Blazars: VLBA and GLAST

Glenn Piner

Whittier College

Overview

• Review of EGRET and current TeV observations.

• VLBA observations of EGRET and TeV blazars.

• Future -ray telescopes (AGILE, GLAST, VERITAS) and predictions of source detections.

• VLBA Observations of GLAST sources.

Two Main Types of Blazars

•Red Blazars (3C279): More luminous, X-rays are inverse-Compton, inverse-Compton peaks at GeV energies, studied with space-based pair production telescopes.

•Blue Blazars (Mrk 501): Less luminous, X-rays are synchrotron, inverse-Compton peaks at TeV energies, studied with ground-based Cerenkov light telescopes.

EGRET Blazar Detections• EGRET detected 93 blazars, 66 with ‘high’

confidence (3rd EGRET catalog).• Apparent -ray luminosity as much as 100 times

greater than that at all other wavelengths for some flaring blazars.

• Rapid time variability provided important evidence for relativistic beaming from compactness arguments (even more true for the TeV blazars, limit > 10 obtained for Mrk 421).

VLBA Observations of EGRET Blazars•Why were some strong radio quasars detected by EGRET while others like 3C345 were not? Are there -ray loud, -ray quiet blazars? •VLBA monitoring of EGRET blazars by Jorstad et al. (2001a) showed EGRET blazars had faster apparent speeds than sources in radio selected samples, and are therefore more strongly beamed.

VLBA Observations of EGRET Blazars

•This is expected from -ray emission models. Both SSC and EC models predict a stronger dependence of -ray emission on than for the radio emission.•GLAST should fill in missing bright flat-spectrum radio sources like 3C345.

VLBA Observations of EGRET Blazars

• VLBA observations have also apparently directly imaged the -ray producing regions.

• Jorstad et al. (2001b) find that ≈50% of EGRET flares are correlated with the ejection of a new superluminal component with an average time delay of 52 days between the epoch of zero-separation and the flare.

• Suggests these gamma-ray flares are occurring in the superluminal radio knots several parsecs downstream of the radio “core”.

Improvements in VLBI Science by Time of GLAST

• EGRET VLBA observations (1994-1997).• More sophisticated understanding of the nature of

“components” from numerical simulations, e.g. Agudo et al. 2001 (stationary components, pattern speed, bulk speed).

• Large multi-epoch surveys (2 cm survey).• Routine VLBI Polarimetry.• Routine Imaging at 86 GHz, possibly inside current

radio core.

TeV Blazars• Confirmed Sources

– Markarian 421 (z=0.03) (15 + 4 epochs)

– Markarian 501 (z=0.03) (12 epochs)

– 1426+428 (z=0.13) (4 epochs)

– 1959+650 (z=0.05) (3 + 3 epochs)

• Unconfirmed Sources– 2155-304 (z=0.12) (3 + 1 epoch)

– 2344+514 (z=0.04) (4 epochs)

– BL Lac (z=0.07)

– 3C66A (z=0.44) (doubtful because of high z)

– M87 (z=0.004) (not a blazar)

VLBA Observations of TeV Blazars

• The jets of TeV blazars appear much the same from epoch to epoch, with little or no component motion.

• The “components” may just be stationary patterns, but where are the moving shocks presumably responsible for -ray flares?

Observations of Mrk 421 after 2001 TeV flares show swing in EVPA of C7, similar to behavior seen by Homan et al. (2002) in four other sources.

AGILE

• Energy Range: 30 MeV - 50 GeV.

• Source Location Determination: 5’-20’ (about twice as good as EGRET).

• Sensitivity: comparable to EGRET on-axis, better than EGRET for off-axis sources.

• FOV: 3 sr, about six times EGRET’s, yielding sensitivities for a 1-year all sky survey 3 times better than EGRET.

• Launch: 2004.

• Blazar Detection: 200-300 blazars.

GLAST Large Area Telescope (LAT)

• Energy Range: 20 MeV - 300 GeV.

• Source Location Determination: 1’-10’ (fainter sources), <0.5’ (brightest sources) (≈30 times better than EGRET).

• FOV: > 2 sr, about four times EGRET FOV.

• Launch: 2006-2007.

• Sensitivity: For a 1-year all sky survey, GLAST will reach a flux limit about 30 times fainter than EGRET.

• Source Detection: estimates range from 3,000-11,000 sources detected after 1 year.

• Will operate in all-sky scanning mode for first year.

LAT Improvements to EGRET Blazar Science

• Do blazars have a quiescent flux level, and what is the duty cycle for flaring?

• Densely sampled light curves, allowing discrimination among flaring models.

• Spectral index evolution during flare (Hard lags or soft lags?).

LAT Rate of Flare Detection

• Dermer & Dingus (2002) calculate rate of detection of bright -ray flares.

• Bright flare defined as flux > 2 x 10-6 ph cm-2 s-1 (> 100 MeV), (about flux of 1991 3C279 flare).

• Detection of a flare at this level, which may have triggered an EGRET multiwavelength Target of Opportunity, should occur once every 3-4 days.

LAT Detection of Faint Sources

What will these sources be like in radio?

• Mattox et al. 1997 showed definitively that EGRET detections are correlated with flat-spectrum ( > -0.5) radio sources above about 1 Jy (Kuhr catalog).

• Correlation between peak -ray flux and 5 GHz radio flux with 99.998% confidence.

• Since GLAST is 30 times more sensitive, we might expect GLAST sources to be correlated with flat-spectrum radio sources above about 30 mJy.

• GLAST may also detect non-blazars: radio galaxies, Seyfert galaxies, LINERs, radio-quiet quasars (All have compact VLBI flux at the mJy level).

Flat-spectrum sources over 30 mJy• ‘CLASS complete sample’ (Myers et al. 2003) is a complete sample of

flat-spectrum sources ( > -0.5 between NVSS and GB6) over 30 mJy (in GB6 catalog).

• The sample contains 11,685 sources between between 0o<<75o, and excluding the galactic plane.

• Observed with the VLA in ‘A’ configuration at 8.4 GHz from 1994-1999.

• 10,906 of 11,685 sources detected.

• CLASS complete sample can be considered as the GLAST candidate list for the northern hemisphere.

• About one CLASS source per square degree, GLAST error circle 0.02 square degrees, will be source confusion for a few percent of GLAST sources.

VLBA Observations of CLASS sources

• VLBA Imaging and Polarimetry survey (VIPS)

• PI: Chris Fassnacht, UC Davis

• Selection criteria:– Above 50 mJy in CLASS– In region of sky covered by Sloan Digital Sky Survey (redshifts).– Yields approximately 1,000 sources.

• Survey to image these sources with dual polarization observations at 5 and 15 GHz, 1.5 hours total per source.

• 500 hours of observing time per year for three years.

• ‘Test’ proposal approved for 48 hours of observing time, full proposal not yet submitted.

Acknowledgements

Thanks to Jim Ulvestad and Seth Digel for supplying some material used in this talk.