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We present a single-dish mapping algorithm with a number of advantages over traditional techniques. (1) Our algorithm makes use of weighted modeling, instead of weighted averaging, to interpolate between signal measurements. This smooths the data, but without blurring the data beyond instrumental resolution. Techniques that rely on weighted averaging blur point sources sometimes as much as 40%. (2) Our algorithm makes use of local, instead of global, modeling to separate astronomical signal from instrumental and/or environmental signal drift along the telescope's scans. Other techniques, such as basket weaving, model this drift with simple functional forms (linear, quadratic, etc.) across the entirety of scans, limiting their ability to remove such contaminants. (3) Our algorithm makes use of a similar, local modeling technique to separate astronomical signal from radio-frequency interference (RFI), even if only continuum data are available. (4) Unlike other techniques, our algorithm does not require data to be collected on a rectangular grid or regridded before processing. (5) Data from any number of observations, overlapping or not, may be appended and processed together. (6) Any pixel density may be selected for the final image. We present our algorithm, and evaluate it using both simulated and real data. We are integrating it into the image-processing library of the Skynet Robotic Telescope Network, which includes optical telescopes spanning four continents, and now also Green Bank Observatory's 20-meter diameter radio telescope in West Virginia. Skynet serves hundreds of professional users, and additionally tens of thousands of students, of all ages. Default data products are generated on the fly, but will soon be customizable after the fact., Comment: 50 pages, 54 figures, 4 tables, accepted for publication in ApJS

We report deep Green Bank Telescope spectroscopy in the redshifted HI 21cm and OH 18cm lines from the $z = 0.765$ absorption system towards PMN J0134-0931. A comparison between the "satellite" OH 18cm line redshifts, or between the redshifts of the HI 21cm and "main" OH 18cm lines, is sensitive to changes in different combinations of three fundamental constants, the fine structure constant $\alpha$, the proton-electron mass ratio $\mu \equiv m_p/m_e$ and the proton g-factor $g_p$. We find that the satellite OH 18cm lines are not perfectly conjugate, with both different line shapes and stronger 1612 MHz absorption than 1720 MHz emission. This implies that the satellite lines of this absorber are not suitable to probe fundamental constant evolution. A comparison between the redshifts of the HI 21cm and OH 18cm lines, via a multi-Gaussian fit, yields the strong constraint $[\Delta F/F] = [-5.2 \pm 4.3] \times 10^{-6}$, where $F \equiv g_p [\mu \alpha^2]^{1.57}$ and the error budget includes contributions from both statistical and systematic errors. We thus find no evidence for a change in the constants between $z = 0.765$ and the present epoch. Incorporating the constraint $[\Delta \mu/\mu ] < 3.6 \times 10^{-7}$ from another absorber at a similar redshift and assuming that fractional changes in $g_p$ are much smaller than those in $\alpha$, we obtain $[\Delta \alpha/\alpha ] = (-1.7 \pm 1.4) \times 10^{-6}$ over a lookback time of 6.7 Gyrs., Comment: 5 pages, 4 figures; accepted for publication in Astrophysical Journal Letters

The 43m telescope at the NRAO site in Green Bank, WV has recently been outfitted with a clone of the Green Bank Ultimate Pulsar Processing Instrument (GUPPI \cite{Ransom:2009}) backend, making it very useful for a number of pulsar related studies in frequency ranges 800-1600 MHz and 220-440 MHz. Some of the recent science being done with it include: monitoring of the Crab pulsar, a blind search for transient sources, pulsar searches of targets of opportunity, and an all-sky mapping project. For the Crab monitoring project, regular observations are searched for giant pulses (GPs), which are then correlated with $\gamma$-ray photons from the \emph{Fermi} spacecraft. Data from the all-sky mapping project are first run through a pipeline that does a blind transient search, looking for single pulses over a DM range of 0-500 pc~cm$^{-3}$. These projects are made possible by MIT Lincoln Labs., Comment: 2 pages, 1 figure, to appear in AIP Conference Proceedings of Pulsar Conference 2010 "Radio Pulsars: a key to unlock the secrets of the Universe", Sardinia, October 2010

