The 4MOST facility simulator: instrument and science optimisation

This paper describes the design and implementation of a facility simulator for the 4 metre Multi-Object Spectroscopic Telescope (4MOST) project, a new survey instrument proposed for the ESO VISTA telescope. The 4MOST Facility Simulator (4FS) has several roles, firstly to optimise the design of the instrument, secondly to devise a survey strategy for the wide field design reference surveys that are proposed for 4MOST, and thirdly to verify that 4MOST, as designed, can indeed achieve its primary science goals. We describe the overall structure of the 4FS, together with details of some important 4FS subsystems. We present the initial results from the 4FS which illustrate clearly the value of having a functioning facility simulator very early in the conceptual design phase of this large project.Comment: 7 pages, 7 figures, 1 tabl

The demographics and evolution of the absorbed AGN population.

It has become increasingly apparent that active galactic nuclei (AGN) have played a key role in the galaxy formation process, leading to the galaxy population we see to day. In order to understand better this inter-relationship, we must first measure the characteristics and evolution of the AGN population over cosmic timescales. Models of the AGN population which reproduce the spectrum and intensity of the extra-galactic X-ray background require a large population of faint AGN, the majority obscured by large column densities of cold material. In the local Universe, where we find mostly low luminosity objects, the obscured AGN make up 80% of the population. However, at higher redshifts, including the epoch when AGN and galaxies were forming most rapidly, the demographics of the obscured AGN population are still poorly understood. For this thesis, I have made a detailed examination of the AGN detected in several of the deepest XMM-Newton "blank-field" observations. I have carried out a detailed set of Monte-Carlo simulations in order to compare directly the X-ray properties of the observed AGN to the predictions of a number of AGN population models. For sources detected in the "13H" deep field, I find that the best fitting model contains AGN with a broad range of obscuration levels, but with significantly absorbed AGN making up at least 75% of the population. Furthermore, by examining the sources in XMM-Newton observations of the "CDFS" field, for which nearly complete redshift determinations are available, I find that the AGN absorption distribution exhibits little redshift or luminosity dependence. I confirm these findings by extending my study to a much larger AGN sample, and investigate field-to-field AGN source density variations

Long Term Wind-Driven X-Ray Spectral Variability of NGC 1365 with Swift

We present long-term (months-years) X-ray spectral variability of the Seyfert 1.8 galaxy NGC 1365 as observed by Swift, which provides well sampled observations over a much longer timescale (6 years) and a much larger flux range than is afforded by other observatories. At very low luminosities the spectrum is very soft, becoming rapidly harder as the luminosity increases and then, above a particular luminosity, softening again. At a given flux level, the scatter in hardness ratio is not very large, meaning that the spectral shape is largely determined by the luminosity. The spectra were therefore summed in luminosity bins and fitted with a variety of models. The best fitting model consists of two power laws, one unabsorbed and another, more luminous, which is absorbed. In this model, we find a range of intrinsic 0.5-10.0 keV luminosities of approximately 1.1-3.5 ergs/s, and a very large range of absorbing columns, of approximately 10^22 - 10^24 cm^-2. Interestingly, we find that the absorbing column decreases with increasing luminosity, but that this result is not due to changes in ionisation. We suggest that these observations might be interpreted in terms of a wind model in which the launch radius varies as a function of ionising flux and disc temperature and therefore moves out with increasing accretion rate, i.e. increasing X-ray luminosity. Thus, depending on the inclination angle of the disc relative to the observer, the absorbing column may decrease as the accretion rate goes up. The weaker, unabsorbed, component may be a scattered component from the wind.Comment: 9 pages, 7 figures, accepted for publication in the Monthly Notices of the Royal Astronomical Societ

Long-Term X-ray Spectral Variability of Seyfert Galaxies with Swift

We present analysis of the long-term X-ray spectral variability of Seyfert galaxies as observed by Swift, which provides well-sampled observations over a much larger flux range and a much longer timescale than any other X-ray observatory. We examine long-term variability of three AGN: NGC 1365 (see Connolly et al. 2014), Mkn 335 and NGC 5548. At high fluxes, the 0.5-10 keV spectra soften with increasing flux, as seen previously within the 2-10 keV band. However, at very low fluxes the sources also become very soft. We have fitted a number of models to the data and find that both intrinsic luminosity variability and variable absorption are required to explain the observations. In some systems, e.g. NGC 1365, the best explanation is a two-component wind model in which one component represents direct emission absorbed by a disc wind wind, with the absorbing column inversely proportional to the intrinsic luminosity, and the second component represents unabsorbed emission reflected from the wind. In other AGN the situation is more complex.Comment: 6 pages, 5 figues, to appear in "Swift: 10 years of discovery", Proceedings of Scienc

A deep Giant Metre-wave Radio Telescope 610-MHz survey of the 1^HXMM–Newton/Chandra survey field

