Search

Deep underground environments are ideal for low background searches due to the attenuation of cosmic rays by passage through the earth. However, they are affected by backgrounds from $\gamma$-rays emitted by $^{40}$K and the $^{238}$U and $^{232}$Th decay chains in the surrounding rock. The LUX-ZEPLIN (LZ) experiment will search for dark matter particle interactions with a liquid xenon TPC located within the Davis campus at the Sanford Underground Research Facility, Lead, South Dakota, at the 4,850-foot level. In order to characterise the cavern background, in-situ $\gamma$-ray measurements were taken with a sodium iodide detector in various locations and with lead shielding. The integral count rates (0--3300~keV) varied from 596~Hz to 1355~Hz for unshielded measurements, corresponding to a total flux in the cavern of $1.9\pm0.4$~$\gamma~$cm$^{-2}$s$^{-1}$. The resulting activity in the walls of the cavern can be characterised as $220\pm60$~Bq/kg of $^{40}$K, $29\pm15$~Bq/kg of $^{238}$U, and $13\pm3$~Bq/kg of $^{232}$Th., Comment: 11 pages, 9 figures

This paper presents data and analysis of SN 2010kd, a low-redshift ($z = 0.101$) H-deficient superluminous supernova (SLSN), based on ultraviolet/optical photometry and optical spectroscopy spanning between $-$28 and +194 days relative to $\mathit{B}$ band maximum light. The $\mathit{B}$ band light curve comparison of SN 2010kd with a subset of well-studied SLSNe I at comparable redshifts indicates that it is a slow-decaying PTF12dam like SLSN. Analytical light-curve modeling using the $\mathtt{Minim}$ code suggests that the bolometric light curve of SN 2010kd favors circumstellar matter interaction for the powering mechanism. $\mathtt{SYNAPPS}$ modeling of the early-phase spectra does not identify broad H or He lines, whereas the photospheric-phase spectra are dominated by O I, O II, C II, C IV and Si II, particularly, presence of both low and high-velocity components of O II and Si II lines. The nebular-phase spectra of SN 2010kd are dominated by O I and Ca II emission lines similar to those seen in other SLSNe I. The line velocities in SN 2010kd exhibit flatter evolution curves similar to SN 2015bn but with comparatively higher values. SN 2010kd shows a higher single-zone local thermodynamic equilibrium temperature in comparison to PTF12dam and SN 2015bn, and it has an upper O I ejected mass limit of $\sim 10~M_\odot$. The host of SN 2010kd is a dwarf galaxy with a high star-formation rate ($\sim 0.18 \pm 0.04~M_\odot$ yr$^{-1}$) and extreme emission lines., 26 pages, 16 figures, Accepted in ApJ, updated to match the accepted version

The LUX-ZEPLIN dark matter search aims to achieve a sensitivity to the WIMP-nucleon spin-independent cross-section down to (1--2)$\times10^{-12}$\,pb at a WIMP mass of 40 GeV/$c^2$. This paper describes the simulations framework that, along with radioactivity measurements, was used to support this projection, and also to provide mock data for validating reconstruction and analysis software. Of particular note are the event generators, which allow us to model the background radiation, and the detector response physics used in the production of raw signals, which can be converted into digitized waveforms similar to data from the operational detector. Inclusion of the detector response allows us to process simulated data using the same analysis routines as developed to process the experimental data., Comment: 24 pages, 19 figures; Corresponding Authors: A. Cottle, V. Kudryavtsev, D. Woodward

We present photometry, spectra, and spectropolarimetry of supernova (SN) 2012ab, mostly obtained over the course of $\sim 300$ days after discovery. SN 2012ab was a Type IIn (SN IIn) event discovered near the nucleus of spiral galaxy 2MASXJ12224762+0536247. While its light curve resembles that of SN 1998S, its spectral evolution does not. We see indications of CSM interaction in the strong intermediate-width emission features, the high luminosity (peak at absolute magnitude $M=-19.5$), and the lack of broad absorption features in the spectrum. The H$\alpha$ emission undergoes a peculiar transition. At early times it shows a broad blue emission wing out to $-14{,}000$ km $\mathrm{s^{-1}}$ and a truncated red wing. Then at late times ($>$ 100$\,$days) it shows a truncated blue wing and a very broad red emission wing out to roughly $+20{,}000$ km $\mathrm{s^{-1}}$. This late-time broad red wing probably arises in the reverse shock. Spectra also show an asymmetric intermediate-width H$\alpha$ component with stronger emission on the red side at late times. The evolution of the asymmetric profiles requires a density structure in the distant CSM that is highly aspherical. Our spectropolarimetric data also suggest asphericity with a strong continuum polarization of $\sim 1-3$% and depolarization in the H$\alpha$ line, indicating asphericity in the CSM at a level comparable to that in other SNe IIn. We estimate a mass-loss rate of $\dot{M} = 0.050\, {\rm M}_{\odot}\,\mathrm{yr^{-1}}$ for $v_{\rm pre} = 100$$\,$km$\,$$\mathrm{s^{-1}}$ extending back at least 75$\,$yr prior to the SN. The strong departure from axisymmetry in the CSM of SN 2012ab may suggest that the progenitor was an eccentric binary system undergoing eruptive mass loss., Comment: 18 pages, 12 figures

The LUX-ZEPLIN (LZ) experiment will search for dark matter particle interactions with a detector containing a total of 10 tonnes of liquid xenon within a double-vessel cryostat. The large mass and proximity of the cryostat to the active detector volume demand the use of material with extremely low intrinsic radioactivity. We report on the radioassay campaign conducted to identify suitable metals, the determination of factors limiting radiopure production, and the selection of titanium for construction of the LZ cryostat and other detector components. This titanium has been measured with activities of $^{238}$U$_{e}$~$, Comment: 13 pages, 3 figures, accepted for publication in Astroparticle Physics

We present the discovery of gamma-ray emission greater than 350 GeV from the BL Lacertae (BL Lac) object 1ES 2344 + 514 with the Whipple Observatory 10 m gamma-ray telescope. This is the third BL Lac object detected at very high energies (VHE, E > 300 GeV), the other two being Markarian 421 (Mrk 421) and Mrk 501. These three active galactic nuclei are all X-ray selected and have the lowest known redshifts of any BL Lac objects currently identified with declination greater than 0°. The evidence for emission from 1ES 2344 + 514 comes mostly from an apparent flare on 1995 December 20 (UT) during which a 6 σ excess was detected with an average flux of I(> 350 GeV) = 6.6 ± 1.9 × 10-11 photons cm-2 s-1. This is approximately 63% of the VHE emission from the Crab Nebula, the standard candle in this field. Observations taken between 1995 October and 1996 January, excluding the night of the flare, yield a 4 σ detection indicating a flux level of I(> 350 GeV) = 1.1 ± 0.4 × 10-11 photons cm-2 s-1, or about 11% of the VHE Crab Nebula flux. Observations taken between 1996 September and 1997 January on this object did not yield a significant detection of a steady flux or any evidence of flaring activity. The 99.9% confidence level upper limit from these observations is I(> 350 GeV) < 8.2 × 10-12 photons cm-2 s-1, ≲8% of the Crab Nebula flux. The low baseline emission level and variation in the nightly and yearly flux of 1ES 2344 + 514 are the same as the VHE emission characteristics of Mrk 421 and Mrk 501.

