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In the present study mechanical performances of injection molded photoluminescent polymers were statistically modelled by applying Weibull distribution. The mechanical properties of samples made of polypropylene (PP) functionalized with photoluminescentpigments were evaluated by performing FIMEC (Flat-top Cylinder Indenter for Mechanical Characterization) test. This technique, based on the use of a flat cylinder penetrating at a constant rate into the material, allowed the authors to evaluate the local mechanical properties, according to pigment concentration.

The formation flight configuration of the Simbol-X mission implies that the X-ray mirror module will be open to Space on both ends. In order to reduce the power required to maintain the thermal stability and, therefore, the high angular resolution of the shell optics, a thin foil thermal shield will cover the mirror module. Different options are presently being studied for the foil material of these shields. We report results of an experimental investigation conducted to verify that the scattering of X-rays, by interaction with the thin foil material of the thermal shield, will not significantly affect the performances of the telescope.

We present the 2nd Palermo Swift‐BAT Catalogue, obtained using 54 months of BAT survey data. The catalog contains 1258 BAT source candidates, of which 1049 have been associated with a known counterpart.

The epochs of origin of the first stars and galaxies, and subsequent growth of the first supermassive black holes, are among the most fundamental questions. Observations of the highest redshift Gamma-Ray Bursts (GRBs) will be the most compelling in situ probe of the history of initial star formation and consequent epoch of reionization if their prompt and precise detection can be followed immediately by sensitive near-IR imaging and spectroscopy. Blazars are the persistent analogs of GRBs and for the same reason (beaming) can be observed at highest redshifts where they might best trace the high accretion rate-driven jets and growth of supermassive black holes in galaxies. The proposed EXIST mission can uniquely probe these questions, and many others, given its unparalled combination of sensitivity and spatial-spectral-temporal coverage and resolution. Here we provide a brief summary of the mission design, key science objectives, mission plan and readiness for EXIST, as proposed to Astro2010., Comment: 6 pages, 4 figures. Invited talk at conference "X-ray Astronomy 2009: Present status, multiwavelength approach and future perspectives", September 2009, Bologna. To appear in AIP Conf. Proc. (editors: A. Comastri, M. Cappi, L. Angelini). Revised (v2) version corrects some references.

Surface microroughness of X‐ray mirrors is a key issue for the angular resolution of Simbol‐X to comply with the required one (

We present a new measurement of the cosmic X-ray background (CXRB) in the 1.5-7 keV energy band, performed by exploiting the Swift X-ray telescope (XRT) data archive. We also present a CXRB spectral model in a wider energy band (1.5-200 keV), obtained by combining these data with the recently published Swift-BAT measurement. From the XRT archive we collect a complete sample of 126 high Galactic latitude gamma-ray burst (GRB) follow-up observations. This provides a total exposure of 7.5 Ms and a sky-coverage of 7 square degrees which represents a serendipitous survey, well suited for a direct measurement of the CXRB in the 1.5-10 keV interval. Our work is based on a complete characterization of the instrumental background and an accurate measurement of the stray-light contamination and vignetting calibration. We find that the CXRB spectrum in the 1.5-7 keV energy band can be equally well fitted by a single power-law with photon index Gamma=1.47+/-0.07 or a single power-law with photon index Gamma=1.41+/-0.06 and an exponential roll-off at 41 keV. The measured flux in the 2-10 keV energy band is 2.18+/-0.13 E-11 erg/(cm2 s deg2) in the 2-10 keV band. Combining Swift-XRT with Swift-BAT (15-200 keV) we find that, in the 1.5-200 keV band, the CXRB spectrum can be well described by two smoothly-joined power laws with the energy break at 29.0+/-0.5 keV corresponding to a nu F_nu peak located at 22.4+/-0.4 keV. Taking advantage of both the Swift high energy instruments (XRT and BAT), we produce an analytical description of the CXRB spectrum over a wide (1.5-200 keV) energy band. This model is marginally consistent with the HEAO1 measurement (~10% higher at energies higher than 20 keV, while it is significantly (30%) higher at low energies (2-10 keV)., Comment: Accepted for publication by A&A; 9 pages, 11 figures. Typo corrected in units of Tab. 2; update Fig. 11

We analyze the effective area of the Simbol‐X mirrors as a function of the off‐axis angle for small oscillations. A reduction is expected due to: 1) geometrical effects, because some of the photons miss the secondary mirror surface; 2) reflectivity effects, caused by the variation of the coating reflectivity with the incidence angle. The former are related to the length of the two mirror surfaces, and can be reduced by making the secondary mirror longer. The second ones are energy‐dependent, and strongly related to the characteristics of the reflecting coating. These effects are analyzed by means of ray‐tracing simulations in order to optimize the mirror and coating design, aiming to improve the effective area stability.

