arXiv subjects

M. Feroci

Publications and source records attributed to M. Feroci.

At least 145 records · Page 8Linked to original sources

arXiv2007

SuperAGILE: the hard X-ray Imager for the AGILE space mission

SuperAGILE is a coded mask experiment based on silicon microstrip detectors. It operates in the 15-45 keV nominal energy range, providing crossed one-dimensional images of the X-ray sky with an on-axis angular resolution of 6 arcmin, over a field of view in excess of 1 steradian. It was designed as the hard X-ray monitor of the AGILE space mission, a small satellite of the Italian Space Agency devoted to image the gamma-ray sky in the 30 MeV - 50 GeV energy band. The AGILE mission was launched in a low-earth orbit on 23^{rd} April 2007. In this paper we describe the SuperAGILE experiment, its construction and test processes, and its performance before flight, based on the on-ground test and calibrations.

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arXiv2006

Scientific performances of the XAA1.2 front-end chip for silicon microstrip detectors

The XAA1.2 is a custom ASIC chip for silicon microstrip detectors adapted by Ideas for the SuperAGILE instrument on board the AGILE space mission. The chip is equipped with 128 input channels, each one containing a charge preamplifier, shaper, peak detector and stretcher. The most important features of the ASIC are the extended linearity, low noise and low power consumption. The XAA1.2 underwent extensive laboratory testing in order to study its commandability and functionality and evaluate its scientific performances. In this paper we describe the XAA1.2 features, report the laboratory measurements and discuss the results emphasizing the scientific performances in the context of the SuperAGILE front-end electronics.

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arXiv2006

Long term spectral variability in the Soft Gamma-ray Repeater SGR 1900+14

We present a systematic analysis of all the BeppoSAX data of SGR1900+14. The observations spanning five years show that the source was brighter than usual on two occasions: ~20 days after the August 1998 giant flare and during the 10^5 s long X-ray afterglow following the April 2001 intermediate flare. In the latter case, we explore the possibility of describing the observed short term spectral evolution only with a change of the temperature of the blackbody component. In the only BeppoSAX observation performed before the giant flare, the spectrum of the SGR1900+14 persistent emission was significantly harder and detected also above 10 keV with the PDS instrument. In the last BeppoSAX observation (April 2002) the flux was at least a factor 1.2 below the historical level, suggesting that the source was entering a quiescent period.

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arXiv2006

Five years of SGR 1900+14 observations with BeppoSAX

We present a systematic analysis of all the BeppoSAX data of the soft gamma-ray repeater SGR 1900+14: these observations allowed us to study the long term properties of the source quiescent emission. In the observation carried out before the 1998 giant flare the spectrum in the 0.8-10 keV energy range was harder and there was evidence for a 20-150 keV emission, possibly associated with SGR 1900+14. This possible hard tail, if compared with the recent INTEGRAL detection of SGR 1900+14, has a harder spectrum (power-law photon index ~1.6 versus ~3) and a 20-100 keV flux ~4 times larger. In the last BeppoSAX observation (April 2002), while the source was entering the long quiescent period that lasted until 2006, the 2-10 keV flux was ~25% below the historical level. We also studied in detail the spectral evolution during the 2001 flare afterglow. This was characterized by a softening that can be interpreted in terms of a cooling blackbody-like component.

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arXiv2006

The first XMM-Newton observations of the Soft Gamma-ray Repeater SGR 1900+14

A ~50 ks XMM-Newton observation of SGR 1900+14 has been carried out in September 2005, after almost three years during which no bursts were detected from this soft gamma-ray repeater. The 0.8-10 keV spectrum was well fit by a power law plus blackbody model with photon index 1.9+/-0.1, temperature kT=0.47+/-0.02 keV and N_H = (2.12+/-0.08)x10^22 cm^-2, similar to previous observations of this source. The flux was ~5x10^{-12} erg/cm2/s, a factor 2 dimmer than the typical value and the smallest ever seen from SGR 1900+14. The long term fading of the persistent emission has been interrupted by the recent burst reactivation of the source. A target of opportunity XMM-Newton observation performed in April 2006 showed a flux ~15% higher. This variation was not accompanied by significant changes in the spectrum, pulsed fraction and light curve profile. We searched for emission and absorption lines in the spectra of the two observations, with negative results and setting tight upper limits of 50-200 eV (3 sigma), depending on the assumed line energy and width, on the equivalent width of lines in the 1-9 keV range.

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arXiv2006

Opening a New Window to Fundamental Physics and Astrophysics: X-ray Polarimetry

An extensive theoretical literature predicts that X-ray Polarimetry can directly determine relevant physical and geometrical parameters of astrophysical sources, and discriminate between models further than allowed by spectral and timing data only. X-ray Polarimetry can also provide tests of Fundamental Physics. A high sensitivity polarimeter in the focal plane of a New Generation X-ray telescope could open this new window in the High Energy Sky.

