Gamma-Rays from Radio Galaxies: Fermi-LAT

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1 Gamma-Rays from Radio Galaxies: Fermi-LAT PAOLA GRANDI INAF/IASF BOLOGNA, ITALY on behalf of the FERMI LAT Collaboration Many thanks to : C. Dermer. G. Ghisellini, L. Maraschi, G. Migliori, E. Torresi, R. Aversa, V. Bianchin HEPRO III High Energy Phenomena in Relativistic Outflows III Barcelona, June 27 - July 1, 2011

2 Fermi (GLAST) Gamma-ray Space Telescope Launched on 11 June 2008 Fermi consists of two instruments: the Large Area Telescope : LAT (20 Mev -300 GeV) the Gamma-ray Burst Monitor : GBM (8 kev -40 MeV).

3 The LAT is an imaging high-energy gamma-ray telescope!! "#$! %&"! '(! )! *)'+,-./0$+('./! 1$2$(-.*$! 3'1#! )! *+$-'('./!1+)-4$+!)/5!-)2.+'6$1$+! FOV =2.3 sr ~ 1/5 of the full sky It scans the entire sky in about 3 hr On-axis effective area! 1500 cm MeV to! 8000 cm 2 at E"1 GeV Energy resolution better than 10% between! 50 MeV and! 50 GeV. Spatial resolution depends on the photon energy R 68! 0.6 # at E! 1 GeV

4 The Fermi sky 1 year 90 BL LACs FSRQs Other Extragalactic Sources 60 The clean sample of the First Catalog of AGN (1LAC) contains 599 sources Abdo, A. A., et al. 2010a, ApJ, 715, 429 (1LAC); Abdo, A. A., et al. 2010b, ApJS, 188, 405 (1FGL) years -90 In the Second Catalog of AGN (2LAC, in preparation), the number of detected AGNs is increased by more than 40% (877 sources). preliminary

5 A small angle of view implies a strong amplification of the jet emission. =1/ (1- cos ) The Doppler factor relates intrinsic and observed flux for a moving source at relativistic speed v= c. For an intrinsic power law spectrum: F ( ) = K (v ) -a the observed flux density is Blazar Γ F ( )= p F ( ) p=f( )

6 The majority of Extragalactic Sources are BL LAC and FSRQs However ~3% of the -sources are not Blazars The other Extragalactic Sources belongs to two broad classes of objects reflecting two different particles acceleration processes: 1. SNR as particle accelerator -- SNR expanding shocks -> CR acceleration -> -rays Starburst Galaxies 2. AGN as par0cle accelerator > Jets Narrow Line Seyfert 1 Sources (Foschini s Talk) Misaligned AGNs h9p://wwwmagic.mppmu.mpg.de/magic/index.html

7 After 24 months of sky survey Non-Blazars BLAZARs preliminary

8 2. AGN as par0cle accelerator: Misaligned AGN (MAGN) With MAGNs we intend Radio Sources (Radio Galaxies and SSRQs) with the jet not directly pointed towards the observer. NLRG MAGNs Γ MAGNs BLRG SSRQs Blazars BL LACs FSRQS 8

9 MAGNs show: Steep radio spectra r >0.5 and/or Resolved and possibly symmetrical structure in radio map FRI are considered the PARENT POPULATION of BL LACs FRII are considered the PARENT POPULATION of FSRQs (SSRQs are in between)

10 FIRST SAMPLE of MAGNS (15 MONTH-DATA) Abdo, A. A., et al. 2010, ApJ, 720, 912 (MAGN) MAGNs are generally faint and soft sources F(>0.1 GeV)~10-8 Phot cm -1 s FR I Radio Galaxy FRII SSRQ

11 LAT COUNTER-PARTS OF 4 COMPLETE RADIO SAMPLES 3CRR sample =178 MHz F> 10.9 Jy 173 sources Molonglo Southern 4Jy sample MS4 =408 MHz F> 4 Jy 228 sources 3CR sample =178 MHz F> 9 Jy 113 sources 2Jy sample declination+10 and redshift z<0.7. =2.7 GHz F> 2 Jy 88 sources 3CR+3CRR+MS4+2JY= North-south-RADIO SAMPLE 0<z<2.5 29<Log (L178 MHz)<37 erg s -1

