119,662 research outputs found
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
Letter from Paul M. Roca on behalf of Carl Hayden to Ray E. Carr, Associated Civic Clubs of Southern Utah
No full textLetter from Paul M. Roca to Ray E. Carr on behalf of Carl Hayden politely declining his invitation
New insights on accretion in supergiant fast X-ray transients from XMM-Newton and INTEGRAL observations of IGR J17544-2619
No full textXMM–Newton observations of the supergiant fast X-ray transient IGR J17544?2619 are reported and placed in the context of an analysis of archival INTEGRAL/IBIS data that provide a refined estimate of the orbital period at 4.9272?±?0.0004?d. A complete outburst history across the INTEGRAL mission is reported. Although the new XMM–Newton observations (each lasting ?15 ks) targeted the peak flux in the phase-folded hard X-ray light curve of IGR J17544?2619, no bright outbursts were observed, the source spending the majority of the exposure at intermediate luminosities of the order of several 1033?erg?s?1 (0.5–10 keV) and displaying only low level flickering activity. For the final portion of the exposure, the luminosity of IGR J17544?2619 dropped to ?4?×?1032?erg?s?1 (0.5–10 keV), comparable with the lowest luminosities ever detected from this source, despite the observations being taken near to periastron. We consider the possible orbital geometry of IGR J17544?2619 and the implications for the nature of the mass transfer and accretion mechanisms for both IGR J17544?2619 and the supergiant fast X-ray transients (SFXTs) population. We conclude that accretion under the ‘quasi-spherical accretion’ model provides a good description of the behaviour of IGR J17544?2619 and suggests an additional mechanism for generating outbursts based upon the mass accumulation rate in the hot shell (atmosphere) that forms around the neutron star under the quasi-spherical formulation. Hence, we hope to aid in explaining the varied outburst behaviours observed across the SFXT population with a consistent underlying physical model
R&D studies for very high energy gamma-ray astrophysics at energies greater than 10 TeV
No full textIn spite of more than 100 discoveries of TeV gamma-ray sources by the current imaging atmospheric Cherenkov telescope (IACT) arrays, Galactic cosmic ray accelerators up to the knee energies (∼ PeV) still remain unclear. PeV Explorer (or PeX) is a future project of a relatively small IACT array, optimized to detect gamma rays of energies greater than 10 TeV and aiming to explore Galactic accelerators up to PeV energies. We present the status of our hardware R & D studies for this project and some extension plans.T. Yoshikoshi, R. W. Clay, B. R. Dawson, Y. Matsubara, M. Mori, T. Naito, K. Nishijima, M. Ohishi, G. P. Rowell, T. Toyam
X-ray detector based on a bulk micromachined photodiode combined with a scintillating crystal
No full textThis paper reports the design, fabrication, assembly and testing of
a x-ray detector based on a bulk micromachined photodiode (BMMPD)
with a cavity filled with a scintillating crystal. The x-ray photons
that reach the detector are first converted to visible light by the
scintillating crystal. The visible light is then detected by the BMMPD,
producing an electric current with value proportional to the
incident x-ray intensity. Tests were performed using two x-ray setups:
an experimental one and a professional one.
The first was powered with a maximum voltage of 35kV, and a
current ranging to 1mA and the second was powered with voltages from
40kV to 60kV and currents ranging from 10mA to 55mA
Discovery of an optical counterpart to the hyperluminous X-ray source in ESO 243-49
No full textThe existence of black holes of masses similar to 10(2)-10(5)M(circle dot) has important implications for the formation and evolution of star clusters and supermassive black holes. One of the strongest candidates to date is the hyperluminous X-ray source (HLX1), possibly located in the S0- a galaxy ESO 243-49, but the lack of an identifiable optical counterpart had hampered its interpretation. Using the Magellan telescope, we have discovered an unresolved optical source with R = 23.80 +/- 0.25 mag and V = 24.5 +/- 0.3 mag within HLX1's positional error circle. This implies an average X-ray/optical flux ratio similar to 500. Taking the same distance as ESO 243-49, we obtain an intrinsic brightness M-R = -11.0 +/- 0.3 mag, comparable to that of a massive globular cluster. Alternatively, the optical source is consistent with a main-sequence M star in the Galactic halo (for example an M4.4 star at approximate to 2.5 kpc). We also examined the properties of ESO 243-49 by combining Swift/Ultraviolet/Optical Telescope (UVOT) observations with stellar population modelling. We found that the overall emission is dominated by a similar to 5-Gyr-old stellar population, but the UV emission at approximate to 2000 angstrom is mostly due to ongoing star formation at a rate of similar to 0.03M(circle dot) yr(-1). The UV emission is more intense (at least a 9 sigma enhancement above the mean) north-east of the nucleus, in the same quadrant as HLX1. With the combined optical and X-ray measurements, we put constraints on the nature of HLX1. We rule out a foreground star and a background AGN. Two alternative scenarios are still viable. HLX1 could be an accreting intermediate mass black hole in a star cluster, which may itself be the stripped nucleus of a dwarf galaxy that passed through ESO 243-49, an event which might have caused the current episode of star formation. Or, it could be a neutron star in the Galactic halo, accreting from an M4-M5 donor star
