1,721,003 research outputs found
BeppoSAX observations of AM Herculis in intermediate and high states
No full textTemporal and spectral analyses from BeppoSAX observations of AM Her performed during both an intermediate and a high stare are presented and discussed. Optical observations taken a few days after the X-ray ones are also presented. During the intermediate state observation, the source was in its "normal", one-pole accretion mode. In the high state it switched to an hitherto unobserved atypical "two-pole" accretion mode, with significant soft and hard X-ray emission from both poles. The emission from the second pole is much softer than that from the primary pole, while the soft X-ray excess of the primary pole is fairly modest in this accretion mode. These facts suggest that accretion onto the secondary is mainly due to blobs penetrating deeply in the photosphere, while that on the primary pole is mostly via a more homogeneous column, giving rise to the classical standing shock. A strong X-ray flaring activity is also observed in the soft X-ray band, but not in the hard X-ray and optical emissions indicating that flares are due to inhomogeneous blobby-accretion events
The long period intermediate polar 1RXS J154814.5-452845
Get PDFWe present the first time resolved medium resolution optical spectroscopy of the recently identified peculiar Intermediate Polar (IP)1RXS J154814.5-452845, which allows us to precisely determine the binary orbital period (P Ω = 9.87 ± 0.03 h) and the white dwarf spin period (P ω = 693.01
± 0.06 s). This system is then the third just outside the purported ∼6–10 h IP orbital period gap and the fifth of the small group of long period IPs, which has a relatively high degree of asynchronism. From the presence of weak red absorption features, we identify the secondary star with a spectral type K2 ± 2 V, which appears to have evolved on the nuclear timescale. From the orbital radial velocities of
emission and the red absorption lines a mass ratio q = 0.65
± 0.12 is found. The masses of the components are estimated to be M WD ≥ 0.5 M and M sec = 0.4−0.79 M and the binary inclination 25 ◦ < i ≤ 58 ◦ . A distance between 540–840 pc is estimated. At this distance, the presence of peculiar absorption features surrounding Balmer emissions cannot be due to the contribution of the white dwarf photosphere and their spin modulation suggests an origin in the magnetically confined accretion flow. The white dwarf is also not accreting at a particularly high rate(. M < 5 × 10
16 g s −1 ), for its orbital period. The spin-to-orbit period ratio P ω /P Ω = 0.02 and the low mass accretion rate suggest that this system is far from spin equilibrium. The magnetic moment of the accreting white dwarf is found to be µ < 4.1 × 10 32 G cm 3, indicating a low magnetic
field system
1RXS J173021.5-055933 : a cataclysmic variable with a fast-spinning magnetic white dwarf
Get PDFAims. We present the first X-ray observations with the XMM-Newton and INTEGRAL satellites of the recently discovered cataclysmic variable 1RXS J173021.5-055933, together with simultaneous UV and coordinated optical photometry aiming at characterising its broad-band temporal and spectral properties and classifying this system as a magnetic one.
Methods. We performed a timing analysis of the X-ray, UV, and optical light curves to identify and to study the energy dependence of the fast 128 s pulsation over a wide energy range. X-ray spectral analysis in the broad 0.2−100 keV X-ray range was performed to characterise the peculiar emission properties of this source.
Results. We find that the X-ray light curve is dominated by the spin period of the accreting white dwarf in contrast to the far-UV range, which turns out to be unmodulated at a 3σ level. Near-UV and optical pulses are instead detected at twice the spin frequency. We identify the contributions from two accreting poles that imply a moderately inclined dipole field allowing, one pole to dominate at energies at least up to 10 keV, and a secondary that instead is negligible above 5 keV. X-ray spectral analysis reveals the presence of multiple emission components consisting of optically thin plasma with temperatures ranging from 0.17 keV to 60 keV and a hot blackbody at ∼90 eV. The spectrum is also strongly affected by peculiar absorption components consisting of two high-density (∼3 × 1021 cm−2 and 2 × 1023 cm−2) intervening columns, plus a warm absorber. The last is detected from an OVII absorption edge at 0.74 keV, which suggests that photoionization of pre-shock material is also occurring in this system.
Conclusions. The observed properties indicate that the accretor in 1RXS J173021.5-055933 is a white dwarf with a likely weak magnetic field, thus confirming this cataclysmic variable as an intermediate polar (IP) with one of the most extreme spin-to-orbit period ratios. This system also joins the small group of IPs showing a soft X-ray reprocessed component, suggesting that this characteristics is not uncommon in these systems
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
INTEGRAL spectroscopy of the accreting millisecond pulsar XTE J1807-294 in outburst
No full textThe transient X-ray accreting millisecond pulsar
XTE J1807-294 was observed during its February/March 2003 outburst by
INTEGRAL, partly simultaneously with the XMM-Newton and
RXTE
satellites. We present here the first study of the 0.5-200 keV broad-band
spectra of the source.
On February 28, the source spectrum was consistent with thermal
Comptonization by electrons of temperature ~40 keV, considerably
higher than the value (~10 keV) previously derived from the low
energy XMM-Newton data alone.
The source is detected by INTEGRAL up to 200 keV with a
luminosity in the energy band (0.1-200) keV of
erg s-1 (assuming a distance of 8 kpc).
22 days later the luminosity dropped to erg s-1.
A re-analysis of XMM-Newton data yields the orbital Doppler
variations of the pulse period and refines the previous ephemeris.
For this source, with shortest orbital period of any known binary
radio or X-ray millisecond pulsar, we constrain the companion mass
, assuming minimum mass transfer driven
by gravitational radiation. Only evolved dwarfs with a C/O composition
are consistent with the Roche lobe and gravitational radiation
constraints, while He dwarfs require an unlikely low inclination
The X-ray emission of the intermediate polar V709 Cas
No full textWe present RXTE and BeppoSAX observations of the Intermediate
Polar V 709 Cas acquired in 1997 and 1998 respectively. The X-ray
emission from
0.1 to 30 keV is dominated by the strong pulsation at the rotational
period of the white dwarf (312.8 s) with no sign of orbital or
sideband periodicity, thus confirming previous ROSAT results.
However, we detect changes in the power spectra between
the two epochs. While the second harmonic of the spin
period is present during both observations, the first harmonic is
absent in 1997. An increase in the amplitude of the spin
pulsation is found between 1997 and 1998 together with a decrease in
the X-ray flux. The average X-ray spectrum from 0.1 to 100 keV is well
described
by an isothermal plasma at ~27 keV plus complex absorption and an
iron Kα fluorescent line, due to reflection from the
white dwarf surface. The rotational pulsation is compatible with complex
absorption dominating the low energy range, while the high energy
spin modulation can be attributed to tall shocks above the
accreting poles. The RXTE spectrum in 1997 also shows
the presence of an absorption edge from ionized iron likely
located in the pre-shock accretion flow. The variations along the
spin period of the partial covering absorber and of reflection are
compatible with the classical accretion curtain scenario. The variations
in the spin pulse characteristics and X-ray flux indicate that
V 709 Cas experiences changes in the mass accretion rate on timescales
from months to years
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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