144 research outputs found
The Orbital Period of Scorpius X-1
The orbital period of Sco X-1 was first identified by Gottlieb et al. (1975).
While this has been confirmed on multiple occasions, this work, based on nearly
a century of photographic data, has remained the reference in defining the
system ephemeris ever since. It was, however, called into question when
Vanderlinde et al. (2003) claimed to find the one-year alias of the historical
period in RXTE/ASM data and suggested that this was the true period rather than
that of Gottlieb et al. (1975). We examine data from the All Sky Automated
Survey (ASAS) spanning 2001-2009. We confirm that the period of Gottlieb et al.
(1975) is in fact the correct one, at least in the optical, with the one-year
alias strongly rejected by these data. We also provide a modern time of minimum
light based on the ASAS data.Comment: 3 pages, 2 figures, accepted for publication in the Astrophysical
Journa
The Quiescent Optical and Infrared Counterpart to EXO 0748-676 = UY Vol
We present optical and infrared photometry of the low-mass X-ray binary EXO
0748-676 in quiescence for the first time in 24 years since it became X-ray
active in 1985. We find the counterpart at average magnitudes of R=22.4 and
J=21.3. We monitored the source approximately nightly through 2008 November to
2009 January. During this time there was considerable night-to-night optical
variability but no long term trends were apparent. The night-to-night
variability reveals a periodicity of P=0.159331+/-0.000012d, consistent with
the X-ray orbital period to within 0.01%. This indicates that the quiescent
optical modulation is indeed orbital in nature rather than a superhump.
Interestingly, the modulation remains single-peaked with a deep minimum
coincident with the times of X-ray eclipse, and there is no indication of a
double-peaked ellipsoidal modulation. This indicates that even in `quiescence'
emission from the accretion disk and/or X-ray heated inner face of the
companion star dominate the optical emission, and implies that obtaining an
accurate dynamical mass estimate in quiescence will be challenging.Comment: Accepted for publication by the Astrophysical Journal Letter
Simultaneous multiwavelength observations of V404 Cygni during its 2015 June outburst decay strengthen the case for an extremely energetic jet-base
We present results of multiband optical photometry of the black hole X-ray
binary system V404 Cygni obtained using Wheaton College Observatory's 0.3m
telescope, along with strictly simultaneous INTEGRAL and Swift observations
during 2015 June 25.15--26.33 UT, and 2015 June 27.10--27.34 UT. These
observations were made during the 2015 June outburst of the source when it was
going through an epoch of violent activity in all wavelengths ranging from
radio to -rays. The multiwavelength variability timescale favors a
compact emission region, most likely originating in a jet outflow, for both
observing epochs presented in this work. The simultaneous INTEGRAL/Imager on
Board the Integral Satellite (IBIS) 20--40 keV light curve obtained during the
June 27 observing run correlates very strongly with the optical light curve,
with no detectable delay between the optical bands as well as between the
optical and hard X-rays. The average slope of the dereddened spectral energy
distribution was roughly flat between the - and -bands during the June
27 run, even though the optical and X-ray flux varied by 25 during
the run, ruling out an irradiation origin for the optical and suggesting that
the optically thick to optically thin jet synchrotron break during the
observations was at a frequency larger than that of -band, which is quite
extreme for X-ray binaries. These observations suggest that the optical
emission originated very close to the base of the jet. A strong H
emission line, probably originating in a quasi-spherical nebula around the
source, also contributes significantly in the -band. Our data, in
conjunction with contemporaneous data at other wavelengths presented by other
groups, strongly suggest that the jet-base was extremely compact and energetic
during this phase of the outburst.Comment: 15 pages, 2 tables, 5 figures. Accepted for publication in Ap
The Dwarf Nova PQ Andromedae
We report a photometric study of the WZ Sagittae-type dwarf nova PQ
Andromedae. The light curve shows strong (0.05 mag full amplitude) signals with
periods of 1263(1) and 634(1) s, and a likely double-humped signal with
P=80.6(2) min. We interpret the first two as nonradial pulsation periods of the
underlying white dwarf, and the last as the orbital period of the underlying
binary. We estimate a distance of 150(50) pc from proper motions and the two
standard candles available: the white dwarf and the dwarf-nova outburst. At
this distance, the K magnitude implies that the secondary is probably fainter
than any star on the main sequence -- indicating a mass below the Kumar limit
at 0.075 M_sol. PQ And may be another "period bouncer", where evolution now
drives the binary out to longer period.Comment: PDF, 13 pages, 2 figures; accepted, in press, to appear September
2005, PASP; more info at http://cba.phys.columbia.edu
Links Between Optical and X-ray Light in Scorpius X-1
We observed the low-mass X-ray binary Sco X-1 for 12 nights simultaneously
using the Rossi X-Ray Timing Explorer and the Otto Struve Telescope at McDonald
Observatory at 1 second time resolution. This is among the most comprehensive
simultaneous X-Ray/optical data sets of Sco X-1. Evidence of reprocessing was
observed in the form of nine positive, near-zero lag peaks in the cross
correlation function, eight of which were relatively small and took the shape
of piecewise exponential functions. These peaks were initially identified by
eye, after which a computational identification scheme was developed to confirm
their significance. Based on their short lags (less than 4 seconds), as well as
their occurrence on the flaring branch and soft apex, the small cross
correlation features are likely to be caused by reprocessing off the outer
disc, although the companion could still make a contribution to their tails.
