The ephemeris, orbital decay, and masses of 10 eclipsing HMXBs

We take advantage of more than 10 years of monitoring of the eclipsing HMXB systems LMC X-4, Cen X-3, 4U 1700-377, 4U 1538-522, SMC X-1, IGR J18027-2016, Vela X-1, IGR J17252-3616, XTE J1855-026, and OAO 1657-415 with the ASM on-board RXTE and ISGRI on-board INTEGRAL to update their ephemeris. These results are used to refine previous measurements of the orbital period decay of all sources (where available) and provide the first accurate values of the apsidal advance in Vela X-1 and 4U 1538-522. Updated values for the masses of the neutron stars hosted in the ten HMXBs are also provided, as well as the long-term lightcurves folded on the sources best determined orbital parameters. These lightcurves reveal complex eclipse ingresses and egresses, that are understood mostly as being due to the presence of accretion wakes. The results reported in this paper constitute a database to be used for population and evolutionary studies of HMXBs, as well as theoretical modelling of long-term accretion in wind-fed X-ray binaries.Comment: Accepted for publication on A&

Unveiling the redback nature of the low-mass X-ray binary XSSJ1227.0-4859 through optical observations

The peculiar low mass X-ray binary XSSJ12270-4859, associated with the Fermi/LAT source 2FGLJ1227.7-4853, was in a X-ray, gamma-ray and optical low-luminosity persistent state for about a decade until the end of 2012, when it has entered into the dimmest state ever observed. The nature of the compact object has been controversial until the detection of a 1.69ms radio pulsar early 2014. We present optical spectroscopy and optical/near-IR photometry during the previous brighter and in the recent faint states. We determine the first spectroscopic orbital ephemeris and an accurate orbital period of 6.91246(5)h. We infer a mid G-type donor star and a distance d=1.8-2.0kpc. The donor spectral type changes from G5V to F5V between inferior and superior conjunction, a signature of strong irradiation effects. We infer a binary inclination 45deg <~ i <~ 65deg and a highly undermassive donor, M_2 ~ 0.06-0.12M_sun for a neutron star mass in the range 1.4-3M_sun. Thus this binary joins as the seventh member the group of "redbacks". In the high state, the emission lines reveal the presence of an accretion disc. They tend to vanish at the donor star superior conjunction, where also flares are preferentially observed together with the occurrence of random dips. This behaviour could be related to the propeller mechanism of the neutron star recently proposed to be acting in this system during the high state. In the low state, the emission lines are absent at all orbital phases indicating that accretion has completely switched-off and that XSSJ12270-4859 has transited from an accretion-powered to a rotation-powered phase.Comment: 12 pages, 9 figures, 3 tables accepted for publication in Monthly Notices Royal Astronomical Society, Main Journa

A Search for Exozodiacal Dust and Faint Companions Near Sirius, Procyon, and Altair with the NICMOS Coronagraph

We observed Sirius, Altair, and Procyon with the NICMOS Coronagraph on the Hubble Space Telescope to look for scattered light from exozodiacal dust and faint companions within 10 AU from these stars. We did not achieve enough dynamic range to surpass the upper limits set by IRAS on the amount of exo-zodiacal dust in these systems, but we did set strong upper limits on the presence of nearby late-type and sub-stellar companions.Comment: 10 pages, 4 figure

