scholarly journals Multiwavelength Observations of AB Doradus

2014 ◽  
Vol 31 ◽  
Author(s):  
O.B. Slee ◽  
N. Erkan ◽  
M. Johnston-Hollitt ◽  
E. Budding
Keyword(s):  
Impulsive Phase ◽  
High Energy ◽  
High Dispersion ◽  
Data Sets ◽  
Full Data ◽  
Multiple Star ◽  
Significance Level ◽  
X Ray ◽  
Low Mass ◽  
Compact Array

AbstractWe have observed the bright, magnetically active multiple star AB Doradus in a multiwavelength campaign centring around two large facility allocations in November 2006 and January, 2007. Our observations have covered at least three large flares. These flares were observed to produce significant hardening of the X-ray spectra during their very initial stages. We monitored flare-related effects using the Suzaku X-ray satellite and the Australia Telescope Compact Array (ATCA) at 3.6 and 6 cm. Observations at 11 and 21 cm were also included, but they were compromised by interference. Optical monitoring was also provided by broadband B and V photometry and some high-dispersion spectrograms. From this multiwavelength coverage we find that the observed flare effects can be mainly associated with a large active region near longitude zero. The second major X-ray and microwave flare of Jan 8, 2007 was observed with a favourable geometry that allowed its initial high-energy impulsive phase to be observed in the higher frequency range of Suzaku’s XIS detectors. The fractional circular polarisation (Stokes V/I) was measured in the uv data for the complete runs, for 25 min integrations and, at 4.80 GHz, for 5 min integrations, using the radio data of Nov 21 2006 and Jan 08 2007. Most of the full data sets showed V/I fractions from AB Dor B that were significant at greater than the 3σ level. In several of the 5 min integrations at 4.80 and 8.64 GHz this fraction reached a significance level between 3 and 9σ. Lack of angular resolution prevented identification of these high V/I values with one or other of the two low-mass red-dwarf components of AB Dor B.

scholarly journals Drifts of the marginally stable burning frequency in the X-ray binaries 4U 1608–52 and Aql X–1

2021 ◽  
Vol 502 (2) ◽  
pp. 1856-1863
Author(s):  
G C Mancuso ◽  
D Altamirano ◽  
M Méndez ◽  
M Lyu ◽  
J A Combi
Keyword(s):  
Frequency Drift ◽  
Soft Or ◽  
Significance Level ◽  
X Ray ◽  
Intermediate States ◽  
Source State ◽  
Nuclear Burning ◽  
Low Mass ◽  
X Ray Binaries ◽  
Stable Burning

ABSTRACT We detect millihertz quasi-periodic oscillations (mHz QPOs) using the Rossi X-ray Time Explorer (RXTE) from the atoll neutron-star (NS) low-mass X-ray binaries 4U 1608–52 and Aql X–1. From the analysis of all RXTE observations of 4U 1608–52 and Aql X–1, we find mHz QPOs with a significance level >3σ in 49 and 47 observations, respectively. The QPO frequency is constrained between ∼4.2 and 13.4 mHz. These types of mHz QPOs have been interpreted as being the result of marginally stable nuclear burning of He on the NS surface. We also report the discovery of a downward frequency drift in three observations of 4U 1608–52, making it the third source that shows this behaviour. We only find strong evidence of frequency drift in one occasion in Aql X–1, probably because the observations were too short to measure a significant drift. Finally, the mHz QPOs are mainly detected when both sources are in the soft or intermediate states; the cases that show frequency drift only occur when the sources are in intermediate states. Our results are consistent with the phenomenology observed for the NS systems 4U 1636–53 and EXO 0748–676, suggesting that all four sources can reach the conditions for marginally stable burning of He on the NS surface. These conditions depend on the source state in the same manner in all four systems.

scholarly journals Variable Magellanic HMXB Sources versus Variable ULX Sources: Nothing to Brag about the ULX Sources

Galaxies ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 70
Author(s):  
Dimitris M. Christodoulou ◽  
Silas G. T. Laycock ◽  
Rigel Cappallo ◽  
Ankur Roy ◽  
Sayantan Bhattacharya  ◽  
...  
Keyword(s):  
Normal Distribution ◽  
Meta Analysis ◽  
Continuous Distribution ◽  
High Mass ◽  
P Value ◽  
Data Sets ◽  
Significance Level ◽  
X Ray ◽  
Log Normal ◽  
Ks Test

