Observations of the post shock break-out emission of SN 2011dh with XMM-Newton

After the occurrence of the type cIIb SN 2011dh in the nearby spiral galaxy M 51 numerous observations were performed with different telescopes in various bands ranging from radio to gamma-rays. We analysed the XMM-Newton and Swift observations taken 3 to 30 days after the SN explosion to study the X-ray spectrum of SN 2011dh. We extracted spectra from the XMM-Newton observations, which took place ~7 and 11 days after the SN. In addition, we created integrated Swift/XRT spectra of 3 to 10 days and 11 to 30 days. The spectra are well fitted with a power-law spectrum absorbed with Galactic foreground absorption. In addition, we find a harder spectral component in the first XMM-Newton spectrum taken at t ~ 7 d. This component is also detected in the first Swift spectrum of t = 3 - 10 d. While the persistent power-law component can be explained as inverse Compton emission from radio synchrotron emitting electrons, the harder component is most likely bremsstrahlung emission from the shocked stellar wind. Therefore, the harder X-ray emission that fades away after t ~ 10 d can be interpreted as emission from the shocked circumstellar wind of SN 2011dh.Comment: Accepted for publication as a Research Note in Astronomy and Astrophysic

Exploring accretion theory with a new subclass of high mass x-ray binaries: interpretation of integral observations of the supergiant fast x-ray transients.

In the last eight years the INTEGRAL satellite has allowed to discover a new class of transient X-ray binaries associated with OB supergiants called Supergiant Fast X-ray Transients (SFXTs). They display a high dynamic range, spanning 3-5 orders of magnitude from a quiescent luminosity of 1032 erg s-1 up to a peak luminosity of \uf0bb 1036 - 1037 erg s-1, and they spend most of the time in an intermediate aring level of emission at around 1033 - 1034 erg s-1. The enigmatic properties emerging from this class of sources raise interesting problems to the standard theories for the accretion of matter onto compact objects, and to the properties of OB supergiants in SFXTs. The aim of this thesis is to gain more information about the peculiar transient behaviour of SFXTs and to explore the accretion mechanisms involved in these enigmatic X-ray sources. I present a new clumpy wind model for OB supergiants, with both spherical and non-spherical geometry, that I have developed to investigate the e_ects of accretion from a clumpy wind on the X-ray variability of SFXTs. I assume that the clumps are con_ned by ram pressure of the ambient gas, and I assume that a fraction of the stellar wind is in form of clumps with power law mass and radius distributions. Then, I compute the expected X-ray lightcurves in the framework of the Bondi-Hoyle accretion theory, modi_ed to take into account the presence of clumps, and I apply this model to reproduce the X-ray lightcurves of _ve representative HMXBs: two persistent supergiant systems (Vela X-1 and 4U 1700-377), and the SFXTs IGR J16479-4514, IGR J11215-5952 and IGR J18483-0311. The model can reproduce the observed lightcurves well, but requiring in all cases an overall mass loss from the supergiants about a factor 3-10 smaller than the values inferred from UV lines studies that assume homogeneous wind, but in agreement with recent studies that assume clumpy winds. Then, I report the systematic analysis of all INTEGRAL observations from 2003 to 2009 of 14 SFXTs (con_rmed and candidates), implying a net exposure time of about 30 Ms. This analysis led to discover several new outbursts from SFXTs. I discuss the e_ects of X-ray photoionization on the accretion in close binary systems, and I show that, because of X-ray photoionization, there is a high probability of formation of transient accretion discs from the capture of angular momentum in IGR J16479-4514. This result suggests that the formation of transient accretion discs could be partly responsible for the aring activity in SFXTs with narrow orbits or in SFXTs with higher orbital periods and high eccentricities, when the neutron star is close to periastron. I also propose an alternative way to explain the origin of ares with peculiar shapes observed with INTEGRAL applying the intermittent accretion model of Lamb et al. (1977). Then, I report the study of the candidate SFXT IGR J16418-4532, for which I obtain a re_ned estimate of the orbital period from Swift/BAT data, and a re_ned estimate of the spin period of the neutron star from INTEGRAL data. I con_rm the presence of a region of the orbital lightcurve with a low ux, probably due to an eclipse, or due to the onset of the centrifugal inhibition of accretion. The uncertainties of the results from infrared observations do not allow an assessment of the spectral class of the counterpart of IGR J16418-4532, which could be a main sequence, giant, or O8.5 supergiant. From considerations involving the expected X-ray luminosities, the duration of the likely eclipse, and the onset of the centrifugal inhibition of accretion, I _nd that in all these cases it is possible to exclude the presence of a O8.5 V star, and the presence of a supergiant is favoured

Exploring accretion theory with a new subclass of high mass x-ray binaries: interpretation of integral observations of the supergiant fast x-ray transients.

