Developing a second generation Laue lens prototype: high reflectivity crystals and accurate assembly

Laue lenses are an emerging technology that will enhance gamma-ray telescope sensitivity by one to two orders of magnitude in selected energy bands of the \sim 100 keV to \sim 1.5 MeV range. This optic would be particularly well adapted to the observation of faint gamma ray lines, as required for the study of Supernovae and Galactic positron annihilation. It could also prove very useful for the study of hard X-ray tails from a variety of compact objects, especially making a difference by providing sufficient sensitivity for polarization to be measured by the focal plane detector. Our group has been addressing the two key issues relevant to improve performance with respect to the first generation of Laue lens prototypes: obtaining large numbers of efficient crystals and developing a method to fix them with accurate orientation and dense packing factor onto a substrate. We present preliminary results of an on-going study aiming to enable a large number of crystals suitable for diffraction at energies above 500 keV. In addition, we show the first results of the Laue lens prototype assembled using our beamline at SSL/UC Berkeley, which demonstrates our ability to orient and glue crystals with accuracy of a few arcsec, as required for an efficient Laue lens telescope.Comment: Published in the proceedings of the SPIE conference held in San Diego in August 201

NuSTAR observation of a Type I X-ray burst from GRS 1741.9-2853

We report on two NuSTAR observations of GRS 1741.9-2853, a faint neutron star low mass X-ray binary burster located 10' away from the Galactic center. NuSTAR detected the source serendipitously as it was emerging from quiescence: its luminosity was $6\times 10^{34}$ erg~s$^{-1}$ on 2013 July 31, and $5\times 10^{35}$ erg~s$^{-1}$ in a second observation on 2013 August 3. A bright, 800-s long, H-triggered mixed H/He thermonuclear Type I burst with mild photospheric radius expansion (PRE) was present during the second observation. Assuming that the luminosity during the PRE was at the Eddington level, a H mass fraction $X=0.7$ in the atmosphere, and a neutron star mass $M=1.4 M_{\odot}$, we determine a new lower limit on the distance for this source of $6.3 \pm 0.5$ kpc. Combining with previous upper limits, this places GRS 1741.9-2853 at a distance of 7 kpc. Energy independent (achromatic) variability is observed during the cooling of the neutron star, which could result from the disturbance of the inner accretion disk by the burst. The large dynamic range of this burst reveals a long power-law decay tail. We also detect, at a 95.6\% confidence level (1.7 $\sigma$), a narrow absorption line at $5.46\pm0.10$ keV during the PRE phase of the burst, reminiscent of the detection by Waki et al. (1984). We propose that the line, if real, is formed in the wind above the photosphere of the neutron star by a resonant K$\alpha$ transition from H-like Cr gravitationally redshifted by a factor $1+z=1.09$, corresponding to a radius range of 29.0 -- 41.4 km for a mass range of 1.4 -- 2.0 $M_{\odot}$.Comment: Accepted for publication in The Astrophysical Journa

Assessment of Three Mitochondrial Genes (16S, Cytb, CO1) for Identifying Species in the Praomyini Tribe (Rodentia: Muridae)

The Praomyini tribe is one of the most diverse and abundant groups of Old World rodents. Several species are known to be involved in crop damage and in the epidemiology of several human and cattle diseases. Due to the existence of sibling species their identification is often problematic. Thus an easy, fast and accurate species identification tool is needed for non-systematicians to correctly identify Praomyini species. In this study we compare the usefulness of three genes (16S, Cytb, CO1) for identifying species of this tribe. A total of 426 specimens representing 40 species (sampled across their geographical range) were sequenced for the three genes. Nearly all of the species included in our study are monophyletic in the neighbour joining trees. The degree of intra-specific variability tends to be lower than the divergence between species, but no barcoding gap is detected. The success rate of the statistical methods of species identification is excellent (up to 99% or 100% for statistical supervised classification methods as the k-Nearest Neighbour or Random Forest). The 16S gene is 2.5 less variable than the Cytb and CO1 genes. As a result its discriminatory power is smaller. To sum up, our results suggest that using DNA markers for identifying species in the Praomyini tribe is a largely valid approach, and that the CO1 and Cytb genes are better DNA markers than the 16S gene. Our results confirm the usefulness of statistical methods such as the Random Forest and the 1-NN methods to assign a sequence to a species, even when the number of species is relatively large. Based on our NJ trees and the distribution of all intraspecific and interspecific pairwise nucleotide distances, we highlight the presence of several potentially new species within the Praomyini tribe that should be subject to corroboration assessments