12 Rate of Detections (%) Source with TS >25 15 and 24 months of sky survey preliminary 1! 0.9! 32 Sources with TS>25 (TS)1/2~ 0.8! 0.7! 0.6! 0.5! 0.4! 0.3! 0.2! 0.1! 0! FRI! FRII! FSRQ! BL LAC! SB! AGU! FRII are the less detected objects The -ray elusiveness of FRIIs has been also confirmed by a dedicated study of Broad Line Radio Galaxies (Kataoka et al. 2011, ApJ submitted)

13 Are FRIIs elusive GeV sources because too far? Maybe not! preliminary Log (f ) 1GeV = a + b x Log(f ) 5GHz a b r P_r TOT TS> (1.6) 0.6 (0.2) % MAGN TS> (1.2) 0.4 (0.1) % Ghirlanda et al The Radio ray fluxes are correlated see also, Ackermann et al ApJ in press CA: Giroletti et al.

14 Predicted 1 GeV of the 3CR+3CRR+MS4+2Jy sources: a first qualitative approach Predicted Observed Log (f ) 1GeV = a + b x Log(f ) 5GHz correlation based on the total sample correlation based only on FRI+FRII objects A large number of FRIIs should cross over the LAT sensitivity threshold. In spite of this, only an handful of FRIIs is seen at GeV energies

15 Radio Flux indicates that the core of FRIIs is bright enough to be visible at very high energies Why does Fermi-LAT preferentially catch FRIs and lose FRIIs? We do not have a firm answer to that. We are trying to understand looking at the SED of single Radio Galaxies

16 FRI jets are complex strucures: a single SSC zone model does not work M87 SSC one zone model Emission from sub-parsec scale jet (core) as suggested by 2008 VHE Chandra VLBA monitoring! =10,! =2.3, " =3.9 n = k # -p p=1.6 [1, 4x10 3 ] p=3.6 [4x10 3, 10 7 ] R=1.4x10 16 cm B=55mG Abdo et al. 2009, ApJ, 699, 31 (CA:Kataoka) One simple zone SSC model! = 1.8 " = 2.3 # = 25 B=0.05 G R=2x10 18 cm n=$ -p p= % $ %960 p= < $ %4x10 5 P jet ~ erg sec -1 Abdo et al. 2009, ApJ,707, 55 CA:Chung & McConville

17 Nuclear SED Modeling NGC6251 Egret Fermi- LAT Model Parameters: =25 o = 2.4 R~10 17 cm B~0.04 G N=K -p p 1 =2.76 p 2 =4.04 K~ cm -3 break =2 104 min =250 max =2 105 see talk of Giulia Migliori The SSC jet is slow compared to typical BL Lac jets (as for other FRIs in LAT MAGN sample)

18 Possible solutions to the problems (not the only ones) Decelerating jet (Georganopoulos & Kazanas 2003) Structured (spine +slower layers) jet (Ghisellini, Tavecchio & Chiaberge 2005) The jet is structured Γ 1 Γ 2 The jet is decelerated In these models, there is an efficient (radiative) feedback between different regions in the jet that increases the IC emission

19 In these models, there is an efficient (radiative) feedback between different regions in the jet that increases the IC emission 19

20 The case of 3C120: radio classified as FRI but hosting a very efficient accretion flow β a = βsinθ 1 βcosθ 3C120 β a = βsinθ 1 βcosθ

21 The inner spine could be the dominant source of -ray photons (3C120 could be an example of Radio Galaxy with an efficient accretion disk: FRII type?). Stratified/decelerating jet not required v =10-15 and =7 can fit the data, the jet is not too slow Grandi, Ghisellini, Maraschi et al. in prep 15month-LAT data

22 Conclusions Gamma-rays in extragalactic sources are signatures of two different engines responsible of particle accelerations: SNR -> CR + dust +field of radiation working in Starburst galaxies Black Hole -> jet + external photons working in AGNs 97% of the Fermi sources are BL LACs and FSRQs. 3% are other kind of objects: NLSy1, SB and MAGNs. The MAGN class is mainly populated by FRI radio galaxies. The presence of a stratified jet in these sources seems to favor their detection. On the contrary, FRIIs are difficult to detect in gamma. The study of all the gamma-counterparts of 4 complete radio catalogs indicates a correlation between the radio core (5 GHz) and gamma (1 GeV) fluxes (essentially driven by Blazars and FRIs). On the basis of this correlation a quite large amount of FRIIs is expected to be observed at GeV energies, BUT only 3-4 FRIIs ARE actually observed above 100 MeV. The radio-gamma flux correlation weakens the hypothesis that the FRIIs are missed because too far (and thus too weak). Are FRII jets spine dominated?