In the last eight years the INTEGRAL satellite has allowed to discover a new class of transient X-ray binaries associated with OB supergiants called Supergiant Fast X-ray Transients (SFXTs). They display a high dynamic range, spanning 3-5 orders of magnitude from a quiescent luminosity of 1032 erg s-1 up to a peak luminosity of 1036 - 1037 erg s-1, and they spend most of the time in an intermediate aring level of emission at around 1033 - 1034 erg s-1. The enigmatic properties emerging from this class of sources raise interesting problems to the standard theories for the accretion of matter onto compact objects, and to the properties of OB supergiants in SFXTs. The aim of this thesis is to gain more information about the peculiar transient behaviour of SFXTs and to explore the accretion mechanisms involved in these enigmatic X-ray sources. I present a new clumpy wind model for OB supergiants, with both spherical and non-spherical geometry, that I have developed to investigate the e_ects of accretion from a clumpy wind on the X-ray variability of SFXTs. I assume that the clumps are con_ned by ram pressure of the ambient gas, and I assume that a fraction of the stellar wind is in form of clumps with power law mass and radius distributions. Then, I compute the expected X-ray lightcurves in the framework of the Bondi-Hoyle accretion theory, modi_ed to take into account the presence of clumps, and I apply this model to reproduce the X-ray lightcurves of _ve representative HMXBs: two persistent supergiant systems (Vela X-1 and 4U 1700-377), and the SFXTs IGR J16479-4514, IGR J11215-5952 and IGR J18483-0311. The model can reproduce the observed lightcurves well, but requiring in all cases an overall mass loss from the supergiants about a factor 3-10 smaller than the values inferred from UV lines studies that assume homogeneous wind, but in agreement with recent studies that assume clumpy winds. Then, I report the systematic analysis of all INTEGRAL observations from 2003 to 2009 of 14 SFXTs (con_rmed and candidates), implying a net exposure time of about 30 Ms. This analysis led to discover several new outbursts from SFXTs. I discuss the e_ects of X-ray photoionization on the accretion in close binary systems, and I show that, because of X-ray photoionization, there is a high probability of formation of transient accretion discs from the capture of angular momentum in IGR J16479-4514. This result suggests that the formation of transient accretion discs could be partly responsible for the aring activity in SFXTs with narrow orbits or in SFXTs with higher orbital periods and high eccentricities, when the neutron star is close to periastron. I also propose an alternative way to explain the origin of ares with peculiar shapes observed with INTEGRAL applying the intermittent accretion model of Lamb et al. (1977). Then, I report the study of the candidate SFXT IGR J16418-4532, for which I obtain a re_ned estimate of the orbital period from Swift/BAT data, and a re_ned estimate of the spin period of the neutron star from INTEGRAL data. I con_rm the presence of a region of the orbital lightcurve with a low ux, probably due to an eclipse, or due to the onset of the centrifugal inhibition of accretion. The uncertainties of the results from infrared observations do not allow an assessment of the spectral class of the counterpart of IGR J16418-4532, which could be a main sequence, giant, or O8.5 supergiant. From considerations involving the expected X-ray luminosities, the duration of the likely eclipse, and the onset of the centrifugal inhibition of accretion, I _nd that in all these cases it is possible to exclude the presence of a O8.5 V star, and the presence of a supergiant is favoured

Mapping Regions of Provenance for Italy

In the follow-up of 1999/105/CE Directive on national level, the new map of regions of provenance for forest reproductive materials of Italy is adopted as reference for the national register of forest basic materials. The new map was outlined to match needs linked to the transposition of European legislation to the complexity of the Peninsula’s environment and the national nursery system. The main objective in this technical note is to present the map units in relation to the distribution of main forest species. The map units of ecoregional meaning might facilitate new allocations for forest reproductive materials which are needed to increase genetic diversity. Furthermore, studies on genetic variability of forest species are required to understand the possible interactions between the ecological amplitude of forest species, their actual genetic diversity, and possible adaptation to future climate conditions

Discovery of spin-phase dependent QPOs in the super-critical accretion regime from the X-ray pulsar RX J0440.9+4431

RX J0440.9+4431 is an accreting X-ray pulsar (XRP) that remained relatively unexplored until recently, when major X-ray outburst activity enabled more in-depth studies. Here, we report on the discovery of ${\sim}0.2$ Hz quasi-periodic oscillations (QPOs) from this source observed with $Fermi$-GBM. The appearance of QPOs in RX J0440.9+4431 is thricely transient, that is, QPOs appear only above a certain luminosity, only at certain pulse phases (namely corresponding to the peak of its sine-like pulse profile), and only for a few oscillations at time. We argue that this newly discovered phenomenon (appearance of thricely transient QPOs -- or ATTO) occurs if QPOs are fed through an accretion disk whose inner region viscosity is unstable to mass accretion rate and temperature variations. Such variations are triggered when the source switches to the super-critical accretion regime and the emission pattern changes. We also argue that the emission region configuration is likely responsible for the observed QPOs spin-phase dependence.Comment: 5 + 2 appendix pages. Accepted on A&A. Proofs versio

