Two years of blazar monitoring with the OVRO 40m telescope at 15GHz

in support of the Fermi GST

Vasiliki Pavlidou (Caltech)on behalf of the OVRO 40m team

The team:

The plan:

• Science

• Observational Program

• Preliminary Results

Science

Blazars (~aligned AGN)

beamed & boosted

fast variability

high apparent luminosity

superluminal motions

high-energy emission

Jets: how are they launched, accelerated, collimated, confined?

What is the jet composition?

How are particles accelerated to relativistic energies?

What are the details of the emission mechanism, and where in the jet is the observed emission coming from?

McKinney 2006

Blandford & Znajek 1977

Marscher et al. 2008

Blandford & Payne 1982

Dermer, Schlickeiser & Mastichiadis 1991

Lind et al. 1989

Blandford & Levinson 1995

Sikora, Begelman & Rees 1994

Science: theory

Science: phenomenology

Blazars (~aligned AGN)

beamed & boosted

fast variability

high apparent luminosity

superluminal motions

high-energy emission

What is the correlation between variability, luminosity, beaming?

How is emission at different wavelengths correlated?

Timelags between flares at different frequencies?

Dependence of variability on spectral properties?

Cosmic evolution of blazar properties?

Phenomenology: strategy

•Sensitive dependence of observed properties on

•Physical processes: everything goes?(different for different blazars or even for different flares of single blazar?)

•Most impressive behavior need not be typical behavior

Need:

• Large sample

• Statistically well-defined sample

• Regular monitoring

multiwavelength

GeV: Fermi Radio (15 GHz): OVRO 40m

The OVRO 40m program: sample and strategy

• Sample: all CGRaBS sources at >200

(additional sources monitored, not used in population studies,

e.g.:non-CGRaBS LAT AGN within accessible sky

VERITAS monitoring…)

• Strategy: twice-a-week flux observations at 15GHz

selected based on radio spectral index, radio flux, and X-ray flux

The OVRO 40m program: data filters and calibration

• Data: available to Fermi collaboration

• released to public at ~ time of Fermi public data release

• regularly updated thereafter

http://www.astro.caltech.edu/GLAST/

The OVRO 40m program: data policy

OVRO 40m program: First Results

• Richards et al. (2009): description of program, lightcurves, statistics of variability for individual objects

• Max-Moerbeck et al. (2009): population studies of radio variability

• (also: Fuhrmann et al. 2009: F-GAMMA program description)

Results: Lightcurves

Results: Lightcurves

Results: Variability Amplitude

• One blazar: quantify using intrinsic modulation index flux rms in units of mean m=/<S>

• Obtain through likelihood analysisaccounting for:– uncertainties in individual observations– number of observations

bimodality!

Results: Variability Amplitude

• Population Studies

• Population studies– Is the distribution of modulation indices the

same at high and low redshifts?

Results: Variability Amplitude

High z (>1.1)

Low z (<1.1)

Results: Time Domain

Results: Correlation with gamma-ray emission

• Need longer lightcurves!

Fermi LAT data

OVRO data

Summary

• Regular multiwavelength monitoring of large and uniform samples critical for blazar science

• OVRO 40m telescope is monitoring ~1200 CGRaBS blazars @15 GHz ~twice a week

• Fermi is continuously monitoring the GeV sky

• First results tantalizing, coming soon at a preprint server near you

• The future is bright, tune (and/or join) in!

Variability Amplitude - population studies

High z / Low z(FSRQs only)

FSRQs vs BLLs

2 random equally-sized subsamples