VHE Gamma Rays from PKS 2155-304

The close X-ray selected BL Lac PKS 2155-304 has been observed using the University of Durham Mark 6 very high energy (VHE) gamma ray telescope during 1996 September/October/November and 1997 October/November. VHE gamma rays with energy > 300 GeV were detected from this object with a time-averaged integral flux of (4.2 +/- 0.7 (stat) +/- 2.0 (sys)) x 10^(-11) per cm2 per s. There is evidence for VHE gamma ray emission during our observations in 1996 September and 1997 October/November, with the strongest emission being detected in 1997 November, when the object was producing the largest flux ever recorded in high-energy X-rays and was detected in > 100 MeV gamma-rays. The VHE and X-ray fluxes show evidence of a correlation.Comment: 14 pages, 6 figures, accepted for publication in Ap.

Synthetic simulations of the extragalactic sky seen by eROSITA I. Pre-launch selection functions from Monte-Carlo simulations

Context. Studies of galaxy clusters provide stringent constraints on models of structure formation. Provided that selection effects are under control, large X-ray surveys are well suited to derive cosmological parameters, in particular those governing the dark energy equation of state. Aims. We forecast the capabilities of the all-sky eROSITA (extended ROentgen Survey with an Imaging Telescope Array) survey to be achieved by the early 2020s. We bring special attention to modelling the entire chain from photon emission to source detection and cataloguing. Methods. The selection function of galaxy clusters for the upcoming eROSITA mission is investigated by means of extensive and dedicated Monte-Carlo simulations. Employing a combination of accurate instrument characterisation and a state-of-the-art source detection technique, we determine a cluster detection efficiency based on the cluster fluxes and sizes. Results. Using this eROSITA cluster selection function, we find that eROSITA will detect a total of approximately 10(5) clusters in the extra-galactic sky. This number of clusters will allow eROSITA to put stringent constraints on cosmological models. We show that incomplete assumptions on selection effects, such as neglecting the distribution of cluster sizes, induce a bias in the derived value of cosmological parameters. Conclusions. Synthetic simulations of the eROSITA sky capture the essential characteristics impacting the next-generation galaxy cluster surveys and they highlight parameters requiring tight monitoring in order to avoid biases in cosmological analyses.Peer reviewe

The application of large amplitude oscillatory stress in a study of fully formed fibrin clots

The suitability of controlled stress large amplitude oscillatory shear (LAOStress) for the characterisation of the nonlinear viscoelastic properties of fully formed fibrin clots is investigated. Capturing the rich nonlinear viscoelastic behaviour of the fibrin network is important for understanding the structural behaviour of clots formed in blood vessels which are exposed to a wide range of shear stresses. We report, for the first time, that artefacts due to ringing exist in both the sample stress and strain waveforms of a LAOStress measurement which will lead to errors in the calculation of nonlinear viscoelastic properties. The process of smoothing the waveforms eliminates these artefacts whilst retaining essential rheological information. Furthermore, we demonstrate the potential of LAOStress for characterising the nonlinear viscoelastic properties of fibrin clots in response to incremental increases of applied stress up to the point of fracture. Alternating LAOStress and small amplitude oscillatory shear measurements provide detailed information of reversible and irreversible structural changes of the fibrin clot as a consequence of elevated levels of stress. We relate these findings to previous studies involving large scale deformations of fibrin clots. The LAOStress technique may provide useful information to help understand why some blood clots formed in vessels are stable (such as in deep vein thrombosis) and others break off (leading to a life threatening pulmonary embolism)

ROSAT Blank Field Sources I: Sample Selection and Archival Data

We have identified a population of blank field sources (or `blanks') among the ROSAT bright unidentified X-ray sources with faint optical counterparts. The extreme X-ray over optical flux ratio of blanks is not compatible with the main classes of X-ray emitters except for extreme BL Lacertae objects. From the analysis of ROSAT archival data we found no indication of variability and evidence for only three sources, out of 16, needing absorption in excess of the Galactic value. We also found evidence for an extended nature for only one of the 5 blanks with a serendipitous HRI detection; this source (1WGAJ1226.9+3332) was confirmed as a z=0.89 cluster of galaxies. Palomar images reveal the presence of a red (O-E~2) counterpart in the X-ray error circle for 6 blanks. The identification process brought to the discovery of another high z cluster of galaxies, one (possibly extreme) BL Lac, two ultraluminous X-ray sources in nearby galaxies and two apparently normal type1 AGNs. These AGNs, together with 4 more AGN-like objects seem to form a well defined group: they present unabsorbed X-ray spectra but red Palomar counterparts. We discuss the possible explanations for the discrepancy between the X-ray and optical data, among which: a suppressed big blue bump emission, an extreme dust to gas (~40-60 the Galactic ratio), a high redshift (z>3.5) QSO nature, an atypical dust grain size distribution and a dusty warm absorber. These AGN-like blanks seem to be the bright (and easier to study) analogs of the sources which are found in deep Chandra observations. Three more blanks have a still unknown nature.Comment: 23 pages, 8 figures, accepted by ApJ main journa

Status, trends, and population demographics of selected sportfish species in the La Grange Reach of the Illinois River

