VLA Observations of XTE J0929-314
Michael Rupen, Amy Mioduszewski, & Vivek Dhawan
Last update: 20 March 2003
Please do not use these results without first
contacting M. Rupen. These results are preliminary, and provided here
primarily to aid other observers.
All error bars are 1sigma unless otherwise noted.
- IAUC 7888: 30apr02 (duplicates ATel #92)
- R. A. Remillard, Massachusetts Institute of Technology (MIT),
for the RXTE ASM Team at MIT and Goddard Space Flight Center,
reports the discovery of a faint x-ray transient at R.A. = 9h29m22s,
Decl. = -31o22'.8 (equinox J2000.0; estimated uncertainty 3', 90-
percent confidence). The source is visible in sky maps computed
from 6-day intervals of ASM data. Average fluxes (2-12 keV): Apr.
13-18, 15 +/- 2 mCrab; Apr. 19-24, 20 +/- 2; Apr. 25-30, 26 +/- 1.
The error circle contains no noteworthy sources in the Simbad
catalogues. The ASM hardness ratios suggest an x-ray spectrum
similar to transients associated with weakly magnetic neutron stars
or some blackhole systems. Optical and radio observations are
- IAUC 7889: 1may02
- J. G. Greenhill, A. B. Giles, and K. M. Hill, University of
Tasmania, report a possible optical counterpart for XTE J0929-314
(cf. IAUC 7888). Observations obtained around May 1.42-1.58 UT at
the 1-m Mt. Canopus telescope show a blue object with V about 18.8
at R.A. = 9h29m20s.16, Decl. = -31o23'02".7 (equinox J2000.0;
uncertainty +/- 0".5). The object was also detected in B, R, and
I, but not on a red plate from the Digitized Sky Survey. The
source faded significantly during the observations.
- IAUC 7893: 7may02
- R. A. Remillard, Massachusetts Institute of Technology; and J.
Swank and T. Strohmayer, Goddard Space Flight Center, NASA, report
the discovery of 185-Hz pulsations in XTE J0929-314 (IAUC 7889).
This source was observed in a brief pointed observation with RXTE
on May 2, while the average flux was 28 mCrab (2-30 keV). A power
spectrum was computed for 800 s of PCA data, and a highly
significant pulsation is seen at 185.09 Hz, with a strong harmonic
at 370.18 Hz. This is the third known pulsar in which pulsations
faster than 10 ms can be seen in the persistent x-ray emission.
Rasters across the source give an improved position R.A. =
9h29m18s, Decl. = -31o23'.1 (equinox J2000.0; systematic
uncertainty 1'), consistent with the optical candidate (IAUC 7889).
- M. P. Rupen, V. Dhawan, and A. J. Mioduszewski, National Radio
Astronomy Observatory, report the detection of a radio counterpart
to the x-ray transient XTE J0929-314 (IAUC 7888). Observations
with the Very Large Array (VLA) at 4.86 GHz show a source with flux
density 0.31 +/- 0.07 mJy on May 3, and 0.36 +/- 0.05 mJy on May 7,
at R.A. = 9h29m20s.194, Decl. = -31o23'03".41 (equinox J2000.0;
uncertainty +/- 0".3). This is 0".8 from the optical position
reported by Greenhill et al. (IAUC 7889) and provides strong
evidence that this optical identification is correct. Further
optical and x-ray observations are strongly encouraged.
- P. Cacella, Brasilia, Brazil, reports that an unfiltered CCD
image taken with a 0.25-m reflector shows a variable (mag 18.3)
that is possibly the optical counterpart to XTE J0929-314 at
position end figures 20s.22, 03".6.
- IAUC 7895: 9may02
- A. J. Castro-Tirado, Instituto de Astrofisica de Andalucia,
Consejo Superior de Investigaciones Cientificas (IAA-CSIC),
Granada; A. Caccianiga, Osservatorio Astronomico di Brera, Milano;
