M. Mouchet

The Supernova Legacy Survey: Measurement of Omega_M, Omega_Lambda and w from the First Year Data Set

We present distance measurements to 71 high redshift type Ia supernovae discovered during the first year of the 5-year Supernova Legacy Survey (SNLS). These events were detected and their multi-color light-curves measured using the MegaPrime/MegaCam instrument at the Canada-France-Hawaii Telescope (CFHT), by repeatedly imaging four one-square degree fields in four bands. Follow-up spectroscopy was performed at the VLT, Gemini and Keck telescopes to confirm the nature of the supernovae and to measure their redshift. With this data set, we have built a Hubble diagram extending to z = 1, with all distance measurements involving at least two bands. Systematic uncertainties are evaluated making use of the multiband photometry obtained at CFHT. Cosmological fits to this first year SNLS Hubble diagram give the following results: {Omega}{sub M} = 0.263 {+-} 0.042 (stat) {+-} 0.032 (sys) for a flat {Lambda}CDM model; and w = -1.023 {+-} 0.090 (stat) {+-} 0.054 (sys) for a flat cosmology with constant equation of state w when combined with the constraint from the recent Sloan Digital Sky Survey measurement of baryon acoustic oscillations.

The core-collapse rate from the Supernova Legacy Survey

We use three years of data from the Supernova Legacy Survey (SNLS) to study the general properties of core-collapse and type Ia supernovae. This is the first such study using the rolling search technique which guarantees well-sampled SNLS light curves and good efficiency for supernovae brighter than i~24. Using host photometric redshifts, we measure the supernova absolute magnitude distribution down to luminosities 4.5 mag fainter than normal SNIa. Using spectroscopy and light-curve fitting to discriminate against SNIa, we find a sample of 117 core-collapse supernova candidates with redshifts z < 0.4 (median redshift of 0.29) and measure their rate to be larger than the type Ia supernova rate by a factor 4.5±0.8(stat.)±0.6 (sys.). This corresponds to a core-collapse rate at z = 0.3 of [ 1.42±0.3(stat.)±0.3(sys.)] ×10-4 yr-1(h_70-1 Mpc)-3.

The ESO/VLT 3rd year Type Ia supernova data set from the supernova legacy survey

Aims: We present 139 spectra of 124 Type Ia supernovae (SNe Ia) that were observed at the ESO/VLT during the first three years of the Canada-France-Hawai Telescope (CFHT) supernova legacy survey (SNLS). This homogeneous data set is used to test for redshift evolution of SN Ia spectra, and will be used in the SNLS 3rd year cosmological analyses. Methods: Spectra have been reduced and extracted with a dedicated pipeline that uses photometric information from deep CFHT legacy survey (CFHT-LS) reference images to trace, at sub-pixel accuracy, the position of the supernova on the spectrogram as a function of wavelength. It also separates the supernova and its host light in ~60% of cases. The identification of the supernova candidates is performed using a spectrophotometric SN Ia model. Results: A total of 124 SNe Ia, roughly 50% of the overall SNLS spectroscopic sample, have been identified using the ESO/VLT during the first three years of the survey. Their redshifts range from z = 0.149 to z = 1.031. The average redshift of the sample is z = 0.63±0.02. This constitutes the largest SN Ia spectral set to date in this redshift range. The spectra are presented along with their best-fit spectral SN Ia model and a host model where relevant. In the latter case, a host subtracted spectrum is also presented. We produce average spectra for pre-maximum, maximum and post-maximum epochs for both z < 0.5 and z ≥ 0.5 SNe Ia. We find that z < 0.5 spectra have deeper intermediate mass element absorptions than z ≥ 0.5 spectra. The differences with redshift are consistent with the selection of brighter and bluer supernovae at higher redshift. Based on observations obtained with FORS1 and FORS2 at the Very Large Telescope on Cerro Paranal, operated by the European Southern Observatory, Chile (ESO Large Programs 171.A-0486 and 176.A-0589). Appendix is only available in electronic form at http://www.aanda.org

