Eve Armstrong

GRB 021004: A Possible Shell Nebula around a Wolf-Rayet Star Gamma-Ray Burst Progenitor*

The rapid localization of GRB 021004 by the HETE-2 satellite allowed nearly continuous monitoring of its early optical afterglow decay, as well as high-quality optical spectra that determined a redshift of z3 = 2.328 for its host galaxy, an active starburst galaxy with strong Lyα emission and several absorption lines. Spectral observations show multiple absorbers at z3A = 2.323, z3B = 2.317, and z3C = 2.293 blueshifted by ~450, ~990, and ~3155 km s-1, respectively, relative to the host galaxy Lyα emission. We argue that these correspond to a fragmented shell nebula that has been radiatively accelerated by the gamma-ray burst (GRB) afterglow at a distance 0.3 pc from a Wolf-Rayet star GRB progenitor. The chemical abundance ratios indicate that the nebula is overabundant in carbon and silicon. The high level of carbon and silicon is consistent with a swept-up shell nebula gradually enriched by a carbon-rich late-type Wolf-Rayet progenitor wind over the lifetime of the nebula prior to the GRB onset. The detection of statistically significant fluctuations and color changes about the jetlike optical decay further supports this interpretation, since fluctuations must be present at some level as a result of irregularities in a clumpy stellar wind medium or if the progenitor has undergone massive ejection prior to the GRB onset. This evidence suggests that the mass-loss process in a Wolf-Rayet star might lead naturally to an iron core collapse with sufficient angular momentum that could serve as a suitable GRB progenitor. Even though we cannot rule out definitely the alternatives of a dormant QSO, large-scale superwinds, or a several hundred year old supernova remnant responsible for the blueshifted absorbers, these findings point to the likelihood of a signature for a massive-star GRB progenitor.

Is FIRST J102347.6+003841 Really a Cataclysmic Binary?*

The radio source FIRST J102347.6+003841 was presented as the first radio-selected cataclysmic variable star. In the discovery paper, Bond et al. (2002) show a spectrum consistent with a magnetic AM Her–type system, or polar, featuring strong Balmer lines, He I and He II emission lines, and a light curve with rapid, irregular flickering. In contrast, Woudt, Warner, and Pretorius found a smoothly varying light curve with a period near 4.75 hr and one minimum per orbit, indicating that the state of the system had changed dramatically. We present time-resolved spectra showing a superficially normal, mid-G type photosphere, with no detectable emission lines. The absorption-line radial velocity varies sinusoidally, with semiamplitude 268 ± 4 km s-1, on the orbital period, which is refined to 0.198094(2) days. At this orbital period, the secondarys spectral type is atypically early, suggesting an unusual evolutionary history. We also obtained photometry around the orbit in B, V, and I. The light curve resembles that observed by Woudt, Warner, and Pretorius, and the colors are modulated in a manner consistent with a heating effect. A simple illumination model matches the observations strikingly well, with a Roche lobe–filling secondary near Teff = 5650 K being illuminated by a primary with an isotropic luminosity of ~2 L⊙. The modest amplitude of the observed modulation constrains the orbital inclination i ~ 55° or less, unless the gravity darkening is artificially reduced. Combining the low i with the secondarys velocity amplitude gives a primary star mass above the Chandrasekhar limit when conventional gravity darkening is assumed. We consider the robustness of this conclusion and examine the possibility that the compact object in this system is not a white dwarf, in which case this is not actually a cataclysmic variable. On close examination, FIRST J102347.6+003841 defies easy classification.

High-speed photometry of SDSS J013701.06 − 091234.9

We present high-speed photometry of the Sloan Digital Sky Survey cataclysmic variable SDSS J013701.06 − 091234.9 in quiescence and during its 2003 December superoutburst. The orbital modulation at 79.71 ± 0.01 min is double-humped; the superhump period is 81.702 ± 0.007 min. Towards the end of the outburst late superhumps with a period of 81.29 ± 0.01 min were observed. We argue that this is a system of very low mass transfer rate, and that it probably has a long outburst interval.