We present a search, using the Murchison Widefield Array (MWA), for electromagnetic (EM) counterparts to two candidate high-energy neutrino events detected by the ANTARES neutrino telescope in 2013 November and 2014 March. These events were selected by ANTARES because they are consistent, within 0 degrees.4, with the locations of galaxies within 20 Mpc of Earth. Using MWA archival data at frequencies between 118 and 182 MHz, taken similar to 20. days prior to, at the same time as, and up to a year after the neutrino triggers, we look for transient or strongly variable radio sources that are consistent with the neutrino positions. No such counterparts are detected, and we set a 5 sigma upper limit for low-frequency radio emission of similar to 10(37) erg s(-1) for progenitors at 20 Mpc. If the neutrino sources are instead not in nearby galaxies, but originate in binary neutron star coalescences, our limits place the progenitors at z greater than or similar to 0.2. While it is possible, due to the high background from atmospheric neutrinos, that neither event is astrophysical, the MWA observations are nevertheless among the first to follow up neutrino candidates in the radio, and illustrate the promise of wide-field instruments like MWA for detecting EM counterparts to such events., This scientific work makes use of the Murchison Radioastronomy Observatory, operated by CSIRO. We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site. Support for the operation of the MWA is provided by the Australian Government Department of Industry and Science and Department of Education (National Collaborative Research Infrastructure Strategy: NCRIS), under a contract with Curtin University, administered by Astronomy Australia Limited. We acknowledge the iVEC Petabyte Data Store and the Initiative in Innovative Computing and the CUDA Center for Excellence sponsored by NVIDIA at Harvard University. D.L.K. and S.D.C. acknowledge support from the US National Science Foundation (grant AST-1412421). We acknowledge the financial support of the funding agencies: Centre National de la Recherche Scientifique (CNRS), Commissariat a l'enegie atomique et aux energies alternatives (CEA), Commission Europeenne (FEDER fund and Marie Curie Program), Region Ile-de-France (DIM-ACAV), Region Alsace (contrat CPER), Region Provence-Alpes-Cote d'Azur, Departement du Var and Ville de La Seyne-sur-Mer, France; Bundesministerium fur Bildung und Forschung (BMBF), Germany; Istituto Nazionale di Fisica Nucleare (INFN), Italy; Stichting voor Fundamenteel Onderzoek der Materie (FOM), Nederlandse organisatie voor Wetenschappelijk Onderzoek (NWO), the Netherlands; Council of the President of the Russian Federation for Young Scientists and Leading Scientific Schools Supporting Grants, Russia; National Authority for Scientific Research (ANCS), Romania; Ministerio de Ciencia e Innovacion (MICINN), Prometeo of Generalitat Valenciana and MultiDark, Spain; Agence de l'Oriental and CNRST, Morocco. We also acknowledge the technical support of Ifremer, AIM, and Foselev Marine for the sea operation and the CC-IN2P3 for the computing facilities. We gratefully acknowledge financial support from the OCEVU LabEx, France. We thank Nathan Whitehorn and the anonymous referee for helpful comments.

We present broadband multi-wavelength observations of GRB 080310 at redshift z = 2.43. This burst was bright and long-lived, and unusual in having extensive optical and near IR follow-up during the prompt phase. Using these data we attempt to simultaneously model the gamma-ray, X-ray, optical and IR emission using a series of prompt pulses and an afterglow component. Initial attempts to extrapolate the high energy model directly to lower energies for each pulse reveal that a spectral break is required between the optical regime and 0.3 keV to avoid over predicting the optical flux. We demonstrate that afterglow emission alone is insufficient to describe all morphology seen in the optical and IR data. Allowing the prompt component to dominate the early-time optical and IR and permitting each pulse to have an independent low energy spectral indices we produce an alternative scenario which better describes the optical light curve. This, however, does not describe the spectral shape of GRB 080310 at early times. The fit statistics for the prompt and afterglow dominated models are nearly identical making it difficult to favour either. However one enduring result is that both models require a low energy spectral index consistent with self absorption for at least some of the pulses identified in the high energy emission model.

SN 2007if was the third over-luminous SN Ia detected after 2003fg and 2006gz. We present the photometric and spectroscopic observations of the supernova and its host by ROTSE-III, HET and Keck. From the H_alpha line identified in the host spectra, we determine a redshift of 0.0736. At this distance, the supernova reached an absolute magnitude of -20.4, brighter than any other SNe Ia ever observed. If the source of luminosity is radioactive decay, a large amount of radioactive nickel (~1.5 solar masses) is required to power the peak luminosity, more than can be produced realistically in a Chandrasekhar mass progenitor. Low expansion velocity, similar to that of 2003fg, is also measured around the maximum light. The observations may suggest that SN 2007if was from a massive white dwarf progenitor, plausibly exploding with mass well beyond 1.4 solar masses. Alternatively, we investigate circumstellar interaction that may contribute to the excess luminosity., 7 pages, 7 figures, accepted for publication in ApJ

WOS: 000269244500040, We report on a complete set of early optical afterglows of gamma-ray bursts (GRBs) obtained with the Robotic Optical Transient Search Experiment (ROTSE-III) telescope network from 2005 March through 2007 June. This set is comprised of 12 afterglows with early optical and Swift/X-Ray Telescope observations, with a median ROTSE-III response time of 45 s after the start of gamma-ray emission (8 s after the GCN notice time). These afterglows span 4 orders of magnitude in optical luminosity, and the contemporaneous X-ray detections allow multi-wavelength spectral analysis. Excluding X-ray flares, the broadband synchrotron spectra show that the optical and X-ray emission originate in a common region, consistent with predictions of the external forward shock in the fireball model. However, the fireball model is inadequate to predict the temporal decay indices of the early afterglows, even after accounting for possible long-duration continuous energy injection. We find that the optical afterglow is a clean tracer of the forward shock, and we use the peak time of the forward shock to estimate the initial bulk Lorentz factor of the GRB outflow, and find 100 less than or similar to Gamma(0) less than or similar to 1000, consistent with expectations., NASA [NNG-04WC41G, NNG-06GI90G, NNX-07AF02G]; NSF [AST-0407061, PHY-0801007, AST-0335588, AST-0707769]; Australian Research Council's Discovery Projects; University of New South Wales; University of Texas; University of Michigan; Michigan Space Grant Consortium, E. S. R. thanks the TABASGO foundation. This work has been supported by NASA grant NNG-04WC41G, NSF grants AST-0407061 and PHY-0801007, the Australian Research Council's Discovery Projects funding scheme, the University of New South Wales, the University of Texas, and the University of Michigan. H. A. F. has been supported by NSF grant AST-0335588 and by the Michigan Space Grant Consortium. F. Y. has been supported under NASA Swift Guest Investigator grants NNG-06GI90G and NNX-07AF02G. J.C.W. is supported in part by NSF grant AST-0707769. Special thanks to David Doss at McDonald Observatory, Toni Hanke at the H. E. S. S. site, and Tuncay Ozisik at TUG.

