1,348 research outputs found
Swift/BAT and RXTE Observations of the Peculiar X-ray Binary 4U 2206+54 - Disappearance of the 9.6 Day Modulation
Observations of the high-mass X-ray binary 4U 2206+54 with the Swift Burst
Alert Telescope (BAT) do not show modulation at the previously reported period
of 9.6 days found from observations made with the Rossi X-ray Timing Explorer
(RXTE) All-Sky Monitor (ASM). Instead, the strongest peak in the power spectrum
of the BAT light curve occurs at a period of 19.25 +/- 0.08 days, twice the
period found with the RXTE ASM. The maximum of the folded BAT light curve is
also delayed compared to the maximum of the folded ASM light curve. The most
recent ASM data folded on twice the 9.6 day period show similar morphology to
the folded BAT light curve. This suggests that the apparent period doubling is
a recent secular change rather than an energy-dependent effect. The 9.6 day
period is thus not a permanent strong feature of the light curve. We suggest
that the orbital period of 4U 2206+54 may be twice the previously proposed
value.Comment: Accepted for publication in The Astrophysical Journa
X-ray Bursts from the Accreting Millisecond Pulsar XTE J1814-338
Since the discovery of the accreting millisecond pulsar XTE J1814-338 a total
of 27 thermonuclear bursts have been observed from the source with the
Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer
(RXTE). Spectroscopy of the bursts, as well as the presence of continuous burst
oscillations, suggests that all but one of the bursts are sub-Eddington. The
remaining burst has the largest peak bolometric flux of 2.64 x E^-8
erg/sec/cm^2, as well as a gap in the burst oscillations, similar to that seen
in Eddington limited bursts from other sources. Assuming this burst was
Eddington limited we obtain a source distance of about 8 kpc. All the bursts
show coherent oscillations at the 314.4 Hz spin frequency. The burst
oscillations are strongly frequency and phase locked to the persistent
pulsations. Only two bursts show evidence for frequency drift in the first few
seconds following burst onset. In both cases the initial drift corresponds to a
spin down of a few tenths of a Hz. The large oscillation amplitude during the
bursts confirms that the burst flux is modulated at the spin frequency. We
detect, for the first time, a significant first harmonic component in burst
oscillations. The ratio of countrate in the first harmonic to that in the
fundamental can be > 0.25 and is, on average, less than that of the persistent
pulsations. If the pulsations result from a single bright region on the
surface, the harmonic strength suggests the burst emission is beamed, perhaps
due to a stronger magnetic field than in non-pulsing LMXBs. Alternatively, the
harmonic content could result from a geometry with two bright regions.Comment: AASTeX, 15 pages, 4 figures. Accepted for publication in the
Astrophysical Journal Letter
Suzaku Observations of Four Heavily Absorbed HMXBs
We report on Suzaku observations of four unidentified sources from the
INTEGRAL and Swift BAT Galactic plane surveys. All the sources have a large
neutral hydrogen column density and are likely members of an emerging class of
heavily absorbed high mass X-ray binary (HMXB) first identified in INTEGRAL
observations. Two of the sources in our sample are approximately constant flux
sources, one source shows periodic variation and one source exhibited a short,
bright X-ray outburst. The periodicity is transient, suggesting it is produced
by a neutron star in an elliptical orbit around a stellar wind source. We
analyze the flaring source in several segments to look for spectral variation
and discuss the implications of the findings for the nature of the source. We
conclude that all four sources in our sample can be identified with the
emerging class of highly absorbed HMXBs, that one is a newly identified
transient X-ray pulsar and that at least one is a newly identified supergiant
fast X-ray transient (SFXT).Comment: 22 pages, 5 figures, submitted to Ap
Secular spin-down of the AMP XTE J1751-305
Context. Of the 13 known accreting millisecond pulsars, only a few showed
more than one outburst during the RXTE era. XTE J1751-305 showed, after the
main outburst in 2002, other three dim outbursts. We report on the timing
analysis of the latest one, occurred on October 8, 2009 and serendipitously
observed from its very beginning by RXTE. Aims. The detection of the pulsation
during more than one outburst permits to obtain a better constraint of the
orbital parameters and their evolution as well as to track the secular spin
frequency evolution of the source. Methods. Using the RXTE data of the last
outburst of the AMP XTE J1751-305, we performed a timing analysis to improve
the orbital parameters. Because of the low statistics, we used an epoch folding
search technique on the whole data set to improve the local estimate of the
time of ascending node passage. Results. Using this new orbital solution we
epoch folded data obtaining three pulse phase delays on a time span of 1.2
days, that we fitted using a constant spin frequency model. Comparing this
barycentric spin frequency with that of the 2002 outburst, we obtained a
secular spin frequency derivative of -0.55(12) x 10^{-14} Hz s^{-1}. In the
hypothesis that the secular spin-down is due to a rotating magneto-dipole
emission, consistently with what is assumed for radio pulsars, we estimate the
pulsar's magnetic dipole value. We derive an estimate of the magnetic field
strength at the polar cap of B_{PC} = 4.0(4) x 10^8 Gauss, for a neutron star
mass of 1.4M\odot, assuming the Friedman Pandharipande Skyrme equation of
state.Comment: 7 pages, 4 figures, accepted for publication on A&
Optimal Extraction of Fibre Optic Spectroscopy
We report an optimal extraction methodology, for the reduction of
