Ultra-High Energy Cosmic-Ray Origin in Light of First Results from the Pierre Auger Observatory and the Fermi Gamma-ray Space Telescope

1
Ultra-High Energy Cosmic-Ray Origin in Light of
First Results from the Pierre Auger Observatory
and the Fermi Gamma-ray Space Telescope

• Charles D. Dermer
• Space Science Division
• US Naval Research Laboratory, Washington, DC
• charles.dermer_at_nrl.navy.mil
• Colloquium at the School of Physics and Astronomy
• University of Minnesota, Minneapolis, MN
• November 12, 2008

2
Outline

• Cosmic Rays and Ultra-High Energy Cosmic Rays
  (UHECRs)
• Pierre Auger Observatory Results and
  Implications
• Criteria for UHECR sources
• Extragalactic
• Emissivity (gt1044 ergs Mpc-3 yr-1)
• Power (gt 1046 ergs s-1)
• Extragalactic Gamma Ray Sources
• Fermi Gamma Ray Space Telescope
• Radio Galaxies and Blazars as Sources of the
  UHECRs
• Gamma-Ray Bursts as Sources of the UHECRs

see Dermer, Razzaque, Finke, Atoyan (2008)
3
Cosmic Rays

• Cosmic rays energetic cosmic particles composed
  mainly of protons and ions
• Cosmic rays an important particle background in
  the space radiation environment

• Particle radiations
• Cosmic Rays
• Solar Energetic Particles
• Neutrinos
• Photon Radiations
• Radio emission (cosmic ray electrons)
• X-rays and g rays (cosmic ray electrons,
  protons, and ions)

• The recent deployment of radiation detectors and
  telescopes on ground and in space is providing
  new data sets for analysis and interpretation to
  solve the problem of cosmic-ray origin

Discovery of cosmic rays by Victor Hess in 1912
4
Cosmic Rays and Space Radiations

• Cosmic Ray Origin Fundamental Unsolved Problem
  in Astronomy
• Galactic Cosmic Rays
• (accelerated by Supernova Remnants?)
• Ultra-high Energy Cosmic Rays (discovered by
  Auger and Rossi in the 1930s)
• Cosmic rays do not point directly to their
  sources, because of magnetic fields in space.
• Gamma rays indicate sites of high-energy
  particles, but can be attenuated by matter or
  other photons at the source or in transit from
  the source to Earth.
• Neutrinos would unambiguously point to the
  sources of the cosmic rays, but are faint and
  difficult to detect.
• The solution to this problem can therefore only
  be achieved by jointly analyzing high-energy
  space radiations, including gamma rays, cosmic
  rays, and neutrinos

5
Highest Energy Cosmic Rays
Knee Feature at 31015 eV Second Knee at 41017
eV Ankle Feature at 51018 eV GZK Cutoff at
61019 eV (predicted by Greisen, Zatsepin, and
Kuzmin in 1968)

• Origin sources of cosmic rays
• Acceleration how accelerated to high energies
• Propagation transport of cosmic rays
• Reception detection at Earth and in space

2-1 through 2-n of N
6
Greisen-Zatsepin-Kuzmin (GZK) Cutoff

• Photopion production cross section
• p g ? p po, n po
• Photo-ion disintegration cross sections
• (Giant dipole resonance) N g ? N? p, n, a

CMB photons reach threshold for p production for
E 1020 eV protons
7
Extragalactic Origin of UHECRs
Galactic Disk Magnetic Field 2 5 mG Thickness
200 pc Galactic Halo Magnetic Field 0.1
mG Thickness 1 5 kpc
Lorentz force equation for a particle with charge
Q Ze and energy E Larmor radius
Hillas 1984
Particle with energy E 60 EeV 60x1018 eV

• Hillas Condition Sources of UHECRs must have rL
  lt source size
• Rules out many classes of potential UHECR
  sources, flare stars, white dwarfs, normal
  neutron stars, Galactic sources (if protons),

8
Pierre Auger Observatory
Flux (gt 1020 eV) 1 particle/km2/century Ni
Flurorescence Detectors Spectroscopy Detectors
(1600 SDs spaced 1.5 km apart) Angular
resolution 1o for E gt 10 EeV Energy
uncertainty 22 for E gt 10 EeV

(Auger Collaboration, Science Magazine, November
2007)
Auger Observatory in Mendoza province in
Argentina
9
2007 Birth of Charged Particle Astronomy
All-sky projection Galactic Center at (0,0)
Arrival directions of highest energy cosmic rays
(gt61019 eV open circles) correlated with active
galaxies (AGNs) () within 100 Mpc Cen A,
radio galaxies, also radio-quiet AGN

