Evidence for UHECR Acceleration from Fermi
Observations of AGNs and GRBs
Chuck Dermer
Space Science Division
US Naval Research Laboratory, Washington, DC
charles.dermer@nrl.navy.mil
TeV Particle Astrophysics 2009
SLAC, July 13-17, 2009
1
Outline

Requirements for UHECR sources:
– Extragalactic (but within the GZK radius)
– Emissivity (>1044 erg Mpc-3 yr-1)
– Apparent Isotropic Power (> few×1045 erg s-1) (for Fermi acceleration)



Extragalactic Gamma Ray Sources from Fermi
Radio Galaxies and Blazars as Sources of the UHECRs
Gamma-Ray Bursts as Sources of the UHECRs
Dermer, Razzaque, Finke, Atoyan (New Journal of Physics, 2009)
Razzaque, Dermer, Finke (Nature Physics, submitted, 2009)
Dermer and Menon, “High Energy Radiation from Black Holes: Gamma Rays,
Cosmic Rays, and Neutrinos” (Princeton University Press, 2009)
2
Black-Hole Jet Sources of UHECRs
Nonthermal g rays  relativistic particles + intense photon fields
Leptonic jet model: radio/optical/ Xrays: nonthermal lepton synchrotron
radiation
Hadronic jet model:
 Photomeson production
second g-ray component
pg → p → g, n, n
Neutrons escape to decay and
become UHECR protons (Neutral
beam model: Atoyan & Dermer 2003)
Large Doppler factors required for g rays
to escape
Photopair/photopion vs. ion synchrotron
3
GZK Horizon Distance for Protons
Horizon distance vs. MFP:
Linear distance where
proton with measured
energy E had energy eE
CMBR only:
Auger
limits:
GZK cutoff consistent
with UHECR protons
For model-dependent definition:
Harari, Mollerach, and Roulet 2006
4
UHECR Emissivity
CR (dE / dVdt )  uUHECR (dE / dV ) / tloss
tloss  rhorizon / c
10 21 erg cm 3
UHECR 
rhorizon( Mpc ) / c
knee
erg
 10
Mpc 3  yr
44
ankle
(Waxman 1995)
5
UHECR Acceleration by Relativistic Jets
Proper frame (´) energy density of relativistic wind with apparent luminosity L
B2
 u  B
8p
L
1
u 
 2
2
4pR c G
x
G
Lorentz contraction 
DR´= G DR
R´= R/ G
Maximum particle energy
Emax  GQBR  GZeB( R / G)
 Emax  2 10 20 Z
L /(1046 ergs s 1 )
eV
G
What extragalactic sources have (apparent isotropic) L /G2 >> 1045 ergs s-1?
Those with (apparent isotropic) Lg > 1044 ergs s-1
6
UHECRs from Blazars

LAT Bright AGN Sample (LBAS): Abdo et al. arXiv:0902.1559 (ApJ, 2009)
0FGL: 205 LAT Bright
Sources
3 month catalog:August 4 – October 30, 2008
Test Statistic > 100
Significance > 10s
132 |b|>10 sources
114 associated with
AGNs
Compare EGRET:
31 >10s sources
(total)
(10 at |b|>10)
11 mo. Source List!
Fermi AGNs reviewed by Jim Chiang, Greg Madejski, D. Paneque
7
Luminosity Distribution vs. Redshift
GZK horizon
For sources within
GZK radius, need >
103 persistent sources
per Gpc3
Abdo et al., ApJS (2009)
(Cen A (>100 MeV)
few×1041 erg/s)
8
Luminosity Density of g-ray Blazars

