300 research outputs found
Coherent optical transfer of Feshbach molecules to a lower vibrational state
Using the technique of stimulated Raman adiabatic passage (STIRAP) we have
coherently transferred ultracold 87Rb2 Feshbach molecules into a more deeply
bound vibrational quantum level. Our measurements indicate a high transfer
efficiency of up to 87%. As the molecules are held in an optical lattice with
not more than a single molecule per lattice site, inelastic collisions between
the molecules are suppressed and we observe long molecular lifetimes of about 1
s. Using STIRAP we have created quantum superpositions of the two molecular
states and tested their coherence interferometrically. These results represent
an important step towards Bose-Einstein condensation (BEC) of molecules in the
vibrational ground state.Comment: 4 pages, 5 figure
Cruising through molecular bound state manifolds with radio frequency
The emerging field of ultracold molecules with their rich internal structure
is currently attracting a lot of interest. Various methods have been developed
to produce ultracold molecules in pre-set quantum states. For future
experiments it will be important to efficiently transfer these molecules from
their initial quantum state to other quantum states of interest. Optical Raman
schemes are excellent tools for transfer, but can be involved in terms of
equipment, laser stabilization and finding the right transitions. Here we
demonstrate a very general and simple way for transfer of molecules from one
quantum state to a neighboring quantum state with better than 99% efficiency.
The scheme is based on Zeeman tuning the molecular state to avoided level
crossings where radio-frequency transitions can then be carried out. By
repeating this process at different crossings, molecules can be successively
transported through a large manifold of quantum states. As an important
spin-off of our experiments, we demonstrate a high-precision spectroscopy
method for investigating level crossings.Comment: 5 pages, 5 figures, submitted for publicatio
Status Update of the Parkes Pulsar Timing Array
The Parkes Pulsar Timing Array project aims to make a direct detection of a
gravitational-wave background through timing of millisecond pulsars. In this
article, the main requirements for that endeavour are described and recent and
ongoing progress is outlined. We demonstrate that the timing properties of
millisecond pulsars are adequate and that technological progress is timely to
expect a successful detection of gravitational waves within a decade, or
alternatively to rule out all current predictions for gravitational wave
backgrounds formed by supermassive black-hole mergers.Comment: 10 pages, 3 figures, Amaldi 8 conference proceedings, accepted by
Classical & Quantum Gravit
Polarization studies of Rotating Radio Transients
We study the polarization properties of 22 known rotating radio transients
(RRATs) with the 64-m Parkes radio telescope and present the Faraday rotation
measures (RMs) for the 17 with linearly polarized flux exceeding the off-pulse
noise by 3. Each RM was estimated using a brute-force search over trial
RMs that spanned the maximum measurable range (in steps of 1 ), followed by an
iterative refinement algorithm. The measured RRAT RMs are in the range |RM|
to rad m with an average linear polarization
fraction of per cent. Individual single pulses are observed to be up
to 100 per cent linearly polarized. The RMs of the RRATs and the corresponding
inferred average magnetic fields (parallel to the line-of-sight and weighted by
the free electron density) are observed to be consistent with the Galactic
plane pulsar population. Faraday rotation analyses are typically performed on
accumulated pulsar data, for which hundreds to thousands of pulses have been
integrated, rather than on individual pulses. Therefore, we verified the
iterative refinement algorithm by performing Monte Carlo simulations of
artificial single pulses over a wide range of S/N and RM. At and above a S/N of
17 in linearly polarized flux, the iterative refinement recovers the simulated
RM value 100 per cent of the time with a typical mean uncertainty of
rad m. The method described and validated here has also been
successfully used to determine reliable RMs of several fast radio bursts (FRBs)
discovered at Parkes.Comment: Submitted to MNRAS, 10 pages, 6 figure
The first interferometric detections of Fast Radio Bursts
We present the first interferometric detections of Fast Radio Bursts (FRBs),
an enigmatic new class of astrophysical transient. In a 180-day survey of the
Southern sky we discovered 3 FRBs at 843 MHz with the UTMOST array, as part of
commissioning science during a major ongoing upgrade. The wide field of view of
UTMOST ( deg) is well suited to FRB searches. The primary beam
is covered by 352 partially overlapping fan-beams, each of which is searched
for FRBs in real time with pulse widths in the range 0.655 to 42 ms, and
dispersion measures 2000 pc cm. Detections of FRBs with the UTMOST
array places a lower limit on their distances of km (limit of
the telescope near-field) supporting the case for an astronomical origin.
