Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Fermi-LAT Observations
of Blazars
Jim Chiang
SLAC/KIPAC
on behalf of the Fermi-LAT collaboration
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Related Talks on Fermi-LAT Results
• Markus Ackermann – Observation of the extragalactic diffuse
continuum gamma-ray emission with Fermi LAT
• Keith Bechtol – GeV gamma-ray observations of galaxy
clusters with the Fermi LAT
• Chuck Dermer – Evidence for ultrahigh energy cosmic rays
from Fermi obsevations of AGN and gamma ray bursts
• David Paneque – Fermi view of the classical TeV high peak BL
Lacs
• Greg Madejski – Gamma-ray spectra of blazars detected by
Fermi/LAT
• Marco Ajello – Cosmological evolution of blazars: new findings
from the Swift/BAT and Fermi/LAT surveys
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Unified Picture of AGNs
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Powered by accretion onto a
central, supermassive black
hole
Accretion disks produce
optical/UV/X-ray emission via
various thermal processes
Jets: highly collimated outflows
with 10
– Large brightness temps,
superluminal motion, rapid
variability in -rays
Unified Model: observer line-ofsight determines source
properties, e.g., radio galaxy vs
blazar
Other factors: accretion rate, BH
mass and spin, host galaxy
Image Credit: C.M.Urry & P. Padovani
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Blazar Spectral Energy Distributions
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Two main components:
– Synchrotron at low energies
– Inverse Compton and/or “hadronic”
at higher energies
Flat Spectrum Radio Quasars (FSRQs)
– Multi-temperature disk emission
and broad lines in OUV
– Non-thermal components peak in IR
& hard X-ray/MeV regime
– Higher luminosity (Liso 1048 erg s1)
and redshift dist. peaks at z  1
BL Lac objects
– Little or no evidence of disk or
broad emission lines (EW < 5Å)
– Non-thermal peaks in UV/soft X-rays
& GeV
– Lower luminosity (Liso1045 erg s1)
and z < 0.5
J. Chiang
3C 279
Hartman et al. 2001
Mrk 421
Donnarumma et al. 2009
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Key Questions for Blazars
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Emission mechanisms (especially for high energy
component)
– Leptonic (IC of synchrotron or external photons)
vs hadronic (0, proton synchrotron)
Emission location
– Single zone for all wavebands (completely
constraining for simplest leptonic models)
– Opacity effects and energy-dependent
photospheres
Particle acceleration mechanisms
– Shocks, Blandford-Znajek
Jet composition
– Poynting flux, leptonic, ions
Jet confinement
– External pressure, magnetic stresses
Accretion disk—black hole—jet connection
Blazars as probes of the extragalactic background
light (EBL)
Effect of blazar emission on host galaxies and
galaxy clusters
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
What is Fermi?
Large Area Telescope (LAT):
• 20 MeV - >300 GeV (including
unexplored region 10-100 GeV)
• 2.4 sr FoV (scans entire sky
every ~3hrs)
Gamma-ray Burst Monitor (GBM)
• 8 keV - 40 MeV
• views entire unocculted sky
Launch 11 June 2008!
• Large leap in all key capabilities, transforming our knowledge
of the gamma-ray universe. Great discovery potential.
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Fermi LAT Overview: Overall Design
Overall LAT Design:
•4x4 array of identical towers
•3000 kg, 650 W (allocation)
•1.8 m  1.8 m  1.0 m
•20 MeV – >300 GeV
Anticoincidence Detector:
• 89 scintillator tiles
• First step in reduction of large charged cosmic
ray background
• Segmentation reduces self veto at high energy

Thermal Blanket:
• And micro-meteorite shield
Precision Si-strip Tracker:
Measures incident gamma direction
18 XY tracking planes. 228 mm pitch.
High efficiency. Good position resolution
12 x 0.03 X0 front end => reduce multiple
scattering.
