1,487 research outputs found
Real time localization of Gamma Ray Bursts with INTEGRAL
The INTEGRAL satellite has been successfully launched in October 2002 and has
recently started its operational phase. The INTEGRAL Burst Alert System (IBAS)
will distribute in real time the coordinates of the GRBs detected with
INTEGRAL. After a brief introduction on the INTEGRAL instruments, we describe
the main IBAS characteristics and report on the initial results. During the
initial performance and verification phase of the INTEGRAL mission, which
lasted about two months, two GRBs have been localized with accuracy of about
2-4 arcmin. These observations have allowed us to validate the IBAS software,
which is now expected to provide quick (few seconds delay) and precise (few
arcmin) localization for about 10-15 GRBs per year.Comment: 6 pages, latex, 3 figures, submitted to Adv. Sp. Res., Proceedings of
the 34th COSPAR Scientific Assembly, Houston, 10-19 October 200
Two and a half years of GRB localizations with the INTEGRAL Burst Alert System
We review the results on Gamma-ray Bursts obtained during the first two and a
half years of operations of the INTEGRAL Burst Alert System (IBAS). In many
cases GRB coordinates have been distributed with an unprecedented combination
of accuracy (3 arcmin) and speed (20-30 s). The resulting rapid follow-ups at
other wavelengths, including sensitive XMM-Newton and Swift observations, have
led to several interesting results.Comment: A shorter version of this paper will be published in the Proceedings
of the 4th Workshop "Gamma-Ray Bursts in the Afterglow Era", Roma, 2004
October 18-22, eds. L. Piro, L. Amati, S. Covino, and B. Gendre. Il Nuovo
Cimento, in pres
On the magnetic fields of Be/X-ray pulsars in the Small Magellanic Cloud
We explore the possibility to explain the properties of the Be/X-ray pulsars
observed in the Small Magellanic Cloud within the magnetic levitation accretion
scenario. This implies that their X-ray emission is powered by a wind-fed
accretion onto a neutron star (NS) which captures matter from a magnetized
stellar wind. The NS in this case is accreting matter from a non-keplerian
magnetically levitating disc (ML-disc) which is surrounding its magnetosphere.
This allows us to explain the observed periods of the pulsars in terms of spin
equilibrium without the need of invoking dipole magnetic fields outside the
usual range ~ 10^11- 10^13 G inferred from cyclotron features of Galactic high
mass X-ray binaries. We find that the equilibrium period of a NS, under certain
conditions, depends strongly on the magnetization of the stellar wind of its
massive companion and, correspondingly, on the magnetic field of the massive
companion itself. This may help to explain why similar NSs in binaries with
similar properties rotate with different periods yielding a large scatter of
periods of the accretion-powered pulsar observed in SMC and our galaxy.Comment: 6 pages, 1 figure, Published in MNRAS 454, 3760-3765 (2015
News on the X-ray emission from hot subdwarf stars
In latest years, the high sensitivity of the instruments on-board the
XMM-Newton and Chandra satellites allowed us to explore the properties of the
X-ray emission from hot subdwarf stars. The small but growing sample of X-ray
detected hot subdwarfs includes binary systems, in which the X-ray emission is
due to wind accretion onto a compact companion (white dwarf or neutron star),
as well as isolated sdO stars, in which X-rays are probably due to shock
instabilities in the wind. X-ray observations of these low-mass stars provide
information which can be useful for our understanding of the weak winds of this
type of stars and can lead to the discovery of particularly interesting binary
systems. Here we report the most recent results we have recently obtained in
this research area.Comment: 8 pages, 3 figures. To appear in the Proceedings of the 8th Meeting
on Hot Subdwarf Stars and Related Objects, 9-15 July 2017, Cracow, Poland.
Eds. A. Baran, A. E. Lynas-Gray, Open Astronomy, in pres
Swift monitoring of the massive X-ray binary SAX J0635.2+0533
SAX J0635.2+0533 is a binary pulsar with a very short pulsation period ( =
33.8 ms) and a high long-term spin down ( 3.8 s
s), which suggests a rotation-powered (instead of an accretion-powered)
nature for this source. While it was discovered at a flux level around
10 erg cm s, between 2003 and 2004 this source was
detected with XMM-Newton at an average flux of about 10 erg cm
s; moreover, the flux varied of over one order of magnitude on time
scales of a few days, sometimes decreasing below erg
cm s. Since both the rotation-powered and the accretion-powered
scenarios have difficulties to explain these properties, the nature of SAX
J0635.2+0533 is still unclear. Here we report on our recent long-term
monitoring campaign on SAX J0635.2+0533 carried out with Swift and on a
systematic reanalysis of all the RXTE observations performed between 1999 and
2001. We found that during this time interval the source remained almost always
active at a flux level above 10 erg cm s.Comment: 8 pages, 6 figures, 2 tables. Accepted for publication in Astronomy &
Astrophysic
- …