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					               Sources of GeV Photons and the Fermi Results

                           Chuck Dermer (NRL)
                http://heseweb.nrl.navy.mil/gamma/~dermer/default.htm

1. GeV instrumentation and the GeV sky with the Fermi Gamma-ray Space
Telescope
2. First Fermi Catalog of Gamma Ray Sources and the Fermi Pulsar Catalog
3. First Fermi AGN Catalog
4. Relativistic jet physics and blazars
5. g rays from cosmic rays in the Galaxy
6. g rays from star-forming galaxies and clusters of galaxies, and the diffuse
extragalactic g-ray background
7. Microquasars, radio galaxies, and the extragalactic background light
8. Fermi Observations of Gamma Ray Bursts
9. Fermi acceleration, ultra-high energy cosmic rays, and Fermi

                                Thanks to C.C. Cheung, J. Finke

                  Dermer      Saas-Fee Lecture 4      15-20 March 2010           1
Dermer   Saas-Fee Lecture 4   15-20 March 2010   2
     3C 454.3 Light Curves


     weekly
      daily




Dermer    Saas-Fee Lecture 4   15-20 March 2010   3
                    Spectral Energy Distributions of Blazars
     Preliminary (not for distribution)                   Abdo, et al. 2009, ApJ, 699, 817

                                                                2008 July 7–August 2
                                                           1048 erg/s              1 MeV




        Mrk 501, z = 0.033                                  3C 454.3
                                                            z = 0.859




                                                            3C 279
                                                            z = 0.538




       PG 1553+113, z < 0.75
       HST: z~0.40-0.43
                                                          Abdo, et al. 2010, Nature, 463, 919

Abdo, et al. 2010, ApJ, 708, 1310
                     Dermer          Saas-Fee Lecture 4         15-20 March 2010                4
               Demonstrations of Relativistic Outflows

1. Compton catastrophe
                                       gg   gg ng R,  gg   T
2. Superluminal motion

3. gg opacity argument                  R < ctvar                    Lg
  g  g   e  e                                     ng 
                                                                   4R cEg
                                                                      2




                                     T Lg            Lg /(1048 erg / s)
                            gg                1000
                                  4me c t var
                                         4
                                                          t var (day)
    3C 120

               Dermer    Saas-Fee Lecture 4     15-20 March 2010          5
               Blazar Modeling

   Nonthermal g rays  relativistic particles +
      intense photon fields

Leptonic jet model:
        Nonthermal synchrotron paradigm
        Associated SSC and EC component(s)
        Location of emission site

Hadronic jet model:
       Secondary nuclear production
                   pN → o,  → g, n, n, e
         Proton and ion synchrotron radiation
                   pB → g
         Photomeson production
                   pg → o, → g, n, n, e
High energy g-ray component from gg′    → e → g by
Compton or synchrotron processes
Neutrons escape to become UHECRs

                      Dermer       Saas-Fee Lecture 4   15-20 March 2010   6
                                                                              Observer
                          Black Hole Jet Physics: AGNs


                                                                         q
Synchrotron/Compton                          BLR clouds
Leptonic Jet Model
                                                                    G
BL Lac vs. FSRQs                            Relativistically
                                            Collimated
Target photons for scattering               Plasma Jet
Accretion regime
                                                                             Dusty Torus

Blob Formalism                                 Accretion       W
                                               Disk
Energy Sources:                                        SMBH
 1. Accretion Power
 2. Rotation Power

Supermassive Black Holes

Identifying hadronic emissions                                      G             Ambient
                                                                                  Radiation
                                                                                  Fields



                 Dermer         Saas-Fee Lecture 4             15-20 March 2010               7
      Doppler Factor