Sportfish species, specifically Yellow Bass Morone mississippiensis, White Bass Morone chrysops, Largemouth Bass Micropterus salmoides, Bluegill Lepomis macrochirus, Black Crappie Pomoxis nigromaculatus, and White Crappie P. annularis, often drive economically valuable fisheries in large river systems, including the Upper Mississippi River System (UMRS). Within the Illinois River, part of the UMRS, these species are routinely sampled by an ongoing long-term fisheries monitoring program. Through this program, we investigated long-term trends (1993-2017) in catch rates and relative weights and quantified demographic rates from 2012-2016. We found all six species, with the exception of Yellow Bass, to have declining catch rates with this decline being most stark in larger, older fishes. Population demographics for Yellow Bass, White Bass, Bluegill, and Black Crappie suggest populations are dominated by younger individuals, with only Black Crappie regularly living to age 3 and older, which may be driving population declines. There are many environmental stressors acting on the Illinois River that could be contributing to the lack of older and larger fishes, including, but not limited to, navigation efforts, altered hydrology, pollution, sedimentation, lack of overwintering habitat, and introduction of invasive species. Results of this study demonstrate that additional research to understand mechanisms driving reduced abundance and stunted age structure are needed to identify effective management actions that would benefit populations of recreationally valuable sportfish species.is peer reviewedOpe

Long-Term X-Ray and TeV variability of Mrk 501

We present X-ray observations of the blazar Mrk501 obtained with RXTE during 1997, 1998, 1999, 2000, and 2004. The goal of this study is twofold: 1) characterize the long-term X-ray flux and spectral variability of the source with a model-independent analysis, and 2) investigate the X-ray and TeV correlation on long timescales. The spectral and temporal variability properties appear to be markedly different compared to those of non-jet-dominated radio-loud and radio-quiet AGN monitored with RXTE. To investigate the X-ray/TeV correlation on long timescales we compared RXTE data with HEGRA and Whipple historical light curves. We confirm the presence of a direct correlation, which appears to be stronger when the source is brighter. The analysis of individual flares shows that the X-ray\TeV correlated activity is heterogeneous. However, more sensitive TeV observations are necessary to confirm these findings, and to put tighter constraints on jet models (abridged).Comment: 20 pages, 11 figures, accepted for publication in Ap

The XMM-Newton serendipitous survey. VII. The third XMM-Newton serendipitous source catalogue

Thanks to the large collecting area (3 x ~1500 cm$^2$ at 1.5 keV) and wide field of view (30' across in full field mode) of the X-ray cameras on board the European Space Agency X-ray observatory XMM-Newton, each individual pointing can result in the detection of hundreds of X-ray sources, most of which are newly discovered. Recently, many improvements in the XMM-Newton data reduction algorithms have been made. These include enhanced source characterisation and reduced spurious source detections, refined astrometric precision, greater net sensitivity and the extraction of spectra and time series for fainter sources, with better signal-to-noise. Further, almost 50\% more observations are in the public domain compared to 2XMMi-DR3, allowing the XMM-Newton Survey Science Centre (XMM-SSC) to produce a much larger and better quality X-ray source catalogue. The XMM-SSC has developed a pipeline to reduce the XMM-Newton data automatically and using improved calibration a new catalogue version has been produced from XMM-Newton data made public by 2013 Dec. 31 (13 years of data). Manual screening ensures the highest data quality. This catalogue is known as 3XMM. In the latest release, 3XMM-DR5, there are 565962 X-ray detections comprising 396910 unique X-ray sources. For the 133000 brightest sources, spectra and lightcurves are provided. For all detections, the positions on the sky, a measure of the quality of the detection, and an evaluation of the X-ray variability is provided, along with the fluxes and count rates in 7 X-ray energy bands, the total 0.2-12 keV band counts, and four hardness ratios. To identify the detections, a cross correlation with 228 catalogues is also provided for each X-ray detection. 3XMM-DR5 is the largest X-ray source catalogue ever produced. Thanks to the large array of data products, it is an excellent resource in which to find new and extreme objects.Comment: 23 pages, version accepted for publication in A&

XMM-Newton 13H Deep field - I. X-ray sources

We present the results of a deep X-ray survey conducted with XMM-Newton, centred on the UK ROSAT 13H deep field area. This region covers 0.18 deg^2 and is the first of two areas covered with XMM-Newton as part of an extensive multi-wavelength survey designed to study the nature and evolution of the faint X-ray source population. We have produced detailed Monte-Carlo simulations to obtain a quantitative characterisation of the source detection procedure and to assess the reliability of the resultant sourcelist. We use the simulations to establish a likelihood threshold above which we expect less than 7 (3%) of our sources to be spurious. We present the final catalogue of 225 sources. Within the central 9 arcmin, 68 per cent of source positions are accurate to 2 arcsec, making optical follow-up relatively straightforward. We construct the N(>S) relation in four energy bands: 0.2-0.5 keV, 0.5-2 keV, 2-5 keV and 5-10 keV. In all but our highest energy band we find that the source counts can be represented by a double powerlaw with a bright end slope consistent with the Euclidean case and a break around 10^-14 cgs. Below this flux the counts exhibit a flattening. Our source counts reach densities of 700, 1300, 900 and 300 deg^-2 at fluxes of 4.1x10^-16, 4.5x10^-16, 1.1x10^-15 and 5.3x10^-15 cgs in the 0.2-0.5, 0.5-2, 2-5 and 5-10 keV energy bands respectively. We have compared our source counts with those in the two Chandra deep fields and Lockman hole and find our source counts to be amongst the highest of these fields in all energy bands. We resolve >51% (>50%) of the X-ray background emission in the 1-2 keV (2-5 keV) energy bands.Comment: 27 pages, 18 figures, MNRAS accepte