Deflection in Galactic magnetic field ? protons
or light nuclei
10
GZK Horizon Distance for Protons

• MFP for Energy Loss vs. Horizon Distance

11
Local Emissivity of UHECRs
12
UHECR Emissivity
Yamamoto et al. (2007)
1020 0.2 1019 1.2 1018 3.5 1017 40
Sources of UHECRs need to have a local luminosity
density (emissivity) of ?1044 ergs/Mpc3-yr
13
UHECR Acceleration by Sources of Relativistic
Winds
Proper frame () energy density of relativistic
wind with luminosity L
x
Maximum particle energy
G
Lorentz contraction ? DR G DR R R/ G
What sources have L gt Lg gt 1046 ergs s-1?
14
Gamma Ray Sources
Compton Gamma-Ray Observatory Pioneering g-ray
space observatory (1991 2000)
270 EGRET sources (3EG) 25 blazars with 5
Spark Chamber Gamma Ray Bursts ground-based
TeV 70 High Confidence Blazars telescopes LMC,
Cen A, NGC 6251 (? see Mukherjee et al. 2002)
15
Fermi Gamma-ray Space Telescope

• International space mission devoted to the study
  of the high-energy gamma rays from the universe
• Successfully launched on June 11,
  2008
  from Cape Canaveral
• Formerly, the Gamma ray Large Area Space
  Telescope (GLAST)

Circular orbit, 565 km altitude (96 min period),
25.6 deg inclination
16
The Fermi Observatory

• Large Area Telescope (LAT)?
• 20 MeV to gt300 GeV
• onboard and ground burst triggers, localization,
  spectroscopy
• Gamma-ray Burst Monitor (GBM)?
• 12 NaI detectors (8 keV to 1 MeV)?
• onboard trigger, onboard and ground
  localizations, spectroscopy
• 2 BGO detectors (150 keV to 30 MeV)?
• spectroscopy

Spectral observations over 7 orders of magnitude
in energy
17
Pair Conversion Technique
?
The anti-coincidence shield vetos incoming
charged particles.
Photon converts to an ee- pair in one of the
conversion foils
The directions of the charged particles are
recorded by particle tracking detectors, the
measured tracks point back to the source.
The energy is measured in the calorimeter
Tracker angular resolution is determined
by multiple scattering (at low energies) gt Many
thin layers position resolution (at high
energies) gt fine pitch detectors Calorimeter Eno
ugh X0 to contain shower, shower leakage
correction. Anti-coincidence detector Must have
high efficiency for rejecting charged particles,
but not veto gamma-rays
18
First Light Sky Map (June 30 July 4, 2008)
Equivalent to full year of data from the Compton
Observatory!

• All sky projection bright central band shows g
  rays from cosmic-ray interactions in our Galaxy
• Already detected many blazars and GRBs
• Identification of localized sources of radiation
  requires detailed spectral and background analysis

NASA Fermi First Light Press Conference August
26, 2008 http//www.nasa.gov/mission_pages/GLAST/n
ews/glast_findings_media.html
19
The Gamma Ray Sky
2-1 through 2-n of N
20
Relativistic Jet Sources of UHECRs
Nonthermal g rays ? nonthermal particles
intense photon fields

• Leptonic jet model optical/X-rays/soft g-rays
  are nonthermal lepton synchrotron
• Hadronic jet model
• Photomeson production
• second g-ray component

Large Doppler factors required for g-rays to
escape
21
UHECRs from Radio Galaxies and Blazars
22
Radio Galaxies and Blazars
Cygnus A
FRII/FSRQ
L 1045 x (f/10-10 ergs cm-2 s-1) ergs s-1
Mrk 421, z 0.031
FRI/BL Lac
3C 279, z 0.538
FRI/II dividing line at radio power ?1042 ergs s-1
L 5x1048 x (f/10-9 ergs cm-2 s-1) ergs s-1
3C 296
BL Lacs optical emission line equivalent widths
lt 5 Å
23
Blazar g-ray Emissivity
gt100 MeV g-Ray fluence
Dermer 2007
24
Flaring Blazar Sources

• Automated search for flaring sources on 6 hour, 1
  day and 1 week timescales.