 D  [G(1   cosq )]1


 x  ct*  Gct '

        d x cosq
t  t*    
        c         c
                     d ( x  x ) cosq
t  t  t*  t*                                           (1  z )dt 
                     c         c                       dt 
         x                                                         D
 t         (1   cosq )  Gt (1   cosq )
         c
         t                                                        D 
 t                              x             x     
         D         q  0  t 
                                   c
                                       (1   )  2
                                                 Gc            (1  z )
              Dermer      Saas-Fee Lecture 4    15-20 March 2010             8
                           Variability and Source Size
                                                    Spherical blob in comoving frame
Source size from direct observations:

                  d                                 rb=r´b          G
rb  d A  2 ( 27A ) (mas) pc
                10 cm
                                                                        arccos
Source size from temporal variability:

                                                    Doppler Factor
                                                 D  [G(1   )]1
              2.5  10  D tvar ( day)
                      15
rb( cm ) 
                      (1  z )

    Variability timescale implies maximum emission region size scale




                   Dermer      Saas-Fee Lecture 4        15-20 March 2010              9
                          Variability and Source Location


                                                                  2GM   ct var
                                                              RS  2 
                                                                   c   (1  z )
                                                G


                                                        1/G
                                 x




Variability timescale implies engine size scale, comoving size scale factor G larger and
emission location ~G2 larger than values inferred for stationary region

Rapid variability by energizing regions within the Doppler cone
                   Dermer       Saas-Fee Lecture 4        15-20 March 2010             10
    Temporal Variability

Size scale in stationary frame: R > RS
Size scale in comoving frame: R = GR > GRS
(Lorentz contracted to size R in stationary frame)
                               >RS
                        G2
              G1
                                                      g rays                 ISM


    RS
                     >RS
                               INTERNAL
 tvar > R/c > GRS/c            SHOCK

 tvar = tvar /G > RS/c                               EXTERNAL
                                                       SHOCK
HESS collaboration incorrectly takes R RS
        e.g., Aharonian et al. 2007, ApJ, 664, L71
                    Dermer       Saas-Fee Lecture 4       15-20 March 2010     11
            Energy Fluxes,
        Blobs and Blast Waves                      Blob (off-axis jet model) vs.
                                                   Blast Wave (observer within jet cone)
    Measured: z ( dL), nFn flux, tv
    and jet angle qj for blob model
                            dE    L
Total Energy Flux:           
                           dAdt 4d L
                                    2

Spectral Energy Flux:
         f  (erg cm 2 s 1 )  nFn
                  Lg
Blob :    D4

                 4d L2


             D L( )
               4
                                  c t
f  nFn                  , rb  D v
                4d L 2
                                  1 z
                           Lg
Blast Wave :   G      2                                        Blob and blast wave
                          4d L 2
                                                                 framework are
            G 2 L( )     cG 2tv                             equivalent for opacity
 f  nFn                ,R        , R  R / G                calculations
               4d L2
                              1 z
                  Dermer      Saas-Fee Lecture 4        15-20 March 2010             12
                           Internal Radiation Fields
  Instantaneous energy flux  (erg cm-2 s-1); variability time tv, redshift z
                    Lg          
                            Lg tesc 3d L 
                                          2
                                                                    t
Blob:     D  4
                        
                     , ug ~                   
                                    ~ 4 2 , tesc ~ r  / c ~ t   D v
               4d L
                   2
                             V       D r c                      1 z
                  3d L (1  z ) 2 
                     2
                                                           3d L (1  z ) 2 f
                                                              2
             
          ug                               or ng ( ) 
                                                  
                       Dtv2c3
                        6
                                                            mec5 2 Dtv2
                                                                        6


                                                 c D tv
                              2

                                                         ,    (1  z )
                          3d L f
        nph ( )                         r 
                     mec3 2 D r 2
                                   4
                                                 1 z                D
Blast Wave:
          4d   2
                    d (1  z )  or n ( ) 
                               2      2         d L (1  z ) 2 f
                                                  2
     
    ug         L
                              L
                                       g
         4 R G c
                2 2
                       G tv c
                         6 2 3
                                                me c 5 2G 6tv2
                                     cG 2tv          (1  z )
                    R   R / G, R         ,  
                                     1 z                G
                      Dermer       Saas-Fee Lecture 4      15-20 March 2010     13
                  Internal Magnetic Fields and Power