Correlated spectro-polarimetric study along the Z track in XTE J1701-462 puts constraints on its coronal geometry

Context. In September 2022, the transient neutron star low-mass X-ray binary XTE J1701-462 went into a new outburst. Aims. The objective of this work is to examine the evolution of the accretion geometry of XTE J1701-462 by studying the spectro-polarimetric properties along the Z track of this source. The simultaneous observations archived by the Insight-Hard X-ray Modulation Telescope (HXMT) and the Imaging X-ray Polarimetry Explorer (IXPE) give us the opportunity. Methods. We present a comprehensive X-ray spectro-polarimetric analysis of XTE J1701-462, using simultaneous observations from IXPE, Insight-HXMT and NuSTAR. For IXPE observations, two methods are employed to measure the polarization: a model-independent measurement with PCUBE and a model-dependent polarization-spectral analysis with XSPEC. The corresponding spectra from Insight-HXMT and NuSTAR are studied with two configurations that correspond to a slab-like corona and a spherical shell-like corona, respectively. Results. Significant polarization characteristics are detected in XTE J1701-462. The polarization degree shows a decreasing trend along the Z track, reducing from (4.84 $\pm$ 0.37)% to (3.76 $\pm$ 0.43)% on the horizontal branch and jumping to less than 1% on the normal branch. The simultaneous spectral analysis from Insight-HXMT and NuSTAR suggests that the redistribution between the thermal and Comptonized emission could be the reason for the PD evolution along the Z track. Based on the correlated spectro-polarimetric properties, we propose that this source likely has a slab coronal geometry and the size/thickness of the corona decreases along the Z track

Accreting on the edge: a luminosity-dependent cyclotron line in the Be/X-ray Binary 2S 1553-542 accompanied by accretion regimes transition

Accreting X-ray pulsars (XRPs) undergo luminous X-ray outbursts during which the luminosity-dependent spectral and timing features of the neutron star's emission can be analyzed in detail, thus shedding light on the accretion regime at work. We took advantage of a monitoring campaign performed with NuSTAR, Swift/XRT, AstroSat and NICER, to follow the Be/X-ray Binary 2S 1553-542 along one of its rare outbursts and trace its spectral and timing evolution. We report the discovery of a luminosity-dependent cyclotron line energy for the first time in this source. The pulse profiles and pulsed fraction also show variability along the outburst, consistently with the interpretation that the source transitions from the sub-critical to the super-critical accretion regime, separated by a critical luminosity of L$_{crit}\approx4\times10^{37}$ erg/s.Comment: Accepted on ApJ. 11 pages, 7 figures, 3 table

The Swift Supergiant Fast X-ray Transients outburst factory

We present the Swift Supergiant Fast X-ray Transients project, which has been exploiting Swift's capabilities in a systematic study of SFXTs and classical supergiant X-ray binaries (SGXBs) since 2007. We performed an efficient long-term monitoring of 16 sources including both SFXTs and classical SGXBs and followed source activity across more than 4 orders of magnitude in X-ray luminosity, sampling the light curves on timescales spanning from few hundred seconds to years. We use our measurements of dynamic ranges, duty cycles as a function of luminosity, and luminosity distributions to highlight systematic differences that help discriminate between different theoretical models proposed to explain the differences between the wind accretion processes in SFXTs and classical SGXBs. Our follow-ups of the SFXT outbursts provide a steady advancement in the comprehension of the mechanisms triggering the high X-ray level emission of these sources. In particular, the recent observations of the outburst of the SFXT prototype IGR J17544-2619 on 2014 October 10, when the source reached a peak luminosity of 3x1038 erg s-1, challenged, for the first time, the maximum theoretical luminosity achievable by a wind-fed neutron star high mass X-ray binary. We propose that this giant outburst was due to the formation of a transient accretion disc around the compact object.We present the Swift Supergiant Fast X-ray Transients project, which has been exploiting Swift's capabilities in a systematic study of SFXTs and classical supergiant X-ray binaries (SGXBs) since 2007. We performed an efficient long-term monitoring of 16 sources including both SFXTs and classical SGXBs and followed source activity across more than 4 orders of magnitude in X-ray luminosity, sampling the light curves on timescales spanning from few hundred seconds to years. We use our measurements of dynamic ranges, duty cycles as a function of luminosity, and luminosity distributions to highlight systematic differences that help discriminate between different theoretical models proposed to explain the differences between the wind accretion processes in SFXTs and classical SGXBs. Our follow-ups of the SFXT outbursts provide a steady advancement in the comprehension of the mechanisms triggering the high X-ray level emission of these sources. In particular, the recent observations of the outburst of the SFXT prototype IGR J17544-2619 on 2014 October 10, when the source reached a peak luminosity of 3x1038 erg s-1, challenged, for the first time, the maximum theoretical luminosity achievable by a wind-fed neutron star high mass X-ray binary. We propose that this giant outburst was due to the formation of a transient accretion disc around the compact object