Supergiant, fast, but not so transient 4U 1907+09

We have investigated the dipping activity observed in the high-mass X-ray binary 4U 1907+09 and shown that the source continues to pulsate in the "off" state, noting that the transition between the "on" and "off" states may be either dip-like or flare-like. This behavior may be explained in the framework of the "gated accretion" scenario proposed to explain the flares in supergiant fast X-ray transients (SFXTs). We conclude that 4U 1907+09 might prove to be a missing link between the SFXTs and ordinary accreting pulsars.Comment: 4 pages 5 figures, accepted in A&

Ten years of INTEGRAL observations of the hard X-ray emission from SGR 1900+14

We exploited the high sensitivity of the INTEGRAL IBIS/ISGRI instrument to study the persistent hard X-ray emission of the soft gamma-ray repeater SGR 1900+14, based on ~11.6 Ms of archival data. The 22-150 keV INTEGRAL spectrum can be well fit by a power law with photon index 1.9 +/- 0.3 and flux F_x = (1.11 +/- 0.17)E-11 erg/cm^2/s (20-100 keV). A comparison with the 20-100 keV flux measured in 1997 with BeppoSAX, and possibly associated with SGR 1900+14, shows a luminosity decrease by a factor of ~5. The slope of the power law above 20 keV is consistent within the uncertainties with that of SGR 1806-20, the other persistent soft gamma-ray repeater for which a hard X-ray emission extending up to 150 keV has been reported.Comment: Accepted for publication in Astronomy & Astrophysics. 4 page

Glancing through the accretion column of EXO 2030+375

We took advantage of the large collecting area and good timing capabilities of the EPIC cameras on-board XMM-Newton to investigate the accretion geometry onto the magnetized neutron star hosted in the high mass X-ray binary EXO 2030+375 during the rise of a source Type-I outburst in 2014. We carried out a timing and spectral analysis of the XMM-Newton observation as function of the neutron star spin phase. We used a phenomenological spectral continuum model comprising the required fluorescence emission lines. Two neutral absorption components are present: one covering fully the source and one only partially. The same analysis was also carried out on two Suzaku observations of the source performed during outbursts in 2007 and 2012, to search for possible spectral variations at different luminosities. The XMM-Newton data caught the source at an X-ray luminosity of $2\times10^{36}$ erg s$^{-1}$ and revealed the presence of a narrow dip-like feature in its pulse profile that was never reported before. The width of this feature corresponds to about one hundredth of the neutron star spin period. From the results of the phase-resolved spectral analysis we suggest that this feature can be ascribed to the self-obscuration of the accretion stream passing in front of the observer line of sight. We inferred from the Suzaku observation carried out in 2007 that the self-obscuration of the accretion stream might produce a significantly wider feature in the neutron star pulsed profile at higher luminosities ($\gtrsim$$2\times10^{37}$ erg s$^{-1}$).Comment: Accepted for publication on A&

New Constraints on Decaying Dark Matter from INTEGRAL/SPI

Based on almost 20 years of data collected by the high-resolution spectrometer SPI on board the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) we present constraints on a decaying dark matter particle undergoing a decay into two bodies, at least one of which is a photon, manifesting itself via a narrow line-like spectral feature. Our ON-OFF type analysis of the Milky Way observations allowed us to constrain the lifetime to be $\gtrsim 10^{20}-10^{21}$ yrs for DM particles with masses $40\,\text{keV}\,<\,M_{\text{DM}}\,<\,14\,\text{MeV}$. Within this mass range our analysis also reveals 32 line-like features detected at $\geq 3\sigma$ significance, 29 of which coincide with known instrumental and astrophysical lines. In particular, we report on the detection of the electron-positron annihilation (511 keV) and $^{26}$Al (1809 keV) lines with spatial profiles consistent with previous results in the literature. For the particular case of the sterile neutrino DM we report the limits on the mixing angle as a function of sterile neutrino mass. We discuss the dominant impact of systematic uncertainties connected to the strongly time-variable INTEGRAL/SPI instrumental background as well as the ones connected to the uncertainties of MW DM density profile measurements on the derived results.Comment: To match accepted MNRAS versio

Meteorological variability and groundwater quality: Examples in different hydrogeological settings

