Orbital phase resolved spectroscopy of 4U1538-52 with MAXI

4U 1538-52, an absorbed high mass X-ray binary with an orbital period of 3.73 days, shows moderate orbital intensity modulations with a low level of counts during the eclipse. Several models have been proposed to explain the accretion at different orbital phases by a spherically symmetric stellar wind from the companion. The aim of this work is to study both the light curve and orbital phase spectroscopy of this source in the long term. Particularly, the folded light curve and the changes of the spectral parameters with orbital phase to analyse the stellar wind of QV Nor, the mass donor of this binary system. We used all the observations made from the Gas Slit Camera on board MAXI of 4U 1538-52 covering many orbits continuously. We obtained the good interval times for every orbital phase range which were the input to extract our data. We estimated the orbital period of the system and then folded the light curves and we fitted the X-ray spectra with the same model for every orbital phase spectrum. We also extracted the averaged spectrum of all the MAXI data available. The MAXI spectra in the 2-20 keV energy range were fitted with an absorbed Comptonization of cool photons on hot electrons. We found a strong orbital dependence of the absorption column density but neither the fluorescence iron emission line nor low energy excess were needed to fit the MAXI spectra. The variation of the spectral parameters over the binary orbit were used to examine the mode of accretion onto the neutron star in 4U 1538-52. We deduce a best value of $\dot{M}/v_\infty=0.65\times 10^{-9}$ $M_{\odot} \, yr^{-1}/(km \, s^{-1})$ for QV Nor.Comment: 12 pages, 5 figures, accepted to be published by A&A, corrected typos (changing bold font to normal one

Footprints in the wind of Vela X-1 traced with MAXI

The stellar wind around the compact object in luminous wind-accreting high mass X-ray binaries is expected to be strongly ionized with the X-rays coming from the compact object. The stellar wind of hot stars is mostly driven by light absorption in lines of heavier elements, and X-ray photo-ionization significantly reduces the radiative force within the so-called Stroemgren region leading to wind stagnation around the compact object. In close binaries like Vela X-1 this effect might alter the wind structure throughout the system. Using the spectral data from Monitor of All-sky X-ray Image (MAXI), we study the observed dependence of the photoelectric absorption as function of orbital phase in Vela X-1, and find that it is inconsistent with expectations for a spherically-symmetric smooth wind. Taking into account previous investigations we develop a simple model for wind structure with a stream-like photoionization wake region of slower and denser wind trailing the neutron star responsible for the observed absorption curve.Comment: 5 pages, 3 figures, accepted in A&

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Orbital phase-resolved spectroscopy of 4U 1538−52 with MAXI

Context. 4U 1538−52, an absorbed high mass X-ray binary with an orbital period of ~3.73 days, shows moderate orbital intensity modulations with a low level of counts during the eclipse. Several models have been proposed to explain the accretion at different orbital phases by a spherically symmetric stellar wind from the companion. Aims. The aim of this work is to study both the light curve and orbital phase spectroscopy of this source in the long term. In particular, we study the folded light curve and the changes in the spectral parameters with orbital phase to analyse the stellar wind of QV Nor, the mass donor of this binary system. Methods. We used all the observations made from the Gas Slit Camera on board MAXI of 4U 1538−52 covering many orbits continuously. We obtained the good interval times for all orbital phase ranges, which were the input for extracting our data. We estimated the orbital period of the system and then folded the light curves, and we fitted the X-ray spectra with the same model for every orbital phase spectrum. We also extracted the averaged spectrum of all the MAXI data available. Results. The MAXI spectra in the 2–20 keV energy range were fitted with an absorbed Comptonisation of cool photons on hot electrons. We found a strong orbital dependence of the absorption column density but neither the fluorescence iron emission line nor low energy excess were needed to fit the MAXI spectra. The variation in the spectral parameters over the binary orbit were used to examine the mode of accretion onto the neutron star in 4U 1538−52. We deduce a best value of Ṁ/v∞ = 0.65 × 10-9M⊙ yr-1/ (km s-1) for QV Nor.Part of this work was supported by the Spanish Ministry of Economy and Competitiveness project numbers ESP2013-48637-C2-2P, and ESP2014-53672-C3-3-P, by the Vicerectorat d’Investigació, Desenvolupament i Innovació de la Universitat d’Alacant project number GRE12-35, and by the Generalitat Valenciana project number GV2014/088. This research made use of MAXI data provided by RIKEN, JAXA, and the MAXI team. J.J.R.R. acknowledges the support by the Matsumae International Foundation Research Fellowship No14G04, and also thanks the entire MAXI team for the collaboration and hospitality in RIKEN. The work of A.G.G. has been supported by the Spanish MICINN under FPI Fellowship BES-2011-050874 associated to the project AYA2010-15431. T.M. acknowledges the grant by the Vicerectorat d’Investigació, Desenvolupament i Innovació de la Universitat d’Alacant under visiting researcher programme INV14-11

