A. Tiengo

Istituto Universitario di Studi Superiori di Pavia, Ticinum, Lombardy, Italy

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Publications (192)598.37 Total impact

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    ABSTRACT: We report on the results of the first XMM-Newton satellite observation of the luminous and helium-rich O-type subdwarf BD +37{\deg} 1977 carried out in April 2014. X-ray emission is detected with a flux of about 4*10^(-14) erg/cm2/s (0.2-1.5 keV), corresponding to a f_X/f_bol ratio about 10^(-7); the source spectrum is very soft, and is well fit by the sum of two plasma components at different temperatures. Both characteristics are in agreement with what is observed in the main-sequence early-type stars, where the observed X-ray emission is due to turbulence and shocks in the stellar wind. A smaller but still significant stellar wind has been observed also in BD +37{\deg} 1977; therefore, we suggest that also in this case the detected X-ray flux has the same origin.
    Astronomy and Astrophysics 06/2015; DOI:10.1051/0004-6361/201526141 · 4.48 Impact Factor
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    ABSTRACT: We present the discovery of a strongly phase-variable absorption feature in the X-ray spectrum of the nearby, thermally-emitting, isolated neutron star RX J0720.4-3125. The absorption line was detected performing detailed phase-resolved spectroscopy in 20 XMM-Newton observations, covering the period May 2000 - September 2012. The feature has an energy of ~750eV, an equivalent width of ~30eV, and it is significantly detected for only ~20% of the pulsar rotation. The absorption feature appears to be stable over the timespan covered by the observations. Given its strong dependence on the pulsar rotational phase and its narrow width, a plausible interpretation is in terms of resonant proton cyclotron absorption/scattering in a confined magnetic structure very close to the neutron star surface. The inferred field in such a magnetic loop is B_loop ~ 2 x 10^{14} G, a factor of ~7 higher than the surface dipolar magnetic field.
    06/2015; 807(1). DOI:10.1088/2041-8205/807/1/L20
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    ABSTRACT: In 2013 April a new magnetar, SGR 1745−2900, was discovered as it entered an outburst, at only 2.4 arcsec angular distance from the supermassive black hole at the centre of the Milky Way, Sagittarius A*. SGR 1745−2900 has a surface dipolar magnetic field of ∼2 × 1014 G, and it is the neutron star closest to a black hole ever observed. The new source was detected both in the radio and X-ray bands, with a peak X-ray luminosity LX ∼ 5 × 1035 erg s−1. Here we report on the long-term Chandra (25 observations) and XMM-Newton (eight observations) X-ray monitoring campaign of SGR 1745−2900 from the onset of the outburst in 2013 April until 2014 September. This unprecedented data set allows us to refine the timing properties of the source, as well as to study the outburst spectral evolution as a function of time and rotational phase. Our timing analysis confirms the increase in the spin period derivative by a factor of ∼2 around 2013 June, and reveals that a further increase occurred between 2013 October 30 and 2014 February 21. We find that the period derivative changed from 6.6 × 10−12 to 3.3 × 10−11 s s−1 in 1.5 yr. On the other hand, this magnetar shows a slow flux decay compared to other magnetars and a rather inefficient surface cooling. In particular, starquake-induced crustal cooling models alone have difficulty in explaining the high luminosity of the source for the first ∼200 d of its outburst, and additional heating of the star surface from currents flowing in a twisted magnetic bundle is probably playing an important role in the outburst evolution.
