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  • pg 1
									                        New insight into Gamma-ray
                        Blazars with the Fermi-LAT

                        Benoît Lott
                        CEN Bordeaux-Gradignan

                        on behalf of the Fermi-LAT collaboration

Journées de Blois /09                               Benoit Lott
                               Unified Picture of AGNs

                                          •   Powered by accretion onto a
                                              central, supermassive black hole
                                          •   Jets: highly collimated outflows
                                              with 10
                                               – Large brightness temps,
                                                 superluminal motion, rapid
                                                 variability in -rays
                                          •   Unified Model: observer line-of-
                                              sight determines source
                                              properties, e.g., radio galaxy vs
                                          •   Other factors: accretion rate, BH
                                              mass and spin, host galaxy
                                          •   Open questions: jet composition,
                                              location of dissipation,
                                              acceleration processes, gamma-
                                              ray emission processes
Image Credit: C.M.Urry & P. Padovani

Journées de Blois /09                                                Benoit Lott
                            Blazar classes

                 class             FSRQs                     BLLacs
        Defining property   strong emission lines        nearly lineless

           Environment      intense radiation field     low radiation field
                             (disk, clouds, torus)
                Power           ~1046-48 erg/s            ~1045-46 erg/s

        Parent population     Fanaroff-Riley 2          Fanaroff-Riley 1
                                                        from J. Kataoka
           Synchrotron           Peak in IR             Peak in Opt/IR: LBL
           hump in SED                                Peak in UV/X-rays: HBL

        EGRET-detected            46 (77%)                  14 (23%)

      Redshift of EGRET            0.1-2.3                     <1

Journées de Blois /09                                             Benoit Lott
LAT performance

                     …. Transient class
                          Source class
                          Diffuse class

    multiple scattering

                            Finite pitch of
                            Si strips
                        The flaring and variable sky

                                       • ~30 Astronomers
                                         telegrams (alert threshold:
                                         F[E> 100 MeV]~1106 ph cm2 s1)
                                          – Discovery of new
                                            gamma-ray blazars PKS
                                            1502+106, PKS 1454-354
                                          – Flares from known
                                            gamma-ray blazars:
                                            3C454.3, PKS 1510-
                                            089,3C273, AO 0235+164,
                                            PSK 0208-512, 3C66A,
                                            PKS 0537-441
                                          – Galactic plane
                                            transients: J0910-5041,
                                            3EG J0903-3531

Journées de Blois /09                                         Benoit Lott
                                   Source monitoring
       Ex: 3C454.3
                                                   • EGRET: sparse 15-day long
                                                   viewing periods
                                                   • difficult to establish variability
                                                   patterns and determine relevant
                                                   parameters (duty cycle…)
                                                   • Fermi: continuous coverage of all
                                                   sources in the sky

                   commissioning     Science operation
                   pointed mode      survey mode

         Light curves of some bright sources are online:
Journées de Blois /09                                                       Benoit Lott
                         Power spectral density

                        slope:-1.7±0.5               slope:-1.2±0.5

Average PDS for 4 bright FSRQs:          Average PDS for 5 bright IBLs/HBLs:
PKS 0454-234, 3C279                      3C66, PKS0447-439, Mrk421,
PKS 1502+106, PKS 1510-08                PG 1553+11, PKS 2155-304

Journées de Blois /09                                            Benoit Lott
                                   MW campaigns
                        3C 454.3 (Lars Fuhrmann)   3C 279 (Masaaki Hayashida)

 Interband timing correlation
 Time resolved SEDs: dynamics of emitting particles
 → Location, environment of emitting zone, acceleration vs cooling
 Other campaigns: Mrk421, Mrk501, 1ES1959+650, 3C66A…

Journées de Blois /09                                           Benoit Lott
                 Optical gamma-ray correlation for 3C454.3

                                                 Bonning et al. 2009
                                                  SMART telescope

Journées de Blois /09                                       Benoit Lott
                PKS 2155304: Spectral Energy Distribution

PKS 2155-304: HBL,
z=0.116                         ATOM       Swift
First simultaneous                                  RXTE
SED including GeV-TeV                                                                HESS

• strong correlation
between optical and
TeV fluxes
• X-ray flux varies
independently of TeV
• correlation between
TeV flux and GeV
photon index               astro-ph 0903-2924
                                                   (contact authors: B. Giebels & J. Chiang)
Challenge simple SSC