The X-ray emission of the intermediate polar V709 Cas

We present RXTE and BeppoSAX observations of the Intermediate Polar V 709 Cas acquired in 1997 and 1998 respectively. The X-ray emission from 0.1 to 30 keV is dominated by the strong pulsation at the rotational period of the white dwarf (312.8 s) with no sign of orbital or sideband periodicity, thus conrming previous ROSAT results. However, we detect changes in the power spectra between the two epochs. While the second harmonic of the spin period is present during both observations, the rst harmonic is absent in 1997. An increase in the amplitude of the spin pulsation is found between 1997 and 1998 together with a decrease in the X-ray flux. The average X-ray spectrum from 0.1 to 100 keV is well described by an isothermal plasma at 27 keV plus complex absorption and an iron K fluorescent line, due to reflection from the white dwarf surface. The rotational pulsation is compatible with complex absorption dominating the low energy range, while the high energy spin modulation can be attributed to tall shocks above the accreting poles. The RXTE spectrum in 1997 also shows the presence of an absorption edge from ionized iron likely located in the pre{shock accretion flow. The variations along the spin period of the partial covering absorber and of reflection are compatible with the classical accretion curtain scenario. The variations in the spin pulse characteristics and X-ray flux indicate that V 709 Cas experiences changes in the mass accretion rate on timescales from months to years.

Unveiling the redback nature of the low-mass X-ray binary XSS J1227.0−4859 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 45 o . i . 65 o and a highly undermassive donor, M2 � 0.06 0.12M⊙ for a neutron star mass in the range 1.4-3M⊙. 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.

The long period intermediate polar 1RXS J154814.5-452845

We present the first time resolved medium resolution optical spectroscopy of the recently identified peculiar Intermediate Polar (IP)1RXS J154814.5-452845, which allows us to precisely determine the binary orbital period (P Ω = 9.87 ± 0.03 h) and the white dwarf spin period (P ω = 693.01 n± 0.06 s). This system is then the third just outside the purported ∼6–10 h IP orbital period gap and the fifth of the small group of long period IPs, which has a relatively high degree of asynchronism. From the presence of weak red absorption features, we identify the secondary star with a spectral type K2 ± 2 V, which appears to have evolved on the nuclear timescale. From the orbital radial velocities of nemission and the red absorption lines a mass ratio q = 0.65 n± 0.12 is found. The masses of the components are estimated to be M WD ≥ 0.5 M and M sec = 0.4−0.79 M and the binary inclination 25 ◦ < i ≤ 58 ◦ . A distance between 540–840 pc is estimated. At this distance, the presence of peculiar absorption features surrounding Balmer emissions cannot be due to the contribution of the white dwarf photosphere and their spin modulation suggests an origin in the magnetically confined accretion flow. The white dwarf is also not accreting at a particularly high rate(. M < 5 × 10 n16 g s −1 ), for its orbital period. The spin-to-orbit period ratio P ω /P Ω = 0.02 and the low mass accretion rate suggest that this system is far from spin equilibrium. The magnetic moment of the accreting white dwarf is found to be µ < 4.1 × 10 32 G cm 3, indicating a low magnetic nfield system.

1RXS J173021.5-055933: a cataclysmic variable with a fast-spinning magnetic white dwarf

