Models of the hard X-ray spectrum of AM Herculis and implications for the accretion rate

Phenomenological fits to the hard X-ray spectrum of AM Herculis left unexplained the high equivalent width (0.8 + or - 0.1 keV) of Fe K alpha emission. A purely thermal origin implies a much steeper spectrum than was observed. With Monte Carlo calculations, scattering and fluorescent line production in a cold or partially ionized accretion column of hard X-rays emitted at the base were investigated. The strength of the iron emission and the flat spectral continuum can be explained by the effects of fluorescence and absorption within the accretion column and the surface of the white dwarf on a thermal X-ray spectrum. Thomson optical depths across the column in the range 0.2 to 0.7 are acceptable. The accretion rate and gravitational power can be deduced from the optical depth across the column, if the column size is known, and, together with the observed hard X-ray and polarized light luminosities, imply a lower limit for the luminosity in the UV to soft X-ray range, for which the observations give model-dependent values. Estimates of the column size differ by a factor of 40. Small spot sizes and low luminosities would be consistent with the soft component being the expected reprocessed bremsstrahlung and cyclotron radiation, although the constraint of matching the spectrum confines one to solutions with fluxes exceeding 20% the Eddington limits

Arbitration and Salary Inflation in Major League Baseball

Major league baseball has undergone significant changes since its inception over a century ago.2 While the game itself remains basically the same, the system governing management and player relations is hardly the same as it was even twenty years ago.\u27 In years past, team owners exercised absolute authority over terms of players\u27 employment including player mobility and salary levels. 4 Under this system, players essentially had no voice in salary determinations and players were contractually restricted from signing with another team.5 Players were forced either to accept the terms as offered by management or to quit the game altogether.

The Ethnobotany of the Acoma and Laguna Indians

The Indian lives close to nature and utilizes the plants which grow about him, and these uses differ among various tribes. In order therefore to understand the ethnobotany of any group of Indians it is necessary to know something of their history, customs, mythology, religion and medicine. Hence in treating the ethnobotany of the Acoma and Laguna Indians the above phases of their culture will be discussed as they relate to these two pueblos

The MXB1916-053/4U1915-05: Burst properties and constraints on a 50 minute binary secondary

Results are presented from OSO-8 and HEAO-1 A2 observations of 34 bursts from the X-ray burster MXB1916-053/4U1915-05 recently discovered to show a 50 minute binary period. While 11 burst previously reported all had similar light curves, 22 observed two years later show a factor of 3 range of peak fluxes and decay times between 3 and 20 s. Recurrence times between successive bursts vary between 3 and 6 hours. A ratio of steady flux to average burst flux of equiv 120 is developed. A burst observed with the HEAO-1 A2 experiment showed an initial temperature rise to a peak black body temperature of equiv 3 keV followed by the cooling typical of type I bursts. The burst was unusual in that the apparent projected size of a blackbody source increased by a factor of 3 during the cooling phase

The X-ray absorption spectrum of 4U1700-37 and its implications for the stellar wind of the companion HD153919

The first high resolution non-dispersive 2-60 KeV X-ray spectra of 4U1700-37 is presented. The continuum is typical of that found from X-ray pulsars; that is a flat power law between 2 and 10 keV and, beyond 10 keV, an exponential decay of characteristic energy varying between 10 and 20 keV. No X-ray pulsations were detected between 160 ms and 6 min with an amplitude greater than approximately 2%. The absorption measured at binary phases approximately 0.72 is comparable to that expected from the stellar wind of the primary. The gravitational capture of material in the wind is found to be more than enough to power the X-ray source. The increase in the average absorption after phi o approximately 0.5 is confirmed. The minimum level of adsorption is a factor of 2 or 3 lower than that reported by previous observers, which may be related to a factor of approximately 10 decline in the average X-ray luminosity over the same interval. Short term approximately 50% variations in adsorption are seen for the first time which appear to be loosely correlated with approximately 10 min flickering activity in the X-ray flux. These most likely originate from inhomogeneities in the stellar wind of the primary

Bounds on Compactness for LMXB Neutron Stars from X-ray Burst Oscillations

We have modelled X-ray burst oscillations observed with the Rossi X-ray Timing Explorer (RXTE) from two low mass X-ray binaries (LMXB): 4U 1636-53 with a frequency of 580 Hz, and 4U 1728-34 at a frequency of 363 Hz. We have computed least squares fits to the oscillations observed during the rising phase of bursts using a model which includes emission from either a single circular hot spot or a pair of circular antipodal hot spots on the surface of a neutron star. We model the spreading of the thermonuclear hot spots by assuming that the hot spot angular size grows linearly with time. We calculate the flux as a function of rotational phase from the hot spots and take into account photon deflection in the relativistic gravitational field of the neutron star assuming the exterior spacetime is the Schwarzschild metric. We find acceptable fits with our model and we use these to place constraints on the compactness of the neutron stars in these sources. For 4U 1636-53, in which detection of a 290 Hz sub-harmonic supports the two spot model, we find that the compactness (i.e., mass/radius ratio) is constrained to be M/R < 0.163 at 90% confidence (G = c = 1). This requires a relatively stiff equation of state (EOS) for the stellar interior. For example, if the neutron star has a mass of 1.4 Msun then its radius must be > 12.8 km. Fits using a single hot spot model are not as highly constraining. We discuss the implications of our findings for recent efforts to calculate the EOS of dense nucleon matter and the structure of neutron stars.Comment: 27 pages, 6 figures, AASTeX. Revised and expanded version. Resubmitted to Astrophysical Journa

Discovery of the Orbit of the Transient X ray Pulsar SAX J2103.5+4545

Using X-ray data from the Rossi X-Ray Timing Explorer (RXTE), we carried out pulse timing analysis of the transient X-ray pulsar SAX J2103.5+4545. An outburst was detected by All Sky Monitor (ASM) October 25 1999 and reached a peak X-ray brightness of 27 mCrab October 28. Between November 19 and December 27, the RXTE/PCA carried out pointed observations which provided us with pulse arrival times. These yield an eccentric orbit (e= 0.4 \pm 0.2) with an orbital period of 12.68 \pm 0.25 days and light travel time across the projected semimajor axis of 72 \pm 6 sec. The pulse period was measured to be 358.62171 \pm 0.00088 s and the spin-up rate (2.50 \pm 0.15) \times 10^{-13} Hz s^{-1}. The ASM data for the February to September 1997 outburst in which BeppoSAX discovered SAX J2103.5+4545 (Hulleman, in't Zand and Heise 1998) are modulated at time scales close to the orbital period. Folded light curves of the 1997 ASM data and the 1999 PCA data are similar and show that the intensity increases at periastron passages.Comment: To appear in The Astrophysical Journal (Letters