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Koptelova E.,National Central University | Koptelova E.,Universitetski Pr 13 | Oknyanskij V.L.,Universitetski Pr 13 | Artamonov B.P.,Universitetski Pr 13 | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present the results of time delay measurements between the A and B components of the gravitationally lensed quasar UM673. The measurements are based on the brightness variations of the quasar components observed with the 1.5-m telescope of the Maidanak Observatory in the V, R and I bands during the 2003-2005 observational period. The amplitudes of variations in the R band are 0.046 and 0.122 mag for Component A and B, respectively. Due to the short visibility period of UM673, about 3 months in a year, the light curves of the quasar components have large annual gaps. It complicates the time delay estimation. From the cross-correlation analysis, we find that the brightness variations in component B follow the brightness variations in Component A by about 150 days. We also explore the possibility of measuring the wavelength-dependent time delay between the brightness variations in the V, R and I bands. We find that in agreement with reprocessing model of quasar variability, the brightness variation at longer wavelengths follows the brightness variations at shorter wavelengths. Finally, we show that the combination of the multiband data corrected for the wavelength-dependent time delay can help to improve the cross-correlation analysis of the light curves with large annual gaps. © 2009 RAS.

Boldin P.A.,National Research Nuclear University | Popov S.B.,Universitetski Pr 13 | Tetzlaff N.,Astrophysikalisches Institute und Universitats Sternwarte Jena
Astronomische Nachrichten | Year: 2011

We present a new web-tool - Net-PSICoNS - for population synthesis of isolated near-by cooling neutron stars (NSs). The main aim is to provide an easy test of models of the NS thermal evolution which can be used by groups studying this subject. A user can upload cooling curves for a set of masses, modify the mass spectrum if necessary, change radii to fit the EoS used for cooling curve calculations, and then a population synthesis of close-by isolated cooling NSs is performed. The output includes the log N -log S distribution confronted with the ROSAT observations and several other sets of data. In this paper, we summarize the idea of the test proposed by Popov et al. (2006), and present a user's manual for the web-tool. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Klochkov D.,University of Tübingen | Ferrigno C.,University of Geneva | Santangelo A.,University of Tübingen | Staubert R.,University of Tübingen | And 4 more authors.
Astronomy and Astrophysics | Year: 2011

Context. Episodic flaring activity is a common feature of X-ray pulsars in HMXBs. In some Be/X-ray binaries flares were observed in quiescence or prior to outbursts. EXO 2030+375 is a Be/X-ray binary showing "normal" outbursts almost every ∼46 days, near periastron passage of the orbital revolution. Some of these outbursts were occasionally monitored with the INTEGRAL observatory. Aims. The INTEGRAL data revealed strong quasi-periodic flaring activity during the rising part of one of the system's outburst. Such activity has previously been observed in EXO 2030+375 only once, in 1985 with EXOSAT. (Some indications of single flares have also been observed with other satellites.) Methods. We present the analysis of the flaring behavior of the source based on INTEGRAL data and compare it with the flares observed in EXO 2030+375 in 1985. Results. Based on the observational properties of the flares, we argue that the instability at the inner edge of the accretion disk is the most probable cause of the flaring activity. © 2011 ESO.

Skinner S.L.,University of Colorado at Boulder | Gudel M.,University of Vienna | Briggs K.R.,ETH Zurich | Lamzin S.A.,Universitetski Pr 13
Astrophysical Journal | Year: 2010

FU Orionis is the prototype of a class of eruptive young stars ("FUors") characterized by strong optical outbursts. We recently completed an exploratory survey of FUors using XMM-Newton to determine their X-ray properties, about which little was previously known. The prototype FU Ori and V1735 Cyg were detected. The X-ray spectrum of FU Ori was found to be unusual, consisting of a cool moderately absorbed component plus a hotter component viewed through an absorption column density that is an order of magnitude higher. We present here a sensitive (99 ks) follow-up X-ray observation of FU Ori obtained at higher angular resolution with Chandra ACIS-S. The unusual multi-component spectrum is confirmed. The hot component is centered on FU Ori and dominates the emission above 2 keV. It is variable (a signature of magnetic activity) and is probably coronal emission originating close to FU Ori's surface viewed through cool gas in FU Ori's strong wind or accretion stream. In contrast, the X-ray centroid of the soft emission below 2 keV is offset 020 to the southeast of FU Ori, toward the near-IR companion (FU Ori S). This offset amounts to slightly less than half the separation between the two stars. The most likely explanation for the offset is that the companion contributes significantly to the softer X-ray emission below 2 keV (and weakly above 2 keV). The superimposed X-ray contributions from FU Ori and the companion resolve the paradox posed by XMM-Newton of an apparently single X-ray source viewed through two different absorption columns. © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.

Popov S.B.,Universitetski Pr 13 | Pons J.A.,University of Alicante | Miralles J.A.,University of Alicante | Boldin P.A.,National Research Nuclear University MEPhI | Posselt B.,Harvard - Smithsonian Center for Astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2010

We perform population synthesis studies of different types of neutron stars (NSs) (thermally emitting isolated NSs, normal radio pulsars, magnetars) taking into account the magnetic field decay and using results from the most recent advances in NS cooling theory. For the first time, we confront our results with observations using simultaneously the log N-log S distribution for nearby isolated NSs, the log N-log L distribution for magnetars, and the distribution of radio pulsars in the diagram. For this purpose, we fix a baseline NS model (all microphysics input), and other relevant parameters to standard values (velocity distribution, mass spectrum, birth rates, etc.), allowing us to vary the initial magnetic field strength. We find that our theoretical model is consistent with all sets of data if the initial magnetic field distribution function follows a lognormal law with 〈log (B0/G)〉 ∼ 13.25 and. The typical scenario includes about 10 per cent of NSs born as magnetars, significant magnetic field decay during the first million years of a NS life (only about a factor of 2 for low-field NSs but more than an order of magnitude for magnetars), and a mass distribution function dominated by low-mass objects. This model explains satisfactorily all known populations. Evolutionary links between different subclasses may exist, although robust conclusions are not yet possible. © 2009 RAS.

Boldin P.A.,National Research Nuclear University MEPhI | Popov S.B.,Universitetski Pr 13
Monthly Notices of the Royal Astronomical Society | Year: 2010

We study the evolution of isolated neutron stars on long time-scales and calculate the distribution of these sources in the main evolutionary stages: ejector, propeller, accretor and georotator. We make comparisons among different initial magnetic field distributions taking into account the possibility of magnetic field decay, and include in our calculations the stage of subsonic propeller.It is shown that though the subsonic propeller stage can be relatively long, initially highly magnetized neutron stars (B0 ≳ 1013 G) reach the accretion regime within the Galactic lifetime if their kick velocities are not too large. The fact that in previous studies made >10 yr ago such objects were not considered results in a slight increase of the accretor fraction in comparison with earlier conclusions. Most of the neutron stars similar to the Magnificent Seven are expected to become accreting from the interstellar medium after a few billion years of their evolution. They are the main predecessors of accreting isolated neutron stars. © 2010 The Authors. Journal compilation © 2010 RAS.

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