LSSA large area silicon sheet task continuous Czochralski process development

A Czochralski crystal growing furnace was converted to a continuous growth facility by installation of a premelter to provide molten silicon flow into the primary crucible. The basic furnace is operational and several trial crystals were grown in the batch mode. Numerous premelter configurations were tested both in laboratory-scale equipment as well as in the actual furnace. The best arrangement tested to date is a vertical, cylindrical graphite heater containing small fused silicon test tube liner in which the incoming silicon is melted and flows into the primary crucible. Economic modeling of the continuous Czochralski process indicates that for 10 cm diameter crystal, 100 kg furnace runs of four or five crystals each are near-optimal. Costs tend to asymptote at the 100 kg level so little additional cost improvement occurs at larger runs. For these conditions, crystal cost in equivalent wafer area of around $20/sq m exclusive of polysilicon and slicing was obtained

Large area Czochralski silicon

The overall cost effectiveness of the Czochralski process for producing large-area silicon was determined. The feasibility of growing several 12 cm diameter crystals sequentially at 12 cm/h during a furnace run and the subsequent slicing of the ingot using a multiblade slurry saw were investigated. The goal of the wafering process was a slice thickness of 0.25 mm with minimal kerf. A slice + kerf of 0.56 mm was achieved on 12 cm crystal using both 400 grit B4C and SiC abrasive slurries. Crystal growth experiments were performed at 12 cm diameter in a commercially available puller with both 10 and 12 kg melts. Several modifications to the puller hoz zone were required to achieve stable crystal growth over the entire crystal length and to prevent crystallinity loss a few centimeters down the crystal. The maximum practical growth rate for 12 cm crystal in this puller design was 10 cm/h, with 12 to 14 cm/h being the absolute maximum range at which melt freeze occurred

Spin frequency distributions of binary millisecond pulsars

Rotation-powered millisecond radio pulsars have been spun up to their present spin period by a $10^8$ - $10^9$ yr long X-ray-bright phase of accretion of matter and angular momentum in a low-to-intermediate mass binary system. Recently, the discovery of transitional pulsars that alternate cyclically between accretion and rotation-powered states on time scales of a few years or shorter, has demonstrated this evolutionary scenario. Here, we present a thorough statistical analysis of the spin distributions of the various classes of millisecond pulsars to assess the evolution of their spin period between the different stages. Accreting sources that showed oscillations exclusively during thermonuclear type I X-ray bursts (nuclear-powered millisecond pulsars) are found to be significantly faster than rotation-powered sources, while accreting sources that possess a magnetosphere and show coherent pulsations (accreting millisecond pulsars) are not. On the other hand, if accreting millisecond pulsars and eclipsing rotation-powered millisecond pulsars form a common class of transitional pulsars, these are shown to have a spin distribution intermediate between the faster nuclear-powered millisecond pulsars and the slower non-eclipsing rotation-powered millisecond pulsars. We interpret these findings in terms of a spin-down due to the decreasing mass-accretion rate during the latest stages of the accretion phase, and in terms of the different orbital evolutionary channels mapped by the various classes of pulsars. We summarize possible instrumental selection effects, showing that even if an unbiased sample of pulsars is still lacking, their influence on the results of the presented analysis is reduced by recent improvements in instrumentation and searching techniques.Comment: Accepted for publication in A&A (6 pages, 4 figures

Comparing supernova remnants around strongly magnetized and canonical pulsars

The origin of the strong magnetic fields measured in magnetars is one of the main uncertainties in the neutron star field. On the other hand, the recent discovery of a large number of such strongly magnetized neutron stars, is calling for more investigation on their formation. The first proposed model for the formation of such strong magnetic fields in magnetars was through alpha-dynamo effects on the rapidly rotating core of a massive star. Other scenarios involve highly magnetic massive progenitors that conserve their strong magnetic moment into the core after the explosion, or a common envelope phase of a massive binary system. In this work, we do a complete re-analysis of the archival X-ray emission of the Supernova Remnants (SNR) surrounding magnetars, and compare our results with all other bright X-ray emitting SNRs, which are associated with Compact Central Objects (CCOs; which are proposed to have magnetar-like B-fields buried in the crust by strong accretion soon after their formation), high-B pulsars and normal pulsars. We find that emission lines in SNRs hosting highly magnetic neutron stars do not differ significantly in elements or ionization state from those observed in other SNRs, neither averaging on the whole remnants, nor studying different parts of their total spatial extent. Furthermore, we find no significant evidence that the total X-ray luminosities of SNRs hosting magnetars, are on average larger than that of typical young X-ray SNRs. Although biased by a small number of objects, we found that for a similar age, there is the same percentage of magnetars showing a detectable SNR than for the normal pulsar population.Comment: 16 pages, 5 figures, Accepted for publication in MNRA

