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  • 1
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    Geochemical features and effects on deep-seated fluids during the May-June 2012 southern Po Valley seismic sequence (2013)
    INGV
    Details
    Publication Date: 2017-04-04
    Description: A periodic sampling of the groundwaters and dissolved and free gases in selected deep wells located in the area affected by the May-June 2012 southern Po Valley seismic sequence has provided insight into seismogenic-induced changes of the local aquifer systems. The results obtained show progressive changes in the fluid geochemistry, allowing it to be established that deep-seated fluids were mobilized during the seismic sequence and reached surface layers along faults and fractures, which generated significant geochemical anomalies. The May-June 2012 seismic swarm (mainshock on May 29, 2012, M 5.8; 7 shocks M 〉5, about 200 events 3 〉 M 〉 5) induced several modifications in the circulating fluids. This study reports the preliminary results obtained for the geochemical features of the waters and gases collected over the epicentral area from boreholes drilled at different depths, thus intercepting water and gases with different origins and circulation. The aim of the investigations was to improve our knowledge of the fluids circulating over the seismic area (e.g. origin, provenance, interactions, mixing of different components, temporal changes). This was achieved by collecting samples from both shallow and deep-drilled boreholes, and then, after the selection of the relevant sites, we looked for temporal changes with mid-to-long-term monitoring activity following a constant sampling rate. This allowed us to gain better insight into the relationships between the fluid circulation and the faulting activity. The sampling sites are listed in Table 1, along with the analytical results of the gas phase.
    Description: Published
    Description: 815-821
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: open
    Keywords: Fluids ; Geochemistry ; Faults ; Temporal changes. ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Coupling geochemical and geophysical signatures to constrain strain changes along thrust faults (2013)
    Details
    Publication Date: 2017-04-04
    Description: Anomalous geochemical signals inferred from elemental and isotopic analyses on spring waters and soil degassing are often detected in response to tectonic loading along faults. Recent results highlighted how the geochemical anomalies are closely related to episodes of crustal deformation. In the present study, the carbon dioxide and radon from soil degassing and the geochemical features of springs spatially related to fault zones in the Friuli-Venezia Giulia region (north-eastern Italy), a seismic-prone area, have been coupled with crustal deformation analyses to better define the possible correlations between fluctuations of geochemical parameters and seismicity, with the aim of gaining new information about local geodynamic processes. The natural CO2 and Rn degassing was evaluated by a soil gas survey carried out by a grid of about 100 measuring sites located over the area that had been hit by strong earthquakes, in the past (Gemona – Idrija 1511, Raveo 1700, Tolmezzo 1788 and 1928, Gemona 1976). The results obtained show a significant amount of crustal-originated gases, especially CO2, possibly related to decarbonation reactions and stress accumulation occurring in deep-seated structures. The spring waters show, in some cases, anomalous geochemical transients, in particular concerning the chloride and Rn concentration, that are not related to seasonal changes and interpreted to reflect distinct fluid pressure regimes within the fault zone, yielding the leakage of pore fluids into the country-rock aquifers. In particular, the changes in the chloride content have been tentatively modeled in terms of pore-fluid expulsion from compacting clays during pressure gradients at shallow crustal levels. The flow regimes and chemical evolution have been related to the strain computed at the outlet sites through the Gutenberg–Richter relation parameters and the regional value of the strain rate. The information provided here may be used to start up a long-term geochemical monitoring of this seismically active area able to detect the modifications occurring in the circulating fluids to gain a better insight on the relationships between the geochemistry of the fluids and the activity of the local seismogenic faults.
