The X‐ray source population of the Andromeda galaxy M 31

First studies of the X‐ray source population of M 31 were performed with the Einstein Observatory and ROSAT. High resolution Chandra Observatory images not only spatially resolved the center area but also supernova remnants (SNRs) in the galaxy. Source catalogues of restricted areas were presented with high astrometric accuracy. Also luminosity function studies and studies of individual sources based on Chandra and XMM‐Newton observations led to a better knowledge of the X‐ray source population. An XMM‐Newton source catalog based on archival observations revealed more than 850 sources down to a 0.2–4.5 keV luminosity of 10³⁵ erg s^–1. EPIC hardness ratios as well as informations from earlier X‐ray, optical, and radio catalogues were used to distinguish between different source classes (SNRs, supersoft sources (SSSs), X‐ray binaries (XRBs), globular cluster sources within M 31, and foreground stars and objects in the background). However, many sources could only be classified as “hard”. These sources may either be XRBs or Crab‐like SNRs in M 31 or background sources. Two of the globular cluster sources could be identified as low mass XRBs with a neutron star as compact object as they showed type I X‐ray bursts. Many of the SSSs were identified as optical novae. Inspired by these results an XMM‐Newton survey of the entire D₂₅ disk of M 31 and a dedicated program to monitor X‐ray counterparts of optical novae in M 31 was started. We discuss implications for further nearby galaxy studies. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Identification of seismic anomalies caused by gas saturation on the basis of theoretical P and PS wavefield in the Carpathian Foredeep,SE Poland

The thin-layer build of the Carpathian Foredeep Miocene formations and large petrophysical parameter variation cause seismic images of gas-saturated zones to be ambiguous, and the location of prospection wells on the basis of anomalous seismic record is risky. A method that assists reservoir interpretation of standard recorded seismic profiles (P waves) can be a converted wave recording (PS waves). This paper presents the results of application of a multicomponent seismic survey for the reservoir interpretation over the Chałupki Dębniańskie gas deposit, carried out for the first time in Poland by Geofizyka Kraków Ltd. for the Polish Oil and Gas Company. Seismic modeling was applied as the basic research tool, using the SeisMod program based on the finite-difference solution of the acoustic wave equation and equations of motion. Seismogeological models for P waves were developed using Acoustic Logs; S-wave model (records only from part of the well) was developed on the basis of theoretical curves calculated by means of the Estymacja program calibrated with average S-velocities, calculated by correlation of recorded P and PS wavefields with 1D modeling. The conformity between theoretical and recorded wavefields makes it possible to apply the criteria established on the basis of modeling for reservoir interpretation. Direct hydrocarbon indicators (bright spots, phase change, time sag) unambiguously identify gas-prone layers within the ChD-2 prospect. A partial range of the indicators observed in the SW part of the studied profile (bright spot that covers a single, anticlinally bent seismic horizon) points to saturation of the horizon. The proposed location is confirmed by criteria determined for converted waves (continuous seismic horizons with constant, high amplitude) despite poorer agreement between theoretical and recorded wavefields.     

Optical short-time variations in GK Persei during the 1983 outburst

During the August 1983 outburst of the old nova GK Persei observations with EXOSAT showed for the first time a 351 second periodicity in X-rays.Our fast photometry (U(B)V with 25 sec time resolution) was made at the end of the outburst in the nights of September 29, and October 1–3, using the 2.2 meter telescope at Calar Alto (Spain).Optical variations up to 10% in U and 4% in V with periodicities in the range 350 to 360 seconds were found, lasting only for few cycles.A comparison with the extrapolated prediction of the X-ray maxima did not show a coincidence, but rather an anticoincidence in several cases. This supports a model of reprocessed X-rays at the inner edge of an accretion disk.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

Fluvial transport as a natural luminescence sensitiser of quartz

The optically stimulated luminescence (OSL) sensitivity of quartz sampled from the bed of the Castlereagh River in inland New South Wales increases linearly with distance downstream, through both a proportional increase in the number of luminescent grains and increases in the sensitivity of individual grains. It is argued that downstream transport provides numerous opportunities for repeated irradiation and bleaching which combine to increase sensitivity of the quartz grains. Individual quartz grains collected from the uppermost sampling site on the Castlereagh River increase in sensitivity in response to repeated cycles of laboratory irradiation, heating and illumination, providing an explanatory analogue. Furthermore, initially non-luminescent grains are shown to be ‘switched on’ by this same laboratory treatment. We conclude that downstream increases in the luminescence sensitivity of quartz observed in the Castlereagh River are due to intrinsic changes within the quartz and not due to any macro changes in the grains, for example polishing, or abrasion and loss of non-luminescent grains. We also infer that the high OSL sensitivity of sedimentary quartz from Australia is due to the predominance of environments which provide numerous opportunities for repeated irradiation, illumination and heating. Observation of the change in luminescence sensitivity of quartz bedload has the potential to provide additional information on the nature of bedload transport processes. Data from the Castlereagh River indicate that the rate of bedload transport is approximately constant along the 325 km sampled reach.     

