Nicholas E. White

X-ray eclipse mapping of AR Lacertae

Exosat data of the binary cycle of the eclipsing RS CVn system AR Lac are studied. The data reveal that at energies of less than 1 ke V a factor of 2 intensity modulation is detected and at energies greater than 1 ke V no orbital modulation is observed. The chi-squared and maximum entropy methods are used to model low-energy modulation. The relation between the low-temperature component and height is examined. It is observed that 50 pct of the X-ray flux comes from a surface area covering up to 16 pct of the K star and 25 pct of the G star and that peak coronal pressure is about 100 dyne/sq cm. 39 refs.

The properties of bursts with short recurrence times from the transient X-ray source EXO 0748-676

On January 13/14 1986 Exosat performed a 11.3-hr observation of the transient X-ray burst source EXO 0748-676. The source was in a low state and emitted 11 type I X-ray bursts, of which 10 were analyzed in detail. The properties of the bursts were similar to those found in previous low-state observations reported in Gottwald et al. (1986). The total energy emitted in the persistent flux between bursts divided by the total energy emitted in the following burst was about 25 with a constant apparent blackbody radius during the burst decay of 4.4 km. A regular burst pattern was identified where long and short recurrence intervals followed each other. The wait time to a burst and the total emitted energy in that burst displayed a linear relation but with an offset energy of 0.3 x 10 to the-7th ergs/sq cm at zero burst interval. This behavior is discussed in context of incomplete consumption of fuel and its subsequent reconsumption in the following bursts. The amount of unburned fuel was found to be about 10-15 percent of the total available nuclear energy. 21 references.

The Frontier in X‐ray Spectroscopy: NASA’s Constellation‐X Mission

This paper briefly describes the Constellation‐X mission, giving its basic performance parameters such as effective area and spectral resolution, describes some example science that may be conducted, and gives a general update on the mission, due for launch in 2016. Constellation‐X is one of the two flagship missions for the Beyond Einstein programand was designated as a high priority, second only to JWST, in the large space observatories category of the most recent National Academy decadal. Constellation‐X will present a great improvement in spectroscopic sensitivity, enabling studies at sensitivities more than 100 times greater than the best high‐resolution spectrometers observing in the 0.25–10 keV band during the current decade. The spectral resolution, R = E/ΔE, will range from 300 to 3000.

Simultaneous X-ray and radio observations of GX 13 + 1

The results of simultaneous X-ray and radio observations of GX 13 + 1, intrinsically one of the brightest Galactic bulge X-ray sources, are presented and possible models are discussed. No evidence is found for correlated X-ray and radio flux density variations. The variation of the 6-20 cm wavelength spectral index from +0.5 to -1.0 indicates that the radio flux is probably produced by a nonthermal emission mechanism. Application of an equipartition synchrotron model to the data suggests that the radio emission originates in a region with a magnetic field of about 1 gauss. If the radio flux density variations are due to injection of relativistic electrons, the equivalent nonthermal particle energy is 10 to the 36th - 10 to the 41st ergs/s. 33 references.

The Generation-X X-ray Observatory Vision Mission and Technology Study

The Generation-X Vision Mission Study investigates the science requirements, mission concepts and technology drivers for an X-ray telescope designed to study the new frontier of astrophysics: the birth and evolution of the first stars, galaxies and black holes in the early Universe. X-ray astronomy offers an opportunity to detect these via the activity of the black holes, and the supernova explosions and gamma-ray burst afterglows of the massive stars. However, such objects are beyond the grasp of current missions which are operating or even under development. Our team has conceived a Generation-X Vision Mission based on an Xray observatory with 100 sq. m. collecting area at 1 keV (1000 times larger than Chandra) and 0.1 arcsecond angular resolution (several times better than Chandra and 50 times better than the Constellation-X resolution goal). Such a high energy observatory will be capable of detecting the earliest black holes and galaxies in the Universe, and will also study extremes of density, gravity, magnetic fields, and kinetic energy which cannot be created in laboratories. NASA has selected the Generation-X mission for study under its Vision Mission Program. We describe the studies being performed to develop the mission concept and define candidate technologies and performance requirements for Generation-X. The baseline Generation-X mission involves four 8m diameter X-ray telescopes operating at SunEarth L2. We trade against an alternate concept of a single 26m diameter telescope with focal plane instruments on a separate spacecraft. A telescope of this size will require either robotic or human-assisted in-flight assembly. The required effective area implies that extremely lightweight grazing incidence X-ray optics must be developed. To achieve the required areal density of at least 100 times lower than in Chandra, we will study 0.1mm thick mirrors which have active on-orbit figure control. We discuss the suite of required detectors, including a large FOV high angular resolution imager, a cryogenic imaging spectrometer and a grating spectrometer.

ASCA observation of 4U1624–49

ASCA observations of the LMXRB 4U1624–49 reveal the presence of extended emission surrounding the X-ray source probably due to a dust scattered halo. The halo spectrum can account for the low energy excess seen in the dip spectrum.

The Luminosity Dependence of the Pulse Period and Profile of the Transient X-ray Pulsar EXO 2030+375

Using the EXOSAT Observatory we have discovered a new, transient, X-ray pulsar, EXO 2030+375 and followed its evolution through two outbursts. During the first outburst the 1-20 keV intensity declined by a factor ≳ 2500 from a discovery value comparable to that of the Crab Nebula. Cyclic variations in the 42 s pulse period give a likely orbital period in the range 44.3-48.6 day and an eccentricity of ~ 0.4. We have measured, for the first time, the dependence of the pulse period time derivative, Ps, on luminosity, L, for an individual pulsar. At high and intermediate luminosities we find that -P s ∝ L 1.08-1.35. This observed dependence is significantly steeper than that predicted by simple accretion torque theory where -P s ∝ L0.86. At low luminosites the determination of this relation is complicated by the interplay between secular and orbital period changes and we await an independent determination of the orbital elements that will allow these effects to be separated.