HET optical spectroscopy and unfiltered ROTSE-III photometry spanning the first 11 months since explosion of the Type II-P SN 2006bp are presented. Flux limits from the days before discovery combined with the initial rapid brightening suggest the supernova was first detected just hours after shock breakout. Optical spectra obtained about 2 days after breakout exhibit narrow emission lines corresponding to HeII 4200, HeII 4686, and CIV 5805 in the rest frame, and these features persist in a second observation obtained 5 hours later; however, these emission lines are not detected the following night nor in subsequent observations. We suggest that these lines emanate from material close to the explosion site, possibly in the outer layers of the progenitor that have been ionized by the high energy photons released at shock breakout. A P-Cygni profile is observed around 4450 A in the +2 and +3 day spectra. Previous studies have attributed this feature to high velocity H-beta, but we discuss the possibility that this profile is instead due to HeII 4687. Further HET observations (14 nights in total) covering the spectral evolution across the photometric plateau up to 73 days after breakout and during the nebular phase around day +340 are presented, and expansion velocities are derived for key features. The measured decay slope for the unfiltered light curve is 0.0073 +/- 0.0004 mag/day between days +121 and +335, which is significantly slower than the decay of rate 56Co. We combine our HET measurements with published X-ray, UV, and optical data to obtain a quasi-bolometric light curve through day +60. We see a slow cooling over the first 25 days, but no sign of an early sharp peak; any such feature from the shock breakout must have lasted less than ~1 day.[ABRIDGED], ApJ accepted, 43 pages

We report on follow-up observations of the GRB 060927 using the ROTSE-IIIa telescope and a suite of larger aperture ground-based telescopes. An optical afterglow was detected 20 s after the burst, the earliest rest-frame detection of optical emission from any GRB. Spectroscopy performed with the VLT about 13 hours after the trigger shows a continuum break at lambda ~ 8070 A produced by neutral hydrogen absorption at z~5.6. We also detect an absorption line at 8158 A which we interpret as SiII at z=5.467. Hence, GRB 060927 is the second most distant GRB with a spectroscopically measured redshift. The shape of the red wing of the spectral break can be fitted by a damped Lyalpha profile with a column density with log(N_HI/cm^-2) ~ 22.5. We discuss the implications of this work for the use of GRBs as probes of the end of the dark ages and draw three main conclusions: i) GRB afterglows originating from z>6 should be relatively easy to detect from the ground, but rapid NIR monitoring is necessary to ensure that they are found; ii) The presence of large HI column densities in some GRBs host galaxies at z>5 makes the use of GRBs to probe the reionization epoch via spectroscopy of the red damping wing challenging; iii) GRBs appear crucial to locate typical star-forming galaxies at z>5 and therefore the type of galaxies responsible for the reionization of the universe., 15 pages, 6 figures, 2 tables, accepted for publication in ApJ, uses emulateapj

We present the unfiltered ROTSE-III light curve of the optical transient associated with GRB 050319 beginning 4 s after the cessation of gamma-ray activity. We fit a power-law function to the data using the revised trigger time given by Chincarini et al. (2005), and a smoothly broken power-law to the data using the original trigger disseminated through the GCN notices. Including the RAPTOR data from Wozniak et al. (2005), the best fit power-law indices are alpha=-0.854 (+/- 0.014) for the single power-law and alpha_1=-0.364 (+/- 0.020), alpha_2= -0.881 (+/- 0.030), with a break at t_b = 418 (+/- 30) s for the smoothly broken fit. We discuss the fit results with emphasis placed on the importance of knowing the true start time of the optical transient for this multi-peaked burst. As Swift continues to provide prompt GRB locations, it becomes more important to answer the question, "when does the afterglow begin" to correctly interpret the light curves., 14 pages including 2 figures; Accepted for publication in ApJ

We present the results of a search for untriggered gamma-ray burst (GRB) afterglows with the Robotic Optical Transient Search Experiment-III (ROTSE-III) telescope array. This search covers observations from September 2003 to March 2005. We have an effective coverage of 1.74 deg^2 yr for rapidly fading transients that remain brighter than ~ 17.5 magnitude for more than 30 minutes. This search is the first large area survey to be able to detect typical untriggered GRB afterglows. Our background rate is very low and purely astrophysical. We have found 4 previously unknown cataclysmic variables (CVs) and 1 new flare star. We have not detected any candidate afterglow events or other unidentified transients. We can place an upper limit on the rate of fading optical transients with quiescent counterparts dimmer than ~ 20th magnitude at a rate of less than 1.9 deg^-2 yr-1 with 95% confidence. This places limits on the optical characteristics of off-axis (orphan) GRB afterglows. As a byproduct of this search, we have an effective ~ 52 deg^2 yr of coverage for very slowly decaying transients, such as CVs. This implies an overall rate of outbursts from high galactic latitude CVs of 0.1 deg^2 yr^-1., Seven pages, five figures, uses emulateapj class file. Accepted to Astrophysical Journal

The Northern Sky Variability Survey (NSVS) is a temporal record of the sky over the optical magnitude range from 8 to 15.5. It was conducted in the course of the first generation Robotic Optical Transient Search Experiment (ROTSE-I) using a robotic system of four co-mounted unfiltered telephoto lenses equipped with CCD cameras. The survey was conducted from Los Alamos, NM, and primarily covers the entire northern sky. Some data in southern fields between declinations 0 and -38 deg is also available, although with fewer epochs and noticeably lesser quality. The NSVS contains light curves for approximately 14 million objects. With a one year baseline and typically 100-500 measurements per object, the NSVS is the most extensive record of stellar variability across the bright sky available today. In a median field, bright unsaturated stars attain a point to point photometric scatter of ~0.02 mag and position errors within 2 arcsec. At Galactic latitudes |b| < 20 deg the data quality is limited by severe blending due to ~14 arcsec pixel size. We present basic characteristics of the data set and describe data collection, analysis, and distribution. All NSVS photometric measurements are available for on-line public access from the Sky Database for Objects in Time-Domain (SkyDOT; http://skydot.lanl.gov) at LANL. Copies of the full survey photometry may also be requested on tape., accepted for publication in Astronomical Journal

The ROTSE-IIIa telescope and the SSO-40 inch telescope, both located at Siding Spring Observatory, imaged the early time afterglow of GRB 030418. In this report we present observations of the early afterglow, first detected by the ROTSE-IIIa telescope 211 s after the start of the burst, and only 76 s after the end of the gamma-ray activity. We detect optical emission that rises for ~600 s, slowly varies around R=17.3 mag for ~1400 s, and then fades as a power law of index alpha=-1.36. Additionally, the ROTSE-IIIb telescope, located at McDonald Observatory, imaged the early time afterglow of GRB 030723. The behavior of this light curve was qualitatively similar to that of GRB 030418, but two magnitudes dimmer. These two afterglows are dissimilar to other afterglows such as GRB 990123 and GRB 021211. We investigate whether the early afterglow can be attributed to a synchrotron break in a cooling synchrotron spectrum as it passes through the optical band, but find this model is unable to accurately describe the early light curve. We present a simple model for gamma-ray burst emission emerging from a wind medium surrounding a massive progenitor star. This model provides an effective description of the data, and suggests that the rise of the afterglow can be ascribed to extinction in the local circumburst environment. In this interpretation, these events provide further evidence for the connection between gamma-ray bursts and the collapse of massive stars., Comment: Five pages, four figures, uses emulateapj class file. Accepted to Astrophysical Journal Letters

