The Timing Properties of Sco X-1 along its Z track as seen with EXOSAT

We present a systematic, homogeneous analysis of all the EXOSAT ME, high time resolution data on Sco X-1. We investigate all power spectral properties of the $<$100 Hz quasi-periodic oscillations (QPO) and noise of Sco X-1 as a function of position on the Z-shaped track traced out in the X-ray colour-colour diagram. Generally, the properties of Sco X-1 vary smoothly as a function of position along the Z track. However, some variability parameters change abruptly at either of the vertices of the Z track indicating that the branches of the Z track represent distinct source states not only in spectral state but also in rapid variability characteristics. We show that the very low frequency noise (VLFN) is consistent with being solely due to motion along the Z track. The QPO show a remarkably rapid change in frequency at or just before the normal-branch/flaring-branch (NB/FB) vertex. This transition happens within 1.5% of the entire extent of the Z track. The QPO themselves are visible for 17% of the Z. We find a new sort of behaviour near the NB/FB vertex, i.e., rapid excursions from the NB into the FB and back again taking only a few minutes.Comment: 30 pages, 15 figures, MNRAS in pres

Long-term Periodicities in the Flux from Low Mass X-ray Binaries

Using data from the All Sky Monitor (ASM) on the Rossi X-ray Timing Explorer (RXTE) we have searched for long term periodicities in the X-ray flux of GX 1+4, Sco X-2 (GX 349+2), and GX 339-4. For GX 1+4 we also used data from BATSE and Galactic Centre scans performed by RXTE. We find no evidence for X-ray modulations at the suggested ~304 d orbital period of GX 1+4. However, we find tentative evidence for a periodicity at 420 d to 460 d. An upper limit of 15% peak-to-peak is set on any sinusoidal modulation in the 1.5 - 3.0 keV flux of Sco X-2 for periods in the 30 to 100 d range. For GX 339-4 we confirm the Low State modulation and report the detection of significant low-frequency modulations in both the High State and Very High State. We fail to detect this modulation in the Off State. We show that if the reported orbital period of GX 339-4 lies in the range 0.5 - 1.7 d, then it is not present in the RXTE ASM light curve.Comment: 7 pages, 8 figures. Accepted for publication in Advanced in Space Research, 16th of March 200

Quantifying and visualizing access to healthy food in a rural area of Australia : a spatial analysis

A Geographical Information System (GIS) using ArcGIS tools was adopted to implement three types of spatial analysis: coverage, density and proximity, to evaluate the geographical access to healthy food of the populations in Dorset Municipality, Tasmania, Australia. Data on food outlets, the aggregated socioeconomic disadvantage index, locations, income and population were collected using the Tasmanian Food Outlet Audit and Tasmanian Healthy Food Basket tools. Spatial autocorrelation was conducted where appropriate to examine the relationship between locations and food access. Healthy food outlets were concentrated in the central areas, areas in proximity to the national road and areas of dense population. Their locations also favored the more socio-economically deprived or disadvantaged areas (Moran’s Index = 0.924, z-score = 5.187, p-value = 0.00 < 0.05). Spatial identification of food deserts in Dorset has been a pioneering attempt to visualize areas with the highest demand for improvement in healthy food access and may be applicable to other areas with similar characteristics. © 2015, Springer Science+Business Media Dordrecht and International Society for Plant Pathology

Discovery of a New Soft Gamma Repeater, SGR 1627-41

We report the discovery of a new soft gamma repeater (SGR), SGR 1627-41, and present BATSE observations of the burst emission and BeppoSAX NFI observations of the probable persistent X-ray counterpart to this SGR. All but one burst spectrum are well fit by an optically thin thermal bremsstrahlung (OTTB) model with kT values between 25 and 35 keV. The spectrum of the X-ray counterpart, SAX J1635.8-4736, is similar to that of other persistent SGR X-ray counterparts. We find weak evidence for a periodic signal at 6.41 s in the light curve for this source. Like other SGRs, this source appears to be associated with a young supernova remnant G337.0-0.1. Based upon the peak luminosities of bursts observed from this SGR, we find a lower limit on the dipole magnetic field of the neutron star B_dipole > 5 * 10^14 Gauss.Comment: 5 pages, 4 figures, submitted to ApJ Letter

