Aoyama Gakuin University

About: Aoyama Gakuin University is a education organization based out in Tokyo, Japan. It is known for research contribution in the topics: Superconductivity & Thin film. The organization has 3494 authors who have published 6419 publications receiving 115648 citations. The organization is also known as: Aoyama gakuin daigaku.

Swift-XRT follow-up of gravitational wave triggers during the third aLIGO/Virgo observing run

Abstract: The Neil Gehrels Swift Observatory followed up 18 gravitational wave (GW) triggers from the LIGO/Virgo collaboration during the O3 observing run in 2019/2020, performing approximately 6500 pointings in total. Of these events, four were finally classified (if real) as binary black hole (BH) triggers, six as binary neutron star (NS) events, two each of NSBH and Mass Gap triggers, one an unmodelled (Burst) trigger, and the remaining three were subsequently retracted. Thus far, four of these O3 triggers have been formally confirmed as real gravitational wave events. While no likely electromagnetic counterparts to any of these GW events have been identified in the X-ray data (to an average upper limit of 3.60 x 10^{-12} erg cm^{-2} s^{-1} over 0.3-10 keV), or at other wavelengths, we present a summary of all the Swift-XRT observations performed during O3, together with typical upper limits for each trigger observed. The majority of X-ray sources detected during O3 were previously uncatalogued; while some of these will be new (transient) sources, others are simply too faint to have been detected by earlier survey missions such as ROSAT. The all-sky survey currently being performed by eROSITA will be a very useful comparison for future observing runs, reducing the number of apparent candidate X-ray counterparts by up to 95 per cent.

A Spectral Study of the Black Hole Candidate XTE J1752-223 in the High/Soft State with MAXI, Suzaku, and Swift

Abstract: We report on an X-ray spectral analysis of the black hole candidate XTE J1752 223 in the 2009–2010 outburst, utilizing data obtained with the MAXI/Gas Slit Camera (GSC), the Swift/XRT, and Suzaku, which work complementarily. As already reported by Nakahira et al. (2010, PASJ, 62, L27), MAXI monitored the source continuously throughout the entire outburst for about eight months. All of the MAXI/GSC energy spectra in the high/soft state, lasting for 2 months, are well represented by a multi-color disk plus power-law model. The innermost disk temperature changed from 0.7 keV to 0.4 keV and the disk flux decreased by an order of magnitude. Nevertheless, the innermost radius is constant at 41D3:5(cos i ) 1=2 km, where D3:5 is the source distance in units of 3.5 kpc and i the inclination. The multi-color disk parameters obtained with the MAXI/GSC are consistent with those with the Swift/XRT and Suzaku. The Suzaku data also suggest a possibility that the disk emission is slightly Comptonized, which could account for broad iron-K features reported previously. Assuming that the obtained innermost radius represents the innermost stable circular orbit for a non-rotating black hole, we estimate the mass of the black hole to be 5.51 0.28Mˇ D3:5(cos i ) , where the correction for the stress-free inner boundary condition and color hardening factor of 1.7 are taken into account. If the inclination is less than 49i, as suggested from radio monitoring of transient jets, and the soft-to-hard transition in 2010 April occurred at 1%–4% of Eddignton luminosity, the fitting of the Suzaku spectra with a relativistic accretion-disk model derives constraints on the mass and the distance to be 3.1–55Mˇ and 2.3–22 kpc, respectively. This confirms that the compact object in XTE J1752 223 is a black hole.

Electronic structure of MgB 2 : X-ray emission and absorption studies

Abstract: Measurements of x-ray emission and absorption spectra of the constituents of ${\mathrm{MgB}}_{2}$ are presented. The results obtained are in good agreement with calculated x-ray spectra, with dipole matrix elements taken into account. The comparison of x-ray emission spectra of graphite, ${\mathrm{AlB}}_{2},$ and ${\mathrm{MgB}}_{2}$ in the binding energy scale supports the idea of charge transfer from $\ensuremath{\sigma}$ to $\ensuremath{\pi}$ bands, which creates holes at the top of the bonding $\ensuremath{\sigma}$ bands and drives the high-${T}_{c}$ superconductivity in ${\mathrm{MgB}}_{2}.$