Fermi-LAT Observations of Blazars

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


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


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


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


J. Chiang 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 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 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!


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


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3 Month Counts Map


J. Chiang 9

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)


J. Chiang 10

Variable sources in the LAT Bright Source List

• Based on 1 week time scales

• 68/205 show variability with probability > 99%

• Isotropic distribution blazars


J. Chiang 11

Fermi Results for Individual AGNs

3C 454.3

PKS 1502+106

PKS 2155304

NGC 1275

PKS 1454354

PMN J0948+002


J. Chiang 12

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)


J. Chiang 13

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


J. Chiang 14

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)


J. Chiang 15

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


J. Chiang 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

LAT counts map, > 200MeV, 4 Aug - 5 Dec100 arcsec across

(contact author: J. Kataoka)


J. Chiang 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, 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


J. Chiang 18

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


J. Chiang 19

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


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



J. Chiang 21


b = 20, 80

E < 3 GeVb = 20

BL Lacs

FSRQs


J. Chiang 22

Luminosity vs Redshift

F>100MeV = 4108 ph cm2 s1


J. Chiang 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

(contact: M. Ajello)

L0.5

L1.5

L1.1


J. Chiang 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.


J. Chiang 25

Backup slides


J. Chiang 26

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


J. Chiang 27

Outline

• Blazar Properties and Fundamental Questions• Fermi LAT Capabilities• Multiwavelength Campaigns• Results on Individual Sources• Population Studies and Extragalactic Diffuse Emission• Summary


J. Chiang 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 >300 GeV, E/E 10–15 %


J. Chiang 29

Publicly Monitored Source List

? Awaiting definitive detection by LAT

†TeV source

?

?

?

†

google: LAT_Monitored_Sources


J. Chiang 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– 2 106 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


J. Chiang 31

• Announcements of flaring sources multiwavelength follow-up

• 25 blazar-related LAT ATELs have been issued on 22 different sources


J. Chiang 32

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)


J. Chiang 33

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)


J. Chiang 34

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


J. Chiang 35

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


J. Chiang 36

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


J. Chiang 37

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)


J. Chiang 38

Gamma-ray vs Radio Properties

Peak -ray flux vs 8.4 GHz flux density -ray photon index vs radio luminosity


J. Chiang 39

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 40


FRSQs BL Lacs


J. Chiang 41


• 34% BL Lac fraction (vs 19% for EGRET)


J. Chiang 42


b = 20, 80

E < 3 GeVb = 20

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Fermi-LAT Observations of Blazars