    Description: Published
    Description: 113-134
    Description: JCR Journal
    Description: restricted
    Keywords: earthquakes ; strain ; soil degassing ; geochemical transients ; Friuli ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 3
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    Study of the reflection spectrum of the accreting neutron star GX 3+1 using XMM-Newton and INTEGRAL (2015)
    Oxford University Press
    Details
    Publication Date: 2015-05-02
    Description: Broad emission features of abundant chemical elements, such as iron, are commonly seen in the X-ray spectra of accreting compact objects and their studies can provide useful information about the geometry of the accretion processes. In this work, we focus our attention on GX 3+1, a bright, persistent accreting low-mass X-ray binary, classified as an atoll source. Its spectrum is well described by an accretion disc plus a stable Comptonizing, optically thick corona which dominates the X-ray emission in the 0.3–20 keV energy band. In addition, four broad emission lines are found and we associate them with reflection of hard photons from the inner regions of the accretion disc, where Doppler and relativistic effects are important. We used self-consistent reflection models to fit the spectra of the 2010 XMM–Newton observation and the stacking of the whole data sets of 2010 INTEGRAL observations. We conclude that the spectra are consistent with reflection produced at ~10 gravitational radii by an accretion disc with an ionization parameter of  ~ 600 erg cm s –1 and viewed under an inclination angle of the system of ~35°. Furthermore, we detected for the first time for GX 3+1, the presence of a power-law component dominant at energies higher than 20 keV, possibly associated with an optically thin component of non-thermal electrons.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    SAX J1808.4-3658, an accreting millisecond pulsar shining in gamma rays? (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-02
    Description: We report the detection of a possible gamma-ray counterpart of the accreting millisecond pulsar SAX J1808.4–3658. The analysis of ~6 yr of data from the Large Area Telescope on board the Fermi gamma-ray Space Telescope ( Fermi -LAT) within a region of 15° radius around the position of the pulsar reveals a point gamma-ray source detected at a significance of ~6 (test statistic TS = 32), with a position compatible with that of SAX J1808.4–3658 within the 95 per cent confidence level. The energy flux in the energy range between 0.6 and 10 GeV amounts to (2.1 ± 0.5) x 10 –12  erg cm –2  s –1 and the spectrum is represented well by a power-law function with photon index 2.1 ± 0.1. We searched for significant variation of the flux at the spin frequency of the pulsar and for orbital modulation, taking into account the trials due to the uncertainties in the position, the orbital motion of the pulsar and the intrinsic evolution of the pulsar spin. No significant deviation from a constant flux at any time-scale was found, preventing a firm identification via time variability. Nonetheless, the association of the LAT source as the gamma-ray counterpart of SAX J1808.4–3658 would match the emission expected from the millisecond pulsar, if it switches on as a rotation-powered source during X-ray quiescence.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Discovery of hard phase lags in the pulsed emission of GRO J1744-28 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-09-14
    Description: We report on the discovery and energy dependence of hard phase lags in the 2.14 Hz pulsed profiles of GRO J1744–28. We used data from XMM–Newton and NuSTAR . We were able to well constrain the lag spectrum with respect to the softest (0.3–2.3 keV) band: the delay shows increasing lag values reaching a maximum delay of ~12 ms, between 6 and 6.4 keV. After this maximum, the value of the hard lag drops to ~7 ms, followed by a recovery to a plateau at ~9 ms for energies above 8 keV. NuSTAR data confirm this trend up to 30 keV, but the measurements are statistically poorer, and therefore, less constraining. The lag-energy pattern up to the discontinuity is well described by a logarithmic function. Assuming this is due to a Compton reverberation mechanism, we derive a size for the Compton cloud R cc  ~ 120 R g , consistent with previous estimates on the magnetospheric radius. In this scenario, the sharp discontinuity at ~6.5 keV appears difficult to interpret and suggests the possible influence of the reflected component in this energy range. We therefore propose the possible coexistence of both Compton and disc reverberation to explain the scale of the lags and its energy dependence.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    GRO J1744-28: an intermediate B-field pulsar in a low-mass X-ray binary (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-15
    Description: The bursting pulsar , GRO J1744–28, went again in outburst after ~18 yr of quiescence in 2014 mid-January. We studied the broad-band, persistent, X-ray spectrum using X-ray data from a XMM–Newton observation, performed almost at the peak of the outburst, and from a close INTEGRAL observation, performed 3 d later, thus covering the 1.3–70.0 keV band. The spectrum shows a complex continuum shape that cannot be modelled with standard high-mass X-ray pulsar models, nor by two-components models. We observe broad-band and peaked residuals from 4 to 15 keV, and we propose a self-consistent interpretation of these residuals, assuming they are produced by cyclotron absorption features and by a moderately smeared, highly ionized, reflection component. We identify the cyclotron fundamental at ~4.7 keV, with hints for two possible harmonics at ~10.4 and ~15.8 keV. The position of the cyclotron fundamental allows an estimate for the pulsar magnetic field of (5.27 ± 0.06) 10 11  G, if the feature is produced at its surface. From the dynamical and relativistic smearing of the disc reflected component, we obtain a lower limit estimate for the truncated accretion disc inner radius (100  R g ) and for the inclination angle (18°–48°). We also detect the presence of a softer thermal component that we associate with the emission from an accretion disc truncated at a distance from the pulsar of 50–115  R g . From these estimates, we derive the magnetospheric radius for disc accretion to be ~0.2 times the classical Alfvén radius for radial accretion.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 7
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    Broad-band spectral analysis of the accreting millisecond X-ray pulsar SAX J1748.9-2021 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-20