PKS 1502106 z 1.84
Preliminary
25
Leptonic Blazar Modeling
Observer
q
Ejection of relativistic plasma from supermassive
black hole
BLR clouds
G
Relativistically Collimated Plasma Outlfows
Dusty Torus
W
Accretion Disk
SMBH
G
Ambient Radiation Fields
z 0.538
BL Lac vs. FSRQ
Böttcher et al. 2007
26
Photo-hadronic Blazar Jet Models
Possible photon targets for p
??? Internal synchrotron radiation
External accretion disk radiation (UV) (i)
direct accretion disk radiation (ii)
accretion disk radiation scattered in the
broad-line region (Atoyan Dermer 2001)
quasi-isotropic, up to RBLR 0.1-1 pc Impact
of the external accretion disk radiation
component high p?-rates lower threshold
energies ???????????????prot?????????MeV/(1-
cos?) ??
??7 (solid) ??10 (dashed) ??15
(dot-dashed) (red - without ADR)
(for 1996 flare of 3C 279)
27
Blazars as High Energy Hadron Accelerators
Powerful blazars / FR-II Neutrons with En gt 100
PeV and ???rays with E? gt 1PeV take away
5-10 of the total energy injected at RltRBLR
(3C 279)
Synchrotron and IC fluxes from the pair-photon
cascade for the Feb 1996 flare of 3C279
dotted - CRs injected during the flare solid -
neutrons escaping from the blob, dashed -
neutrons escaping from Broad Line Region (ext.
UV) dot-dashed - g rays escaping external UV
field (from neutrons outside the
blob) 3dot-dashed- Protons remaining in the blob
at l RBLR
astro-ph/0610195
Sreekumar et al. (1998)
28
Hadronic g-Ray Emission from Blazars
29
UHE neutrons ?-rays energy momentum
transport from AGN core

• UHE ?-ray pathlengths in CMBR
• l?? 10 kpc - 1Mpc
• for En 1016 - 1019 eV
• Neutron decay pathlength
• ld (?n) ?0 c ?n (?0 900 s)
• ? ld 1 kpc - 1Mpc
• for E 1017 - 1020 eV

solid z 0 dashed z 0.5
Detection of single high-energy n from blazars ?
neutral beams could power large-scale jets
30
Pictor A
d 200 Mpc l jet 1 Mpc (lproj 240
kpc) Deposition of energy through ultra-high
energy neutral beams (Atoyan and Dermer 2003)
Pictor A in X-rays and radio (Wilson et al, 2001
ApJ 547)
31
Neutrinos expected fluences/numbers

• Expected ?? - fluences calculated for 2 flares,
  in 3C 279 and Mkn 501, assuming
• proton aceleration rate Qprot(acc) Lrad(obs)
  red curves - contribution due to
• internal photons, green curves - external
  component (Atoyan Dermer 2003)
• Expected numbers of ?? for IceCube-scale
  detectors, per flare
• 3C 279 N? 0.35 for ? 6 (solid curve) and
  N? 0.18 for ? 6 (dashed)
• Mkn501 N? 1.2 10-5 for ? 10 (solid) and N?
  10-5 for ? 25 (dashed)
• (persistent') ? -level of 3C279 0.1 F?
  (flare) , ( external UV for p? )
• ? N?? few - several per year can be expected
  from poweful ? FSRQ blazars.

32
UHECRs from GRBs
33
Gamma Ray Bursts

• GRB Burst of g rays accompanying black-
• hole formation
• Classes of GRBs
• Long duration GRBs
• (collapse of massive star core)
• Short hard class of GRBs
• (coalescence of compact objects)
• Low luminosity GRBs

All-sky g ray map in Galactic coordinates
(Galactic coordinates)
g-ray Light Curve of GRB
Swift mission discovered that short hard class of
GRBs are related to old stellar population
(Gehrels et al. 2005)
34
GRB X-ray/g-ray Emissivity
GRB fluence
gt 20 keV fluence distribution of 1,973 BATSE
GRBs (477 short GRBs and 1,496 long GRBs). 670
BATSE GRBs/yr (full sky)
Vietri 1995 Waxman 1995
(independent of beaming) Baryon loading
(Band 2001)
35
Ultra-high Energy Cosmic Rays from Gamma Ray
Bursts

• Proposed Solution to the Origin of Ultra-High
  Energy Cosmic Rays
• Hypothesis requires that GRBs can accelerate
  cosmic rays to energies gt 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

Wick, Dermer, and Atoyan 2004

Test UHECR origin hypothesis by detailed fits to
measured cosmic-ray spectrum
36
Effects of Different Star Formation Rates
g-ray signatures of UHECRs at source can confirm
this hypothesis
Hopkins Beacom 2006
37
Leptonic GRB Modeling

• Dominant synchrotron radiation at X-g energies
• Two peaks in nFn distribution
• Power-law afterglow decay
• Generic rise in intensity until tdec, followed by
  constant or decreasing flux (except in
  self-absorbed regime or in synchrotron/SSC trough)

