1,309 research outputs found
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
4U2206+54 - an Unusual High Mass X-ray Binary with a 9.6 Day Orbital Period but No Strong Pulsations
Rossi X-ray Timing Explorer All-Sky Monitor observations of the X-ray source
4U2206+54, previously proposed to be a Be star system, show the X-ray flux to
be modulated with a period of approximately 9.6 days. If the modulation is due
to orbital variability then this would be one of the shortest orbital periods
known for a Be star X-ray source. However, the X-ray luminosity is relatively
modest whereas a high luminosity would be predicted if the system contains a
neutron star accreting from the denser inner regions of a Be star envelope.
Although a 392s pulse period was previously reported from EXOSAT observations,
a reexamination of the EXOSAT light curves does not show this or any other
periodicity. An analysis of archival RXTE Proportional Counter Array
observations also fails to show any X-ray pulsations. We consider possible
models that may explain the properties of this source including a neutron star
with accretion halted at the magnetosphere and an accreting white dwarf.Comment: Accepted for publication in the Astrophysical Journa
Evidence for a very slow X-ray pulsar in 2S0114+650 from RXTE All-Sky Monitor Observations
Rossi X-ray Timing Explorer (RXTE) All-Sky Monitor (ASM) observations of the
X-ray binary 2S0114+650 show modulations at periods close to both the optically
derived orbital period (11.591 days) and proposed pulse period (~ 2.7 hr). The
pulse period shows frequency and intensity variability during the more than 2
years of ASM observations analyzed. The pulse properties are consistent with
this arising from accretion onto a rotating neutron star and this would be the
slowest such period known. The shape of the orbital light curve shows
modulation over the course of the entire orbit and a comparison is made with
the orbital light curve of Vela X-1. However, the expected phase of eclipse,
based on an extrapolation of the optical ephemeris, does not correspond with
the observed orbital minimum. The orbital period derived from the ASM light
curve is also slightly longer than the optical period.Comment: To be published in the Astrophysical Journal, 1999, volume 511. 9
figure
Fast synthesis and redox switching of di- And tetra-substituted bisthioxanthylidene overcrowded alkenes
A rapid and efficient method for the synthesis of overcrowded alkenes using (trimethylsilyl)diazomethane provides a range of substituted bisthioxanthylidenes. We show large conformational redox switching from folded to orthogonal states, which tolerates many substitution patterns. The facile access to bisthioxanthylidene switches with the potential for further functionalization, in combination with the reliable redox chemistry, provides major opportunities for the design of electrochemically responsive systems
The development of Bitcoin futures : exploring the interactions between cryptocurrency derivatives
We utilise a high-frequency analysis to investigate the period surrounding the establishment of two new futures contracts based on the performance of Bitcoin. Our analysis shows that there have been significant pricing effects sourced from both fraudulent and regulatory unease within the industry. While analysing breakpoints in efficiency, we verify the view that Bitcoin futures dominate price discovery relative to spot markets. However, we add to this research by finding that CBOE futures are found to be the leading source of informational flow when compared directly to their CME equivalent
Fermi LAT Gamma-ray Detections of Classical Novae V1369 Centauri 2013 and V5668 Sagittarii 2015
We report the Fermi Large Area Telescope (LAT) detections of high-energy
(>100 MeV) gamma-ray emission from two recent optically bright classical novae,
V1369 Centauri 2013 and V5668 Sagittarii 2015. At early times, Fermi
target-of-opportunity observations prompted by their optical discoveries
provided enhanced LAT exposure that enabled the detections of gamma-ray onsets
beginning ~2 days after their first optical peaks. Significant gamma-ray
emission was found extending to 39-55 days after their initial LAT detections,
with systematically fainter and longer duration emission compared to previous
gamma-ray detected classical novae. These novae were distinguished by multiple
bright optical peaks that encompassed the timespans of the observed gamma rays.