Minimum luminosity density of Radio Galaxies from LBAS
(5×1040 erg/s
w/i 3.5 Mpc)
1044 ergs Mpc-3 yr-1
9
Centaurus A
~100 kpc × 500 kpc lobes
Need >> 1045 erg s-1 apparent power to accelerate
UHECR protons by Fermi processes
Cen A power:
Bolometric radio luminosity: 4×1042 erg s-1
Gamma-ray power (from Fermi): few ×1041 erg s-1
Hard X-ray/soft g-ray power: 5×1042 erg s-1
UHECR power: few ×1040 erg s-1
10
What is Average Absolute Jet Power of Cen A?
Total energy and lifetime:
Cocoon dynamics (Begelman and Cioffi 1989 for Cyg A)
Dermer, Razzaque, Finke, Atoyan, NJP 09
Use synchrotron theory to determine minimum
energy B field, absolute jet power Pj. Jet/counterjet asymmetry gives outflow speed:
Hardcastle et al. 2009
B2
P  p r ( c)G (  upar )
8p
*
j
'2
b
2
Celotti and Fabian 93
11
Mean B-field and Average Absolute Jet Power in Cen A
Hardcastle et al. 2009
Pj(Cen A)  1044 erg s-1
Apparent jet power 20 x larger?
12
Search for UHECRs Enhancements from
Radio Galaxies and Blazars
Blue: Auger, > 56 EeV (1◦)
Red: HiRes > 56 EeV (1◦)
Magenta: AGASA, > 56
EeV (1.8◦)
Orange: AGASA, 40-56
EeV (1.8◦)
Pink and purple circles:
GC
angular deflections of
UHECRs with 40 EeV and
20 EeV from source AGN,
respectively, in the galactic
disk magnetic field.
Green circles represent
angular deflections in
assumed 0.1 nG
intergalactic magnetic field,
assuming no magnetic-field
reversals.
GC
MW magnetic deflection UHECR protons
If blazars accelerate UHECR protons, then mean IGM field
BIGM 
E20 Ninv
nG
d (200 Mpc)
13
UHECRs from Gamma Ray Bursts
Luminosity density of GRBs
GRB fluence:
 102 ergs cm 2 yr 1
 GRB 
4pd 2  102 ergs cm 2 yr 1
4pd 3 / 3
 0.75  1044 ergs Mpc 3 yr 1
( d  4000 Mpc; z  1)
> 20 keV fluence distribution of 1,973
BATSE GRBs (477 short GRBs and 1,496
long GRBs).
670 BATSE GRBs/yr (full sky)
(Band 2001)
GRB  UHECR ( 1020 eV )
Vietri 1995; Waxman 1995
(independent of beaming)
Baryon loading
14
UHECR Spectrum from Long-Duration GRBs

Inject 2.2 spectrum of UHECR
protons to E > 1020 eV

Injection rate density determined
by birth rate of GRBs early in the
history of the universe

High-energy (GZK) cutoff from
photopion interactions with
cosmic microwave radiation
photons

Ankle formed by pair production
effects (Berezinskii, Gazizov,
Grigoreva)
Wick, Dermer, and Atoyan 2004
Test UHECR origin hypothesis by detailed fits to measured cosmic-ray spectrum
15
Effects of Different Star Formation Rates
Hopkins & Beacom 2006
g-ray and n signatures of UHECRs at source
tests GRB source hypothesis
16
Light Curves of GRBs 080825C, 081024B
First LAT GRB. Note:
• delayed onset of high-energy emission
• extended (“long-lived”) high-energy g rays
(Fermi GRBs reviewed by H. Tajima)
First short GRB with >1
GeV photon detected
Light Curves of GRB 080916C
8 keV –
260 keV
260 keV –
5 MeV
LAT raw
LAT > 100
MeV
LAT > 1
GeV
T
0
Again, two notable features:
1. Delayed onset of high-energy emission
2. Extended (“long-lived”) high-energy g rays
seen in both long duration and short hard GRBs
Interpretation of Delayed Onset of >100 MeV Emission

Random collisions between plasma shells
 Separate emission regions from forward/reverse shock systems
 Second pair of colliding shells produce, by chance, a harder spectrum
 Expect no time delays for >100 MeV in some GRBs, yet to be detected
Opacity effects
 Expansion of compact cloud, becoming
optically thin to >100 MeV photons
 Expect spectral softening break evolve
to higher energy in time, not observed
 Up-scattered cocoon emission
Synchrotron-self-Compton for < MeV
External Compton of cocoon photons, arriving
late from high-latitude, to >100 MeV

GRB 080916C
Toma, Wu, Meszaros (2009)

Proton synchrotron radiation
Inherent delay to build-up proton
synchrotron flux which sweeps into LAT
energy range from high-energy end
Razzaque, Dermer and Finke (2009)
19
Synchotron Radiation from UHE Protons
Instantaneous energy flux F (erg cm-2 s-1); variability time tv, redshift z
4pd L2 F
(1  z ) 2 d L2 F
ug  2

