly radiative phase from UHECR escape in blastwave evolution proposed to explain rapid X-ray declines in Swift GRB light curves
Predictions:
1. Hadronic -ray light consisting of cascading photopion and proton synchrotron radiation varying independently of leptonic synchrotron
2. Strong GeV-TeV radiation and/or ultra-high energy (>1017 eV) neutrinos correlated with rapidly decaying X-ray emission
3. UHECR emissivity following the GRB formation rate history of the universe
Back-up Slides
Synchrotron and SSC Radiation
Strong dependence of GRB emissions on
Selection bias to detect GRBs with Epk within waveband of detector
Dominant SSC component in some cases
Chiang and Dermer (1999)
Two-Step Collapse (Short-Delay Supranova) Model
1. Standard SNIb/c (56Ni production)2. Magnetar Wind Evacuates Poles3. GRB in collapse of NS to BH4. Prompt Phase due to External Shocks with
Shell/Circumburst Material5. Standard Energy Reservoir (NS collapse to BH)
6. Beaming from mechanical/B-field collimation
Delay time ~< 1 day (GRB 030329)
Infall Velocity