Black hole candidate XTE J1752-223: Swift observations of canonical states during outburst

We present Swift broadband observations of the recently discovered black hole candidate, X-ray transient, XTE J1752-223, obtained over the period of outburst from October 2009 to June 2010. From Swift-UVOT data we confirm the presence of an optical counterpart which displays variability correlated, in the soft state, to the X-ray emission observed by Swift-XRT. The optical counterpart also displays hysteretical behaviour between the states not normally observed in the optical bands, suggesting a possible contribution from a synchrotron emitting jet to the optical emission in the rising hard state. We offer a purely phenomenological treatment of the spectra as an indication of the canonical spectral state of the source during different periods of the outburst. We find that the high energy hardness-intensity diagrams over two separate bands follows the canonical behavior, confirming the spectral states. Our XRT timing analysis shows that in the hard state there is significant variability below 10Hz which is more pronounced at low energies, while during the soft state the level of variability is consistent with being minimal. These properties of XTE J1752-223 support its candidacy as a black hole in the Galactic centre region.Comment: 8 pages, 8 figures; MNRAS in pres

A contribution of stellar flares to the GRXE -- based on MAXI observations --

Using unbiased observations of MAXI/GSC the potential contribution of stellar flares and CVs to GRXE luminosity is estimated in the energy range of 2 - 10 keV. Currently, a reasonable luminosity has been obtained extrapolating the number of stellar flares and that of CVs toward the Galactic ridge from those of the observed flares and CVs near the solar system. The ionized emission lines of Si to Fe are also simulated making the composite thermal spectrum which is based on MAXI observations of stellar flares and CVs. The present estimated result strongly supports a picture that the cumulative stellar flares contribute primarily to the GRXE in terms of the composite thermal spectrum with emission lines and secondary contribution is due to the thermal spectrum with high temperature from CVs

A decelerating jet observed by the EVN and VLBA in the X-ray transient XTE J1752-223

The recently discovered Galactic X-ray transient XTE J1752-223 entered its first known outburst in 2010, emitting from the X-ray to the radio regimes. Its general X-ray properties were consistent with those of a black hole candidate in various spectral states, when ejection of jet components is expected. To verify this, we carried out very long baseline interferometry (VLBI) observations. The measurements were carried out with the European VLBI Network (EVN) and the Very Long Baseline Array (VLBA) at four epochs in 2010 February. The images at the first three epochs show a moving jet component that is significantly decelerated by the last epoch, when a new jet component appears that is likely to be associated with the receding jet side. The overall picture is consistent with an initially mildly relativistic jet, interacting with the interstellar medium or with swept-up material along the jet. The brightening of the receding ejecta at the final epoch can be well explained by initial Doppler deboosting of the emission in the decelerating jet.Comment: Accepted for publication in MNRAS Letters. 5 pages, 2 figure

携帯端末を使用した演奏映像提出の現状と今後の課題

2011年度の児童学科「児童音楽Ⅰ」の授業において, 非対面指導の一環として約100名の履修者が各自の携帯端末を使って自身のピアノ演奏を録画し, インターネット上の指定サイトにアップロード提出する試みを実施した。この実践中に生じた幾つかの問題は受信側 (指導者, サーバ管理者) と送信側 (履修者) 双方に起因するが, 受信側が解決すべき点は, アップロードサイトが扱う文字コードを変更すること, アップロード中の表示をよりわかりやすくすること, 履修者の使用メディア, データ容量やアップロードの方法に標準的なガイドラインを示すことなどであった。また, 履修者も, 携帯端末とパーソナルコンピュータ (以下, PC) 間のデータ転送の方法を習得し, マルチメディアを取り扱うことへの"抵抗感"を取り払う努力をすべきである