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Register a new userCompleting the puzzle of the 2004-2005 outburst in V0332+53: the brightening phase included
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Added by
Alexander Lutovinov
Publication date
2009
fields
Physics
and research's language is
English
Authors
S. Tsygankov
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Analysis of the data obtained with the RXTE observatory during a powerful outburst of the X-ray pulsar V0332+53 in 2004-2005 is presented. Observational data covering the outburst brightening phase are analysed in detail for the first time. A comparison of source parameters and their evolution during the brightening and fading phases shows no evidence for any hysteresis behaviour. It is found that the dependences of the energy of the cyclotron absorption line on the luminosity during the brightening and fading phases are almost identical. The complete data sequence including the outburst brightening and fading phases makes it possible to impose the more stringent constraints on the magnetic field in the source. The pulse profile and pulsed fraction are studied as functions of the luminosity and photon energy.
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We present results of observations of the transient X-ray pulsar V0332+53 performed during a very powerful outburst in Dec, 2004 -- Feb, 2005 with the INTEGRAL and RXTE observatories in a wide (3-100 keV) energy band. A cyclotron resonance scattering line at an energy of ~26 keV has been detected in the source spectrum together with its two higher harmonics at ~50 and ~73 keV, respectively. We show that the energy of the line is not constant but linearly changes with the source luminosity. Strong pulse profile variations, especially near the cyclotron line, are revealed for different levels of the source intensity. We discuss the obtained results in terms of the theoretical models of X-ray pulsars.
We report on changes of the cyclotron resonance energies of the recurrent transient pulsar, X0331+53 (V0332+53). The whole RXTE data acquired in the 2004-2005 outburst were utilized. The 3-80 keV source luminosity varied between 1.7x10^36 and 3.5x10^38 ers/s, assuming a distance of 7 kpc. We confirmed that the fundamental cyclotron resonance energy changed from ~22 to ~27 keV in a clear anti-correlation to the source luminosity, and without any hysteresis effects between the rising and declining phases of the outburst. In contrast, the second harmonic energy changed from ~49 to ~54 keV, implying a weaker fractional change as a function of the luminosity. As a result, the observed resonance energy ratio between the second harmonic and the fundamental was ~2.2 when the source was most luminous, whereas the ratio decreased to the nominal value of 2.0 at the least luminous state. Although the significance of this effect is model dependent, these results suggest that the fundamental and second harmonic resonances represent different heights in the accretion column, depending on the mass accretion rate.
We present an analysis of the 2-150 keV spectrum of the transient X-ray pulsar V0332+53 taken with the Rossi X-Ray Timing Explorer (RXTE) in 2004 December. We report on the detection of three cyclotron resonance features at 27, 51, and 74 keV in the phase-averaged data, corresponding to a polar magnetic field of 2.7 x 10^12 G. After 4U0115+63, this makes V0332+53 the second accreting neutron star in which more than two cyclotron lines have been detected; this has now also been confirmed by INTEGRAL. Pulse-phase spectroscopy reveals remarkably little variability of the cyclotron line through the 4.4 s X-ray pulse.
We present the analysis of a 100ksec Integral(3-100kev) observation of the transient X-ray pulsar V0332+53 inoutburst. The source is pulsating at P=4.3751+/-0.0002s with a clear double pulse from 6 kev to 60 kev. The average flux was ~550mCrab between 20 kev and 60 kev. We modeled the broad band continuum from 5 kev to 100 kev with a power-law modified by an exponential cut off. We observe three cyclotron lines: the fundamental line at 24.9+/-0.1 kev, the first harmonic at 50.5+/-0.1 kev as well as the second harmonic at71.7+/-0.8 kev, thus confirming the discovery of the harmonic lines by Coburn et al. (2005) in RXTE data.
How the accreted mass settling on the surface of a neutron star affects the topology of the magnetic field and how the secular evolution of the binary system depends on the magnetic field change is still an open issue. We report evidence for a clear drop in the observed magnetic field in the accreting pulsar V0332+53 after undergoing a bright 3-month long X-ray outburst. We determine the field from the position of the fundamental cyclotron line in its X-ray spectrum and relate it to the luminosity. For equal levels of luminosity, in the declining phase we measure a systematically lower value of the cyclotron line energy with respect to the rising phase. This results in a drop of ~1.7 x 10^11 G of the observed field between the onset and the end of the outburst. The settling of the accreted plasma onto the polar cap seems to induce a distortion of the magnetic field lines weakening their intensity along the accretion columns. Therefore the dissipation rate of the magnetic field could be much faster than previously estimated, unless the field is able to restore its original configuration on a time-scale comparable with the outbursts recurrence time.
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