27 research outputs found
The MAVERIC Survey: Simultaneous Chandra and VLA observations of the transitional millisecond pulsar candidate NGC 6652B
Transitional millisecond pulsars are millisecond pulsars that switch between a rotation-powered millisecond pulsar state and an accretion-powered X-ray binary state, and are thought to be an evolutionary stage between neutron star low-mass X-ray binaries and millisecond pulsars. So far, only three confirmed systems have been identified in addition to a handful of candidates. We present the results of a multiwavelength study of the low-mass X-ray binary NGC 6652B in the globular cluster NGC 6652, including simultaneous radio and X-ray observations taken by the Karl G. Jansky Very Large Array and the Chandra X-ray Observatory, and optical spectroscopy and photometry. This source is the second brightest X-ray source in NGC 6652 (Lx~1.8 × 1034 erg, s-1) and is known to be variable. We observe several X-ray flares over the duration of our X-ray observations, in addition to persistent radio emission and occasional radio flares. Simultaneous radio and X-ray data show no clear evidence of anticorrelated variability. Optical spectra of NGC 6652B indicate variable, broad H α emission that transitions from double-peaked emission to absorption over a time-scale of hours. We consider a variety of possible explanations for the source behaviour, and conclude that based on the radio and X-ray luminosities, short time-scale variability and X-ray flaring, and optical spectra, NGC 6652B is best explained as a transitional millisecond pulsar candidate that displays prolonged X-ray flaring behaviour. However, this could only be confirmed with observations of a change to the rotation-powered millisecond pulsar state
The Relationship Between X-ray Luminosity and Duty Cycle for Dwarf Novae and their Specific Frequency in the Inner Galaxy
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139596.pdf (preprint version ) (Open Access
The Quiescent Optical Counterpart to Swift J174510.8-262411
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Identification of 23 accreting binaries in the Galactic Bulge Survey
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127868.pdf (preprint version ) (Open Access
Sco X-1 revisited withKepler, MAXI and HERMES: outflows, time-lags and echoes unveiled
Sco X-1 has been the subject of many multi-wavelength studies in the past,
being the brightest persistent extra-solar X-ray source ever observed. Here we
revisit Sco X-1 with simultaneous short cadence Kepler optical photometry and
MAXI X-ray photometry over a 78 day period, as well as optical spectroscopy
obtained with HERMES. We find Sco X-1 to be highly variable in all our
datasets. The optical fluxes are clearly bimodal, implying the system can be
found in two distinct optical states. These states are generally associated
with the known flaring/normal branch X-ray states, although the flux
distributions associated with these states overlap. Furthermore, we find that
the optical power spectrum of Sco X-1 differs substantially between optical
luminosity states. Additionally we find rms-flux relations in both optical
states, but only find a linear relation during periods of low optical
luminosity. The full optical/X-ray discrete correlation function displays a
broad ~12.5 hour optical lag. However during the normal branch phase the X-ray
and optical fluxes are anti-correlated, whilst being correlated during the
flaring branch. We also performed a Cepstrum analysis on the full Kepler light
curve to determine the presence of any echoes within the optical light curve
alone. We find significant echo signals, consistent with the optical lags found
using the discrete cross-correlation. We speculate that whilst some of the
driving X-ray emission is reflected by the disk, some is absorbed and
re-processed on the thermal timescale, giving rise to both the observed optical
lags and optical echoes.Comment: 13 pages, 15 figures. Accepted for publication in MNRA
X-ray observations of two candidate symbiotic binaries in the galactic bulge
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236335.pdf (Publisher’s version ) (Open Access