A systematic and semi-automatic timing analysis is applyied to several
archival
HRI and PSPC ROSAT
fields (
WGA catalogue ) in order to reveal periodicities which can be arisen
from X-ray
pulsators,
pulsars, nearby old neutron stars accreting from ISM and CVs
as well. The used methods rely upon FFTs and Rayleigh analysis which have
been modified and generalised to unevenly space and non-poissonian noise
dominated data (see Time Series Analysis). A sample of recent
results are now available. People involved in this project are: Luigi
Stella (Rome/MontePorzio Astronomical
Observatory), Giampiero Tagliaferri (Brera
Astronomical Observatory), Aldo Treves (SISSA),
Nick White and Lorella Angelini (HEASARC),
and Paolo Giommi (SAX SDC).
Time
Series Analysis:
Periodic phenomena play a crucial role in high energy astrophysics:
choerent signals are usually detected from statistically significant peaks
in the power spectra of the light curves. Nevertheless the detection of
periodic phenomena faces different difficulties, depending, on the wavelength,
spacing, number and signal to noise ratio of the data and the shape and
intensity of the periodic modulation. Some problems were taken into account
and developed:
The resulting software will be available as soon as possible
through the
Xronos
Timing Analysis Software Package (Xanadu,
which also include Xspec
and Ximage)
which was first developed at ESTEC
by Luigi Stella and Lorella Angelini for EXOSAT
spacecraft data and now distribuited by
HEASARC.
Black
Holes Candidates, LMXRBs and X-ray Pulsators:
The identification of the optical counterparts of X-ray pulsators (transient
or persistent in nature) is an essential step in determining the nature
of individual sources and preparing for future, deeper studies. The spectral
information and the presence of peculiar features (especially emission
lines such as Halpha, Hbeta, HeI, HeII and/or non-thermal continua) are
powerful tools to discern between an accreting neutron star in a binary
system (often associated with O-B stars) from a cataclysmic variable (mainly
K-M main sequence companion stars). Moreover the lack of a plausible optical
counterpart can be used to select isolated neutron stars accreting from
the interstellar medium, anomalous X-ray pulsars and magnetars/soft gamma-ray
repeaters.
For the majority of the cases, the position uncertainty is large (> 1'
radius) and the number of objects within the error circle may be such that
a detailed search is time-prohibitive. A time-saving approach is the slitless
multiobject spectroscopy (Polcaro
& Viotti 1998) which we used to select peculiar emission lines
expected from the companion star of this kind of binary systems. This method,
which was tuned at the 1.5m
telescope of the Observatory
of Bologna (FOSC + CCD with a 13'.5 X 13'.5 field of view) and at the
1.5m
Danish telescope of the ESO (La
Silla, Chile; DFOSC + CCD with
a 13'.5 X 13'.5 field of view), allow to perform a good spectrum over a
large number of sources and to select stars with strong (respect to the
continuum) emission-lines, even for relatively faint objects (m_V of the order of
16-18 depending on the telescope, time exposure and number of stars).
In the last 2 years we discovered the likely optical
counterpart of 10 X-ray pulsators.
my
Curriculum Vitae
Periodic
Time Variability Survey of
ROSAT
fields:
Time
Series Analysis:
Black
Holes Candidates, LMXRBs and X-ray Pulsators:
Optical
Identification of X-ray Pulsars
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scientific Home Page