The observation of a prompt optical flash from GRB990123 convincingly demonstrated the value of autonomous robotic telescope systems. Pursuing a program of rapid follow-up observations of gamma-ray bursts, the Robotic Optical Transient Search Experiment (ROTSE) has developed a next-generation instrument, ROTSE-III, that will continue the search for fast optical transients. The entire system was designed as an economical robotic facility to be installed at remote sites throughout the world. There are seven major system components: optics, optical tube assembly, CCD camera, telescope mount, enclosure, environmental sensing & protection and data acquisition. Each is described in turn in the hope that the techniques developed here will be useful in similar contexts elsewhere., 19 pages, including 4 figures. To be published in PASP in January, 2003. PASP Number IP02-110

We present extensive optical ($UBVRI$, $g'r'i'z'$, and open CCD) and near-infrared ($ZYJH$) photometry for the very nearby Type IIP SN ~2013ej extending from +1 to +461 days after shock breakout, estimated to be MJD $56496.9\pm0.3$. Substantial time series ultraviolet and optical spectroscopy obtained from +8 to +135 days are also presented. Considering well-observed SNe IIP from the literature, we derive $UBVRIJHK$ bolometric calibrations from $UBVRI$ and unfiltered measurements that potentially reach 2\% precision with a $B-V$ color-dependent correction. We observe moderately strong Si II $\lambda6355$ as early as +8 days. The photospheric velocity ($v_{\rm ph}$) is determined by modeling the spectra in the vicinity of Fe II $\lambda5169$ whenever observed, and interpolating at photometric epochs based on a semianalytic method. This gives $v_{\rm ph} = 4500\pm500$ km s$^{-1}$ at +50 days. We also observe spectral homogeneity of ultraviolet spectra at +10--12 days for SNe IIP, while variations are evident a week after explosion. Using the expanding photosphere method, from combined analysis of SN 2013ej and SN 2002ap, we estimate the distance to the host galaxy to be $9.0_{-0.6}^{+0.4}$ Mpc, consistent with distance estimates from other methods. Photometric and spectroscopic analysis during the plateau phase, which we estimated to be $94\pm7$ days long, yields an explosion energy of $0.9\pm0.3\times10^{51}$ ergs, a final pre-explosion progenitor mass of $15.2\pm4.2$~M$_\odot$ and a radius of $250\pm70$~R$_\odot$. We observe a broken exponential profile beyond +120 days, with a break point at +$183\pm16$ days. Measurements beyond this break time yield a $^{56}$Ni mass of $0.013\pm0.001$~M$_\odot$., Comment: 29 pages, 23 figures, 15 tables, Published in The Astrophisical Journal

The X-ray nova XTE J1118+480 exhibited two outbursts in the early part of 2000. As detected by the Rossi X-Ray Timing Explorer (RXTE), the first outburst began in early January and the second began in early March. Routine imaging of the northern sky by the Robotic Optical Transient Search Experiment (ROTSE) shows the optical counterpart to XTE J1118+480 during both outbursts. These data include over 60 epochs from January to June 2000. A search of the ROTSE data archives reveal no previous optical outbursts of this source in selected data between 1998 April and 2000 January. While the X-ray-to-optical flux ratio of XTE J1118+480 was low during both outbursts, we suggest that they were full X-ray novae and not minioutbursts based on comparison with similar sources. The ROTSE measurements taken during the 2000 March outburst also indicate a rapid rise in the optical flux that preceded the X-ray emission measured by the RXTE by approximately 10 days. Using these results, we estimate a preoutburst accretion disk inner truncation radius of ~1.2 × 104 Schwarzschild radii.

Gamma-ray bursts of short duration may harbor vital clues to the range of phenomena producing bursts. However, recent progress from the observation of optical counterparts has not benefitted the study of short bursts. We have searched for early optical emission from six gamma-ray bursts using the ROTSE-I telephoto array. Three of these events were of short duration, including GRB 980527 which is among the brightest short bursts yet observed. The data consist of unfiltered CCD optical images taken in response to BATSE triggers delivered via the GCN. For the first time, we have analyzed the entire 16 degree by 16 degree field covered for five of these bursts. In addition, we discuss a search for the optical counterpart to GRB 000201, a well-localized long burst. Single image sensitivities range from 13th to 14th magnitude around 10 s after the initial burst detection, and 14 - 15.8 one hour later. No new optical counterparts were discovered in this analysis suggesting short burst optical and gamma-ray fluxes are uncorrelated., 8 pages, 2 figures, subm. to ApJ Lett

In order to observe nearly simultaneous emission from gamma-ray bursts (GRBs), the Robotic Optical Transient Search Experiment (ROTSE) receives triggers via the GRB Coordinates Network (GCN). Since beginning operations in 1998 March, ROTSE has also taken useful data for 10 SGR events: eight from SGR 1900+14 and two from SGR 1806-20. We have searched for new or variable sources in the error regions of these SGRs, and no optical counterparts were observed. Limits are in the range mROTSE ≈ 12.5-15.5 during the period 20 s to 1 hr after the observed SGR events.

Observations of photons at E ≥ 550 GeV from the Crab Nebula are presented and used to assess the potential of multi-telescope systems for γ-ray astronomy. The Whipple observatory 10 m and 8 m imaging atmospheric Cerenkov telescopes have been used to provide a stereoscopic view of air showers to make a more complete measurement of air shower parameters. Here we present a measurement of the spread in the arrival direction of primary γ-rays originating from a point source. The data show that the shower arrival direction can be reconstructed with an accuracy of σ = 0.°14.

Although atmospheric Cherenkov telescopes have restricted fields of view, their fluence sensitivity warrants a search for gamma-ray burst phenomena. A search for 400 GeV gamma-ray bursts on a 1 s time-scale using archival data taken between 1988 and 1992 with the Whipple Collaboration 10 m reflector is presented. No evidence of such bursts is found. Bursts of TeV gamma rays have been predicted from exotic astrophysical objects such as Primordial Black Holes and Cosmic Strings. An upper limit to the number density of exploding PBH of 3.0±1.0×10 6 pc −3 yr −1 is calculated.

We report on observations of Mrk 421 and Mrk 501 at E γ >300 GeV during the 1995 and 1996 seasons. A multiwavelength observing campaign on Mrk 421 in the period 1995 April 20 to May 5 indicates correlations in the γ-ray, X-ray, extreme ultraviolet, and optical wavelengths. Dramatic outbursts of TeV γ-rays were detected on two occasions in May of 1996 where the γ-ray flux reached the highest levels ever recorded (a factor of ∼20 greater than typical levels) with variability timescales ≲1hr. Together with the multiwavelength correlations these provide serious constraints on the Doppler factor ( δ ≳ 9.9), the size and location of the emission region ( R ≲ 10 −4 pc) and the mechanism responsible for the γ-ray emission.

We present the gamma-ray spectrum of the BL Lacertae object, Markarian 421, above 500 GeV during its most intense recorded TeV flare, on 1996 May 7. The spectrum is well fitted by a power law with an exponent of 22.5650.0750.1 (statistical and systematic errors). The spectrum extends above 5 TeV with no evidence for a cutoff, favoring determinations of the extragalactic infrared energy density that do not produce a sharp cutoff at these energies.

