37 research outputs found
Precision Ephemerides For Gravitational Wave Searches: II. Cyg X-2
Accreting neutron stars in low-mass X-ray binaries (LMXBs) are candidate
high-frequency persistent gravitational wave sources. These may be detectable
with next generation interferometers such as Advanced LIGO/VIRGO within this
decade. However, the search sensitivity is expected to be limited principally
by the uncertainty in the binary system parameters. We combine new optical
spectroscopy of Cyg X-2 obtained with the Liverpool Telescope (LT) with
available historical radial velocity data, which gives us improved orbital
parameter uncertainties based on a 44-year baseline. We obtained an improvement
of a factor of 2.6 in the orbital period precision and a factor of 2 in the
epoch of inferior conjunction T_0. The updated orbital parameters imply a mass
function of 0.65 +/- 0.01 M_sun, leading to a primary mass (M_1) of 1.67 +/-
0.22 M_sun (for i=62.5 +/- 4 deg). In addition, we estimate the likely orbital
parameter precision through to the expected Advanced LIGO and VIRGO detector
observing period and quantify the corresponding improvement in sensitivity via
the required number of templates.Comment: 7 pages, 3 figures, accepted for publication by Ap
A Doppler Map and Mass-ratio Constraint for the Black-Hole X-ray Nova Ophiuchi 1977
We have reanalyzed Keck observations of Nova Oph 1977 to extend the work done
by Filippenko et al. (1997), who recently determined a mass function f(M_x) =
4.86 +/- 0.13 M_o for the compact object. We constrain the rotational
broadening, v sin i < 79 km/s, at the 90% confidence level, which gives a mass
ratio q < 0.053. The K-type companion star of Nova Oph 1977 contributes 28-37%
of the light at red wavelengths. The abnormal LiI 6708 absorption line from the
companion star is not detected (EW < 0.12 A), in contrast to four other X-ray
binaries. An Halpha Doppler image of the system shows emission from the
companion star in addition to the accretion disk.Comment: 14 pages of text and tables plus 3 figures, to appear in the
Astronomical Journa
A Dynamical Study of the Black Hole X-ray Binary Nova Muscae 1991
We present a dynamical study of the Galactic black hole binary system Nova
Muscae 1991 (GS/GRS 1124-683). We utilize 72 high resolution Magellan
Echellette (MagE) spectra and 72 strictly simultaneous V-band photometric
observations; the simultaneity is a unique and crucial feature of this
dynamical study. The data were taken on two consecutive nights and cover the
full 10.4-hour orbital cycle. The radial velocities of the secondary star are
determined by cross-correlating the object spectra with the best-match template
spectrum obtained using the same instrument configuration. Based on our
independent analysis of five orders of the echellette spectrum, the
semi-amplitude of the radial velocity of the secondary is measured to be K_2 =
406.8+/-2.7 km/s, which is consistent with previous work, while the uncertainty
is reduced by a factor of 3. The corresponding mass function is f(M) =
3.02+/-0.06 M_\odot. We have also obtained an accurate measurement of the
rotational broadening of the stellar absorption lines (v sin i = 85.0+/-2.6
km/s) and hence the mass ratio of the system q = 0.079+/-0.007. Finally, we
have measured the spectrum of the non-stellar component of emission that veils
the spectrum of the secondary. In a future paper, we will use our
veiling-corrected spectrum of the secondary and accurate values of K_2 and q to
model multi-color light curves and determine the systemic inclination and the
mass of the black hole.Comment: ApJ accepted version; minor revision; added a subsection about
systematic uncertaintie
Tomography of X-ray Nova Muscae 1991: Evidence for ongoing mass transfer and stream-disc overflow
We present a spectroscopic analysis of the black hole binary Nova Muscae 1991
in quiescence using data obtained in 2009 with MagE on the Magellan Clay
telescope and in 2010 with IMACS on the Magellan Baade telescope at the Las
Campanas Observatory. Emission from the disc is observed in H alpha, H beta and
Ca II (8662 A). A prominent hotspot is observed in the Doppler maps of all
three emission lines. The existence of this spot establishes ongoing mass
transfer from the donor star in 2009-2010 and, given its absence in the
1993-1995 observations, demonstrates the presence of a variable hotspot in the
system. We find the radial distance to the hotspot from the black hole to be
consistent with the circularization radius. Our tomograms are suggestive of
stream-disc overflow in the system. We also detect possible Ca II (8662 A)
