885 research outputs found
The binary period and outburst behaviour of the SMC X-ray binary pulsar system SXP504
A probable binary period has been detected in the optical counterpart to the
X-ray source CXOU J005455.6-724510 = RX J0054.9-7245 = AXJ0054.8-7244 = SXP504
in the Small Magellanic Cloud. This source was detected by Chandra on 04 Jul
2002 and subsequently observed by XMM-Newton on 18 Dec 2003. The source is
coincident with an Optical Gravitational Lensing (OGLE) object in the
lightcurves of which several optical outburst peaks are visible at ~ 268 day
intervals. Timing analysis shows a period of 268.6 +/- 0.1 days at > 99%
significance. Archival Rossi X-ray Timing Explorer (RXTE) data for the 504s
pulse-period has revealed detections which correspond closely with predicted or
actual peaks in the optical data. The relationship between this orbital period
and the pulse period of 504s is within the normal variance found in the Corbet
diagram.Comment: Accepted by MNRAS. 1 LATEX page. 4 figure
The Use of Gamma-ray Bursts as Direction and Time Markers in SETI Strategies
When transmitting a signal over a large distance it is more efficient to send
a brief beamed signal than a continuous omni-directional transmission but this
requires that the receiver knows where and when to look for the transmission.
For SETI, the use of various natural phenomena has previously been suggested to
achieve the desired synchronization. Here it is proposed that gamma-ray bursts
may well the best ``synchronizers'' of all currently known phenomena due to
their large intrinsic luminosities, high occurrence rate, isotropic sky
distribution, large distance from the Galaxy, short duration, and easy
detectability. For targeted searches, precise positions for gamma-ray bursts
are required together with precise distance measurements to a target star. The
required burst position determinations are now starting to be obtained, aided
in large part by the discovery of optical afterglows. Good distance
measurements are currently available from Hipparcos and even better
measurements should be provided by spacecraft now being developed. For
non-targeted searches, positional accuracies simply better than a detector's
field of view may suffice but the time delay between the detection of a
gamma-ray burst and the reception of the transmitted signal cannot be predicted
in an obvious way.Comment: 8 pages, accepted for publication in PAS
Species Abundance Patterns in Complex Evolutionary Dynamics
An analytic theory of species abundance patterns (SAPs) in biological
networks is presented. The theory is based on multispecies replicator dynamics
equivalent to the Lotka-Volterra equation, with diverse interspecies
interactions. Various SAPs observed in nature are derived from a single
parameter. The abundance distribution is formed like a widely observed
left-skewed lognormal distribution. As the model has a general form, the result
can be applied to similar patterns in other complex biological networks, e.g.
gene expression.Comment: 4 pages, 3 figures. Physical Review Letters, in pres
X-Ray and Optical Observations of XTE J0052-723 a Transient Be/X-Ray Pulsar in the Small Magellanic Cloud
On December 27th 2000 during our regular SMC monitoring program with Rossi
X-ray Timing Explorer, strong pulsations were detected with a period of 4.78
seconds. Subsequent slew observations performed on Jan 9th and 13th across the
field of view allowed localisation of the pulsar's position to RA: 0 52 17,
Dec: 72 19 51 (J2000). The outburst continued until Jan 24th, 7 PCA
observations were obtained during this period, yielding a maximum X-ray
luminosity ~10^38 ergs/s. Following calculation of the pulsar position, optical
observations of the RXTE error box were made on Jan 16th 2001 with the 1m
telescope of the South African Astronomical Observatory (SAAO) while the source
was still in X-ray outburst. Candidate Be stars identified from their
photometric colours were subsequently observed with the SAAO 1.9m on Nov 7th
2001 to obtain spectra. Only one of the photometrically identified stars
[MA93]537 showed prominent H emission, with a double peaked
line-profile (EW= -43.3+/-0.7 A, separation velocity= 200+/-15 km/s) confirming
the presence of a substantial circumstellar disk.Comment: 8 pages, 8 figures, Accepted for publication in MNRA
The impacts of environmental warming on Odonata: a review
Climate change brings with it unprecedented rates of increase in environmental temperature, which will have major consequences for the earth's flora and fauna. The Odonata represent a taxon that has many strong links to this abiotic factor due to its tropical evolutionary history and adaptations to temperate climates. Temperature is known to affect odonate physiology including life-history traits such as developmental rate, phenology and seasonal regulation as well as immune function and the production of pigment for thermoregulation. A range of behaviours are likely to be affected which will, in turn, influence other parts of the aquatic ecosystem, primarily through trophic interactions. Temperature may influence changes in geographical distributions, through a shifting of species' fundamental niches, changes in the distribution of suitable habitat and variation in the dispersal ability of species. Finally, such a rapid change in the environment results in a strong selective pressure towards adaptation to cope and the inevitable loss of some populations and, potentially, species. Where data are lacking for odonates, studies on other invertebrate groups will be considered. Finally, directions for research are suggested, particularly laboratory studies that investigate underlying causes of climate-driven macroecological patterns
