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Fermi-LAT Observations

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Title: Fermi-LAT Observations


1
Fermi-LAT Observations of Blazars
Jim Chiang SLAC/KIPAC
on behalf of the Fermi-LAT collaboration
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

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
4
Blazar Spectral Energy Distributions
3C 279
  • 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 lt 5Å)
  • Non-thermal peaks in UV/soft X-rays GeV
  • Lower luminosity (Liso?1045 erg s?1) and z lt 0.5

Hartman et al. 2001
Mrk 421
Donnarumma et al. 2009
5
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 diskblack holejet connection
  • Blazars as probes of the extragalactic background
    light (EBL)
  • Effect of blazar emission on host galaxies and
    galaxy clusters

6
What is Fermi?
  • Large Area Telescope (LAT)
  • 20 MeV - gt300 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.

7
Fermi LAT Overview Overall Design
  • 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 gt300 GeV
  • 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 gt reduce multiple
scattering. 4 x 0.18 X0 back-end gt increase
sensitivity gt1GeV
  • Hodoscopic CsI Calorimeter
  • Segmented array of 1536 CsI(Tl) crystals
  • 8.5 X0 shower max contained lt100 GeV
  • Measures the incident gamma energy
  • Rejects cosmic ray backgrounds
  • Electronics System
  • Includes flexible, highly-efficient, multi-level
    trigger

8
3 Month Counts Map
9
3 Month High Confidence Source List
  • 205 sources with significance gt 10? (EGRET found
    fewer than 30)
  • Typical 95 CL error radius is lt10 arcmin
  • (Abdo et al. 2009 ApJS, 183, 46)

10
Variable sources in the LAT Bright Source List
  • Based on 1 week time scales
  • 68/205 show variability with probability gt 99
  • Isotropic distribution ? blazars

11
Fermi Results for Individual AGNs
PKS 1502106
PMN J0948002
PKS 1454?354
NGC 1275
3C 454.3
PKS 2155?304
12
3C 454.3
  • OVV quasar, very active since 2000 z 0.859
    superluminal motion
  • Variability time scales of lt 3 days ? ? gt 6 (cf.
    ?VLBI ? 25)
  • First definitive evidence of a spectral break
    above 100 MeV
  • ??1.2 gt 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)
13
PKS 2155?304 The Campaign
  • PKS 2155-304 HBL, z0.116
  • Detectable by HESS routinely in lt 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

14
PKS 2155?304 Spectral Energy Distribution
  • Time-averaged SED is well described by a single
    zone SSC model

ATOM
Swift
Fermi
RXTE
HESS
  • Highest energy electrons (?egt2?105) produce the
    X-ray emission, but contribute relatively little
    above 0.2 TeV

(contact authors B. Giebels J. Chiang)
15
PKS 2155?304 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
    lt 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

16
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, gt 200MeV, 4 Aug - 5 Dec
(contact author J. Kataoka)
17
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, L??1044-1045 erg s?1,
    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
Fermi
EGRET
18
Narrow-Line Seyfert 1 PMN J09480022
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)
19
Blazar Population Properties
  • Aug/Sep/Oct high confidence list 205 sources
    with gt10? detection
  • 132 with b gt 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)

arXiv0902.1559 Abdo et al, ApJ in
press
20
Blazar Population Properties
nFn
  • 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

n
Photon index
21
Blazar Population Properties
b 20?, 80?
FSRQs
BL Lacs
E lt 3 GeV b 20?
22
Luminosity vs Redshift
23
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

L?1.5
L?0.5
L?1.1
(contact M. Ajello)
24
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.