    Monthly Notices of the Royal Astronomical Society 03/2015; 449(3):2685-2699. DOI:10.1093/mnras/stv480 · 5.23 Impact Factor
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    ABSTRACT: We report on an X-ray observation of the Be X-ray Binary Pulsar RX J0059.2-7138, performed by XMM-Newton in March 2014. The 19 ks long observation was carried out about three months after the discovery of the latest outburst from this Small Magellanic Cloud transient, when the source luminosity was Lx ~ 10$^{38}$ erg/s. A spin period of P=2.762383(5) s was derived, corresponding to an average spin-up of $\dot{P}_{\mathrm{spin}} = -(1.27\pm0.01)\times10^{-12}$ s $s^{-1}$ from the only previous period measurement, obtained more than 20 years earlier. The time-averaged continuum spectrum (0.2-12 keV) consisted of a hard power-law (photon index ~0.44) with an exponential cut-off at a phase-dependent energy (20-50 keV) plus a significant soft excess below about 0.5 keV. In addition, several features were observed in the spectrum: an emission line at 6.6 keV from highly ionized iron, a broad feature at 0.9-1 keV likely due to a blend of Fe L-shell lines, and narrow emission and absorption lines consistent with transitions in highly ionized oxygen, nitrogen and iron visible in the high resolution RGS data (0.4-2.1 keV). Given the different ionization stages of the narrow line components, indicative of photoionization from the luminous X-ray pulsar, we argue that the soft excess in RX J0059.2-7138 is produced by reprocessing of the pulsar emission in the inner regions of the accretion disc.
    Monthly Notices of the Royal Astronomical Society 03/2015; 449(4). DOI:10.1093/mnras/stv580 · 5.23 Impact Factor
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    ABSTRACT: The EXTraS project (Exploring the X-ray Transient and variable Sky) will harvest the hitherto unexplored temporal domain information buried in the serendipitous data collected by the European Photon Imaging Camera (EPIC) instrument onboard the ESA XMM-Newton X-ray observatory since its launch. This will include a search for fast transients, as well as a search and characterization of variability (both periodic and aperiodic) in hundreds of thousands of sources spanning more than nine orders of magnitude in time scale and six orders of magnitude in flux. X-ray results will be complemented by multiwavelength characterization of new discoveries. Phenomenological classification of variable sources will also be performed. All our results will be made available to the community. A didactic program in selected High Schools in Italy, Germany and the UK will also be implemented. The EXTraS project (2014-2016), funded within the EU/FP7 framework, is carried out by a collaboration including INAF (Italy), IUSS (Italy), CNR/IMATI (Italy), University of Leicester (UK), MPE (Germany) and ECAP (Germany).
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    ABSTRACT: Supergiant fast X-ray transients (SFXTs) are high mass X-ray binaries associated with OB supergiant companions and characterised by an X-ray flaring behaviour whose dynamical range reaches 5 orders of magnitude on timescales of a few hundred to thousands of seconds. Current investigations concentrate on finding possible mechanisms to inhibit accretion in SFXTs and explain their unusually low average X-ray luminosity. We present the Swift observations of an exceptionally bright outburst displayed by the SFXT IGR J17544-2619 on 2014 October 10 when the source achieved a peak luminosity of $3\times10^{38}$ erg s$^{-1}$. This extends the total source dynamic range to $\gtrsim$10$^6$, the largest (by a factor of 10) recorded so far from an SFXT. Tentative evidence for pulsations at a period of 11.6 s is also reported. We show that these observations challenge, for the first time, the maximum theoretical luminosity achievable by an SFXT and propose that this giant outburst was due to the formation of a transient accretion disc around the compact object.
    Astronomy and Astrophysics 02/2015; 576. DOI:10.1051/0004-6361/201525749 · 4.48 Impact Factor
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    ABSTRACT: This is a White Paper in support of the mission concept of the Large Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We discuss the potential of LOFT for the study of magnetospheres of isolated neutron stars. For a summary, we refer to the paper.
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    ABSTRACT: Diffuse radio emission was detected around the soft gamma-ray repeater SGR 1806-20, after its 2004 powerful giant flare. We study the possible extended X-ray emission at small scales around SGR 1806-20, in two observations by the High Resolution Camera Spectrometer (HRC-S) on board of the Chandra X-ray Observatory: in 2005, 115 days after the giant flare, and in 2013, during quiescence. We compare the radial profiles extracted from data images and PSF simulations, carefully considering various issues related with the uncertain calibration of the HRC PSF at sub-arcsecond scales. We do not see statistically significant excesses pointing to an extended emission on scales of arcseconds. As a consequence, SGR 1806-20 is compatible with being point-like in X-rays, months after the giant flare, as well as in quiescence.