Internal energy density u = ug/e implies a jet magnetic field

                         B  8 Bug /  e
                                    
e is fraction of total energy density in nonthermal electrons assumed to
    be producing the g rays
B is fraction of total energy density in magnetic field
Apparent Jet Power
                 Pj  4R2 cG2 (u  upar  ug )
                                  B
                                               

                                                                        c D t v
Absolute Jet Power                                              rb 
                                  G2                                  1 z
                                                      
              Pj  2 rb2 c D  2  (u  upar  ug )
                               2
                                   B
                                  D

                Dermer      Saas-Fee Lecture 4   15-20 March 2010                  14
              gg Opacity




Dermer   Saas-Fee Lecture 4   15-20 March 2010   15
gg Opacity: -function approximation




Dermer   Saas-Fee Lecture 4   15-20 March 2010   16
           gg Opacity : -function approximation for Blob

        
d gg (1 )                                           2
              d   gg ( s)nph ( ),  gg ( s)   T  ( s  2)
   dx         0                                       3
                    2              (   2 / 1)
       gg (1)   T r  d                      nph ( )            2 / 1
                    3         0           1
                               
          2  T r nph (2 /  1 )                   3d L (1  z ) 2 f
                                                         2
                                       ng ( ) 
                                          
          3          1                              me c5 2 Dtv2
                                                                  6


                     2
  nph ( ) 
                  3d L f                           2 T     2
                                                          3d L f
                                       gg (1 ) 
                                              
               mec3 2 D r 2
                          4
                                                    31 mec3 2 D r 
                                                                 4



           (1  z )
     
             D

               Dermer       Saas-Fee Lecture 4       15-20 March 2010               17
          Minimum Doppler factor approximation for Blob

                  2 T     2
                         d L f                                      2 / 1
      gg (1 ) 
            
                   1 mec3 2 D r 
                               4
                                                                         (1  z ) 1
                                                                 1 
                                                                            D
                    T d L f 1
                         2
                                
       gg (1) 
                    2 me c 3 D r 
                              4
                                                                       c D tv
                                                                  r          ,
                                                                       1 z
                 T (1  z ) 2 d L fˆ1
                                  2
    gg (1 ) 
                     2me c 4 Dtv
                                4



Minimum bulk Lorentz factor:    gg ( 1 )  1
                                              1/ 6
               T (1  z ) d f  
                               2     2
                                                                            2 D2
   D ,min                     
                                     L  1
                                       ˆ
                                                         1  2   
                                                                     ˆ
                    2me c 4tv                                          (1  z ) 2 1

                  Dermer           Saas-Fee Lecture 4        15-20 March 2010            18
gg Opacity : -function approximation for Blast Wave




       Dermer    Saas-Fee Lecture 4   15-20 March 2010   19
  Minimum Doppler factor approximation for Blast Wave




                                                                                     1/ 6
                                                        T (1  z ) d f  
                                                                         2   2
                                           D ,m in                      
                                                                             L  1
                                                                               ˆ

                                                             2me c 4tv    
31/ 6  1.2009...
            Dermer   Saas-Fee Lecture 4               15-20 March 2010               20
                                          gg opacity and Gmin for PKS 2155-304

                                              1/ 6
              T (1  z ) 2 d L f ˆ 1 
                               2
 D ,m in                              
                   2me c 4tv            
                  2 D2
            
            ˆ
               (1  z ) 2 1

  z = 0.116, dL = 1.65×1027 cm

  tv= 300 t5m s

Solve iteratively, quickly converges

                                                                  1/ 6
                    ( f ˆ / 10   10
                                         erg s cm ) E1 (TeV ) 
                                              1     2
 D ,min  32                                                          • Code of Finke et al. (2008)
                                            t5 m                       • Includes internal gg opacity but not
                                                                         pair reinjection
                            ( D / 36) 2                                • Sensitive to EBL model
              E (keV )  0.6                                             • Fit to 2006 flare
                              E1 (TeV )
                   Synchrotron Self-Compton Model

Basic tool is one-zone synchrotron/SSC model with synchrotron self-
   absorption and internal pair production

Even this lacks pair reinjection; multiple self-Compton components

Deducing source redshift from high-energy spectra requires both good
  spectral model and good EBL model

What portion of synchrotron spectrum should be fitted?