2
G 4p R c
G 6 c 3tv2
Implies a jet magnetic field
B(kG)  2
 B rb F  5
G33tv ( s )
 r b   tv 

 60 
 B 
 100   0.1 s 
1 / 2
rb is baryon loading-parameter (particle vs. g-ray energy density)
xB gives relative energy density in magnetic field vs. particles
G > Gmin 
103G
3
from gg opacity arguments Gmin
1/ 6
 s T d (1  z ) F 1 

 
4
 6tv me c ln(  u /   ) 
2
L
2
20
Fermi Acceleration of Protons in GRB Blast Waves
Protons gain energy on timescales exceeding Larmor timescale,
implying acceleration rate
eB
 ,p 
gacc
f is acceleration efficiency
1 / 2

g

f
Saturation Lorentz factor: sat, p
f mpc
m p  Bcr 1 / 2
9
2  10 8




me  B 
4 f
(f / 10)1 / 2 B51 / 2
Proton saturation frequency (in mec2 units):
 sat, p
G
G 1 m p 27 1.6 107 G3
 ,p 

 sat
f

1 z
1 z
me 8 f
(f / 10)
Observer measures a time
for protons to reach gacc, p
t sat 
1  z 1/ 2
f
G
1/ 2
m 2p c  6p 


3 
me  es T B 

0.01 f / 10
s
3/ 2
G3 B5
21
Time for Proton Synchrotron Radiation to Brighten
gg processes induce second
generation electron synchotron
spectrum at
 sat,e
3 G B   2  m p 27

f 
2 1  z Bcr
 me 16 f
2
3

10
G3 B5
 
2

(
f
/
10
)

i.e., ~ 500 MeV for standard
parameters
Time for proton synchrotron radiation
to reach sat,e:
tcl  t sat
Bcr me 64 f 4 1 z m p cBcr
f

f
B m p 81
3 G
eB2
mp
(f /10)
 1.4
s
me
G3 B52
22
Long GRBs as the Sources of UHECRs
 2 10
20
G3
eV
(f / 10) B5

Maximum energy of escaping protons

Long GRB rate 2fb Gpc-3 yr-1 at the typical redshift z  1–2
10 smaller at 100d100 Mpc due to the star formation
fb > 200 larger due to a beaming factor

60E60 EeV UHECR deflected by an angle
1 1/ 2 1/ 2
 4.4 ZBnG E 60
d100 l1
IGM field with mean strength BnGnG coherence length of l1 Mpc

Number of GRB sources within 100 Mpc with jets pointing within 4 of our
2
2 3 / 2
line-of-sight is
 30( 
f b / 200) BnG E 60 l1
 If typical long duration GRBs have a narrow core accelerating UHECRs,
then GRBs could account for Auger events within GZK radius.
23
Extended High Energy Emission

LAT detected GRBs show significant
high energy emission extending after the
GBM emission returns to background
(discovered originally with EGRET on
Compton Observatory; Hurley et al. 1994)

Could be due to …
 Delayed arrival of SSC
 Long-lived hadronic emissions
(Böttcher and Dermer 1998)

GRB 080916C
Abdo et al., Science (2009)
Greiner et al., A&A (2009)
Injection problem
 Internal shells
 External shock
 extended (> 1016 cm) wind/shell
24
UHECR Origin
Auger UHECR arrival directions correlated with matter within 100 Mpc
Ruled out:
Galactic sources
young neutron stars or pulsars, black holes,
GRBs in the Galaxy
Particle physics sources
superheavy dark matter particles in galactic halo
top-down models
Clusters of galaxies
Viable:
Jets of AGNs: radio-loud or radio-quiet? Cen A!, M87?
 nG IGM magnetic field
(long) GRBs: Requires nano-Gauss intergalactic magnetic field
UHECRs accelerated by black-hole jets
25
Unresolved g-Ray Background
BL Lacs: ~2 - 4% (at 1 GeV)
FSRQs: ~ 10 - 15%
Star-forming galaxies (Pavlidou & Fields 2002)
Starburst galaxies (Thompson et al. 2006)
Galaxy cluster shocks (Keshet et al. 2003, Blasi
Gabici & Brunetti 2007)
Thermal black holes
(accretion)
Dermer (2007)
Nonthermal black holes
(jet)
Data: Sreekumar et al. (1998)
Strong, Moskalenko, & Reimer (2000)
26
Fermi LAT GRBs as of 090510
192 GBM GRBs
~30 short GRBs
8 LAT GRBs
(reviewed by H. Tajima,
this conference)
(distinguish long vs.
short GBM GRBs)