The intriguing nature of the high energy gamma ray source XSSJ12270-4859

The nature of the hard X-ray source XSSJ12270-4859 is still unclear though it was claimed to be a magnetic Cataclysmic Variable. We here present a broad-band X-ray and gamma ray study based on a recent XMM-Newton observation and archival INTEGRAL and RXTE data. From the Fermi/LAT 1-year point source catalogue, we tentatively associate XSSJ12270-4859 with 1FGLJ1227.9-4852, a source of high energy gamma rays with emission up to 10GeV. We complement the study with UV photometry from XMM-Newton and ground-based optical and near-IR photometry. The X-ray emission is highly variable showing flares and intensity dips. The X-ray flares consist of flare-dip pairs. Flares are also detected in the UV range but not the dips. Aperiodic dipping behaviour is also observed during X-ray quiescence but not in the UV. The 0.2-100keV spectrum is featureless and described by a power law model with Gamma=1.7. The 100MeV-10GeV spectrum is instead represented by a power law index of 2.45. The luminosity ratio between 0.1-100GeV and 0.2--100keV is ~0.8, hence the GeV emission is a significant component of the total energy output. Furthermore, the X-ray spectrum does not greatly change during flares, quiescence and the dips seen in quiescence but it hardens during the post-flare dips. Optical photometry reveals a period of 4.32hr likely related to the binary orbit. Near-IR, possibly ellipsoidal, variations are detected. Large amplitude variability on shorter (tens mins) timescales are found to be non-periodic. The observed variability at all wavelengths and the spectral characteristics strongly favour a low-mass atypical low-luminosity X-ray binary and are against a Cataclysmic Variable nature. The association with a Fermi/LAT high energy gamma ray source further strengths this interpretation.Comment: 12 pages, 11 figures, 3 tables; Accepted for publication in Astronomy & Astrophysics Main Journ

Neutronic study of slightly modified water reactors and application to transition scenarios

International audienceIn this paper we have studied slightly modified water reactors and their applications to transition scenarios. The PWR and CANDU reactors have been considered. New fuels based on Thorium have been tested : Thorium/Plutonium and Thorium/Uranium- 233, with different fissile isotope contents. Changes in the geometry of the assemblies were also explored to modify the moderation ratio, and consequently the neutron flux spectrum. A core equivalent assembly methodology was introduced as an exploratory approach and to reduce the computation time. Several basic safety analyses were also performed. We have finally developed a new scenario code, named OSCAR (Optimized Scenario Code for Advanced Reactors), to study the efficiency of these modified reactors in transition to GenIV reactors or in symbiotic fleet

Uranium resources, scenarios, nuclear and energy dynamics

ISBN 978-1-49-51-6286-2International audienceA dynamic simulation of coupled supply and demand of energy, resources and nuclear reactors is done with the global model Prospective Outlook for Long Term Energy Supply (POLES) over this century. In this model, both electricity demand and uranium supply are not independent of the cost of all base load electricity suppliers. Uranium consuming Thermal Neutron Reactors and future generation, free from the uranium market once started, breeder reactors are only one part of the market and are in a global competition, not limited to the other nuclear generation. In this paper we present a new model of the impact of uranium scarcity on the development of nuclear reactors. Many scenarios rely on the subjective definition of ultimate uranium resources. We suggest that when uranium will mainly be extracted together with other resources, its cost should not be simply a function of cumulated uranium mined but also of mine yearly outputs. We describe the sensitivities of our model to breeder reactor physical performance indicators. Used fuels can be seen as a liability or as a source of usable material and a scarce resource limiting fast reactor startups in fast development in India or China. We present the impact of synergetic strategies where countries with opposite strategies share used fuels

Recent Outbursts from the Transient X-Ray Pulsar Cep X-4 (GS 2138+56)

We report on X-ray observations of the 66 s period transient X-ray pulsar Cep X-4 (GS 2138+56) with the Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory (CGRO) and with the Rossi X-ray Timing Explorer (RXTE). Two outbursts from Cep X-4 were observed with BATSE in 1993 June-July and 1997 July. Pulse frequencies of 15.0941 +/- 0.0002 mHz on 1993 June 25 (MJD 49,163) and 15.0882 +/- 0.0002 mHz on 1997 July 12 (MJD 50,641) were each measured from 2 day spans of BATSE data near each outburst's peak. Cep X-4 showed an average spin down rate of (-4.14 +/- 0.08)*10^(-14) Hz/s between the 1993 and 1997 outbursts. After BATSE could no longer detect Cep X-4, public observations were performed on 1997 July 18 & 25 with the Proportional Counter Array (PCA) on RXTE. A pulse frequency of 15.088 +/- 0.004 mHz was measured from observations on 1997 July 18 (MJD 50,647). Significant aperiodic noise, with an rms variance of ~18% in the frequency range 0.01-1.0 Hz was observed on both days. Energy and intensity dependent pulse shape variations were also seen in these data. Recently published optical observations associate Cep X-4 with a Be companion star. If all 4 outbursts observed from Cep X-4 are assumed to occur at the same orbital phase, we find that the orbital period is between 23 days and 147.3 days.Comment: 19 pages (LaTeX) including 9 figures. Accepted for publication in the Astrophysical Journa