absorption from the donor star.Comment: 10 pages, 11 figures, 1 table. Accepted for publication in MNRA
Evidence of magnetic accretion in an SW Sex star: discovery of variable circular polarization in LS Pegasi
We report on the discovery of variable circular polarization in the SW Sex
star LS Pegasi. The observed modulation has an amplitude of ~0.3 % and a period
of 29.6 minutes, which we assume as the spin period of the magnetic white
dwarf. We also detected periodic flaring in the blue wing of Hbeta, with a
period of 33.5 minutes. The difference between both frequencies is just the
orbital frequency, so we relate the 33.5-min modulation to the beat between the
orbital and spin period. We propose a new accretion scenario in SW Sex stars,
based on the shock of the disk-overflown gas stream against the white dwarf's
magnetosphere, which extends to the corotation radius. From this geometry, we
estimate a magnetic field strength of B(1) ~ 5-15 MG. Our results indicate that
magnetic accretion plays an important role in SW Sex stars and we suggest that
these systems are probably Intermediate Polars with the highest mass accretion
rates.Comment: Accepted by ApJ Letters. LaTeX, 14 pages, 3 PostScript figure
Search for Gravitational Waves from Scorpius X-1 in LIGO O3 Data With Corrected Orbital Ephemeris
Improved observational constraints on the orbital parameters of the low-mass
X-ray binary Scorpius~X-1 were recently published in Killestein et al (2023).
In the process, errors were corrected in previous orbital ephemerides, which
have been used in searches for continuous gravitational waves from Sco~X-1
using data from the Advanced LIGO detectors. We present the results of a
re-analysis of LIGO detector data from the third observing run of Advanced LIGO
and Advanced Virgo using a model-based cross-correlation search. The corrected
region of parameter space, which was not covered by previous searches, was
about 1/3 as large as the region searched in the original O3 analysis, reducing
the required computing time. We have confirmed that no detectable signal is
present over a range of gravitational-wave frequencies from to
, analogous to the null result of Abbott et al (2022). Our
search sensitivity is comparable to that of Abbott et al (2022), who set upper
limits corresponding, between and , to an
amplitude of about when marginalized isotropically over the
unknown inclination angle of the neutron star's rotation axis, or less than
assuming the optimal orientation.Comment: 8 pages, 3 figures, 2 tables. Typeset with AASTeX 6.3.1. Accepted for
publication in The Astrophysical Journal. arXiv admin note: text overlap with
arXiv:2209.0286
On the Production and Survival of Carbon Fuel for Superbursts on Accreting Neutron Stars: Implications for Mass Donor Evolution
(abridged) We have investigated the physical conditions under which accreting
neutron stars can both produce and preserve sufficient quantities of carbon
fuel to trigger superbursts. Our models span the plausible ranges of neutron
star thermal conductivities, core neutrino emission mechanisms, and areal
radii, as well as the CNO abundances in the accreted material. We find that
neutron stars that accrete hydrogen-rich material with CNO mass fractions <~
that of the Sun will not exhibit superbursts under any circumstances. Neutron
stars that accrete material with CNO mass fractions >~ 4 times that of the Sun
will exhibit superbursts at accretion rates in the observed range. On this
basis, we suggest that the mass donors of superburst systems must have enhanced
CNO abundances. The accreted CNO acts only as a catalyst for hydrogen burning
via the hot CNO cycle, and therefore it is only the sum of the three elements'
mass fractions that is important. Systems that exhibit superbursts are observed
to differ from those that do not exhibit superbursts in the nature of their
helium-triggered Type I X-ray bursts: the bursts have shorter durations and
much greater alpha-values. Increasing the CNO abundance of the accreted
material in our models reproduces both of these observations. Many compact
binary systems have been observed in which the abundances of the accreting
material are distinctly non-solar. Though abundance analyses of the systems
that exhibit superbursts currently do not exist, Bowen fluorescence blend
profiles of 4U 1636-536 and Ser X-1 suggest that the mass donor stars may
indeed have non-solar CNO metallicities. More detailed abundance analyses of
the accreting matter in systems that exhibit superbursts are needed to verify
our assertion that the matter is rich in CNO elements.Comment: accepted by Ap
Recommended from our members