Synchrotron/SSC model: Best fit model; parameter studies; extracting
   underlying electron distribution; variability analysis




                Dermer      Saas-Fee Lecture 4    15-20 March 2010     22
                          Synchrotron/SSC Modeling

Approximations (in the one-zone model)

1. -function approximation
         zero-fold for synchrotron; 1 fold for SSC
         Take KN effects into account by terminating integration when
                  scattering enters the KN regime
         Useful for analytic results; equipartition estimates; jet power
                  calculations

2. Uniform approximation: B, D, and R’
         a. Integrate elementary synchrotron emissivity over electron
                   g-factor distribution (assumed uniform throughout sphere)
         b. Average synchrotron spectrum over blob to get target photon
                   spectrum
         c. Compton-scatter synchrotron photons using (isotropic) Jones
                   formula, valid throughout Thomson and KN regimes
         Provides accurate absolute power estimates (photon, particle, B-field)
                   given observing angle
                   for blazars, GD; for radio galaxies inferred from observations
   Fitting Routine

   Code written by
    Justin Finke
Write SSC as a function of:                   Minimize c2
D, B, rb′, z, Ne(g).

Use electron spectrum to
calculate SSC using Jones (1968)
formula

nFnsyn gives Ne(g)
(CS86 expression)

Internal and EBL absorption
calculated                                         Opacity corrections

Leaves two unknowns to fit:
D and B


                     Dermer   Saas-Fee Lecture 4          15-20 March 2010   24
                              Jet Power
      G
                                  ,ke




            Total jet power = sum of particle kinetic and magnetic field
            Minimum jet power for equipartition (minimum energy) magnetic field
            Minimize jet power for measured synchrotron flux

 Jet power: total power available in jet (in observer frame)
 Lj = 2rb′G2c(u′B + u′p) (Celotti & Fabian 1993)
 dLj / dB = 0  Bmin (equipartition)
 B < Bmin  u′p >> u′B and fSSC > fsyn
Synchrotron spectrum implies minimum jet power; additionally
  fitting g rays gives deviation of model from minimum jet power

            Dermer      Saas-Fee Lecture 4     15-20 March 2010           25
                                          Results
                                                              HESS data: 28 July, 2007
                                                              Swift data: 30 July 2007

                                                             Model       D       B      tvar        Lj
                                                                                [mG]     [s]       [1047
                                                                                                  erg s-1]

                                                               1         872     2.7       30       4.4

                                                               3         367     3.6     300        2.7

                                                               5         185     2.7     3000       2.1

                                                             g′min = 1
                                                            Using EBL of Stecker et al. (2006).

                                                            Unreasonably high D and Lj.

                                                            LEdd = 1047 erg s-1
                                                            From radio obs., D < 10
See Finke et al., ApJ, 686, 181 (2008), ApJ, for details    Can a lower IBL resolve problem?


                       Dermer          Saas-Fee Lecture 4          15-20 March 2010               26
           gg absorption by Extragalactic Background Light (EBL)




                                                                e-
                                                          e+

                                                                       g
Stecker et al. (2006, 2007)




                      Dermer   Saas-Fee Lecture 4   15-20 March 2010       27
               Results


                              Model       D        B       tvar        Lj
                                                  [mG]      [s]       [1047
                                                                     erg s-1]
                                6        895       2.5      30            4.5
                                8        390       3.0      300           2.7
                               16        261       81       30            0.5
                               18        139       57       300           0.4



                               g′min = 100               Lower EBL


                              G < 10 on pc scales (Piner & Edwards
                              2004)

                              GLAST could distinguish between these
                              models

Dermer   Saas-Fee Lecture 4           15-20 March 2010               28
              Results

                              Model    D       B      tvar      Lj
                                              [mG]     [s]     [1046
                                                              erg s-1]
                               25     246      89      30       3.2
                               26     118      77      300      2.1
                               27      64      47    3000       2.2



