A Search for X-Ray Flashes with XMM-Newton

We searched for X-ray flashes (XRFs) -- which we defined as ~10s duration transient X-ray events observable in the 0.4-15 keV passband -- in fields observed using XMM-Newton with the EPIC/pn detector. While we find two non-Poissonian events, the astrophysical nature of the events is not confirmed in fully simultaneous observations with the EPIC/MOS detectors, and we conclude that the events are anomalous to the EPIC/pn detector. We find a 90% upper limit on the number of flashes per sky per year at two different incoming flash fluxes: 4.0x10^9 events / sky / year for a flux of 7.1x10^-13 erg / cm^2 / s and 6.8x10^7 events / sky / year for 1.4x10^-11 erg / cm^2 / s. These limits are consistent with an extrapolation from the BeppoSAX/WFC XRF rate at much higher fluxes (about a factor of 10^5), assuming an homogenous population, and with a previous, more stringent limit derived from ROSAT pointed observations.Comment: Version accepted by MNRAS (minor changes

Sus scrofa: Population Structure, Reproduction and Condition in Tropical North Eastern Australia

Three feral pig populations inhabiting contrasting environments along the north easterncoast of Australia have been investigated with respect to population structure, individual condition andreproduction. The population on Prince of Wales Island contains a large proportion of juvenile andsub-adult pigs but lacks pigs in the higher age classes. Individuals also breed at an earlier age thananimals of the mainland populations. Pig populations on Cape York Peninsula show a largerproportion of older animals and feral pigs living in rainforest habitats show a low proportion ofanimals in very young and very old age classes. Pigs from the lowland rainforest population are inbetter condition than those of the other populations for most of the year, reflecting the availability offood all year round in this environment. Differences in the population structure of the threepopulations are discussed with respect to fecundity and several mortality factors such as predation anddiseases/parasites

New BeppoSAX-WFC results on superbursts

Presently seven superbursters have been identified representing 10% of the total Galactic X-ray burster population. Four superbursters were discovered with the Wide Field Cameras (WFCs) on BeppoSAX and three with the All-Sky Monitor and Proportional Counter Array on RXTE. We discuss the properties of superbursters as derived from WFC observations. There are two interesting conclusions. First, the average recurrence time of superbursts among X-ray bursters that are more luminous than 10% of the Eddington limit is 1.5 yr per object. Second, superbursters systematically have higher alpha values and shorter ordinary bursts than most bursters that have not exhibited superbursts, indicating a higher level of stable thermonuclear helium burning. Theory predicts hitherto undetected superbursts from the most luminous neutron stars. We investigate the prospects for finding these in GX~17+2.Comment: Submitted in January 2004 for the Proceedings of the meeting 'X-Ray Timing 2003: Rossi and Beyond', eds. P. Kaaret, F. K. Lamb, & J. H. Swank (Melville, NY: American Institute of Physics

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

The Rocky Mountain Arsenal: Groundwater Contamination and Clean-Up Activities

26 pages (includes illustrations and map)