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arXiv2006

XMM-Newton observation of the Soft Gamma Ray Repeater SGR 1627-41 in a low luminosity state

The sky region containing the soft gamma-ray repeater SGR 1627-41 has been observed three times with XMM-Newton in February and September 2004. SGR 1627-41 has been detected with an absorbed flux of ~9x10^{-14} erg cm^{-2} s^{-1} (2-10 keV). For a distance of 11 kpc, this corresponds to a luminosity of ~3x10^{33} erg s^{-1}, the smallest ever observed for a Soft Gamma Repeater and possibly related to the long period of inactivity of this source. The observed flux is smaller than that seen with Chandra in 2001-2003, suggesting that the source was still fading and had not yet reached a steady quiescent level. The spectrum is equally well fit by a steep power law (photon index \~3.2) or by a blackbody with temperature kT~0.8 keV. We also report on the INTEGRAL transient IGR J16358-4726 that lies at ~10' from SGR 1627-41. It was detected only in September 2004 with a luminosity of ~4x10^{33} erg s^{-1} (for d=7 kpc), while in February 2004 it was at least a factor 10 fainter.

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arXiv2005

Two years of INTEGRAL monitoring of the Soft Gamma-Ray Repeater SGR 1806-20: from quiescence to frenzy

SGR 1806-20 has been observed for more than 2 years with the INTEGRAL satellite. In this period the source went from a quiescent state into a very active one culminating in a giant flare on December 27 2004. Here we report on the properties of all the short bursts detected with INTEGRAL before the giant flare. We derive their number-intensity distribution and confirm the hardness-intensity correlation for the bursts found by Gotz et al. (2004a). Our sample includes a very bright outburst that occurred on October 5 2004, during which over one hundred bursts were emitted in 10 minutes, involving an energy release of 3 x 1E42 erg. We present a detailed analysis of it and discuss our results in the framework of the magnetar model.

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arXiv2005

The BeppoSAX catalog of GRB X-ray afterglow observations

We present the X-ray afterglow catalog of BeppoSAX from the launch of the satellite to the end of the mission. Thirty-three X-ray afterglows were securely identified based on their fading behavior out of 39 observations. We have extracted the continuum parameters (decay index, spectral index, flux, absorption) for all available afterglows. We point out a possible correlation between the X-ray afterglow luminosity and the energy emitted during the prompt $γ$-ray event. We do not detect a significant jet signature within the afterglows, implying a lower limit on the beaming angle, neither a standard energy release when X-ray fluxes are corrected for beaming. Our data support the hypothesis that the burst should be surrounded by an interstellar medium rather than a wind environment, and that this environment should be dense. This may be explained by a termination shock located near the burst progenitor. We finally point out that some dark bursts may be explained by an intrinsic faintness of the event, while others may be strongly absorbed.

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arXiv2005

The puzzling case of GRB 990123: prompt emission and broad-band afterglow modeling

We report on BeppoSAX simultaneous X- and gamma-ray observations of the bright GRB 990123. We present the broad-band spectrum of the prompt emission, including optical, X- and gamma-rays, confirming the suggestion that the emission mechanisms at low and high frequencies must have different physical origins. In the framework of the standard fireball model, we discuss the X-ray afterglow observed by the NFIs and its hard X-ray emission up to 60 keV several hours after the burst, detected for about 20 ks by the PDS. Considering the 2-10 keV and optical light curves, the 0.1-60 keV spectrum during the 20 ks in which the PDS signal was present and the 8.46 GHz upper limits, we find that the multi-wavelength observations cannot be readily accommodated by basic afterglow models. While the temporal and spectral behavior of the optical afterglow is possibly explained by a synchrotron cooling frequency between the optical and the X-ray energy band during the NFIs observations, in X-rays this assumption only accounts for the slope of the 2-10 keV light curve, but not for the flatness of the 0.1-60 keV spectrum. Including the contribution of Inverse Compton (IC) scattering, we solve the problem of the flat X-ray spectrum and justify the hard X-ray emission; we suggest that the lack of a significant detection of 15-60 keV emission in the following 75 ks and last 70 ks spectra, should be related to poorer statistics rather than to an important suppression of IC contribution. However, considering also the radio band data, we find the 8.46 GHz upper limits violated. On the other hand, leaving unchanged the emission mechanism requires modifying the hydrodynamics by invoking an ambient medium whose density rises rapidly with radius and by having the shock losing energy. Thus we are left with an open puzzle which requires further inspection.

