252 research outputs found
Transformations of Lines and Conics in The Z-Plane
The purpose of the problem was to investigate the behavior of curves under some simple complex transformations. The transformations used were limited tow,= z 2 w = z2 1 , , and w = -z • The curves considered were limited to straight lines and conic sections. However, the general cases of the conics were usually too complicated to be dealt with in the thesis. Therefore, most of the conics considered were special cases which were simpler and from which some indication of t he behavior of more general cases might be found. Some interesting special cases of the more complicated transformations were treated briefly, as were practical applications of complex transformations. Sketches were included showing the results of the transformations in graphic form. It was noted that, in general, subjection of a curve to a transformation complicated that curve. Cases in which the curve was simplified were less numerous, but usually had gr eater chance of application
Quantifying Rapid Variability in Accreting Compact Objects
I discuss some practical aspects of the analysis of millisecond time
variability X-ray data obtained from accreting neutron stars and black holes.
First I give an account of the statistical methods that are at present commonly
applied in this field. These are mostly based on Fourier techniques. To a large
extent these methods work well: they give astronomers the answers they need.
Then I discuss a number of statistical questions that astronomers don't really
know how to solve properly and that statisticians may have ideas about. These
questions have to do with the highest and the lowest frequency ranges
accessible in the Fourier analysis: how do you determine the shortest time
scale present in the variability, how do you measure steep low-frequency noise.
The point is stressed that in order for any method that resolves these issues
to become popular, it is necessary to retain the capabilities the current
methods already have in quantifying the complex, concurrent variability
processes characteristic of accreting neutron stars and black holes.Comment: To be published in the Proceedings of "Statistical Challenges in
Modern Astronomy II", University Park PA, USA, June 199
Updating the orbital ephemeris of Her X-1; rate of decay and eccentricity of the orbit
We present an update of the orbital ephemeris of the binary X-ray pulsar Her
X-1 and determine an improved value for the rate of orbital decay. In addition,
we report the first measurement of the orbital eccentricity. We have analyzed
pulse timing data of Her X-1 from X-ray observations by RXTE (Rossi X-Ray
Timing Explorer) and INTEGRAL over the period 1996-2007. Accurate pulse arrival
times were determined from solar system bary-centered photon arrival times by
generating pulse profiles averaged over appropriately short integration times.
Applying pulse phase connection techniques, it was possible to determine
sufficiently accurate local ephemeris data for seven observation periods
distributed over 12 years. Combining the new local T90 values with historical
values from the literature we update the orbital ephemeris of Her X-1 to T90 =
MJD 46359.871940(6) and Porb = 1.700167590(2) d and measure a continuous change
of the orbital period of dPorb/dt = -(4.85 +/- 0.13) x 10-11 s/s. For the first
time, a value for the eccentricity of the orbit of Her X-1 is measured to be e
= (4.2 +/- 0.8) x 10-4.Comment: 7 pages, 4 figures, accepted by A&A on 30.03.200
Continuous monitoring of pulse period variations in Her X-1 using Swift/BAT
Context: Monitoring of pulse period variations in accreting binary pulsars is
an important tool to study the interaction between the magnetosphere of the
neutron star and the accretion disk. While the X-ray flux of the brightest
X-ray pulsars have been successfully monitored over many years (e.g. with
RXTE/ASM, CGRO/BATSE, Swift/BAT), the possibility to monitor their pulse timing
properties continuously has so far been very limited. Aims: In our work we show
that the Swift/BAT observations can be used to monitor coherent pulsations of
bright X-ray sources and use the Swift archival data to study one of the most
enigmatic X-ray pulsars, Hercules X-1. A quasi-continuous monitoring of the
pulse period and the pulse period derivative of an X-ray pulsar, here Her X-1,
is achieved over a long time (<~ 4 yrs). We compare our observational results
with predictions of accretion theory and use them to test different aspects of
