The Robo-AO Kepler Planetary Candidate Survey is observing every Kepler planet candidate host star with laser adaptive optics imaging to search for blended nearby stars, which may be physically associated companions and/or responsible for transit false positives. In this paper we present the results from the 2012 observing season, searching for stars close to 715 Kepler planet candidate hosts. We find 53 companions, 43 of which are new discoveries. We detail the Robo-AO survey data reduction methods including a method of using the large ensemble of target observations as mutual point-spread-function references, along with a new automated companion-detection algorithm designed for large adaptive optics surveys. Our survey is sensitive to objects from ≈0. 15 to 2. 5 separation, with magnitude differences up to ∆m ≈ 6. We measure an overall nearby-star-probability for Kepler planet candidates of 7.4%±1.0%, and calculate the effects of each detected nearby star on the Kepler -measured planetary radius. We discuss several KOIs of particular interest, including KOI-191 and KOI-1151, which are both multi-planet systems with detected stellar companions whose unusual planetary system architecture might be best explained if they are "coincident multiple" systems, with several transiting planets shared between the two stars. Finally, we find 98%-confidence evidence that short-period giant planets are 2-3× more likely than longer period planets to be found in wide stellar binaries.

We present first results on polarization swings in optical emission of blazars obtained by RoboPol, a monitoring programme of an unbiased sample of gamma-ray bright blazars specially designed for effective detection of such events. A possible connection of polarization swing events with periods of high activity in gamma rays is investigated using the data set obtained during the first season of operation. It was found that the brightest gamma-ray flares tend to be located closer in time to rotation events, which may be an indication of two separate mechanisms responsible for the rotations. Blazars with detected rotations during non-rotating periods have significantly larger amplitude and faster variations of polarization angle than blazars without rotations. Our simulations show that the full set of observed rotations is not a likely outcome (probability ≤ 1.5 × 10 −2 ) of a random walk of the polarization vector simulated by a multicell model. Furthermore, it is highly unlikely (∼ 5 × 10 −5 ) that none of our rotations is physically connected with an increase in gamma-ray activity.

We present average R-band optopolarimetric data, as well as variability parameters, from the first and second RoboPol observing season. We investigate whether gammaray-loud and gamma-ray-quiet blazars exhibit systematic differences in their optical polarization properties. We find that gamma-ray-loud blazars have a systematically higher polarization fraction (0.092) than gamma-ray-quiet blazars (0.031), with the hypothesis of the two samples being drawn from the same distribution of polarization fractions being rejected at the 3σ level. We have not found any evidence that this discrepancy is related to differences in the redshift distribution, rest-frame R-band luminosity density, or the source classification. The median polarization fraction versus synchrotron-peak-frequency plot shows an envelope implying that high synchrotronpeaked sources have a smaller range of median polarization fractions concentrated around lower values. Our gamma-ray-quiet sources show similar median polarization fractions although they are all low synchrotron-peaked. We also find that the randomness of the polarization angle depends on the synchrotron peak frequency. For high synchrotron-peaked sources it tends to concentrate around preferred directions while for low synchrotron-peaked sources it is more variable and less likely to have a preferred direction. We propose a scenario which mediates efficient particle acceleration in shocks and increases the helical B-field component immediately downstream of the shock.

We present measurements of rotations of the optical polarization of blazars during the second year of operation of RoboPol, a monitoring programme of an unbiased sample of gamma-ray bright blazars specially designed for effective detection of such events, and we analyse the large set of rotation events discovered in two years of observation. We investigate patterns of variability in the polarization parameters and total flux density during the rotation events and compare them to the behaviour in a non-rotating state. We have searched for possible correlations between average parameters of the polarization-plane rotations and average parameters of polarization, with the following results: (1) there is no statistical association of the rotations with contemporaneous optical flares; (2) the average fractional polarization during the rotations tends to be lower than that in a non-rotating state; (3) the average fractional polarization during rotations is correlated with the rotation rate of the polarization plane in the jet rest frame; (4) it is likely that distributions of amplitudes and durations of the rotations have physical upper bounds, so arbitrarily long rotations are not realised in nature.

We describe the data reduction pipeline and control system for the RoboPol project. The RoboPol project is monitoring the optical R-band magnitude and linear polarization of a large sample of active galactic nuclei that is dominated by blazars. The pipeline calibrates and reduces each exposure frame, producing a measurement of the magnitude and linear polarization of every source in the 13 × 13 field of view. The control system combines a dynamic scheduler, realtime data reduction, and telescope automation to allow high-efficiency unassisted observations.

