* Astronomy

Blobrana · L

RE: RX J0440.9+4431

Blobrana · L

Title: The first spectra for the RX J0440.9+4431 from 2m Terskol telescope
Authors: Andrew Simon (1), A. V. Bondar (2), V. M. Reshetnyk (1) ((1) National Taras Shevchenko University of Kyiv, Glushkova ave., Kyiv, Ukraine, (2) International Centre for Astronomical, Medical and Ecological Research, Terskol Observatory)

We present the first results on the spectra of Be/X-ray binary RX J0440.9+4431 obtained with the 2m Ritchey-Cretein-Coude telescope with Cassegrain Multi Mode Spectrograph (CMMS) (with R = 14000) at Terskol observatory. The H-alpha line profile indicates that the new episode of the V/R variability is occurring in the system. The profiles of the H-alpha, H-beta and HeI 7065.71, 6678.15, 5875.97 lines were analysed and equivalent width were determined. We compared our H-alpha line profile parameters with the previous results from the literature and estimated characteristic time scale for disc changes as about 14 years.

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Title: Outburst of LS V+44 17 Observed by MAXI and RXTE, and Discovery of a Dip Structure in the Pulse Profile
Authors: Ryuichi Usui, Mikio Morii, Nobuyuki Kawai, Takayuki Yamamoto, Tatehiro Mihara, Mutsumi Sugizaki, Masaru Matsuoka, Kazuo Hiroi, Masaki Ishikawa, Naoki Isobe, Masashi Kimura, Hiroki Kitayama, Mitsuhiro Kohama, Takanori Matsumura, Satoshi Nakahira, Motoki Nakajima, Hitoshi Negoro, Motoko Serino, Megumi Shidatsu, Tetsuya Sootome, Kousuke Sugimori, Fumitoshi Suwa, Takahiro Toizumi, Hiroshi Tomida, Yoko Tsuboi, Hiroshi Tsunemi, Yoshihiro Ueda, Shiro Ueno, Kazutaka Yamaoka, Kyohei Yamazaki, Atsumasa Yoshida

We report on the first observation of an X-ray outburst of a Be/X-ray binary pulsar LS V +44 17/RX J0440.9+4431, and the discovery of an absorption dip structure in the pulse profile. An outburst of this source was discovered by MAXI GSC in 2010 April. It was the first detection of the transient activity of LS V +44 17 since the source was identified as a Be/X-ray binary in 1997. From the data of the follow-up RXTE observation near the peak of the outburst, we found a narrow dip structure in its pulse profile which was clearer in the lower energy bands. The pulse-phase-averaged energy spectra in the 3-100 keV band can be fitted with a continuum model containing a power-law function with an exponential cutoff and a blackbody component, which are modified at low energy by an absorption component. A weak iron K \alpha emission line is also detected in the spectra. From the pulse-phase-resolved spectroscopy we found that the absorption column density at the dip phase was much higher than those in the other phases. The dip was not seen in the subsequent RXTE observations at lower flux levels. These results suggest that the dip in the pulse profile originates from the eclipse of the radiation from the neutron star by the accretion column.

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Blobrana · L

Title: Broadband Observations of the Be/X-ray Binary Pulsar RX J0440.9+4431: Discovery of a Cyclotron Absorption Line
Authors: S. Tsygankov (1,2,3,4), R. Krivonos (3,4), A. Lutovinov (4,2) ((1) FINCA, University of Turku, Finland, (2) University of Oulu, Finland, (3) MPA, Germany, (4) IKI, Moscow, Russia)

We report the results of an analysis of data obtained with the INTEGRAL, Swift and RXTE observatories during the 2010 April and September outbursts of the X-ray pulsar RX J0440.9+4431. The temporal and spectral properties of the pulsar in a wide energy band (0.6-120 keV) were studied for the first time. We discovered a ~32 keV cyclotron resonant scattering feature in the source spectrum, that allowed us to estimate the magnetic field strength of the neutron star as B~3.2 x 10^12 G. The estimate of the magnetic field strength was confirmed by a comprehensive analysis of the noise power spectrum of the source. Based on the recurrence time between Type I outbursts the orbital period of the binary system can be estimated as ~155 days. We have shown that the pulse profile has a sinusoidal-like single-peaked shape and has practically no dependence on the source luminosity or energy band.

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Blobrana · L

Title: XMM-Newton observation of the persistent Be/NS X-ray binary pulsar RX J0440.9+4431
Authors: N. La Palombara (1), L. Sidoli (1), P. Esposito (2), A. Tiengo (1,3), S. Mereghetti (1) ((1) INAF/IASF Milano, Italy, (2) INAF/OA Cagliari, Italy, (3) IUSS Pavia, Italy)

Many X-ray accreting pulsars have a soft excess below 10 keV. This feature has been detected also in faint sources and at low luminosity levels, suggesting that it is an ubiquitous phenomenon. In the case of the high luminosity pulsars (Lx > 10^36 erg/s), the fit of this component with thermal emission models usually provides low temperatures (kT < 0.5 keV) and large emission regions (R > a few hundred km); for this reason, it is referred to as a 'soft' excess. On the other hand, we recently found that in persistent, low-luminosity (Lx ~ 10^34 erg/s) and long-period (P > 100 s) Be accreting pulsars the observed excess can be modelled with a rather hot (kT > 1 keV) blackbody component of small area (R < 0.5 km), which can be interpreted as emission from the NS polar caps. In this paper we present the results of a recent XMM-Newton observation of the Galactic Be pulsar RX J0440.9+4431, which is a poorly studied member of this class of sources. We have found a best-fit period P = 204.96(±0.02) s, which implies an average pulsar spin-down during the last 13 years, with dP/dt ~ 6x10^(-9) s/s. The estimated source luminosity is Lx ~ 8x10^(34) erg/s: this value is higher by a factor < 10 compared to those obtained in the first source observations, but almost two orders of magnitude lower than those measured during a few outbursts detected in the latest years. The source spectrum can be described with a power law plus blackbody model, with kTbb = 1.34(±0.04) keV and Rbb = 273(±16) m, suggesting a polar-cap origin of this component. Our results support the classification of RX J0440.9+4431 as a persistent Be/NS pulsar, and confirm that the hot blackbody spectral component is a common property of this class of sources.

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