380 research outputs found
Pulsar spin-down: the glitch-dominated rotation of PSR J0537-6910
The young, fast-spinning, X-ray pulsar J0537-6910 displays an extreme glitch
activity, with large spin-ups interrupting its decelerating rotation every ~100
days. We present nearly 13 years of timing data from this pulsar, obtained with
the {\it Rossi X-ray Timing Explorer}. We discovered 22 new glitches and
performed a consistent analysis of all 45 glitches detected in the complete
data span. Our results corroborate the previously reported strong correlation
between glitch spin-up size and the time to the next glitch, a relation that
has not been observed so far in any other pulsar. The spin evolution is
dominated by the glitches, which occur at a rate ~3.5 per year, and the
post-glitch recoveries, which prevail the entire inter-glitch intervals. This
distinctive behaviour provides invaluable insights into the physics of
glitches. The observations can be explained with a multi-component model which
accounts for the dynamics of the neutron superfluid present in the crust and
core of neutron stars. We place limits on the moment of inertia of the
component responsible for the spin-up and, ignoring differential rotation, the
velocity difference it can sustain with the crust. Contrary to its rapid
decrease between glitches, the spin-down rate increased over the 13 years, and
we find the long-term braking index , the only negative
braking index seen in a young pulsar. We briefly discuss the plausible
interpretations of this result, which is in stark contrast to the predictions
of standard models of pulsar spin-down.Comment: Minor changes to match the MNRAS accepted versio
The enigmatic spin evolution of PSR J0537-6910: r-modes, gravitational waves and the case for continued timing
We discuss the unique spin evolution of the young X-ray pulsar PSR
J0537-6910, a system in which the regular spin down is interrupted by glitches
every few months. Drawing on the complete timing data from the Rossi X-ray
Timing Explorer (RXTE, from 1999-2011), we argue that a trend in the
inter-glitch behaviour points to an effective braking index close to ,
much larger than expected. This value is interesting because it would accord
with the neutron star spinning down due to gravitational waves from an unstable
r-mode. We discuss to what extent this, admittedly speculative, scenario may be
consistent and if the associated gravitational-wave signal would be within
reach of ground based detectors. Our estimates suggest that one may, indeed, be
able to use future observations to test the idea. Further precision timing
would help enhance the achievable sensitivity and we advocate a joint observing
campaign between the Neutron Star Interior Composition ExploreR (NICER) and the
LIGO-Virgo network.Comment: 10 pages, 4 figures, emulate ApJ forma
Neutron star glitches have a substantial minimum size
Glitches are sudden spin-up events that punctuate the steady spin down of
pulsars and are thought to be due to the presence of a superfluid component
within neutron stars. The precise glitch mechanism and its trigger, however,
remain unknown. The size of glitches is a key diagnostic for models of the
underlying physics. While the largest glitches have long been taken into
account by theoretical models, it has always been assumed that the minimum size
lay below the detectability limit of the measurements. In this paper we define
general glitch detectability limits and use them on 29 years of daily
observations of the Crab pulsar, carried out at Jodrell Bank Observatory. We
find that all glitches lie well above the detectability limits and by using an
automated method to search for small events we are able to uncover the full
glitch size distribution, with no biases. Contrary to the prediction of most
models, the distribution presents a rapid decrease of the number of glitches
below ~0.05 Hz. This substantial minimum size indicates that a glitch must
involve the motion of at least several billion superfluid vortices and provides
an extra observable which can greatly help the identification of the trigger
mechanism. Our study also shows that glitches are clearly separated from all
the other rotation irregularities. This supports the idea that the origin of
glitches is different to that of timing noise, which comprises the unmodelled
random fluctuations in the rotation rates of pulsars.Comment: 8 pages; 4 figures. Accepted for publication in MNRA
Isoperibolic study of hydroxylamine in aqueous solutions in the presence of selected inorganic salts
PresentationThe thermal decomposition of hydroxylamine aqueous solutions in two different concentrations and two temperatures was studied in the presence of KCl, NaCl and Na2SO4 using isoperibolic calorimetry. It was found that Na2SO4 was substantially reducing its decomposition rate, while the other two compounds had a rather insignificant influence on hydroxylamine decomposition rate. The results are compared with the effect that the same salts have on ammonium nitrate decomposition rate and similarities and differences are discussed
A new small glitch in Vela discovered with a hidden Markov model
A striking feature of the Vela pulsar (PSR J08354510) is that it undergoes
sudden increases in its spin frequency, known as glitches, with a fractional
amplitude on the order of approximately every 900 days. Glitches of
smaller magnitudes are also known to occur in Vela. Their distribution in both
time and amplitude is less well constrained but equally important for
understanding the physical process underpinning these events. In order to
better understand these small glitches in Vela, an analysis of high-cadence
observations from the Mount Pleasant Observatory is presented. A hidden Markov
model (HMM) is used to search for small, previously undetected glitches across
24 years of observations covering MJD 44929 to MJD 53647. One previously
unknown glitch is detected around MJD 48636 (Jan 15 1992), with fractional
frequency jump and frequency
derivative jump . Two
previously reported small glitches are also confidently re-detected, and
independent estimates of their parameters are reported. Excluding these events,
90% confidence frequentist upper limits on the sizes of missed glitches are
also set, with a median upper limit of . Upper limits of this kind are enabled by the semi-automated and
computationally efficient nature of the HMM, and are crucial to informing
studies which are sensitive to the lower end of the glitch size distribution.Comment: 10 pages, 7 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Core vs. diet -associated and postprandial bacterial communities of the rainbow trout (Oncorhynchus mykiss) midgut and feaces
ACKNOWLEDGMENTS: Eleni Mente was awarded a visiting fellowship by Marine Alliance for Science and Technology Scotland (MASTS). Part of Eleni’s Nikouli’s work in this paper was carried out under the program “Scholarships of IKY in the Marine and Inland Management of Water Resources” and was co-funded by EEA grants– Financial Mechanism 2009-2014 (85%) and the General Secretariat for Investments and Development (15%). The authors declare no competing interests.Peer reviewedPublisher PD
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