Monte-Carlo simulations of the background of the coded-mask camera for X- and Gamma-rays on-board the Chinese-French GRB mission SVOM

For several decades now, wide-field coded mask cameras have been used with success to localise Gamma-ray bursts (GRBs). In these instruments, the event count rate is dominated by the photon background due to their large field of view and large effective area. It is therefore essential to estimate the instrument background expected in orbit during the early phases of the instrument design in order to optimise the scientific performances of the mission. We present here a detailed study of the instrument background and sensitivity of the coded-mask camera for X- and Gamma-rays (CXG) to be used in the detection and localisation of high-redshift GRBs on-board the international GRB mission SVOM. To compute the background spectrum, a Monte-Carlo approach was used to simulate the primary and secondary interactions between particles from the main components of the space environment that SVOM will encounter along its Low Earth Orbit (LEO) (with an altitude of 600 km and an inclination of ~ 30 deg) and the body of the CXG. We consider the detailed mass model of the CXG in its latest design. According to our results, i) the design of the passive shield of the camera ensures that in the 4-50 keV imaging band the cosmic X-Gamma-ray background is dominant whilst the internal background should start to become dominant above 70-90 keV; ii) the current camera design ensures that the CXG camera will be more sensitive to high-redshift GRBs than the Swift Burst Alert Telescope thanks to a low-energy threshold of 4 keV.Comment: 16 pages, 10 figures (1 colour), accepted for publication in Nuclear Instruments and Methods in Physics Research: Section

First evidence for spectral state transitions in the ESO243-49 hyper luminous X-ray source HLX-1

The brightest Ultra-Luminous X-ray source (ULX), ESO 243-49 HLX-1, with a 0.2 - 10 keV X-ray luminosity of up to 10^42 erg s^-1, provides the strongest evidence to date for the existence of intermediate mass black holes. Although small scale X-ray spectral variability has already been demonstrated, we have initiated a monitoring campaign with the X-ray Telescope onboard the Swift satellite to search for luminosity-related spectral changes and to compare its behavior with the better studied stellar mass black holes. In this paper, we report a drop in the XRT count rate by a factor of ~8 which occurred simultaneously with a hardening of the X-ray spectrum. A second observation found that the source had re-brightened by a factor of ~21 which occurred simultaneously with a softening of the X-ray spectrum. This may be the first evidence for a transition between the low/hard and high/soft states.Comment: Accepted by ApJ Letter, 2 figure

Discovery of a new INTEGRAL source: IGR J19140+0951

IGR J19140+0951 (formerly known as IGR J19140+098) was discovered with the INTEGRAL satellite in March 2003. We report the details of the discovery, using an improved position for the analysis. We have performed a simultaneous study of the 5-100 keV JEM-X and ISGRI spectra from which we can distinguish two different states. From the results of our analysis we propose that IGR J19140+0951 is a persistent Galactic X-ray binary, probably hosting a neutron star although a black hole cannot be completely ruled out.Comment: 4 pages, 4 figures. Accepted for publication in A&A

Implications of the delayed 2013 outburst of the ESO 243-49 HLX-1

After showing four outbursts spaced by $\sim 1$ year from 2009 to 2012, the hyper luminous X-ray source ESO 243-49 HLX-1, currently the best intermediate mass black hole (IMBH) candidate, showed an outburst in 2013 delayed by more than a month. In Lasota et al. (2011), we proposed that the X-ray lightcurve is the result of enhanced mass transfer episodes at periapsis from a donor star orbiting the IMBH in a highly eccentric orbit. In this scenario, the delay can be explained only if the orbital parameters can change suddenly from orbit to orbit. To investigate this, we ran Newtonian smooth particle hydrodynamical simulations starting with an incoming donor approaching an IMBH on a parabolic orbit. We survey a large parameter space by varying the star-to-BH mass ratio ($10^{-5}-10^{-3}$) and the periapsis separation $r_p$ from 2.2 to $2.7~r_t$ with $r_t$, the tidal radius. To model the donor, we choose several polytropes ($\Gamma = 5/2,~n=3/2$; $\Gamma=3/2,~n=2$; $\Gamma=5/3,~n=2$ & $n=3$). Once the system is formed, the orbital period decreases until reaching a minimum. Then, the period tends to increase over several periapsis passages due to tidal effects and increasing mass transfer, leading ultimately to the ejection of the donor. The development of stochastic fluctuations inside the donor could lead to sudden changes in the orbital period from orbit to orbit with the appropriate order of magnitude of what has been observed for HLX-1. Given the constraints on the BH mass ($M_{\rm BH} > 10^4~M_\odot$) and assuming that HLX-1 is currently near a minimum in period of $\sim 1$ yr, the donor has to be a white dwarf or a stripped giant core. We predict that if HLX-1 is indeed emerging from a minimum in orbital period, then the period would generally increase with each passage, although substantial stochastic fluctuations can be superposed on this trend.Comment: 22 pages, 10 figures, accepted for publication in ApJ (acceptance date: 2014-08-01

Update on the ICUD-SIU consultation on multi-parametric magnetic resonance imaging in localised prostate cancer