 Journées de Blois /09                                                       Benoit Lott
                            Non power-law spectra
•   First definitive evidence of
    a spectral break above
    100 MeV
•   General feature in FSRQs
    and many LBLs                                   LBL
•   Absent in HBLs
•   Broken power law model
    seems to be favored
•   ~1.0 > 0.5  not from
    radiative cooling
•   Possible explanations:
      – “intrinsic” absorption via
         opacity from accretion
        disk or BLR photons
      – feature in the underlying
        particle distribution
•   Implications for EBL
    studies and blazar
    contribution to
    extragalactic diffuse
    Journées de Blois /09                           Benoit Lott
                        LAT Bright AGN Sample (LBAS)

3-month dataset, 10-s significance: 106 sources at |b|>0° with high-confidence
AGN associations (CGRaBS/CRATES/BZCat)
2/3 of the sources were not detected by EGRET
57 FSRQs
42 BLLacs (40%) including 10 HBLs
5 of Unknown type
2 Radio Galaxies (Cen A, NGC1275)
Journées de Blois /09                                                   Benoit Lott
                                       Index vs flux
                                           (l,b)=(40°,80°) (40°,20°)
Radio Galaxies

                         E< 3 GeV

 Journées de Blois /09                                                 Benoit Lott
                                                          Photon index distributions
                                      rms: 0.19

                                                                                  LBLs        n
                                      rms: 0.15

Number of sources

                                    rms: 0.22



                                                       rms: 0.14

                    Journées de Blois /09
                                                Photon index                              n       Benoit Lott
                        Luminosity Functions

  • FSRQs
         – Strong cosmological
           evolution                                 L1.5
         – More complicated than pure   L0.5
           density or pure luminosity
         – The 3 month LAT AGN
           sample measures the bright
           end of the luminosity

  • BL Lac objects
         – No evidence of evolution

  • Combined emission from
    individual blazars in 3 month
    sample corresponds to 7%
    of EGRET extragalactic
    diffuse                                     (contact: M. Ajello)
Journées de Blois /09                             Benoit Lott
                 detection of NGC 1275
  •     Classic example of a “cooling core”
  •     Voids or “bubble” seen in the X-ray must
        be inflated by some central source of
        power, i.e., an AGN
  •     Variable emission on month to year time
        scales  AGN Cannot be dark matter or
        diffuse cluster emission
  •     Inferred blazar luminosity, L1044-1045                                            Fermi
        erg s1, is consistent with power needed                            EGRET
        to inflate the voids

                                                   •   SED fitted with single zone SSC
                                                       model (solid curve) and spine-
                                                       sheath model (dashed)
                                                            Contact: J. Kataoka
Journées de Blois /09                                                               Benoit Lott
                         Narrow-Line Quasar PMN J0948+0022

Optical spectrum of narrow-line Seyfert 1 type
(usually radio quiet).

Radio emission is strongly variable
and with flat spectrum -> suggests Doppler
boosting, now confirmed by LAT.

                                                    First -ray detection of such an object

                                             SED modeling shows this is a typical FSRQ,
                                             although with a relatively low power.

                                             Many questions open:
                                             •Is this a new type of -ray emitting AGN?
                                             •Are there other sources of this type?
                                             •What is the impact of narrow-lines?
                                                                  (Contact author:L. Foschini)
 Journées de Blois /09                                                       Benoit Lott
  • The LAT is providing unprecedented-quality data in terms of:
       – statistical accuracy
       – time sampling
       – numbers of sources
    opening a new era in blazar science.
  The newly enabled studies
       – variability patterns
       – spectral features
       – time-resolved SEDs, interband timing correlation
       – census of blazar populations, evolution
  will undoubtedly yield a better understanding of the blazar

Journées de Blois /09                                    Benoit Lott
                        Backup slides

Journées de Blois /09                   Benoit Lott
                        0FGL: 132 sources with TS>100, |b|>10°
                              7 pulsars, 125 AGN candidates
    CGRaBS (Healey et al. 08)                        BZCat (Massaro et al. 08)
1627 radio sources from CRATES                 Compilation of 2500 known blazars
association based on Figure-of-Merit           association   based     on      spatial
(spatial, radio and X spectrum)                coincidence (Mattox et al., 01)
established from EGRET
                                   galactic                                        celestial

101 high-conf. (P>90%) associations            102 high-conf. (P>90%) associations
14 low-conf. (40%<P<90%) associations          4 low-conf. (40%<P<90%)
Journées de Blois /09                                                    Benoit Lott

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