Andrew G. Peele

Evidence for a Very Slow X-Ray Pulsar in 2S 0114+650 from Rossi X-Ray Timing Explorer All-Sky Monitor Observations

Rossi X-Ray Timing Explorer (RXTE) all-sky monitor (ASM) observations of the X-ray binary 2S 0114+650 show modulations at periods close to both the optically derived orbital period (11.591 days) and proposed pulse period (~2.7 hr). The pulse period shows frequency and intensity variability during the more than 2 years of ASM observations analyzed. The pulse properties are consistent with this arising from accretion onto a rotating neutron star, and this would be the slowest such period known. The shape of the orbital light curve shows modulation over the course of the entire orbit, and a comparison is made with the orbital light curve of Vela X-1. However, the expected phase of eclipse, based on an extrapolation of the optical ephemeris, does not correspond with the observed orbital minimum. The orbital period derived from the ASM light curve is also slightly longer than the optical period.

Rossi X-Ray Timing Explorer Observations of the X-Ray Pulsar XTE J1855–026: A Possible New Supergiant System

A new X-ray source, XTE J1855-026, was discovered during Rossi X-Ray Timing Explorer (RXTE) scans along the Galactic plane. The source shows pulsations at a period of 361 s and also modulation at a period of 6.1 days, which we interpret as the orbital period of the system. The X-ray spectrum above ~3 keV can be fitted with an absorbed power-law model with a high-energy cutoff and an iron emission line at approximately 6.4 keV. We interpret these results as indicating that XTE J1855-026 is likely to consist of a neutron star accreting from the wind of an O or B supergiant primary. A less likely interpretation is that XTE J1855-026 is instead a Be/neutron star binary, in which case it would have the shortest known orbital period for such a system.

RXTE Observations of the Be Star X-Ray Transient X0726–260 (4U 0728–25): Orbital and Pulse Periods

Rossi X-Ray Timing Explorer (RXTE) All-Sky Monitor observations of the transient Be star X-ray source X0726-260 suggest a 34.5 day period. This is apparently confirmed by a serendipitous RXTE Proportional Counter Array (PCA) slew detection of the source on 1997 May 5, near the time of a predicted flux maximum. A subsequent 5 ks pointed observation of X0726-260 with the RXTE PCA detector was carried out on 1997 June 7, when X0726-260 was predicted to be bright again, and this revealed pulsations at a period of 103.2 s. If the 34.5 day period is orbital, then the pulse period is surprisingly long compared with that predicted by the correlation between orbital period and spin period observed for other Be/neutron star systems. A possible similarity with GRO J2058+42 is briefly discussed.

Recent studies of lobster-eye optics

Lobster-eye optics have been proposed as an exciting development in the field of x-ray all-sky monitors. However, to date their potential has mainly been analyzed in the context of an all-sky monitor for a small satellite mission. We examine the wide range of parameters available for lobster-eye optics with different configurations. The sensitivity of the various schemes is calculated. We have also examined the current state of the art in actual lobster-eye optics. We present our experimental results and discuss realistic targets for manufacture. The impact of these targets on the calculated sensitivities is also described.

A lobster-eye on the x-ray sky

We propose an x-ray all-sky monitor for the International Space Station (ISS) that will be ten times more sensitive than past monitors and that opens up a new band of the soft x-ray spectrum (0.1 −3.0 keV) for study. Taking advantage of the power telemetry and space available on the ISS we can use a telescope geometry and detectors that will provide better than 4 arc minute resolution of the entire sky in a 1.5 hr duty cycle. To achieve this sensitivity and resolution we use focusing optics based on the lobster-eye geometry. We propose two approaches to the construction of the optics. The first method, well within the reach of existing technology, is to approximate the lobster-eye geometry by building crossed arrays of planar reflectors, this gives great control over the reflecting surface but is limited in terms of resolution at the baseline 4 arc minute level. The second method is to use microchannel plates: this technology has the potential to greatly exceed the baseline resolution and sensitivity but ...

Practical implementation of lobster-eye optics

The concept of the lobster eye optics was proposed in the nineteen seventies. It has gained widespread interest in x- ray astronomy for its potential for constructing compact and focusing x-ray all sky monitors with unprecedented sensitivities. The majority of the efforts of developing a practical implementation of this optics has been devoted toward slumping square-pore micro-channel plates. While the advantages of the slumped micro-channel plates are obvious in that they can achieve potentially arc-second angular resolutions, the smoothness requirements for reflecting x- rays are hard to meet by micro-channel plates. It is not clear how the interior of the micro-channel plate pores can be polished to the desired smoothness. In this paper we propose the feasibility of a more straightforward approach of implementing the lobster eye optics with flat glass mirrors assembled in a standard Kirkpatrick-Baez configuration. We demonstrate with both simulations and laboratory test results that this implementation is both practical and meets al the requirements of an x-ray all sky monitor.

Square microchannel arrays for focusing neutrons and x rays

Conditioning neutron and X-ray beams is best achieved with glancing-incidence reflective optics. Square micro-channel arrays offer an increasingly practical geometry for this implementation. We present results for focussing neutrons with two such arrays, one with channel size of 32 micrometer, which places us truly in the microscopic regime. These two arrays, designed for soft X-rays, perform comparably with neutrons.