GeV emitting zone in fast bright blazars Amanda Dotson UMBC Markos Georganopoulos advisor UMBCGSFC Eileen Meyer STScI Kevin McCann UMBC AAS Meeting Washington DC January 2014 ID: 614565
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Slide1
Determining the location of the GeV emitting zone in fast, bright blazars
Amanda Dotson, UMBCMarkos Georganopoulos (advisor), UMBC/GSFCEileen Meyer, STScI Kevin McCann, UMBC
AAS Meeting, Washington DC
January 2014Slide2
Where is the gamma-ray emission zone (GEZ) in blazars?
?
?
The Issue At Hand
Molecular Torus (pc scale)
Jet
Broad Line Region (sub-pc scale)
Not to scale!Slide3
Locating the GEZ with Flare Decay TimesUnknown:GEZ Location
Observable: Fast gamma ray flares
???Slide4
Locating the GEZ with Flare Decay TimesThomson Regime(γε0
≤1)Klein-Nishina Regime(γε0≥1)
ε
0
,MT
= 10
-7
(~.1
eV
) ε
0,BLR
= 10
-5
(~10 eV)
Critical difference between
GEZ in BLR vs MT
energy of the seed photons.
Seed photon energy
GEZ Location
Electron cooling time energy dependence
Observable:
Flare decay time energy dependence
Published in
ApJL
Dotson, et al. 2012Slide5
Cooling time nearly flat (energy independent)Cooling time energy dependent
MT
BLR
Locating the GEZ with Flare Decay Times
Falling time
Electron
cooling
Seed Photons
Photon origin
Dotson, et al. 2012Slide6
Split data into high energy (HE) and low energy (LE) bands of ≈TS
Application to Fermi Data
Fit exponential rise/decay to each peak:
PKS 1510 Unused Flare
PKS 1510
“Good”
FlareSlide7
Application to
Fermi Data
Fit multiple models
Choose best fit using Bayesian information criterion (
BIC
L: Likelihood
k
: # model parameters
n: # data points
1 peak model
B
IC
= 0.863
B
IC
= 0.545
2 peak model
BIC = 5.91
BIC = 5.61
PKS 1510-089Slide8
An Interesting Flaring State of PKS 1510-089
Plots from Marscher 2010
Optical EVPA rotated by ~720° over the course of 5-day flaring period (6 flares total)
% Optical polarization and R-band spike during
γ
-ray flaring period
Later detection of new superluminal knot ejected from radio core
Interpretation (from
Marscher
2010): flaring state caused by knot travelling down spiral magnetic field and passing through a shock at pc-scaleSlide9
An Interesting Flaring State of PKS 1510-089
Plots from Marscher 2010
Optical EVPA rotated by ~720° over the course of 5-day flaring period (6 flares total)
% Optical polarization and R-band spike during
γ
-ray flaring period
Later detection of new superluminal knot ejected from radio core
Interpretation (from
Marscher
2010): flaring state caused by knot travelling down spiral magnetic field and passing through a shock at pc scale
Image from
Marscher
2010Slide10
Application to PKS 1510 Interesting Flares: Flare 5
Flux (ph s-1 cm-2)
LE (E<
500
MeV
)
HE (E
>500
MeV
)Slide11
Application to PKS 1510 Interesting Flares:
Flare 7Flux (ph s-1 cm-2)
LE (E<
500
MeV
)
HE (E
>500
MeV
)Slide12
Application to PKS 1510 Interesting Flares: Flare
7Flux (ph s-1 cm-2)
LE (E<
500
MeV
)
HE (E
>500
MeV
)Slide13
An unusual case: Flare 8Flux (ph s
-1 cm-2)Very fast falling times (<3h)Fit unsuccessful
LE flare seems to fall faster than HE flare
LE (E<
500
MeV
)
HE (E
>500
MeV
)Slide14
Summary & ConclusionsSummaryTheory predicts flare decay time energy dependence GeV
photon origin (Dotson et al. 2012)Distinct falling times of flares 5, 7 (and 8?) indicate MT location of GeV emission zoneIn agreement withConclusionsThis method has been successful in locating the GeV photon origin in 5 of the brightest flares of
Fermi blazars
within a few pc of the central black hole.Slide15
Back-up SlidesSlide16
Inside BLROutside BLRAccretion Disk Photons
U’AD ~ 10-3 ergs cm-3U’AD~10-3
ergs cm-3
BLR Photons
U’
BLR
~ 1.0 ergs cm
-3
U’
BLR
~ 10
-6
ergs cm
-3
MT Photons
U’MT
~ 10-2 ergs cm-3
U’MT~10
-2 ergs cm-3
Dominant Source of Seed Photons
Assumptions:
Ldisk = 1045 ergs s
-1 , Lext=0.1L
disk,Lsynch=1046
ergs s-1
RBLR = 1017 cm, R
MT = 1018 cm, R
blob=1016 cm Γ
bulk=10Slide17
BLRU’=2.6 ergs cm-3
Dominated by emission lines ε0 = 10-5 (~10 eV)R = 1017 cm
Cooling Differences
MT
U’=2.6 ×10
-2
ergs cm
-3
BB emission, peaking at T~1000 K
ε
0
= 10
-7
(~.1
eV
)R = 1018-19 cm
The critical
difference between the BLR and the MT is the energy of the seed photons.Slide18
What values of U and
Γ are allowed?Slide19
Thomson vs KN RegimeThomson cross section (purely classical):
γε0 ≤1Klein-Nishina
cross section (derived through QED):
γε
0
≥1
Scattering in the KN regime is much less efficient than scattering in the Thomson regimeSlide20
Will light-travel effects erase cooling differences?
Short answer: No.Slide21
Application to
Fermi
Data
Upper limit on region of photon emission (
R
GeV
)Slide22
FittingEach component fit with exponential rise and decay:
Fit different models (change # peaks, flat/sloped background,etc)Choose best fit model using BIC and AIC
L: Likelihood
k
: # model parameters
n: # data pointsSlide23
Future WorkHow does SSC model compare with these results?What is the energy dependence of T
f in the case of SSC?Is there a similar way of constraining RGeV for SSC seed photons?