25
Backup slides
26
Measuring the EBL with Fermi Blazars
  • The effects of EBL absorption will occur at lower
    energies for higher redshift sources
  • Blazars with z gt 1 will begin to show these
    effects in the LAT band

Credit L. Reyes
27
Outline
  • Blazar Properties and Fundamental Questions
  • Fermi LAT Capabilities
  • Multiwavelength Campaigns
  • Results on Individual Sources
  • Population Studies and Extragalactic Diffuse
    Emission
  • Summary

28
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 gt300 GeV, ?E/E ? 1015

29
Publicly Monitored Source List
TeV source
? Awaiting definitive detection by LAT
google LAT_Monitored_Sources
30
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 ? 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

31
  • Announcements of flaring sources ?
    multiwavelength follow-up
  • 25 blazar-related LAT ATELs have been issued on
    22 different sources

32
Multiwavelength Campaigns
  • 3C 454.3 JulOct radio, opt, UV, Swift
  • BL Lac 15 Aug5 Sep opt, UV, X-ray
  • PKS 2155-304 25 Aug6 Sep radio, opt, UV,
    X-ray, TeV (HESS)
  • 1ES 1959650 SepNov
  • PKS 0528134 27 SepOct radio, IR, opt, UV,
    X-ray
  • 3C 273 31 Oct7 Feb radio, opt, X-ray
  • 3C 279 AugMar radio, opt, X-ray, TeV
  • Mrk 421 JanMay radio, opt, X-ray, TeV
    (VERITAS, MAGIC)

33
Flaring Blazars
  • PKS 1454?354 factor ?5 increase of gt100 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 1502106 z1.84, factor 3 increase in lt12
    hrs, highest ?L/?t in GeV band

Preliminary
(contact author S. Ciprini)
34
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
Abdo et al.2009 ApJ Contact Author J.Kataoka
35
NGC1275 Long Term g-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

36
Spectral Energy Distribution
  • LAT spectrum0)-G
  • 2.17 0.05
  • (1) one-zone SSC
  • B 0.05 G
  • R 0.7 pc
  • 2.3, G 1.8
  • Ljet 2.3e45 erg/s
  • (2) Decelerating flow
  • B 0.2 G
  • D 0.2 pc
  • R 0.01 pc
  • G 10 -gt 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

37
LAT Detection of a Narrow Line Seyfert 1
  • Seyfert galaxies are not normally associated with
    blazar emission
  • PMN J09480022 SED is similar to an FSRQs, 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

(contact author L. Foschini)
38
Gamma-ray vs Radio Properties
?-ray photon index vs radio luminosity
Peak ?-ray flux vs 8.4 GHz flux density
39
Astronomers Telegrams
  • 1628, 24 Jul 2008, 3C 454.3, z0.859, FSRQ
  • 1650, 8 Aug 2008, PKS 1502106, z1.84, FSRQ
  • 1701, 5 Sep 2008, PKS 1454-354, z1.42, FSRQ
  • 1707, 8 Sep 2008, 3C 273, z0.158, FSRQ
  • 1743, 26 Sep 2008, PKS 1510-089, z0.360, FSRQ
  • 1744, 26 Sep 2008, AO0235164, z0.940, BL Lac
  • 1759, 3 Oct 2008, 3C 66A, z0.44?, IBL (VERITAS
    Atel 1753)
  • 1759, 3 Oct 2008, PKS 0208-512, z0.999
  • 1759, 3 Oct 2008, PKS 0537-441, z0.894, BL Lac
  • 1784, 15 Oct 2008, AO0235164, z0.940, BL Lac
  • 1864, 6 Dec 2008, 3C 279, z0.536, FSRQ
  • 1877, 16 Dec 2008, QSO B013347, z0.859
  • 1888, 4 Jan 2009, CRATES J12390443
    (3EGJ12360457), z1.76?
  • 1894, 8 Jan 2009, PKS 1244-255, z0.64, FSRQ
  • 1897, 9 Jan 2009, PKS 1510-089, z0.360, FSRQ
  • blazar-only

40
Blazar Population Properties
41
Blazar Population Properties
  • 34 BL Lac fraction (vs 19 for EGRET)

42
Blazar Population Properties
b 20?, 80?
E lt 3 GeV b 20?
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