1,943 research outputs found
The Orbital Period of the Be/Neutron Star Binary RX J0812.4-3114
We present the results of Rossi X-ray Timing Explorer observations of the Be
star X-ray binary system RX J0812.4-3114. A light curve obtained with the RXTE
All-Sky Monitor shows that the source is currently in an active state with
outbursts occurring at approximately 80 day intervals. The source underwent a
transition from an inactive state to this regular outburst state early in 1998.
An observation of RX J0812.4-3114 was obtained with the RXTE Proportional
Counter Array close to the time of a predicted maximum in March 1999 and strong
pulsations were detected at a period of 31.88 seconds. This confirms the result
of an earlier PCA observation by Reig & Roche which was serendipitously also
obtained near the predicted maximum flux of the 80 day period and also near the
start of the current active state. We interpret the periodicity in the ASM
light curve as indicating the orbital period of RX J0812.4-3114 with outbursts
occurring around periastron passage
The Orbit and Position of the X-ray Pulsar XTE J1855-026 - an Eclipsing Supergiant System
A pulse timing orbit has been obtained for the X-ray binary XTE J1855-026
using observations made with the Proportional Counter Array on board the Rossi
X-ray Timing Explorer. The mass function obtained of ~16Mo together with the
detection of an extended near-total eclipse confirm that the primary star is a
supergiant as predicted. The orbital eccentricity is found to be very low with
a best fit value of 0.04 +/- 0.02. The orbital period is also refined to be
6.0724 +/- 0.0009 days using an improved and extended light curve obtained with
RXTE's All Sky Monitor. Observations with the ASCA satellite provide an
improved source location of R.A. = 18h 55m 31.3s}, decl. = -02o 36' 24.0"
(2000) with an estimated systematic uncertainty of less than 12". A
serendipitous new source, AX J1855.4-0232, was also discovered during the ASCA
observations.Comment: Accepted for publication in the Astrophysical Journa
Spin-Down of the Long-Period Accreting Pulsar 4U 2206+54
4U 2206+54 is a high mass X-ray binary which has been suspected to contain a
neutron star accreting from the wind of its companion BD +53 2790. Reig et al.
have recently detected 5560 s period pulsations in both RXTE and INTEGRAL
observations which they conclude are due to the spin of the neutron star. We
present observations made with Suzaku which are contemporaneous with their RXTE
observation of this source. We find strong pulsations at a period of 5554 +/- 9
s in agreement with their results. We also present a reanalysis of BeppoSAX
observations of 4U 2206+54 made in 1998, in which we find strong pulsations at
a period of 5420 +/- 28 seconds, revealing a spin-down trend in this
long-period accreting pulsar. Analysis of these data suggests that the neutron
star in this system is an accretion-powered magnetar.Comment: Submitted to The Astrophysical Journa
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
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
Discovery of a new Transient X-ray Pulsar in the Small Magellanic Cloud
Rossi X-Ray Timing Explorer observations of the Small Magellanic Cloud have
revealed a previously unknown transient X-ray pulsar with a pulse period of
95s. Provisionally designated XTE SMC95, the pulsar was detected in three
Proportional Counter Array observations during an outburst spanning 4 weeks in
March/April 1999. The pulse profile is double peaked reaching a pulse fraction
\~0.8. The source is proposed as a Be/neutron star system on the basis of its
pulsations, transient nature and characteristically hard X-ray spectrum. The
2-10 keV X-ray luminosity implied by our observations is > 2x10^37 erg/s which
is consistent with that of normal outbursts seen in Galactic systems. This
discovery adds to the emerging picture of the SMC as containing an extremely
dense population of transient high mass X-ray binaries.Comment: Accepted by A&A. 7 pages, 6 figure
The X-ray Properties of M101 ULX-1 = CXOKM101 J140332.74+542102
We report our analysis of X-ray data on M101 ULX-1, concentrating on high
state Chandra and XMM-Newton observations. We find that the high state of M101
ULX-1 may have a preferred recurrence timescale. If so, the underlying clock
may have periods around 160 or 190 days, or possibly around 45 days. Its
short-term variations resemble those of X-ray binaries at high accretion rate.