                               Use electron spectrum
                               to underfit optical data

                               Limited by gg in blob

                               X/g correlations depends on
                               gg attenuation



Dermer   Saas-Fee Lecture 4      15-20 March 2010              29
                        PKS 2155-304 Modeling

  Finke et al. (2008) model
using Primack et al. (2005)
EBL

tvar = 2 days
p1 = 3.2, 7.9e3 < g < 3.2e5
p2 = 4.7, 3.2e5 < g < 7e6

B = 0.044 G
G  D  23.4
                                          Preliminary—not for distribution

Jet power = 3.5e45 ergs/s
LB = 9.1e43 ergs/s
Lpar = 3.4e45 ergs/s                   10 times more energy in nonthermal
                                       protons/hadrons as electrons

                    Dermer     Saas-Fee Lecture 4      15-20 March 2010      30
               Synchrotron/SSC Modeling of PKS 2155-304



• Fermi/HESS
campaigns from 2008
• Fermi/RXTE
campaigns from
2008/2009




                                   Aharonian et al. 2009, ApJ, 696, L150




Preliminary—not for distribution
              Monte Carlo Simulation of Synchrotron/SSC Model

Improved accuracy

Use accurate Compton kernel in the head-on
approximation (Compton scattering, not inverse     R
Compton scattering)

Mersenne Twister for Random Number Generator

Check uniformity assumption
         (cf. Gould 1979)

Can consider non-radial electron distributions

Realistic gg opacity calculations

High energy tail for EBL studies

Photon conservation
                     Synchrotron with Photon Conservation

                                                15
                                           10
Standard parameters:

ne (g )  keog H (g ; g 1 , g 2 )
               p                               14
                                           10


R  1015 cm, p  2.2                       10
                                                13




                                    flux
B 1G
       neo ( p  1)
                                                12
                                           10
 keo  1 p 1 p
      g1  g 2                                  11
                                                                                  flux_num
                                                                                  flux_MC
                                           10
  neo  10 10 cm3 ,
                                                                                  flux_esc_MP




  g 1  10 , g 2  10
                                                10
           5            6                  10
                                                     10        12        14            16        18        20
                                                10        10        10           10         10        10
                                                                              n (Hz)
Scattering in KN regime
Solves “line of death” problem in GRB physics?
                              Monte Carlo Synchrotron/SSC with Uniform Electrons and B-field

                                                       g 1  10 4 , g 2  10 5                                                                                                   g 1  10 3 , g 2  10 4
                                                                                                                                                  0
                                                                                                                                             10
                         2
                    10
         erg s )




                                                                                                                                                  -1
                                                                                                                                             10
n L (10 erg s )-1




                                                                                                                                  erg s-1)
-1




                                                                                                                              erg s )
                                                                                                                             -1
                         0
                    10                                                                                                                       10
                                                                                                                                                  -2
40
      40




                                                                                                                             40
                                                                                                                                                  -3
                                                                                                                                             10




                                                                                                                                  (1040
                         -2




                                                                                                                             n L (10
     nLn (10




                    10
         n




                                                                                                                                  n
                                                                                                                                                  -4
                                                                                                                                             10




                                                                                                                                nLn
                         -4
                    10
                                                                                                                                                  -5
                                                                                                                                             10

                         -6                                                                                                                       -6
                    10                                                                                                                       10
                              10        12        14        16        18        20        22        24        26        28                             10        12        14        16        18        20        22        24        26        28
                         10        10        10        10        10        10        10        10        10        10                             10        10        10        10        10        10        10        10        10        10
                                                                       n (Hz)                                                                                                                   n (Hz)


                         Comparison with -function approximation
                         Discrepancies in amplitude
                         Discrepancies in high-energy cutoff (could improve it by using exponential
                         cutoff in electron distribution)
                         Excellent agreement with numerical calculation (mean escape length = 3R/4)
     Non-power law spectra                       Abdo et al., 2010, ApJ, 710, 1271