Chasing the Identification of ASCA Galactic Objects (ChIcAGO) - An X-ray Survey of Unidentified Sources in the Galactic Plane I: Source Sample and Initial Results
We present the Chasing the Identification of ASCA Galactic Objects (ChIcAGO) survey, which is designed to identify the unknown X-ray sources discovered during the ASCA Galactic Plane Survey (AGPS). Little is known about most of the AGPS sources, especially those that emit primarily in hard X-rays (2-10 keV) within the Fx ~ 10â13 to 10â11 erg cmâ2 sâ1 X-ray flux range. In ChIcAGO, the subarcsecond localization capabilities of Chandra have been combined with a detailed multiwavelength follow-up program, with the ultimate goal of classifying the >100 unidentified sources in the AGPS. Overall to date, 93 unidentified AGPS sources have been observed with Chandra as part of the ChIcAGO survey. A total of 253 X-ray point sources have been detected in these Chandra observations within 3' of the original ASCA positions. We have identified infrared and optical counterparts to the majority of these sources, using both new observations and catalogs from existing Galactic plane surveys. X-ray and infrared population statistics for the X-ray point sources detected in the Chandra observations reveal that the primary populations of Galactic plane X-ray sources that emit in the Fx ~ 10â13 to 10â11 erg cmâ2 sâ1 flux range are active stellar coronae, massive stars with strong stellar winds that are possibly in colliding wind binaries, X-ray binaries, and magnetars. There is also another primary population that is still unidentified but, on the basis of its X-ray and infrared properties, likely comprises partly Galactic sources and partly active galactic nuclei.Astronom
Chasing the Identification of ASCA Galactic Objects (ChIcAGO): An X-Ray Survey of Unidentified Sources in the Galactic Plane. I. Source Sample and Initial Results
We present the Chasing the Identification of ASCA Galactic Objects (ChIcAGO) survey, which is designed to identify the unknown X-ray sources discovered during the ASCA Galactic Plane Survey (AGPS). Little is known about most of the AGPS sources, especially those that emit primarily in hard X-rays (2-10 keV) within the F_x ~ 10^(â13) to 10^(â11) erg cm^(â2) s^(â1) X-ray flux range. In ChIcAGO, the subarcsecond localization capabilities of Chandra have been combined with a detailed multiwavelength follow-up program, with the ultimate goal of classifying the >100 unidentified sources in the AGPS. Overall to date, 93 unidentified AGPS sources have been observed with Chandra as part of the ChIcAGO survey. A total of 253 X-ray point sources have been detected in these Chandra observations within 3' of the original ASCA positions. We have identified infrared and optical counterparts to the majority of these sources, using both new observations and catalogs from existing Galactic plane surveys. X-ray and infrared population statistics for the X-ray point sources detected in the Chandra observations reveal that the primary populations of Galactic plane X-ray sources that emit in the F_x ~ 10^(â13) to 10^(â11) erg cm^(â2) s^(â1) flux range are active stellar coronae, massive stars with strong stellar winds that are possibly in colliding wind binaries, X-ray binaries, and magnetars. There is also another primary population that is still unidentified but, on the basis of its X-ray and infrared properties, likely comprises partly Galactic sources and partly active galactic nuclei
Heavy element production in a compact object merger observed by JWST
The mergers of binary compact objects such as neutron stars and black holes are of central interest to several areas of astrophysics, including as the progenitors of gamma-ray bursts (GRBs) 1, sources of high-frequency gravitational waves (GWs) 2 and likely production sites for heavy-element nucleosynthesis by means of rapid neutron capture (the r-process) 3. Here we present observations of the exceptionally bright GRB 230307A. We show that GRB 230307A belongs to the class of long-duration GRBs associated with compact object mergers 4â6 and contains a kilonova similar to AT2017gfo, associated with the GW merger GW170817 (refs. 7â12). We obtained James Webb Space Telescope (JWST) mid-infrared imaging and spectroscopy 29 and 61 days after the burst. The spectroscopy shows an emission line at 2.15 microns, which we interpret as tellurium (atomic mass A = 130) and a very red source, emitting most of its light in the mid-infrared owing to the production of lanthanides. These observations demonstrate that nucleosynthesis in GRBs can create r-process elements across a broad atomic mass range and play a central role in heavy-element nucleosynthesis across the Universe