    Description: We analysed a 115-ks XMM–Newton observation and the stacking of 8 d of INTEGRAL observations, taken during the raise of the 2015 outburst of the accreting millisecond X-ray pulsar SAX J1748.9–2021. The source showed numerous type-I burst episodes during the XMM–Newton observation, and for this reason we studied separately the persistent and burst epochs. We described the persistent emission with a combination of two soft thermal components, a cold thermal Comptonization component (~2 keV) and an additional hard X-ray emission described by a power law ( ~ 2.3). The continuum components can be associated with an accretion disc, the neutron star (NS) surface and a thermal Comptonization emission coming out of an optically thick plasma region, while the origin of the high-energy tail is still under debate. In addition, a number of broad ( = 0.1–0.4 keV) emission features likely associated with reflection processes have been observed in the XMM–Newton data. The estimated 1.0–50 keV unabsorbed luminosity of the source is ~5 x 10 37  erg s –1 , about 25 per cent of the Eddington limit assuming a 1.4 M NS. We suggest that the spectral properties of SAX J1748.9–2021 are consistent with a soft state, differently from many other accreting X-ray millisecond pulsars which are usually found in the hard state. Moreover, none of the observed type-I burst reached the Eddington luminosity. Assuming that the burst ignition and emission are produced above the whole NS surface, we estimate an NS radius of ~7–8 km, consistent with previous results.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Testing rate-dependent corrections on timing mode EPIC-pn spectra of the accreting neutron star GX 13+1 (2014)
    Oxford University Press
    Details
    Publication Date: 2014-11-01
    Description: When the EPIC-pn instrument on board XMM–Newton is operated in Timing mode, high count rates (〉100 counts s –1 ) of bright sources may affect the calibration of the energy scale, resulting in a modification of the real spectral shape. The corrections related to this effect are then strongly important in the study of the spectral properties. Tests of these calibrations are more suitable in sources which spectra are characterized by a large number of discrete features. Therefore, in this work, we carried out a spectral analysis of the accreting neutron star GX 13+1, which is a dipping source with several narrow absorption lines and a broad emission line in its spectrum. We tested two different correction approaches on an XMM–Newton EPIC-pn observation taken in Timing mode: the standard rate-dependent charge transfer inefficiency (RDCTI or epfast ) and the new, rate-dependent pulse height amplitude (RDPHA) corrections. We found that, in general, the two corrections marginally affect the properties of the overall broad-band continuum, while hints of differences in the broad emission line spectral shape are seen. On the other hand, they are dramatically important for the centroid energy of the absorption lines. In particular, the RDPHA corrections provide a better estimate of the spectral properties of these features than the RDCTI corrections. Indeed the discrete features observed in the data, applying the former method, are physically more consistent with those already found in other Chandra and XMM–Newton observations of GX 13+1.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 9
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    Suzaku broad-band spectrum of 4U 1705-44: probing the reflection component in the hard state (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-06
    Description: Iron emission lines at 6.4–6.97 keV, identified with Kα radiative transitions, are among the strongest discrete features in the X-ray band. These are one of the most powerful probes to infer the properties of the plasma in the innermost part of the accretion disc around a compact object. In this paper, we present a recent Suzaku observation, 100-ks effective exposure, of the atoll source and X-ray burster 4U 1705–44, where we clearly detect signatures of a reflection component which is distorted by the high-velocity motion in the accretion disc. The reflection component consists of a broad iron line at about 6.4 keV and a Compton bump at high X-ray energies, around 20 keV. All these features are consistently fitted with a reflection model, and we find that in the hard state the smearing parameters are remarkably similar to those found in a previous XMM–Newton observation performed in the soft state. In particular, we find that the inner disc radius is R in  = 17 ± 5 R g (where R g is the gravitational radius, GM / c 2 ), the emissivity dependence from the disc radius is r –2.5 ± 0.5 , the inclination angle with respect to the line of sight is i  = 43° ± 5°, and the outer radius of the emitting region in the disc is R out  〉 200 R g . We note that the accretion disc does not appear to be truncated at large radii, although the source is in a hard state at ~3 per cent of the Eddington luminosity for a neutron star. We also find evidence of a broad emission line at low energies, at 3.03 ± 0.03 keV, compatible with emission from mildly ionized argon (Ar XVI–XVII). Argon transitions are not included in the self-consistent reflection models that we used and we therefore added an extra component to our model to fit this feature. The low-energy line appears compatible with being smeared by the same inner disc parameters found for the reflection component.
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    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 10
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    Timing of the accreting millisecond pulsar SAX J1748.9-2021 during its 2015 outburst (2016)
    Oxford University Press
    Details
    Publication Date: 2016-04-23
    Description: We report on the timing analysis of the 2015 outburst of the intermittent accreting millisecond X-ray pulsar SAX J1748.9–2021 observed on March 4 by the X-ray satellite XMM–Newton . By phase connecting the time of arrivals of the observed pulses, we derived the best-fitting orbital solution for the 2015 outburst. We investigated the energy pulse profile dependence finding that the pulse fractional amplitude increases with energy while no significant time lags are detected. Moreover, we investigated the previous outbursts from this source, finding previously undetected pulsations in some intervals during the 2010 outburst of the source. Comparing the updated set of orbital parameters, in particular the value of the time of passage from the ascending node, with the orbital solutions reported from the previous outbursts, we estimated for the first time the orbital period derivative corresponding with $\dot{P}_{{\rm orb}}=(1.1\pm 0.3)\times 10^{-10}$  s s –1 . We note that this value is significant at 3.5 confidence level, because of significant fluctuations with respect to the parabolic trend and more observations are needed in order to confirm the finding. Assuming the reliability of the result, we suggest that the large value of the orbital-period derivative can be explained as a result of a highly non-conservative mass transfer driven by emission of gravitational waves, which implies the ejection of matter from a region close to the inner Lagrangian point. We also discuss possible alternative explanations.
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    Topics: Physics
    Published by Oxford University Press
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