scholarly journals X-ray spectroscopy of newly identified ULXs associated with M87’s globular cluster population

2020 ◽  
Vol 497 (1) ◽  
pp. 596-608 ◽  
Author(s):  
Kristen C Dage ◽  
Stephen E Zepf ◽  
Erica Thygesen ◽  
Arash Bahramian ◽  
Arunav Kundu ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Component Model ◽  
X Ray ◽  
Two Component ◽  
Long Time ◽  
Order Of Magnitude ◽  
Best Fitting ◽  
Component Models ◽  
Best Fit

ABSTRACT We have identified seven ultraluminous X-ray sources (ULXs) that are coincident with globular cluster candidates (GC) associated with M87. ULXs in the old GC environment represent a new population of ULXs, and ones likely to be black holes. In this study, we perform detailed X-ray spectroscopic follow-up to seven GC ULXs across a wealth of archival Chandra observations and long time baseline of 16 yr. This study brings the total known sample of GC ULXs to 17. Two of these sources show variability in their X-ray luminosity of an order of magnitude over many years, and one of these sources shows intra-observational variability on the scale of hours. While the X-ray spectra of the majority of GC ULXs are best fit by single-component models, one of the sources studied in this paper is the second GC ULX to be best fit by a two-component model. We compare this new sample of GC ULXs to the previously studied sample, and compare the X-ray and optical properties counterparts across the samples. We find that the clusters that host ULXs in M87 have metallicities from g − z = 1.01 to g − z = 1.70. The best-fitting power-law indices of the X-ray spectra range from Γ = 1.37 to 2.21, and the best-fitting inner blackbody disc temperatures range from kT = 0.56 to 1.90 keV.

GINGA OBSERVATIONS OF X0512–401 IN THE GLOBULAR CLUSTER NGC1851

1993 ◽  
Vol 02 (04) ◽  
pp. 497-507
Author(s):  
E.N. ERCAN ◽  
A.M. CRUISE ◽  
B.J. KELLETT
Keyword(s):  
Neutron Star ◽  
Emission Line ◽  
Accretion Disk ◽  
Power Law ◽  
Globular Cluster ◽  
Third Body ◽  
X Ray ◽  
Two Component ◽  
Low Mass ◽  
Best Fit

We present here the first detailed spectral observations of the low-mass X-ray binary source X0512–401 located in the globular cluster NGC1851 obtained by Ginga. We have found that the Ginga LAC data of X0512–401 are best fitted by a “two-component” spectral model: power-law with exponential cut-off and a blackbody. The inclusion of a 6.7 KeV Fe emission line did not improve our best fit. In the light of the present observations and the previous studies concerning the importance of Comptonization, our model requires a scattering cloud surrounding the neutron star, with a Thomson optical depth of ~5. The detection of ~30–40 hr periodicity is hard to interpret in terms of the possible binary period of the system, since most of these systems have binary periods of a few hours or even less. It may either suggest that the accretion disk around the neutron star is precessing or there is a third body in the system.

scholarly journals Validity of two-component models for estimating body fat of black men

2001 ◽  
Vol 90 (2) ◽  
pp. 649-656 ◽  
Author(s):  
Dale R. Wagner ◽  
Vivian H. Heyward
Keyword(s):  
Black Men ◽  
Body Fat ◽  
Predictive Accuracy ◽  
Component Model ◽  
Suitable Alternative ◽  
Heterogeneous Sample ◽  
Four Component Model ◽  
Two Component ◽  
Model Conversion ◽  
Component Models

Commonly used two-component model conversion formulas that estimate relative body fat (%BF) from body density (Db) were cross-validated on a heterogeneous sample of black men ( n = 30; age = 19–45 yr). A four-component model was used to obtain criterion measures of %BF, and linear regression and analysis of individual residual scores were conducted to assess the predictive accuracy of the formulas under investigation. The two-component formula commonly used to estimate %BF of black men (Schutte JE, Townsend EJ, Hugg J, Shoup RF, Malina RM, and Blomqvist CG. J Appl Physiol 56: 1647–1649, 1984) significantly ( P ≤ 0.01) and systematically (87% of sample) overestimated %BF (−1.28%); thus we developed the following two-component Db conversion formula: %BF = [(4.858/Db) − 4.394] × 100. Because our formula was derived from a four-component model and a larger, more heterogeneous sample than the commonly used two-component formula, we recommend using it to convert Db to %BF for black men. Additionally, there was good agreement between dual-energy X-ray absorptiometry and the four-component model, making this a suitable alternative for estimating the %BF of black men.

scholarly journals Discovery and follow-up of ASASSN-19dj: an X-ray and UV luminous TDE in an extreme post-starburst galaxy