The optics of Simbol‐X are very thin compared to previous X‐ray missions (like XMM). Therefore their shells floppy and are unable to maintain the correct shape. To avoid the deformations of their very thin X‐ray optics during the integration process we adopt two stiffening rings with a good roundness. In this article the procedure used for the first three prototypes of the Simbol‐X optics is presented with a description of the problems involved and with an analysis of the degradation of the performances during the integration. This analysis has been performed with the UV vertical bench measurements at INAF‐OAB.

Swift‐XRT observations of the X‐ray emission from gamma ray bursts (GRBs) and during the GRB afterglow have led to many new results during the past two years. One of these exciting results is that ∼1/3−1/2 of GRBs contain detectable X‐ray flares. The mean fluence of the X‐ray flares is ∼10× less than that of the initial prompt emission, but in some cases the flare is as energetic as the prompt emission itself. The flares display fast rises and decays, and they sometimes occur at very late times relative to the prompt emission (sometimes as late as 105 s after T0) with very high peak fluxes relative to the underlying afterglow decay that has clearly begun prior to some flares. The temporal and spectral properties of the flares are found to favor models in which flares arise due to the same GRB internal engine processes that spawned the prompt GRB emission. Therefore, both long and short GRB internal engine models must be capable of producing high fluences in the X‐ray band at very late times.

We test the correlation between temporal variability and peak luminosity of the gamma‐ray profile on a homogeneous sample of 36 Swift/BAT GRBs with firm redshift determination. This is the first time that this correlation can be tested on a homogeneous data sample. The correlation is confirmed, as long as the 6 GRBs with low luminosity (

The X‐ray light curves of hundreds of bursts are now available, thanks to the X‐ray Telescope on board the Swift satellite, on time scales from ∼ 1 minute up to weeks and in some cases months from the burst explosion. These data allow us to investigate the physics of the highly relativistic fireball outflow and its interaction with the circumburst environment. Here we review the main results of the XRT observations, with particular regard to the evolution of the X‐ray light curves in the early phases. Unexpectedly, they are characterised by different slopes, with a very steep decay in the first few hundred of seconds, followed by a flatter decay and, a few thousand of seconds later, by a somewhat steeper decay. Often strong flare activity up to few hours after the burst explosion is also seen. These flares, most likely, are still related to the central engine activity, that last much longer than expected and it is still dominating the X‐ray light curve well after the prompt phase, up to a few thousand of ...

GRBs 050223 and 050911 were discovered by the Swift Burst Alert Telescope (BAT) on 23rd February and 11th September 2005 respectively. The observation of GRB 050223 showed a faint, fading X‐ray source, which was identified as the afterglow; GRB 050911, however, was not detected, making any X‐ray afterglow extremely faint. The faintness of the afterglow of GRB 050223 could be explained by a large opening or viewing angle, or by the burst being at high redshift. The non‐detection of GRB 050911 may indicate the burst occurred in a low‐density environment, or, alternatively, was due to a compact object merger, in spite of the apparent long duration of the burst.

Swift‐XRT observations of the X‐ray emission from gamma ray bursts (GRBs) and during the GRB afterglow have led to many new results during the past two years. These results have included the first ever detection of an afterglow from short GRBs, the detection of X‐ray emission from extremely high redshift GRBs (including one at z=6.3), the detection of many X‐ray afterglows that have no evidence of a late‐time jet break, the characterization of a new multi‐phase light curve following the initial GRB prompt emission (sometimes including the initial prompt emission itself), and the detection of X‐ray flares that sometimes occur at very late times relative to the initial prompt emission. While each of these results is exciting, this paper will concentrate exclusively on the X‐ray flares from GRBs. The mean fluence of the X‐ray flares is ≈ 10× less than that of the initial prompt emission, but in some cases the flare is as energetic as the prompt emission itself. The flares also display a fast rise and decay a...

We present a detailed analysis of the GRB 050326 prompt and afterglow emission. The combined capabilities of Swift (which sampled the light curve for a relatively long time span) and XMM (which ensured a large statistics) allowed to obtain a thorough characterization of the afterglow properties.

