1,333 research outputs found
Swift/BAT and RXTE Observations of the Peculiar X-ray Binary 4U 2206+54 - Disappearance of the 9.6 Day Modulation
Observations of the high-mass X-ray binary 4U 2206+54 with the Swift Burst
Alert Telescope (BAT) do not show modulation at the previously reported period
of 9.6 days found from observations made with the Rossi X-ray Timing Explorer
(RXTE) All-Sky Monitor (ASM). Instead, the strongest peak in the power spectrum
of the BAT light curve occurs at a period of 19.25 +/- 0.08 days, twice the
period found with the RXTE ASM. The maximum of the folded BAT light curve is
also delayed compared to the maximum of the folded ASM light curve. The most
recent ASM data folded on twice the 9.6 day period show similar morphology to
the folded BAT light curve. This suggests that the apparent period doubling is
a recent secular change rather than an energy-dependent effect. The 9.6 day
period is thus not a permanent strong feature of the light curve. We suggest
that the orbital period of 4U 2206+54 may be twice the previously proposed
value.Comment: Accepted for publication in The Astrophysical Journa
Diverse Long-Term Variability of Five Candidate High-Mass X-ray Binaries from Swift Burst Alert Telescope Observations
We present an investigation of long-term modulation in the X-ray light curves
of five little-studied candidate high-mass X-ray binaries using the Swift Burst
Alert Telescope. IGR J14488-5942 and AX J1700.2-4220 show strong modulation at
periods of 49.6 and 44 days, respectively, which are interpreted as orbital
periods of Be star systems. For IGR J14488-5942, observations with Swift X-ray
Telescope show a hint of pulsations at 33.4 s. For AX J1700.2-4220, 54 s
pulsations were previously found with XMM. Swift J1816.7-1613 exhibits
complicated behavior. The strongest peak in the power spectrum is at a period
near 150 days, but this conflicts with a determination of a period of 118.5
days by La Parola et al. (2014). AX J1820.5-1434 has been proposed to exhibit
modulation near 54 days, but the extended BAT observations suggest modulation
at slightly longer than double this at approximately 111 days. There appears to
be a long-term change in the shape of the modulation near 111 days, which may
explain the apparent discrepancy. The X-ray pulsar XTE J1906+090, which was
previously proposed to be a Be star system with an orbital period of ~30 days
from pulse timing, shows peaks in the power spectrum at 81 and 173 days. The
origins of these periods are unclear, although they might be the orbital period
and a superorbital period respectively. For all five sources, the long-term
variability, together with the combination of orbital and proposed pulse
periods, suggests that the sources contain Be star mass donors.Comment: Accepted for publication in The Astrophysical Journal. 15 pages, 27
figures. (v2 corrects citation
Volatility spillover effects in leading cryptocurrencies: A BEKK-MGARCH analysis
Through the application of three pair-wise bivariate BEKK models, this paper examines the conditional volatility dynamics along with interlinkages and conditional correlations between three pairs of cryptocurrencies, namely Bitcoin-Ether, Bitcoin-Litecoin, and Ether-Litecoin. While cryptocurrency price volatility is found to be dependent on its own past shocks and past volatility, we find evidence of bi-directional shock transmission effects between Bitcoin and both Ether and Litecoin, and uni-directional shock spillovers from Ether to Litecoin. Finally, we identify bi-directional volatility spillover effects between all the three pairs and provide evidence that time-varying conditional correlations exist and are mostly positive
A Study of the 20 Day Superorbital Modulation in the High-Mass X-ray Binary IGR J16493-4348
We report on Nuclear Spectroscopic Telescope Array (NuSTAR), Neil Gehrels
Swift Observatory (Swift) X-ray Telescope (XRT) and Swift Burst Alert Telescope
(BAT) observations of IGR J16493-4348, a wind-fed Supergiant X-ray Binary
(SGXB) showing significant superorbital variability. From a discrete Fourier
transform of the BAT light curve, we refine its superorbital period to be
20.058 0.007 days. The BAT dynamic power spectrum and a fractional root
mean square analysis both show strong variations in the amplitude of the
superorbital modulation, but no observed changes in the period were found. The
superorbital modulation is significantly weaker between MJD 55,700 and MJD
56,300. The joint NuSTAR and XRT observations, which were performed near the
minimum and maximum of one cycle of the 20 day superorbital modulation, show
that the flux increases by more than a factor of two between superorbital
minimum and maximum. We find no significant changes in the 3-50 keV pulse
profiles between superorbital minimum and maximum, which suggests a similar
accretion regime. Modeling the pulse-phase averaged spectra we find a possible
Fe K emission line at 6.4 keV at superorbital maximum. The feature is
not significant at superorbital minimum. While we do not observe any
significant differences between the pulse-phase averaged spectral continua
apart from the overall flux change, we find that the hardness ratio near the
broad main peak of the pulse profile increases from superorbital minimum to
maximum. This suggests the spectral shape hardens with increasing luminosity.
