6,311 research outputs found
Outbursts, State Transitions, and Periodicities Observed with the RXTE All-Sky Monitor
Results from the All-Sky Monitor (ASM) on the Rossi X-ray Timing Explorer are
reviewed. A number of recurrent transient sources have been detected, while
only a few previously unreported sources have been discovered. The ASM light
curves show a wide variety of phenomena in general, and, in particular, those
of transient sources show a wide range of properties. Examples are used to
illustrate that the distinction between persistent and transient sources may be
very unclear. The results of searches for periodicities in the ASM light curves
are summarized, and other astrophysical investigations using ASM light curves
are suggested. The latter include investigations of the possible causes of
long-term quasiperiodic and chaotic variability, and comparative studies on the
basis of the observed variability.Comment: 8 pages, 4 figures, in proceedings of the conference "The Active
X-ray Sky: Results from BeppoSAX and Rossi-XTE, Rome, Italy, 21-24 October,
1997. Nuclear Physics B Proceedings Supplement
The Use of Weighting in Periodicity Searches in All-Sky Monitor Data: Applications to the GLAST LAT
The light curves produced by all-sky monitors, such as the Rossi X-ray Timing
Explorer All-Sky Monitor and the Swift Burst Alert Telescope (BAT), generally
have non-uniform error bars. In searching for periodic modulation in this type
of data using power spectra it can be important to use appropriate weighting of
data points to achieve the best sensitivity. It was recently demonstrated that
for Swift BAT data a simple weighting scheme can actually sometimes reduce the
sensitivity of the power spectrum depending on source brightness. Instead, a
modified weighting scheme, based on the Cochran semi-weighted mean, gives
improved results independent of source brightness. We investigate the benefits
of weighting power spectra in period searches using simulated GLAST LAT
observations of gamma-ray binaries.Comment: 2 pages. To appear in the Proceedings of the First International
GLAST Symposium, Febuary 5-8, 2007, Stanford University, AIP, Eds. S. Ritz,
P. F. Michelson, and C. Meega
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
X-ray observations of Be/X-ray binaries in the SMC
(shortened) Fifteen Be/X-ray binaries and candidates in the SMC were observed
serendipitously with the EPIC instruments of XMM-Newton during two observations
of SNR 0047-73.5 and SNR 0103-72.6 in October 2000. A total of twelve of those
sources are detected. For eleven of them an accurate position and in part
detection of X-ray pulsations support the proposed identification as Be/X-ray
binaries. The detection of pulsations (172.2 s, 320.1 s and 751 s) from three
hard X-ray sources with periods known from ASCA observations confirm their
proposed identifications with ROSAT sources and their optical Be star
counterparts. In addition, pulsations with a period of 263.6 s were found from
XMMUJ004723.7-731226=RXJ0047.3-7312. For SAXJ0103.2-7209 a pulse period of
341.20.5 s was determined, continuing the large spin-up seen with ASCA,
BeppoSAX and Chandra between 1996 and 1999 with a period derivative of 1.6 s
yr covering now 4.5 years. The 0.3-10.0 keV EPIC spectra of all eleven
Be/X-ray binaries and candidates are consistent with power-law energy
distributions with derived photon indices strongly peaked at 1.00 with a
standard deviation of 0.16. No pulsations are detected from RXJ0049.2-7311 and
RXJ0049.5-7310 (both near the 9 s pulsar AXJ0049-732) and RXJ0105.1-7211 (near
AXJ0105-722, which may pulsate with 3.3 s), leaving the identification of the
ASCA sources with ROSAT and corresponding XMM-Newton objects still unclear. We
present an updated list of high mass X-ray binaries (HMXBs) and candidates in
the SMC incorporating improved X-ray positions obtained from Chandra and
XMM-Newton observations. Including the results from this work and recent
publications the SMC HMXB catalogue comprises 65 objects with at least 37
showing X-ray pulsations.Comment: 10 pages, 7 figures, accepted for publication in A&
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