36 research outputs found
Upper Limits on Pulsed Radio Emission from the 6.85 s X-ray Pulsar XTE J0103-728 in the Small Magellanic Cloud
X-ray pulsations with a 6.85 s period were recently detected in the SMC and
were subsequently identified as originating from the Be/X-ray binary system XTE
J0103-728. The recent localization of the source of the X-ray emission has made
a targeted search for radio pulsations from this source possible. The detection
of pulsed radio emission from XTE J0103-728 would make it only the second
system after PSR B1259-63 that is both a Be/X-ray binary and a radio pulsar. We
observed XTE J0103-728 in Feb 2008 with the Parkes 64-m radio telescope soon
after the identification of the source of X-ray pulsations was reported in
order to search for corresponding radio pulsations. We used a continuous 6.4
hour observation with a 256 MHz bandwidth centered at 1390 MHz using the center
beam of the Parkes multibeam receiver. In the subsequent data analysis, which
included a folding search, a Fourier search, a fast-folding algorithm search,
and a single-pulse search, no pulsed signals were found for trial dispersion
measures (DMs) between 0 and 800 pc cm^-3. This DM range easily encompasses the
expected values for sources in the SMC. We place an upper limit of ~45 mJy
kpc^2 on the luminosity of periodic radio emission from XTE J0103-728 at the
epoch of our observation, and we compare this limit to a range of luminosities
measured for PSR B1259-63, the only Be/X-ray binary currently known to emit
radio pulses. We also compare our limit to the radio luminosities of neutron
stars having similarly long spin periods to XTE J0103-728. Since the radio
pulses from PSR B1259-63 are eclipsed and undetectable during the portion of
the orbit near periastron, repeated additional radio search observations of XTE
J0103-728 may be valuable if it is undergoing similar eclipsing and if such
observations are able to sample the orbital phase of this system well.Comment: 16 pages, including 1 table. Accepted for publication in Ap
A Radio Pulsar/X-ray Binary Link
Radio pulsars with millisecond spin periods are thought to have been spun up
by transfer of matter and angular momentum from a low-mass companion star
during an X-ray-emitting phase. The spin periods of the neutron stars in
several such low-mass X-ray binary (LMXB) systems have been shown to be in the
millisecond regime, but no radio pulsations have been detected. Here we report
on detection and follow-up observations of a nearby radio millisecond pulsar
(MSP) in a circular binary orbit with an optically identified companion star.
Optical observations indicate that an accretion disk was present in this system
within the last decade. Our optical data show no evidence that one exists
today, suggesting that the radio MSP has turned on after a recent LMXB phase.Comment: published in Scienc
Green Bank and Effelsberg Radio Telescope Searches for Axion Dark Matter Conversion in Neutron Star Magnetospheres
Axion dark matter (DM) may convert to radio-frequency electromagnetic
radiation in the strong magnetic fields around neutron stars. The radio
signature of such a process would be an ultra-narrow spectral peak at a
frequency determined by the mass of the axion particle. We analyze data we
collected from the Robert C. Byrd Green Bank Telescope in the L-band and the
Effelsberg 100-m Telescope in the L-Band and S-band from a number of sources
expected to produce bright signals of axion-photon conversion, including the
Galactic Center of the Milky Way and the nearby isolated neutron stars RX
J0720.4-3125 and RX J0806.4-4123. We find no evidence for axion DM and are able
to set some of the strongest constraints to-date on the existence of axion DM
in the highly-motivated mass range between ~5-11 eV.Comment: 7+20 pages, 2+17 figures, Supplementary Data at
http://github.com/joshwfoster/RadioAxionSearc
The LOFAR pilot surveys for pulsars and fast radio transients
We have conducted two pilot surveys for radio pulsars and fast transients
with the Low-Frequency Array (LOFAR) around 140 MHz and here report on the
first low-frequency fast-radio burst limit and the discovery of two new
pulsars. The first survey, the LOFAR Pilot Pulsar Survey (LPPS), observed a
large fraction of the northern sky, ~1.4 x 10^4 sq. deg, with 1-hr dwell times.
Each observation covered ~75 sq. deg using 7 independent fields formed by
incoherently summing the high-band antenna fields. The second pilot survey, the
LOFAR Tied-Array Survey (LOTAS), spanned ~600 sq. deg, with roughly a 5-fold
increase in sensitivity compared with LPPS. Using a coherent sum of the 6 LOFAR
"Superterp" stations, we formed 19 tied-array beams, together covering 4 sq.
deg per pointing. From LPPS we derive a limit on the occurrence, at 142 MHz, of
dispersed radio bursts of 107 Jy
for the narrowest searched burst duration of 0.66 ms. In LPPS, we re-detected
65 previously known pulsars. LOTAS discovered two pulsars, the first with LOFAR
or any digital aperture array. LOTAS also re-detected 27 previously known
pulsars. These pilot studies show that LOFAR can efficiently carry out all-sky
surveys for pulsars and fast transients, and they set the stage for further
surveying efforts using LOFAR and the planned low-frequency component of the
Square Kilometer Array.Comment: 18 pages, 10 figures, accepted for A&
Millisecond Pulsar Scintillation Studies with LOFAR: Initial Results
High-precision timing of millisecond pulsars (MSPs) over years to decades is a promising technique for direct detection of gravitational waves at nanohertz frequencies. Time-variable, multi-path scattering in the interstellar medium is a significant source of noise for this detector, particularly as timing precision approaches 10 ns or better forMSPs in the pulsar timing array. Formany MSPs, the scattering delay above 1 GHz is at the limit of detectability; therefore, we study it at lower frequencies. Using the LOw-Frequency ARray (LOFAR) radio telescope, we have analyzed short (5-20 minutes) observations of 3 MSPs in order to estimate the scattering delay at 110-190 MHz, where the number of scintles is large and, hence, the statistical uncertainty in the scattering delay is small. We used cyclic spectroscopy, still relatively novel in radio astronomy, on baseband-sampled data to achieve unprecedented frequency resolution while retaining adequate pulse-phase resolution. We detected scintillation structure in the spectra of theMSPs PSR B1257+12, PSR J1810+1744, and PSR J2317+1439 with diffractive bandwidths of 6 +/- 3, 2.0 +/- 0.3, and similar to 7 kHz, respectively, where the estimate for PSR J2317+1439 is reliable to about a factor of two. For the brightest of the three pulsars, PSR J1810+1744, we found that the diffractive bandwidth has a powerlaw behavior Delta nu(d) proportional to nu(alpha) where. is the observing frequency and alpha = 4.5 +/- 0.5, consistent with a Kolmogorov inhomogeneity spectrum. We conclude that this technique holds promise for monitoring the scattering delay of MSPs with LOFAR and other high-sensitivity, low-frequency arrays like the low-frequency component of the Square Kilometre Array