To constrain the giant pulse (GP) emission mechanism and test the model of Lyutikov (2007) for GP emission, we have carried out a campaign of simultaneous observations of the Crab pulsar at gamma-ray (Fermi) and radio (Green Bank Telescope) wavelengths. Over 10 hours of simultaneous observations we obtained a sample of 2.1x10^4 giant pulses, observed at a radio frequency of 9 GHz, and 77 Fermi photons, with energies between 100 MeV and 5 GeV. The majority of GPs came from the interpulse (IP) phase window. We found no change in the GP generation rate within 10-120 s windows at lags of up to +-40 min of observed gamma-ray photons. The 95% upper limit for a gamma-ray flux enhancement in pulsed emission phase window around all GPs is 4 times the average pulsed gamma-ray flux from the Crab. For the subset of IP GPs, the enhancement upper limit, within the IP emission window, is 12 times the average pulsed gamma-ray flux. These results suggest that GPs, at least high-frequency IP GPs, are due to changes in coherence of radio emission rather than an overall increase in the magnetospheric particle density., Comment: 9 pages, 6 figures; to appear in The Astrophysical Journal, February 2011

From a survey for redshifted HI 21-cm and OH 18-cm absorption in the hosts of a sample of radio galaxies and quasars, we detect HI in three of the ten and OH in none of the fourteen sources for which useful data were obtained. As expected from our recent result, all of the 21-cm detections occur in sources with ultra-violet continuum luminosities of L < 10^23 W/Hz. At these "moderate" luminosities, we also obtain four non-detections, although, as confirmed by the equipartition of detections between the type-1 and type-2 objects, this near-50% detection rate cannot be attributed to unified schemes of active galactic nuclei (AGN). All of our detections are at redshifts of z < 0.67, which, in conjunction with our faint source selection, biases against UV luminous objects. The importance of ultra-violet luminosity (over AGN type) in the detection of 21-cm is further supported by the non-detections in the two high redshift z ~ 3.6 - 3.8 radio galaxies, which are both type-2 objects, while having L > 10^23 W/Hz. Our 21-cm detections in combination with those previously published, give a total of eight (associated and intervening) HI absorbing sources searched and undetected in OH. Using the detected 21-cm line strengths to normalise the limits, we find that only two of these eight may have been searched sufficiently deeply in OH, although even these are marginal., Comment: 10 pages, submitted to MNRAS

To constrain the giant pulse (GP) emission mechanism and test the model of Lyutikov (2007) of GP emission, we are carrying out a campaign of simultaneous observations of the Crab pulsar between gamma-rays (Fermi) and radio wavelengths. The correlation between times of arrival of radio GPs and high-energy photons, whether it exists or not, will allow us to choose between different origins of GP emission and further constrain the emission physics. Our foremost goal was testing whether radio GPs are due to changes in the coherence of the radio emission mechanism, variations in the pair creation rate in the pulsar magnetosphere, or changes in the beaming direction. Accomplishing this goal requires an enormous number of simultaneous radio GPs and gamma-photons. Thus, we organized a radio observations campaign using the 42-ft telescope at the Jodrell Bank Observatory (UK), the 140-ft telescope, and the 100-m Robert C. Byrd Green Bank Telescope (GBT) at the Green Bank Observatory (WV). While the observations with the two first ones are ongoing, here we present the preliminary results of 20 hrs of observations with the GBT at the high frequency of 8.9 GHz. These particular observations were aimed to probe the model of GP emission by Lyutikov (2007) which predicts that GPs at frequencies > 4 GHz should be accompanied by gamma-ray photons of energies of 1-100 GeV., Comment: 2009 Fermi Symposium, eConf Proceedings C091122

We report the first attempt to observe the secondary eclipse of a transiting extra-solar planet at radio wavelengths. We observed HD 189733 b with the Robert C. Byrd Green Bank Telescope of the NRAO over about 5.5 hours before, during and after secondary eclipse, at frequencies of 307 - 347 MHz. In this frequency range, we determine the 3-sigma upper limit to the flux density to be 81 mJy. The data are consistent with no eclipse or a marginal reduction in flux at the time of secondary eclipse in all subsets of our bandwidth; the strongest signal is an apparent eclipse at the 2-sigma level in the 335.2 - 339.3 MHz region. Our observed upper limit is close to theoretical predictions of the flux density of cyclotron-maser radiation from the planet., Comment: 7 pages, 6 figures, accepted for publication in MNRAS