    Journal of High Energy Astrophysics 11/2014; 3-4. DOI:10.1016/j.jheap.2014.10.001
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    ABSTRACT: X-ray observations of sdO stars are a useful tool to investigate their properties, but so far only two sdO stars were detected at X-rays. We observed a complete flux-limited sample of 19 sdO stars with the Chandra HRC-I camera to measure the count rate of the detected sources or to set a tight upper limit on it for the undetected sources. We obtained a robust detection of BD+37 1977 and Feige 34 and a marginal detection of BD+28 4211. The estimated luminosity of BD+37 1977 is above 10^31 erg/s, which is high enough to suggest the possible presence of an accreting compact companion. This possibility is unlikely for all the other targets (both detected and undetected), since in their case L_X < 10^30 erg/s. On the other hand, for all 19 targets the estimated value of L_X (or its upper limit) implies an X-ray/bolometric flux ratio that agrees with log(L_X/L_bol) = -6.7 +/- 0.5, which is the range of values typical of main-sequence and giant O stars. Therefore, for Feige 34 and BD+28 4211 the observed X-ray flux is most probably due to intrinsic emission. The same is possibile for the 16 undetected stars.
    Astronomy and Astrophysics 04/2014; 566. DOI:10.1051/0004-6361/201423571 · 4.48 Impact Factor
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    ABSTRACT: Little observational data are available on the weak stellar winds of hot subdwarf stars of B spectral type (sdB). Close binary systems composed of an sdB star and a compact object (white dwarf, neutron star or black hole) could be detected as accretion-powered X-ray sources. The study of their X-ray emission can probe the properties of line-driven winds of sdB stars that can not be derived directly from spectroscopy because of the low luminosity of these stars. Here we report on the first sensitive X-ray observations of two sdB binaries with compact companions. CD -30 11223 is the sdB binary with the shortest known orbital period (1.2 h) and its companion is certainly a white dwarf. PG 1232-136 is an sdB binary considered the best candidate to host a black hole companion. We observed these stars with XMM-Newton in August 2013 for 50 ks and in July 2009 for 36 ks, respectively. None of them was detected and we derived luminosity upper limits of about 1.5x10^29 erg/s for CD -30 11223 5x10^29 erg/s for PG 1232-136. The corresponding mass loss rate for PG 1232-136 is poorly constrained, owing to the unknown efficiency for black hole accretion. On the other hand, in the case of CD -30 11223 we could derive, under reasonable assumptions, an upper limit of about 3x10^-13 solar masses/yr on the wind mass loss rate from the sdB star. This is one of the few observational constraints on the weak winds expected in this class of low mass hot stars. We also report the results on the X-ray emission from a cluster of galaxies serendipitously discovered in the field of CD -30 11223.
    Monthly Notices of the Royal Astronomical Society 04/2014; 441(3). DOI:10.1093/mnras/stu773 · 5.23 Impact Factor
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    ABSTRACT: The source IGR J17200-3116 was discovered in the hard X-ray band by INTEGRAL. A periodic X-ray modulation at ~326 s was detected in its Swift light curves by our group (and subsequently confirmed by a Swift campaign). In this paper, we report on the analysis of all the Swift observations, which were collected between 2005 and 2011, and of a ~20 ks XMM-Newton pointing that was carried out in 2013 September. During the years covered by the Swift and XMM-Newton observations, the 1-10 keV fluxes range from ~1.5 to 4E-11 erg/cm^2/s. IGR J17200-3116 displays spectral variability as a function of the pulse phase and its light curves show at least one short (a few hundreds of seconds) dip, during which the flux dropped at 20-30% of the average level. Overall, the timing and spectral characteristics of IGR J17200-3116 point to an accreting neutron star in a high-mass system but, while the pulse-phase spectral variability can be accounted for by assuming a variable local absorbing column density, the origin of the dip is unclear. We discuss different possible explanations for this feature, favouring a transition to an ineffective accretion regime, instead of an enhanced absorption along the line of sight.
