Andrew Pawl

Rotse all sky surveys for variable stars I: test fields

The Robotic Optical Transient Search Experiment I (ROTSE-I) experiment has generated CCD photometry for the entire northern sky in two epochs nightly since 1998 March. 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 roughly 2000 deg2, we identify 1781 periodic variable stars with mean magnitudes between mv = 10.0 and mv = 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.

Prompt Optical Observations of Gamma-Ray Bursts

The Robotic Optical Transient Search Experiment (ROTSE) seeks to measure simultaneous and early afterglow optical emission from gamma-ray bursts (GRBs). A search for optical counterparts to six GRBs with localization errors of 1 deg2 or better produced no detections. The earliest limiting sensitivity is mROTSE>13.1 at 10.85 s (5 s exposure) after the gamma-ray rise, and the best limit is mROTSE>16.0 at 62 minutes (897 s exposure). These are the most stringent limits obtained for the GRB optical counterpart brightness in the first hour after the burst. Consideration of the gamma-ray fluence and peak flux for these bursts and for GRB 990123 indicates that there is not a strong positive correlation between optical flux and gamma-ray emission.

Detecting intracluster gas motion in galaxy clusters: Mock Astro-E2 observations

We explore the detectability of bulk motions in the X-ray-emitting intracluster medium using a catalog of 1836 mock Astro-E2 observations of simulated clusters of galaxies. We generate high-resolution mock spectra for two observing strategies: a four-pointing mosaic and a single central pointing. Normalizing to 200 (400) photons in the iron Kα region for the mosaic (central) study, we fit Poisson realizations of each simulated spectrum to a velocity-broadened isothermal plasma emission model. We confirm that the velocity characteristics (mean and dispersion) returned by the spectral fittings are unbiased measures of the emission-weighted values within the observed region, with scatter ±55 km s-1. The maximum velocity difference between mosaic element pairs Δvmax has ~6% likelihood of being transonic (Δvmax ≥ 0.5cs), and the likelihood falls steeply, p ∝ (Δvmax/cs)-4, at high Mach number. The velocity-broadening parameter σv from the central pointing fit exceeds the thermal value in 49% of the cases, with again a σ tail at large dispersion. We present as case studies the clusters that yield the strongest signal for each observing strategy.

Rapid optical follow-up observations of SGR events with ROTSE-I

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 March, 1998, ROTSE has also taken useful data for 10 SGR events: 8 from SGR 1900+14 and 2 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 m_ROTSE ~ 12.5 - 15.5 during the period 20 seconds to 1 hour after the observed SGR events.

Q-ball formation in Affleck–Dine baryogenesis with gravity-mediated SUSY breaking

Abstract To date, the properties of Q-balls arising from an Affleck–Dine condensate in gravity-mediated SUSY breaking have been obtained primarily through numerical simulations. In this work, we will derive the expected charge of the Q-balls formed in such a scenario through an analytical treatment. We will also examine the numerically observed difference between Q-ball formation in weakly charged condensates and formation in strongly charged condensates.

Discrete gauge symmetries, baryon number and large extra dimensions

Krauss and Wilczek have shown that an unbroken discrete gauge symmetry is respected by gravitationally mediated processes. This has led to a search for such a symmetry compatible with the standard model or MSSM that would protect protons from gravitationally mediated decay in a universe with a low scale for quantum gravity (large extra dimensions). The fact that the discrete symmetry must remain unbroken and have a gauge origin puts important restrictions on the space of possible discrete symmetries.

Decay of Affleck-Dine condensates with application to Q-balls

Abstract Analytical and numerical estimates show that a charged Affleck–Dine condensate will fracture into Q-balls only when the Hubble time is significantly larger than the inverse soft-breaking mass of the field in question. This would generally imply that the decay of the field into light fermions will compete with Q-ball formation. We will show that for typical flat directions the large field value will significantly suppress decays of the condensate to fermions even if no baryon charge asymmetry exists. We will consider the details of the decay process for a condensate that does carry charge, and show that it is qualitatively different from that of an uncharged condensate. Finally, we will consider the possibility of resonant production of heavy bosons. We will show that this can have a strong effect on the condensate. Contrary to intuition, however, our results indicate that boson production would actually assist Q-ball formation in condensates with significant charge.