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[show abstract]
[hide abstract]
ABSTRACT: We report our multiwavelength study of the 2011 outburst evolution of the
newly discovered black hole candidate X-ray binary Swift J1357.2-0933. We
analysed the Swift X-ray telescope and Ultraviolet/Optical telescope (UVOT)
data taken during the ~7 months duration of the outburst. It displayed a 2-10
keV X-ray peak luminosity of ~1E35(D/1.5 kpc)^2 erg s-1 which classifies the
source as a very faint X-ray transient. We found that the X-ray spectrum at the
peak was consistent with the source being in the hard state, but it softened
with decreasing luminosity, a common behaviour of black holes at low
luminosities or returning to quiescence from the hard state. The correlations
between the simultaneous X-ray and ultraviolet/optical data suggest a system
with a black hole accreting from a viscous disc that is not irradiated. The
UVOT filters provide the opportunity to study these correlations up to
ultraviolet wavelengths a regime so far unexplored. If the black hole nature is
confirmed, Swift J1357.2-0933 would be one of the very few established black
hole very-faint X-ray transients.
07/2012;
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[show abstract]
[hide abstract]
ABSTRACT: The X-ray transient XTE J1719-291 was discovered with RXTE/PCA during its
outburst in 2008 March, which lasted at least 46 days. Its 2-10 keV peak
luminosity is 7E35 erg/s assuming a distance of 8 kpc, which classifies the
system as a very faint X-ray transient. The outburst was monitored with Swift,
RXTE, Chandra and XMM-Newton. We analysed the X-ray spectral evolution during
the outburst. We fitted the overall data with a simple power-law model
corrected for absorption and found that the spectrum softened with decreasing
luminosity. However, the XMM-Newton spectrum can not be fitted with a simple
one-component model, but it can be fitted with a thermal component (black body
or disc black body) plus power-law model affected by absorption. Therefore, the
softening of the X-ray spectrum with decreasing X-ray luminosity might be due
to a change in photon index or alternatively it might be due to a change in the
properties of the soft component. Assuming that the system is an X-ray binary,
we estimated a long-term time-averaged mass accretion rate of ~ 7.7E-13
M_sun/yr for a neutron star as compact object and ~ 3.7E10-13 M_sun/yr in the
case of a black hole. Although no conclusive evidence is available about the
nature of the accretor, based on the X-ray/optical luminosity ratio we
tentatively suggest that a neutron star is present in this system.
04/2011;
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D. Altamirano,
Y. Cavecchi,
A. Patruno,
A. Watts,
M. Linares,
N. Degenaar,
M. Kalamkar,
M. van der Klis,
N. Rea,
P. Casella, M. Armas Padilla,
R. Kaur,
Y. J. Yang,
P. Soleri,
and R. Wijnands
[show abstract]
[hide abstract]
ABSTRACT: We report on the discovery and the timing analysis of the first eclipsing accretion-powered millisecond X-ray pulsar (AMXP): SWIFT J1749.4-2807. The neutron star rotates at a frequency of ~517.9 Hz and is in a binary system with an orbital period of 8.8 hr and a projected semimajor axis of ~1.90 lt-s. Assuming a neutron star between 0.8 and 2.2 M ☉ and using the mass function of the system and the eclipse half-angle, we constrain the mass of the companion and the inclination of the system to be in the ~0.46-0.81 M ☉ and ~ 744-773 range, respectively. To date, this is the tightest constraint on the orbital inclination of any AMXP. As in other AMXPs, the pulse profile shows harmonic content up to the third overtone. However, this is the first AMXP to show a first overtone with rms amplitudes between ~6% and ~23%, which is the strongest ever seen and which can be more than two times stronger than the fundamental. The fact that SWIFT J1749.4-2807 is an eclipsing system that shows uncommonly strong harmonic content suggests that it might be the best source to date to set constraints on neutron star properties including compactness and geometry.