The gamma-ray light curves and spectra of the two novae are presented along
with representative hadronic and leptonic models, and comparisons to other
novae detected by the LAT are discussed.Comment: 13 pages, 6 figures, 4 tables, ApJ accepte
The Orbital Solution and Spectral Classification of the High-Mass X-Ray Binary IGR J01054-7253 in the Small Magellanic Cloud
We present X-ray and optical data on the Be/X-ray binary (BeXRB) pulsar IGR
J01054-7253 = SXP11.5 in the Small Magellanic Cloud (SMC). Rossi X-ray Timing
Explorer (RXTE) observations of this source in a large X-ray outburst reveal an
11.483 +/- 0.002s pulse period and show both the accretion driven spin-up of
the neutron star and the motion of the neutron star around the companion
through Doppler shifting of the spin period. Model fits to these data suggest
an orbital period of 36.3 +/- 0.4d and Pdot of (4.7 +/- 0.3) x 10^{-10}
ss^{-1}. We present an orbital solution for this system, making it one of the
best described BeXRB systems in the SMC. The observed pulse period, spin-up and
X-ray luminosity of SXP11.5 in this outburst are found to agree with the
predictions of neutron star accretion theory. Timing analysis of the long-term
optical light curve reveals a periodicity of 36.70 +/- 0.03d, in agreement with
the orbital period found from the model fit to the X-ray data. Using blue-end
spectroscopic observations we determine the spectral type of the counterpart to
be O9.5-B0 IV-V. This luminosity class is supported by the observed V-band
magnitude. Using optical and near-infrared photometry and spectroscopy, we
study the circumstellar environment of the counterpart in the months after the
X-ray outburst.Comment: 12 pages, 13 figures and 3 tables. This paper has been accepted for
publication in MNRA
XMM-Newton discovery of transient X-ray pulsar in NGC 1313
We report on the discovery and analysis of the transient X-ray pulsar XMMU
J031747.5-663010 detected in the 2004 November 23 XMM-Newton observation of the
spiral galaxy NGC 1313. The X-ray source exhibits pulsations with a period
P~765.6 s and a nearly sinusoidal pulse shape and pulsed fraction ~38% in the
0.3-7 keV energy range. The X-ray spectrum of XMMU J031747.5-663010 is hard and
is well fitted with an absorbed simple power law of photon index ~1.5 in the
0.3-7 keV energy band. The X-ray properties of the source and the absence of an
optical/UV counterpart brighter than 20 mag allow us to identify XMMU
J031747.5-663010 as an accreting X-ray pulsar located in NGC 1313. The
estimated absorbed 0.3-7 keV luminosity of the source L~1.6\times 10^{39}
ergs/s, makes it one of the brightest X-ray pulsars known. Based on the
relatively long pulse period and transient behaviour of the source, we classify
it as a Be binary X-ray pulsar candidate. XMMU J031747.5-663010 is the second
X-ray pulsar detected outside the Local Group, after transient 18 s pulsating
source CXOU J073709.1+653544 discovered in the nearby spiral galaxy NGC 2403.Comment: 6 pages, 4 figures. Accepted for publication in MNRAS. Updated to
match the accepted versio
Sex ratio in Gomphidae (Odonata) at emergence: is there a relationship with water temperature?
The discovery of 8.9s pulsations from the variable X-ray source 2E0050.1-7247 in the small Magellanic cloud
During a systematic search for periodic signals in a sample of ROSAT PSPC
light curves, we discovered ~ 8.9s X-ray pulsations in 2E0050.1-7247, a
variable X-ray source in the Small Magellanic Cloud. The source was detected
several times between 1979 and 1993 at luminosity levels ranging from about 5
times 10^{34} erg/s up to 1.4 times 10^{36} erg/s with both the Einstein IPC
and ROSAT PSPC. The X-ray energy spectrum is consistent with a power law
spectrum which steepens as the source luminosity decreases. We revealed a
pronounced Halpha activity from at least two B stars in the X-ray error
circles. These results strongly suggest that the X-ray pulsar 2E0050.1-7247 is
in a Be-type massive binary.Comment: 13 pages plus 3 postscript figures, AAS style LaTeX file Accepted for
publication in the Astrophysical Journal Letter
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