During moonlit nights, observations with ground-based Cherenkov telescopes at very high energies (VHE, $E>100$ GeV) are constrained since the photomultiplier tubes (PMTs) in the telescope camera are extremely sensitive to the background moonlight. Ob
servations with the VERITAS telescopes in the standard configuration are performed only with a moon illumination less than 35$%$ of full moon. Since 2012, the VERITAS collaboration has implemented a new observing mode under bright moonlight, by either reducing the voltage applied to the PMTs (reduced-high-voltage configuration, RHV), or by utilizing UV-transparent filters. While these operating modes result in lower sensitivity and increased energy thresholds, the extension of the available observing time is useful for monitoring variable sources such as blazars and sources requiring spectral measurements at the highest energies. In this paper we report the detection of $gamma$-ray flaring activity from the BL Lac object 1ES 1727+502 during RHV observations. This detection represents the first evidence of VHE variability from this blazar. The integral flux is $(1.1pm0.2)times10^{-11}mathrm{cm^{-2}s^{-1}}$ above 250 GeV, which is about five times higher than the low-flux state. The detection triggered additional veritas observations during standard dark-time. Multiwavelength observations with the FLWO 48 telescope, and the Swift and Fermi satellites are presented and used to produce the first spectral energy distribution (SED) of this object during $gamma$-ray flaring activity. The SED is then fitted with a standard synchrotron-self-Compton model, placing constraints on the properties of the emitting region and of the acceleration mechanism at the origin of the relativistic particle population in the jet.
We present results from VERITAS observations of the BL Lac object PG 1553+113 spanning the years 2010, 2011, and 2012. The time-averaged spectrum, measured between 160 and 560,GeV, is well described by a power law with a spectral index of $4.33 pm 0.
09$. The time-averaged integral flux above $200,$GeV measured for this period was $(1.69 pm 0.06) times 10^{-11} , mathrm{ph} , mathrm{cm}^{-2} , mathrm{s}^{-1}$, corresponding to 6.9% of the Crab Nebula flux. We also present the combined $gamma$-ray spectrum from the Fermi Large Area Telescope and VERITAS covering an energy range from 100~MeV to 560~GeV. The data are well fit by a power law with an exponential cutoff at $rm {101.9 pm 3.2 , mathrm{GeV}} $. The origin of the cutoff could be intrinsic to PG~1553+113 or be due to the $gamma$-ray opacity of our universe through pair production off the extragalactic background light (EBL). Given lower limits to the redshift of $rm z egthinspace > egthinspace 0.395$ based on optical/UV observations of PG~1553+113, the cutoff would be dominated by EBL absorption. Conversely, the small statistical uncertainties of the VERITAS energy spectrum have allowed us to provide a robust upper limit on the redshift of PG 1553+113 of $z egthinspace leq egthinspace 0.62$. A strongly-elevated mean flux of $(2.50 pm 0.14) times 10^{-11} , mathrm{ph} , mathrm{cm}^{-2} , mathrm{s}^{-1}$ (10.3% of the Crab Nebula flux) was observed during 2012, with the daily flux reaching as high as $(4.44 pm 0.71) times 10^{-11} , mathrm{ph} , mathrm{cm}^{-2} , mathrm{s}^{-1}$ (18.3% of the Crab Nebula flux) on MJD 56048. The light curve measured during the 2012 observing season is marginally inconsistent with a steady flux, giving a $chi^2$ probability for a steady flux of 0.03%.