2020 ◽  
Vol 500 (2) ◽  
pp. 1673-1696 ◽  
Author(s):  
Jason T Hinkle ◽  
T W-S Holoien ◽  
K Auchettl ◽  
B J Shappee ◽  
J M M Neustadt ◽  
...  
Keyword(s):  
Optical Emission ◽  
Starburst Galaxy ◽  
Late Time ◽  
X Rays ◽  
Tidal Disruption ◽  
X Ray ◽  
Bolometric Luminosity ◽  
Order Of Magnitude ◽  
High Cadence

ABSTRACT We present observations of ASASSN-19dj, a nearby tidal disruption event (TDE) discovered in the post-starburst galaxy KUG 0810+227 by the All-Sky Automated Survey for Supernovae (ASAS-SN) at a distance of d ≃ 98 Mpc. We observed ASASSN-19dj from −21 to 392 d relative to peak ultraviolet (UV)/optical emission using high-cadence, multiwavelength spectroscopy and photometry. From the ASAS-SN g-band data, we determine that the TDE began to brighten on 2019 February 6.8 and for the first 16 d the rise was consistent with a flux ∝t2 power law. ASASSN-19dj peaked in the UV/optical on 2019 March 6.5 (MJD = 58548.5) at a bolometric luminosity of L = (6.2 ± 0.2) × 1044 erg s−1. Initially remaining roughly constant in X-rays and slowly fading in the UV/optical, the X-ray flux increased by over an order of magnitude ∼225 d after peak, resulting from the expansion of the X-ray emitting region. The late-time X-ray emission is well fitted by a blackbody with an effective radius of ∼1 × 1012 cm and a temperature of ∼6 × 105 K. The X-ray hardness ratio becomes softer after brightening and then returns to a harder state as the X-rays fade. Analysis of Catalina Real-Time Transient Survey images reveals a nuclear outburst roughly 14.5 yr earlier with a smooth decline and a luminosity of LV ≥ 1.4 × 1043 erg s−1, although the nature of the flare is unknown. ASASSN-19dj occurred in the most extreme post-starburst galaxy yet to host a TDE, with Lick HδA = 7.67 ± 0.17 Å.

Statistical Analysis of Price Volatility of Agricultural Commodities Traded at the Ethiopian Commodity Exchange (ECX) Using Multiplicative GARCH-MIDAS Two-component Model

2020 ◽  
pp. 097215091989562
Author(s):  
Teshome Hailemeskel Abebe ◽  
Emmanuel Gabreyohannes Woldesenbet ◽  
Belaineh Legesse Zeleke
Keyword(s):  
Price Volatility ◽  
Absolute Error ◽  
Fuel Oil ◽  
Component Model ◽  
Real Effective Exchange Rate ◽  
Time Varying ◽  
Data Sampling ◽  
Commodity Exchange ◽  
Two Component ◽  
Component Models

We applied multiplicative GARCH-MIDAS two component models for price return volatility of selected commodities traded at the Ethiopian commodity exchange (ECX). Unlike the ‘traditional’ generalized autoregressive conditional heteroscedasticity (GARCH) family models, GARCH-MIDAS component model can capture the time-varying conditional as well as unconditional volatilities, and accommodates macroeconomic variables observed at different frequencies through mixed interval data sampling (MIDAS) specification. The results of our specification tests revealed the existence of both time-varying conditional and unconditional variance. The fitted GARCH-MIDAS component models showed that realized volatility, inflation rate and fuel oil price have had an increasing effect on the price volatility of the commodities under consideration, while real effective exchange rate (REER) had the opposite effect. Furthermore, mean square error (MSE), mean absolute error (MAE) and Diebold and Mariano (DM) test were used for evaluating and comparing the forecasting ability of GARCH-MIDAS component models against standard GARCH models. The results revealed that GARCH-MIDAS component models outperformed the standard GARCH model for high-frequency data.

Four-component model for the assessment of body composition in humans: comparison with alternative methods, and evaluation of the density and hydration of fat-free mass

1992 ◽  
Vol 82 (6) ◽  
pp. 687-693 ◽  
Author(s):  
N. J. Fuller ◽  
S. A. Jebb ◽  
M. A. Laskey ◽  
W. A. Coward ◽  
M. Elia
Keyword(s):  
Body Composition ◽  
Skinfold Thickness ◽  
Dual Energy ◽  
Fat Free Mass ◽  
Component Model ◽  
Alternative Methods ◽  
X Ray ◽  
Four Component Model ◽  
Deuterium Dilution ◽  
Component Models