XRF 050416A was discovered by the Swift Burst Alert Telescope and re‐pointed with the Swift narrow field instruments only 64.5 s after the burst onset. The 15 – 150 keV BAT average spectrum has a photon index of Γ ∼ 3.0 which classifies the bursts as an X‐ray flash. The afterglow X‐ray emission was monitored by the Swift X‐Ray Telescope up to 74 days after the burst. The X‐ray light curve shows a decay with three different phases: an initial steep decay with a decay slope of ∼ 2.4 (phase A), then, starting at ∼172 s from the burst onset, a second phase with a flat decay slope of ∼ 0.44 (phase B), and finally, after ∼1450 s from the burst onset, a third long‐lasting phase with a decay slope of ∼ 0.88 (phase C). We find evidence of spectral evolution from a softer emission in the phase A of the afterglow decay, with Γ ∼ 3.0, to a harder emission with Γ ∼ 2.0 in the phases B and C. A redshift of 0.6535 was measured for the source. The spectra show intrinsic absorption in the host galaxy of ∼ 6.8 × 1021 cm−2....

The Swift X‐ray Telescope (XRT) is designed to make astrometric, spectroscopic and photometric observations of the X‐ray emission from Gamma‐ray bursts and their afterglows, in the energy band 0.2–10 keV. Here we report the results of the analysis of Swift XRT Point Spread Function (PSF) as measured in the first four months of the mission during the instrument calibration phase. The analysis includes the study of the PSF of different point‐like sources both on‐axis and off‐axis with different spectral properties. We compare the in‐flight data with the expectations from the on‐ground calibration. On the basis of the calibration data we built an analytical model to reproduce the PSF as a function of the energy and the source position within the detector which can be applied in the PSF correction calculation for any extraction region geometry. All the results of this study are implemented in the standard public software.

During the first year of operations of the Swift observatory, the X‐ray Telescope has made a number of discoveries concerning the nature of X‐ray afterglows of both long and short GRBs. We highlight the key findings, which include rapid declines at early times, a standard template of afterglow light curve shapes, common flaring, and the discovery of the first short GRB afterglow.

Observations of gamma ray bursts (GRBs) with Swift produced the initially surprising result that many bursts have large X-ray flares superimposed on the underlying afterglow. These flares were sometimes intense, rapid, and late relative to the nominal prompt phase. The most intense of these flares was observed by XRT with a flux >500 the afterglow. This burst then surprised observers by flaring again after >10000 s. The intense flare can be most easily understood within the context of the standard fireball model, if the internal engine that powers the prompt GRB emission is still active at late times. Recent observations indicate that X-ray flares are detected in ~1/3 of XRT detected afterglows. By studying the properties of the varieties of flares (such as rise/fall time, onset time, spectral variability, etc.) and relating them to overall burst properties, models of flare production and the GRB internal engine can be constrained., To appear in the proceedings of the 16th Annual October Astrophysics Conference in Maryland "Gamma Ray Bursts in the Swift Era"

Swift discovered the high redshift (z=6.29) GRB 050904 with the Burst Alert Telescope and began observing with its narrow field instruments only 161 s after the burst onset. GRB 050904 was a long, multi‐peaked, bright GRB with a presence of flaring activity lasting up to 1–2 hours after the burst onset. The spectral energy distribution shows a clear softening trend along the burst evolution with a photon index decreasing from −1.2 up to −1.9. The observed variability is more dramatic than the typical Swift afterglow, the amplitude and rise/fall times of the flares are consistent with the behavior of nearby (z ⩽ 1) long GRBs and suggest the interpretation of the BAT and XRT data as a single continuous observation of long lasting prompt emission.

The fast and autonomous response of the Swift satellite to newly detected Gamma‐Ray Bursts (GRBs) has provided a new view on their X‐ray and optical afterglows. We present here the X‐ray Telescope observations of GRB 050607. The striking feature of the X‐ray emission is the intense flaring activity during the early afterglow phase, indicative of central engine activity extended to several hundred seconds after the burst detection. The flares have very rapid timing variations and asymmetric shapes, similar to the FREDs that are frequently observed in the prompt GRB emission. After the flares, the X‐ray lightcurve entered a phase of slow decay during which the forward shocks were probably being refreshed, followed by a late steepening consistent with the standard external shock model. Analysis of the X‐ray emission showed spectral variations during the flares, with a harder spectrum at the flares onset and a softer component that lingered longer, as each flare decayed.

