Swift monitoring observation of the Be/X-ray transient GX 304-1 in quiescence and its current outburst

On 2016 May 17, the Be/X-ray transient GX 30-41 was found (using MAXIand BAT) to exhibit a new outburst although this was not yet expected based on the previous outbursts of the source (Atel #9064)

Quiescent X-ray variability in the neutron star Be/X-ray transient GRO J1750-27

The Be/X-ray transient GRO J1750-27 exhibited a type-II (giant) outburst in 2015. After the source transited to quiescence, we triggered our multi-year Chandra monitoring programme to study its quiescent behaviour. The programme was designed to follow the cooling of a potentially heated neutron-star crust due to accretion of matter during the preceding outburst, similar to what we potentially have observed before in two other Be/X-ray transients, namely 4U 0115+63 and V 0332+53. However, unlike for these other two systems, we do not find any strong evidence that the neutron-star crust in GRO J1750-27 was indeed heated during the accretion phase. We detected the source at a rather low X-ray luminosity (~10^33 erg/s) during only three of our five observations. When the source was not detected it had very low-luminosity upper limits (<10^32 erg/s; depending on assumed spectral model). We interpret these detections and the variability observed as emission likely due to very low-level accretion onto the neutron star. We also discuss why the neutron-star crust in GRO J1750-27 might not have been heated while the ones in 4U 0115+63 and V 0332+53 possibly were.Comment: 13 pages, 6 figures, 5 tables. Accepted for A&

Dramatic spectral transition of X-ray pulsar GX 304-1 in low luminous state

We report on the discovery of a dramatic change in the energy spectrum of the X-ray pulsar GX 304-1 appearing at low luminosity. Particularly, we found that the cutoff power-law spectrum typical for accreting pulsars, including GX 304-1 at higher luminosities of $L_{\rm X}\sim 10^{36} - 10^{37}$ erg s$^{-1}$, transformed at lower luminosity of $L_{\rm X}\sim 10^{34}$ erg s$^{-1}$ to a two-component spectrum peaking around 5 and 40 keV. We suggest that the observed transition corresponds to a change of the dominant mechanism responsible for the deceleration of the accretion flow. We argue that the accretion flow energy at low accretion rates is released in the atmosphere of the neutron star, and the low-energy component in the source spectrum corresponds to the thermal emission of the optically thick, heated atmospheric layers. The most plausible explanations for the high-energy component are either the cyclotron emission reprocessed by the magnetic Compton scattering or the thermal radiation of deep atmospheric layers partly Comptonized in the overheated upper layers. Alternative scenarios are also discussed.Comment: 5 pages, 2 figures, accepted by MNRAS Letter

Discovery of accretion-driven pulsations in the prolonged low X-ray luminosity state of the Be/X-ray transient GX 304-1

We present our Swift monitoring campaign of the slowly rotating neutron star Be/X-ray transient GX 304-1 (spin period of ~275 s) when the source was not in outburst. We found that between its type-I outbursts the source recurrently exhibits a slowly decaying low-luminosity state (with luminosities of 10^(34-35) erg/s). This behaviour is very similar to what has been observed for another slowly rotating system, GRO J1008-57. For that source, this low-luminosity state has been explained in terms of accretion from a non-ionised ('cold') accretion disk. Due to the many similarities between both systems, we suggest that GX 304-1 enters a similar accretion regime between its outbursts. The outburst activity of GX 304-1 ceased in 2016. Our continued monitoring campaign shows that the source is in a quasi-stable low-luminosity state (with luminosities a few factors lower than previously seen) for at least one year now. Using our NuSTAR observation in this state, we found pulsations at the spin period, demonstrating that the X-ray emission is due to accretion of matter onto the neutron star surface. If the accretion geometry during this quasi-stable state is the same as during the cold-disk state, then matter indeed reaches the surface (as predicted) during this latter state. We discuss our results in the context of the cold-disk accretion model.Comment: 5 pages, 2 figures, accepted for A&A Letter

Unusual magneto-transport of YBa2Cu3O7-d films due to the interplay of anisotropy, random disorder and nanoscale periodic pinning

We study the general problem of a manifold of interacting elastic lines whose spatial correlations are strongly affected by the competition between random and ordered pinning. This is done through magneto-transport experiments with YBa2Cu3O7-d thin films that contain a periodic vortex pinning array created via masked ion irradiation, in addition to the native random pinning. The strong field-matching effects we observe suggest the prevalence of periodic pinning, and indicate that at the matching field each vortex line is bound to an artificial pinning site. However, the vortex-glass transition dimensionality, quasi-2D instead of the usual 3D, evidences reduced vortex-glass correlations along the vortex line. This is also supported by an unusual angular dependence of the magneto-resistance, which greatly differs from that of Bose-glass systems. A quantitative analysis of the angular magnetoresistance allows us to link this behaviour to the enhancement of the system anisotropy, a collateral effect of the ion irradiation

La renuncia al Ministerio Petrino. Nota teológica

La renuncia de Benedicto XVI invita a profundizar en la comprensión del ministerio petrino en continuidad con los concilios Vaticano I y II, y concretamente en el contexto de una teología del ministerio y de una eclesiología propiamente sacramentales. La forma de ejercicio del primado por Benedicto XVI y, en particular, la renuncia en que ha culminado, podría significar un paso histórico en la búsqueda –propuesta por Juan Pablo II en Ut unum sint– de formas renovadas de ejercicio del ministerio petrino que, sin negar nada de su sustancia dogmática, respondan mejor a las nuevas necesidades de la unidad de la Iglesia universal.Benedict XVI’s resignation asks for a deeper understanding of the Petrine Ministry in continuity with both Vatican councils and carried out in the context of a theology of the ministry and the Church that is properly sacramental. The way in which Benedict exercised the primate and especially his final resignation could mean an important step in the quest –proposed by John Paul II in Ut unum sint– for renewed forms of exercising the petrine ministry that respond better to the universal Church’s need for unity