The Z track was parameterized using a rank number scheme so that the system's
location on the track could be numerically defined. Plotting the results
against the optical reveals an increasing step function when moving from the
horizontal to the normal to the flaring branch, with differential optical
levels at ~0.47, ~0.57, and ~1.1 respectively. An additional correlation
between Z track location and the optical was found on the upper flaring branch.
An optical intensity histogram reveals a transition region between the normal
and flaring branches with only intermediate fluxes.Comment: Accepted for publication in the Monthly Notices of the Royal
Astronomical Societ
Modeling the Low State Spectrum of the X-Ray Nova XTE J1118+480
Based on recent multiwavelength observations of the new X-ray nova XTE
J1118+480, we can place strong constraints on the geometry of the accretion
flow in which a low/hard state spectrum, characteristic of an accreting black
hole binary, is produced. We argue that the absence of any soft blackbody-like
component in the X-ray band implies the existence of an extended hot
optically-thin region, with the optically-thick cool disk truncated at some
radius R_{tr} > 55 R_{Schw}. We show that such a model can indeed reproduce the
main features of the observed spectrum: the relatively high optical to X-ray
ratio, the sharp downturn in the far UV band and the hard X-ray spectrum. The
absence of the disk blackbody component also underscores the requirement that
the seed photons for thermal Comptonization be produced locally in the hot
flow, e.g. via synchrotron radiation. We attribute the observed spectral break
at 2 keV to absorption in a warm, partially ionized gas.Comment: 6 pages, including 1 figure; LaTeX (emulateapj5.sty), to appear in
Ap
The Spectrum of the Black Hole X-ray Nova V404 Cygni in Quiescence as Measured by XMM-Newton
We present XMM observations of the black hole X-ray nova V404 Cygni in
quiescence. Its quiescent spectrum can be best fitted by a simple power-law
with slope 2. The spectra are consistent with that expected for the
advection-dominated accretion flow (ADAF). V404 Cyg was roughly equal in
luminosity compared to the previous observation of Chandra. We see variability
of a factor of 4 during the observation. We find no evidence for the presence
of fluorescent or H-like/He-like iron emission, with upper limits of 52 eV and
110 eV respectively. The limit on the fluorescent emission is improved by a
factor of 15 over the previous estimate, and the restriction on H-like/He-like
emission is lower than predicted from models by a factor of roughly 2.Comment: 6 pages, 7 figures, ApJ accepte
Optical and UV Light Curves of the Accretion Disk Corona Source 4U 1822-371
The eclipsing low-mass X-ray binary 4U is the prototypical accretion disk
corona (ADC) system. We have obtained new time-resolved UV spectrograms of 4U
with the Hubble Space Telescope and new V- and J-band light curves with the
1.3-m SMARTS telescope at CTIO. We present an updated ephemeris for the times
of the optical/UV eclipses. Model light curves do not give acceptable fits to
the UV eclipses unless the models include an optically-thick ADC.Comment: 3 pages, 2 figures, from A Population Explosion: The Nature and
Evolution of X-ray Binaries in Diverse Environment
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