Active Galactic Nuclei observed by Fermi-LAT"The extreme Universe viewed in very-high-energy gamma-rays 2015”
2016.1.13-14

Shinya Saito (Rikkyo Univ.)Fermi-LAT updates in 2015•

Pass8: Major update on instrument response function.
Effective area and PSF has been significantly improved.

•All the 7.5-year data has been reprocessed with Pass8 andavailable now.

MOTIVATION:PASS
MOTIVATION:
PASS
8 8Figure 3.1: Schematic view of the Large Area Telescope onboar

put below Silicon-strip layers and the overall detector system>30% increasescintillators to reject particles. The telescope’s dimensions aThe power required and the mass are 650 W and 2789 kg, res<0.1deg PSF(68%) above 50 GeVWood+15

E>50 GeV sky observed by Fermi-LAT
2FHL catalog (Ackermann+15) based on Pass8 reprocessed 80-month data.
61,000 photons in 50 GeV < E < 2 TeV
360 sources detected• 90% of the 2FHL sources (excluding un IDs) are extragalactic sources, and most ofthem are blazars or blazar candidates.
•50 GeV - 2 TeV

Ackermann+15
0.001

0.005

0.013

0.029

0.06

0.12

0.25

0.5

124

BlazarsBlazar : Radio galaxy with a relativistic jet direct toward the earth.
FSRQs … emission line of EW>5Å, mass accretion rate of >1% Eddington limit
BL Lacs … no emission line, low mass accretion rate

LAT range– 48 –

FSRQ

inverse Compton

Synchrotron

3.2

BL Lacs

gamma-ray
Photonspectral
spectral indexindex

•3

FSRQs
LSP-BLISP-BLHSP-BL

FSRQ

2.8
2.6

BL Lacs

2.4
2.2
2
1.8
1.6
1.4
1.2
12

Ackermann+15
131415log(ν Speak,rest [Hz])161718

Synchrotron peak frequency
Ghisellini+13

SFig. 10.— Photon index versus frequency of the synchrotron peak νpeak,rest. Red: FSR
LSP-BL Lacs, light blue: ISP-BL Lacs, dark blue: HSP-BL Lacs.

Source population
100 MeV - 300 GeV 3033 sources
Non-blazar AGNs
BL Lacs0%

Blazarcandidates

FSRQs

20%

3FGL catalog (Acero+15)

40%

Galactic sources
un IDs

60%

80%

100%

50 GeV - 2 TeV 360 sources
Non-blazar AGNs
FSRQs
Blazarcandidates

BL Lacs

0%

20%

40%

60%

2FHL catalog (Ackermann+15)

Galactic sources
un IDs80%

100%

Source population0%

Number of Sources

100 MeV - 300 GeV 50
3033sources
GeV- 2 TeV (360 sources)
3FGL catalog (Acero+15)100
Non-blazar AGNs
IACT detected
non-IACTdetected
BlazarGalacticsources
BL Lacs
FSRQs
80
un IDs, etc…
candidates

60 20%

40%60%

80%

100%

50 GeV - 2 TeV 360 sources

0%•4020

Non-blazar AGNs
FSRQs
BL Lacs−11.020%

Blazarcandidates−10.0 60% −9.5
−10.5
40%
log10 (F50/ ph cm−2 s−1)

2FHL catalog (Ackermann+15)

Galactic sources
un IDs, etc…

−9.0
80%

Fig. 15.— Photon flux distributions of the 2FHL population that has been detected already by IACTs(purple) and that has not yet been detected (green). The medians of the distributions are shown withvertical lines.

282 (78%) of 2FHL sources have not been detected yet with IACTs.
→ promising targets for CTA.

100%

What can we infer from gamma-ray observations of AGNs?
Recent works with Fermi-LAT

Physics of AGN jets
•Locating blazar zone and inferring underlying particle acceleration in relativistic
AGN jets.
— Simultaneous broadband observations (e.g. 3C279; Hayahida+15)— Time-dependent modelling of flares (Asano+15, Saito+15)— Gamma-ray / VLBA observation of a radio galaxy (3C120; Tanaka+15, Casadio+15)

Cosmological measurements•

Extragalactic gamma-ray background (EGB)— Resolving EGB into individual components (Ajello+15)— Constraints on cross section of dark matter annihilation (Ajello+15)— Constraints on TeV gamma-ray background (Inoue+15)•EBL / intergalactic conditions— Testing EBL models (Atwood+13, Ackermann+15)— Constraints on inter galactic magnetic field (IGMF) (Finke+15)

Constraining emission zonein AGN jets

Location of Emission Zone in Blazars• Kinetic luminosity of FSRQs is comparable to accretion power during flares.
• The site and structure of the emission region is controversial. – 12 –• Variability of a few hours is observed with Fermi-LAT. (Foschini+11, Saito+13, Brown +13, Rani+13, Hayashida+15)
et al.:→PKSLocation
1510-089 of emission site: R < cδΓΔt/(1+z) ≒ 1016 cm ~ 100 RG (Δt=2hours, Γ=10 )Fermi-LAT (MAGIC simultaneous)Fermi-LAT (Low state)

