89 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
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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MACHO 311.37557.169: A VY Scl star
Optical surveys, such as theMACHO project, often uncover variable stars whose
classification requires follow-up observations by other instruments. We performed
X-ray spectroscopy and photometry of the unusual variable starMACHO
311.37557.169 with XMM-Newton in April 2018, supplemented by archival X-ray
and optical spectrographic data. The star has a bolometric X-ray luminosity
of about 1 × 1032 erg s−1 cm−2 and a heavily absorbed two-temperature plasma
spectrum. The shape of its light curve, its overall brightness, its X-ray spectrum,
and the emission lines in its optical spectrum suggest that it is most likely a VY
Scl cataclysmic variable
Cyclotron modeling phase-resolved infrared spectroscopy of polars I: EF Eridani
We present phase-resolved low resolution infrared spectra of the polar EF
Eridani obtained over a period of 2 years with SPEX on the IRTF. The spectra,
covering the wavelength range 0.8 to 2.4 microns, are dominated by cyclotron
emission at all phases. We use a ``Constant Lambda'' prescription to attempt to
model the changing cyclotron features seen in the spectra. A single cyclotron
emission component with B = 12.6 MG, and a plasma temperature of kT = 5.0 keV,
does a reasonable job in matching the features seen in the H and K bands, but
fails to completely reproduce the morphology shortward of 1.6 microns. We find
that a two component model, where both components have similar properties, but
whose contributions differ with viewing geometry, provides an excellent fit to
the data. We discuss the implications of our models and compare them with
previously published results. In addition, we show that a cyclotron model with
similar properties to those used for modeling the infrared spectra, but with a
field strength of B = 115 MG, can explain the GALEX observations of EF Eri.Comment: 25 pages, 5 figures, to appear in Ap
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