The Gamma-Ray Optical Counterpart Search Experiment (GROCSE) has searched for contemporaneous optical counterparts to gamma-ray bursts (GRBs) using an automated rapidly slewing wide field of view optical telescope at Lawrence Livermore National Laboratory. The telescope was triggered in real time by the Burst and Transient Source Experiment (BATSE) data telemetry stream as processed and distributed by the BATSE COordinates DIstribution NEtwork (BACODINE). GROCSE recorded sky images for 28 GRB triggers between 1994 January and 1996 June. The analysis of the 12 best events is presented here, half of which were recorded during detectable gamma-ray emission. No optical counterparts have been detected to limiting magnitudes mV ≤ 8.5 despite nearly complete coverage of burst error boxes.

We present evidence for the first detection of gamma rays from the extragalactic object BL Lacertae. Observations taken with EGRET on the Compton Gamma Ray Observatory between 1995 January 24 and 1995 February 14 indicate a 4.4 σ excess from the direction of BL Lacertae. The corresponding flux is (40 ± 12) × 10-8 photons cm-2 s-1 above 100 MeV. The combination of all previous observations where BL Lacertae was in EGRET's field of view result in a 2.4 σ excess and a corresponding 95% confidence upper limit of 14 × 10-8 photons cm-2 s-1, indicating that its gamma-ray emission is variable, at least on timescales of several months. Observations of BL Lacertae between 22 and 375 GHz were also taken between 1995 January 24 and 1995 February 14, and the flux levels for those measurements are similar to the historical average values for this object. A deep exposure on BL Lacertae with the Whipple Observatory 10 m gamma-ray telescope shows no evidence of emission above 350 GeV during a period 9 months after the EGRET observations. The 99.9% confidence flux upper limit derived from these observations is 0.53 × 10-11 photons cm-2 s-1, which implies a large reduction in the gamma-ray emission of BL Lacertae between EGRET and Whipple Observatory energies. This reduction should result from processes intrinsic to BL Lacertae because it is near enough to Earth that intergalactic background IR fields should not significantly reduce the flux of gamma rays to which the Whipple Observatory telescope is sensitive.

A hybrid version of the Whipple Observatory's atmospheric Cherenkov imaging camera that permits observation during periods of bright moonlight is described. The hybrid camera combines a blue-light blocking filter with the standard Whipple imaging camera to reduce sensitivity to wavelengths greater than 360 nm. Data taken with this camera are found to be free from the effects of the moonlit night-sky after the application of simple off-line noise filtering. This camera has been used to successfully detect TeV gamma rays, in bright moon light, from both the Crab Nebula and the active galactic nucleus Markarian 421 at the 4.9σ and 3.9σ levels of statistical significance, respectively. The energy threshold of the camera is estimated to be 1.1 ( +0.6 −0.3 ) TeV from Monte Carlo simulations.

We calculate the volumetric rate of superluminous supernovae (SLSNe) based on 5 events discovered with the ROTSE-IIIb telescope. We gather light curves of 19 events from the literature and our own unpublished data and employ crude k-corrections to constrain the pseudo-absolute magnitude distributions in the rest frame ROTSE-IIIb (unfiltered) band pass for both the hydrogen poor (SLSN-I) and hydrogen rich (SLSN-II) populations. We find that the peak magnitudes of the available SLSN-I are narrowly distributed ($M = -21.7 \pm 0.4$) in our unfiltered band pass and may suggest an even tighter intrinsic distribution when the effects of dust are considered, although the sample may be skewed by selection and publication biases. The presence of OII features near maximum light may uniquely signal a high luminosity event, and we suggest further observational and theoretical work is warranted to assess the possible utility of such SN 2005ap-like SLSN-I as distance indicators. Using the pseudo-absolute magnitude distributions derived from the light curve sample, we measure the SLSN-I rate to be about (32^{+77}_{-26}) events Gpc^{-3} yr^{-1} h_{71}^{3} at a weighted redshift of z = 0.17, and the SLSN-II rate to be about (151^{+151}_{-82}) events Gpc^{-3} yr^{-1} h_{71}^{3} at z = 0.15. Given that the exact nature and limits of these populations are still unknown, we discuss how it may be difficult to distinguish these rare SLSNe from other transient phenomena such as AGN activity and tidal disruption events even when multi-band photometry, spectroscopy, or even high resolution imaging are available. Including one spectroscopically peculiar event, we determine a total rate for SLSN-like events of (199^{+137}_{-86}) events Gpc^{-3} yr^{-1} h_{71}^{3} at z = 0.16., 12 pages; MNRAS Accepted

We report on the γ-ray variability of Mrk 421 at Eγ > 300 GeV during the 1995 season, and concentrate on the results of an intense multiwavelength observing campaign in the period April 20 to May 5, which included >100 MeV γ-ray, X-ray, extreme-ultraviolet, optical, and radio observations, some of which show evidence for correlated behavior. Rapid variations in the TeV γ-ray light curve with doubling and decay times of 1 day require a compact emission region and significant Doppler boosting. The TeV data reveal that the γ-ray emission is best characterized by a succession of rapid flares with a relatively low baseline level of steady emission.

We present a sample of 23 spectroscopically confirmed Type Ia supernovae that were discovered in the background of galaxy clusters targeted by ROTSE-IIIb and use up to 18 of these to determine the local (z = 0.05) volumetric rate. Since our survey is flux limited and thus biased against fainter objects, the pseudo-absolute magnitude distribution (pAMD) of SNeIa in a given volume is an important concern, especially the relative frequency of high to low-luminosity SNeIa. We find that the pAMD derived from the volume limited Lick Observatory Supernova Search (LOSS) sample is incompatible with the distribution of SNeIa in a volume limited (z -16) galaxies, whereas only 1 out 79 nearby SDSS-II SNeIa have such faint hosts. It is possible that previous works have under-counted either low luminosity SNeIa, SNeIa in low luminosity hosts, or peculiar SNeIa (sometimes explicitly), and the total SNeIa rate may be higher than the canonical value., 18 pages; accepted for publication in The Astronomical Journal

We present the study on GRB 071112C X-ray and optical light curves. In these two wavelength ranges, we have found different temporal properties. The R-band light curve showed an initial rise followed by a single power-law decay, while the X-ray light curve was described by a single power-law decay plus a flare-like feature. Our analysis shows that the observed temporal evolution cannot be described by the external shock model in which the X-ray and optical emission are produced by the same emission mechanism. No significant color changes in multi-band light curves and a reasonable value of the initial Lorentz factor ({\Gamma}0 = 275 \pm 20) in a uniform ISM support the afterglow onset scenario as the correct interpretation for the early R-band rise. The result suggests the optical flux is dominated by afterglow. Our further investigations show that the X-ray flux could be created by an additional feature related to energy injection and X-ray afterglow. Different theoretical interpretations indicate the additional feature in X-ray can be explained by either late internal dissipation or local inverse-Compton scattering in the external shock., Comment: 20 pages, 3 figures, accepted for publication in ApJ

Electromagnetic (EM) observations of gravitational-wave (GW) sources would bring unique insights into a source which are not available from either channel alone. However EM follow-up of GW events presents new challenges. GW events will have large sky error regions, on the order of 10-100 square degrees, which can be made up of many disjoint patches. When searching such large areas there is potential contamination by EM transients unrelated to the GW event. Furthermore, the characteristics of possible EM counterparts to GW events are also uncertain. It is therefore desirable to be able to assess the statistical significance of a candidate EM counterpart, which can only be done by performing background studies of large data sets. Current image processing pipelines such as that used by ROTSE are not usually optimised for large-scale processing. We have automated the ROTSE image analysis, and supplemented it with a post-processing unit for candidate validation and classification. We also propose a simple ad hoc statistic for ranking candidates as more likely to be associated with the GW trigger. We demonstrate the performance of the automated pipeline and ranking statistic using archival ROTSE data. EM candidates from a randomly selected set of images are compared to a background estimated from the analysis of 102 additional sets of archival images. The pipeline's detection efficiency is computed empirically by re-analysis of the images after adding simulated optical transients that follow typical light curves for gamma-ray burst afterglows and kilonovae. We show that the automated pipeline rejects most background events and is sensitive to simulated transients to limiting magnitudes consistent with the limiting magnitude of the images.