   First definitive evidence of a
    spectral break above 100 MeV
   General feature in FSRQs and
    many BLLac-LSPs
   Absent in BLLac-HSPs
   Broken power law model seems
    to be favored
   G~1.0 > 0.5  not from
    radiative cooling
   Favored explanation: feature in
    the underlying particle
    distribution
   Implications for EBL studies
    and blazar contribution to
    extragalactic diffuse emission




                                                         FSRQs
                                      Challenge for modelers to account for the break
                                                         BLLac-ISPs
                                                        BLLac-HSPs
                                                         BLLac-LSPs
                                      and the relative constancy of spectral index with time
                     Dermer       Saas-Fee Lecture 4       15-20 March 2010              35
                              FSRQ Modeling

At least three additional
   spectral components:                                       Dermer et al. (2009)
   Accretion disk
   EC Disk
   EC BLR

Lots of parameters

External radiation field
   provides a new source of
   opacity; need to perform
   Compton scattering and gg
   opacity self-consistently

Opacity spectral break at a
  few GeV

                     Dermer     Saas-Fee Lecture 4   15-20 March 2010                36
                                                Abdo., et al. 2010, Nature, 463, 919
             3C 279
   Where are the g-rays made?
   Monitor long-term behavior of
    light curve
   Correlates with changes in
    optical polarization and flux
   Highly ordered magnetic field
    over long timescale
   g ray dissipation location at
    multi-pc scale?




                   3C 279
                   z = 0.538




                Dermer         Saas-Fee Lecture 4        15-20 March 2010              37
            Origin of Spectral Break in 3C454.3
                                                            Abdo, et al. 2009, ApJ, 699, 817




                                                     Glow  2.27 ± 0.03, Ghigh  3.5 ± 0.03
                                                               Ebr  2.4 ± 0.03 GeV




Finke and Dermer, 2010, submitted



                  Dermer        Saas-Fee Lecture 4      15-20 March 2010                38
           Relativistic jet physics

New results on blazars and radio galaxies:
1. LBAS / 1LAC catalogs
2. Multi-GeV spectral softening in FSRQs, LBLs, IBLs;
   not XBLs
3. Multiwavelength quasi-simultaneous SEDs including
   GeV emission for radio galaxies, BL Lacs and FSRQs
4. 3C 279, PKS 1510-089: location of emission site;
   complexity of magnetic field
5. Use SED to constrain redshift from EBL model
6. Long (mo – yr) timescale light curves
7. High energy photons from blazar sources: minimum
   Doppler factor
8. Contemporaneous data sets for, e.g.,
    1. FSRQs 3C 454.3, 3C 279
    2. BL Lacs: Mrk 421, PKS 2155-304
    3. Radio galaxies: Cen A, M87, 3C 84



  Dermer      Saas-Fee Lecture 4     15-20 March 2010   39
         Back-up Slides




Dermer   Saas-Fee Lecture 4   15-20 March 2010   40
          Synchrotron/SSC model in the Thomson regime


Can measure 6 defining quantities for syn/SSC model:
z, tv                     nFn = f
                                        Ls             LC


                                                                     AC = LC/Ls


                                                                         
                                         s            C

                                              (Ghisellini et al. 1996)

G> Gmin


                              Thomson regime


              Dermer    Saas-Fee Lecture 4        15-20 March 2010            41
             Nonthermal Electron Synchrotron Radiation

If electrons are assumed to radiate the observed synchrotron nFn
    spectrum, then in the -function approximation for synchrotron
    emissivity
                D L( )
                 4
                                           4     B2 2
       fsyn                ,  L( )  c T    g   g  Ne (g )
                                                               
                  4d L2
                                           3     8

                  D L( )
                   4
                                             24 2 d L fsyn
                                                     2
 So
         fsyn                 N e (g ) 
                                   
                    4d L2
                                             cB2 Dg 3
                                                       4




           B 2          D        (1  z ) Bcr
            g  ,         g 
           Bcr          1 z             D B


                Dermer     Saas-Fee Lecture 4    15-20 March 2010        42


				
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