First unambiguous detection of the return of pulsations in the accreting white dwarf SDSS J074531.92+453829.6 after an outburst

The primary white dwarf of the cataclysmic variable SDSS J074531.92+453829.6 was discovered to exhibit non-radial pulsations in 2006 January. This accreting white dwarf underwent its first recorded dwarf nova outburst in 2006 October, during which its brightness increased by more than 5 mag. A Hubble Space Telescope (HST) ultraviolet spectrum, obtained one year after the outburst, revealed a white dwarf temperature of 16,500 K, hotter than all other known accreting white dwarf pulsators. This implies that the accreting primary white dwarf of SDSS J074531.92+453829.6 was heated to temperatures beyond the instability strip during the outburst. Optical observations acquired a year after the outburst did not reveal any evidence of pulsations, suggesting that the white dwarf had not cooled to quiescence by then. We recently acquired optical high-speed time-series photometry on this cataclysmic variable SDSS J074531.92+453829.6 more than three years after its outburst to find that pulsations have now returned to the primary white dwarf. Moreover, the observed pulsation periods agree with pre-outburst periods within the uncertainties of a few seconds. This discovery is significant because it indicates that the outburst did not affect the interior stellar structure, which governs the observed pulsation frequencies. It also suggests that the surface of the white dwarf has now cooled to quiescence. Using this discovery in addition to the prior HST temperature measurement of 16,500 K, we have been able to constrain the matter accreted during the 2006 outburst. This is the first time an accreting white dwarf was unambiguously observed to resume pulsating after an outburst.

Orbital, Superhump, and Superorbital Periods in the Cataclysmic Variables AQ Mensae and IM Eridani

We report photometric detections of orbital and superorbital signals, and negative orbital sidebands, in the light curves of the nova-like cataclysmic variables AQ Mensae and IM Eridani. The frequencies of the orbital, superorbital, and sideband signals are 7.0686 (3), 0.263 (3), and 7.332 (3) cycles per day (c d -1 ) in AQ Mensae, and 6.870 (1), 0.354 (7), and 7.226 (1) c d -1 in IM Eridani. We also find a spectroscopic orbital frequency in IM Eridani of 6.86649 (2) c d -1 . These observations can be reproduced by invoking an accretion disc that is tilted with respect to the orbital plane. This model works well for X-ray binaries, in which irradiation by a primary neutron star can account for the disc’s tilt. A likely tilt mechanism has yet to be identified in CVs, yet the growing collection of observational evidence indicates that the phenomenon of tilt is indeed at work in this class of object. The results presented in this paper bring the number of CVs known to display signals associated with retrograde disc precession to twelve. We also find AQ Men to be an eclipsing system. The eclipse depths are highly variable, which suggests that the eclipses are grazing. This finding raises the possibility of probing variations in disc tilt by studying systematic variations in the eclipse profile.

An optimization-based approach to calculating neutrino flavor evolution

Author(s): Armstrong, Eve; Patwardhan, Amol V; Johns, Lucas; Kishimoto, Chad T; Abarbanel, Henry DI; Fuller, George M

The photometric period in ES Ceti

We present ULTRACAM photometry of ES Cet, an ultracompact binary with a 620-s orbital period. The mass transfer in systems such as this one is thought to be driven by gravitational radiation, which causes the binary to evolve to longer periods since the semidegenerate donor star expands in size as it loses mass. We supplement these ULTRACAM+William Herschel Telescope (WHT) data with observations made with smaller telescopes around the world over a 9-yr baseline. All of the observations show variation on the orbital period, and by timing this variation we track the period evolution of this system. We do not detect any significant departure from a linear ephemeris, implying a donor star that is of small mass and close to a fully degenerate state. This finding favours the double white dwarf formation channel for this AM Canum Venaticorum (AM CVn) star. An alternative explanation is that the system is in the relatively short-lived phase in which the mass transfer rate climbs towards its long-term value.

Superhumps in Cataclysmic Binaries. XXV. Q~c~r~i~t' epsilon(q) and Mass-Radius

ABSTRACT We report on successes and failures in searching for positive superhumps in cataclysmic variables, and show the superhumping fraction as a function of orbital period. Basically, all short‐period system do, all long‐period systems do not, and a 50% success rate is found at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

The New Eclipsing Cataclysmic Variable SDSS 154453+2553

P_{\mathrm{orb}\,}=3.1\pm 0.2

Return of Pulsations in SDSS 0745+4538

\end{document} hr. We can use this to measure the critical mass ratio for the creation of superhumps. With a mass‐radius relation appropriate for cataclysmic variables, and ...