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Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
J. Chiang 1
Fermi-LAT Observationsof Blazars
Jim ChiangSLAC/KIPAC
on behalf of the Fermi-LAT collaboration
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
J. Chiang 2
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
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
J. Chiang 3
Unified Picture of AGNs
• 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-of-sight 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
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
J. Chiang 4
Blazar Spectral Energy Distributions
• 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 s1) 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 (Liso1045 erg s1) and z < 0.5
3C 279
Hartman et al. 2001
Mrk 421
Donnarumma et al. 2009
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Key Questions for Blazars
• 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
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
J. Chiang 6
What is Fermi?
• Large leap in all key capabilities, transforming our knowledge of the gamma-ray universe. Great discovery potential.
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!
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
J. Chiang 7
Fermi LAT Overview: Overall Design
e+ e–
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
Electronics System:• Includes flexible, highly-efficient,
multi-level trigger
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
Anticoincidence Detector:• 89 scintillator tiles• First step in reduction of large charged
cosmic ray background• Segmentation reduces self veto at high energy
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
Thermal Blanket:• And micro-meteorite shield
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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3 Month Counts Map
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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3 Month High Confidence Source List
• 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)
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Variable sources in the LAT Bright Source List
• Based on 1 week time scales
• 68/205 show variability with probability > 99%
• Isotropic distribution blazars
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Fermi Results for Individual AGNs
3C 454.3
PKS 1502+106
PKS 2155304
NGC 1275
PKS 1454354
PMN J0948+002
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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3C 454.3
• 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
=2.3
=3.5
(contact authors: G. Madejski & B. Lott)
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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PKS 2155304: The Campaign
• 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
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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PKS 2155304: Spectral Energy Distribution
• Time-averaged SED is well described by a single zone SSC model:
HESS
FermiRXTE
SwiftATOM
p0=1.3
p1=3.2
p2=4.3e+e distribution
• Highest energy electrons (e>2105) produce the X-ray emission, but contribute relatively little above 0.2 TeV
(contact authors: B. Giebels & J. Chiang)
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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PKS 2155304: Light Curves and Correlated Variability
• 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 X-
rays 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
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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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
LAT counts map, > 200MeV, 4 Aug - 5 Dec100 arcsec across
(contact author: J. Kataoka)
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Fermi-LAT detection of NGC 1275
• Variable emission on month to year time scales AGN Cannot be dark matter or diffuse cluster emission
• Inferred blazar luminosity, L1044-1045 erg s1, is consistent with power needed to inflate the voids
• SED fitted with single zone SSC model (solid curve) and spine-sheath model (dashed)
COS-B
EGRET
Fermi
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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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)
Narrow-Line Seyfert 1 PMN J0948+0022
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Blazar Population Properties
• 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)FSRQBL LacRadio GalaxyUncertain
arXiv:0902.1559Abdo et al, ApJ in press
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
J. Chiang 20Photon index
FSRQs
F
BLLacs
FRSQs
BL Lacs
All
=2.40.2
=2.00.2
• FSRQ and BL Lac index distributions differ at 1 1012 level
• 42% BL Lac fraction (vs 23% for EGRET), 10 HBLs
• 8 TeV Blazars
Blazar Population Properties
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Blazar Population Properties
b = 20, 80
E < 3 GeVb = 20
BL Lacs
FSRQs
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Luminosity vs Redshift
F>100MeV = 4108 ph cm2 s1
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Luminosity Functions
• 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
• 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)
L0.5
L1.5
L1.1
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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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.
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Backup slides
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Measuring the EBL with Fermi Blazars
• 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
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Outline
• Blazar Properties and Fundamental Questions• Fermi LAT Capabilities• Multiwavelength Campaigns• Results on Individual Sources• Population Studies and Extragalactic Diffuse Emission• Summary
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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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 %
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Publicly Monitored Source List
? Awaiting definitive detection by LAT
†TeV source
?
?
?
†
google: LAT_Monitored_Sources
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Source Monitoring Activities
• 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– 2 106 ph cm2 s1 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
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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• Announcements of flaring sources multiwavelength follow-up
• 25 blazar-related LAT ATELs have been issued on 22 different sources
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Multiwavelength Campaigns
• 3C 454.3: Jul–Oct; radio, opt, UV, Swift
• BL Lac: 15 Aug–5 Sep; opt, UV, X-ray
• PKS 2155-304: 25 Aug–6 Sep; radio, opt, UV, X-ray, TeV (HESS)
• 1ES 1959+650: Sep–Nov
• PKS 0528+134: 27 Sep–Oct; radio, IR, opt, UV, X-ray
• 3C 273: 31 Oct–7 Feb; radio, opt, X-ray
• 3C 279: Aug—Mar; radio, opt, X-ray, TeV
• Mrk 421: Jan–May; radio, opt, X-ray, TeV (VERITAS, MAGIC)
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Flaring Blazars
• PKS 1502+106: z=1.84, factor 3 increase in <12 hrs, highest L/t in GeV band
• PKS 1454354: 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 2155304)
Preliminary
(contact author: L. Foschini)
(contact author: S. Ciprini)
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Fermi Radio Galaxy Detections
Cen A
NGC1275(Perseus A)
3 month all-sky map
Confirmed EGRET detection of Cen A NGC 1275 consistent with point
source and no significant variability within initial four month span of LAT Observations
Abdo et al.2009 ApJContact Author: J.Kataoka
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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NGC1275: Long Term -ray variability &Correlation with Radio?
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
Contours: Aug ‘08 VLBA 15 GHzColor: Sep ‘07 map subtractedFrom MOJAVE program
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Spectral Energy Distribution
SED LBL-like: possible unification of BL Lac and Radio Galaxies
LAT spectrum:0)-
= 2.17 ± 0.05
(1) one-zone SSCB= 0.05 GR= 0.7 pc= 2.3, = 1.8Ljet = 2.3e45 erg/s
(2) Decelerating flowB = 0.2 GD = 0.2 pcR = 0.01 pc = 10 -> 2 Ljet = 6.0e43 erg/s
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
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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LAT Detection of a Narrow Line Seyfert 1
• 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)
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Gamma-ray vs Radio Properties
Peak -ray flux vs 8.4 GHz flux density -ray photon index vs radio luminosity
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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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
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Blazar Population Properties
FRSQs BL Lacs
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Blazar Population Properties
• 34% BL Lac fraction (vs 19% for EGRET)
Fermi-LAT Observations of Blazars TeVPA, SLAC, 14 July 2009
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Blazar Population Properties
b = 20, 80
E < 3 GeVb = 20