4 x 0.18 X0 back-end => increase
sensitivity >1GeV
Hodoscopic CsI Calorimeter:
• Segmented array of 1536 CsI(Tl) crystals
• 8.5 X0: shower max contained <100 GeV
• Measures the incident gamma energy
• Rejects cosmic ray backgrounds
J. Chiang
e+
e–
Electronics System:
• Includes flexible, highly-efficient,
multi-level trigger
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
3 Month Counts Map
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
3 Month High Confidence Source List
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205 sources with significance > 10 (EGRET found fewer than 30)
Typical 95% CL error radius is <10 arcmin
(Abdo et al. 2009 ApJS, 183, 46)
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Variable sources in the LAT Bright Source List
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Based on 1 week time scales
68/205 show variability with probability > 99%
Isotropic distribution  blazars
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Fermi Results for Individual AGNs
PKS 1502+106
PMN J0948+002
PKS 1454354
NGC 1275
3C 454.3
J. Chiang
PKS 2155304
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
3C 454.3
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OVV quasar, very active since
2000; z = 0.859; superluminal
motion
Variability time scales of < 3
days   > 6 (cf. VLBI  25)
First definitive evidence of a
spectral break above 100 MeV
=1.2 > 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 emission
=3.5
=2.3
(contact authors: G. Madejski & B. Lott)
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
PKS 2155304: The Campaign
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PKS 2155-304: HBL, z=0.116
– Detectable by HESS routinely in < 1 h even in low state (0.1 Crab)
– July 2006 flare: 7 Crab, VHE strongly correlated with X-rays, an SSC
prediction; but t ~ 5min poses difficulties for SSC models
Our Campaign: 11 nightly obs. using HESS, ATOM, RXTE (+ Swift)
– First multiwaveband observations of a blazar SED using Fermi and an ACT
– Monitor for very high state outburst similar to the July 2006 flare seen by
HESS (Swift ToO)
– Study correlated variability between various bands
Aharonian et al. 2007
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
PKS 2155304: Spectral Energy Distribution
• Time-averaged SED is
well described by a
single zone SSC
model:
e+e distribution
ATOM
Swift
Fermi
RXTE
HESS
p2=4.3
p1=3.2
p0=1.3
• Highest energy electrons (e>2105) produce the X-ray emission,
but contribute relatively little above 0.2 TeV
(contact authors: B. Giebels & J. Chiang)
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
PKS 2155304: Light Curves and Correlated
Variability
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X-ray and VHE fluxes are not
correlated, in contrast to July
2006 flare
Lack of spectral variability in
HESS band (VHE < 0.2)  weak
radiative cooling regime
Significant spectral variability in
X-rays (X  0.5)  strong
cooling regime
 Electrons producing the Xrays have higher energies
than those producing the TeV
Optical and VHE fluxes are
correlated
 Optical is driving the TeV
variability
Lack of opt-GeV correlation
Multi-zone SSC models are required
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
NGC 1275 (3C 84, Perseus A)
• Classic example of a “cooling core” cluster
• Voids or “bubble” seen in the X-ray must be inflated by some
central source of power, i.e., an AGN
100 arcsec across
LAT counts map, > 200MeV, 4 Aug - 5 Dec
(contact author: J. Kataoka)
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Fermi-LAT detection of NGC 1275
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Variable emission on month to
year time scales  AGN
Cannot be dark matter or diffuse
cluster emission
Inferred blazar luminosity,
L1044-1045 erg s1, is consistent
with power needed to inflate the
voids
COS-B
Fermi
EGRET
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J. Chiang
SED fitted with single zone SSC
model (solid curve) and spinesheath model (dashed)
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Narrow-Line Seyfert 1 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.
•Is this a new type of -ray emitting AGN?
•Are there other sources of this type?
•What is the impact of narrow-lines?
