High Energy Emission in Extragalactic Nonblazar Sources Chuck Dermer U.S. Naval Research Laboratory July 4, 2006 Multi-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) (~ ) 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 BATSE Rapid X-ray Declines Discovered with Swift 2.Blast Wave Model: Leptonic Processes 3.Blast Wave Model: Hadronic Processes 4.GRB/Cosmic Ray/  -ray/Neutrino Connection 5.SGRBs Clusters of Galaxies: 1.Merger and Accretion Shocks 2.Spectral Analysis 3.Predictions

subsecond variability 1. Gamma Ray Bursts

GRB Long (>90 min)  -ray emission (Hurley et al. 1994)

GRB  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

Second 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 Bromm & Schaefer 1999

O’Brien et al. (2006) Swift Observations of Rapid X-Ray Temporal Decays Tagliaferri et al. (2005)

GRB  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 

Nonthermal  -Ray Emission:  Transparency Argument for Bulk Relativistic Motion In comoving frame, avoiding threshold condition for  interactions requires Requirement that  optical depth be less than unity: Dermer, astro-ph/ Baring 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 jet Colliding Shells

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

Photopion Production Threshold  m   150 MeV 1.Resonance Production  + (1232), N + (1440),… 2.Direct Production p  n  +, p   ++  -, p   0  + 3.Multi-pion production QCD fragmentation models 4.Diffraction Couples photons with  0,  Mücke et al r Two-Step Function Approximation for Photopion Cross Section Atoyan and Dermer 2003 (useful for energy- loss rate estimates) ErEr

Photopion Processes in a GRB Blast Wave Fast cooling s = 2 cc   =  c   =  min    abs 4/3 a= 1/2 b = (2-p)/2  Threshold energy of protons interacting with photons with energy  pk (as measured by outside observer) Describe F spectrum as a broken power law Protons with E > interact with photons with  <  pk, and vice versa

Photopion Energy Loss Rate in a GRB Blast Wave Relate F spectrum to comoving photon density n ph (  ´) for blast-wave geometry (  ´ 2 n ph (  ´)  d L 2 f  /x 2  2 ) Calculate comoving rate t´ -1  (E p ) = r  in comoving frame using photopion (  ) cross-section approximation r  K  All factors can be easily derived from blast-wave physics (in the external shock model)

Choose Blast-Wave Physics Model Adiabatic blast wave with apparent total isotropic energy release E 54 ergs (cf. Friedman and Bloom 2004) Assume uniform surrounding medium with density 100 n 2 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 s10 s (Chiang and Dermer 1999) (Mészáros and Rees 1993)

Energies and Fluxes for Standard Parameters Standard parameter set: z = 1 F flux ~ ergs cm -2 s - 1 E pk ~ 200 keV at start of GRB Characteristic hard-to-soft evolution Duration ~ 30 s Requires very energetic protons (> eV) to interact with peak of the synchrotron spectrum

Photopion Rate vs. Available Time for Standard Parameters Standard parameter set: z = 1 Photopion rate increases with time for protons with energy E p that have photopion interactions with photons with  pk Unless the rate is greater than the inverse of the available time, then no significant losses

Acceleration Rate vs. Available Time for Standard Parameters Standard 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 E p Implicitly assumes Type 2 Fermi acceleration, through gyroresonant interactions in blast wave shell Makes very hard proton spectrum n´(  ´ p )  1/  ´ p Dermer and Humi 2001

Escape Rate vs. Available Time for Standard Parameters Standard parameter set: z = 1 Diffusive escape from blast wave with comoving width = x/(12  ). Calculate escape timescale using Bohm diffusion approximation No significant escape for protons with energy E p until >>10 3 s

Proton Synchrotron Loss Rate vs. Available Time Standard parameter set: z = 1 Proton synchrotron energy- loss rate: No significant proton sychrotron energy loss for protons with energy E p

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 > 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 eV Protons Standard parameter set: z = 1 For these parameters, it takes too long to accelerate particles before undergoing photopion losses or escaping.

Rates for 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

Rates for 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)

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 = 6x10 16 cm. Transition to radiative solution Rapid reduction in blast wave Lorentz factor  = (P 2 +1) 1/2 Rapid decay in emissions from blast wave, limited by 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 Nonthermal Baryon Loading Factor f b = 1 Requires large baryon load to explain GRB  tot = 3  ergs cm -2  = 100

Photon attenuation strongly dependent on  and t var in collapsar model  Optical Depth   evolves in collapsar model due to evolving Doppler factor and internal radiation field

Neutrinos from GRBs in the Collapsar Model (~2/yr) Nonthermal Baryon Loading Factor f b = 20 Dermer & Atoyan 2003 requires Large Baryon-Loading

Rapidly Declining X-ray Emission Observed with Swift Zhang et al 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

Implications and Predictions Photopion production Cascade radiation, including proton synchrotron radiation, forms a new  -ray emission component: Explanation of GRB , GRB ,… 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; ~10 15 M sun ; kT ~ 5-10 keV, L X ~ ergs s -1 ) Velocity dispersions ~ km s -1 Poor clusters ( hundreds of Galaxies; ~10 14 M sun ; kT ~ 1-5 keV, L X ~ ergs s -1 ) Velocity dispersions ~ 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 U CMBR (z) = U CMBR (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 E tot  ergs

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 (>10 17 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 E pk 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 ( 56 Ni production) 2.Magnetar Wind Evacuates Poles 3.GRB in collapse of NS to BH 4.Prompt Phase due to External Shocks with Shell/Circumburst Material 5.Standard Energy Reservoir (NS collapse to BH) 6.Beaming from mechanical/B-field collimation Delay time ~< 1 day (GRB )

Infall Velocity