X-ray Flashes or soft Gamma-ray Bursts? The case of the likely distant XRF 040912

In this work, we present a multi-wavelength study of XRF 040912, aimed at measuring its distance scale and the intrinsic burst properties. We performed a detailed spectral and temporal analysis of both the prompt and the afterglow emission and we estimated the distance scale of the likely host galaxy. We then used the currently available sample of XRFs with known distance to discuss the connection between XRFs and classical Gamma-ray Bursts (GRBs). We found that the prompt emission properties unambiguously identify this burst as an XRF, with an observed peak energy of E_p=17+/-13 keV and a burst fluence ratio S(2-30keV)/S(30-400keV)>1. A non-fading optical source with R~24 mag and with an apparently extended morphology is spatially consistent with the X-ray afterglow, likely the host galaxy. XRF 040912 is a very dark burst since no afterglow optical counterpart is detected down to R>25 mag (3 sigma limiting magnitude) at 13.6 hours after the burst. The host galaxy spectrum detected from 3800A to 10000A, shows a single emission line at 9552A. The lack of any other strong emission lines blue-ward of the detected one and the absence of the Ly alpha cut-off down to 3800A are consistent with the hypothesis of the [OII] line at redshift z=1.563+/-0.001. The intrinsic spectral properties rank this XRF among the soft GRBs in the E_peak-E_iso diagram. Similar results were obtained for most XRFs at known redshift. Only XRF 060218 and XRF 020903 represent a good example of instrinsic XRF(i-XRF) and are possibly associated with a different progenitor population. This scenario may calls for a new definition of XRFs.Comment: 10 pages, 7 figures, accepted for publication in Astronomy & Astrophysic

Compressive Sensing for Dynamic XRF Scanning

X-Ray Fluorescence (XRF) scanning is a widespread technique of high importance and impact since it provides chemical composition maps crucial for several scientific investigations. There are continuous requirements for larger, faster and highly resolved acquisitions in order to study complex structures. Among the scientific applications that benefit from it, some of them, such as wide scale brain imaging, are prohibitively difficult due to time constraints. However, typically the overall XRF imaging performance is improving through technological progress on XRF detectors and X-ray sources. This paper suggests an additional approach where XRF scanning is performed in a sparse way by skipping specific points or by varying dynamically acquisition time or other scan settings in a conditional manner. This paves the way for Compressive Sensing in XRF scans where data are acquired in a reduced manner allowing for challenging experiments, currently not feasible with the traditional scanning strategies. A series of different compressive sensing strategies for dynamic scans are presented here. A proof of principle experiment was performed at the TwinMic beamline of Elettra synchrotron. The outcome demonstrates the potential of Compressive Sensing for dynamic scans, suggesting its use in challenging scientific experiments while proposing a technical solution for beamline acquisition software.Comment: 16 pages, 7 figures, 1 tabl

Could the GRB-Supernovae GRB 031203 and XRF 060218 be Cosmic Twins?

The gamma-ray burst (GRB) / X-ray flash (XRF) events GRB 031203, discovered by INTEGRAL, and XRF 060218, discovered by Swift, represent two of only five GRB-SNe with optical spectroscopic confirmation of their SN components. Yet their observed high-energy properties offer a sharp contrast: While GRB 031203 was detected as a short 40-s burst with a spectrum peaking at E_peak > 190 keV, XRF 060218 was a T_90 ~ 2100-s long, smoothly-evolving burst with peak energy E_peak = 4.9 keV. At the same time, the properties of the two expanding dust-scattered X-ray halos observed in a fast-response XMM-Newton observation of GRB 031203 reveal that this event was accompanied by an "X-ray blast" with fluence comparable to or greater than that of the prompt gamma-ray event. Taking this observation as our starting point, we investigate the likely properties of the X-ray blast from GRB 031203 via detailed modeling of the XMM data, discovering a third halo due to scattering off a more distant dust sheet at d_3 = 9.94 +/- 0.39 kpc, and constraining the timing of the X-ray blast relative to the GRB trigger time to be t_0 = 11 +/- 417 s. Using our constraints, we compare the properties of GRB 031203 to those of other GRB-SNe in order to understand the likely nature of its X-ray blast, concluding that a bright X-ray flare, as in GRB 050502B, or shock breakout event, as in XRF 060218, provide the most likely explanations. In the latter case, we consider the added possibility that XRF 060218 may have manifested an episode of bright gamma-ray emission prior to the burst observed by Swift, in which case GRB 031203 and XRF 060218 would be "cosmic twin" explosions with nearly identical high-energy properties.Comment: MNRAS in press; 12 pages, 6 figures. v2: Expanded discussion of related papers and minor changes in response to referee repor