(Abdo, et al 2009 ApJ, 699, 976. Contact author: L. Foschini)
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Blazar Population Properties
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Aug/Sep/Oct high confidence list: 205 sources with >10 detection
132 with |b| > 10 (7 pulsars, 9 unid)
– 116/125 are bright, flat spectrum radio sources
– 58 FRSQs, 42 BL Lacs, 4 Unc., 2 radio galaxies (+10 low CL associations)
– CRATES (all-sky radio catalog), CGRaBS (all-sky optical spectra), BZCAT
(multifrequency blazar catalog)
FSRQ
BL Lac
Radio Galaxy
Uncertain
arXiv:0902.1559
Abdo et al, ApJ in press
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Blazar Population Properties
All
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FRSQs
=2.00.2
BL Lacs
nFn
=2.40.2
FSRQs
BLLacs
FSRQ and BL Lac index
distributions differ at 1  1012 level
42% BL Lac fraction (vs 23% for
EGRET), 10 HBLs
8 TeV Blazars
J. Chiang
Photon index
n
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Blazar Population Properties
FSRQs
b = 20, 80
BL Lacs
E < 3 GeV
b = 20
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Luminosity vs Redshift
F>100MeV = 4108 ph cm2 s1
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Luminosity Functions
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FSRQs
– Strong evolution
– More complicated than pure
density or pure luminosity
evolution
– The 3 month LAT AGN
sample measures the bright
end of the luminosity
distribution
L1.5
L0.5
BL Lac objects
– No evidence of evolution
Combined emission from
individual blazars in 3 month
sample corresponds to 7% of
EGRET extragalactic diffuse
J. Chiang
L1.1
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(contact: M. Ajello)
Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Conclusions
• The LAT is performing spectacularly well, both operationally
and scientifically.
• Several multiwavelength campaigns have been completed and
others are on-going.  Many more papers on individual
blazars are forthcoming.
• The LAT team is busy performing detailed spectral and
variability studies for a deeper sample of AGNs utilizing the full
1st year dataset.
• We are undertaking population studies relating the LAT blazar
properties to radio, optical, X-ray, and TeV observations.
• Current results on AGNs are just the tip of the iceberg.
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Backup slides
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Measuring the EBL with Fermi Blazars
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The effects of EBL absorption will occur at lower energies for higher
redshift sources
Blazars with z > 1 will begin to show these effects in the LAT band:
Credit: L. Reyes
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Outline
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Blazar Properties and Fundamental Questions
Fermi LAT Capabilities
Multiwavelength Campaigns
Results on Individual Sources
Population Studies and Extragalactic Diffuse Emission
Summary
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
The Fermi Large Area Telescope
• Launched 11 June 2008
• 2.4 sr FOV
• First year survey mod operation: 35 rocking about orbital
plane each orbit  full sky coverage every 3 hours
• Energy range: 20 MeV to >300 GeV, E/E  10–15 %
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Publicly Monitored Source List
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TeV source
? Awaiting definitive detection by LAT
google: LAT_Monitored_Sources
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Source Monitoring Activities
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Automated Science Processing (ASP)
– Transient detection: Source detection algorithm to find all point
sources in data from each epoch (6hr, day, week)
– Follow-up monitoring: Full likelihood analysis on sources from
transient detection step + “publicly monitored” sources
– 2  106 ph cm2 s1 threshold (day time scale) for public release of
others
Flare Advocates:
– LAT scientists from Galactic and Extragalactic groups examine
ASP output and perform follow-up analyses, produce ATels, and
propose ToOs
3C 454.3
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Fermi-LAT Observations of Blazars
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TeVPA, SLAC, 14 July 2009
Announcements of flaring sources  multiwavelength follow-up
25 blazar-related LAT ATELs have been issued on 22 different sources
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Multiwavelength Campaigns
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3C 454.3: Jul–Oct; radio, opt, UV, Swift
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BL Lac: 15 Aug–5 Sep; opt, UV, X-ray
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PKS 2155-304: 25 Aug–6 Sep; radio, opt, UV, X-ray, TeV (HESS)
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1ES 1959+650: Sep–Nov
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PKS 0528+134: 27 Sep–Oct; radio, IR, opt, UV, X-ray
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3C 273: 31 Oct–7 Feb; radio, opt, X-ray
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3C 279: Aug—Mar; radio, opt, X-ray, TeV
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Mrk 421: Jan–May; radio, opt, X-ray, TeV (VERITAS, MAGIC)
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Flaring Blazars
• PKS 1454354: factor 5
increase of >100 MeV flux in 12
hours; achromatic flux
variations
 weak radiative cooling regime,
GeV variability driven by seed
photon changes (cf. PKS
2155304)
(contact author: L. Foschini)
• PKS 1502+106: z=1.84, factor 3 increase in <12 hrs, highest
L/t in GeV band
Preliminary
J. Chiang
(contact author: S. Ciprini) 33
Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Fermi Radio Galaxy Detections
Confirmed EGRET detection of Cen A
NGC 1275 consistent with point source
and no significant variability within initial
four month span of LAT Observations
3 month all-sky map
Cen A
Abdo et
al.2009 ApJ
Contact
Author:
J.Kataoka
J. Chiang
NGC1275
(Perseus A)
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
NGC1275: Long Term -ray variability &
Correlation with Radio?