The Astrophysical Journal Letters 12/2010; 727(1):L18. · 5.53 Impact Factor
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M. Linares,
A. Watts,
D. Altamirano,
P. Soleri,
N. Degenaar,
Y. Yang,
R. Wijnands,
P. Casella,
J. Homan,
D. Chakrabarty,
N. Rea, M. Armas-Padilla,
Y. Cavecchi,
M. Kalamkar,
R. Kaur,
A. Patruno,
and M. van der Klis
[show abstract]
[hide abstract]
ABSTRACT: We report the detection of 15 X-ray bursts with RXTE and Swift observations of the peculiar X-ray binary Circinus X-1 (Cir X-1) during its 2010 May X-ray re-brightening. These are the first X-ray bursts observed from the source after the initial discovery by Tennant and collaborators, 25 years ago. By studying their spectral evolution, we firmly identify nine of the bursts as type I (thermonuclear) X-ray bursts. We obtain an arcsecond location of the bursts that confirms once and for all the identification of Cir X-1 as a type I X-ray burst source, and therefore as a low magnetic field accreting neutron star. The first five bursts observed by RXTE are weak and show approximately symmetric light curves, without detectable signs of cooling along the burst decay. We discuss their possible nature. Finally, we explore a scenario to explain why Cir X-1 shows thermonuclear bursts now but not in the past, when it was extensively observed and accreting at a similar rate.
The Astrophysical Journal Letters 07/2010; 719(1):L84. · 5.53 Impact Factor
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D. Altamirano,
Y. Cavecchi,
A. Patruno,
A. Watts,
M. Linares,
N. Degenaar,
M. Kalamkar,
M. van der Klis,
N. Rea,
P. Casella, M. Armas Padilla,
R Kaur,
Y. J. Yang,
P. Soleri,
R. Wijnands
[show abstract]
[hide abstract]
ABSTRACT: We report on the timing analysis of the first eclipsing accretion-powered millisecond X-ray pulsar (AMXP): SWIFT J1749.4-2807. The neutron star rotates at a frequency of ~517.9 Hz and is in a binary system with an orbital period of 8.8 hrs and a projected semi-major axis of ~1.90 lt-s. Based on the mass function and the eclipse half-angle, we constrain the inclination of the system to be between ~76 and ~80 deg. This is to date the tightest constraint on the orbital inclination of any AMXP. We also estimate the mass of the companion to be in the 0.6-0.8 Msun range. As in other AMXPs, the pulse profile shows harmonic content up to the 3rd overtone. However, this is the first AMXP to show a 1st overtone with rms amplitudes between 5 and 25%, which is the strongest ever seen, and which can be more than two times stronger than the fundamental. The fact that SWIFT J1749.4-2807 is an eclipsing system which shows uncommonly strong harmonic content suggests that it might be the best source to date to set constraints on neutron star properties including compactness and geometry. Comment: 5 pages, 4 Figures, Submitted to ApJ Letters
05/2010;
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M. Linares,
P. Soleri,
D. Altamirano, M. Armas-Padilla,
Y. Cavecchi,
N. Degenaar,
M. Kalamkar,
R. Kaur,
M. van der Klis,
A. Patruno,
A. Watts,
R. Wijnands,
Y. Yang,
P. Casella,
N. Rea,
D. Chakrabarty,
J. Homan
[show abstract]
[hide abstract]
ABSTRACT: Following the recent re-brightening (ATel #2608) and RXTE-PCA detection
of X-ray bursts from the peculiar X-ray binary Cir X-1 between May 15
and 25 (ATel #2643), we obtained a series of Swift-XRT observations of
the field (see also ATel #2650). Swift-XRT detected an X-ray burst
on 2010-05-28 at 12:08:19 UTC, which lasted about 60 seconds and had a
FRED profile, typical of type I X-ray bursts.
The Astronomer's Telegram. 04/2010; 2651:1.
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Y. J. Yang,
D. M. Russell,
R. Wijnands,
M. van der Klis,
D. Altamirano,
A. Patruno,
A. Watts, M. Armas Padilla,
Y. Cavecchi,
N. Degenaar,
M. Kalamkar,
R. Kaur,
M. Linares,
P. Casella,
N. Rea,
P. Soleri,
F. Lewis,
A. K. H. Kong
[show abstract]
[hide abstract]
ABSTRACT: We analyzed seven, target ID 31686, Swift follow-up observations of the
neutron-star X-ray transient Swfit J1749.4-2807 (Wijnands et al. 2009)
currently in outburst and which was found to be an accreting millisecond
X-ray pulsar (ATel #2565). The observations span from April 11 to April
20.
The Astronomer's Telegram. 03/2010; 2579:1.