Periodicities In The X-Ray Intensity Variations of TV Columbae: An Intermediate Polar

We present results from a temporal analysis of the longest and the most sensitive X-ray observations of TV Columbae--an intermediate polar. The observations were carried out with the RXTE PCA, ROSAT PSPC, and ASCA. Data were analyzed using a 1-dimensional CLEAN and Bayesian algorithms. The presence of a nearly sinusoidal modulation due to the spin of the white dwarf is seen clearly in all the data, confirming the previous reports based on the EXOSAT data. An improved period of 1909.7+/-2.5s is derived for the spin from the RXTE data.The binary period of 5.5hr is detected unambiguously in X-rays for the first time. Several side-bands due to the interaction of these periods are observed in the power spectra, thereby suggesting contributions from both the disk-fed and the stream-fed accretion for TV Col. The accretion disk could perhaps be precessing as side-bands due to the influence of 4 day period on the orbital period are seen. The presence of a significant power at certain side-bands of the spin frequency indicates that the emission poles are asymmetrically located. The strong power at the orbital side-bands seen in both the RXTE and ROSAT data gives an indication for an absorption site fixed in the orbital frame. Both the spin and the binary modulation are found to be energy-dependent. Increased hardness ratio during a broad dip in the intensity at binary phase of 0.75--1.0 confirms the presence of a strong attenuation due to additional absorbers probably from an impact site of the accretion stream with the disk or magnetosphere. Hardness ratio variations and the energy dependent modulation depth during the spin modulation can be explained by partially covered absorbers in the path of X-ray emission region in the accretion stream.Comment: 34 pages, including 12 figures, Accepted for publication in Astronomical Journal, scheduled for January 2004 issue (vol. 127

X-ray follow-ups of XSSJ12270-4859: a low-mass X-ray binary with gamma ray FERMI-LAT association

XSSJ1227.0-4859 is a peculiar, hard X-ray source recently positionally associated to the Fermi-LAT source 1FGLJ1227.9-4852/2FGLJ1227.7-4853. Multi-wavelength observations have added information on this source, indicating a low-luminosity low-mass X-ray binary (LMXB), but its nature is still unclear. To progress in our understanding, we present new X-ray data from a monitoring campaign performed in 2011 with the XMM-Newton, RXTE, and Swift satellites and combine them with new gamma-ray data from the Fermi and AGILE satellites. We complement the study with simultaneous near-UV photometry from XMM-Newton and with previous UV/optical and near-IR data. The X-ray history of XSSJ1227.0-4859 over 7yr shows a persistent and rather stable low-luminosity (~6x10^33 d_{1\,kpc}^2 erg/s) source, with flares and dips being peculiar and permanent characteristics. The associated Fermi-LAT source 2FGLJ1227.7-4853 is also stable over an overlapping period of 4.7\,yr. Searches for X-ray fast pulsations down to msec give upper limits to pulse fractional amplitudes of 15-25% that do not rule out a fast spinning pulsar. The combined UV/optical/near-IR spectrum reveals a hot component at ~13\,kK and a cool one at ~4.6\,kK. The latter would suggest a late-type K2-K5 companion star, a distance range of1.4--3.6kpc and an orbital period of 7--9 h. A near-UV variability (>6\,h) also suggests a longer orbital period than previously estimated. The analysis shows that the X-ray and UV/optical/near-IR emissions are more compatible with an accretion-powered compact object than with a rotational powered pulsar. The X-ray to UV bolometric luminosity ratio could be consistent with a binary hosting a neutron star, but the uncertainties in the radio data may also allow an LMXB black hole with a compact jet. In this case it would be the first associated with a high-energy gamma-ray source.Comment: 17 pages, 14 figures, 1 table; Accepted for publication in Astronomy & Astrophysics Main Journa