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veritas is an array of four 12 m diameter imaging atmospheric cherenkov telescopes ( iact ) located at the fred lawrence whipple observatory in southern arizona at an elevation of 1268 m @xcite . in less than 50 hours of observations
, veritas can detect a source at the 1% crab flux level in the energy range from 100 gev to greater than 30 tev .
the array can reconstruct events with an energy resolution of @xmath115% and an angular resolution ( 68% containment ) of @xmath10.1@xmath2 .
for more details on the veritas instrument and techniques , see @xcite .
the veritas capabilities are well suited to the study and search for blazars in the northern hemisphere and will become further enhanced once a planned move of one of the telescopes is completed later this year which will yield a @xmath115% improvement in sensitivity .        a large fraction of the @xmath1750 hours of dark time ( plus an additional @xmath1250 hours of moon time ) during the veritas observing season is dedicated to observing active galactic nuclei ( agn ) .
the focus of these observations is two fold : one , to study known vhe agn such as mrk421 or 1es 1218 + 304 to learn about blazar emission mechanisms , black hole accretion and the extragalactic background light ( ebl ) and , two , to discover new types of vhe blazars which will expand the current vhe blazar catalog and perhaps reveal unknown vhe phenomenon . for more details about the veritas blazar key science program ,
see w.  benbow s contribution in this conference@xcite .    .
the de - absorbed spectrum is calculated by applying the extragalactic absorption model according to franceschini , 2008@xcite.,width=240 ]    blazars are characterized by their double - humped spectral energy distribution ( sed ) and are further classified according to the location of the lower energy hump , usually interpreted as synchrotron emission from relativistic electrons .
most of the @xmath125 vhe blazars detected by ground - based iact are high - frequency peaked bl lac ( hbl ) objects .
veritas has discovered two hbl objects , 1es 0806 + 524 and , more recently rgb j0710 + 591 .
in addition to these two hbl , veritas has discovered two intermediate - frequency peaked bl lac ( ibl ) objects , 3c 66a and w com .
this contribution describes the discovery of vhe @xmath3-rays from these four blazars .
there are several other contributions in this conference which will detail the veritas observations of known blazars , including multiwavelength ( mw ) observations and ebl studies ( @xcite ) .
the discovery @xcite of the hbl 1es 0806 + 524 was made with a combination of observations from the commissioning phase of veritas ( 30 hours ) and full array time ( 35 hours ) .
these observations resulted in 245 excess events corresponding to a detection at the 6.3@xmath4 level .
figure [ fig:0806theta2 ] shows the distribution of the squared angular distance between the shower direction and the location of 1es 0806 + 524 indicating that this source is point - like . the photon spectrum shown in figure [ fig:0806spectrum ]
is characterized by a power law with photon index @xmath5 between 300 and 700 gev .
the integral flux above 300 gev is @xmath6 corresponding to 1.8% of the crab nebula s flux . assuming absorption on the infrared component of the ebl according to franceschini , 2008 @xcite , the de - absorbed spectrum is calculated to be @xmath7 . the veritas data together with simultaneous _
swift _ observations in the uv to optical to x - ray energies was used to construct a spectral energy distribution ( sed ) of the object .
the sed is well fit by a pure synchrotron - self - compton ( ssc ) model @xcite . for more details on the multiwavelength observations of this object
see j.  grube s talk in this conference @xcite .
veritas discovered the first ibl in vhe @xmath3-rays , w com , in a flaring state in march 2008 @xcite ( see figure [ fig : wcomskymap ] ) .
w com is a known @xmath3-ray source detected previously by egret in the 100 mev - 10 gev band @xcite .
the flare , which lasted only four days ( see figure [ fig : wcomlightcurve ] ) resulted in a detection at the 8@xmath4 level .
the significance of the full data set is 4.9@xmath4 .
70% of the total excess was from the four - day flaring period and during the two brightest nights , w comae was observed at the 9% crab flux level . using quasi - simultaneous multiwavelength data ,
the sed can be reasonably modeled with a simple one - zone ssc but this yields an extraordinarily low magnetic field value ( b = 0.007 g ) .
a more natural set of fit parameters is obtained with an external - compton model indicating that the higher optical luminosity is likely providing a seed population of photons for inverse - compton scattering .
a second vhe flare was observed from w comae in june 2008 wherein the flux was @xmath13 times brighter than the previous flare @xcite . for more details on this second flare ,
see g.  maier s contribution @xcite in this conference .
a multiwavelength campaign was triggered during this time and will be the subject of a future paper .
interestingly , the vhe hbl 1es 1218 + 304 can also be seen in the field - of - view ( fov ) of the w comae observations which highlights the capabilities of off - axis observations with veritas ( see figure [ fig : wcomskymap ] ) .