E1054 ergs n0100 cm-3 eB 10-4

• nFn spectra shown at 10i seconds after GRB
• gg opacity included

38
GRBs at High Energy Signatures of Hadrons?

• Little is known about GRB emission above 100 MeV
  prior to Fermi Telescope
• Prompt HE gamma emission
• Prompt GeV emission with no HE cutoff (combined
  with rapid variability) implies highly
  relativistic bulk motion
• EGRET detections from a few GRBs, e.g. GRB940217
• New HE extra component, with independent
  temporal evolution (GRB 941017) inconsistent with
  the synchrotron model! (Gonzalez 03)?
• Extended or delayed HE emission
• It may require more than one emission mechanism,
  and remains one of the unsolved problems
• GRB 940217 (EGRET)?
• GRB 080514B (AGILE)?
• HE emission clearly has different time dependence
• What is its spectral shape?
• Need more sensitivity and larger FOV

GRB941017
GRB080514B
-18 to 14 sec 14 to 47 sec 47 to 80 sec
80-113 sec 113-211 sec
39
Hadronic GRB Modeling

• Nonthermal Baryon Loading Factor fb 30

Energy injected in protons normalized to GRB
synchrotron fluence
Injected proton distribution
Cooled proton distribution
Escaping neutron distribution
Forms neutral beam of neutrons, g rays, and
neutrinos
40
Photohadronic Cascade Radiation Fluxes
Photomeson Cascade
Nonthermal Baryon Loading Factor fb 1
C2
Ftot 3?10-4 ergs cm-2
C3
emits synchrotron (S1) and Compton (C1)
photons emits
synchrotron (S2) and Compton (C2) photons,
etc.
Total
C4

• S1

S2
C1
S3
C5
S4
Photon index between -1.5 and -2
MeV
d 100
41
Photon and Neutrino Fluence during Prompt Phase
Nonthermal Baryon Loading Factor fb 1
Ftot 3?10-4 ergs cm-2
d 100

• Hard g-ray emission component from
  hadronic-induced electromagnetic cascade
  radiation inside GRB blast wave
• Second component from outflowing high-energy
  neutral beam of neutrons, g-rays, and neutrinos

42
Neutrinos from GRBs in the Collapsar Model
requires Large Baryon-Loading
Nonthermal Baryon Loading Factor fb 20
(2/yr)
Dermer Atoyan 2003
43
GZK neutrinos from UHECRs produced by GRBs
Barwick et al. 2006
44
GRB 080916C Luminous Fermi GRB

• 30 deg region around GRB 080916C
• GRB at 48 from the LAT boresight at T0?
• RGB lt100 MeV, 100 MeV - 1 GeV, gt1 GeV

Before the burst (T0-100 s to T0)?
During the burst (T0 to T0100 s)?
Black region out of FoV
45
Light Curves of GRB 080916C
PRELIMINARY!

• Light curves arebackground subtracted
• First low energy peak not observed at Large Area
  Telescope (LAT) energies
• Spectroscopy needs LAT event selection (gt100
  MeV)?
• 5 intervals for time-resolved spectral
  analysis0 3.6 7.7 16 55 100 s
• 14 events above 1 GeV

46
Multiple detector light curve
PRELIMINARY!

• The bulk of the emission of the 2nd peak is
  moving toward later times as the energy increases
• Clear signature of spectral evolution

47
Spectroscopy of the main LAT peak
Models for GRB 080916C Hadronic
emission Separate Shell Collisions Opacity
Effects
PRELIMINARY!

• Consistent with smooth Band function from 10
  keV to 10 GeV
• No evidence for any other component
• No evidence for any roll-off

48
Summary
UHECRs from GRBs and Radio-Loud AGNs Why
(these) Black Holes? 1. Extragalactic 2.
Powerful 3. Emissivity How to confirm
origin? Association of arrival directions with
sources g-ray signatures of UHECR
acceleration Neutrino emission from GRBs or
Blazars
49
2005-2015 A Decade of Discovery

• Swift Gamma-ray Burst Explorer (NASA 2004 MidEx)
• High Energy Stereoscopic Observatory (HESS)
• (Ground-based g-ray telescope Namibia, 2004)
• Very Energetic Radiation Imaging
• Telescope Array System
• (VERITAS) (Arizona 2007)
• Auger High Energy Cosmic
• Ray Observatory
• (Argentina 2007)
• IceCube NSFs
• South Pole km-scale
• neutrino telescope
• (km-scale design
• sensitivity in 2012)
• Fermi Gamma-ray
• Space Telescope (2008)

Swift
Auger
IceCube
VERITAS