149 research outputs found
Background subtraction and transient timing with Bayesian Blocks
Aims: To incorporate background subtraction into the Bayesian Blocks
algorithm so that transient events can be timed accurately and precisely even
in the presence of a substantial, rapidly variable, background. Methods: We
developed several modifications to the algorithm and tested them on a simulated
XMM-Newton observation of a bursting and eclipsing object. Results: We found
that bursts can be found to good precision for almost all background
subtraction methods, but eclipse ingresses and egresses present problems for
most methods. We found one method that recovered these events with precision
comparable to the interval between individual photons, in which both source and
background region photons are combined into a single list and weighted
according to the exposure area. We have also found that adjusting the Bayesian
Blocks change points nearer to blocks with higher count rate removes a
systematic bias towards blocks of low count rate.Comment: 10 pages, 13 figures, 1 tabl
Distant clusters of galaxies in the 2XMM/SDSS footprint: follow-up observations with the LBT
Context: Galaxy clusters at high redshift are important to test cosmological
models and models for the growth of structure. They are difficult to find in
wide-angle optical surveys, however, leaving dedicated follow-up of X-ray
selected candidates as one promising identification route. Aims: We aim to
increase the number of galaxy clusters beyond the SDSS-limit, z ~ 0.75.
Methods: We compiled a list of extended X-ray sources from the 2XMMp catalogue
within the footprint of the Sloan Digital Sky Survey. Fields without optical
counterpart were selected for further investigation. Deep optical imaging and
follow-up spectroscopy were obtained with the Large Binocular Telescope,
Arizona (LBT), of those candidates not known to the literature. Results: From
initially 19 candidates, selected by visually screening X-ray images of 478
XMM-Newton observations and the corresponding SDSS images, 6 clusters were
found in the literature. Imaging data through r,z filters were obtained for the
remaining candidates, and 7 were chosen for multi-object (MOS) spectroscopy.
Spectroscopic redshifts, optical magnitudes, and X-ray parameters (flux,
temperature, and luminosity) are presented for the clusters with spectroscopic
redshifts. The distant clusters studied here constitute one additional redshift
bin for studies of the L-T relation, which does not seem to evolve from high to
low redshifts. ...Comment: This is a abridged version of the paper. The full version can be
downloaded at the following URL:
https://cloud.aip.de/index.php/s/2Btv7ST1KTLHfT
X-ray and ultraviolet observations of the eclipsing cataclysmic variables OV Bootis and SDSS J103533.02+055158.3 with degenerate donors
The majority of cataclysmic variables are predicted to be post-period minimum
systems with degenerate donor stars, the period bouncers. Owing to their
intrinsic faintness, however, only a handful of these systems have so far been
securely identified. We want to study the X-ray properties of two eclipsing
period bouncers, OV Bootis and SDSS J103533.02+055158.3, that were selected for
this study due to their proximity to Earth. We have obtained XMM-Newton
phase-resolved X-ray and ultraviolet observations of the two objects for
spectral and timing analysis. Owing to a recent dwarf nova outburst OV Boo was
much brighter than SDSS J103533.02+055158.3 at X-ray and ultraviolet
wavelengths and the eclipse could be studied in some detail. An updated eclipse
ephemeris was derived. The X-rays were shown to originate close to the white
dwarf, the boundary layer, with significant absorption affecting its spectrum.
There was no absorption in SDSS J103533.02+055158.3, despite being observed at
the same inclination indicating different shapes of the disk and the disk rim.
The white-dwarf temperature was re-determined for both objects: the white dwarf
in OV Boo was still hot (23,000 K) five months after a dwarf nova outburst, and
the white dwarf in SDSS J103533.02+055158.3 hotter than assumed previously
(Teff = 11,500 K). All three cataclysmic variables with degenerate donors
studied so far in X-rays, including SDSS J121209.31+013627.7, were clearly
discovered in X-rays and revealed mass accretion rates dot(M) >= 8 x 10^(-15)
Msun/ yr. If their X-ray behavior is representative of the subpopulation of
period bouncers, the all-sky X-ray surveys with eROSITA together with
comprehensive follow-up will uncover new objects in sufficient number to
address the remaining questions concerning late-stage cataclysmic variable
evolution.Comment: 12 pages, 13 figures, accepted for publication in A&
The complex X-ray spectrum of the isolated neutron star RBS1223
We present a first analysis of a deep X-ray spectrum of the isolated neutron
star RBS1223 obtained with XMM-Newton. Spectral data from four new monitoring
observations in 2005/2006 were combined with archival observations obtained in
2003 and 2004 to form a spin-phase averaged spectrum containing 290000 EPIC-pn
photons. This spectrum shows higher complexity than its predecessors, and can
be parameterised with two Gaussian absorption lines superimposed on a
blackbody. The line centers, E_2 ~ 2E_1, could be regarded as supporting the
cyclotron interpretation of the absorption features in a field B ~ 4 x 10**13
G. The flux ratio of those lines does not support this interpretation. Hence,
either feature might be of truly atomic origin.Comment: 4 pages, 1 figure, to appear in Astrophysics and Space Science, in
the proceedings of "Isolated Neutron Stars: from the Interior to the
Surface", edited by D. Page, R. Turolla and S. Zan
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