891 research outputs found
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
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
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
Discovery of a 75 day orbit in XTE J1543-568
Dedicated monitoring of the transient X-ray pulsar XTE J1543-568 during the
first year after its discovery has revealed the unambiguous detection of a
binary orbit. The orbital period is 75.56+/-0.25 d, and the projected
semi-major axis 353+/-8 lt-sec. The mass function and position in the pulse
period versus orbital period diagram are consistent with XTE J1543-568 being a
Be X-ray binary. The eccentricity of less than 0.03 (2 sigma) is among the
lowest for the 12 Be X-ray binaries whose orbits have now been measured. This
confirms the suspicion that small kick velocities of neutron stars during
supernovae are more common than expected. The distance is estimated to be
larger than 10 kpc, and the luminosity at least 1E37 erg/s.Comment: Accepted for publication in ApJ Letter
Orbital Period Determinations for Four SMC Be/X-ray Binaries
We present an optical and X-ray study of four Be/X-ray binaries located in
the Small Magellanic Cloud (SMC). OGLE I-band data of up to 11 years of
semi-continuous monitoring has been analysed for SMC X-2, SXP172 and SXP202B,
providing both a measurement of the orbital period (Porb = 18.62, 68.90, and
229.9 days for the pulsars respectively) and a detailed optical orbital profile
for each pulsar. For SXP172 this has allowed a direct comparison of the optical
and X-ray emission seen through regular RXTE monitoring, revealing that the
X-ray outbursts precede the optical by around 7 days. Recent X-ray studies by
XMM-Newton have identified a new source in the vicinity of SXP15.3 raising
doubt on the identification of the optical counterpart to this X-ray pulsar.
Here we present a discussion of the observations that led to the proposal of
the original counterpart and a detailed optical analysis of the counterpart to
the new X-ray source, identifying a 21.7 d periodicity in the OGLE I-band data.
The optical characteristics of this star are consistent with that of a SMC
Be/X-ray binary. However, this star was rejected as the counterpart to SXP15.3
in previous studies due to the lack of H{\alpha} emission.Comment: Accepted for publication in MNRAS, 11 pages, 17 figure
The Orbital Solution and Spectral Classification of the High-Mass X-Ray Binary IGR J01054-7253 in the Small Magellanic Cloud
We present X-ray and optical data on the Be/X-ray binary (BeXRB) pulsar IGR
J01054-7253 = SXP11.5 in the Small Magellanic Cloud (SMC). Rossi X-ray Timing
Explorer (RXTE) observations of this source in a large X-ray outburst reveal an
11.483 +/- 0.002s pulse period and show both the accretion driven spin-up of
the neutron star and the motion of the neutron star around the companion
through Doppler shifting of the spin period. Model fits to these data suggest
an orbital period of 36.3 +/- 0.4d and Pdot of (4.7 +/- 0.3) x 10^{-10}
ss^{-1}. We present an orbital solution for this system, making it one of the
best described BeXRB systems in the SMC. The observed pulse period, spin-up and
X-ray luminosity of SXP11.5 in this outburst are found to agree with the
predictions of neutron star accretion theory. Timing analysis of the long-term
optical light curve reveals a periodicity of 36.70 +/- 0.03d, in agreement with
the orbital period found from the model fit to the X-ray data. Using blue-end
spectroscopic observations we determine the spectral type of the counterpart to
be O9.5-B0 IV-V. This luminosity class is supported by the observed V-band
magnitude. Using optical and near-infrared photometry and spectroscopy, we
study the circumstellar environment of the counterpart in the months after the
X-ray outburst.Comment: 12 pages, 13 figures and 3 tables. This paper has been accepted for
publication in MNRA
ROSSI X-RAY TIMING EXPLORER AND BeppoSAX OBSERVATIONS OF THE TRANSIENT X-RAY PULSAR XTE J1859+083
We present observations of the 9.8 s X-ray pulsar XTE J1859+083 made with the All Sky Monitor (ASM) and Proportional Counter Array (PCA) on board the Rossi X-ray Timing Explorer, and the Wide Field Camera (WFC) on board BeppoSAX. The ASM data cover a 12 year time interval and show that an extended outburst occurred between approximately MJD 50,250 and 50,460 (1996 June 16 to 1997 January 12). The ASM data excluding this outburst interval suggest a possible modulation with a period of 60.65 ± 0.08 days. Eighteen sets of PCA observations were obtained over an approximately one month interval in 1999. The flux variability measured with the PCA appears consistent with the possible period found with the ASM. The PCA measurements of the pulse period showed it to decrease nonmonotonically and then to increase significantly. Doppler shifts due to orbital motion rather than accretion torques appear to be better able to explain the pulse period changes. Observations with the WFC during the extended outburst give a position that is consistent with a previously determined PCA error box, but which has a significantly smaller error. The transient nature of XTE J1859+083 and the length of its pulse period are consistent with it being a Be/neutron star binary. The possible 60.65 day orbital period would be of the expected length for a Be star system with a 9.8 s pulse period
RXTE and BeppoSAX Observations of the Transient X-ray Pulsar XTE J 18591+083
We present observations of the 9.8 s X-ray pulsar XTE J159+083 made with the All-Sky Monitor (ASM) and Proportional Counter Array (PCA) on board the Rossi X-ray Timing Explorer (RXTE), and the Wide Field Cameras (WFC) on board BeppoSAX. The ASM data cover a 12 year time interval and show that an extended outburst occurred between approximately MJD50, 250, and 50, 460 (1996 June 16 to 1997 January 12). The ASM data excluding this outburst interval suggest a possible 61 day modulation. Eighteen sets of PCA observations were obtained over an approx. one month interval in 1999. The flux variability measured with the PCA appears consistent with the possible period found with the ASM. The PCA measurements of the pulse period showed it to decrease non-monotonically and then to increase significantly. Doppler shifts due to orbital motion rather than accretion torques appear to be better able to explain the pulse period changes. Observations with the WFC during the extended outburst give an error box which is consistent with a previously determined PCA error box but is significantly smaller. The transient nature of XTE J1859+083 and the length of its pulse period are consistent with it being a Be/neutral star binary. The possible 61 day orbital period would be of the expected length for a Be star system with a 9.8 s pulse period
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