The Swift X‐ray Telescope is designed to make astrometric, spectroscopic and photometric observations of the X‐ray emission from Gamma‐Ray Bursts and their afterglows in the 0.2–10 keV energy band. Here we report some results on the in‐flight calibration of the Swift XRT effective area obtained analyzing observations of cosmic sources with different the analysis of cosmic sources intrinsic spectra and using the on‐ground calibration and ray‐tracing simulations as a starting point Our analysis includes the study of the effective area for different XRT operating modes.

We present observations of XRF 050406, an X‐ray flash with a relatively low fluence (∼ 10−7 erg cm−2 in the 15–350 keV band), a soft spectrum (photon index Γγ = 2.65), no significant flux above ∼ 50 keV and a peak energy Ep < 15 keV. XRF 050406 is the first burst detected by Swift clearly showing a flare in its X‐ray light curve. The flare peaks 210 s after the BAT trigger, presents a flux variation δF/F ∼ 6 in a timescale δt/tpeak ≪ 1 and a measured fluence of 1–15% of the prompt one. We argue that the producing mechanism is late internal shocks, which implies that the central engine is still active at 210 s, though with a reduced power with respect to the prompt emission. The X‐ray light curve flattens to a more shallow slope with a decay index of ∼ 0.5 after ∼ 4400 s, also supporting continued central engine activity.

The Swift X-ray Telescope (XRT) focal plane camera is a front-illuminated MOS CCD, providing a spectral response kernel of 144 eV FWHM at 6.5 keV. We describe the CCD calibration program based on celestial and on-board calibration sources, relevant in-flight experiences, and developments in the CCD response model. We illustrate how the revised response model describes the calibration sources well. Loss of temperature control motivated a laboratory program to re-optimize the CCD substrate voltage, we describe the small changes in the CCD response that would result from use of a substrate voltage of 6V.

We present optical observations of the short/hard gamma‐ray burst GRB 050709, the first such event with an identified optical counterpart. The object is located inside a galaxy at redshift z = 0.1606 ± 0.0002 but slightly off‐center. Late‐time monitoring places strong limits on any supernova simultaneous with the GRB. The host galaxy is not of early type: it has blue colours and a star formation rate of ∼ 2–3.5 M⊙ yr−1.

The Swift X‐ray Telescope autonomously refines the Burst Alert Telescope positions (∼1–4′ uncertainty) to better than 5 arcsec, within 5 seconds of target acquisition by the observatory for typical bursts. The results of the rapid positioning capability of the XRT are presented here for both known sources and newly discovered GRBs, demonstrating the ability to automatically utilise one of two integration times according to the burst brightness, and to correct the position for alignment offsets caused by the fast pointing performance and variable thermal environment of the satellite as measured by the Telescope Alignment Monitor. We present an evaluation of the position accuracy for both the onboard centroiding software and the ground software for the calibration targets and show that a significant improvement in position accuracy is obtained if the boresight detector position is optimised relative to the spacecraft pointing. Finally, we present an updated catalogue of Swift GRB X‐ray positions obtained in Photon Counting Mode using the improved, calibrated boresight.

We present the current on‐orbit calibration and operational plans for the Swift XRT. The XRT is a largely autonomous instrument and requires very little manual commanding for normal operations. A detailed calibration plan is being developed to verify the instrumental performance on‐orbit, including effective area, point spread function, vignetting, spectroscopic performance, and timing accuracy. Operational plans include regular calibration measurements using on‐board calibration sources as well as periodic calibration observations using celestial targets.

The X‐ray Telescope (XRT) for the SWIFT mission, built by the international consortium from Pennsylvania State University (US), University of Leicester (UK) and Osservatorio Astronomico di Brera (Italy), is already installed on the SWIFT spacecraft. The XRT has two key functions on SWIFT; to determine locations of GRBs to better than 5 arc seconds within 100 seconds of initial detection of a burst and to measure spectra and light curves of the X‐ray afterglow over around four orders of magnitude of decay in the afterglow intensity. This paper summarises the XRT performance, operating modes and sensitivity for the detection of prompt and extended X‐ray afterglows from gamma‐ray bursts. The performance characteristics have been determined from data taken during the ground calibration campaign at MPE’s Panter facility in September 2002.

The Swift XRT [4] uses a 12 shell grazing incidence mirror developed for the JET‐X telescope and an open electrode CCD detector developed for XMM‐Newton [9]. The mirror has recently undergone re‐characterization at the Panter facility and the flight detector is currently being calibrated at the University of Leicester. We present key performance characteristics of the mirror/detector combination, in particular, the point spread function (PSF) and centroiding capability and the impact of background events, as well as the telescope effective area and spectral response.

