Mutifrequency scalings
and lags in Blazar flares

Stefan J. Wagner
Landessternwarte
Heidelberg, Germany
Marcus Hauser, Bagmeet Behera: LSW Heidelberg, Germany
Omar Kurtanidze: Abastumani Observatory, Georgia

2009 Fermi Symposium

Washington DC: November 2-6, 2009

The relationship between opticaland GeV -ray variability in Blazars
Motivation: How are gamma-rays produced?
Hadronic models are no ruled out.
Can Compton models explain any relationship?
Leptonic (IC) models: Do we understandparticle acceleration (distribution function) and seed fields?
Within a given system repeated experiments with slightly different
initial conditions (different flares) – probed in the synchrotron domainshould produce predictable outcome (gamma-ray emission).
Optical is always in the synchrotron domain and never optically thick.
S. Wagner: Multifrequency Scalings and Lags in Blazar Flares2009 Fermi Symposium

The EGRET legacy
Variability in the GeV band:
1st light (3C279 brighter than in COS-B)
GeV - variability on time-scales of days (3C279)
Variability of synchrotron emission:
Collectively: GeV sources were id'd with BLO, OVV, and IDV-FSRQ
Correlations:
PKS 1406-076, PKS 0420-014, S5 0836+710, S5 0716+714,
S5 0954+658, 3C 279, PKS 0528+134, PKS 1622-297,
BL Lac, NRAO 190, Mrk 501, 3C273, ...
(varying degrees of significance and usefulness)

S. Wagner: Multifrequency Scalings and Lags in Blazar Flares2009 Fermi Symposium

Questions to be addressed
Do all flares have counterparts?
Can cross-identifications result by chance?
Is there a unique amplitude scaling within and among flares?
Are there any lags between different bands?
Does spectral evolution within the two bands reflect each other?
Is there any indication for variability in EIC photon fields?
Dependencies of all of the above on L, D, M, … ?
S. Wagner: Multifrequency Scalings and Lags in Blazar Flares2009 Fermi Symposium

Observations
GeV: FGST: Public data (subset for statistics)
eV: ATOM (Automatic Telescope for Optical Monitoring)
Robotic 0.8m telescope at HESS site (latitude -23), R(BVI) bands
All southern VHE, EGRET, 0FGL-Blazars with diff. duty cycles.
230 objects (1/d – 1/10d) + flare-triggers (flagged data)

Northern hemisphere complement: Abastumani Observatory
S. Wagner: Multifrequency Scalings and Lags in Blazar Flares2009 Fermi SymposiumData set, examples, binning
3C 454.3
EGRET-detected,
very prominent AGILE flares,
very active since Fermi launch.
Overall correlation very close.
High states match high states.
Difference in detail.
Daily data
Weekly data
Daily UL
Weekly UL
Binning(Same phase)

FGeV – FeV Relations
3C454.3 and PKS 2155-304
Only simultaneous data.
Correlation highly significant
Individual measurements
consistent with trend, but
statistically significant scatter
Different slopes,different average ratios,
but different types of Blazar

S. Wagner: Multifrequency Scalings and Lags in Blazar Flares2009 Fermi Symposium

FGeV – FeV Relations
3C454.3, PKS 0235+164
and PKS 2155-304.
Even for Blazars of similar
type, slopes and average
flux ratios are different.
With fixed observing band,slopes and ratios depend on
relative locations of bands
w.r.t. peaks within SED.

S. Wagner: Multifrequency Scalings and Lags in Blazar Flares2009 Fermi Symposium

FGeV – FeV Relations
PKS 1510-089 and
PKS 2155-304
Scatter of individual
points highly significant.
Slopes and average ratios
vary in single object
between different flares
Spectral lags widern scatter.
Different flares modify
location of peaks differently.
S. Wagner: Multifrequency Scalings and Lags in Blazar Flares2009 Fermi Symposium

FGeV – FeV Relations
PKS 1510-089 and
PKS 2155-304
Scatter of individual
points highly significant.
Slopes and average ratios
vary in single object
between different flares
Spectral lags widern scatter.
Different flares modify
location of peaks differently.
S. Wagner: Multifrequency Scalings and Lags in Blazar Flares2009 Fermi SymposiumOther examples:
PKS 0537-441:
high states in optical synchrotron
match bright states in gamma-rays
Scatter in flux scalings

PKS 2155-304:
General match but
differences in detail.
Lags or different flares?

.

No correlation in detail.
Lags or blends?
Chance?

.