As new large-scale astronomical surveys greatly increase the number of objects targeted and discoveries made, the requirement for efficient follow-up observations is crucial. Adaptive optics imaging, which compensates for the image-blurring effects of Earth's turbulent atmosphere, is essential for these surveys, but the scarcity, complexity and high demand of current systems limits their availability for following up large numbers of targets. To address this need, we have engineered and implemented Robo-AO, a fully autonomous laser adaptive optics and imaging system that routinely images over 200 objects per night with an acuity 10 times sharper at visible wavelengths than typically possible from the ground. By greatly improving the angular resolution, sensitivity, and efficiency of 1-3 m class telescopes, we have eliminated a major obstacle in the follow-up of the discoveries from current and future large astronomical surveys.

We present first results from RoboPol, a novel-design optical polarimeter operating at the Skinakas Observatory in Crete. The data, taken during the May -June 2013 commissioning of the instrument, constitute a single-epoch linear polarization survey of a sample of gamma-ray-loud blazars, defined according to unbiased and objective selection criteria, easily reproducible in simulations, as well as a comparison sample of, otherwise similar, gamma-ray-quiet blazars. As such, the results of this survey are appropriate for both phenomenological population studies and for tests of theoretical population models. We have measured polarization fractions as low as 0.015 down to R magnitude of 17 and as low as 0.035 down to 18 magnitude. The hypothesis that the polarization fractions of gamma-ray-loud and gamma-ray-quiet blazars are drawn from the same distribution is rejected at the 3σ level. We therefore conclude that gamma-ray-loud and gamma-ray-quiet sources have different optical polarization properties. This is the first time this statistical difference is demonstrated in optical wavelengths. The polarization fraction distributions of both samples are well-described by exponential distributions with averages of p = 6.4 +0.9 −0.8 ×10 −2 for gamma-ray-loud blazars, and p = 3.2 +2.0 −1.1 × 10 −2 for gamma-ray-quiet blazars. The most probable value for the difference of the means is 3.4 +1.5 −2.0 × 10 −2 . The distribution of polarization angles is statistically consistent with being uniform.

Knowledge of the properties of ␥-ray bursts has increased substantially following recent detections of counterparts at X-ray, optical and radio wavelengths. But the nature of the underlying physical mechanism that powers these sources remains unclear. In this context, an important question is the total energy in the burst, for which an accurate estimate of the distance is required. Possible host galaxies have been identified for the first two optical counterparts discovered, and a lower limit obtained for the redshift of one of them, indicating that the bursts lie at cosmological distances. A host galaxy of the third optically detected burst has now been identified and its redshift determined to be z ¼ 3:42. When combined with the measured flux of ␥-rays from the burst, this large redshift implies an energy of 3 ؋ 10 53 erg in the ␥-rays alone, if the emission is isotropic. This is much larger than the energies hitherto considered, and it poses a challenge for theoretical models of the bursts.Ever since their discovery nearly three decades ago 1 , it was understood that progress in solving the puzzle of ␥-ray bursts (GRBs) depends on their identification at other-preferably opticalwavelengths, so that the distances could be measured using standard spectroscopic techniques. From distances and flux measurements one can then infer luminosities and other physical parameters, which can then be used to test theoretical models of the bursts and their origins.A recent breakthrough in this field was the precise localization of bursts by the BeppoSAX satellite 2 , which has led to the first identifications of GRBs at other wavelengths: X-rays 3 , optical 4 and radio 5 . This has further led to the determination of the distance scale of GRBs, with the detection of intergalactic absorption lines 6 in the optical transient 7,8 (OT) of GRB970508 (refs 9, 10). Apparent host galaxies have been detected for the first two optical afterglows found 11-14 .Here we report follow-up studies of the OT 15 of a relatively bright burst, GRB971214 (refs 16-18). As the OT faded away, we found an extended object with a red-band magnitude R ¼ 25:6 Ϯ 0:15 at the position of the OT. Based on the excellent positional coincidence, 0:06 Ϯ 0:06 arcsec, we argue here that this is the host galaxy of GRB971214. Spectroscopic observations show that the host is a typical star-forming galaxy 19-21 at a redshift z ¼ 3:418.Given this high redshift, the ␥-ray energy release of this burst is unexpectedly large, about 3 ϫ 10 53 erg, assuming isotropic emission, corresponding to about 16% of the rest-mass energy of our Sun. Energy released in other forms of radiation, for example, neutrinos or gravity waves, is not included in this energy budget. Nonetheless, the inferred energy release in ␥-rays alone is so substantial that it may present difficulties for some of the currently popular theoretical models for the origin of the bursts (coalescence of neutron stars). We may be forced to consider even more energetic possibilities 22,23 or to find ways of extracting...