We present the results of a deep 610-MHz survey of the 1^HXMM–Newton/Chandra survey area with the Giant Metre-wave Radio Telescope. The resulting maps have a resolution of ~7 arcsec and an rms noise limit of 60 μJy. To a 5σ detection limit of 300 μJy, we detect 223 sources within a survey area of 64 arcmin in diameter. We compute the 610-MHz source counts and compare them to those measured at other radio wavelengths. The well-known flattening of the Euclidean-normalized 1.4-GHz source counts below ~2 mJy, usually explained by a population of starburst galaxies undergoing luminosity evolution, is seen at 610 MHz. The 610-MHz source counts can be modelled by the same populations that explain the 1.4-GHz source counts, assuming a spectral index of −0.7 for the starburst galaxies and the steep spectrum active galactic nucleus (AGN) population. We find a similar dependence of luminosity evolution on redshift for the starburst galaxies at 610 MHz as is found at 1.4 GHz (i.e. 'Q'= 2.45^(+0.3)_(−0.4))

A tidal disruption flare in a massive galaxy? Implications for the fuelling mechanisms of nuclear black holes

We argue that the `changing look' AGN recently reported by LaMassa et al. could be a luminous flare produced by the tidal disruption of a super-solar mass star passing just a few gravitational radii outside the event horizon of a $\sim 10^8 M_{\odot}$ nuclear black hole. This flare occurred in a massive, star forming galaxy at redshift $z=0.312$, robustly characterized thanks to repeated late-time photometric and spectroscopic observations. By taking difference-photometry of the well sampled multi-year SDSS Stripe-82 light-curve, we are able to probe the evolution of the nuclear spectrum over the course of the outburst. The tidal disruption event (TDE) interpretation is consistent with the very rapid rise and the decay time of the flare, which displays an evolution consistent with the well-known $t^{-5/3}$ behaviour (with a clear superimposed re-brightening flare). Our analysis places constraints on the physical properties of the TDE, such as the putative disrupted star's mass and orbital parameters, as well as the size and temperature of the emitting material. The properties of the broad and narrow emission lines observed in two epochs of SDSS spectra provide further constraints on the circum-nuclear structure, and could be indicative that the system hosted a moderate-luminosity AGN as recently as a few $10^4$ years ago, and is likely undergoing residual accretion as late as ten years after peak, as seen from the broad H$\alpha$ emission line. We discuss the complex interplay between tidal disruption events and gas accretion episodes in galactic nuclei, highlighting the implications for future TDE searches and for estimates of their intrinsic rates.Comment: 20 pages, 9 figures, 3 tables. Accepted for publication in MNRA

Finding counterparts for All-sky X-ray surveys with Nway: a Bayesian algorithm for cross-matching multiple catalogues

We release the AllWISE counterparts and Gaia matches to 106,573 and 17,665 X-ray sources detected in the ROSAT 2RXS and XMMSL2 surveys with |b|>15. These are the brightest X-ray sources in the sky, but their position uncertainties and the sparse multi-wavelength coverage until now rendered the identification of their counterparts a demanding task with uncertain results. New all-sky multi-wavelength surveys of sufficient depth, like AllWISE and Gaia, and a new Bayesian statistics based algorithm, NWAY, allow us, for the first time, to provide reliable counterpart associations. NWAY extends previous distance and sky density based association methods and, using one or more priors (e.g., colors, magnitudes), weights the probability that sources from two or more catalogues are simultaneously associated on the basis of their observable characteristics. Here, counterparts have been determined using a WISE color-magnitude prior. A reference sample of 4524 XMM/Chandra and Swift X-ray sources demonstrates a reliability of ~ 94.7% (2RXS) and 97.4% (XMMSL2). Combining our results with Chandra-COSMOS data, we propose a new separation between stars and AGN in the X-ray/WISE flux-magnitude plane, valid over six orders of magnitude. We also release the NWAY code and its user manual. NWAY was extensively tested with XMM-COSMOS data. Using two different sets of priors, we find an agreement of 96% and 99% with published Likelihood Ratio methods. Our results were achieved faster and without any follow-up visual inspection. With the advent of deep and wide area surveys in X-rays (e.g. SRG/eROSITA, Athena/WFI) and radio (ASKAP/EMU, LOFAR, APERTIF, etc.) NWAY will provide a powerful and reliable counterpart identification tool.Comment: MNRAS, Paper accepted for publication. Updated catalogs are available at www.mpe.mpg.de/XraySurveys/2RXS_XMMSL2 . NWAY available at https://github.com/JohannesBuchner/nwa

A KINEMATIC DESCRIPTION OF THE POST PUBESCENT WINDMILL SOFTBALL PITCHING MOTION

The purpose of this study was to describe the kinematics of the windmill softball pitch. Throughout the first three phases of the movement, both the pelvis and the trunk were rotated to a closed position while the throwing shoulder was flexed and externally rotated, and the throwing elbow was flexed. During the latter stages of the movement, the pelvis and torso opened up to face the plate, the throwing shoulder moved through an arc of hyperextension and was internally rotated while the throwing elbow extended. The kinematics identified may contribute to overuse injuries commonly reported by post pubescent softball pitchers. However, due to the limited data describing the windmill softball pitch, addition research is needed