RXTE Observations of the Anomalous Pulsar 4U 0142+61

We observed the anomalous X-ray pulsar 4U 0142+61 using the Proportional Counter Array (PCA) aboard the Rossi X-ray Timing Explorer (RXTE) in March 1996. The pulse frequency was measured as f = 0.11510039(3) Hz with an upper limit of df/dt < 4 * 10^(-13) Hz/s upon the short term change in frequency over the 4.6 day span of the observations. A compilation of all historical measurements showed an overall spin-down trend with slope df/dt = (-3.0 +/- 0.1) * 10^(-14) Hz/s. Searches for orbital modulations in pulse arrival times yielded an upper limit of a_x sin i < 0.26 lt-s (99% confidence) for the period range 70 s to 2.5 days. These limits combined with previous optical limits and evolutionary arguments suggest that 4U 0142+61 is probably not a member of a binary system.Comment: 20 pages (LaTeX) including 7 figures. Accepted for publication in the Astrophysical Journa

An Unusual Burst from Soft Gamma Repeater SGR 1900+14: Comparisons with Giant Flares and Implications for the Magnetar Model

The Soft Gamma Repeater SGR 1900+14 entered a remarkable phase of activity during the summer of 1998. This activity peaked on August 27, 1998 when a giant periodic gamma-ray flare resembling the famous March 5, 1979 event from SGR 0526-66 was recorded. Two days later (August 29), a strong, bright burst was detected with RXTE and BATSE. This event reveals several similarities to the giant flares of August 27 and March 5, and shows a number of unique features not previously seen in SGR bursts. Unlike typically short SGR bursts, this event features a 3.5 s burst peak that was preceded by an extended (~ 1 s) complex precursor, and followed by a long (~ 1000 s) periodic tail modulated at the 5.16 s stellar rotation period. Spectral analysis shows a striking distinction between the spectral behavior of the precursor, burst peak and extended tail. While the spectrum during the peak is uniform, a significant spectral evolution is detected in both the precursor and tail emissions. Temporal behavior shows a sharp rise (~ 9.8 ms) at the event onset and a rapid cutoff (~ 17 ms) of the end of the burst peak. The tail pulsations show a simple pulse profile consisting of one 5.16 s peak that did not evolve with time. The spectral and temporal signatures of this event imply that the precursor, main peak, and extended tail are produced by different physical mechanisms. We discuss these features and their implications in the context of the magnetar model. The energetics of the August 29 event, and its close proximity to the August 27 flare, suggest that it is an `aftershock' of the preceding giant flare. "P.S. This is an abbreviated version of the original abstract.

Robustness assessment of clinical adaptive proton and photon radiotherapy for oesophageal cancer in the model-based approach

Purpose In the Netherlands, oesophageal cancer (EC) patients are selected for intensity modulated proton therapy (IMPT) using the expected normal tissue complication probability reduction (ΔNTCP) when treating with IMPT compared to volumetric modulated arc therapy (VMAT). In this study, we evaluate the robustness of the first EC patients treated with IMPT in our clinic in terms of target and organs-at-risk (OAR) dose with corresponding NTCP, as compared to VMAT. Materials and Methods For 20 consecutive EC patients, clinical IMPT and VMAT plans were created on the average planning 4DCT. Both plans were robustly evaluated on weekly repeated 4DCTs and if target coverage degraded, replanning was performed. Target coverage was evaluated for complete treatment trajectories with and without replanning. The planned and accumulated mean lung dose (MLD) and mean heart dose (MHD) were additionally evaluated and translated into NTCP. Results Replanning in the clinic was performed more often for IMPT (15x) than would have been needed for VMAT (8x) (p = 0.11). Both adaptive treatments would have resulted in adequate accumulated target dose coverage. Replanning in the first week of treatment had most clinical impact, as anatomical changes resulting in insufficient accumulated target coverage were already observed at this stage. No differences were found in MLD between the planned dose and the accumulated dose. Accumulated MHD differed from the planned dose (p < 0.001), but since these differences were similar for VMAT and IMPT (1.0 and 1.5 Gy, respectively), the ΔNTCP remained unchanged. Conclusion Following an adaptive clinical workflow, adequate target dose coverage and stable OAR doses with corresponding NTCPs was assured for both IMPT and VMAT