the physical model of the system. Methods: In our analysis we use the data
accumulated with Swift/BAT starting from the beginning of 2005 (shortly after
launch) until the present time. To search for pulsations and for their
subsequent analysis we used the count rate measured by the BAT detector in the
entire field of view. Results: The slope of the correlation between the locally
determined spin-up rate and the X-ray luminosity is measured for Her X-1 and
found to be in agreement with predictions of basic accretion torque theory. The
observed behaviour of the pulse period together with the previously measured
secular decrease of the system's orbital period is discussed in the frame of a
model assuming ejection of matter close to the inner boundary of the accretion
disk.Comment: 7 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Studies of extraterrestrial dust at 40 kilometers /1966/ Final report
Extraterrestrial dust in stratospheric sampling collected by balloon-borne prob
Timing of the 2008 Outburst of SAX J1808.4-3658 with XMM-Newton: A Stable Orbital Period Derivative over Ten Years
We report on a timing analysis performed on a 62-ks long XMM-Newton
observation of the accreting millisecond pulsar SAX J1808.4-3658 during the
latest X-ray outburst that started on September 21, 2008. By connecting the
time of arrivals of the pulses observed during the XMM observation, we derived
the best-fit orbital solution and a best-fit value of the spin period for the
2008 outburst. Comparing this new set of orbital parameters and, in particular,
the value of the time of ascending-node passage with the orbital parameters
derived for the previous four X-ray outbursts of SAX J1808.4-3658 observed by
the PCA on board RXTE, we find an updated value of the orbital period
derivative, which turns out to be s/s. This new value of the orbital period derivative agrees with the
previously reported value, demonstrating that the orbital period derivative in
this source has remained stable over the past ten years. Although this timespan
is not sufficient yet for confirming the secular evolution of the system, we
again propose an explanation of this behavior in terms of a highly
non-conservative mass transfer in this system, where the accreted mass (as
derived from the X-ray luminosity during outbursts) accounts for a mere 1% of
the mass lost by the companion.Comment: 4 pages, 3 figures. Final version, including editing corrections, to
appear on A&A Letter
Giant outburst of EXO 2030+375: pulse-phase resolved analysis of INTEGRAL data
In June-September 2006 the Be/X-ray binary EXO 2030+375 experienced the
second giant outburst since its discovery. The source was shown to have a
complicated pulse-averaged X-ray spectral continuum with possible evidence of
cyclotron absorption features. In this paper we present the first pulse-phase
resolved analysis of the broad band X-ray spectra of EXO 2030+375 obtained with
the INTEGRAL observatory close to the maximum and during the decay phase of the
giant outburst. We report a strong variability of the spectrum with pulse
phase. Alternative spectral continuum models are discussed. The dependence of
the spectral parameters on pulse phase during the maximum of the outburst and
the evolution of the pulse profiles with time are qualitatively consistent with
the pulsar's emission diagram changing from the fan-beam geometry close to the
maximum of the outburst to a combination of pencil and fan beams (of comparable
intesities) at the end of the decay phase. Evidence of a cyclotron absorption
line around 63 keV at the pulse phase interval preceeding the main peak of the
pulse profile is present in the spectrum obtained close to the maximum of the
outburst.Comment: 8 pages, 10 figures, accepted for publication in A&
Study of the cyclotron feature in MXB 0656-072
We have monitored a type II outburst of the Be/X-ray binary MXB 0656−072 in a series of pointed RXTE observations during October through December 2003. The source spectrum shows a cyclotron resonance scattering feature at 32.8 +0.5
−0.4 keV, corresponding to a magnetic field strength of 3.67
+0.06 −0.04 × 10 12 G and is stable through the outburst and over the pulsar spin phase. The pulsar, with an average pulse period of 160.4 ± 0.4s,shows a spin-up of 0.45 s over the duration of the outburst. From optical data, the source distance is estimated to be 3.9 ± 0.1 kpc and this is used to estimate the X-ray luminosity and a theoretical prediction of the pulsar spin-up during the outburst
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