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An All-Sky Survey for Candidate Gamma-Ray Blazars

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It’s a blazar!. It’s a quasar!. My eye!. I’m an AGN!. An All-Sky Survey for Candidate Gamma-Ray Blazars. Steve Healey GLAST Science Lunch 24 February 2005. Note: Figure is not to scale. Basic Premise of the Survey. EGRET blazars. Figure of merit.

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slide1

It’s a blazar!

It’s a quasar!

My eye!

I’m an AGN!

An All-Sky Survey forCandidate Gamma-Ray Blazars

Steve HealeyGLAST Science Lunch24 February 2005

Note: Figure is not to scale.

basic premise of the survey
Basic Premise of the Survey

EGRET blazars

Figure of merit

Evaluate radio/X-ray sources in EGRET contour

everywhere

Optical spectroscopy:ID and redshift

blazar vs blazar candidate
Blazar vs. Blazar Candidate
  • “Blazar” label reserved for objects known to be gamma ray sources
  • Blazar candidates exhibit properties of EGRET blazars at other wavelengths but are not (yet) confirmed gamma ray sources
the foundation radio
The Foundation: Radio
  • Start with 4.85 GHz measurements
    • GB6 for d > 0°; PMN for d < 0°
    • Require S4.85 ≥ 65 mJy
  • Identify low-frequency sources
    • NVSS (1.4 GHz) for d > -40°;SUMSS (0.84 GHz) for d < -40°
  • Require flat spectra
    • Spectral index alow/4.85 ≤ 0.5 (S  n–a)
  • Obtain 8.4 GHz measurements
    • CLASS for d > 0°;Winn/CGRaBS for d > -40°
radio coverage
Radio Coverage
  • Completeness of 8.4 GHz observations:
    • “North” (0° < d < 75°): 91%
    • “South” (-40° < d < 0°): 90%
    • “Far South” (-90° < d < -40°): <50%
  • Far South: PKSCAT90, PQJ, Southern Flat-Spectrum, … ?
  • Satisfactory coverage in Far South may be difficult
almost done with radio
Almost Done with Radio

8.4 GHz measurement

Calculate figure of merit

{

  • Flux at 8.4 GHz
  • Spectral index from low frequency to 8.4 GHz
  • X-ray counts (RASS)

FoM depends on:

rigorous survey definition
Rigorous Survey Definition
  • An object is in CGRaBS if it has:
    • Galactic latitude |b| ≥ 10°
    • 4.85 GHz flux S4.85 ≥ 65 mJy
    • Initial spectral index alow/4.85 ≤ 0.5
    • Final spectral index -1 ≤ alow/8.4 ≤ 0.5
    • Figure of merit FoM > 0.04
  • Obvious non-blazar interlopers are rejected when possible
    • Nearby galaxies, H II regions, stars, …
  • 1500-2000 candidates all-sky
optical classification
Optical Classification
  • First: Vet candidates against catalogues of known quasars (Veron, Sloan, CGRaBS)
  • Find optical counterparts of unIDed candidates
    • USNO-B1.0 catalogue
    • SDSS catalogue
  • Observe targets to confirm type IDs and determine redshifts
optical spectroscopy
Optical Spectroscopy
  • Hobby-Eberly Telescope
    • Low-ResolutionSpectrograph:4150 Å – 10100 Å
    • Able to observe -10° < d < 70°
  • 83% of candidates are flat-spectrum radio quasars
    • 13% are BL Lacertae objects
    • 4% are narrow-line radio galaxies or other non-blazars
a typical spectrum
A Typical Spectrum

J1347+1835Magnitude: 19.5Type ID: FSRQz = 2.17

HET LRS spectrumTaken 11 Jan 2005

all sky optical work
All-Sky Optical Work
  • McDonald 2.7 m for brightest targets
  • CTIO 4 m for Southern/Far Southern targets
  • Keck for faint targets?
  • Freebies from Veron
  • Once again, satisfactory Far Southern coverage will be difficult
redshift distribution
Redshift Distribution

Solid line: CGRaBS; Dashed line: 3EG blazars

current status
Current Status

Green: Predicted FoM > 0.04Blue: FoM > 0.04Red: IDed/redshift found

concluding thoughts
Concluding Thoughts
  • Northern sky is in good shape, should exceed 90% completion by GLAST launch
  • Much remains to be done, in radio and in optical, in the South
  • Survey has identified blazar candidates suitable for EBL absorption studies
    • 20% of survey has z > 2
    • 26 objects have z > 3; five have z > 4
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