Probing large-scale wind structures in Vela X-1 using off-states with INTEGRAL

Vela X-1 is the prototype of the class of wind-fed accreting pulsars in high mass X-ray binaries hosting a supergiant donor. We have analyzed in a systematic way ten years of INTEGRAL data of Vela X-1 (22-50 keV) and we found that when outside the X-ray eclipse, the source undergoes several luminosity drops where the hard X-rays luminosity goes below 3x10^35 erg/s, becoming undetected by INTEGRAL. These drops in the X-ray flux are usually referred to as "off-states" in the literature. We have investigated the distribution of these off-states along the Vela X-1 ~8.9 d orbit, finding that their orbital occurrence displays an asymmetric distribution, with a higher probability to observe an off-state near the pre-eclipse than during the post-eclipse. This asymmetry can be explained by scattering of hard X-rays in a region of ionized wind, able to reduce the source hard X-ray brightness preferentially near eclipse ingress. We associate this ionized large-scale wind structure with the photoionization wake produced by the interaction of the supergiant wind with the X-ray emission from the neutron star. We emphasize that this observational result could be obtained thanks to the accumulation of a decade of INTEGRAL data, with observations covering the whole orbit several times, allowing us to detect an asymmetric pattern in the orbital distribution of off-states in Vela X-1.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society (5 pages, 3 figures). A few typos fixed to match the published versio

Probing the Dzyaloshinskii-Moriya interaction in CoFeB ultrathin films using domain wall creep and Brillouin light spectroscopy

We have characterized the strength of the interfacial Dyzaloshinskii-Moriya interaction (DMI) in ultrathin perpendicularly magnetized CoFeB/MgO films, grown on different underlayers of W, TaN, and Hf, using two experimental methods. First, we determined the effective DMI field from measurements of field-driven domain wall motion in the creep regime, where applied in-plane magnetic fields induce an anisotropy in the wall propagation that is correlated with the DMI strength. Second, Brillouin light spectroscopy was employed to quantify the frequency non-reciprocity of spin waves in the CoFeB layers, which yielded an independent measurement of the DMI. By combining these results, we show that DMI estimates from the different techniques only yield qualitative agreement, which suggests that open questions remain on the underlying models used to interpret these results.Comment: 8 page

Capsule endoscopy in Crohn’s disease surveillance: A monocentric, retrospective analysis in Italy

Background: Crohn’s disease (CD) is a potentially debilitating condition that burdens Italian healthcare substantially. The symptomatic management relies on prompt therapy adjustment to reduce flares and follow-up diagnostic inputs to maximise remission. Capsule endoscopy (CE) has introduced advantages in CD diagnostics, allowing the direct inspection of the entire gastrointestinal mucosa. The diagnostic procedure is comparable in effort to standard ileocolonoscopy (IC) but requires no anaesthesia. Whether CE follow-up improves clinical outcomes remains to be defined. Objectives: To provide a preliminary evaluation of CE in terms of clinical outcomes with respect to the standard of care ileocolonoscopy/MRE in Italy. Methods: This retrospective analysis utilises anonymised, monocentric data from the S. Orsola-Malpighi Hospital IBD database in Bologna, Italy, collected between 1999 and 2019. Out of 421 adult patient records, 100 were included in the analysis (50 per arm, matched per demographic and clinical characteristics). The CE represented the intervention arm, whereas ileocolonoscopy/magnetic resonance enterography was the standard of care. The use of biologics, symptomatology course, and surgery were the outcomes. Results: The two techniques performed similarly overall. In general, no significant difference emerged in the use of biologics. The use of biologics appears reduced in the CE group, only in L4 patients after the first follow-up year. Similarly, surgery was seemingly less frequent among L4 patients in the CE group. No difference was found between groups in flare occurrence and duration. CE patients might have experienced longer and earlier first remissions, but no long-term difference persisted. Conclusions: The CE group showed an apparent reduction in biologics and surgery, limiting to L4 diagnoses. More extensive, prospective, multicentre, randomised studies must corroborate these preliminary findings

The Eclipsing Binary BG Geminorum: Improved Constraints on the Orbit and the Structure of the Accretion Disk

We describe new optical photometric and spectroscopic observations of the semi-detached eclipsing binary BG Geminorum. A large change in the amount of Mg I absorption at secondary maximum indicates the presence of cool material in the outer edge of the disk surrounding the unseen primary star. Detection of weak He I emission implies a hot radiation source at the inner edge of the disk. If the velocity variations in the Hbeta emission line track the orbital motion of the primary star, the primary star has an orbital semiamplitude of K1 = K(Hbeta) = 16.0 +- 4.6 km/sec. This result yields a mass ratio, q = 0.22 +- 0.07, consistent with the q = 0.1 derived from the large ellipsoidal variation. Despite this progress, the nature of the primary star - B-type star or black hole - remains uncertain.Comment: 9 pages of text, 3 tables, and 4 figures; to appear in AJ, August 200