Aims. We present the first X-ray observations with the XMM-Newton and INTEGRAL satellites of the recently discovered cataclysmic variable 1RXS J173021.5-055933, together with simultaneous UV and coordinated optical photometry aiming at characterising its broad-band temporal and spectral properties and classifying this system as a magnetic one. Methods. We performed a timing analysis of the X-ray, UV, and optical light curves to identify and to study the energy dependence of the fast 128 s pulsation over a wide energy range. X-ray spectral analysis in the broad 0.2−100 keV X-ray range was performed to characterise the peculiar emission properties of this source. Results. We find that the X-ray light curve is dominated by the spin period of the accreting white dwarf in contrast to the far-UV range, which turns out to be unmodulated at a 3σ level. Near-UV and optical pulses are instead detected at twice the spin frequency. We identify the contributions from two accreting poles that imply a moderately inclined dipole field allowing, one pole to dominate at energies at least up to 10 keV, and a secondary that instead is negligible above 5 keV. X-ray spectral analysis reveals the presence of multiple emission components consisting of optically thin plasma with temperatures ranging from 0.17 keV to 60 keV and a hot blackbody at ∼90 eV. The spectrum is also strongly affected by peculiar absorption components consisting of two high-density (∼3 × 10 21 cm −2 and 2 × 10 23 cm −2 ) intervening columns, plus a warm absorber. The last is detected from an OVII absorption edge at 0.74 keV, which suggests that photoionization of pre-shock material is also occurring in this system. Conclusions. The observed properties indicate that the accretor in 1RXS J173021.5-055933 is a white dwarf with a likely weak magnetic field, thus confirming this cataclysmic variable as an intermediate polar (IP) with one of the most extreme spin-to-orbit period ratios. This system also joins the small group of IPs showing a soft X-ray reprocessed component, suggesting that this characteristics is not uncommon in these systems.

Light curves of five type Ia supernovae at intermediate redshift

Aims. We present multi-band light curves and distances for five type Ia supernovae at intermediate redshifts, 0.18 < z < 0.27. n nMethods. Three telescopes on the Canary Island of La Palma, INT, NOT, and JKT, were used for discovery and follow-up of type Ia supernovae in the g and r filters. Supernova fluxes were measured by simultaneously fitting a supernova and host galaxy model to the data, and then calibrated using star catalogues from the Sloan Digital Sky Survey. n nResults. The light curve shape and colour corrected peak luminosities are consistent with the expectations of a flat ΛCDM universe at the 1.5σ level. One supernova in the sample, SN1999dr, shows surprisingly large reddening, considering both that it is located at a significant distance from the core of its host (~4 times the fitted exponential radius) and that the galaxy can be spectroscopically classified as early-type with no signs of ongoing star formation.

The white dwarf revealed in the intermediate polar V709 Cassiopeiae

Results are presented from the first detailed spectroscopic observations of the recently identified inter- mediate polar RXJ0028.8+5917/V709 Cas. The study of the emission line radial velocities allows us to remove the uncertainties on the different aliases of the orbital period and a best value is found at (0.2225±0.0002) day. It is also found that the system shows significant EW� (2-4)u broad absorptions affecting the Balmer lines from Hδ to Hβ. These broad absorptions are interpreted as the contribution of an underlying white dwarf atmosphere. The characteristics of the absorptions are found to be consistent with a DA log g =8 white dwarf at a temperature of �23000K, contributing �17% (at 4500u to the overall flux. This is the first direct detection of a white dwarf in an intermediate polar system. The absence of significant Zeeman splitting indicates a magnetic field lower than 10 MG, confirming that, at least in some cases, intermediate polars have weaker fields than polars. Different possibilities are discussed to explain the substantial contribution of the white dwarf to the overall flux.

IGR J00234+6141: a new INTEGRAL source identified as an intermediate polar

Context. Following an extensive survey of the galactic plane by the INTEGRAL satellite, new hard X-ray sources are discovered with a significant fraction of Cataclysmic Variables (CVs) among them. Aims. We report here the identification of one of these hard X-ray sources, IGR J00234+6141, as an accreting magnetic white dwarf of intermediate polar type. Methods. We analyse the high energy emission of the INTEGRAL source using all available data and provide complementary optical photometric and spectroscopic data obtained in August and October 2006, respectively. Results. Based on a refined INTEGRAL position, we confirm the proposed optical identification. We clearly detect the presence of a 564 s periodic optical modulation that we identify as the rotation of the white dwarf. The analysis of the optical spectrum also demonstrates that the emission lines show a modulation in radial velocity with an orbital period of Porb = (4.033 ± 0.005) h. Conclusions. The two periodicities indicate that IGR J00234+6141 is a magnetic CV of the intermediate polar type. This is one of the faintest and hardest sources of this type detected by INTEGRAL. This confirms earlier conclusions that intermediate polars contribute significantly to the population of galactic X-ray sources and represent a significant fraction of the high energy background.