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arXiv2005

The GRB of 1999 January 23: prompt emission and broad-band afterglow modeling

We report on BeppoSAX simultaneous X- and gamma-ray observations of the bright gamma-ray burst (GRB) 990123. We present the broad-band spectrum of the prompt emission, including optical, X- and gamma-rays, confirming the suggestion that the emission mechanisms at low and high frequencies must have different physical origins. We discuss the X-ray afterglow observed by the Narrow Field Instruments (NFIs) on board BeppoSAX and its hard X-ray emission up to 60 keV several hours after the burst, in the framework of the standard fireball model. The effects of including an important contribution of Inverse Compton scattering or modifying the hydrodynamics are studied.

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arXiv2005

GRB990123: multiwavelength afterglow study

We report on the BeppoSAX and multiwavelength data analysis of the afterglow of Gamma-Ray Burst (GRB) 990123. Mainly due to its exceptional brightness, this is the only source for which the Wide Field Cameras have allowed an early detection of the X-ray afterglow between about 20 and 60 min after the GRB trigger. Besides, again for the first time, high-energy emission from the afterglow was detected up to 60 keV. The backwards extrapolation of the afterglow decay smoothly reconnects with the late GRB emission, thus indicating that both are consistent with being produced by the same phenomenon. For the X-ray afterglow we found a power-law decay with index alpha_X = 1.46 +/- 0.04; the spectrum has a power-law shape with photon index Gamma about 2. An extensive set of multiwavelength observations on the afterglow, collected from the literature and made during the BeppoSAX pointing, allowed constructing a Spectral Flux Distribution. We performed an analysis of the GRB afterglow emission in the context of the "fireball" model.

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arXiv2005

The puzzling case of GRB 990123: multiwavelength afterglow study

We report on the BeppoSAX data analysis of the afterglow of Gamma-Ray Burst (GRB) 990123, one of the brightest GRBs detected by BeppoSAX. Mainly due to its exceptional brightness, this is the only source for which the Wide Field Cameras have allowed an early detection of the X-ray afterglow between about 20 and 60 min after the GRB trigger. Besides, again for the first time, high-energy emission from the afterglow was detected up to 60 keV. For the X-ray afterglow we found a power-law decay with index alpha = 1.46 +/- 0.04; the spectrum has a power-law shape with photon index Gamma about 1.9. The backward extrapolation of the afterglow decay smoothly reconnects with the late GRB emission, thus suggesting that both emissions are produced by the same phenomenon. An extensive set of multiwavelength observations for the GRB 990123 afterglow made during the BeppoSAX pointing was collected from the literature. The hard X-ray to radio range coverage allowed to construct a spectral flux distribution and to perform an analysis of the GRB afterglow in the context of the "fireball" model. We also report the results of temporal and spectral analysis of an X-ray source serendipitously observed about 22 arcmin north of the GRB afterglow, along with the optical spectroscopy of its possible counterpart to establish the nature of this source.

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arXiv2005

A XMM-Newton View of the Soft Gamma-ray Repeater SGR 1806--20: Long Term Variability in the pre-Super Giant Flare Epoch

The low energy (<10 keV) X-ray emission of the Soft Gamma-ray Repeater SGR1806-20 has been studied by means of four XMM-Newton observations carried out in the last two years, the latter performed in response to a strong sequence of hard X-ray bursts observed on 2004 October 5. The source was caught in different states of activity: over the 2003-2004 period the 2-10 keV flux doubled with respect to the historical level observed previously. The long term raise in luminosity was accompanied by a gradual hardening of the spectrum, with the power law photon index decreasing from 2.2 to 1.5, and by a growth of the bursting activity. The pulse period measurements obtained in the four observations are consistent with an average spin-down rate of 5.5x10e-10 s/s, higher than the values observed in the previous years. The long-term behavior of SGR1806-20 exhibits the correlation between spectral hardness and spin-down rate previously found only by comparing the properties of different sources (both SGRs and Anomalous X-ray Pulsars). The best quality spectrum (obtained on 6 September 2004) cannot be fitted by a single power law, but it requires an additional blackbody component (kT=0.79 keV, R_BB = 1.9 (d/15 kpc)^2 km), similar to the spectra observed in other SGRs and in Anomalous X-ray Pulsars. No spectral lines were found in the persistent emission, with equivalent width upper limits in the range 30-110 eV. Marginal evidence for an absorption feature at 4.2 keV is present in the cumulative spectrum of 69 bursts detected in September-October 2004.

