1,245 research outputs found
On the Nature of the Binary Components of RX J0806.3+1527
We present imaging circular polarimetry and near-infrared photometry of the
suspected ultra-short period white-dwarf binary RX J0806.3+1527 obtained with
the ESO VLT and discuss the implications for a possible magnetic nature of the
white dwarf accretor and the constraints derived for the nature of the donor
star. Our V-filter data show marginally significant circular polarization with
a modulation amplitude of ~0.5% typical for cyclotron emission from an
accretion column in a magnetic field of order 10 MG and not compatible with a
direct-impact accretor model. The optical to near-infrared flux distribution is
well described by a single blackbody with temperature kT_bb = 35000 K and
excludes a main-sequence stellar donor unless the binary is located several
scale heights above the galactic disk population.Comment: 2 pages including 2 figures. To appear in RevMexAA(SC) Conference
Series, Proc. of IAU Colloquium 194 `Compact Binaries in the Galaxy and
Beyond', La Paz (Mexico), eds. G. Tovmassian & E. Sio
Probing the accretion processes in soft X-ray selected polars
High-energy data of accreting white dwarfs give access to the regime of the
primary accretion-induced energy release and the different proposed accretion
scenarios. We perform XMM-Newton observations of polars selected due to their
ROSAT hardness ratios close to -1.0 and model the emission processes in
accretion column and accretion region. Our models consider the
multi-temperature structure of the emission regions and are mainly determined
by mass-flow density, magnetic field strength, and white-dwarf mass. To
describe the full spectral energy distribution from infrared to X-rays in a
physically consistent way, we include the stellar contributions and establish
composite models, which will also be of relevance for future X-ray missions. We
confirm the X-ray soft nature of three polars.Comment: Accepted for publication in Acta Polytechnica, Proceedings of "The
Golden Age of Cataclysmic Variables and Related Objects II
No periodicity revealed for an "eclipsing" ultraluminous supersoft X-ray source in M81
Luminous supersoft X-ray sources found in the Milky Way and Magellanic Clouds
are likely white dwarfs that steadily or cyclically burn accreted matter on
their surface, which are promising type Ia supernova progenitors. Observations
of distant galaxies with Chandra and XMM-Newton have revealed supersoft sources
that are generally hotter and more luminous, including some ultraluminous
supersoft sources (ULSs) that are possibly intermediate mass black holes of a
few thousand solar masses. In this paper we report our X-ray spectral and
timing analysis for M81-ULS1, an ultraluminous supersoft source in the nearby
spiral galaxy M81. M81-ULS1 has been persistently supersoft in 17 Chandra ACIS
observations spanning six years, and its spectrum can be described by either a
eV blackbody for a white dwarf, or a
eV multicolor accretion disk for a
intermediate mass black hole. In two observations, the light curves exhibited
dramatic flux drop/rise on time scales of seconds, reminiscent of
eclipse ingress/egress in eclipsing X-ray binaries. However, the exhaustive
search for periodicity in the reasonable range of 50 ksec to 50 days failed to
reveal an orbital period. The failure to reveal any periodicity is consistent
with the long period ( yrs) predicted for this system given the optical
identification of the secondary with an asymptotic giant star. Also, the
eclipse-like dramatic flux changes in hours are hard to explain under the white
dwarf model, but can in principle be explained by disk temperature changes
induced by accretion rate variations under the intermediate mass black hole
model.Comment: 19 pages, 7 figures, 1 table, to appear in ApJ
Multifrequency Behaviour of Polars
Cataclysmic variables emit over a wide range of the electromagnetic spectrum. In this paper I will review observations of polars in relevant passbands obtained during the last decade and will discuss their diagnostical potential to access the physics of the main components within the binary systems. This will include a discussion of intrinsic source variability and the quest for simultaneous multi-frequency observations
The high-field magnetic white dwarf LP 790-29: not a fast rotator
We have investigated the nature of the magnetic white dwarf LP 790-29 = LHS
2293 by polarimetric monitoring, searching for short-term variability. No
periodicity was found and we can exclude rotation periods between 4 sec and 1.5
hour with a high confidence. Maximum amplitudes of sinusoidal variations are
Delta R < 0.009 mag and Delta V_R < 0.7% for a mean value of the R-band
circular polarization of V_R = +9.1+/-0.3%. Combined with earlier results by
other authors, our observation suggests that LP 790-29 is, in fact, an
extremely slowly rotating single white dwarf and not an unrecognized fast
rotator and/or disguised cataclysmic variable.Comment: 4 pages, 2 figures, accepted for publication by A&
The high-field polar RX J1007.5-2017
We report optical and X-ray observations of the high-field polar
RXJ1007.5-2017 performed between 1990 and 2012. It has an orbital period of
208.60 min determined from the ellipsoidal modulation of the secondary star in
an extended low state. The spectral flux of the dM3- secondary star yields a
distance of 790+-105 pc. At low accretion levels, \RX{} exhibits pronounced
cyclotron emission lines. The second and third harmonic fall in the optical
regime and yield a field strength in the accretion spot of 94 MG. The source is
highly variable on a year-to-year basis and was encountered at visual
magnitudes between V \sim 20 and V \sim 16. In the intermediate state of 1992
and 2000, the soft X-ray luminosity exceeds the sum of the luminosities of the
cyclotron source, the hard X-ray source, and the accretion stream by an order
of magnitude. An X-ray high state, corresponding to the brightest optical
level, has apparently not been observed so far.Comment: To be published in A&
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