Death of a palaeochannel: Slow abandonment of an avulsed channel on the Riverine Plains,SE Australia

Avulsion of rivers can be a gradual process that is associated with a metamorphosis of channel pattern or changed channel characteristics. The processes controlling avulsion, and hence anastomosis, often operate too slowly to study by measuring active river systems, and hence well preserved Late Quaternary rivers offer one of the best ways to study the long-term development of avulsive systems. The modern and ancient channels of the Murrumbidgee River provide a classic example of long-lived, semi-static anastomosis, operating on timescales that include stadial and interstadial climate cycles. Over the last glacial cycle, regional avulsions have occurred every ~12 ka while maintaining an anastomosing pattern through the slow infill of abandoned channels. The Yanco Creek Palaeochannel System emerged from a period of high discharge linked to snowmelt in the terminal Pleistocene. Here, geomorphological mapping of the Yanco System was conducted together with single-grain, optically stimulated luminescence dating of sediments in the channel belt. Since the main phase of channel construction during the Last Glacial Maximum, the Yanco system has functioned as a flood conduit and minor anabranch of the Murrumbidgee River, with reworking of ancient channel sediments by an underfit stream that is ongoing to the present day. Our new ages of ~13–14 ka are interpreted as channel sedimentation during an underfit phase following avulsion. The prevalence of full and partial avulsion in this environment may be complicating palaeohydrological interpretations of ages for channel activity, and reworking has gone unrecognised. We contend that some previous interpretations of the significance of ages for sediments collected from palaeochannels in the Riverine Plain may need revision.     

Exosat observations of H2252-035: Pulse phase and orbital phase dependent low energy absorption and iron line emission

The 805 sec pulsing X-ray source H2252-035 has been observed for 7 h on September 14/15 and on September 17, 1983 in X-rays with the low energy telescope and the medium energy detectors of EXOSAT. While below 2 keV the semiamplitude of the 805 s pulses is 100% in the 2.3–7.9 keV band it is only 40%. X-ray dips that are more pronounced in low energies occur simultaneously with the orbital minimum of the optical light curve. The medium energy spectra during dips with respect to the non dip spectrum can be explained by just enhanced cold gas absorption of an additional absorbing column of 2 10²² cm^–2. Model spectra for the 805 s minimum have to include a strong iron emission line at 6.55 keV with an equivalent width of 3 keV in addition to a reduced continuum intensity (radiating area) and enhanced low energy absorption.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

X‐ray emission from optical novae in M 31

The first supersoft source (SSS) identification with an optical nova in M 31 was based on ROSAT observations. Twenty additional X‐ray counterparts (mostly identified as SSS by their hardness ratios) were detected using archival ROSAT, XMM‐Newton and Chandra observations obtained before July 2002. Based on these results optical novae seem to constitute the major class of SSS in M 31. An analysis of archival Chandra HRC‐I and ACIS‐I observations obtained from July 2004 to February 2005 demonstrated that M 31 nova SSS states lasted from months to about 10 years. Several novae showed short X‐ray outbursts starting within 50 d after the optical outburst and lasting only two to three months. The fraction of novae detected in soft X‐rays within a year after the optical outburst was more than 30%. Ongoing optical nova monitoring programs, optical spectral follow‐up and an up‐to‐date nova catalogue are essential for the X‐ray work. Re‐analysis of archival nova data to improve positions and find additional nova candidates are urgently needed for secure recurrent nova identifications. Dedicated XMM‐Newton/Chandra monitoring programs for X‐ray emission from optical novae covering the centre area of M 31 continue to provide interesting new results (e.g. coherent 1105 s pulsations in the SSS counterpart of nova M31N 2007‐12b). The SSS light curves of novae allow us – together with optical information – to estimate the mass of the white dwarf, of the ejecta and the burned mass in the outburst. Observations of the central area of M 31 allow us – in contrast to observations in the Galaxy – to monitor many novae simultaneously and proved to be prone to find many interesting SSS and nova types (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Supersoft sources in M31: Comparing the XMM‐Newton deep survey,ROSAT and Chandra catalogues