The $^{13}C$ substitutions of molecule $HC_7N$ were observed in TMC-1 using the J = 12 - 11, J = 13 - 12 rotational transitions in the frequency range 12.4 to 13.6 GHz. We present the first detection the $^{13}C$ isotopic species of $HC_7N$ in the interstellar medium, based on the average of a number of weak rotational transitions. This paper describes the calibration and data averaging process that is also used in a search for large cyanopolyyne molecules in TMC-1 using the 100m Robert C. Byrd Green Bank Telescope (GBT). The capabilities of the GBT 11 to 15 GHz observing system are described along with a discussion of numerical methods for averaging observations of a number of weak spectral lines to detect new interstellar molecules.

We have detected the four 18cm OH lines from the $z \sim 0.765$ gravitational lens toward PMN J0134-0931. The 1612 and 1720 MHz lines are in conjugate absorption and emission, providing a laboratory to test the evolution of fundamental constants over a large lookback time. We compare the HI and OH main line absorption redshifts of the different components in the $z \sim 0.765$ absorber and the $z \sim 0.685$ lens toward B0218+357 to place stringent constraints on changes in $F \equiv g_p [\alpha^2/\mu]^{1.57}$. We obtain $[\Delta F/F] = (0.44 \pm 0.36^{\rm stat} \pm 1.0^{\rm syst}) \times 10^{-5}$, consistent with no evolution over the redshift range $0 < z < 0.7$. The measurements have a $2 \sigma$ sensitivity of $[\Delta \alpha/\alpha] < 6.7 \times 10^{-6}$ or $[\Delta \mu/\mu] < 1.4 \times 10^{-5}$ to fractional changes in $\alpha$ and $\mu$ over a period of $\sim 6.5$ Gyr, half the age of the Universe. These are among the most sensitive current constraints on changes in $\mu$., Comment: 4 pages, 3 figures. Final version, with minor changes to match the version in print in Phys. Rev. Lett

We have measured a velocity dispersion for the foreground galaxy in this gravitationally lensed system. Our dispersion confirms the prediction from lens models, provided that the source is distant enough ($z_{_S}>0.2$). Current interpretations of lensing statistics depend sensitively on how the optical and mass dispersions are related. For $z_{_S}>0.5$, our observations favor $\sigma_{mass}/\sigma_{opt}\simeq1$, but our uncertainties prevent us from clearly distinguishing between dynamical models. We could not obtain a unique mass profile from lensing constraints, but models with a constant mass-to-light ratio are possible. We also found unusual rotation in the lensing galaxy, and confirmed its redshift., Comment: 11 pages, 6 PostScript figures, uses AAS LaTex style aaspp.sty, To appear in AJ (1996.05), Submitted 1995.09.22, Accepted 1996.01.17

VLA radio images of MG 1654+1346, a candidate for an Einstein Ring gravitational lens, reveal two components which are separated by about 7 arcsec. Two optical counterparts, a 19-mag galaxy coincident with the center of the radio ring and a blue 21-mag stellar object located about 3 arcsec northeast of the galaxy, are identified. A model representing the source as a quasar with two extended radio lobes and the lens as an elliptical potential at the position of the galaxy is found to reasonably reproduce the radio observations.

The discovery of extremely unusual structure in the radio source MG1131+0456 is reported. In a radio map with subsarcsecond resolution the object appears as an elliptical ring of emission accompanied by a pair of more compact sources, nearly diametrically opposed and offset by about 0.3 arcsec to the southwest of the ring. There is a faint, slightly extended, optical counterpart. A continuum but no emission lines is detected in its spectrum; therefore, the redshift of the counterpart is unknown. The radio morphology suggests that this source may be an example of an 'Einstein ring', a highly symmetric case of gravitational lensing in which the source is imaged into a ring. Other explanations are considered and excluded by the data. Another possibility is that MG1131+04565 represents a new type of astronomical object.