Rainfall and temperature variability causes changes in groundwater recharge that can also influence groundwater quality by different processes. The aim of this study is the analysis of the hydrogeochemical variations over time due to meteorological variability in two different study areas in Italy: an alluvial aquifer in the Piedmont Po plain and an alluvial-pyroclastic aquifer in the Campanian plain. The examined plains show groundwater with natural quality not satisfying the European drinking water standards, or anthropogenic contamination. The peculiar natural quality is due, in the Campanian plain, to the closeness of volcanic areas, and to the presence of reducing conditions. In Piedmont plain a test site is characterized by a point-source contamination by heavy metals, due to the presence of past industrial activities. In all the examined areas there is a diffuse nitrate contamination. The fluctuations of the ions As, F, Fe, Mn, Cr VI, NO3, and Cl were analyzed and compared, using statistical methods, with the variations over time in precipitation, temperature, and piezometric levels, sometimes significant. Results highlight the importance of the groundwater and meteorological monitoring and the key role of the recharge variation in the hydrogeochemical processes. The linking degree between rainfall/temperature variability and hydrogeochemistry is variable, in function of the typology of chemical species, their origin, and of the aquifer characteristics. The fluctuation of climate variables determines sudden changes in the geochemistry of shallow unconfined aquifers (e.g., in the Piedmont plain), while semiconfined or confined aquifers (e.g., in the Volturno-Regi Lagni plain) react with a greater delay to these variations. Moreover, natural quality is more affected by climatic variations than anthropogenic contamination, which is the result of multiple environmental and anthropic factors

The 100-month Swift catalogue of supergiant fast X-ray transients I. BAT on-board and transient monitor flares

We investigate the characteristics of bright flares for a sample of supergiant fast X-ray transients and their relation to the orbital phase. We have retrieved all Swift/BAT Transient Monitor light curves, and collected all detections in excess of $5\sigma$ from both daily- and orbital-averaged light curves in the time range of 2005-Feb-12 to 2013-May-31. We also considered all on-board detections as recorded in the same time span and selected those within 4 arcmin of each source in our sample and in excess of $5\sigma$. We present a catalogue of over a thousand BAT flares from 11 SFXTs, down to 15-150keV fluxes of $\sim6\times10^{-10}$ erg cm$^{-2}$ s$^{-1}$ (daily timescale) and $\sim1.5\times10^{-9}$ erg cm$^{-2}$ s$^{-1}$ (orbital timescale, averaging $\sim800$s) and spanning 100 months. The great majority of these flares are unpublished. This population is characterized by short (a few hundred seconds) and relatively bright (in excess of 100mCrab, 15-50keV) events. In the hard X-ray, these flares last in general much less than a day. Clustering of hard X-ray flares can be used to indirectly measure the length of an outburst, even when the low-level emission is not detected. We construct the distributions of flares, of their significance (in terms of sigma) and their flux as a function of orbital phase, to infer the properties of these binary systems. In particular, we observe a trend of clustering of flares at some phases as $P_{\rm orb}$ increases, as consistent with a progression from tight, circular or mildly eccentric orbits at short periods, to wider and more eccentric orbits at longer orbital periods. Finally, we estimate the expected number of flares for a given source for our limiting flux and provide the recipe for calculating them for the limiting flux of future hard X-ray observatories. (Abridged).Comment: Accepted for publication in Astronomy and Astrophysics. 23 pages, 8 figures. Full catalog files will be available at CDS and at http://www.ifc.inaf.it/sfxt/ Fixed typos and updated reference

Cardiovascular magnetic resonance myocardial perfusion: methods and applications in patients with coronary artery disease

Perfusion CMR is an attractive imaging modality that is becoming comparable with other clinically diagnostic tests. SPECT and PET are well clinically validated and have good accuracy for detection of significant CAD. However, these techniques have a rather low spatial resolution and are not suitable for the detection of subendocardial perfusion defect. In addition, the radiation burden, the potential for attenuation artefacts (SPECT) and the limited availability (PET) are limitations of these imaging techniques. An integrated assessment of myocardial perfusion, function and viability is feasible with CMR. In addition, compared to other clinically available imaging techniques, CMR perfusion has excellent spatial resolution and no ionising radiation exposure. However, it is not widely available and there is a need of protocol and pulse sequence standardization. Most perfusion analysis remains observer-dependent (“eyeball” analysis) or dependent on bolus dispersion (semi-quantitative analysis). Fully quantitative analysis using CMR perfusion is currently time-consuming for clinical application. Perfusion CMR is an evolving field with numerous future directions