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An All-Sky Survey for Candidate Gamma-Ray Blazars

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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An All-Sky Survey for Candidate Gamma-Ray Blazars

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  1. 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.

  2. Basic Premise of the Survey EGRET blazars Figure of merit Evaluate radio/X-ray sources in EGRET contour everywhere Optical spectroscopy:ID and redshift

  3. 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

  4. 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°

  5. 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

  6. 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:

  7. 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

  8. 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

  9. 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

  10. A Typical Spectrum J1347+1835Magnitude: 19.5Type ID: FSRQz = 2.17 HET LRS spectrumTaken 11 Jan 2005

  11. 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

  12. Redshift Distribution Solid line: CGRaBS; Dashed line: 3EG blazars

  13. Current Status Green: Predicted FoM > 0.04Blue: FoM > 0.04Red: IDed/redshift found

  14. 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

  15. THE END

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