We present optical photometric and low-resolution spectroscopic observations of the Type II plateau supernova (SN) 2008in, which occurred in the outskirts of the nearly face-on spiral galaxy M 61. Photometric data in the X-rays, ultraviolet and near-infrared bands have been used to characterize this event. The SN field was imaged with the ROTSE-IIIb optical telescope about seven days before the explosion. This allowed us to constrain the epoch of the shock breakout to JD = 2454825.6. The duration of the plateau phase, as derived from the photometric monitoring, was ~ 98 days. The spectra of SN 2008in show a striking resemblance to those of the archetypal low-luminosity IIP SNe 1997D and 1999br. A comparison of ejecta kinematics of SN 2008in with the hydrodynamical simulations of Type IIP SNe by Dessart et al. (2010) indicates that it is a less energetic event (~ 5$\times10^{50}$ erg). However, the light curve indicates that the production of radioactive $^{56}$Ni is significantly higher than that in the low-luminosity SNe. Adopting an interstellar absorption along the SN direction of $A_V$ ~ 0.3 mag and a distance of 13.2 Mpc, we estimated a synthesized Ni mass of ~ 0.015 $M_{\odot}$. Employing semi-analytical formulae (Litvinova & Nadezhin 1985), we derived a pre-SN radius of ~ 126$R_{\odot}$, an explosion energy of ~ 5.4$\times10^{50}$ erg and a total ejected mass of ~ 16.7$M_{\odot}$. The latter indicates that the zero age main-sequence mass of the progenitor did not exceed 20$M_{\odot}$. Considering the above properties of SN 2008in, and its occurrence in a region of sub-solar metallicity ([O/H] ~ 8.44 dex), it is unlikely that fall-back of the ejecta onto a newly formed black hole occurred in SN 2008in. We therefore favor a low-energy explosion scenario of a relatively compact, moderate-mass progenitor star that generates a neutron star., Accepted for publication in the Astrophysical Journal

WOS: 000274848100054, We present a multi-wavelength study of GRB 081008, at redshift 1.967, by Swift, ROTSE-III, and Gamma-Ray Burst Optical/NearInfrared Detector. Compared to other Swift GRBs, GRB 081008 has a typical gamma-ray isotropic equivalent energy output (similar to 10(53) erg) during the prompt phase, and displayed two temporally separated clusters of pulses. The early X-ray emission seen by the Swift X-Ray Telescope was dominated by the softening tail of the prompt emission, producing multiple flares during and after the Swift Burst Alert Telescope detections. Optical observations that started shortly after the first active phase of gamma-ray emission showed two consecutive peaks. We interpret the first optical peak as the onset of the afterglow associated with the early burst activities. A second optical peak, coincident with the later gamma-ray pulses, imposes a small modification to the otherwise smooth light curve and thus suggests a minimal contribution from a probable internal component. We suggest the early optical variability may be from continuous energy injection into the forward shock front by later shells producing the second epoch of burst activities. These early observations thus provide a potential probe for the transition from the prompt phase to the afterglow phase. The later light curve of GRB 081008 displays a smooth steepening in all optical bands and X-ray. The temporal break is consistent with being achromatic at the observed wavelengths. Our broad energy coverage shortly after the break constrains a spectral break within optical. However, the evolution of the break frequency is not observed. We discuss the plausible interpretations of this behavior., NASA [NNX-08AN25G, NAS5-00136, NNX-08AV63G, PHY-0801007]; STFC; DFG; Australian Research Council; University of New South Wales; University of Texas; University of Michigan; Leibniz-Prize [HA 1850/28-1]; Science and Technology Facilities Council [ST/H001972/1], F.Y. gratefully acknowledges useful discussions with S. B. Pandey. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. F. Y. is supported by the NASA Swift Guest Investigator grants NNX-08AN25G. J.L.R. acknowledges support for this work from NASA contract NAS5-00136. R. W. and P.T.O. gratefully acknowledge funding from the STFC for Swift at the University of Leicester. T. K. acknowledges support by the DFG cluster of excellence "Origin and Structure of the Universe." ROTSE-III has been supported by NASA grant NNX-08AV63G, NSF grant PHY-0801007, the Australian Research Council, the University of New South Wales, the University of Texas, and the University of Michigan. Special thanks to the H. E. S. S. staff, especially Toni Hanke. Part of the funding for GROND (both hardware as well as personnel) was generously granted from the Leibniz-Prize (DFG grant HA 1850/28-1) to Professor G. Hasinger (IPP).

From the launch of the Fermi Gamma-ray Space Telescope to July 9, 2010, the Gamma-ray Burst Monitor (GBM) has detected 497 probable GRB events. Twenty-two of these satisfy the simultaneous requirements of an estimated burst direction within 52^\circ of the Fermi Large Area Telescope (LAT) boresight and a low energy fluence exceeding 5 $\mu$erg/cm^2. Using matched filter techniques, the spatially correlated Fermi/LAT photon data above 100 MeV have been examined for evidence of bursts that have so far evaded detection at these energies. High energy emission is detected with great confidence for one event, GRB 090228A. Since the LAT has significantly better angular resolution than the GBM, real-time application of these methods could open the door to optical identification and richer characterization of a larger fraction of the relatively rare GRBs that include high energy emission., Comment: 4 pages, 3 figures, 2 tables, accepted for publication in ApJ Letters, minor revisions

We report the discovery by the Robotic Optical Transient Experiment (ROTSE-IIIb) telescope of SN 2008es, an overluminous supernova (SN) at z=0.205 with a peak visual magnitude of -22.2. We present multiwavelength follow-up observations with the Swift satellite and several ground-based optical telescopes. The ROTSE-IIIb observations constrain the time of explosion to be 23+/-1 rest-frame days before maximum. The linear decay of the optical light curve, and the combination of a symmetric, broad H\alpha emission line profile with broad P Cygni H\beta and Na I \lambda5892 profiles, are properties reminiscent of the bright Type II-L SNe 1979C and 1980K, although SN 2008es is greater than 10 times more luminous. The host galaxy is undetected in pre-supernova Sloan Digital Sky Survey images, and similar to Type II-L SN 2005ap (the most luminous SN ever observed), the host is most likely a dwarf galaxy with M_r > -17. Swift Ultraviolet/Optical Telescope observations in combination with Palomar photometry measure the SED of the SN from 200 to 800 nm to be a blackbody that cools from a temperature of 14,000 K at the time of the optical peak to 6400 K 65 days later. The inferred blackbody radius is in good agreement with the radius expected for the expansion speed measured from the broad lines (10,000 km/s). The bolometric luminosity at the optical peak is 2.8 x 10^44 erg/s, with a total energy radiated over the next 65 days of 5.6 x 10^50 erg. We favor a model in which the exceptional peak luminosity is a consequence of the core-collapse explosion of a progenitor star with a low-mass extended hydrogen envelope and a stellar wind with a density close to the upper limit on the mass-loss rate measured from the lack of an X-ray detection by the Swift X-Ray Telescope. (Abridged)., Comment: Accepted to ApJ, 14 pages, 7 figures, 3 tables, emulateapj, corrections from proofs added