We discuss different mechanisms that might drive the observed superorbital
modulation.Comment: 17 pages, 14 figures, 3 tables, accepted for publication in The
Astrophysical Journal on 2019 May 1
Rossi X-ray Timing Explorer Observations of the X-ray Pulsar EXO 1722-363 - a Candidate Eclipsing Supergiant System
Observations made of the X-ray pulsar EXO 1722-363 using the Proportional
Counter Array and All Sky Monitor on board the Rossi X-ray Timing Explorer
reveal the orbital period of this system to be 9.741 +/- 0.004 d from periodic
changes in the source flux. The detection of eclipses, together with the values
of the pulse and orbital periods, suggest that this source consists of a
neutron star accreting from the stellar wind of an early spectral type
supergiant companion. Pulse timing measurements were also obtained but do not
strongly constrain the system parameters. The X-ray spectra can be well fitted
with a model consisting of a power law with a high energy cutoff and, for some
spectra, a blackbody component with a temperature of approximately 0.85 keV.Comment: Accepted for publication in The Astrophysical Journal. 27 pages
including 10 figure
Monitoring and Discovering X-ray Pulsars in the Small Magellanic Cloud
Regular monitoring of the SMC with RXTE has revealed a huge number of X-ray
pulsars. Together with discoveries from other satellites at least 45 SMC
pulsars are now known. One of these sources, a pulsar with a period of
approximately 7.8 seconds, was first detected in early 2002 and since discovery
it has been found to be in outburst nine times. The outburst pattern clearly
shows a period of 45.1 +/- 0.4 d which is thought to be the orbital period of
this system. Candidate outburst periods have also been obtained for nine other
pulsars and continued monitoring will enable us to confirm these. This large
number of pulsars, all located at approximately the same distance, enables a
wealth of comparative studies. In addition, the large number of pulsars found
(which vastly exceeds the number expected simply by scaling the relative mass
of the SMC and the Galaxy) reveals the recent star formation history of the SMC
which has been influenced by encounters with both the LMC and the Galaxy.Comment: 5 pages, 4 figures, AIP conference proceedings format. Contribution
to "X-ray Timing 2003: Rossi and Beyond." meeting held in Cambridge, MA,
November, 200
Where we go and what we do : mapping the extension footprint of Animal Science
We trialled a process to map the footprint of Animal Science (AS) extension activities. This included aggregating existing extension records from eight separate datasets, mapping these records to agricultural property locations, and developing a set of tools and data sets with which AS staff can interrogate and present the spatialised data.
We were able to map more than 4996 interactions with agricultural producers on agricultural properties covering 30% of the state. While not a complete record of AS extension activities, this is the most substantial attempt to map extension activities in AS from February 2002 to date, and for many of the contributing projects, the first time they were able to see their work mapped.
We also generated four tiers of tools and datasets with which AS staff can investigate and summarise their extension data. These include a full spatial file geodatabase which support advanced analysis in ArcGIS software; map packages ready for use in ArcReader software and suitable for users with very limited spatial skills; Excel spreadsheets and pivot tables for analysis by staff with moderate data analysis skills; and prepared PDF maps suitable for simple presentation of footprint areas.
We also developed a plan for future mapping of the AS extension footprint. The plan is not for a simple continuation of the work done here. It defines a clear goal for future work, and identifies five critical requirements for a viable long term effort that produces timely accessible spatial information for all levels of staff. These requirements should improve on the efficiency of the current work without adding to the workload of the extension staff
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