Evidence of Compton cooling during an X-ray flare supports a neutron star nature of the compact object in 4U1700-37

Based on new Chandra X-ray telescope data, we present empirical evidence of plasma Compton cooling during a flare in the non pulsating massive X-ray binary 4U1700-37. This behaviour might be explained by quasispherical accretion onto a slowly rotating magnetised neutron star. In quiescence, the neutron star in 4U1700-37 is surrounded by a hot radiatively cooling shell. Its presence is supported by the detection of mHz quasi periodic oscillations likely produced by its convection cells. The high plasma temperature and the relatively low X-ray luminosity observed during the quiescence, point to a small emitting area about 1 km, compatible with a hot spot on a NS surface. The sudden transition from a radiative to a significantly more efficient Compton cooling regime triggers an episode of enhanced accretion resulting in a flare. During the flare, the plasma temperature drops quickly. The predicted luminosity for such transitions, Lx = 3 x 10^35 erg s-1, is very close to the luminosity of 4U1700-37 during quiescence. The transition may be caused by the accretion of a clump in the stellar wind of the donor star. Thus, a magnetised NS nature of the compact object is strongly favoured.Comment: Accepted for publication in MNRA

Emissions from pre-Hispanic metallurgy in the South American atmosphere

This is the final version of the article. Available from Public Library of Science via the DOI in this record.Metallurgical activities have been undertaken in northern South America (NSA) for millennia. However, it is still unknown how far atmospheric emissions from these activities have been transported. Since the timing of metallurgical activities is currently estimated from scarce archaeological discoveries, the availability of reliable and continuous records to refine the timing of past metal deposition in South America is essential, as it provides an alternative to discontinuous archives, as well as evidence for global trace metal transport. We show in a peat record from Tierra del Fuego that anthropogenic metals likely have been emitted into the atmosphere and transported from NSA to southern South America (SSA) over the last 4200 yrs. These findings are supported by modern time back-trajectories from NSA to SSA. We further show that apparent anthropogenic Cu and Sb emissions predate any archaeological evidence for metallurgical activities. Lead and Sn were also emitted into the atmosphere as by-products of Inca and Spanish metallurgy, whereas local coal-gold rushes and the industrial revolution contributed to local contamination. We suggest that the onset of pre-Hispanic metallurgical activities is earlier than previously reported from archaeological records and that atmospheric emissions of metals were transported from NSA to SSA.This research is supported by a Young Researcher Grant of the Agence Nationale de la Recherche (ANR) to F. De Vleeschouwer (Project ANR-2011-JS56-006-01 “PARAD”). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

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 analysed in a systematic way 10years of INTEGRAL data of VelaX-1 (22-50keV) and we found that when outside the X-ray eclipse, the source undergoes several luminosity drops where the hard X-rays luminosity goes below ∼3×1035ergs−1, 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 VelaX-1∼8.9d 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 VelaX-

4U 1909+07: a well-hidden pearl

We present the first detailed spectral and timing analysis of the High Mass X-ray Binary (HMXB) 4U 1909+07 with INTEGRAL and RXTE. 4U 1909+07 is detected in the ISGRI 20-40 keV energy band with an average countrate of 2.6 cps. The pulse period of ~604 sec is not stable, but changing erratically on timescales of years. The pulse profile is strongly energy dependent: it shows a double peaked structure at low energies, the secondary pulse decreases rapidly with increasing energy and above 20 keV only the primary pulse is visible. This evolution is consistent between PCA, HEXTE, and ISGRI. The phase averaged spectrum can be well described by the sum of a photoabsorbed power law with a cutoff at high energies and a blackbody component. To investigate the pulse profile, we performed phase resolved spectral analysis. We find that the changing spectrum can be best described with a variation of the folding energy. We rule out a correlation between the black body component and the continuum variation and discuss possible accretion geometries.Comment: 9 pages, 11 figures, accepted for publication in A&A Sect.

Magnetization reversal and exchange bias effects in hard/soft ferromagnetic bilayers with orthogonal anisotropies

21 p.The magnetization reversal processes are discussed for exchange-coupled ferromagnetic hard/soft bilayers made from Co0.66Cr0.22Pt0.12 (10 and 20 nm)/Ni (from 0 to 40 nm) films with out-of-plane and in-plane magnetic easy axes respectively, based on room temperature hysteresis loops and first-order reversal curve analysis. On increasing the Ni layer thicknesses, the easy axis of the bilayer reorients from out-of-plane to in-plane. An exchange bias effect, consisting of a shift of the in-plane minor hysteresis loops along the field axis, was observed at room temperature after in-plane saturation. This effect was associated with specific ferromagnetic domain configurations experimentally determined by polarized neutron reflectivity. On the other hand, perpendicular exchange bias effect was revealed from the out-of-plane hysteresis loops and it was attributed to residual domains in the magnetically hard layer.CAR and DN gratefully acknowledge the support of the National Science Foundation and the MIT-Spain/La Cambra de Barcelona Seed Fund. CR and DN thank the Ministerio de Economia y Competitividad for financial support (MAT2010-20798-C05-02)

Further evidence for the presence of a neutron star in 4U 2206+54. INTEGRAL and VLA observations

The majority of High Mass X-ray Binaries (HMXBs) behave as X-ray pulsars, revealing that they contain a magnetised neutron star. Among the four HMXBs not showing pulsations, and that do not show the characteristics of accreting black holes, there is the unusual HMXB 4U 2206+54. Here we present contemporaneous high-energy and radio observations of this system conducted with INTEGRAL and the VLA in order to unveil its nature. The high-energy spectra show clear indications of the presence of an absorption feature at ~32 keV. This is the third high-energy observatory which reveals marginal evidence of this feature, giving strong support to the existence of a cyclotron resonance scattering feature, which implies a magnetic field of 3.6 x 10^12 G. On the other hand, the source is not detected at centimetre radio wavelengths with a 3 sigma upper limit of 0.039 mJy. The expected radio emission for an accreting black hole in the low/hard state, inferred from X-ray flux measurements, would be at least 60 times greater than the measured upper limit. Both results firmly indicate that, in spite of the absence of pulsations, 4U 2206+54 hosts a magnetic accreting neutron star, the first one not to be observed as an X-ray pulsar.Comment: 10 pages, 7 figures. Submitted to A&A on 2004 October 19; Accepted for Publication on 2005 March 2

Luminosity dependent accretion state change in GRO J1008-57

In a former publication, we have analyzed the transient neutron star X-ray binary GRO J1008-57 using all available RXTE-, Swift-, and Suzaku-data. As we have found, the source's spectral components, i.e., a power-law with high exponential cutoff and a black-body, are strongly correlated with the hard X-ray flux (15-50 keV). We update the analytical description of these dependence, including a change in the photon index behaviour from a flat to a logarithmic function. The flux, where the change occurs, is consistent with the onset of the black-body emission. Thus, a change of the accretion state always occurs in GRO J1008-57 at a particular flux level