2 2009 Fermi Symposium, Washington, D.C., Nov. 2-5
3. VERITAS Blazar KSP
VERITAS observes for ∼ 750 h and ∼ 250 h each
year during periods of astronomical darkness and par-
tial moonlight, respectively. The moonlight observa-
tions are almost exclusively used for a blazar discovery
program, and a large fraction of the dark time is used
for the blazar KSP, which consists of:
• A VHE blazar discovery program ( ∼ 200 h / yr):
Each year ∼ 10 targets are selected to receive
∼ 10 h of observations each during astronomi-
cal darkness. These data are supplemented by
discovery observations during periods of partial
moonlight.
• A target-of-opportunity (ToO) observation pro-
gram (∼ 50 h / yr): VERITAS blazar obser-
vations can be triggered by either a VERI-
TAS blazar discovery, a VHE ﬂaring alert (>2
Crab) from the blazar monitoring program of
the Whipple 10-m telescope or from another
VHE instrument, or a lower-energy ﬂaring alert
(optical, X-ray or Fermi-LAT). Should the guar-
anteed allocation be exhausted, further time can
be requested from a pool of director’s discre-
tionary time.
• Multi-wavelength (MWL) studies of VHE
blazars (∼ 50 h / yr + ToO): Each year one
blazar receives a deep exposure in a pre-planned
campaign of extensive, simultaneous MWL (X-
ray, optical, radio) measurements. ToO observa-
tion proposals for MWL measurements are also
submitted to lower-energy observatories (e.g.
Swift) and are triggered by a VERITAS discov-
ery or ﬂaring alert.
• Distant VHE blazar studies to constrain the ex-
tragalactic background light (EBL): Here dis-
tant targets are given a higher priority in the
blazar discovery program, as well as for the
MWL observations of known VHE blazars, par-
ticularly those with hard VHE spectra.
4. Blazar Discovery Program
The blazars observed in the discovery program are
largely high-frequency-peaked BL Lac objects. How-
ever, the program also includes IBLs (intermediate-
peaked) and LBLs (low-peaked), as well as ﬂat spec-
trum radio quasars (FSRQs), in an attempt to in-
crease the types of blazars known to emit VHEγ-rays.
The observed targets are drawn from a target listcon-
taining objects visible to the telescopes at reasonable
zenith angles (− 8◦ < δ < 72◦), without a previously
published VHE limit below 1.5% Crab, and with a
measured redshiftz < 0. 3. To further the study of the
EBL a few objects having a large ( z > 0. 3) are also
included in the target list. The target list includes:
• All nearby ( z < 0. 3) HBL and IBL recom-
mended as potential VHE emitters in [5, 6, 7].
• The X-ray brightest HBL ( z < 0. 3) in the recent
Sedentary [8] and ROXA [9] surveys.
• Four distant ( z > 0. 3) BL Lac objects recom-
mended by [5, 10].
• Several FSRQ recommended as potential VHE
emitters in [6, 11].
• All nearby ( z < 0. 3) blazars detected by
EGRET [12].
• All nearby ( z < 0. 3) blazars contained in the
Fermi-LAT Bright AGN Sample [13].
• All sources ( |b| > 10◦) detected by Fermi-LAT
where extrapolations of their MeV-GeV γ-ray
spectrum (including EBL absorption; assuming
z = 0.3 if the redshift is unknown) indicates a
possible VERITAS detection in less than 20 h.
This criteria is the focus of the 2009-10 VERI-
TAS blazar discovery program.
5. VERITAS AGN Detections
VERITAS has detected VHE γ-ray emission from
16 AGN (15 blazars), including 8 VHE discoveries.
These AGN are shown in Table I, and each has been
detected by the Large Area Telescope (LAT) instru-
ment aboard the Fermi Gamma-ray Space Telescope.
Every blazar discovered by VERITAS was the sub-
ject of ToO MWL observations to enable modeling of
its simultaneously-measured SED. The known VHE
blazars detected by VERITAS were similarly the tar-
gets of MWL observations.
5.1. Recent VERITAS Blazar Discoveries
Prior to the launch of Fermi VERITAS had discov-
ered VHE emission from 2 blazars. These included
the ﬁrst VHE-detected IBL, W Comae [14, 15], and
the HBL 1ES 0806+524 [16]. VERITAS has discov-