Calibrating hydrogen-rich core-collapse supernovae for their use as distance indicators independently of type Ia supernovae

Using our new general-relativistic, radiation hydrodynamics, Lagrangian code, we computed a rather extended grid of hydrogen-rich core-collapse supernova (CC-SN) models and explored the potentials of their "standardization" as distance indicators. We discuss the properties of some calibrations previously reported in the literature and present new correlations based on the behavior of the light curve, that can be employed for calibrating hydrogen-rich CC-SNe using only photometric data.Comment: 2 pages, 3 figures, to appear in Proceedings of IAU Symp. 281, Binary Paths to Type Ia Supernovae Explosions, ed. R. Di Stefano and M. Ori

Quasi-Periodic Oscillations and energy spectra from the two brightest Ultra-Luminous X-ray sources in M82

Ultra-Luminous X-ray sources are thought to be accreting black holes that might host Intermediate Mass Black Holes (IMBH), proposed to exist by theoretical studies, even though a firm detection (as a class) is still missing. The brightest ULX in M82 (M82 X-1) is probably one of the best candidates to host an IMBH. In this work we analyzed the data of the recent release of observations obtained from M82 X-1 taken by XMM-Newton. We performed a study of the timing and spectral properties of the source. We report on the detection of (46+-2) mHz Quasi-Periodic Oscillations (QPOs) in the power density spectra of two observations. A comparison of the frequency of these high-frequency QPOs with previous detections supports the 1:2:3 frequency distribution as suggested in other studies. We discuss the implications if the (46+-2) mHz QPO detected in M82 X-1 is the fundamental harmonic, in analogy with the High-Frequency QPOs observed in black hole binaries. For one of the observations we have detected for the first time a QPO at 8 mHz (albeit at a low significance), that coincides with a hardening of the spectrum. We suggest that the QPO is a milli-hertz QPO originating from the close-by transient ULX M82 X-2, with analogies to the Low-Frequency QPOs observed in black hole binaries.Comment: 9 pages (with 4 figures and 4 tables). Accepted for publication in MNRAS (26/09/13

Ultra-luminous X-ray sources and remnants of massive metal-poor stars

Massive metal-poor stars might form massive stellar black holes (BHs), with mass 25<=mBH/Msun<=80, via direct collapse. We derive the number of massive BHs (NBH) that are expected to form per galaxy through this mechanism. Such massive BHs might power most of the observed ultra-luminous X-ray sources (ULXs). We select a sample of 64 galaxies with X-ray coverage, measurements of the star formation rate (SFR) and of the metallicity. We find that NBH correlates with the number of observed ULXs per galaxy (NULX) in this sample. We discuss the dependence of our model on the SFR and on the metallicity. The SFR is found to be crucial, consistently with previous studies. The metallicity plays a role in our model, since a lower metallicity enhances the formation of massive BHs. Consistently with our model, the data indicate that there might be an anticorrelation between NULX, normalized to the SFR, and the metallicity. A larger and more homogeneous sample of metallicity measurements is required, in order to confirm our results.Comment: 21 pages, 8 figures, accepted for publication in MNRA

Monin-Obukhov similarity theory consistent stability functions for the Prandtl turbulence closure model of the stable atmospheric boundary layer

A new derivation of the stability functions for the Prandtl-Blackadar atmospheric boundary layer model from the Monin-Obukhov similarity theory is proposed by invoking the consistency between the surface layer and the boundary layer turbulent fluxes. The new stability functions are compared to the Louis stability functions and validated, against an ensemble of large eddy simulations, in the context of a single column model simulation of the stably stratified, shear driven, boundary layer. The results of the new stability functions are superior to those of the Louis model and are suggested for the boundary layer parameterization in the atmospheric numerical models

Ultraluminous X-ray Sources forming in low metallicity natal environments

In the last few years multiwavelength observations have boosted our understanding of Ultraluminous X-ray Sources (ULXs). Yet, the most fundamental questions on ULXs still remain to be definitively answered: do they contain stellar or intermediate mass black holes? How do they form? We investigate the possibility that the black holes hosted in ULXs originate from massive (40-120 $M_\odot$) stars in low metallicity natal environments. Such black holes have a typical mass in the range $\sim 30-90 M_\odot$ and may account for the properties of bright (above $\sim 10^{40}$ erg s$^{-1}$) ULXs. More than $\sim 10^5$ massive black holes might have been generated in this way in the metal poor Cartwheel galaxy during the last $10^7$ years and might power most of the ULXs observed in it. Support to our interpretation comes from NGC 1313 X-2, the first ULX with a tentative identification of the orbital period in the optical band, for which binary evolution calculations show that the system is most likely made by a massive donor dumping matter on a $50-100 M_\odot$ black hole.Comment: 4 pages. To appear in the Proceedings of the Conference "X-Ray Astronomy 2009: Present Status, Multiwavelength Approach and Future Perspectives", Bologna, Italy, September 2009, Eds. A. Comastri, M. Cappi, L. Angelini, 2010 AIP (in press)

Radiation-hydrodynamical modelling of Core-Collapse Supernovae: light curves and the evolution of photospheric velocity and temperature

We have developed a relativistic, radiation-hydrodynamics Lagrangian code, specifically tailored to simulate the evolution of the main observables (light curve, evolution of photospheric velocity and temperature) in core-collapse supernova (CC-SN) events. The distinctive features of the code are an accurate treatment of radiative transfer coupled to relativistic hydrodynamics, a self-consistent treatment of the evolution of the innermost ejecta taking into account the gravitational effects of the central compact remnant, and a fully implicit Lagrangian approach to the solution of the coupled non-linear finite difference system of equations. Our aim is to use it as numerical tool to perform calculations of grid of models to be compared with observation of CC-SNe. In this paper we present some testcase simulations and a comparison with observations of SN 1987A, as well as with the results obtained with other numerical codes. We also briefly discuss the influence of the main physical parameters (ejected mass, progenitor radius, explosion energy, amount of \chem{56}{Ni}) on the evolution of the ejecta, and the implications of our results in connection with the possibility to "standardize" hydrogen-rich CC-SNe for using them as candles to measure cosmological distances.Comment: Accepted for publication in ApJ (16 pages, 22 figures