Linking the X-ray timing and spectral properties of the glitching AXP 1RXS J170849-400910

Previous studies of the X-ray flux and spectral properties of 1RXS J170849-400910 showed hints of a possible correlation with the spin glitches that occurred in 1999 and 2001. However, due to the sparseness of spectral measurements and the paucity of detected glitches no firm conclusion could be drawn. We retrieved and analysed archival XTE pointings of 1RXS J170849-400910 covering the time interval between January 2003 and June 2006 and carried out a detailed timing analysis by means of phase fitting techniques. We detected two relatively large glitches Delta nu / nu of 1.2 and 2.1 10^-6 occurred in January and June 2005. Interestingly, the occurrence times of these glitches are in agreement with the predictions made in our previous studies. This finding strongly suggests a connection between the flux, spectral and timing properties of 1RXS J170849-400910.Comment: Submitted to A&A, 4 pages; results presented at the INT meeting "The Neutron Star Crust and Surface: Observations and Models" on June 27; referee comments adde

The Spectral Evolution of Transient Anomalous X-ray Pulsar XTE J1810--197

(Abridged) We present a multi-epoch spectral study of the Transient Anomalous X-ray Pulsar XTE J1810-197 obtained with the XMM X-ray telescope. Four observations taken over the course of a year reveal strong spectral evolution as the source fades from outburst. The origin of this is traced to the individual decay rates of the pulsar's spectral components. A 2-T fit at each epoch requires nearly constant temperatures of kT=0.25 & 0.67 keV while the component luminosities decrease exponentially with tau=900 & 300d, respectively. One possible interpretation is that the slowly decaying cooler component is the radiation from a deep heating event that affected a large fraction of the crust, while the hotter component is powered by external surface heating at the foot-points of twisted magnetic field lines, by magnetospheric currents that are decaying more rapidly. The energy-dependent pulse profile of XTE J1810-197 is well modeled at all epochs by the sum of a sine and triangle function. These profiles peak at the same phase, suggesting a concentric surface emission geometry. The spectral and pulse evolution together argue against the presence of a significant ``power-law'' contribution to the X-ray spectrum below 8 keV. The extrapolated flux is projected to return to the historic quiescent level, characterized by an even cooler blackbody spectrum, by the year 2007.Comment: 12 pages, 6 Figures, Latex, emulateapj. To appear in the Astrophysical Journa

VLT observations of the magnetar CXO J164710.2-455216 and the detection of a candidate infrared counterpart

We present deep observations of the field of the magnetar CXOJ164710.2-455216 in the star cluster Westerlund 1, obtained in the near-infrared with the adaptive optics camera NACO@VLT. We detected a possible candidate counterpart at the {\em Chandra} position of the magnetar, of magnitudes $\mathrm{J} = 23.5 \pm 0.2$, $\mathrm{H} = 21.0 \pm 0.1$, and $\mathrm{K}_\mathrm{S} = 20.4 \pm 0.1$. The K$_{\rm S}$-band measurements available for two epochs (2006 and 2013) do not show significant signs of variability but only a marginal indication that the flux varied (at the 2 $\sigma$ level), consistent with the fact that the observations were taken when CXOJ164710.2-455216 was in quiescence. At the same time, we also present colour--magnitude and colour--colour diagrams in the J, H, and K$_{\rm S}$ bands from the 2006 epoch only, the only one with observations in all three bands, showing that the candidate counterpart lies in the main bulk of objects describing a relatively well--defined sequence. Therefore, based on its colours and lack of variability, we cannot yet associate the candidate counterpart to CXOJ164710.2-455216. Future near-infrared observations of the field, following-up a source outburst, would be crucial to confirm the association from the detection of near-infrared variability and colour evolution.Comment: 5 pages, 3 figures, accepted for publication in MNRA

Long term hard X-ray variability of the anomalous X-ray pulsar 1RXS J170849.0-400910 discovered with INTEGRAL

We report on a multi-band high-energy observing campaign aimed at studying the long term spectral variability of the Anomalous X-ray Pulsar (AXP) 1RXS J170849.0-400910, one of the magnetar candidates. We observed 1RXS J170849.0-400910 in Fall 2006 and Spring 2007 simultaneously with Swift/XRT, in the 0.1-10 keV energy range, and with INTEGRAL/IBIS, in the 20-200 keV energy range. Furthermore, we also reanalyzed, using the latest calibration and software, all the publicly available INTEGRAL data since 2002, and the soft X-ray data starting from 1999 taken using BeppoSAX, Chandra, XMM, and Swift/XRT, in order to study the soft and hard X-ray spectral variability of 1RXS J170849.0-400910. We find a long-term variability of the hard X-ray flux, extending the hardness-intensity correlation proposed for this source over 2 orders of magnitude in energy.Comment: 5 pages, 2 figures, accepted for publication in Astronomy & Astrophysics main journa