The Athena x-ray optics development and accommodation

The Athena mission, under study and preparation by ESA as its second Large-class science mission, requires the largest X-ray optics ever flown, building on a novel optics technology based on mono crystalline silicon. Referred to as Silicon Pore Optics technology (SPO), the optics is highly modular and benefits from technology spin-in from the semiconductor industry. The telescope aperture of about 2.5 meters is populated by around 700 mirror modules, accurately co-aligned to produce a common focus. The development of the SPO technology is a joint effort by European industrial and research entities, working together to address the challenges to demonstrate the imaging performance, robustness and efficient series production of the Athena optics. A technology development plan was established and is being regularly updated to reflect the latest developments, and is fully funded by the ESA technology development programmes. An industrial consortium was formed to ensure coherence of the individual technology development activities. The SPO technology uses precision machined mirror plates produced using the latest generation top quality 12 inch silicon wafers, which are assembled into rugged stacks. The surfaces of the mirror plates and the integral support structure is such, that no glue is required to join the individual mirror plates. Once accurately aligned with respect to each other, the surfaces of the mirror plates merge in a physical bonding process. The resultant SPO mirror modules are therefore very accurate and stable and can sustain the harsh conditions encountered during launch and are able to tolerate the space environment expected during operations. The accommodation of the Athena telescope is also innovative, relying on a hexapod mechanism to align the optics to the selected detector instruments located in the focal plane. System studies are complemented by dedicated technology development activities to demonstrate the capabilities before the adoption of the Athena mission

NuSTAR Hard X-ray Survey of the Galactic Center Region I: Hard X-ray Morphology and Spectroscopy of the Diffuse Emission

We present the first sub-arcminute images of the Galactic Center above 10 keV, obtained with NuSTAR. NuSTAR resolves the hard X-ray source IGR J17456–2901 into non-thermal X-ray filaments, molecular clouds, point sources, and a previously unknown central component of hard X-ray emission (CHXE). NuSTAR detects four non-thermal X-ray filaments, extending the detection of their power-law spectra with Γ ~ 1.3–2.3 up to ~50 keV. A morphological and spectral study of the filaments suggests that their origin may be heterogeneous, where previous studies suggested a common origin in young pulsar wind nebulae (PWNe). NuSTAR detects non-thermal X-ray continuum emission spatially correlated with the 6.4 keV Fe Kα fluorescence line emission associated with two Sgr A molecular clouds: MC1 and the Bridge. Broadband X-ray spectral analysis with a Monte-Carlo based X-ray reflection model self-consistently determined their intrinsic column density (~1023 cm−2), primary X-ray spectra (power-laws with Γ ~ 2) and set a lower limit of the X-ray luminosity of Sgr A* flare illuminating the Sgr A clouds to LX gsim 1038 erg s−1. Above ~20 keV, hard X-ray emission in the central 10 pc region around Sgr A* consists of the candidate PWN G359.95–0.04 and the CHXE, possibly resulting from an unresolved population of massive CVs with white dwarf masses MWD ~ 0.9 M⊙. Spectral energy distribution analysis suggests that G359.95–0.04 is likely the hard X-ray counterpart of the ultra-high gamma-ray source HESS J1745–290, strongly favoring a leptonic origin of the GC TeV emission.Astronom