92 research outputs found
The long period intermediate polar RX J1548-4528
No full textInternational audiencePhase-resolved optical spectroscopy of the recently identified Intermediate Polar (IP) RX J1548-4528 (Haberl et al. 2002) reveals radial velocity variability of emission lines at the 693 s X-ray and photometric period, confirming the identification of the white dwarf (WD) spin period as well as at a 9.87 hr period, which we identify as the orbital period. RX J1548-4528 is then the fourth longest period IP known so far. The optical spectrum is peculiar with broad absorptions around Balmer emission lines resembling those observed in V 709 Cas (Bonnet-Bidaud et al. 2001). Their origin, the WD or disc, remains unclear. An evolved G9-K3 secondary star is detected in the red spectra
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
Can White Dwarfs in Intermediate Polars be Unveiled?
No full textInternational audienceThe properties of white dwarf primaries in Intermediate Polars are mostly unknown because they almost never undergo low accretion states which can reveal the stellar components. V 709 Cas (Bonnet-Bidaud et al. 2001) and RX J1548-45 (Haberl et al. 2002) are the only two IPs known so far to show a peculiar optical spectrum, with broad absorption features around Balmer emissions but not around He lines, suggesting an origin in the white dwarf atmosphere. New optical observations and UV data of these systems make the white dwarf identification uncertain and leave the origin of the absorption features still controversial
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
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
Rapid variability of accretion in AM Herculis
No full textWe present the last pointed observation of AM Her carried out during the life of the BeppoSAX satellite. It was bright at the beginning of the observation, but dropped to the lowest X-ray level ever observed so far. The X-ray emission during the bright period is consistent with accretion occurring onto the main pole of the magnetized white dwarf. The rapid change from the active state to the low deep state indicates a drop by a factor of 17 in the accretion rate and hence that accretion switched-off. The short timescale (less than one hour) of this variation still remains a puzzle. Optical photometry acquired simultaneousy during the low state shows that the white dwarf remains heated, although a weak emission from the accretion stream could be still present. Cyclotron radiation, usually dominating the V and R bands, is negligible thus corroborating the possibility that AM Her was in an off-accretion state. The X-ray emission during the inactive state is consistent with coronal emission from the secondary late type star
High-Energy pulse profile of the Transient X-ray Pulsar SAX J2103.5+4545
Get PDFTwo recent INTEGRAL papers report a timing and spectral analysis of the transient Be/X-ray pulsar SAX J2103.5+4545 at high energies (5-200 keV). In this work we present for the first time a study of the pulse profile at energies above 20 keV using INTEGRAL data. The spin-pulse profile shows a prominent (with a duty cycle of 14%) and broad (with a FWHM of similar to 51 s) peak and a secondary peak which becomes more evident above 20 keV. The pulsed fraction increases with energy from similar to 45% at 5-40 keV to similar to 80% at 40-80 keV. The morphology of the pulse profile also changes as a function of energy, consistent with variations in the spectral components that are visible in the pulse phase resolved spectra. A study of the double peaked profile shows that the difference in the two peaks can be modeled by a different scattering fraction between the radiation from the two magnetic poles
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
A deep X-ray low state of AM Herculis
No full textWe present a BeppoSAX observation of AM Her during a prolonged low state. The source was observed for similar to 4 hrs at a flux level comparable to previous low states, followed by a rapid (similar to 40 min) drop by a factor of similar to 7 to the deepest X-ray low state ever detected. While the active phase X-ray flux is likely to be accretion induced, coronal emission from the secondary may contribute significantly during the inactive phase. The timescale of this dramatic change in the accretion rate is of the order of the dynamical timescale of the secondary star; no available model can satisfactorily explain the evolution of the X-ray flux detected in these BeppoSAX data
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