590 research outputs found
Sequential and continuum bifurcations in degenerate elliptic equations
We examine the bifurcations to positive and sign-changing solutions of degenerate elliptic equations. In the problems we study, which do not represent Fredholm operators, we show that there is a critical parameter value at which an infinity of bifurcations occur from the trivial solution. Moreover, a bifurcation occurs at each point in some unbounded interval in parameter space. We apply our results to non-monotone eigenvalue problems, degenerate semi-linear elliptic equations, boundary value differential-algebraic equations and fully non-linear elliptic equations
RXTE confirmation of the intermediate polar status of IGR J15094-6649
Aims. To establish the X-ray properties of the intermediate polar candidate
IGR J15094-6649 and therefore confirm its inclusion into the class.
Methods. 42 856 s of X-ray data from RXTE was analysed. Frequency analysis
was used to constrain temporal variations and spectral analysis used to
characterise the emission and absorption properties.
Results. A spin period of 809.7+-0.6 s is present, revealed as a complex
pulse profile whose modulation depth decreases with increasing X-ray energy.
The spectrum is well fitted by either a 19+-4 keV Bremsstrahlung or
Gamma=1.8+-0.1 power law, with an iron emission line feature and significant
absorption in each case.
Conclusions. IGR J15094-6649 is confirmed to be an intermediate polar.Comment: 3 pages, 5 figures. Submitted to A&
Short-period X-ray oscillations in super-soft novae and persistent SSS
Transient short-period <100s oscillations have been found in the X-ray light
curves of three novae during their SSS phase and in one persistent SSS. We
pursue an observational approach to determine possible driving mechanisms and
relations to fundamental system parameters such as the white dwarf mass.
We performed a systematic search for short-period oscillations in all
available XMM-Newton and Chandra X-ray light curves of persistent SSS and novae
during their SSS phase. To study time evolution, we divided each light curve
into short time segments and computed power spectra. We then constructed
dynamic power spectra from which we identified transient periodic signals even
when only present for a short time. From all time segments of each system, we
computed fractions of time when periodic signals were detected.
In addition to the previously known systems with short-period oscillations,
RS Oph (35s), KT Eri (35s), V339 Del (54s), and Cal 83 (67s), we found one
additional system, LMC 2009a (33s), and also confirm the 35s period from
Chandra data of KT Eri. The amplitudes of oscillations are of order <15% of the
respective count rates and vary without any clear dependence on the X-ray count
rate. The fractions of the time when the respective periods were detected at
2-sigma significance (duty cycle) are 11.3%, 38.8%, 16.9%, 49.2%, and 18.7% for
LMC 2009a, RS Oph, KT Eri, V339 Del, and Cal 83, respectively. The respective
highest duty cycles found in a single observation are 38.1%, 74.5%, 61.4%,
67.8%, and 61.8%.Comment: accepted for publication in A&
EUVE Observations of the Magnetic Cataclysmic Variable QQ Vulpeculae
We present simultaneous X-ray (lambda_peak ~ 44A) and EUV (lambda_peak = 89A)
light curves for the magnetic cataclysmic variable QQ Vulpeculae, obtained with
the EUVE satellite. We find that the unique shape of the X-ray light curve is
different from previously obtained X-ray light curves of QQ Vul and provides
evidence for two-pole accretion. Detailed examination of the photometric data
indicates that QQ Vul undergoes a stellar eclipse of the X-ray emitting region,
indicative of a high binary inclination. We discuss possible implications for
the nature of this system given the observed shape of its EUV and X-ray light
curves.Comment: 12 pages including 4 figures, accepted to PAS
Lord of the Rings â Return of the King: Swift-XRT observations of dust scattering rings around V404 Cygni
