Title: Fermi-LAT Observations
1 Fermi-LAT Observations of Blazars
Jim Chiang SLAC/KIPAC
on behalf of the Fermi-LAT collaboration
2Related 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
3Unified 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
4Blazar 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
5Key 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
6What 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.
7Fermi 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
83 Month Counts Map
93 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)
10Variable sources in the LAT Bright Source List
- Based on 1 week time scales
- 68/205 show variability with probability gt 99
- Isotropic distribution ? blazars
11Fermi Results for Individual AGNs
PKS 1502106
PMN J0948002
PKS 1454?354
NGC 1275
3C 454.3
PKS 2155?304
123C 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)
13PKS 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
14PKS 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)
15PKS 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
16NGC 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)
17Fermi-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
18Narrow-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)
19Blazar 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
20Blazar 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
21Blazar Population Properties
b 20?, 80?
FSRQs
BL Lacs
E lt 3 GeV b 20?
22Luminosity vs Redshift
23Luminosity 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)
24Conclusions
- 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.
25Backup slides
26Measuring 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
27Outline
- Blazar Properties and Fundamental Questions
- Fermi LAT Capabilities
- Multiwavelength Campaigns
- Results on Individual Sources
- Population Studies and Extragalactic Diffuse
Emission - Summary
28The 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
29Publicly Monitored Source List
TeV source
? Awaiting definitive detection by LAT
google LAT_Monitored_Sources
30Source 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
32Multiwavelength 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)
33Flaring 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)
34Fermi 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
35NGC1275 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
36Spectral 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
37LAT 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)
38Gamma-ray vs Radio Properties
?-ray photon index vs radio luminosity
Peak ?-ray flux vs 8.4 GHz flux density
39Astronomers 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
40Blazar Population Properties
41Blazar Population Properties
- 34 BL Lac fraction (vs 19 for EGRET)
42Blazar Population Properties
b 20?, 80?
E lt 3 GeV b 20?