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arXiv2004

Probing the environment in Gamma-ray bursts: the case of an X-ray precursor, afterglow late onset and wind vs constant density profile in GRB011121 and GRB011211

In this paper we present BeppoSax and XMM observations of two long Gamma-ray bursts, the X-ray rich event of December 11, 2001 (GRB011211) and the hard and very bright event of November 21, 2001 (GRB011121). In both events we find evidence of a late X-ray burst, taking place several minutes after the prompt emission. The temporal and spectral behaviour of this phenomenon suggest that it represents the onset of the afterglow. Broad band spectral modelling of the afterglow indicate that the fireball evolution in the December burst takes place in a ISM environment. On the contrary in the November burst the wind case is revealed by an X-ray decay slower than that observed in the optical ($δ_{\rm X}=1.29\pm0.04$ vs $δ_{\rm O}=1.66\pm0.06$). The wind profile should change into a constant density profile at large radii, in order to reconcile late-time radio data with a jet. Two other results are obtained for this burst. An X-ray burst is preceding by about 30 s the much harder GRB. Contrary to the prediction of simple models of precursor activity for collapsars, its spectrum is not consistent with a black body. Finally, a substantial absorption column ($\NH=(7\pm2)\times10^{22}$ cm$^{-2}$) is detected during the early part of the prompt emission. This is much greater than that of the wind, and it is thus likely associated with the region surrounding the burst.

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arXiv2004

The Interplanetary Network Supplement to the BATSE Catalogs of Untriggered Cosmic Gamma Ray Bursts

We present Interplanetary Network (IPN) detection and localization information for 211 gamma-ray bursts (GRBs) observed as untriggered events by the Burst and Transient Source Experiment (BATSE), and published in catalogs by Kommers et al. (2001) and Stern et al. (2001). IPN confirmations have been obtained by analyzing the data from 11 experiments. For any given burst observed by BATSE and one other distant spacecraft, arrival time analysis (or ``triangulation'') results in an annulus of possible arrival directions whose half-width varies between 14 arcseconds and 5.6 degrees, depending on the intensity, time history, and arrival direction of the burst, as well as the distance between the spacecraft. This annulus generally intersects the BATSE error circle, resulting in a reduction of the area of up to a factor of ~650. When three widely separated spacecraft observed a burst, the result is an error box whose area is as much as 30000 times smaller than that of the BATSE error circle. Because the IPN instruments are considerably less sensitive than BATSE, they generally did not detect the weakest untriggered bursts, but did detect the more intense ones which failed to trigger BATSE when the trigger was disabled. In a few cases, we have been able to identify the probable origin of bursts as soft gamma repeaters. The vast majority of the IPN-detected events, however, are GRBs, and the confirmation of them validates many of the procedures utilized to detect BATSE untriggered bursts.

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arXiv2004

The prompt X-ray emission of GRB011211: possible evidence of a transient absorption feature

We report on observation results of the prompt X- and gamma-ray emission from GRB011211. This event was detected with the Gamma-Ray Burst Monitor and one of the Wide Field Cameras aboard the BeppoSAX satellite. The optical counterpart to the GRB was soon identified and its redshift determined (z = 2.140), while with the XMM-Newton satellite, the X-ray afterglow emission was detected. Evidence of soft X-ray emission lines was reported by Reeves et al. (2002), but not confirmed by other authors. In investigating the spectral evolution of the prompt emission we find the possible evidence of a transient absorption feature at 6.9^{+0.6}_{-0.5} keV during the rise of the primary event. The significance of the feature is derived with non parametric tests and numerical simulations, finding a chance probability which ranges from 3x10^{-3} down to 4x10^{-4}. The feature shows a Gaussian profile and an equivalent width of 1.2^{+0.5}_{-0.6} keV. We discuss our results and their possible interpretation.

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arXiv2004

Prompt and afterglow X-ray emission from the X-Ray Flash of 2002 April 27

We report on the X-ray observations of the X-ray flash (XRF) which occurred on 2002 April 27, three days before BeppoSAX was switched off. The event was detected with the BeppoSAX Wide Field Cameras but not with the Gamma ray Burst Monitor. A follow-up observation with the BeppoSAX Narrow Field Instruments was soon performed and a candidate afterglow source was discovered. We present the results obtained. We also include the results obtained from the observations of the XRF field with the Chandra X-ray satellite. The spectral analysis of the prompt emission shows that the peak energy of the EF(E) spectrum is lower than 5.5 keV, with negligible spectral evolution. The X-ray afterglow spectrum is consistent with a power law model with photon index of about 2, while the 2-10 keV flux fades as a power law with a decay index -1.33. Both these indices are typical of GRBs. A very marginal excess around 4.5-5 keV is found in the afterglow spectrum measured by BeppoSAX . As for many GRBs, the extrapolation of the 2-10 keV fading law back to the time of the prompt emission is consistent with the X-ray flux measured during the second part of the event. We estimate a possible range of values of the redshift and discuss our results in the light of current models of XRFs.

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