Gamma-Rays from Radio Galaxies: Fermi-LAT PAOLA GRANDI INAF/IASF - - PowerPoint PPT Presentation

Gamma-Rays from Radio Galaxies: Fermi-LAT

PAOLA GRANDI

INAF/IASF BOLOGNA, ITALY

• n 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 Monday, July 11, 2011

Fermi consists of two instruments: the Large Area Telescope : LAT (20 Mev -300 GeV) the Gamma-ray Burst Monitor : GBM (8 keV -40 MeV).

Fermi (GLAST) Gamma-ray Space Telescope Launched on 11 June 2008

Monday, July 11, 2011

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 cm2

100 MeV to 8000 cm2 at E1 GeV

• Energy resolution better than 10% between 50 MeV and 50 GeV.
• Spatial resolution depends on the photon energy

R68 0.6 at E 1 GeV

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BL LACs FSRQs Other Extragalactic Sources

Abdo, A. A., et al. 2010a, ApJ, 715, 429 (1LAC); Abdo, A. A., et al. 2010b, ApJS, 188, 405 (1FGL)

In the Second Catalog of AGN (2LAC, in preparation) , the number of detected AGNs is increased by more than 40% (877 sources). The clean sample of the First Catalog

• f AGN (1LAC) contains 599 sources

The Fermi sky

1 year 2 years

preliminary

Monday, July 11, 2011

A small angle of view implies a strong amplification of the jet emission. δ =1/Γ(1-β cosθ) Γ

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 F()= p F’’ () p=f()

Blazar

Monday, July 11, 2011

1.
SNR as particle accelerator -- SNR expanding shocks -> CR acceleration -> -rays

Narrow Line Seyfert 1 Sources (Foschini’s Talk) Misaligned AGNs




























































 2.
AGN
as
par0cle
accelerator

‐>
Jets

Starburst Galaxies The “other” Extragalactic Sources belongs to two broad classes of

• bjects reflecting two different particles acceleration processes:

h9p://wwwmagic.mppmu.mpg.de/magic/index.html

The majority of Extragalactic Sources are BL LAC and FSRQs However ~3% of the -sources are not Blazars

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After 24 months of sky survey preliminary

BLAZARs Non-Blazars

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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.

Blazars MAGNs NLRG BLRG


 SSRQs

BL
LACs FSRQS

MAGNs

Γ

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Steep
radio
spectra
 r >0.5 Resolved
and
possibly
symmetrical
 structure
in
radio
map
 and/or MAGNs show:

FRI are considered the PARENT POPULATION of BL LACs FRII are considered the PARENT POPULATION of FSRQs (SSRQs are in between)

Monday, July 11, 2011

FIRST SAMPLE of MAGNS (15 MONTH-DATA)

Abdo, A. A., et al. 2010, ApJ, 720, 912 (MAGN)

FR I Radio Galaxy FRII SSRQ MAGNs are generally faint and soft sources F(>0.1 GeV)~10-8 Phot cm-1 s-2   2.4

Monday, July 11, 2011

LAT COUNTER-PARTS OF 4 COMPLETE RADIO SAMPLES

3CRR sample  =178 MHz F> 10.9 Jy 173 sources 2Jy sample declination+10° and redshift z<0.7.  =2.7 GHz F> 2 Jy 88 sources Molonglo Southern 4Jy sample MS4  =408 MHz F> 4 Jy 228 sources 3CR sample  =178 MHz F> 9 Jy 113 sources

0<z<2.5 29<Log (L178 MHz)<37 erg s-1 3CR+3CRR+MS4+2JY= North-south-RADIO SAMPLE

Monday, July 11, 2011

Rate of Detections (%) Source with TS >25

15 and 24 months of sky survey

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)

preliminary

32 Sources with TS>25 (TS)1/2~

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 FRI FRII FSRQ BL LAC SB AGU

Monday, July 11, 2011

Are FRIIs elusive GeV sources because too far? Maybe not!

a b r P_r

TOT TS>25 MAGN TS>25 6.2 (1.6) 0.6 (0.2) 0.65 99.9% 7.9 (1.2) 0.4 (0.1) 0.66 97.4%

The Radio ray fluxes are correlated

see also, Ackermann et al. 2011 ApJ in press CA: Giroletti et al.

Log (f )1GeV = a + b x Log(f )5GHz

Ghirlanda et al. 2011

preliminary

Monday, July 11, 2011

Predicted fluxes @ 1 GeV of the 3CR+3CRR+MS4+2Jy sources: a first “qualitative” approach

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

Log (f )1GeV = a + b x Log(f )5GHz

Predicted Observed

correlation based on the total sample correlation based only on FRI+FRII objects Monday, July 11, 2011

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

Monday, July 11, 2011

M87

Abdo et al. 2009, ApJ , 699, 31

(CA:Kataoka)

Abdo et al. 2009, ApJ ,707, 55 CA:Chung & McConville

FRI jets are complex strucures: a single SSC zone model does not work

One simple zone SSC model = 1.8 = 2.3 = 25° B=0.05 G R=2x1018 cm n=-p p=2.1 800 960 p=3.1 960< 4x105 Pjet ~ 1044 erg sec-1

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, 4x103] p=3.6 [4x103, 107] R=1.4x1016 cm B=55mG

 

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Model Parameters: =25o = 2.4

R~1017 cm B~0.04 G 
N=K-p p1=2.76 p2=4.04 
K~2×106 cm-3 break=2×104 







min=250 max=2×105

Nuclear SED Modeling NGC6251

The SSC jet is slow compared to typical BL Lac jets (as for other FRIs in LAT MAGN sample)

Fermi- LAT Egret

see talk of Giulia Migliori

Monday, July 11, 2011

The jet is structured The jet is decelerated

Γ2

Γ1

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

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

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The case of 3C120: radio classified as FRI but hosting a very efficient accretion flow

3C120

βa =

βsinθ 1−βcosθ

βa =

βsinθ 1−βcosθ

βa =

βsinθ 1−βcosθ

Monday, July 11, 2011

• 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 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?).

Monday, July 11, 2011

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

• bserved 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?

Conclusions

Monday, July 11, 2011