The Swift Gamma‐Ray Burst Explorer is designed to make prompt multiwavelength observations of Gamma‐Ray Bursts (GRBs) and their afterglows. The X‐ray Telescope (XRT) provides key capabilities that permit Swift to determine GRB positions with several arcsecond accuracy within 100 seconds of the burst onset. We present an overview of the XRT and its capabilities. The XRT is designed to observe GRB afterglows covering 7 orders of magnitude in flux in the 0.2–10 keV band, with completely autonomous operation. Accurate GRB positions are determined within seconds of target acquisition and are sent to the ground for distribution over the GCN. The XRT can also measure redshifts of GRBs if they have Fe line emission or other spectral features.

We present the first results obtained from a systematic search of periodicities carried out over two samples of X-ray sources: (i) those detected in the public ROSAT HRI fields, and (ii) a selected number of candidate High Mass X-ray Binaries in the Small Magellanic Cloud observed by BeppoSAX.

We present the X-ray variability properties of the TeV blazars PKS 2155-304 and MKN 421 as observed with BeppoSAX and ASCA. The minimum timescales of ∼ 1000 s are suggested. For PKS 2155-304 we found that the soft X-ray lags (relative to higher energies) are inversely correlated with the source intensity, i.e. the lag is longer when the source is fainter. In April 1998 a flare of MKN 421 was detected, during which higher energy X-rays lagged lower energy ones by ∼ 2500 s. The origin of these lags is briefly discussed.

We report on the BeppoSAX observations of four "extreme" BL Lacs, selected to have high synchrotron peak frequencies. All have been detected also in the PDS band. For 1ES 0120+340, PKS 0548-322 and H 2356-309 the spectrum is well fitted by a convex broken power-law, thus locating the synchrotron peak around 1 - 4 keV. 1ES 1426+428 presents a flat energy spectral index (alpha_x= 0.92) up to 100 keV, thus constraining the synchrotron peak to lie near or above that value. For their extreme properties, all sources could be strong TeV emitters., To appear in the proceedings of the conference "X-Ray Astronomy '99", Bologna, Italy, September 1999; 4 pages, 3 figures, uses bo99.sty. Corrected authors' list

We observed three blazars in an active state with BeppoSAX. For ON 231 and BL Lac, we detected simultaneously both the synchrotron and the Compton component. Fast time variability was present in both sources, only for the synchrotron component. PKS 2005-489 was observed in a very high state and the 0.1–200 keV X-ray spectrum is well accounted for by the sole synchrotron emission. No fast time variability was detected. The SED of the three sources are well described by pure SSC models.

In this paper we describe a neural network-based acoustic noise identification procedure. In particular, we have performed some experimental tests on a classic Michelson interferometer used as a microphone, that although different from the VIRGO antenna provides us with global information on the performance of neural networks. The preliminary results appear to be very promising for the analysis of real VIRGO outputs.

The BL Lac object Mkn 501 was observed with the BeppoSAX satellite on 7, 11, and 16 April 1997 during a phase of high activity at TeV energies, as monitored with the Whipple, HEGRA and CAT Cherenkov telescopes. Over the whole 0.1–200 keV range the spectrum was exceptionally hard (α⩽1, with Fν∝ν−α) indicating that the X-ray power output peaked at (or above) ∼100 keV. This represents a shift of at least two orders of magnitude with respect to previous observations of Mkn 501, a behavior never seen before in this or any other blazar. The overall X-ray spectrum hardens with increasing intensity and, at each epoch, it is softer at larger energies. The correlated variability from soft X-rays to the TeV band points to models in which the same population of relativistic electrons produces the X-ray continuum via synchrotron radiation and the TeV emission by inverse Compton scattering of the synchrotron photons or other seed photons.

ROSAT PSPC observations of the blazars PKS 1034–293 and PKS 1335–127 are presented. In both cases the spectra are well fitted by a single absorbed power law. For PKS 1034–293 we obtain F1keV=0.23±0.02 μJy, Γ=1.23+0.54−0.50, nH=1.31.7−1.2 (1020 cm−2) (90% uncertainty). The column density is significantly smaller than the galactic value derived from Stark et al. 1992. For PKS 1335–127 we find FkeV=0.50±0.02 μJy, Γ=2.29+0.55−0.51, nH=6.60+3.00−2.23 (1020 cm−2): in this case the column density derived from the fit is in good agreement with the recent determination by Jackson et al. 1993.