Aleksic+14: PKS1510-089

Fermi best fit model, extrapolated-910Fermi extrapolated+EBL attenuation
AGILE-GRID (Flare-II)
AGILE-GRID (Low intermediate)
MAGIC observed
MAGIC de-absorbed-10105992

nsepinedsoxiis
tly

riled
chily

10-11

10-12

Fermi
10-1

1MAGIC
10102

Energy [GeV]

Integral flux (>100 GeV) [cm-2 s-1]

E2dN/dE [erg cm-2 s-1]

Fermi-LAT (High state)-9×1010.9

Exponential fit (χ2=4.45/3)-3

slope: (1.30± 0.15)× 10 s-1

Aleksic+11: 4C 21.35

0.8
0.70.6

Linear fit (χ2=5.68/3)-13slope = (3.7± 0.8)×10 cm-2s-1 • s-1

Background - constant fit (χ2=2.34/4)

0.5
0.4

10 min

0.3
0.2

MAGIC

0.1
0

21:50:00

22:00:00

22:10:00

22:20:00
Time (UT)•Fig.
Smoothconnectionof GeVand TeV
spectra4. The γ-ray
SED constructedfrom AGILE,
Fermi-LATand during GeV flare.
17 cm,
MAGIC
data. The AGILE-GRID
data (greyfilled squares)
cor-Fig. 2.— PKS→Suggestingco-spatialityof GeV/TeVemission
zoneoutside>101222+21locating
light curve above
100 GeV, in 6BLR;
minutes bins(black filledcircles).
respond to the data of Flare-II (from MJD 55977.5 to 55991.5).
+ewas− .carried out on MJD 55364. The black solid line is a fit with an exTheobservation
sinceVHE
photonisabsorbed
inBLR
duetoγγ→eThe Fermi-LAT spectrum (black open circles) combines all

events of time intervals coincident with the MAGIC observa-ponential function and the black dotted line a fit with a linear function. The grey opention window (MJD 55976 to 55991 and from 56001 to 56020)squares denote the fluxes from the background events and the grey dashed line is a fit with
•withVariabilityof several minutes in TeV range
the blue lines showing the log parabola fit to the data anda constant function to these points.
its statistical uncertainty (the thinner lines). The fit and the errors

Time-dependent modeling of FSRQ flaresConstraining emission zone of FSRQs by modeling time evolution of SEDs duringflares and fitting the simulated GeV gamma-ray light curves to observed ones.
(Saito+15)

Flare1

Flare2
PKS1510­089(Fermi-LAT)• “Finer time resolution” is required to the data
since an apparently coherent flare would beresolved into superposition of sub-flares with
better resolution.

Saito+13

Constraints on the geometry of emission zone
• Time dependent single-zone model with given electron injection spectra.

8• Distance of gamma-ray emission zone from the SMBH:
0.7x1018 cm (0.2pc) ; Γθjet =1
4.5x1018 cm (1.5pc) ; Γθjet =0.1 (e.g. Jorstad+05, Clausen-Brown+13)

4

Saito et al.

6• Low magnetic luminosity is implied.

102-6-2 -1
Flux (>100MeV)[10phcm]18
the emission zone (1018s cm)

2Lacc ≒ 5x1045 erg/s

40
10.4

0.6

0.8

1Rstart [1018 cm]

1.2

1.6

Rs = 0.7x1018 cm

Rs = 0.1x1018 cm

1001.4

Rs = 1.5x1018 cm

30

20

0.2

02

1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4

Rstart [1018 cm]

15Le ≒ 1047 erg/s
Le/LB > 102105Saito+15000Saito+152

Rstart (10 cm)

204

best-fit location ofFlux (>100MeV) [10-6 ph cm-2 s-1]

PKS1510-089 γ-ray flare
50 (θobs=θjet = 2.6 )10046810 1214

Hours from MJD 55853.5

16PKS 1510-089(MJD55853 ﬂare)Le ≒ 1046 erg/s
25 Le/LB > 100

102181230 jet opening
102030 viewing
40 angle)
50 (deg)angle(=(deg)jet

Hours from MJD 55872

MWL observation of 3C279 huge flare
Prominent gamma-ray flare with Γ~1.7 and fine variability profile. (Hayashida+15)• One zone model could not explain X-ray spectrum.
• Low jet magnetisation; LB/Lj<10-4• Acceleration by turbulence with varying magnetic field could explain time evolution ofbroadband SED during the flare. (Asano+15)•

The Astrophysical Journal Letters, 808:L18 (5pp), 2015 July 20

he Astrophysical Journal, 807:79 (18pp), 2015 July 1

Hayashida et al.

