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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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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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