Correlation on day-time scales(sometimes) stronger betweeneV and TeV (Fermi/HESS)PKS 1510-089
EGRET-detected PKS 1510-089 shows “overall” correlation(bright synchrotron state during bright gamma state and vv),
but displays differencesin detailed comparisonsthroughout full 1st year.
This involves lags,different amplitude scalings,
and changes of base level.
IIIIII

IVV

Changes in optical spectra,
optical colours, and
X-ray spectral slope

PKS 1510-089
EGRET-detected PKS 1510-089 shows “overall” correlation(bright synchrotron state during bright gamma state and vv),
but displays differencesin detailed comparisonsthroughout full 1st year.
This involves lags,different amplitude scalings,
and changes of base level.
IIIIIIIVV

Changes in optical spectra,
optical colours, andX-ray spectral slope

PKS 1510-089
EGRET-detected PKS 1510-089 shows “overall” correlation(bright synchrotron state during bright gamma state and vv),
but displays differencesin detailed comparisonsthroughout full 1st year.
This involves lags,different amplitude scalings,
and changes of base level.
IIIIIIIVV

Changes in optical spectra,
optical colours, andX-ray spectral slope

PKS 1510-089
EGRET-detected PKS 1510-089 shows “overall” correlation(bright synchrotron state during bright gamma state and vv),
but displays differencesin detailed comparisonsthroughout full 1st year.
This involves lags,different amplitude scalings,
and changes of base level.
IIIIIIIV

V

Changes in optical spectra,
optical colours, andX-ray spectral slope

PKS 1510-089
EGRET-detected PKS 1510-089 shows “overall” correlation(bright synchrotron state during bright gamma state and vv),
but displays differencesin detailed comparisonsthroughout full 1st year.
This involves lags,different amplitude scalings,
and changes of base level.
IIIIII

IVV

Changes in optical spectra,
optical colours, and
X-ray spectral slope

PKS 1510-089
EGRET-detected PKS 1510-089 shows “overall” correlation(bright synchrotron state during bright gamma state and vv),
but displays differencesin detailed comparisonsthroughout full 1st year.
This involves lags,different amplitude scalings,
and changes of base level.
IIIIIIIV

V

Changes in optical spectra,
optical colours, and
X-ray spectral slope

Statistical Analysis
Confine analysis to sources with published light curves (Fermi)
and unbiased optical subset (disregard TOO triggered ATOM data).
Statistics of duty cycles and correlations.
Confine to subset of homogeneously monitored sources (ATOM)With low duty cycles (F > [F] in < 20% of total time); [F] quiescence
Statistics of lags (peaks in DCCF)
Complete data (and subday time-scales)for detailed mapping of events.

S. Wagner: Multifrequency Scalings and Lags in Blazar Flares2009 Fermi SymposiumStatistical properties
FGST-data ATOM-data common
GeVeV
Variability (weekly)
Residual variations (daily)
Baseline (weekly)<Duty cycle><No of flares/12 months><chance coincidence><Amplitude>

1816861%
4.2

1918868%5.686%

21%

1816759%
4.2
93.6%

Lags: In all cases which have significant Fermi detections on
day-time scales for > 14 days, simultaneous optical data
indicate significant variability on sub-day time scales:
Lags of one-day binned data affected by phasing.
Lags from unbinned data affected by window function.
S. Wagner: Multifrequency Scalings and Lags in Blazar Flares2009 Fermi Symposium

Questions to be addressed(very) preliminary answers
Do all flares have counterparts?
Yes
Can cross-identifications result by chance?
NoIs there a unique amplitude scaling within and among flares?
NoAre there any lags between different bands?
Yes
Does spectral evolution within the two bands reflect each other?
Is there any indication for variability in EIC photon fields?
Dependencies of all of the above on L, D, M, … ?
S. Wagner: Multifrequency Scalings and Lags in Blazar Flares2009 Fermi SymposiumSummary
FGST is the best monitor for Blazars in any waveband (coverage),but GeV gamma ray studies still have very limited dynamic range.
EGRET-selected (biased) set studied homogeneously over 12 months.
GeV and eV high states correspond to each other.
Flux correlations with different slopes, zeropoints, and scatter,reflecting relative location of observing bands and peaks in SED
Flux scalings and lags are affected by binning and intraday-coverage.
Temporal lags differ (sign, amplitude) within and between sources.
Different spectral evolution of different flares. Biases affect statistics.
S. Wagner: Multifrequency Scalings and Lags in Blazar Flares2009 Fermi SymposiumnotesMany monitoring efforts, see also:
P2, Sakamoto et al. ; P10, Kurtanidze et al.; P39, Chatterjee et al.;P56, Carraminana at al.; P59, Mori et al. and many others.
Compliments and thanks to the LAT team for having set up the most
homogeneous Blazar monitor of any waveband

.

.
HESS
collaboration

PKS 2155-304
2006“high state”“bright flare”/ // // // // // /Binning/averaging affects amplitudes,
different binning/coverage affect ratios and can introduce spurious “lags”