1,851 research outputs found
Discovery of a new Transient X-ray Pulsar in the Small Magellanic Cloud
Rossi X-Ray Timing Explorer observations of the Small Magellanic Cloud have
revealed a previously unknown transient X-ray pulsar with a pulse period of
95s. Provisionally designated XTE SMC95, the pulsar was detected in three
Proportional Counter Array observations during an outburst spanning 4 weeks in
March/April 1999. The pulse profile is double peaked reaching a pulse fraction
\~0.8. The source is proposed as a Be/neutron star system on the basis of its
pulsations, transient nature and characteristically hard X-ray spectrum. The
2-10 keV X-ray luminosity implied by our observations is > 2x10^37 erg/s which
is consistent with that of normal outbursts seen in Galactic systems. This
discovery adds to the emerging picture of the SMC as containing an extremely
dense population of transient high mass X-ray binaries.Comment: Accepted by A&A. 7 pages, 6 figure
Looking for Stars and Finding the Moon: Effects of Lunar Gamma-ray Emission on Fermi LAT Light Curves
We are conducting a search for new gamma-ray binaries by making high
signal-to-noise light curves of all cataloged Fermi LAT sources and searching
for periodic variability using appropriately weighted power spectra. The light
curves are created using a variant of aperture photometry where photons are
weighted by the probability that they came from the source of interest. From
this analysis we find that the light curves of a number of sources near the
ecliptic plane are contaminated by gamma-ray emission from the Moon. This shows
itself as modulation on the Moon's sidereal period in the power spectra. We
demonstrate that this contamination can be removed by excluding times when the
Moon was too close to a source. We advocate that this data screening should
generally be used when analyzing LAT data from a source located close to the
path of the Moon.Comment: 2012 Fermi Symposium proceedings - eConf C12102
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
Asymmetric mean reversion of Bitcoin price returns
© 2018 Elsevier Inc. Non-linearity is characterised by an asymmetric mean-reverting property, which has been found to be inherent in the short-term return dynamics of stocks. In this paper, we explore as to whether cryptocurrency returns, as represented by Bitcoin, exhibit similar asymmetric reverting patterns for minutely, hourly, daily and weekly returns between June 2010 and February 2018. We identify several differences in the behaviour of Bitcoin price returns in the pre- and post-$1000 sub-periods and evidence of asymmetric reverting patterns in the Bitcoin price returns under all the ANAR models employed, regardless of the data frequency considered. We also present evidence indicating stronger reverting behaviour of negative price returns in terms of both reverting speed and magnitude compared to positive returns and evidence of positive serial correlation with prior positive price returns. Finally, we also investigated asymmetries in Bitcoin price return series’ persistence by employing higher order ANAR models, finding evidence of a higher persistence of positive returns than negative returns, a result that further supports the existence of asymmetric reverting behaviour in the Bitcoin price returns
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
Natural Hosts of Mosquitoes in Northern Ellesmere Island
Aedes impiger and A. nigripes, near Lake Hazen, were observed to take blood from musk-oxen, birds(mainly the eider ducks), and man. Precipitin tests showed several specimens contained blood of two kinds. The reaction of the host to harassment by mosquitos appears to determine which hosts are fed on successfully.Les Hôtes naturels des moustiques dans le nord de l'île d'Ellesmere. Près du lac Hazen, T. du N.-O. (81°49'N., 71°18'O.), les auteurs ont effectué des observations sur l'alimentation en sang et des tests à la précipitine sur des femelles gorgées d'Aedes impiger et A. nigripes. On donne une liste des vertébrés terrestres mentionnés pour la région. Dans la nature, les deux espèces de moustiques soutirent du sang des bœufs musqués et des oiseaux (également des humains); plusieurs spécimens contiennent du sang des deux espèces (déterminations par les tests à la précipitine). La réaction de l'hôte au harassement par les moustiques est évidemment le facteur majeur qui détermine lequel des hôtes possibles sera attaqué avec succès. D'après leur comportement et leur situation, on estime que les bœufs musqués et les oiseaux nichés dans des sites aquatiques sont les plus susceptibles de fournir du sang. Les auteurs discutent brièvement des méthodes servant à déterminer les préférences envers les hôtes dans l'Arctique
Platelet rich plasma in the treatment of periodontal intrabony defects
published_or_final_versio
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
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
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