To investigate the transient nature of supersoft sources (SSSs) in M 31, we compared SSS candidates ofthe XMM‐Newton Deep Survey, ROSAT PSPC surveys and the Chandra catalogues in the same field. We found 40 SSSs in the XMM‐Newton observations. While 12 of the XMM‐Newton sources were brighter than the limiting flux of the ROSAT PSPC survey, only two were detected with ROSAT ∼10 yr earlier. Five correlate with recent optical novae which explains why they were not detected by ROSAT. The remaining 28 XMM‐Newton SSSs have fluxes below the ROSAT detection threshold. Nevertheless we found one correlation with a ROSAT source, which had significantly larger fluxes than during the XMM‐Newton observations. Ten of the XMM‐Newton SSSs were detected by Chandra with <1– ∼6yr between the observations. Five were also classified as SSSs by Chandra. Of the 30 ROSAT SSSs three were confirmed with XMM‐Newton, while for 11 sources other classifications are suggested. Of the remaining 16 sources one correlates with an optical nova. Of the 42 Chandra very‐soft sources five are classified as XMM‐Newton SSSs, while for 22 we suggest other classifications. Of the remaining 15 sources, nine are classified as transient by Chandra, one of them correlates with an optical nova. These findings underlined the high variability of the sources of this class and the connection between SSSs and optical novae. Only three sources, were detected by all three missions as SSSs. Thus they are visible for more than a decade, despite their variability (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A 100 ka record of fluvial activity in the Fitzroy River Basin,tropical northeastern Australia

This study reports the nature and timing of Quaternary fluvial activity in the Fitzroy River basin, which drains a diverse 143,000 km² area in northeastern Queensland, before discharging into the Great Barrier Reef Marine Park. The catchment consists of an extensive array of channel and floodplain types that we show have undergone large-scale fluvial adjustment in-channel planform, geometry and sinuosity. Optically stimulated luminescence (OSL) dating of quartz sediments from fifteen (3–18 m) floodplain cores throughout the basin indicates several discrete phases of active bedload activity: at ～105–85 ka in Marine Isotope Stage (MIS) 5, at ～50–40 ka (MIS 3), and at ～30–10 ka (MIS 3/2). The overall timing of late Quaternary fluvial activity correlates well with previous accounts from across Australia with rivers being primarily active during interstadials. Fluvial activity, however, does not appear to have been synchronous throughout the basin’s major sub-catchments. Fluvial activity throughout MIS 2 (i.e. across the Last Glacial Maximum) in the meandering channels of the Fitzroy correlates well with regional data in tropical northeastern Queensland, and casts new light on the river response to reduced rainfall and vegetation cover suggested by regional palaeoclimate indicators. Moreover, the absence of a strong Holocene signal is at odds with previous accounts from elsewhere throughout Australia. The latitudinal position of the Fitzroy across the Tropic of Capricorn places this catchment at a key location for elucidating the main hydrological drivers of Quaternary fluvial activity in northeastern Australia, and especially for determining tropical moisture sources feeding into the headwaters of Cooper Creek, a major river system of the continental interior.     

Variable source contributions to river bed sediments across three size fractions

Sediment tracing using geochemical properties is an efficient way to identify the spatial sources of transported sediments delivered to waterways. Here, the contribution of soil sources to river bed sediments has been quantified in Emu Creek, a headwater catchment in south eastern Queensland, Australia. Soil samples were collected from the eight major rock types present in the catchment and were related to river bed sediments collected from eight sites along the main channel. Geochemistry, as characterized by 39 elemental concentrations, was measured using inductively coupled plasma mass spectrometry and inductively coupled plasma optical emission spectrometry. Three particle size fractions were examined, <10, 10–63 and 63–212 µm, with the three resultant mixing models showing divergent results. We conclude that the results of sediment mixing models based on the analysis of one grain size should not be assumed to apply across the entire particle size range of transported sediment, emphasizing the need to match the size fraction used in tracing studies to that size fraction of interest in downstream sinks. Furthermore, we present results highlighting the control transport distance plays in source dominance, with this particularly evident in the coarser fraction, where local sources dominate over more distant sources. Copyright © 2015 John Wiley & Sons, Ltd.