On 2015 June 15, the black hole X-ray binary V404 Cygni went into outburst, exhibiting extreme X-ray variability which culminated in a final flare on June 26. Over the following days, the Swift-X-ray Telescope detected a series of bright rings, comprising five main components that expanded and faded with time, caused by X-rays scattered from the otherwise unobservable dust layers in the interstellar medium in the direction of the source. Simple geometrical modelling of the ringsâ angular evolution reveals that they have a common temporal origin, coincident with the final, brightest flare seen by INTEGRAL's JEM X-1, which reached a 3â10 keV flux of ~25 Crab. The high quality of the data allows the dust properties and density distribution along the line of sight to the source to be estimated. Using the RayleighâGans approximation for the dust scattering cross-section and a power-law distribution of grain sizes a, â a-q, the average dust emission is well modelled by q = 3.90+0.09-0.08 and maximum grain size of a+ = 0.147+0.024-0.004 ÎŒm, though significant variations in q are seen between the rings. The recovered dust density distribution shows five peaks associated with the dense sheets responsible for the rings at distances ranging from 1.19 to 2.13 kpc, with thicknesses of ~40 â 80 pc and a maximum density occurring at the location of the nearest sheet. We find a dust column density of Ndust ~ (2.0â2.5) Ă 1011 cm-2, consistent with the optical extinction to the source. Comparison of the inner ringsâ azimuthal X-ray evolution with archival Wide-field Infrared Survey Explorer (WISE) mid-IR data suggests that the second most distant ring follows the general IR emission trend, which increases in brightness towards the Galactic north side of the source
The early and late-time spectral and temporal evolution of GRB 050716
We report on a comprehensive set of observations of Gamma Ray Burst 050716,
detected by the Swift satellite and subsequently followed-up rapidly in X-ray,
optical and near infra-red wavebands. The prompt emission is typical of
long-duration bursts, with two peaks in a time interval of T90 = 68 seconds (15
- 350 keV). The prompt emission continues at lower flux levels in the X-ray
band, where several smaller flares can be seen, on top of a decaying light
curve that exhibits an apparent break around 220 seconds post trigger. This
temporal break is roughly coincident with a spectral break. The latter can be
related to the extrapolated evolution of the break energy in the prompt
gamma-ray emission, and is possibly the manifestation of the peak flux break
frequency of the internal shock passing through the observing band. A possible
3 sigma change in the X-ray absorption column is also seen during this time.
The late-time afterglow behaviour is relatively standard, with an electron
distribution power-law index of p = 2 there is no noticable temporal break out
to at least 10 days. The broad-band optical/nIR to X-ray spectrum indicates a
redshift of z ~> 2 for this burst, with a host-galaxy extinction value of
E(B-V) ~ 0.7 that prefers an SMC-like extinction curve.Comment: Accepted to MNRAS. 8 pages, 5 figure
Pan-chromatic observations of the remarkable nova LMC 2012
We present the results of an intensive multiwavelength campaign on nova LMC
2012. This nova evolved very rapidly in all observed wavelengths. The time to
fall two magnitudes in the V band was only 2 days. In X-rays the super soft
phase began 135 days after discovery and ended around day 50 after
discovery. During the super soft phase, the \Swift/XRT and \Chandra\ spectra
were consistent with the underlying white dwarf being very hot, 1 MK,
and luminous, 10 erg s. The UV, optical, and near-IR
photometry showed a periodic variation after the initial and rapid fading had
ended. Timing analysis revealed a consistent 19.240.03 hr period in all
UV, optical, and near-IR bands with amplitudes of 0.3 magnitudes which
we associate with the orbital period of the central binary. No periods were
detected in the corresponding X-ray data sets. A moderately high inclination
system, = 6010^{\arcdeg}, was inferred from the early optical
emission lines. The {\it HST}/STIS UV spectra were highly unusual with only the
\ion{N}{5} (1240\AA) line present and superposed on a blue continuum. The lack
of emission lines and the observed UV and optical continua from four epochs can
be fit with a low mass ejection event, 10 M, from a hot
and massive white dwarf near the Chandrasekhar limit. The white dwarf, in turn,
significantly illuminated its subgiant companion which provided the bulk of the
observed UV/optical continuum emission at the later dates. The inferred extreme
white dwarf characteristics and low mass ejection event favor nova LMC 2012
being a recurrent nova of the U Sco subclass.Comment: 18 figures, 6 tables (one online only containing all the photometry
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