multi-object fibre spectroscopy data, operating in the regime of tightly packed
(and hence significantly overlapping) fibre profiles. The routine minimises
crosstalk between adjacent fibres and statistically weights the extraction to
reduce noise. As an example of the process we use simulations of the numerous
modes of operation of the AAOmega fibre spectrograph and observational data
from the SPIRAL Integral Field Unit at the Anglo-Australian Telescope.Comment: Accepted for publication in PAS
Monitoring and Discovering X-ray Pulsars in the Small Magellanic Cloud
Regular monitoring of the SMC with RXTE has revealed a huge number of X-ray
pulsars. Together with discoveries from other satellites at least 45 SMC
pulsars are now known. One of these sources, a pulsar with a period of
approximately 7.8 seconds, was first detected in early 2002 and since discovery
it has been found to be in outburst nine times. The outburst pattern clearly
shows a period of 45.1 +/- 0.4 d which is thought to be the orbital period of
this system. Candidate outburst periods have also been obtained for nine other
pulsars and continued monitoring will enable us to confirm these. This large
number of pulsars, all located at approximately the same distance, enables a
wealth of comparative studies. In addition, the large number of pulsars found
(which vastly exceeds the number expected simply by scaling the relative mass
of the SMC and the Galaxy) reveals the recent star formation history of the SMC
which has been influenced by encounters with both the LMC and the Galaxy.Comment: 5 pages, 4 figures, AIP conference proceedings format. Contribution
to "X-ray Timing 2003: Rossi and Beyond." meeting held in Cambridge, MA,
November, 200
Search for L5 Earth Trojans with DECam
Most of the major planets in the Solar system support populations of co-orbiting bodies, known as Trojans, at their L4 and L5 Lagrange points. In contrast, Earth has only one known co-orbiting companion. This paper presents the results from a search for Earth Trojans (ETs) using the DECam instrument on the Blanco Telescope at CTIO. This search found no additional Trojans in spite of greater coverage compared to previous surveys of the L5 point. Therefore, the main result of this work is to place the most stringent constraints to date on the population of ETs. These constraints depend on assumptions regarding the underlying population properties, especially the slope of the magnitude distribution (which in turn depends on the size and albedo distributions of the objects). For standard assumptions, we calculate upper limits to a 90 perâcent confidence limit on the L5 population of N_(ET) < 1 for magnitude H < 15.5, N_(ET) = 60â85 for H < 19.7, and N_(ET) = 97 for H = 20.4. This latter magnitude limit corresponds to Trojans âŒ300 m in size for albedo 0.15. At H = 19.7, these upper limits are consistent with previous L4 ET constraints and significantly improve L5 constraints
On the Origin of Radio Emission in the X-ray States of XTE J1650-500 during the 2001-2002 Outburst
We report on simultaneous radio and X-ray observations of the black hole
candidate XTE J1650-500 during the course of its 2001-2002 outburst. The
scheduling of the observations allowed us to sample the properties of XTE
J1650-50 in different X-ray spectral states, namely the hard state, the steep
power-law state and the thermal dominant state, according to the recent
spectral classification of McClintock & Remillard. The hard state is consistent
with a compact jet dominating the spectral energy distribution at radio
frequencies; however, the current data suggest that its contribution as direct
synchrotron emission at higher energies may not be significant. In that case,
XTE J1650-50 may be dominated by Compton processes (either inverse
Comptonization of thermal disk photons and/or SSC from the base of the compact
jet) in the X-ray regime. We, surprisingly, detect a faint level of radio
emission in the thermal dominant state that may be consistent with the emission
of previously ejected material interacting with the interstellar medium,
similar (but on a smaller angular scale) to what was observed in XTE J1550-564
by Corbel and co-workers. Based on the properties of radio emission in the
steep power-law state of XTE J1650-50, and taking into account the behavior of
other black hole candidates (namely GX 339-4, XTE J1550-564, and XTE J1859+226)
while in the intermediate and steep power-law states, we are able to present a
general pattern of behavior for the origin of radio emission in these two
states that could be important for understanding the accretion-ejection
coupling very close to the black hole event horizon.Comment: Accepted for publication in The Astrophysical Journal. 33 pages, 10
figure
Rossi X-ray Timing Explorer Observations of the X-ray Pulsar EXO 1722-363 - a Candidate Eclipsing Supergiant System
Observations made of the X-ray pulsar EXO 1722-363 using the Proportional
Counter Array and All Sky Monitor on board the Rossi X-ray Timing Explorer
reveal the orbital period of this system to be 9.741 +/- 0.004 d from periodic
changes in the source flux. The detection of eclipses, together with the values
of the pulse and orbital periods, suggest that this source consists of a
neutron star accreting from the stellar wind of an early spectral type
supergiant companion. Pulse timing measurements were also obtained but do not
strongly constrain the system parameters. The X-ray spectra can be well fitted
with a model consisting of a power law with a high energy cutoff and, for some
spectra, a blackbody component with a temperature of approximately 0.85 keV.Comment: Accepted for publication in The Astrophysical Journal. 27 pages
including 10 figure
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