59 research outputs found
Detailed Analysis of the Pulsations During and After Bursts from the Bursting Pulsar (GRO J1744-28)
The hard X-ray bursts observed during both major outbursts of the Bursting
Pulsar (GRO J1744-28) show pulsations near the neutron star spin frequency with
an enhanced amplitude relative to that of the persistent emission. Consistent
with previous work, we find that the pulsations within bursts lag behind their
expected arrival times based upon the persistent pulsar ephemeris. For an
ensemble of 1293 bursts recorded with the Burst and Transient Source
Experiment, the average burst pulse time delay is 61.0 +/- 0.8 ms in the 25 -
50 keV energy range and 72 +/- 5 ms in the 50 - 100 keV band. The residual time
delay from 10 to 240 s following the start of the burst is 18.1 +/- 0.7 ms (25
- 50 keV). A significant correlation of the average burst time delay with burst
peak flux is found. Our results are consistent with the model of the pulse time
lags presented by Miller (1996).Comment: 11 pages, accepted for publication in Ap
An explanation for metallicity effects on X-ray Binary properties
We show that irradiation induced stellar winds can explain two important
metallicity effects in X-ray binaries - the higher numbers and the softer
spectra of the X-ray binaries in metal rich globular clusters compared to the
metal poor ones. As has been previously noted by Iben, Tutukov and Fedorova,
the winds should be stronger at lower metallicity due to less efficient line
cooling. This will speed up the evolution of the LMXBs in metal poor clusters,
hence reducing their numbers. These winds can also provide extra material near
the accreting object which may create an intrinsic absorber to harden the X-ray
spectra of the metal poor cluster systems relative to the metal rich ones, as
suggested by observations. We outline some additional observational predictions
of the model.Comment: 6 pages, no figures, accepted to Ap
Having Fun in Learning Formal Specifications
There are many benefits in providing formal specifications for our software.
However, teaching students to do this is not always easy as courses on formal
methods are often experienced as dry by students. This paper presents a game
called FormalZ that teachers can use to introduce some variation in their
class. Students can have some fun in playing the game and, while doing so, also
learn the basics of writing formal specifications in the form of pre- and
post-conditions. Unlike existing software engineering themed education games
such as Pex and Code Defenders, FormalZ takes the deep gamification approach
where playing gets a more central role in order to generate more engagement.
This short paper presents our work in progress: the first implementation of
FormalZ along with the result of a preliminary users' evaluation. This
implementation is functionally complete and tested, but the polishing of its
user interface is still future work
Bacille Calmette-Guérin (BCG) vaccination at birth and antibody responses to childhood vaccines. A randomised clinical trial
Contains fulltext :
169904.pdf (publisher's version ) (Open Access)INTRODUCTION: BCG vaccination has been associated with beneficial non-specific effects on child health. Some immunological studies have reported heterologous effects of vaccines on antibody responses to heterologous vaccines. Within a randomised clinical trial of Bacille Calmette-Guerin (BCG) vaccination at birth, The Danish Calmette Study, we investigated the effect of BCG at birth on the antibody response to the three routine vaccines against DiTeKiPol/Act-Hib and Prevenar 13 in a subgroup of participants. METHODS: Within 7days after birth, children were randomised 1:1 to BCG vaccination or to the control group (no intervention). After three routine vaccinations given at age 3, 5 and 12months, antibodies against DiTeKiPol/Act-Hib and Prevenar 13 (Streptococcus pneumoniae serotype type 4, 6B, 9V, 14, 18C, 19F and 23F) were measured 4weeks after the third vaccine dose. RESULTS: Among the 300 included children (178 BCG; 122 controls), almost all children (>96%) had antibody responses above the protective levels. Overall BCG vaccination at birth did not affect the antibody level. When stratifying by 'age at randomisation' we found a possible inducing effect of BCG on antibodies against B. pertussis and all pneumococcal serotypes, when BCG was given after the first day of life. Girls had significantly higher antibody levels for Haemophilus influenza type b and pneumococcus than boys. CONCLUSIONS AND RELEVANCE: Three routine vaccinations with DiTeKiPol/Act-Hib and Prevenar 13 induced sero-protective levels in almost all children. No overall effect of neonatal BCG vaccination was observed
Large amplitude variability from the persistent ultracompact X-ray binary in NGC 1851
Using archival RXTE data, we show that the ultracompact X-ray binary in NGC
1851 exhibits large amplitude X-ray flux varations of more than a factor of 10
on timescales of days to weeks and undergoes sustained periods of months where
the time-averaged luminosty varies by factors of two. Variations of this
magnitude and timescale have not been reported previously in other ultracompact
X-ray binaries. Mass transfer in ultracompact binaries is thought to be driven
by gravitational radiation and the predicted transfer rates are so high that
the disks of ultracompact binaries with orbits as short as that of this object
should not be susceptible to ionization instabilities. Therefore the
variability characteristics we observe were unexpected, and need to be
understood. We briefly discuss a few alternatives for producing the observed
variations in light of the fact that the viscous timescale of the disk is of
order a week, comparable to the shorter time scale variation that is observed