    Monthly Notices of the Royal Astronomical Society 04/2014; 441(2). DOI:10.1093/mnras/stu659 · 5.23 Impact Factor
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    ABSTRACT: An absorption feature, the properties of which strongly depend on the pulse phase, has been recently discovered in the X-ray spectrum of the soft gamma repeater SGR0418+5729. If interpreted as a proton cyclotron line, its energy implies a magnetic field ranging from 2× 1014 G to more than 1015 G, which confirms the magnetar interpretation for this source and provides us with the most direct measurement of the magnetic field intensity of an isolated neutron star. The lower value of the dipole field inferred from the timing parameters for SGR 0418+5729 (B = 6× 1012 G) requires that the high magnetic field responsible for the observed feature resides in a strong multi-polar component located close to the neutron star surface, in agreement with the predictions of the magnetar model. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Astronomische Nachrichten 03/2014; 335(3). DOI:10.1002/asna.201312031 · 1.12 Impact Factor
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    ABSTRACT: We report on the quiescent state of the Soft Gamma Repeater SGR 0501+4516 observed by XMM-Newton on 2009 August 30. The source exhibits an absorbed flux ~75 times lower than that measured at the peak of the 2008 outburst, and a rather soft spectrum, with the same value of the blackbody temperature observed with ROSAT back in 1992. This new observation is put into the context of all existing X-ray data since its discovery in August 2008, allowing us to complete the study of the timing and spectral evolution of the source from outburst until its quiescent state. The set of deep XMM-Newton observations performed during the few-years timescale of its outburst allows us to monitor the spectral characteristics of this magnetar as a function of its rotational period, and their evolution along these years. After the first ~10 days, the initially hot and bright surface spot progressively cooled down during the decay. We discuss the behaviour of this magnetar in the context of its simulated secular evolution, inferring a plausible dipolar field at birth of 3x10^14 G, and a current (magneto-thermal) age of ~10 kyr.
    Monthly Notices of the Royal Astronomical Society 12/2013; 438(4). DOI:10.1093/mnras/stt2432 · 5.23 Impact Factor
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    ABSTRACT: After more than ten years of operation of the EPIC camera on board the X-ray observatory XMM-Newton we have reviewed the status of its thin and medium filters by performing both analysis of data collected in-flight and laboratory measurements on on-ground back-up filters. We have investigated the status of the EPIC thin and medium filters by performing an analysis of the optical loading in the PN offset maps to gauge variations in the optical and UV transmission of the filters. We both investigated repeated observations of single optically bright targets and performed a statistical analysis of the extent of loading versus visual magnitude at different epochs. We report the results of these measurements.
    Proceedings of SPIE - The International Society for Optical Engineering 09/2013; DOI:10.1117/12.2030897 · 0.20 Impact Factor
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    ABSTRACT: After more than ten years of operation of the EPIC camera on board the X-ray observatory XMM-Newton, we have reviewed the status of its Thin and Medium filters by performing both laboratory measurements on back-up filters, and analysis of data collected in-flight. We have selected a set of Thin and Medium back-up filters among those still available in the EPIC consortium, and have started a program to investigate their status by different laboratory measurements including: UV/VIS transmission, X-ray transmission, RAMAN IR spectroscopy, X-Ray Photoelectron Spectroscopy, and Atomic Force Microscopy. We report the results of the measurements conducted up to now, and point out some lessons learned for the development and calibration programs of filters for X-ray detectors in future Astronomy missions.
