Blazars: VLBA and GLAST

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Blazars VLBA and GLAST

• Glenn Piner
• Whittier College

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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.

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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.

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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 ? gt 10 obtained for Mrk 421).

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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.

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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.

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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.

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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.

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TeV Blazars

• Confirmed Sources
• Markarian 421 (z0.03) (15 4 epochs)
• Markarian 501 (z0.03) (12 epochs)
• 1426428 (z0.13) (4 epochs)
• 1959650 (z0.05) (3 3 epochs)
• Unconfirmed Sources
• 2155-304 (z0.12) (3 1 epoch)
• 2344514 (z0.04) (4 epochs)
• BL Lac (z0.07)
• 3C66A (z0.44) (doubtful because of high z)
• M87 (z0.004) (not a blazar)

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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?

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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.
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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 EGRETs, yielding
  sensitivities for a 1-year all sky survey 3 times
  better than EGRET.
• Launch 2004.
• Blazar Detection 200-300 blazars.

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GLAST Large Area Telescope (LAT)

• Energy Range 20 MeV - 300 GeV.
• Source Location Determination 1-10 (fainter
  sources), lt0.5 (brightest sources) (30 times
  better than EGRET).
• FOV gt 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.

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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?).

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LAT Rate of Flare Detection

• Dermer Dingus (2002) calculate rate of
  detection of bright ?-ray flares.
• Bright flare defined as flux gt 2 x 10-6 ph cm-2
  s-1 (gt 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.

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LAT Detection of Faint Sources
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What will these sources be like in radio?

• Mattox et al. 1997 showed definitively that EGRET
  detections are correlated with flat-spectrum (? gt
  -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).

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Flat-spectrum sources over 30 mJy

• CLASS complete sample (Myers et al. 2003) is a
  complete sample of flat-spectrum sources (? gt
  -0.5 between NVSS and GB6) over 30 mJy (in GB6
  catalog).
• The sample contains 11,685 sources between
  between 0olt?lt75o, 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.

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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.

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