If this analogy is correct, we infer that the accretor is a 20-40 Msun object.
This is consistent with our spectral analysis of the high state spectra of M101
ULX-1, from which we find no evidence for an extreme (> 10^40 ergs/s)
luminosity. We present our interpretation in the framework of a high mass X-ray
binary system consisting of a B supergiant mass donor and a large stellar-mass
black hole.Comment: 23 pages, 7 figures, accepted for publication in the Astrophysical
Journa
X-ray Pulsars in the Small Magellanic Cloud
XMM-Newton archival data for the Small Magellanic Cloud have been examined
for the presence of previously undetected X-ray pulsars. One such pulsar, with
a period of 202 s, is detected. Its position is consistent with an early B star
in the SMC and we identify it as a high mass X-ray binary (HMXB). In the course
of this study we determined the pulse period of the possible AXP CXOU
J010043.1-721134 to be 8.0 s, correcting an earlier report (Lamb et al 2002b)
of a 5.4 s period for this object. Pulse profiles and spectra for each of these
objects are presented as well as for a recently discovered (Haberl & Pietsch
2004) 263 s X-ray pulsar. Properties of an ensemble of 24 optically identified
HMXB pulsars from the SMC are investigated. The locations of the pulsars and an
additional 22 X-ray pulsars not yet identified as having high mass companions
are located predominately in the young (ages years) star
forming regions of the SMC as expected on the basis of binary evolution models.
We find no significant difference between the distribution of spin periods for
the HMXB pulsars of the SMC compared with that of the Milky Way. For those HMXB
pulsars which have Be companions we note an inverse correlation between spin
period and maximum X-ray flux density. (This anti-correlation has been
previously noted for all X-ray binary pulsars by Stella, White & Rosner 1986).
The anti-correlation for the Be binaries may be a reflection of the fact that
the spin periods and orbital periods of Be HMXBs are correlated. We note a
similar correlation between X-ray luminosity and spin period for the Be HMXB
pulsars of the Milky Way and speculate that exploitation of the correlation
could serve as a distance indicator.Comment: final version accepted in The Astrophysical Journa
Historical changes in the phenology of British Odonata are related to climate
Responses of biota to climate change take a number of forms including distributional shifts, behavioural changes and life history changes. This study examined an extensive set of biological records to investigate changes in the timing of life history transitions (specifically emergence) in British Odonata between 1960 and 2004. The results show that there has been a significant, consistent advance in phenology in the taxon as a whole over the period of warming that is mediated by life history traits. British odonates significantly advanced the leading edge (first quartile date) of the flight period by a mean of 1.51 ±0.060 (SEM, n=17) days per decade or 3.08±1.16 (SEM, n=17) days per degree rise in temperature when phylogeny is controlled for. This study represents the first review of changes in odonate phenology in relation to climate change. The results suggest that the damped temperature oscillations experienced by aquatic organisms compared with terrestrial organisms are sufficient to evoke phenological responses similar to those of purely terrestrial taxa
4U2206+54 - an Unusual High Mass X-ray Binary with a 9.6 Day Orbital Period but No Strong Pulsations
Rossi X-ray Timing Explorer All-Sky Monitor observations of the X-ray source
4U2206+54, previously proposed to be a Be star system, show the X-ray flux to
be modulated with a period of approximately 9.6 days. If the modulation is due
to orbital variability then this would be one of the shortest orbital periods
known for a Be star X-ray source. However, the X-ray luminosity is relatively
modest whereas a high luminosity would be predicted if the system contains a
neutron star accreting from the denser inner regions of a Be star envelope.
Although a 392s pulse period was previously reported from EXOSAT observations,
a reexamination of the EXOSAT light curves does not show this or any other
periodicity. An analysis of archival RXTE Proportional Counter Array
observations also fails to show any X-ray pulsations. We consider possible
models that may explain the properties of this source including a neutron star
with accretion halted at the magnetosphere and an accreting white dwarf.Comment: Accepted for publication in the Astrophysical Journa
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