The optical afterglow of long-duration GRB 071003 is among the brightest yet to be detected from any GRB, with R ~ 12 mag in KAIT observations starting 42 s after the GRB trigger, including filtered detections during prompt emission. However, our high S/N ratio afterglow spectrum displays only extremely weak absorption lines at what we argue is the host redshift of z = 1.60435 - in contrast to the three other, much stronger Mg II absorption systems observed at lower redshifts. Together with Keck adaptive optics observations which fail to reveal a host galaxy coincident with the burst position, our observations suggest a halo progenitor and offer a cautionary tale about the use of Mg II for GRB redshift determination. We present early through late-time observations spanning the electromagnetic spectrum, constrain the connection between the prompt emission and early variations in the light curve (we observe no correlation), and discuss possible origins for an unusual, marked rebrightening that occurs a few hours after the burst: likely either a late-time refreshed shock or a wide-angle secondary jet. Analysis of the late-time afterglow is most consistent with a wind environment, suggesting a massive star progenitor. Together with GRB 070125, this may indicate that a small but significant portion of star formation in the early universe occurred far outside what we consider a normal galactic disk., 24 pages, 14 figures, 12 tables. Accepted for publication by ApJ. Contains minor revisions and additional authors

In recent years, there has been a proliferation of wide-field sky surveys to search for a variety of transient objects. Using relatively short focal lengths, the optics of these systems produce undersampled stellar images often marred by a variety of aberrations. As participants in such activities, we have developed a new algorithm for image subtraction that no longer requires high quality reference images for comparison. The computational efficiency is comparable with similar procedures currently in use. The general technique is cross-convolution: two convolution kernels are generated to make a test image and a reference image separately transform to match as closely as possible. In analogy to the optimization technique for generating smoothing splines, the inclusion of an RMS width penalty term constrains the diffusion of stellar images. In addition, by evaluating the convolution kernels on uniformly spaced subimages across the total area, these routines can accomodate point spread functions that vary considerably across the focal plane., 6 pages including 2 figures, accepted for publication in ApJ

We present unfiltered photometric observations with ROTSE-III and optical spectroscopic follow-up with the HET and Keck of the most luminous supernova yet identified, SN 2005ap. The spectra taken about 3 days before and 6 days after maximum light show narrow emission lines (likely originating in the dwarf host) and absorption lines at a redshift of z=0.2832, which puts the peak unfiltered magnitude at -22.7 +/- 0.1 absolute. Broad P-Cygni features corresponding to H-alpha, CIII, NIII, and OIII, are further detected with a photospheric velocity of ~20,000 km/s. Unlike other highly luminous supernovae such as 2006gy and 2006tf that show slow photometric evolution, the light curve of SN 2005ap indicates a 1-3 week rise to peak followed by a relatively rapid decay. The spectra also lack the distinct emission peaks from moderately broadened (FWHM ~ 2,000 km/s) Balmer lines seen in SN 2006gy and SN 2006tf. We briefly discuss the origin of the extraordinary luminosity from a strong interaction as may be expected from a pair instability eruption or a GRB-like engine encased in a H/He envelope., ApJ Letters Accepted; 4 pages

We present several cases of optical observations during gamma-ray bursts (GRBs) which resulted in prompt limits but no detection of optical emission. These limits constrain the prompt optical flux densities and the optical brightness relative to the gamma-ray emission. The derived constraints fall within the range of properties observed in GRBs with prompt optical detections, though at the faint end of optical/gamma flux ratios. The presently accessible prompt optical limits do not require a different set of intrinsic or environmental GRB properties, relative to the events with prompt optical detections., Comment: ApJ accepted. 20 pages in draft manuscript form, which includes 6 pages of tables and 2 figures

ROTSE-III is a homogeneous worldwide array of 4 robotic telescopes. They were designed to provide optical observations of γ -ray burst (GRB) afterglows as close as possible to the start of γ -ray emission. ROTSE-III is fulfilling its potential for GRB science, and provides optical observations for a variety of astrophysical sources in the interim between GRB events. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The robotic ROTSE-III telescope network detected prompt optical emission contemporaneous with the gamma-ray emission of Swift events GRB051109A and GRB051111. Both datasets have continuous coverage at high signal-to-noise levels from the prompt phase onwards, thus the early observations are readily compared to the Swift XRT and BAT high energy detections. In both cases, the optical afterglow is established, declining steadily during the prompt emission. For GRB051111, there is evidence of an excess optical component during the prompt emission. The component is consistent with the flux spectrally extrapolated from the gamma-rays, using the gamma-ray spectral index. A compilation of spectral information from previous prompt detections shows that such a component is unusual. The existence of two prompt optical components - one connected to the high-energy emission, the other to separate afterglow flux, as indicated in GRB051111 - is not compatible with a simple ``external-external'' shock model for the GRB and its afterglow., Comment: ApJ accepted. 32 pages (in preprint form), 5 tables, 5 figures

We present lightcurves of the afterglow of GRB050502A, including very early data at t-t_{GRB} < 60s. The lightcurve is composed of unfiltered ROTSE-IIIb optical observations from 44s to 6h post-burst, R-band MDM observations from 1.6 to 8.4h post-burst, and PAIRITEL J H K_s observations from 0.6 to 2.6h post-burst. The optical lightcurve is fit by a broken power law, where t^{alpha} steepens from alpha = -1.13 +- 0.02 to alpha = -1.44 +- 0.02 at \~5700s. This steepening is consistent with the evolution expected for the passage of the cooling frequency nu_c through the optical band. Even in our earliest observation at 44s post-burst, there is no evidence that the optical flux is brighter than a backward extrapolation of the later power law would suggest. The observed decay indices and spectral index are consistent with either an ISM or a Wind fireball model, but slightly favor the ISM interpretation. The expected spectral index in the ISM interpretation is consistent within 1 sigma with the observed spectral index beta = -0.8 +- 0.1; the Wind interpretation would imply a slightly (~2 sigma) shallower spectral index than observed. A small amount of dust extinction at the source redshift could steepen an intrinsic spectrum sufficiently to account for the observed value of beta. In this picture, the early optical decay, with the peak at or below 4.7e14 Hz at 44s, requires very small electron and magnetic energy partitions from the fireball., Comment: 22 pages, including 3 tables and 1 figure, Accepted by ApJ