Ray R. Vermillion
No full textThe Oklahoma A&M College World War I Veterans collection captures the memories and experiences of the men and women of Oklahoma Agricultural and Mechanical College who served in World War I. In 1919, a project headed by Maude Cass, the editor of the 1919 Redskin; Professor Maroney of the Department of History; Margaret Walters, Librarian; and J.W. Cantwell, the College President, was undertaken to survey these veterans. The surveys were returned along with photographs, letters, and newspaper clippings documenting these veterans’ experiences during World War I
Novel spectral-timing methods for X-ray binary variability studies
No full textThis work explores the connection between the spectral properties of the X-ray emission produced by black hole X-ray binaries (BHXRBs) and the variability properties of these sources that are embedded in light curves. While BHXRBs are mostly studied using ‘static observables‘ such as the average energy spectrum, a variability timescale-resolved study (in terms of Fourier-frequencies) provides a much stronger and more reliable tool for understanding the intricate physics and geometrical properties of accretion flows around stellar-mass black holes.In the present Thesis, we first show how the geometrical properties of the accretion disc can be mapped by combining spectra and frequency-resolved time-lags. A time-scale-dependent reflection model is developed in terms of Fourier-frequencies and compared to observational hard-state data of GX 339–4 obtained with XMM-Newton. Secondly, we explore the variability properties of the accretion disc in SWIFT J1753.5–0127 using a combination of novel spectral timing methods and the soft X-ray coverage of XMM-Newton. Finally, we show the development of a novel technique for fitting correlated signals in the Fourier domain as a function of energy and Fourier-frequency that can prove particularly useful with high signal-to-noise datasets from future X-ray missions
Nonlinear time series analysis with R
No full textIn the process of data analysis, the investigator is often facing highly-volatile and random-appearing observed data. A vast body of literature shows that the assumption of underlying stochastic processes was not necessarily representing the nature of the processes under investigation and, when other tools were used, deterministic features emerged. Non Linear Time Series Analysis (NLTS) allows researchers to test whether observed volatility conceals systematic non linear behavior, and to rigorously characterize governing dynamics. Behavioral patterns detected by non linear time series analysis, along with scientific principles and other expert information, guide the specification of mechanistic models that serve to explain real-world behavior rather than merely reproducing it. Often there is a misconception regarding the complexity of the level of mathematics needed to understand and utilize the tools of NLTS (for instance Chaos theory). However, mathematics used in NLTS is much simpler than many other subjects of science, such as mathematical topology, relativity or particle physics. For this reason, the tools of NLTS have been confined and utilized mostly in the fields of mathematics and physics. However, many natural phenomena investigated I many fields have been revealing deterministic non linear structures. In this book we aim at presenting the theory and the empirical of NLTS to a broader audience, to make this very powerful area of science available to many scientific areas. This book targets students and professionals in physics, engineering, biology, agriculture, economy and social sciences as a textbook in Nonlinear Time Series Analysis (NLTS) using the R computer language
M-Quantile Models for Small Area Estimation
No full textSmall area estimation techniques are employed when sample data are insufficient for acceptably precise direct estimation in domains of interest. These techniques typically rely on regression models that use both covariates and random effects to explain variation between domains. However, such models also depend on strong distributional assumptions, require a formal specification of the random part of the model and do not easily allow for outlier robust inference. We describe a new approach to small area estimation that is based on modelling quantile-like parameters of the conditional distribution of the target variable given the covariates. This avoids the problems associated with specification of random effects, allowing inter-domain differences to be characterized by the variation of area-specific M-quantile coefficients. The proposed approach is easily made robust against outlying data values and can be adapted for estimation of a wide range of area specific parameters, including that of the quantiles of the distribution of the target variable in the different small areas. Results from two simulation studies comparing the performance of the M-quantile modelling approach with more traditional mixed model approaches are also provided
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