An All-Sky Survey forCandidate Gamma-Ray Blazars

It’s a quasar!

It’s a blazar!

My eye! I’m an AGN!

Steve HealeyGLAST Science Lunch

24 February 2005Note: Figure is not to scale.

Basic Premise of the Survey

EGRET blazars

Figure of merit

Evaluate radio/X-ray sources in EGRET contour

Optical spectroscopy:ID and redshift

everywhere

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• Start with 4.85 GHz measurements

– GB6 for > 0°; PMN for < 0°

– Require S4.85 ≥ 65 mJy

• Identify low-frequency sources– NVSS (1.4 GHz) for > -40°;

SUMSS (0.84 GHz) for < -40°

• Require flat spectra– Spectral index low/4.85 ≤ 0.5 (S –)

• Obtain 8.4 GHz measurements– CLASS for > 0°;

Winn/CGRaBS for > -40°

Radio Coverage

• Completeness of 8.4 GHz observations:– “North” (0° < < 75°): 91%– “South” (-40° < < 0°): 90%– “Far South” (-90° < < -40°): <50%

• Far South: PKSCAT90, PQJ, Southern Flat-Spectrum, … ?

• Satisfactory coverage in Far South may be difficult

Almost Done with Radio

8.4 GHz measuremen

t

Calculate figure of merit

FoM depends on:

1. Flux at 8.4 GHz

2. Spectral index from low frequency to 8.4 GHz

3. X-ray counts (RASS){

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 low/4.85 ≤ 0.5

– Final spectral index -1 ≤ low/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

• 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

• Hobby-Eberly Telescope– Low-Resolution

Spectrograph: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

J1347+1835Magnitude: 19.5

Type ID: FSRQz = 2.17

HET LRS spectrumTaken 11 Jan 2005

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

Solid line: CGRaBS; Dashed line: 3EG blazars

Current Status

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

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

THE END