Repeating FRBs at UTMOST or an FRB detected simultaneously with the Parkes
radio telescope and UTMOST, would allow a few arcsec localisation, thereby
providing an excellent means of identifying FRB host galaxies, if present. Up
to 100 hours of follow-up for each FRB has been carried out with the UTMOST,
with no repeating bursts seen. From the detected position, we present 3
error ellipses of 15 arcsec x 8.4 deg on the sky for the point of origin for
the FRBs. We estimate an all-sky FRB rate at 843 MHz above a fluence of 11 Jy ms of events sky d at the 95
percent confidence level. The measured rate of FRBs at 843 MHz is of order two
times higher than we had expected, scaling from the FRB rate at the Parkes
radio telescope, assuming that FRBs have a flat spectral index and a uniform
distribution in Euclidean space. We examine how this can be explained by FRBs
having a steeper spectral index and/or a flatter log-log
distribution than expected for a Euclidean Universe.Comment: 13 pages, 8 figures, 2 table
Development of a pulsar-based timescale
Using observations of pulsars from the Parkes Pulsar Timing Array (PPTA)
project we develop the first pulsar-based timescale that has a precision
comparable to the uncertainties in international atomic timescales. Our
ensemble of pulsars provides an Ensemble Pulsar Scale (EPS) analogous to the
free atomic timescale Echelle Atomique Libre (EAL). The EPS can be used to
detect fluctuations in atomic timescales and therefore can lead to a new
realisation of Terrestrial Time, TT(PPTA11). We successfully follow features
known to affect the frequency of the International Atomic Timescale (TAI) and
we find marginally significant differences between TT(PPTA11) and TT(BIPM11).
We discuss the various phenomena that lead to a correlated signal in the pulsar
timing residuals and therefore limit the stability of the pulsar timescale.Comment: Accepted for publication in MNRA
Timing analysis for 20 millisecond pulsars in the Parkes Pulsar Timing Array
We present timing models for 20 millisecond pulsars in the Parkes Pulsar
Timing Array. The precision of the parameter measurements in these models has
been improved over earlier results by using longer data sets and modelling the
non-stationary noise. We describe a new noise modelling procedure and
demonstrate its effectiveness using simulated data. Our methodology includes
the addition of annual dispersion measure (DM) variations to the timing models
of some pulsars. We present the first significant parallax measurements for
PSRs J1024-0719, J1045-4509, J1600-3053, J1603-7202, and J1730-2304, as well as
the first significant measurements of some post-Keplerian orbital parameters in
six binary pulsars, caused by kinematic effects. Improved Shapiro delay
measurements have resulted in much improved pulsar mass measurements,
particularly for PSRs J0437-4715 and J1909-3744 with
and respectively. The improved orbital
period-derivative measurement for PSR J0437-4715 results in a derived distance
measurement at the 0.16% level of precision, pc, one of the
most fractionally precise distance measurements of any star to date.Comment: 21 pages, 5 figures, 7 tables. Accepted for publication in MNRA
The UTMOST pulsar timing programme I: overview and first results
We present an overview and the first results from a large-scale pulsar timing
programme that is part of the UTMOST project at the refurbished Molonglo
Observatory Synthesis Radio Telescope (MOST) near Canberra, Australia. We
currently observe more than 400 mainly bright southern radio pulsars with up to
daily cadences. For 205 (8 in binaries, 4 millisecond pulsars) we publish
updated timing models, together with their flux densities, flux density
variability, and pulse widths at 843 MHz, derived from observations spanning
between 1.4 and 3 yr. In comparison with the ATNF pulsar catalogue, we improve
the precision of the rotational and astrometric parameters for 123 pulsars, for
47 by at least an order of magnitude. The time spans between our measurements
and those in the literature are up to 48 yr, which allows us to investigate
their long-term spin-down history and to estimate proper motions for 60
pulsars, of which 24 are newly determined and most are major improvements. The
results are consistent with interferometric measurements from the literature. A
model with two Gaussian components centred at 139 and fits the transverse velocity distribution best. The pulse duty
cycle distributions at 50 and 10 per cent maximum are best described by
log-normal distributions with medians of 2.3 and 4.4 per cent, respectively. We
discuss two pulsars that exhibit spin-down rate changes and drifting subpulses.
Finally, we describe the autonomous observing system and the dynamic scheduler
that has increased the observing efficiency by a factor of 2-3 in comparison
with static scheduling.Comment: 31 pages, 14 figures, 6 tables, accepted for publication in MNRA
The UTMOST Survey for Magnetars, Intermittent pulsars, RRATs and FRBs I: System description and overview
We describe the ongoing `Survey for Magnetars, Intermittent pulsars, Rotating
radio transients and Fast radio bursts' (SMIRF), performed using the newly
refurbished UTMOST telescope. SMIRF repeatedly sweeps the southern Galactic
plane performing real-time periodicity and single-pulse searches, and is the
first survey of its kind carried out with an interferometer. SMIRF is
facilitated by a robotic scheduler which is capable of fully autonomous
commensal operations. We report on the SMIRF observational parameters, the data
analysis methods, the survey's sensitivities to pulsars, techniques to mitigate
radio frequency interference and present some early survey results. UTMOST's
wide field of view permits a full sweep of the Galactic plane to be performed
every fortnight, two orders of magnitude faster than previous surveys. In the
six months of operations from January to June 2018, we have performed
sweeps of the Galactic plane with SMIRF. Notable blind re-detections include
the magnetar PSR J16224950, the RRAT PSR J09413942 and the eclipsing
pulsar PSR J17482446A. We also report the discovery of a new pulsar, PSR
J170554. Our follow-up of this pulsar with the UTMOST and Parkes telescopes
at an average flux limit of mJy and mJy respectively,
categorizes this as an intermittent pulsar with a high nulling fraction of Comment: Submitted to MNRAS, comments welcom
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