Introduction: Prostate cancer (PCa) imaging is a rapidly evolving field. Dramatic improvements in prostate MRI during the last decade will probably change the accuracy of diagnosis. This chapter reviews recent current evidence about MRI diagnostic performance and impact on PCa management. Materials and methods: The International Consultation on Urological Diseases nominated a committee to review the literature on prostate MRI. A search of the PubMed database was conducted to identify articles focussed on MP-MRI detection and staging protocols, reporting and scoring systems, the role of MP-MRI in diagnosing PCa prior to biopsy, in active surveillance, in focal therapy and in detecting local recurrence after treatment. Results: Differences in opinion were reported in the use of the strength of magnets [1.5 Tesla (T) vs. 3T] and coils. More agreement was found regarding the choice of pulse sequences; diffusion-weighted MRI (DW-MRI), dynamic contrast-enhanced MRI (DCE MRI), and/or MR spectroscopy imaging (MRSI) are recommended in addition to conventional T2-weighted anatomical sequences. In 2015, the Prostate Imaging Reporting and Data System (PI-RADS version 2) was described to standardize image acquisition and interpretation. MP-MRI improves detection of clinically significant PCa (csPCa) in the repeat biopsy setting or before the confirmatory biopsy in patients considering active surveillance. It is useful to guide focal treatment and to detect local recurrences after treatment. Its role in biopsy-naive patients or during the course of active surveillance remains debated. Conclusion: MP-MRI is increasingly used to improve detection of csPCa and for the selection of a suitable therapeutic approach

Optical variability of the accretion disk around the intermediate mass black hole ESO 243-49 HLX-1 during the 2012 outburst

We present dedicated quasi-simultaneous X-ray (Swift) and optical (Very Large Telescope (VLT), V- and R-band) observations of the intermediate mass black hole candidate ESO 243-49 HLX-1 before and during the 2012 outburst. We show that the V-band magnitudes vary with time, thus proving that a portion of the observed emission originates in the accretion disk. Using the first quiescent optical observations of HLX-1, we show that the stellar population surrounding HLX-1 is fainter than V~25.1 and R~24.2. We show that the optical emission may increase before the X-ray emission consistent with the scenario proposed by Lasota et al. (2011) in which the regular outbursts could be related to the passage at periastron of a star circling the intermediate mass black hole in an eccentric orbit, which triggers mass transfer into a quasi-permanent accretion disk around the black hole. Further, if there is indeed a delay in the X-ray emission we estimate the mass-transfer delivery radius to be ~1e11 cm.Comment: 9 pages, 2 figures, accepted for publication in ApJ

Periodic Thermonuclear X-ray Bursts from GS 1826-24 and the Fuel Composition as a Function of Accretion Rate

We analyze 24 type I X-ray bursts from GS 1826-24 observed by the Rossi X-ray Timing Explorer between 1997 November and 2002 July. The bursts observed between 1997-98 were consistent with a stable recurrence time of 5.74 +/- 0.13 hr. The persistent intensity of GS 1826-24 increased by 36% between 1997-2000, by which time the burst interval had decreased to 4.10 +/- 0.08 hr. In 2002 July the recurrence time was shorter again, at 3.56 +/- 0.03 hr. The bursts within each epoch had remarkably identical lightcurves over the full approx. 150 s burst duration; both the initial decay timescale from the peak, and the burst fluence, increased slightly with the rise in persistent flux. The decrease in the burst recurrence time was proportional to Mdot^(-1.05+/-0.02) (where Mdot is assumed to be linearly proportional to the X-ray flux), so that the ratio alpha between the integrated persistent and burst fluxes was inversely correlated with Mdot. The average value of alpha was 41.7 +/- 1.6. Both the alpha value, and the long burst durations indicate that the hydrogen is burning during the burst via the rapid-proton (rp) process. The variation in alpha with Mdot implies that hydrogen is burning stably between bursts, requiring solar metallicity (Z ~ 0.02) in the accreted layer. We show that solar metallicity ignition models naturally reproduce the observed burst energies, but do not match the observed variations in recurrence time and burst fluence. Low metallicity models (Z ~ 0.001) reproduce the observed trends in recurrence time and fluence, but are ruled out by the variation in alpha. We discuss possible explanations, including extra heating between bursts, or that the fraction of the neutron star covered by the accreted fuel increases with Mdot.Comment: 9 pages, 6 figures, accepted by ApJ. Minor revisions following the referee's repor

The X-/Gamma-ray camera ECLAIRs for the Gammay-ray burst mission SVOM

We present ECLAIRs, the Gamma-ray burst (GRB) trigger camera to fly on-board the Chinese-French mission SVOM. ECLAIRs is a wide-field ($\sim 2$\,sr) coded mask camera with a mask transparency of 40\% and a 1024 $\mathrm{cm}^2$ detection plane coupled to a data processing unit, so-called UGTS, which is in charge of locating GRBs in near real time thanks to image and rate triggers. We present the instrument science requirements and how the design of ECLAIRs has been optimized to increase its sensitivity to high-redshift GRBs and low-luminosity GRBs in the local Universe, by having a low-energy threshold of 4 keV. The total spectral coverage ranges from 4 to 150 keV. ECLAIRs is expected to detect $\sim 200$ GRBs of all types during the nominal 3 year mission lifetime. To reach a 4 keV low-energy threshold, the ECLAIRs detection plane is paved with 6400 $4\times 4~\mathrm{mm}^2$ and 1 mm-thick Schottky CdTe detectors. The detectors are grouped by 32, in 8x4 matrices read by a low-noise ASIC, forming elementary modules called XRDPIX. In this paper, we also present our current efforts to investigate the performance of these modules with their front-end electronics when illuminated by charged particles and/or photons using radioactive sources. All measurements are made in different instrument configurations in vacuum and with a nominal in-flight detector temperature of $-20^\circ$C. This work will enable us to choose the in-flight configuration that will make the best compromise between the science performance and the in-flight operability of ECLAIRs. We will show some highlights of this work.Comment: 15 pages, 12 figures, Proceeding SPIE - Montreal 201