We present the spectral evolution, light curve, and corresponding interpretation for the "normal-bright" Type Ia Supernova 2005cg discovered by ROTSE-IIIc. The host is a low-luminosity (M_r = -16.75), blue galaxy with strong indications of active star formation and an environment similar to that expected for SNe Ia at high redshifts. Early-time (t ~ -10 days) optical spectra obtained with the HET reveal an asymmetric, triangular-shaped Si II absorption feature at about 6100 \AA with a sharp transition to the continuum at a blue shift of about 24,000 km s^-1. By 4 days before maximum, the Si II absorption feature becomes symmetric with smoothly curved sides. Similar Si II profile evolution has previously been observed in other supernovae, and is predicted by some explosion models, but its significance has not been fully recognized. Although the spectra predicted by pure deflagration and delayed detonation models are similar near maximum light, they predict qualitatively different chemical abundances in the outer layers and thus give qualitatively different spectra at the earliest phases. The Si line observed in SN 2005cg at early times requires the presence of burning products at high velocities and the triangular shape is likely to be formed in an extended region of slowly declining Si abundance that characterizes delayed detonation models. The spectra show a high-velocity Ca II IR feature that coincides in velocity space with the Si II cutoff. This supports the interpretation that the Ca II is formed when the outer layers of the SN ejecta sweep up about 5 x 10^-3 M_sun of material within the progenitor system. (Abridged), Comment: 6 pages, Accepted for publication in ApJ

A wide field space-based imaging telescope is necessary to fully exploit the technique of observing dark matter via weak gravitational lensing. This first paper in a three part series outlines the survey strategies and relevant instrumental parameters for such a mission. As a concrete example of hardware design, we consider the proposed Supernova/Acceleration Probe (SNAP). Using SNAP engineering models, we quantify the major contributions to this telescope's Point Spread Function (PSF). These PSF contributions are relevant to any similar wide field space telescope. We further show that the PSF of SNAP or a similar telescope will be smaller than current ground-based PSFs, and more isotropic and stable over time than the PSF of the Hubble Space Telescope. We outline survey strategies for two different regimes - a ``wide'' 300 square degree survey and a ``deep'' 15 square degree survey that will accomplish various weak lensing goals including statistical studies and dark matter mapping., 25 pages, 8 figures, 1 table, replaced with Published Version

Using two identical telescopes at widely separated longitudes, the ROTSE-III network observed decaying emission from the remarkably bright afterglow of GRB 030329. In this report we present observations covering 56% of the period from 1.5-47 hours after the burst. We find that the light curve is piecewise consistent with a powerlaw decay. When the ROTSE-III data are combined with data reported by other groups, there is evidence for five breaks within the first 20 hours after the burst. Between two of those breaks, observations from 15.9-17.1 h after the burst at 1-s time resolution with McDonald Observatory's 2.1-m telescope reveal no evidence for fluctuations or deviations from a simple power law. Multiple breaks may indicate complex structure in the jet. There are also two unambiguous episodes at 23 and 45 hours after the burst where the intensity becomes consistent with a constant for several hours, perhaps indicating multiple injections of energy into the GRB/afterglow system., Comment: Four pages, two figures, uses emulateapj class file. Accepted to Astrophysical Journal Letters

We present an untriggered search for optical bursts with the ROTSE-I telephoto array. Observations were taken which monitor an effective 256 square degree field continuously over 125 hours to m_{ROTSE}=15.7. The uniquely large field, moderate limiting magnitude and fast cadence of $\sim$10 minutes permits transient searches in a new region of sensitivity. Our search reveals no candidate events. To quantify this result, we simulate potential optical bursts with peak magnitude, m_{p}, at t=10 s, which fade as f=(\frac{t}{t_{0}}) ^{\alpha_{t}}, where \alpha_t < 0. Simple estimates based on observational evidence indicate that a search of this sensitivity begins to probe the possible region occupied by GRB orphan afterglows. Our observing protocol and image sensitivity result in a broad region of high detection efficiency for light curves to the bright and slowly varying side of a boundary running from [\alpha_{t},m_{p}]=[-2.0,6.0] to [-0.3,13.2]. Within this region, the integrated rate of brief optical bursts is less than 1.1\times 10^{-8} {\rm s}^{-1} {\rm deg}^{-2}. At $\sim$22 times the observed GRB rate from BATSE, this suggests a limit on \frac{\theta_{opt}}{\theta_{\gamma}}\lesssim 5 where \theta_{opt} and \theta_{\gamma} are the optical and gamma-ray collimation angles, respectively. Several effects might explain the absence of optical bursts, and a search of the kind described here but more sensitive by about 4 magnitudes should offer a more definitive probe., Comment: 8 pages, 6 figures, 1 table

We present optical and near-infrared (NIR) photometry for three gamma-ray burst supernovae (GRB-SNe): GRB 120729A, GRB 130215A/SN 2013ez, and GRB 130831A/SN 2013fu. For GRB 130215A/SN 2013ez, we also present optical spectroscopy at t − t0 = 16.1 d, which covers rest-frame 3000-6250 Å. Based on Fe ii λ5169 and Si ii λ6355, our spectrum indicates an unusually low expansion velocity of ~4000-6350 km s-1, the lowest ever measured for a GRB-SN. Additionally, we determined the brightness and shape of each accompanying SN relative to a template supernova (SN 1998bw), which were used to estimate the amount of nickel produced via nucleosynthesis during each explosion. We find that our derived nickel masses are typical of other GRB-SNe, and greater than those of SNe Ibc that are not associated with GRBs. For GRB 130831A/SN 2013fu, we used our well-sampled R-band light curve (LC) to estimate the amount of ejecta mass and the kinetic energy of the SN, finding that these too are similar to other GRB-SNe. For GRB 130215A, we took advantage of contemporaneous optical/NIR observations to construct an optical/NIR bolometric LC of the afterglow. We fit the bolometric LC with the millisecond magnetar model of Zhang & Mészáros (2001, ApJ, 552, L35), which considers dipole radiation as a source of energy injection to the forward shock powering the optical/NIR afterglow. Using this model we derive an initial spin period of P = 12 ms and a magnetic field of B = 1.1 × 1015 G, which are commensurate with those found for proposed magnetar central engines of other long-duration GRBs.

The spectrum of gamma rays from the Crab Nebula has been measured in the energy range 500 GeV-8 TeV at the Whipple Observatory by the atmospheric Cerenkov technique. Two methods of analysis that were used to derive spectra, in order to reduce the chance of calibration errors, gave good agreement, as did analysis of observations made with changed equipment several years apart. It is concluded that stable and reliable energy spectra can now be made in the TeV range. The spectrum can be represented in this energy range by the power-law fit, J = (3.20 ± 0.17 ± 0.6) × (E/1 TeV)-2.49±0-06±0-04 m-2 s-1 TeV-1, or by the following form, which extends much better to the GeV domain: J = (3.25 ± 0.14 ± 0.6) × 10-7 E-2.44±0-06±0.04-0.151 log10 E m-2 s-1 TeV-1 (E in TeV) The integral flux above 1 TeV is (2.1 ± 0.2 ± 0.3) × 10-7 m-2 s-1. Using the complete spectrum of the Crab Nebula, the spectrum of relativistic electrons is deduced, and the spectrum of the inverse Compton emission that they would generate is in good agreement with the observed gamma-ray flux from 1 GeV to many TeV, if the magnetic field in the region where these scattered photons originate (essentially the X-ray-emitting region, around 0.4 pc from the pulsar) is ∼16 nT (160 μG), in reasonable agreement with the field deduced by Aharonian and Atoyan. If the same field strength were present throughout the nebula, there would be no clear need for an additional radiation source in the GeV domain such as has recently been suggested; the results give an indication that the magnetic field is well below the often-assumed equipartition strength (35-60 nT). Further accurate gamma-ray spectral measurements over the range from 1 GeV to tens of TeV have the potential to probe the growth in the magnetic field in the inner region of the nebula. © 1998. The American Astronomical Society. All rights reserved.