1. Body composition was assessed in 28 healthy subjects (body mass index 20–28 kg/m2) by dual-energy X-ray absorptiometry, deuterium dilution, densitometry, 40K counting and four prediction methods (skinfold thickness, bioelectrical impedance, near-i.r. interactance and body mass index). Three- and four-component models of body composition were constructed from combinations of the reference methods. The results of all methods were compared. Precision was evaluated by analysis of propagation of errors. The density and hydration fraction of the fat-free mass were determined. 2. From the precision of the basic measurements, the propagation of errors for the estimation of fat (± sd) by the four-component model was found to be ± 0.54 kg, by the three-component model, ± 0.49 kg, by deuterium dilution, ± 0.62 kg, and by densitometry, ± 0.78 kg. Precision for the measurement of the density and hydration fraction of fat-free mass was ± 0.0020 kg/l and ± 0.0066, respectively. 3. The agreement between reference methods was generally better than between reference and alternative methods. Dual-energy X-ray absoptiometry predicted three- and four-component model body composition slightly less well than densitometry or deuterium dilution (both of which greatly influence these multi-component models). 4. The hydration fraction of fat-free mass was calculated to be 0.7382 ± 0.0213 (range 0.6941–0.7837) and the density of fat-free mass was 1.1015 ± 0.0073 kg/1 (range 1.0795–1.1110 kg/1), with no significant difference between men and women for either. 5. The results suggest that the three- and four-component models are not compromised by errors arising from individual techniques. Dual-energy X-ray absorptiometry would appear to be a suitable alternative method for the assessment of body composition in these healthy adults. The traditional mean value assumed for density of the fat-free mass in classic densitometry (1.1 kg/l) appears to be appropriate, and the mean hydration fraction was close to values which are generally applied to the fat-free mass (0.72–0.73). Despite concealing considerable inter-individual variation, these mean values may be applied to groups with characteristics similar to those in this study. Finally, with the notable exception of skinfold thickness, bedside prediction methods show poor agreement with both the three- and the four-component models.

A Discussion on solar studies with special reference to space observations - New results of x-ray flare studies

1971 ◽  
Vol 270 (1202) ◽  
pp. 135-142 ◽  
Keyword(s):  
Special Reference ◽  
Electron Beams ◽  
Emission Measure ◽  
Wavelength Band ◽  
Filamentary Structure ◽  
X Ray ◽  
Two Component ◽  
Component Plasma ◽  
Order Of Magnitude ◽  
Main Component

Polarization of X-ray emission is found in the wavelength band around 0.1 nm during the rising phase of three X-ray flares. This shows that in the X-ray flare regions directed electron beams are present. It is established that X-ray flare regions generally have a filamentary structure with bright knots and rapid spatial alterations. Very short X-ray bursts are frequently observed in some flare regions. The region of an X-ray flare may be considered as a two-component plasma the main component with a temperature of about 7 to 9 x 10 6 K, an emission measure of about 0.02 to 0.1 Baumbach and an electron density 1 to 2 x 10 10 cm-3 containing a dispersed hot (up to 15—30 x 10 6 K.) small nuclei having an overall emission measure one order of magnitude smaller.

scholarly journals XMM-Newton spectrum of the magnetar CXOU J171405.7–381031

2019 ◽  
Vol 71 (4) ◽  
Author(s):  
Haruka Watanabe ◽  
Aya Bamba ◽  
Shinpei Shibata ◽  
Eri Watanabe
Keyword(s):  
Power Law ◽  
Time Variation ◽  
Supernova Remnant ◽  
Component Model ◽  
Time Variability ◽  
Spectral Parameters ◽  
X Ray ◽  
Two Component ◽  
Photon Index ◽  
Higher Temperature

Abstract We observe the magnetar CXOU J171405.7−381031 with XMM-Newton and obtain the most reliable X-ray spectral parameters for this magnetar. After removing the flux from the surrounding supernova remnant CTB 37B, the radiation of CXOU J171405.7−381031 is best described by a two-component model, consisting of a blackbody and power law. We obtain a blackbody temperature of $0.58^{+0.03}_{-0.03}$ keV, a photon index of $2.15^{+0.62}_{-0.68}$, and an unabsorbed 2–10 keV band flux of $2.33^{+0.02}_{-0.02} \times 10^{-12}$ erg cm−2 s−1. These new parameters enable us to compare CXOU J171405.7−381031 with other magnetars, and it is found that the luminosity, temperature, and photon index of CXOU J171405.7−381031 are aligned with the known trend among the magnetar population with a slightly higher temperature, which could be caused by its young age. All magnetars with a spin-down age of less than 1000 yr show time variation or bursts except for CXOU J171405.7−381031. We explore the time variability for six observations between 2006 and 2015, but there is no variation larger than ∼10%.