but much less than the longer term variation. We also discuss the implications
for interpretation of observations of extragalactic binaries if the type of
variability seen in the source in NGC 1851 is typical.Comment: 7 pages, 5 figures, accepted for publication in MNRA
XMM-Newton light curves of the low-mass X-ray binary EXO 0748--676: dips, eclipses, and bursts
We present an analysis of XMM-Newton light curves of the dipping, bursting,
and eclipsing low-mass X-ray binary EXO 0748-676, focusing on the variability
on time scales of seconds to hours. The observed variability can be roughly
divided in three types: dips, eclipses and bursts. We find that the appearance
of the latter two, depends strongly on the strength of the first. We show that
the absorption dips change from spectrally hard to spectrally soft as they
become deeper, which supports suggestions that the source is composed of a
spectrally hard compact source and a spectrally soft extended source. The fast
variability in the soft light curve indicates that the large structures causing
the dips are made up of smaller absorption cores. We present the first clear
detection with XMM-Newton of eclipses below 2 keV in this source, and show that
dipping activity is apparently unrelated to the source luminosity. We also test
several proposed models for the spectral evolution during dips and confirm the
presence of a scatter/reflection component in the eclipse spectrum.Comment: Accepted for publication in A&A, 14 page
Trends in Space Astronomy and Cosmic Vision 2015-2025
To be published in the proceedings of the 2005 ESLAB Symposium "Trends in Space Science and Cosmic Vision 2020", held at ESTEC, 19-21 April 2005, F. Favata (ed)As a short introduction to the astronomy session, the response of the community to the Call for Themes issued by ESA and the specific themes selected by the Astronomy Working Group are briefly presented in connection with the four grand themes finally selected for the ESA Science Programme. They are placed in the context of the main discoveries of the past decade and the astronomy projects currently in their development or definition phase. Finally, possible strategies for their implementation are summarised
Disk, Corona, Jet Connection in the Intermediate State of MAXI J1820+070 Revealed by NICER Spectral-timing Analysis
We analyze five epochs of Neutron star Interior Composition Explorer (NICER) data of the black hole X-ray binary MAXI J1820+070 during the bright hard-to-soft state transition in its 2018 outburst with both reflection spectroscopy and Fourier-resolved timing analysis. We confirm the previous discovery of reverberation lags in the hard state, and find that the frequency range where the (soft) reverberation lag dominates decreases with the reverberation lag amplitude increasing during the transition, suggesting an increasing X-ray emitting region, possibly due to an expanding corona. By jointly fitting the lag-energy spectra in a number of broad frequency ranges with the reverberation model reltrans, we find the increase in reverberation lag is best described by an increase in the X-ray coronal height. This result, along with the finding that the corona contracts in the hard state, suggests a close relationship between spatial extent of the X-ray corona and the radio jet. We find the corona expansion (as probed by reverberation) precedes a radio flare by ~5 days, which may suggest that the hard-to-soft transition is marked by the corona expanding vertically and launching a jet knot that propagates along the jet stream at relativistic velocities
X-ray Reverberation Mapping of Ark 564 using Gaussian Process Regression
Ark 564 is an extreme high-Eddington Narrow-line Seyfert 1 galaxy, known for
being one of the brightest, most rapidly variable soft X-ray AGN, and for
having one of the lowest temperature coronae. Here we present a 410-ks NuSTAR
observation and two 115-ks XMM-Newton observations of this unique source, which
reveal a very strong, relativistically broadened iron line. We compute the
Fourier-resolved time lags by first using Gaussian processes to interpolate the
NuSTAR gaps, implementing the first employment of multi-task learning for
application in AGN timing. By fitting simultaneously the time lags and the flux
spectra with the relativistic reverberation model RELTRANS, we constrain the
mass at , although additional components
are required to describe the prominent soft excess in this source. These
results motivate future combinations of machine learning, Fourier-resolved
timing, and the development of reverberation models.Comment: 19 pages, 9 figures. Accepted for publication in The Astrophysical
Journa
A High Statistics Search for Ultra-High Energy Gamma-Ray Emission from Cygnus X-3 and Hercules X-1
We have carried out a high statistics (2 Billion events) search for
ultra-high energy gamma-ray emission from the X-ray binary sources Cygnus X-3
and Hercules X-1. Using data taken with the CASA-MIA detector over a five year
period (1990-1995), we find no evidence for steady emission from either source
at energies above 115 TeV. The derived upper limits on such emission are more
than two orders of magnitude lower than earlier claimed detections. We also
find no evidence for neutral particle or gamma-ray emission from either source
on time scales of one day and 0.5 hr. For Cygnus X-3, there is no evidence for
emission correlated with the 4.8 hr X-ray periodicity or with the occurrence of
large radio flares. Unless one postulates that these sources were very active
earlier and are now dormant, the limits presented here put into question the
earlier results, and highlight the difficulties that possible future
experiments will have in detecting gamma-ray signals at ultra-high energies.Comment: 26 LaTeX pages, 16 PostScript figures, uses psfig.sty to be published
in Physical Review
- …