The XMM-Newton survey of the Small Magellanic Cloud: XMMUJ005011.2-730026 = SXP214, a Be/X-ray binary pulsar
In the course of the XMM-Newton survey of the Small Magellanic Cloud (SMC), a
region to the east of the emission nebula N19 was observed in November 2009. To
search for new candidates for high mass X-ray binaries the EPIC PN and MOS data
of the detected point sources were investigated and their spectral and temporal
characteristics identified. A new transient (XMMUJ005011.2-730026= SXP214) with
a pulse period of 214.05 s was discovered; the source had a hard X-ray spectrum
with power-law index of ~0.65. The accurate X-ray source location permits the
identification of the X-ray source with a ~15th magnitude Be star, thereby
confirming this system as a new Be/X-ray binary.Comment: 8 pages 11 figures. Accepted for publication in MNRA
The Orbit of the Eclipsing X-ray Pulsar EXO 1722-363
With recent and archival Rossi X-Ray Timing Explorer (RXTE) X-ray
measurements of the heavily obscured X-ray pulsar EXO 1722-363 (IGR
J17252-3616), we carried out a pulse timing analysis to determine the orbital
solution for the first time. The binary system is characterized by a_x sin(i) =
101 +/- 3 lt-s and P_orb = 9.7403 +/- 0.0004 days (90% confidence), with the
precision of the orbital period being obtained by connecting datasets separated
by more than 7 years (272 orbital cycles). The orbit is consistent with
circular, and e < 0.19 at the 90% confidence level. The mass function is 11.7
+/- 1.2 M_sun and confirms that this source is a High Mass X-ray Binary (HMXB)
system. The orbital period, along with the previously known ~414 s pulse
period, places this system in the part of the Corbet diagram populated by
supergiant wind accretors. Using previous eclipse time measurements by Corbet
et al. and our orbital solution, combined with the assumption that the primary
underfills its Roche lobe, we find i > 61 degrees at the 99% confidence level,
the radius of the primary is between 21 R_sun and 37 R_sun, and its mass is
less than about 22 M_sun. The acceptable range of radius and mass shows that
the primary is probably a supergiant of spectral type B0I-B5I. Photometric
measurements of its likely counterpart are consistent with the spectral type
and luminosity if the distance to the system is between 5.3 kpc and 8.7 kpc.
Spectral analysis of the pulsar as a function of orbital phase reveals an
evolution of the hydrogen column density suggestive of dense filaments of gas
in the downstream wake of the pulsar, with higher levels of absorption seen at
orbital phases 0.5-1.0, as well as a variable Fe K_alpha line.Comment: Submitted to ApJ, 11 pages, 11 figure
Discovery of luminous pulsed hard X-ray emission from anomalous X-ray pulsars 1RXS J1708-4009, 4U 0142+61 and 1E 2259+586 by INTEGRAL and RXTE
We report on the discovery of hard spectral tails for energies above 10 keV
in the total and pulsed spectra of anomalous X-ray pulsars 1RXS J1708-4009, 4U
0142+61 and 1E 2259+586 using RXTE PCA (2-60 keV) and HEXTE (15-250 keV) data
and INTEGRAL IBIS ISGRI (20-300 keV) data. Improved spectral information on 1E
1841-045 is presented. The pulsed and total spectra measured above 10 keV have
power-law shapes and there is so far no significant evidence for spectral
breaks or bends up to ~150 keV. The pulsed spectra are exceptionally hard with
indices measured for 4 AXPs approximately in the range -1.0 -- 1.0. We also
reanalyzed archival CGRO COMPTEL (0.75-30 MeV) data to search for signatures
from our set of AXPs. No detections can be claimed, but the obtained
upper-limits in the MeV band indicate that for 1RXS J1708-4009, 4U 0142+61 and
1E 1841-045 strong breaks must occur somewhere between 150 and 750 keV.Comment: Accepted for publication in ApJ; 19 pages; 4 Tables; 15 Figures (6
color
XTE J1946+274 = GRO J1944+26: An Enigmatic Be/X-ray Binary
XTE J1946+274 = GRO J1944+26 is a 15.8 s Be/X-ray pulsar discovered
simultaneously in 1998 September with the Burst and Transient Source Experiment
(BATSE) on the Compton Gamma Ray Observatory (CGRO) and the All-Sky Monitor
(ASM) on the Rossi X-ray Timing Explorer (RXTE). Here we present new results
from BATSE and {\em RXTE} including a pulse timing analysis, spectral analysis,
and evidence for an accretion disk. Our pulse timing analysis yielded an
orbital period of 169.2 days, a moderate eccentricity of 0.33, and implied a
mass function of 9.7 M_sun. We observed evidence for an accretion disk, a
correlation between measured spin-up rate and flux, which was fitted to obtain
a distance estimate of 9.5 +/- 2.9 kpc. XTE J1946+274 remained active from 1998
September - 2001 July, undergoing 13 outbursts that were not locked in orbital
phase. Comparing RXTE PCA observations from the initial bright outburst in 1998
and the last pair of outbursts in 2001, we found energy and intensity dependent
pulse profile variations in both outbursts and hardening spectra with
increasing intensity during the fainter 2001 outbursts. In 2001 July, optical
Halpha observations indicate a density perturbation appeared in the Be disk as
the X-ray outbursts ceased. We propose that the equatorial plane of the Be star
is inclined with respect to the orbital plane in this system and that this
inclination may be a factor in the unusual outburst behavior of the system.Comment: 18 pages, 15 figures, To appear in ApJ v584, Feb 20, 2003 issu
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