We carry out a meta-analysis of ultraluminous X-ray (ULX) sources that show large variabilities (by factors of >10) between their highest and lowest emission states in the X-ray energy range of 0.3–10 keV. We are guided by a recent stringent compilation of 25 such X-ray sources by Song et al. We examine the relation of logN versus logSmax, where N is the number of sources radiating above the maximum-flux level Smax. We find a strong deviation from all previously determined slopes in various high-mass X-ray binary (HMXB) samples. In fact, the ULX data clearly show a slope of −0.91. Thus, ULX sources do not appear to be uniform and isotropic in our Universe. We compare the ULX results against the local X-ray luminosity function of HMXBs in the Small Magellanic Cloud (SMC) constructed from our latest library that includes 41 Chandra 0.3–8 keV sources and 56 XMM-Newton 0.2–12 keV sources. The ULX data are not drawn from the same continuous distribution as the SMC data (the ULX data peak at the low tails of the SMC distributions), and none of our data sets is drawn from a normal distribution or from a log-normal distribution (they all show marked excesses at both tails). At a significance level of α=0.05 (2σ), the two-sample p-value of the Kolmogorov–Smirnov (KS) test gives p=4.7×10−3<α for the ULX versus the small Chandra sample and p=1.1×10−5<<α for the ULX versus the larger XMM-Newton sample, respectively. This adds to the evidence that ULX sources are not simply the higher end of the known local Be/X-ray pulsar distribution, but they represent a class of X-ray sources different from the young sources found in the SMC and in individual starburst galaxies. On the other hand, our two main SMC data sets are found to be statistically consistent, as they are drawn from the same continuous parent distribution (null hypothesis H0): at the α=0.05 significance level, the two-sample KS test shows an asymptotic p-value of 0.308>α, which tells us to accept H0.

Comparative study of X-ray charge-density data on CoSb3

2013 ◽  
Vol 69 (6) ◽  
pp. 570-582 ◽  
Author(s):  
Mette Stokkebro Schmøkel ◽  
Lasse Bjerg ◽  
Finn Krebs Larsen ◽  
Jacob Overgaard ◽  
Simone Cenedese ◽  
...  
Keyword(s):  
Charge Density ◽  
High Performance ◽  
Theoretical Data ◽  
High Energy ◽  
Data Sets ◽  
High Symmetry ◽  
X Ray ◽  
Structure Factors ◽  
Small Crystals ◽  
Density Analysis

CoSb3is an example of a highly challenging case for experimental charge-density analysis due to the heavy elements (suitability factor of ∼0.01), the perfect crystallinity and the high symmetry of the compound. It is part of a family of host–guest structures that are potential candidates for use as high-performance thermoelectric materials. Obtaining and analysing accurate charge densities of the undoped host structure potentially can improve the understanding of the thermoelectric properties of this family of materials. In a previous study, analysis of the electron density gave a picture of covalent Co–Sb and Sb–Sb interactions together with relatively low atomic charges based on state-of-the-art experimental and theoretical data. In the current study, several experimental X-ray diffraction data sets collected on the empty CoSb3framework are compared in order to probe the experimental requirements for obtaining data of high enough quality for charge-density analysis even in the case of very unsuitable crystals. Furthermore, the quality of the experimental structure factors is tested by comparison with theoretical structure factors obtained from periodic DFT calculations. The results clearly show that, in the current study, the data collected on high-intensity, high-energy synchrotron sources and very small crystals are superior to data collected at conventional sources, and in fact necessary for a meaningful charge-density study, primarily due to greatly diminished effects of extinction and absorption which are difficult to correct for with sufficient accuracy.

On the calibration of high-energy X-ray diffraction setups. I. Assessing tilt and spatial distortion of the area detector

2014 ◽  
Vol 47 (3) ◽  
pp. 1042-1053 ◽  
Author(s):  
Andras Borbely ◽  
Loic Renversade ◽  
Peter Kenesei ◽  
Jonathan Wright
Keyword(s):  
Rotation Axis ◽  
Strain Tensor ◽  
Calibration Procedure ◽  
High Energy ◽  
European Synchrotron Radiation Facility ◽  
Data Sets ◽  
X Ray Diffraction ◽  
Spatial Distortion ◽  
X Ray ◽  
Area Detector

The geometry of high-energy X-ray diffraction setups using an area detector and a rotation axis is analysed. The present paper (part 1) describes the methodology for determining continuously varying spatial distortions and tilt of the area detector based on the reference diffraction rings of a certified powder. Analytical expressions describing the degeneration of Debye rings into ellipses are presented and a robust calibration procedure is introduced. It is emphasized that accurate detector calibration requires the introduction of spatial distortion into the equation describing the tilt. The method is applied to data sets measured at the Advanced Photon Source and at the European Synchrotron Radiation Facility using detectors with different physical characteristics, the GE 41RT flat-panel and the FReLoN4M detector, respectively. The spatial distortion of the detectors is compared with regard to their use in structural and strain tensor analysis, a subject treated in part 2 of the calibration work [Borbély, Renversade & Kenesei (2014).J. Appl. Cryst.Submitted].