    Proceedings of SPIE - The International Society for Optical Engineering 09/2013; DOI:10.1117/12.2030896 · 0.20 Impact Factor
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    ABSTRACT: Soft-γ-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are slowly rotating, isolated neutron stars that sporadically undergo episodes of long-term flux enhancement (outbursts) generally accompanied by the emission of short bursts of hard X-rays. This behaviour can be understood in the magnetar model, according to which these sources are mainly powered by their own magnetic energy. This is supported by the fact that the magnetic fields inferred from several observed properties of SGRs and AXPs are greater than-or at the high end of the range of-those of radio pulsars. In the peculiar case of SGR 0418+5729, a weak dipole magnetic moment is derived from its timing parameters, whereas a strong field has been proposed to reside in the stellar interior and in multipole components on the surface. Here we show that the X-ray spectrum of SGR 0418+5729 has an absorption line, the properties of which depend strongly on the star's rotational phase. This line is interpreted as a proton cyclotron feature and its energy implies a magnetic field ranging from 2 × 10(14) gauss to more than 10(15) gauss.
    Nature 08/2013; 500(7462):312-4. DOI:10.1038/nature12386 · 42.35 Impact Factor
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    ABSTRACT: The old pulsar PSR B0943+10 (P=1.1 s, characteristic age tau=5 Myr) is the best example of mode-switching radio pulsar. Its radio emission alternates between a highly organized state with regular drifting subpulses (B mode) and a chaotic emission pattern (Q mode). We present the results of XMM-Newton observations showing that the X-ray properties of PSR B0943+10 depend on its radio state (Hermsen et al. 2013). During the radio fainter state (Q mode) the X-ray flux is more than a factor two larger than during the B-mode and X-ray pulsations with about 50% pulsed fraction are detected. The X-ray emission of PSR B0943+10 in the B-mode is well described by thermal emission with blackbody temperature kT=0.26 keV coming from a small hot spot with luminosity of 7x10^28 erg/s, in good agreement with the prediction of the partially screened gap model, which also explains the properties of the radio emission in this mode. We derived an upper limit of 46% on the X-ray pulsed fraction in the B-mode, consistent with the geometry and viewing angle of PSR B0943+10 inferred from the radio data. The higher flux observed during the Q-mode is consistent with the appearance of an additional component with a power-law spectrum with photon index 2.2. We interpret it as pulsed non-thermal X-rays produced in the star magnetosphere. A small change in the beaming pattern or in the efficiency of acceleration of the particles responsible for the non-thermal emission can explain the reduced flux of this component during the radio B-mode.
    Monthly Notices of the Royal Astronomical Society 08/2013; 435(3). DOI:10.1093/mnras/stt1472 · 5.23 Impact Factor
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    ABSTRACT: Local-Group galaxies provide access to samples of X-ray source populations of whole galaxies. The XMM-Newton survey of the Small Magellanic Cloud (SMC) completely covers the bar and eastern wing with a 5.6 deg^2 area in the (0.2-12.0) keV band. To characterise the X-ray sources in the SMC field, we created a catalogue of point sources and sources with moderate extent. Sources with high extent (>40") have been presented in a companion paper. We searched for point sources in the EPIC images using sliding-box and maximum-likelihood techniques and classified the sources using hardness ratios, X-ray variability, and their multi-wavelength properties. The catalogue comprises 3053 unique X-ray sources with a median position uncertainty of 1.3" down to a flux limit for point sources of ~10^-14 erg cm^-2 s^-1 in the (0.2-4.5) keV band, corresponding to 5x10^33 erg s^-1 for sources in the SMC. We discuss statistical properties, like the spatial distribution, X-ray colour diagrams, luminosity functions, and time variability. We identified 49 SMC high-mass X-ray binaries (HMXB), four super-soft X-ray sources (SSS), 34 foreground stars, and 72 active galactic nuclei (AGN) behind the SMC. In addition, we found candidates for SMC HMXBs (45) and faint SSSs (8) as well as AGN (2092) and galaxy clusters (13). We present the most up-to-date catalogue of the X-ray source population in the SMC field. In particular, the known population of X-ray binaries is greatly increased. We find that the bright-end slope of the luminosity function of Be/X-ray binaries significantly deviates from the expected universal high-mass X-ray binary luminosity function.