Γ~1.7

Hayashida+15

Asano+15

Radio galaxies• ~15 radio galaxies has been detected by Fermi-LAT, which realize complementary studyof AGN jets. (e.g. propagation of radio knots, monitoring physical change in jet and disk)• Gamma-ray/radio observation of FR1 radio galaxy 3C120 (Tanaka+15, Casadio+15)• Radio knot emerged 60 days after the gamma-ray brightening. Based on the time lag,gamma-ray emission site is estimated around ~0.1-0.3 pc from the central BH.
The Astrophysical Journal Letters, 799:L18 (6pp), 2015 January 30

Tanaka et al.
The Astrophysical Journal Letters, 799:L18 (6pp), 2015 January 30

Fermi-LAT
0.5-100GeV

43GHz Core flux

Knot flux
43GHz
Knot position
Tanaka+15
Tanaka+15Figure 3. Sequence of 43 GHz VLBA images of 3C 120 at epochs MJDand radio phenomena.
VLBA core was estima
between the X-ray det al. 2009). The app
derived here and the t
the γ-ray and VLBA
position of the γ-ray emthese two phenomena a
projected distance of∼35 days, respectively,projected distance of
43 GHz VLBA core. Gaxis and our line of si
the γ-ray emission reg
the central BH. Hereconstant and if the acce
the BH and VLBA cor(2008), the distance fr
the order of sub-parsec
It is difﬁcult to prtimescale from the Feﬂux. But since thedominated by several
we assume here that thderived distance betwe
together with the assu
and previously measu
et al. 2005), allow us
radius of the em
R 1 cdtvar = 4.7 ´ 10ing a simple conical s
opening angle (q jet ) is
the distance from thBlazars as a probe forcosmological measurements

Extragalactic gamma-ray background
Blazars constitute ~50% of extragalactic gamma-ray background (EGB) above 100 MeV.
• TeV background was constrained by Fermi-LAT/ VHE data (Inoue+15, Inoue+12)• Dark matter annihilation cross section could be constrained within unresolved EGB andThe Astrophysical Journal Letters, 800:L27 (7pp), 2015 February 20
Ajello et al.
uncertainty of EGB estimation. (Ajello+15)•EBL attenuation of VHE photons from BL Lacs

Ajello+15

Figure 3. Top panel: integrated emission of blazars (with and without EBL

Figure 4. Upper limits on the self-annihilation cross secti
and t +t - (bottom) channels as derived in this work (see Sto the conservative and sensitivity-reach limits reported i(2014b). The blue band reﬂects the range of the theore
signal intensities due to the uncertainties inAjello+15
the description

– Sources become softer at higher energies– Sources becomes softer at high redshift

Testing EBL models through high-z blazars
Photon index distribution vs redshift• VHE photons interact with EBL photons through pairproduction.
→Softer VHE spectral index at higher redshifts.

photon index(E>50 GeV )γTeV + γeV → e+ + e-Ackermann+15•

Detection of VHE photons from high redshift objects
gives a test for current EBL models.

14Domı́nguez+ 11Finke+ 10 Model C
Gilmore+ 12 Fiducial

E>100GeV photons from high-z blazarse.g.)
PKS0426+380(z=1.1) Tanaka+13
PKS1441+25 (z=0.94) Ahnen+15(MAGIC)

Energy [TeV]

10.5

1.0 1.5
τ,

2.0

2.5

Domı́nguez+ 11

Ackermann+15

0.1

CTA will provide a more extensive test of EBL models.
0.0

0.5

1.0Redshift

1.5

2.0

Constraints on intergalactic magnetic field•Cascade emission

γTeV + γEBL → e+ + ee+/- + γCMB → γGeV•Intergalactic magnetic field (IGMF) deflects e+/e- pairs and suppress the cascade emission
component.

HE/VHE observations of BL Lacs at known redshifts constrain IGMF strength andConstraints from Gamma Ray Observations
13
coherenceIGMF
lengthsince the expected cascade should
be below the observed
flux.
IGMFGeV
Constraintsf• B <10-19 G is ruled out for various EBL models. (Finke+15)•-101010-2-1

Finke+15-17

B = 10 G-16
B = 10 G -15
B = 10 G

0.0

unabsorbed
log(B/Gauss)-11νFν [erg s cm ]significance for ruling out the parameter set (σ)

１ES 0229+200, z=0.139-1210cascade-1310-14102310241025102610ν [Hz]271028102910

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.00

24-6-8-10-12-14-16-18-20-10-8-6-4-2log(LB/Mpc)

Finke+15

Summary•Fermi-LAT detects 360 sources above 50 GeV, where ~80% of them has not been
detected yet by any IACTs. The number of the Fermi-LAT samples will gradually
increase as statistics increases. Catalogs like 2FHL will provide a promising target
list for future CTA observations.

•Emission zone in AGN jets has been a long lasting problem, while recent studies
with different approaches (e.g. time dependet modelling, MWL fitting) suggests
blazar zone be locating at sub-pc distance from the SMBH. Future MWL
observations including CTA with excellent photon statistics would remove
degeneracy of jet models.

•Extragalactic gamma-ray background from 0.1GeV to ~ 1TeV is mostly resolved
into blazars, radio galaxies, and star forming galaxies. Small room of unresolved
EGB and uncertainty of the EGB estimation gives a tight constraint for annihilation
cross section of the dark matter.

•CTA can test various EBL models through observations of high-z blazars.