Achille Nucita

ESA XMM­Newton Postdoc 

I had my degree in Physics in 1998 at University of Lecce (Italy)
defending a Thesis entitled Emission of Gravitational Waves from
Stellar Clusters. After a one year INFN fellowship at University of
Pisa (Italy), where I collaborated with the VIRGO project team, I
started my PhD in physics. I obtained the PhD in 2003 at University
of Lecce (Italy) with a dissertation entitled Astrophysics of the
Galactic Central Regions. My research activity has focused on the
study of some astrophysical sources of gravitational waves possibly
the target of future space based interferometers, physics of black
holes and neutron stars, astrophysics of massive black holes (also
binaries) hosted in the cores of many galaxies like active galactic
nuclei (AGNs) and Quasars (QSOs). 

As far as the study of gravitational wave sources, I have
investigated the possibility of existence of massive black hole
binaries in the center of many galaxies and in particular of
ellipticals. According to the common evolution scenario, elliptical
galaxies may form as a consequence of the interaction between two
spiral galaxies each of which contains a massive black hole with
mass in the range 10^6 - 10^9 solar masses at its center. The
gravitational interaction and the subsequent orbital decay due to,
for example, dynamical friction effects could produce an hard
massive binary whose evolution is then driven by General Relativity
effects like the emission of gravitational waves. I have shown
that, in some cases, the emitted gravitational wave signal is in
the frequency band of the next space based interferometers like
LISA and ASTROD and that the detection of such a signal could help
in determining the orbital parameters of the binaries. Up to now in
fact, revealing a massive black hole binary is done by looking for
signal periodicity (for example in the X­ray, Gamma ­ray and radio
bands). The observed periodicity is obviously linked to the orbital
motions of some components but depends on the detail of the orbit,
so that a precise estimation of the black hole masses is diffcult.
Hence, I have extended some results known in literature taking into
account some orbital parameters (semi­major axis, eccentricity and
so on) of massive binaries possibly hosted in some objects like MKN
501 or 3C66B. 

After the PhD, I switched to the gravitational lensing physics
since I had a Post.Doc. position at the University of Lecce where I
was involved in lensing, microlensing, pixel lensing and
strong­lensing phenomena. I was also interested in the interaction
between the gravitational wave signal and the gravitational field
of a source. In this context, I have proposed that also a
gravitational wave signal may suffer, at least in principle and
under particular conditions, a gravitational lensing effect so that
the amplitude h of a given signal is increased by a factor sqrt(A),
being A the well known Paczinski amplification factor. I had
research interests in the study of Dark Matter (DM) in galaxies and
in micro­lensing and pixel­lensing techniques as tools to measure
the amount of barionic DM which is present in both our Galaxy and
M31 galaxy. This research activity is still open showing that Monte
Carlo simulations are fundamental for our knowledge of the Dark
Matter amount in Andromeda. In this way, starting from the
available photometric and kinematic data for both the Galaxy and
M31 and following well known de­projection techniques, a 3­D
structure of the considered galaxy is obtained. 

At present, I'm also involved in a series of pixel lensing
observations towards M31 at the Loiano Telescope in Bologna
(Italy). The next campaign will start on 19 of November up to 28 of
November. 

I had a second (1 year and half) Post.Doc. position in order to
collaborate with the VST (VLT Survey Telescope) team. In
particular, I developed codes (both C, IDL and Fortran77, Fortran
90) for Monte Carlo simulation of deep field images up to magnitude
24. These image will be used for the training of Neural Network
systems appositely developed for pattern recognition, so that an
automatic selection of different objects can be done. My interest
in the physics of black holes and in the astrophysics of
gravitational lensing have been linked, in some sense together,
through a 100 ks XMM Newton telescope observation toward the MACHO
microlensing candidate MACHO BLG­95. This peculiar microlensing
candidate event has been characterized by a long enough duration
which allowed to use parallax methods in order to infer the lens
distance. Hence, an estimate of the lens mass has been obtained. In
particular, MACHO BLG­95 seems to be an object of 3­10 solar masses
at a distance 0.5­2 kpc from Earth. The unusual huge mass of the
lens opens the possibility that MACHO BLG­95 is an isolated neutron
star or a stellar mass black hole. In both cases, I expected that
the object accretes the surrounding interstellar matter (for
example via Bondi accretion mechanism) and emits radiation in the
X­ray band. The expected X­ray flux is 10^(-15) erg/sec cm-2 , so
that we have requested, and obtained, observing time (100 ks) with
the XMM Newton telescope. The data analysis performed on both the
EPIC and MOS images allowed us to put an upper limit to the X­ray
flux of 10^(-15) erg s -1 cm -2 coming from the source so that
strong constraints on the Black Hole accretion mechanism can be
put. 

At present, my research interests span from the application of the
GR theory to the Galactic Center to the physics of AGNs (studied
with the RGS camera in order to obtain good spectra possibly fitted
by Cloudy simulations) and to the physics of LMXRB and IMBH.