    Astronomy and Astrophysics 07/2013; 558. DOI:10.1051/0004-6361/201219935 · 4.48 Impact Factor
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    ABSTRACT: The center of our Galaxy hosts a supermassive black hole, Sagittarius (Sgr) A*. Young, massive stars within 0.5 pc of SgrA* are evidence of an episode of intense star formation near the black hole a few Myr ago, which might have left behind a young neutron star traveling deep into SgrA*'s gravitational potential. On 2013 April 25, a short X-ray burst was observed from the direction of the Galactic center. Thanks to a series of observations with the Chandra and the Swift satellites, we pinpoint the associated magnetar at an angular distance of 2.4+/-0.3 arcsec from SgrA*, and refine the source spin period and its derivative (P=3.7635537(2) s and \dot{P} = 6.61(4)x10^{-12} s/s), confirmed by quasi simultaneous radio observations performed with the Green Bank (GBT) and Parkes antennas, which also constrain a Dispersion Measure of DM=1750+/-50 pc cm^{-3}, the highest ever observed for a radio pulsar. We have found that this X-ray source is a young magnetar at ~0.07-2 pc from SgrA*. Simulations of its possible motion around SgrA* show that it is likely (~90% probability) in a bound orbit around the black hole. The radiation front produced by the past activity from the magnetar passing through the molecular clouds surrounding the Galactic center region, might be responsible for a large fraction of the light echoes observed in the Fe fluorescence features.
    The Astrophysical Journal Letters 07/2013; 775(2). DOI:10.1088/2041-8205/775/2/L34 · 5.60 Impact Factor
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    ABSTRACT: The XMM-Newton survey of the Small Magellanic Cloud (SMC) yields a complete coverage of the bar and eastern wing in the 0.2-12.0keV band. This catalogue comprises 3053 unique X-ray point sources and sources with moderate extent that have been reduced from 5236 individual detections found in observations between April 2000 and April 2010. Sources have a median position uncertainty of 1.3" (1σ) and limiting fluxes down to ~1*10-14erg/s/cm2 in the 0.2-4.5keV band, corresponding to 5*1033erg/s for sources in the SMC. Sources have been classified using hardness ratios, X-ray variability, and their multi-wavelength properties. In addition to the main-field (5.58deg2) available outer fields have been included in the catalogue, yielding a total field area of 6.32deg2. X-ray sources with high extent (>40", e.g. supernova remnants and galaxy cluster) have been presented by Haberl et al. (2012, Cat. J/A+A/545/A128) (2 data files).

Publication Stats

2k Citations
598.37 Total Impact Points

Institutions

  • 2012–2015
    • Istituto Universitario di Studi Superiori di Pavia
      Ticinum, Lombardy, Italy
    • Los Alamos National Laboratory
      Los Alamos, California, United States
  • 2009–2014
    • INFN - Istituto Nazionale di Fisica Nucleare
      Frascati, Latium, Italy
  • 2006–2014
    • University of Pavia
      Ticinum, Lombardy, Italy
  • 2013
    • National Radio Astronomy Observatory
      Charlottesville, Virginia, United States
  • 2010
    • Università degli Studi di Torino
      • Department of Physics
      Torino, Piedmont, Italy
  • 2007
    • Università degli Studi dell'Insubria
      Varese, Lombardy, Italy
  • 2005
    • University of Padova
      Padua, Veneto, Italy
    • National Institute of Astrophysics
      • Institute of Space Astrophysics and Cosmic Physics IASF - Rome
      Roma, Latium, Italy
  • 2004–2005
    • University of Milan
      • Department of Physics
      Milano, Lombardy, Italy
  • 2002
    • University of St Andrews
      • School of Physics and Astronomy
      Saint Andrews, Scotland, United Kingdom
  • 2000
    • Politecnico di Milano
      • Department of Physics
      Milano, Lombardy, Italy