the ibl 3c 66a was discovered by veritas in 33 hours of observations resulting in a 21.2@xmath4 detection ( 1791 excess events ) @xcite .
variability is seen on day time scales ( see figure [ fig:3c66alightcurve ] ) during a strong flare observed in october , 2008 . the observed spectrum is well - fit by a soft power law with an index of @xmath8 .
the redshift of 3c 66a is uncertain .
it was measured to be 0.444 based on a single line @xcite and there is a lower limit of 0.096 @xcite . if the measured value of 0.444 is correct , the softness of the measured spectrum could be completely due to ebl attenuation of vhe photons ( see figure [ fig:3c66aspectrum ] )
. using the model of franceschini @xcite and assuming a redshift of @xmath9 , the de - absorbed spectral index is calculated to be a very hard @xmath10 .
3c 66a lies only @xmath11 from the radio galaxy 3c 66b and care must be taken in identifying the source of @xmath3-rays from this region .
recently , the magic collaboration reported the detection of vhe gamma - rays from the region in observations carried out in 2007 and claimed marginal evidence ( at the 85% confidence level ) for association with 3c 66b @xcite .
however , the veritas data exclude the position of 3c 66b at the 4.3@xmath4 level ( see figure [ fig:3c66askymap ] ) .
in addition to this , the measured veritas spectrum does not agree with that measured by magic .
one explanation of the discrepancy in source localization is that 3c66b must have been considerably brighter in 2007 than 2008 , and similarly 3c 66a must have been considerably brighter in 2008 than 2007 .
recently the lat instrument on the fermi satellite also observed bright emission in the mev - gev range at a level higher than that reported by egret .
in addition , observations of the blazar were made by the _
swift _ and _ chandra _ satellites .
details of these multiwavelength observations will be the subject of a future paper and are highlighted in l.  reyes contribution @xcite .
rgb j0710 + 591 was only recently discovered to emit vhe emission and is the fourth veritas blazar discovery @xcite .
located at a redshift of 0.125 , veritas observed rgb j0710 for @xmath12 hours resulting in a @xmath13 detection from 140 @xmath3-rays corresponding to @xmath14 of the crab nebula s flux .
a future publication will describe the veritas observations as well as multiwavelength observations from the _ swift _ , _ chandra _ and fermi satellites .
a preliminary skymap is shown in figure [ fig : rgbj0710skymap ] .
the preliminary observed spectrum can be described as a power law with photon index @xmath15 . while not as hard as 1es 0229 + 200 which placed the strongest constraints to date on the density of the ebl in the mind - infrared band , the moderately high distance and relatively hard spectrum of rgb j0710 + 591 confirms the constraints presented in @xcite .
-ray excess including the statistical and systematic error .
the dashed circle is the integration region.,width=240 ]    [ cols="^,^,^,^,^,^,^,^,^,^ " , ]
to date , veritas has detected more than a dozen blazars and has discovered vhe emission from four blazars : 1es 0806 + 524 , rgb j0710 + 591 w com and 3c 66a ( see table [ tab : blazars ] ) .
the first two of these are hbl objects while the latter two are ibl objects .
the discovery of 1es 0806 + 524 highlights the capabilities of veritas to detect low - flux objects while the detection of the two ibl objects opens a new window into the study of blazar populations in the vhe regime .
additionally , the detection of 1es 1218 + 304 in the fov of w com provides an example of the ability to detect objects at the edge of veritas fov .
future studies of the moderately distant rgb j0710 + 591 might provide interesting constrains on the ebl .
this research was supported by grants from the u.s .
department of energy , the u.s . national science foundation and the smithsonian institution , by nserc in canada , by science foundation ireland and by stfc in the uk .
blazars are among the most energetic and violent objects in the universe . by observing blazars at very high energies ( vhe , e @xmath0 100 gev ) 
 we can better understand blazar emission mechanisms , jet structure , black hole accretion and the extragalactic background light ( ebl ) . 
 veritas , an array of four 12-meter diameter imaging atmospheric - cherenkov telescopes , performs vhe studies of blazars through intense monitoring and discovery campaigns . 
 most blazars known to emit vhe gamma rays are high - frequency - peaked bl lacertae ( hbl ) objects , and veritas has discovered vhe emission from two of these : 1es 0806 + 524 and rgb j0710 + 591 . 
 veritas has also discovered vhe gamma rays from two intermediate - frequency - peaked bl lacertae ( ibl ) objects : w com and 3c 66a . 
 the expansion of the vhe catalog to include ibl objects enables a better understanding of the agn population as a whole . 
 this contribution presents recent results from the veritas blazar discovery program .    
 gamma - ray astronomy , active galactic nuclei , veritas