Contours: Aug ‘08 VLBA 15 GHz
Color: Sep ‘07 map subtracted
From MOJAVE program
LAT flux 6x brighter than EGRET limit
Historical COS-B detection while radio in
high radio state
Radio light curve rising during the Fermi observations
with pc-scale outburst seen in MOJAVE maps
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Spectral Energy Distribution
LAT spectrum:0)-
 = 2.17 ± 0.05
(1) one-zone SSC
B= 0.05 G
R= 0.7 pc
= 2.3,  = 1.8
Ljet = 2.3e45 erg/s
(2) Decelerating flow
B = 0.2 G
D = 0.2 pc
R = 0.01 pc
 = 10 -> 2
Ljet = 6.0e43 erg/s
SED LBL-like: possible unification of BL Lac and Radio Galaxies
Jet power close to the power required to inflate the
lobes of 3C 84 against the pressure of the hot cluster gas
(0.3-1.2)x
1044 erg/s: Dunn & Fabian 2004
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
LAT Detection of a Narrow Line Seyfert 1
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Seyfert galaxies are not normally associated with blazar emission
PMN J0948+0022 SED is similar to an FSRQ’s, but at much lower
luminosity
Seyfert galaxies have lower mass BHs (107Msun) & NS1s have high
accretion rates  Eddington ratio is a key determinant of SED
characteristics
Peak -ray flux vs 8.4 GHz flux
(contact author: L. Foschini)
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Gamma-ray vs Radio Properties
Peak -ray flux vs 8.4 GHz flux density
J. Chiang
-ray photon index vs radio luminosity
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Astronomer’s Telegrams*
#1628, 24 Jul 2008, 3C 454.3,
z=0.859, FSRQ
#1650, 8 Aug 2008, PKS 1502+106,
z=1.84, FSRQ
#1701, 5 Sep 2008, PKS 1454-354,
z=1.42, FSRQ
#1707, 8 Sep 2008, 3C 273, z=0.158,
FSRQ
#1743, 26 Sep 2008, PKS 1510-089,
z=0.360, FSRQ
#1744, 26 Sep 2008, AO0235+164,
z=0.940, BL Lac
#1759, 3 Oct 2008, 3C 66A, z=0.44?,
IBL (VERITAS Atel 1753)
#1759, 3 Oct 2008, PKS 0208-512,
z=0.999
#1759, 3 Oct 2008, PKS 0537-441,
z=0.894, BL Lac
#1784, 15 Oct 2008, AO0235+164,
z=0.940, BL Lac
#1864, 6 Dec 2008, 3C 279, z=0.536,
FSRQ
#1877, 16 Dec 2008, QSO B0133+47,
z=0.859
#1888, 4 Jan 2009, CRATES
J1239+0443 (3EGJ1236+0457),
z=1.76?
#1894, 8 Jan 2009, PKS 1244-255,
z=0.64, FSRQ
#1897, 9 Jan 2009, PKS 1510-089,
z=0.360, FSRQ
* blazar-only
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Blazar Population Properties
FRSQs
J. Chiang
BL Lacs
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Blazar Population Properties
• 34% BL Lac fraction (vs 19% for EGRET)
J. Chiang
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Fermi-LAT Observations of Blazars
TeVPA, SLAC, 14 July 2009
Blazar Population Properties
b = 20, 80
E < 3 GeV
b = 20
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