RAPTOR observations of delayed explosive activity in the high-redshift gamma-ray burst GRB 060206

The RAPid Telescopes for Optical Response (RAPTOR) system at Los Alamos National Laboratory observed GRB 060206 starting 48.1 minutes after gamma-ray emission triggered the Burst Alert Telescope (BAT) on-board the Swift satellite. The afterglow light curve measured by RAPTOR shows a spectacular re-brightening by ~1 mag about 1 h after the trigger and peaks at R ~ 16.4 mag. Shortly after the onset of the explosive re-brightening the OT doubled its flux on a time-scale of about 4 minutes. The total R-band fluence received from GRB 060206 during this episode is 2.3e-9 erg/cm2. In the rest frame of the burst (z = 4.045) this yields an isotropic equivalent energy release of ~0.7e50 erg in just a narrow UV band 130 +/- 22 nm. We discuss the implications of RAPTOR observations for untriggered searches for fast optical transients and studies of GRB environments at high redshift.Comment: Submitted to ApJ Letter

ROTSE All Sky Surveys for Variable Stars I: Test Fields

The ROTSE-I experiment has generated CCD photometry for the entire Northern sky in two epochs nightly since March 1998. These sky patrol data are a powerful resource for studies of astrophysical transients. As a demonstration project, we present first results of a search for periodic variable stars derived from ROTSE-I observations. Variable identification, period determination, and type classification are conducted via automatic algorithms. In a set of nine ROTSE-I sky patrol fields covering about 2000 square degrees we identify 1781 periodic variable stars with mean magnitudes between m_v=10.0 and m_v=15.5. About 90% of these objects are newly identified as variable. Examples of many familiar types are presented. All classifications for this study have been manually confirmed. The selection criteria for this analysis have been conservatively defined, and are known to be biased against some variable classes. This preliminary study includes only 5.6% of the total ROTSE-I sky coverage, suggesting that the full ROTSE-I variable catalog will include more than 32,000 periodic variable stars.Comment: Accepted for publication in AJ 4/00. LaTeX manuscript. (28 pages, 11 postscript figures and 1 gif

RAPTOR observations of the early optical afterglow from GRB 050319

The RAPid Telescopes for Optical Response (RAPTOR) system at Los Alamos National Laboratory observed GRB 050319 starting 25.4 seconds after gamma-ray emission triggered the Burst Alert Telescope (BAT) on-board the Swift satellite. Our well sampled light curve of the early optical afterglow is composed of 32 points (derived from 70 exposures) that measure the flux decay during the first hour after the GRB. The GRB 050319 light curve measured by RAPTOR can be described as a relatively gradual flux decline (power-law index alpha = -0.37) with a transition, at about 400 s after the GRB, to a faster flux decay (alpha = -0.91). The addition of other available measurements to the RAPTOR light curve suggests that another emission component emerged after 10^4 s. We hypothesize that the early afterglow emission is powered by extended energy injection or delayed reverse shock emission followed by the emergence of forward shock emission.Comment: Accepted for publication in ApJ Letters. To see a short movie of fading GRB 050319 go to http://www.raptor.lanl.gov/images/GRB050319/grb050319_movie_annotated.gi

229Th the Bridge Between Nuclear and Atomic Interactions

The precise measurement of time has been a goal of physicists for centuries. With every new increase in our ability to measure time we have discovered new phenomena. The most advanced clocks available to us currently are atomic clocks that use electronic transitions to track the passage of time. In this proposal, I put forward the framework for the first nuclear clock estimated to be 1000 to 10000 times more precise than the current atomic clocks. This research will explore in detail the atomic nuclear interactions and help perfect and refine current atomic-nuclear interaction models. The realization of a {sup 229}Th nuclear clock will allow tests of cosmology by measuring the change of the fine structure constant as a function of time. The results of these experiments could dramatically alter our view of the universe, its past and future evolution. Precision clocks - with fundamental physics applications - require a long-lived quantum transition (two-level system) that is immune to external perturbations. Nuclear transitions would be better suited than atomic transitions for these applications except that nuclear transitions are typically much higher in energy and therefore cannot be accessed with table-top lasers. There is, however, one promising nuclear transition: the doublet between the ground and first excited states of the {sup 229}Th nucleus discovered by Helmer and Reich. This doublet has an energy splitting of 7.6 {+-} 0.5 eV, a spin difference of 1 h-bar, and an excited state half-life that could be as long as hours. A precision clock based on the {sup 229}Th nuclear doublet has been proposed by Peik et al. Their design is similar to the ion clock research being conducted at NIST in Boulder, CO. However, the NIST researchers use atomic transitions for their frequency standards. In the {sup 229}Th nuclear doublet transition is the frequency standard while atomic transitions are used to cool the ions and for probing the state of the {sup 229}Th nucleus. Recently, Campbell et al. have trapped and cooled {sup 232}Th{sup 3+} at Georgia Institute of Technology. This is a large step forward in the realization of a nuclear clock. The Georgia Tech group is already a collaborator on this project and we are in discussions with the NIST Boulder group about collaboration. In order to determine the suitability of the {sup 229}Th nuclear doublet for a precision clock, the half-life of the excited-state needs to be measured. Current estimates of the half-life vary from 10 {micro}s to 1000 hours. The longer the half-life, the narrower the natural linewidth of the state and the more desirable the transition is for potential applications. In this proposal, I outline the necessary research to be conducted to determine the half-life and exact wavelength of the nuclear doublet transition in {sup 229}Th. This research will lead to a deeper understanding of atomic-nuclear interactions important for our knowledge of high energy density science. It will provide a spectroscopy measurement of the lowest known nuclear transition ever and open the doorway for the development of a nuclear clock with unprecedented precision

The ROTSE-III Robotic Telescope System

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.Comment: 19 pages, including 4 figures. To be published in PASP in January, 2003. PASP Number IP02-11

Observations of the Optical Counterpart to XTE J1118+480 During Outburst by the ROTSE-I Telescope

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 April 1998 and January 2000. 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 mini-outbursts based on comparison with similar sources. The ROTSE measurements taken during the March 2000 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 pre-outburst accretion disk inner truncation radius of 1.2 x 10^4 Schwarzschild radii.Comment: 9 pages, 1 table, 2 figure

Energy input and response from prompt and early optical afterglow emission in gamma-ray bursts

The taxonomy of optical emission detected during the critical first few minutes after the onset of a gamma-ray burst (GRB) defines two broad classes: prompt optical emission correlated with prompt gamma-ray emission, and early optical afterglow emission uncorrelated with the gamma-ray emission. The standard theoretical interpretation attributes prompt emission to internal shocks in the ultra-relativistic outflow generated by the internal engine; early afterglow emission is attributed to shocks generated by interaction with the surrounding medium. Here we report on observations of a bright GRB that, for the first time, clearly show the temporal relationship and relative strength of the two optical components. The observations indicate that early afterglow emission can be understood as reverberation of the energy input measured by prompt emission. Measurements of the early afterglow reverberations therefore probe the structure of the environment around the burst, whereas the subsequent response to late-time impulsive energy releases reveals how earlier flaring episodes have altered the jet and environment parameters. Many GRBs are generated by the death of massive stars that were born and died before the Universe was ten per cent of its current age, so GRB afterglow reverberations provide clues about the environments around some of the first stars.Comment: 13 pages, 4 figures, 1 table. Note: This paper has been accepted for publication in Nature, but is embargoed for discussion in the popular press until formal publication in Natur