The first Swift X-ray Flash: The faint afterglow of XRF 050215B

We present the discovery of XRF 050215B and its afterglow. The burst was detected by the Swift BAT during the check-out phase and observations with the X-ray telescope began approximately 30 minutes after the burst. These observations found a faint, slowly fading X-ray afterglow near the centre of the error box as reported by the BAT. Infrared data, obtained at UKIRT after 10 hours also revealed a very faint K-band afterglow. The afterglow appear unusual since it is very faint, especially in the infrared with K>20 only 9 hours post burst. The X-ray and infrared lightcurves exhibit a slow, monotonic decay with alpha=0.8 and no evidence for steepening associated with the jet break to 10 days post burst. We discuss possible explanations for the faintness and slow decay in the context of present models for the production of X-ray Flashes.Comment: 8 pages, 5 figures, accepted for publication in Ap

X-ray Fluorescence Analysis of Feldspars and Silicate Glass: Effects of Melting Time on Fused Bead Consistency and Volatilisation

Reproducible preparation of lithium tetraborate fused beads for XRF analysis of glass and mineral samples is of paramount importance for analytical repeatability. However, as with all glass melting processes, losses due to volatilisation must be taken into account and their effects are not negligible. Here the effects of fused bead melting time have been studied for four Certified Reference Materials (CRM’s: three feldspars, one silicate glass), in terms of their effects on analytical variability and volatilisation losses arising from fused bead preparation. At melting temperatures of 1065 °C, and for feldspar samples, fused bead melting times shorter than approximately 25 min generally gave rise to a greater deviation of the XRF-analysed composition from the certified composition. This variation might be due to incomplete fusion and/or fused bead inhomogeneity but further research is needed. In contrast, the shortest fused bead melting time for the silicate glass CRM gave an XRF-analysed composition closer to the certified values than longer melting times. This may suggest a faster rate of glass-in-glass dissolution and homogenization during fused bead preparation. For all samples, longer melting times gave rise to greater volatilisation losses (including sulphates and halides) during fusion. This was demonstrated by a linear relationship between SO3 mass loss and time1/2, as predicted by a simple diffusion-based model. Iodine volatilisation displays a more complex relationship, suggestive of diffusion plus additional mechanisms. This conclusion may have implications for vitrification of iodine-bearing radioactive wastes. Our research demonstrates that the nature of the sample material impacts on the most appropriate fusion times. For feldspars no less than ~25 min and no more than ~60 min of fusion at 1065 °C, using Li2B4O7 as the fusion medium and in the context of feldspar samples and the automatic fusion equipment used here, strikes an acceptable (albeit non-ideal) balance between the competing factors of fused bead quality, analytical consistency and mitigating volatilisation losses. Conversely, for the silicate glass sample, shorter fusion times of less than ~30 min under the same conditions provided more accurate analyses whilst limiting volatile losses

How unusual is XRF 060218 ?

Light curves are calculated for an off-axis observer due the scattering of primary radiation by extended baryonic material. The unusually long duration and the chromaticity of the light curves above several KeV of XRF 060218 can be explained as a result of the acceleration of the baryonic scattering material by the primary radiation. The observed light curves by our model and detailed fits to the data are presented. The model predicts that $\sim 4\times 10^{48}$ ergs are put into accelerated, mildly relativistic baryons by the radiation pressure at large radii from the central engine. It is suggested that the emission below 3 KeV, which lies {\it below} the Amati relation, is a baryon contaminated fireball.Comment: 7 pages, 5 figures, Appeared in ApJL, Volume 713, Issue 1, pp. L55, 201

X-Ray fluorescence analysis of feldspars and silicate glass: effects of melting time on fused bead consistency and volatilisation

Reproducible preparation of lithium tetraborate fused beads for XRF analysis of glass and mineral samples is of paramount importance for analytical repeatability. However, as with all glass melting processes, losses due to volatilization must be taken into account and their effects are not negligible. Here the effects of fused bead melting time have been studied for four Certified Reference Materials (CRM’s-three feldspars, one silicate glass), in terms of their effects on analytical variability and volatilization losses arising from fused bead preparation. At melting temperatures of 1065 °C, and for feldspar samples, fused bead melting times shorter than approximately 25 minutes generally gave rise to greater deviation of XRF-analyzed composition from certified composition. This variation might be due to incomplete fusion and / or fused bead inhomogeneity but further research is needed. In contrast, the shortest fused bead melting time for the silicate glass CRM gave an XRF-analyzed composition closer to the certified values than longer melting times. This may suggest a faster rate of glass-in-glass dissolution and homogenization during fused bead preparation. For all samples, longer melting times gave rise to greater volatilization losses (including sulphates and halides) during fusion. This was demonstrated by a linear relationship between SO3 mass loss and time1/2, as predicted by a simple diffusion-based model. Iodine volatilization displays a more complex relationship, suggestive of diffusion plus additional mechanisms. This conclusion may have implications for vitrification of iodine-bearing radioactive wastes. Our research demonstrates that the nature of the sample material impacts on the most appropriate fusion times. For feldspars no less than ~25 min and no more than ~60 min of fusion at 1065 °C, using Li2B4O7 as the fusion medium and in the context of feldspar samples and the automatic fusion equipment used here, strikes an acceptable (albeit non-ideal) balance between the competing factors of fused bead quality, analytical consistency and mitigating volatilization losses. Conversely, for the silicate glass sample, shorter fusion times of less than ~30 minutes under the same conditions provided more accurate analyses whilst limiting volatile losses