J. Gorosabel, IAA-CSIC; P. Kilmartin, University of Canterbury; P.
Tristram and P. Yock, University of Auckland; C. Sanchez-Fernandez,
Laboratorio de Astrofisica Espacial y Fisica Fundamental, Instituto
Nacional de Tecnica Aeroespacial, Madrid; and M. E. Alcoholado-
Feltstrom, Sociedad Malaguena de Astronomia, Malaga, communicate:
"We have observed the optical counterpart of the x-ray transient
XTE J0929-314 (IAUC 7888, 7889, 7893) with the European Southern
Observatory 3.6-m telescope at La Silla. Two 1200-s spectra (350-
800 nm) were obtained on May 6.96 and 7.96 UT. The combined
spectrum shows emission lines from the C III-N III (464.0-465.0 nm)
blend (EW = 0.14 nm for N III) and H-alpha (656.3 nm, EW = 0.14
nm). These lines are superposed on a blue continuum and are
typical of soft-x-ray transients in outburst. Monitoring with the
0.6-m telescope (+ MOA camera) at Mt. John Observatory reveals that
the counterpart has not changed in brightness by more than 0.1 mag
since May 1.6. Additional spectroscopy and photometry during the
outburst will be highly valuable."
- IAUC 7897: 9may02
- D. K. Galloway, E. H. Morgan, R. A. Remillard, and D.
Chakrabarty, Massachusetts Institute of Technology, write:
"Observations of the recently discovered 185-Hz accreting
millisecond pulsar XTE J0929-314 (cf. IAUC 7888, 7889, 7893, 7895)
with RXTE/PCA on May 9.5 UT indicate that the pulsar is still
active at a flux level of about 20 mCrab (2-10 keV), down from 30
mCrab on May 2. Orbital Doppler shifts of the pulse frequency were
clearly detected. Further RXTE observations are scheduled over the
next few days. Multiwavelength follow-up observations are strongly
- IAUC 7900: 16may02
- D. K. Galloway, E. H. Morgan, R. A. Remillard and D.
Chakrabarty, Massachusetts Institute of Technology, report: "We
have computed provisional orbital elements for XTE J0929-314 (cf.
IAUC 7897), using pulse frequency measurements from RXTE/PCA
observations between May 2.54 and 13.83 UT. Assuming a constant
pulsar spin frequency and a circular orbit, our preliminary orbital
solution has binary period 2614.75(15) s, projected semimajor axis
6.1(3) light-ms, and orbital epoch (time of 90 deg mean longitude)
2002 May 11.4941(2) UT at the solar-system barycenter. The derived
barycentric pulsar spin frequency is 185.1052(1) Hz. The inferred
mass function of 2.7 x 10**-7 solar mass is the smallest measured
for any stellar binary. For a 1.4-solar-mass neutron star, the
minimum companion mass is 0.008 solar mass (or 8.5 Jupiter masses).
The x-ray source was active at a flux of 13 mCrab (2-10 keV) on May
15.69. RXTE observations are continuing."
- IAUC 7905: 20may02
- Corrigendum. On IAUC 7900, line 8, *for* UT *read* TDB
The plot below shows the RXTE daily averages as of 11may02 (MJD 52405);
the arrows show the dates of the VLA measurements so far.
The plot below shows the radio light curve as of 8may02; the solid
points with 1-sigma error bars represent the flux densities at 4.86 GHz,
while the upper limit is a 3-sigma non-detection at 8.46 GHz. The
4.86 GHz data are consistent with a point source with a constant flux density
of 0.320+/-0.027 mJy.
Observations at 4.89 GHz on 3, 7, and 8 May 2002 gave clear detections
near the optical position.
Data taken at 8.46 GHz at nearly the same time on 3may02 with an
rms of 0.082 mJy/beam showed no source; the peak within 0.5arcsec
was 0.29 mJy/beam, so this is not a very stringent limit.
In these contour plots the circle shows the optical position (+/-0.5arcsec)
from IAUC 7889; the large cross to the SE shows the optical position from
VSNET/P. Cacella (see below); and the two smaller crosses show the VLA
positions from Gaussian fits to these data (3 and 7 May 2002). My interpretation
is that the positions agree reasonably well.
The best VLA position, based on comparing the 3, 7, and 8 May 2002 4.86 GHz images:
09 29 20.194+/-0.003 -31 23 03.46+/-0.1
The error bars are based on a generous estimate of the scatter between those
three images. This position is measured relative to the IRCF source J0921-2618,
a VLBI and VLA calibrator which is 5.4 degrees away. The reported
optical positions are
09 29 20.16 -31 23 02.7 +/-0.5arcsec;
Greenhill et al., IAUC 7889
09 29 20.222 -31 23 03.58
Please send any questions, comments, or suggestions to Michael Rupen
at the e-mail address given below.
Last modified 20 March 2003