scholarly journals INVESTIGATION OF DENSE GAS TOWARDS RELATIVISTIC OUTFLOW SOURCES

2014 ◽  
Vol 28 ◽  
pp. 1460198
Author(s):  
J. HAWKES ◽  
G. ROWELL ◽  
B. DAWSON ◽  
F. AHARONIAN ◽  
M. BURTON ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Line Emission ◽  
High Energy ◽  
Dense Gas ◽  
Relativistic Jets ◽  
Hii Region ◽  
X Ray ◽  
Stellar Cluster ◽  
Radio Recombination Line ◽  
Low Mass

We probe the interstellar medium towards the objects Circinus X-1, a low-mass X-ray binary with relativistic jets; and the highly energetic Westerlund 2 stellar cluster, which is located towards TeV gamma-ray emission and interesting arc- and jet-like features seen in Nanten 12CO data. We have mapped both regions with the Mopra radio telescope, in 7 mm and 12 mm wavebands, looking for evidence of disrupted/dense gas caused by the interaction between high energy outflows and the ISM. Towards Westerlund 2, peaks in CS(J=1-0) emission indicate high density gas towards the middle of the arc and the endpoint of the jet; and radio recombination line emission is seen overlapping the coincident HII region RCW49. Towards Circinus X-1, 12CO(J = 1-0) Nanten data reveals three molecular clouds that lie in the region of Cir X-1. Gas parameters for each cloud are presented here.

scholarly journals The MAVERIC survey: a hidden pulsar and a black hole candidate in ATCA radio imaging of the globular cluster NGC 6397

2020 ◽  
Vol 493 (4) ◽  
pp. 6033-6049 ◽  
Author(s):  
Yue Zhao ◽  
Craig O Heinke ◽  
Vlad Tudor ◽  
Arash Bahramian ◽  
James C A Miller-Jones ◽  
...  
Keyword(s):  
Black Hole ◽  
Globular Cluster ◽  
Radio Observation ◽  
Millisecond Pulsar ◽  
Radio Flux ◽  
X Ray ◽  
Black Hole Candidate ◽  
Radio Imaging ◽  
Low Mass ◽  
Compact Array

ABSTRACT Using a 16.2-h radio observation by the Australia Telescope Compact Array and archival Chandra data, we found &gt;5σ radio counterparts to four known and three new X-ray sources within the half-light radius (rh) of the Galactic globular cluster NGC 6397. The previously suggested millisecond pulsar (MSP) candidate, U18, is a steep-spectrum (Sν ∝ να; $\alpha =-2.0^{+0.4}_{-0.5}$) radio source with a 5.5-GHz flux density of 54.7 ± 4.3 $\mu \mathrm{ Jy}$. We argue that U18 is most likely a ‘hidden’ MSP that is continuously hidden by plasma shocked at the collision between the winds from the pulsar and companion star. The non-detection of radio pulsations so far is probably the result of enhanced scattering in this shocked wind. On the other hand, we observed the 5.5-GHz flux of the known MSP PSR J1740−5340 (U12) to decrease by a factor of &gt;2.8 during epochs of 1.4-GHz eclipse, indicating that the radio flux is absorbed in its shocked wind. If U18 is indeed a pulsar whose pulsations are scattered, we note the contrast with U12’s flux decreases in eclipse, which argues for two different eclipse mechanisms at the same radio frequency. In addition to U12 and U18, we also found radio associations for five other Chandra X-ray sources, four of which are likely background galaxies. The last, U97, which shows strong H α variability, is mysterious; it may be either a quiescent black hole low-mass X-ray binary or something more unusual.

scholarly journals Non thermal emission from T Tauri stars

2010 ◽  
Vol 6 (S275) ◽  
pp. 404-405
Author(s):  
María V. del Valle ◽  
Gustavo E. Romero
Keyword(s):  
Main Sequence ◽  
Thermal Emission ◽  
High Energy ◽  
Magnetic Activity ◽  
T Tauri Stars ◽  
Main Sequence Stars ◽  
High Energy Radiation ◽  
X Ray ◽  
T Tauri ◽  
Low Mass

AbstractT Tauri stars are low mass, pre-main sequence stars. These objects are surrounded by an accretion disk and present strong magnetic activity. T Tauri stars are copious emitters of X-ray emission which belong to powerful magnetic reconnection events. Strong magnetospheric shocks are likely outcome of massive reconnection. Such shocks can accelerate particles up to relativistic energies through Fermi mechanism. We present a model for the high-energy radiation produced in the environment of T Tauri stars. We aim at determining whether this emission is detectable. If so, the T Tauri stars should be very nearby.

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