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Fermi-LAT Observations of Blazars

Fermi-LAT Observations of Blazars. Jim Chiang SLAC/KIPAC. on behalf of the Fermi-LAT collaboration. Related Talks on Fermi-LAT Results. Markus Ackermann – Observation of the extragalactic diffuse continuum gamma-ray emission with Fermi LAT

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Fermi-LAT Observations of Blazars

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  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. 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 Unified Picture of AGNs Image Credit: C.M.Urry & P. Padovani

  4. 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 Blazar Spectral Energy Distributions 3C 279 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 disk—black hole—jet 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 - >300 GeV (including unexplored region 10-100 GeV) • 2.4 sr FoV (scans entire sky every ~3hrs) • Large leap in all key capabilities, transforming our knowledge of the gamma-ray universe. Great discovery potential. • Gamma-ray Burst Monitor (GBM) • 8 keV - 40 MeV • views entire unocculted sky Launch 11 June 2008!

  7. e– e+ 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 – >300 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 => 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 • 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 > 10 (EGRET found fewer than 30) • Typical 95% CL error radius is <10 arcmin (Abdo et al. 2009 ApJS, 183, 46)

  10. Based on 1 week time scales 68/205 show variability with probability > 99% Isotropic distribution  blazars Variable sources in the LAT Bright Source List

  11. Fermi Results for Individual AGNs PKS 1502+106 PMN J0948+002 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 < 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)

  13. Aharonian et al. 2007 PKS 2155304: 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

  14. e+e distribution p2=4.3 p1=3.2 p0=1.3 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 (e>2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< 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, > 200MeV, 4 Aug - 5 Dec (contact author: J. Kataoka)

  17. 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) Fermi-LAT detection of NGC 1275 COS-B Fermi EGRET

  18. 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)

  19. FSRQ BL Lac Radio Galaxy Uncertain 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) arXiv:0902.1559 Abdo et al, ApJ in press

  20. All FSRQs =2.40.2 FRSQs BL Lacs =2.00.2 BLLacs 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 < 3 GeV b = 20

  22. F>100MeV = 4108 ph cm2 s1 Luminosity vs Redshift

  23. 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 Luminosity Functions 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 > 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 >300 GeV, E/E  10–15 %

  29. ? ? † ? Publicly Monitored Source List †TeV source ?Awaiting definitive detection by LAT google: LAT_Monitored_Sources

  30. 3C 454.3 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: 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)

  33. 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) • PKS 1502+106: z=1.84, factor 3 increase in <12 hrs, highest L/t in GeV band (contact author: L. Foschini) 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 Cen A 3 month all-sky map NGC1275 (Perseus A) 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 risingduring the Fermi observations with pc-scale outburst seen in MOJAVE maps

  36. Spectral Energy Distribution • LAT spectrum:0)-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 -> 2 • Ljet = 6.0e43 erg/s • SED LBL-like: possible unification of BL Lacand 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. Peak -ray flux vs 8.4 GHz flux 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 (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. #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 Astronomer’s Telegrams*

  40. BL Lacs FRSQs Blazar Population Properties

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

  42. Blazar Population Properties b = 20, 80 E < 3 GeV b = 20

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