scholarly journals Testing two-component models on very high-energy gamma-ray-emitting BL Lac objects

2020 ◽  
Vol 640 ◽  
pp. A132
Author(s):  
◽  
V. A. Acciari ◽  
S. Ansoldi ◽  
L. A. Antonelli ◽  
A. Arbet Engels ◽  
...  
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Component Model ◽  
Bl Lac Objects ◽  
Two Component ◽  
Very High Energy ◽  
Component Models ◽  
Very High ◽  
Optical Polarisation

Context. It has become evident that one-zone synchrotron self-Compton models are not always adequate for very high-energy (VHE) gamma-ray-emitting blazars. While two-component models perform better, they are difficult to constrain due to the large number of free parameters. Aims. In this work, we make a first attempt at taking into account the observational constraints from very long baseline interferometry (VLBI) data, long-term light curves (radio, optical, and X-rays), and optical polarisation to limit the parameter space for a two-component model and test whether or not it can still reproduce the observed spectral energy distribution (SED) of the blazars. Methods. We selected five TeV BL Lac objects based on the availability of VHE gamma-ray and optical polarisation data. We collected constraints for the jet parameters from VLBI observations. We evaluated the contributions of the two components to the optical flux by means of decomposition of long-term radio and optical light curves as well as modelling of the optical polarisation variability of the objects. We selected eight epochs for these five objects based on the variability observed at VHE gamma rays, for which we constructed the SEDs that we then modelled with a two-component model. Results. We found parameter sets which can reproduce the broadband SED of the sources in the framework of two-component models considering all available observational constraints from VLBI observations. Moreover, the constraints obtained from the long-term behaviour of the sources in the lower energy bands could be used to determine the region where the emission in each band originates. Finally, we attempt to use optical polarisation data to shed new light on the behaviour of the two components in the optical band. Our observationally constrained two-component model allows explanation of the entire SED from radio to VHE with two co-located emission regions.

Suppression of Optokinetic Velocity Storage in Humans by Static Tilt in Pitch

1990 ◽  
Vol 1 (1) ◽  
pp. 39-48
Author(s):  
S.H. Lafortune ◽  
D.J. Ireland ◽  
R.M. Jell
Keyword(s):  
Time Constant ◽  
Component Model ◽  
Velocity Storage ◽  
Indirect Pathway ◽  
Otolith Organ ◽  
Optokinetic Afternystagmus ◽  
Slow Decay ◽  
Two Component ◽  
Long Time ◽  
Short Time

The effects of static tilts about the pitch axis on human horizontal optokinetic afternystagmus OKAN (HOKAN) were examined. Static tilts in pitch produced tilt-dependent HOKAN suppression. The slow decay (indirect pathway) component (coefficient C and long time constant 1/D) of the two-component model for OKAN was significantly reduced, while the short decay (direct pathway) component (coefficient A and short time constant 1/B) remained invariant as angle of tilt was increased. These results provide further evidence that otolith organ activity can couple to horizontal velocity storage in humans; in accordance with models proposed in the literature.

scholarly journals Rapid spectral transition of the black hole binary V404 Cygni

2020 ◽  
Vol 634 ◽  
pp. A94
Author(s):  
J. J. E. Kajava ◽  
C. Sánchez-Fernández ◽  
J. Alfonso-Garzón ◽  
S. E. Motta ◽  
A. Veledina
Keyword(s):  
Black Hole ◽  
Optical Data ◽  
X Ray ◽  
Rapid Changes ◽  
Photon Index ◽  
Order Of Magnitude ◽  
Best Fitting ◽  
Black Hole Binary ◽  
Flux Increase ◽  
Magnitude Increase

During the June 2015 outburst of the black hole binary V404 Cyg, rapid changes in the X-ray brightness and spectra were common. The INTEGRAL monitoring campaign detected spectacular Eddington-limited X-ray flares, but also rapid variations at much lower flux levels. On 2015 June 21 at 20 h 50 min, the 3–10 keV JEM-X data as well as simultaneous optical data started to display a gradual brightening from one of these low-flux states. This was followed 15 min later by an order-of-magnitude increase of flux in the 20–40 keV IBIS/ISGRI light curve in just 15 s. The best-fitting model for both the pre- and post-transition spectra required a Compton-thick partially covering absorber. The absorber parameters remained constant, but the spectral slope varied significantly during the event, with the photon index decreasing from Γ ≈ 3.7 to Γ ≈ 2.3. We propose that the rapid 20–40 keV flux increase was either caused by a spectral state transition that was hidden from our direct view, or that there was a sudden reduction in the amount of Compton down-scattering of the primary X-ray emission in the disk outflow.

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