663 research outputs found
A search for rotating radio transients and fast radio bursts in the Parkes high-latitude pulsar survey
Discoveries of rotating radio transients and fast radio bursts (FRBs) in
pulsar surveys suggest that more of such transient sources await discovery in
archival data sets. Here we report on a single-pulse search for dispersed radio
bursts over a wide range of Galactic latitudes (|b| < ) in data
previously searched for periodic sources by Burgay et al. We re-detected 20 of
the 42 pulsars reported by Burgay et al. and one rotating radio transient
reported by Burke-Spolaor. No FRBs were discovered in this survey. Taking into
account this result, and other recent surveys at Parkes, we corrected for
detection sensitivities based on the search software used in the analyses and
the different backends used in these surveys and find that the all-sky FRB
event rate for sources with a fluence above 4.0 Jy ms at 1.4 GHz to be FRBs day sky, where the
uncertainties represent a confidence interval. While this rate is lower
than inferred from previous studies, as we demonstrate, this combined event
rate is consistent with the results of all systematic FRB searches at Parkes to
date and does not require the need to postulate a dearth of FRBs at
intermediate latitudes.Comment: Accepted, 10 pages, 6 figure
Review of X-ray pulsar spacecraft autonomous navigation
This article provides a review on X-ray pulsar-based navigation (XNAV). The
review starts with the basic concept of XNAV, and briefly introduces the past,
present and future projects concerning XNAV. This paper focuses on the advances
of the key techniques supporting XNAV, including the navigation pulsar
database, the X-ray detection system, and the pulse time of arrival estimation.
Moreover, the methods to improve the estimation performance of XNAV are
reviewed. Finally, some remarks on the future development of XNAV are provided.Comment: has been accepted by Chinese Journal of Aeronautic
A Norm-Minimization Algorithm for Solving the Cold-Start Problem with XNAV
An algorithm is presented for solving the cold-start problem using
observations of X-ray pulsars. Using a norm-minimization-based approach, the
algorithm extends Lohan's banded-error intersection model to 3-dimensional
space while reducing compute time by an order of magnitude. Higher-fidelity
X-ray pulsar signal models, including the parallax effect, Shapiro delay, time
dilation, and higher-order pulsar timing models, are considered. The
feasibility of solving the cold-start problem using X-ray pulsar navigation is
revisited with the improved models and prior knowledge requirements are
discussed. Monte Carlo simulations are used to establish upper bounds on
uncertainty and determine the accuracy of the algorithm. Results indicate that
it is necessary to account for the parallax effect, time dilation, and
higher-order pulsar timing models in order to successfully determine the
position of the spacecraft in a cold-start scenario. The algorithm can uniquely
identify a candidate spacecraft position within a 10 AU 10 AU
0.01 AU spheroid domain by observing eight to nine pulsars. The median position
error of the algorithm is on the order of 15 km. Prior knowledge of spacecraft
position is technically required, but only to an accuracy of 100 AU, making it
practically unnecessary for navigation within the Solar System. Results further
indicate that choosing lower-frequency pulsars increases the maximum domain
size but also increases position error.Comment: 20 pages, 15 figures. Conference paper at the AAS/AIAA Astrodynamics
Specialist Conference, Charlotte, NC, August 2022. AAS 22-56
Dense matter with eXTP
In this White Paper we present the potential of the Enhanced X-ray Timing and
Polarimetry (eXTP) mission for determining the nature of dense matter; neutron
star cores host an extreme density regime which cannot be replicated in a
terrestrial laboratory. The tightest statistical constraints on the dense
matter equation of state will come from pulse profile modelling of
accretion-powered pulsars, burst oscillation sources, and rotation-powered
pulsars. Additional constraints will derive from spin measurements, burst
spectra, and properties of the accretion flows in the vicinity of the neutron
star. Under development by an international Consortium led by the Institute of
High Energy Physics of the Chinese Academy of Science, the eXTP mission is
expected to be launched in the mid 2020s.Comment: Accepted for publication on Sci. China Phys. Mech. Astron. (2019
Fast On-orbit Pulse Phase Estimation of X-ray Crab Pulsar for XNAV Flight Experiments
The recent flight experiments with Neutron Star Interior Composition Explorer
(\textit{NICER}) and \textit{Insight}-Hard X-ray Modulation Telescope
(\textit{Insight}-HXMT) have demonstrated the feasibility of X-ray pulsar-based
navigation (XNAV) in the space. However, the current pulse phase estimation and
navigation methods employed in the above flight experiments are computationally
too expensive for handling the Crab pulsar data. To solve this problem, this
paper proposes a fast algorithm of on-orbit estimating the pulse phase of Crab
pulsar called X-ray pulsar navigaTion usIng on-orbiT pulsAr timiNg (XTITAN).
The pulse phase propagation model for Crab pulsar data from
\textit{Insight}-HXMT and \textit{NICER} are derived. When an exposure on the
Crab pulsar is divided into several sub-exposures, we derive an on-orbit timing
method to estimate the hyperparameters of the pulse phase propagation model.
Moreover, XTITAN is improved by iteratively estimating the pulse phase and the
position and velocity of satellite. When applied to the Crab pulsar data from
\textit{NICER}, XTITAN is 58 times faster than the grid search method employed
by \textit{NICER} experiment. When applied to the Crab pulsar data from
\textit{Insight}-HXMT, XTITAN is 180 times faster than the Significance
Enhancement of Pulse-profile with Orbit-dynamics (SEPO) which was employed in
the flight experiments with \textit{Insight}-HXMT. Thus, XTITAN is
computationally much efficient and has the potential to be employed for onboard
computation
Application of Pulsar-Based Navigation for Deep-Space CubeSats
This paper investigates the use of pulsar-based navigation for deep-space CubeSats. A novel approach for dealing with the onboard computation of navigational solutions and timekeeping capabilities of a spacecraft in a deep-space cruise is shown, and the related implementation and numerical simulations are discussed. The pulsarâs signal detection, processing, and exploitation are simulated for navigation onboard a spacecraft, thus showing the feasibility of autonomous state estimation in deep space even for miniaturized satellites
Pathway to the Square Kilometre Array - The German White Paper -
The Square Kilometre Array (SKA) is the most ambitious radio telescope ever
planned. With a collecting area of about a square kilometre, the SKA will be
far superior in sensitivity and observing speed to all current radio
facilities. The scientific capability promised by the SKA and its technological
challenges provide an ideal base for interdisciplinary research, technology
transfer, and collaboration between universities, research centres and
industry. The SKA in the radio regime and the European Extreme Large Telescope
(E-ELT) in the optical band are on the roadmap of the European Strategy Forum
for Research Infrastructures (ESFRI) and have been recognised as the essential
facilities for European research in astronomy.
This "White Paper" outlines the German science and R&D interests in the SKA
project and will provide the basis for future funding applications to secure
German involvement in the Square Kilometre Array.Comment: Editors: H. R. Kl\"ockner, M. Kramer, H. Falcke, D.J. Schwarz, A.
Eckart, G. Kauffmann, A. Zensus; 150 pages (low resolution- and colour-scale
images), published in July 2012, language English (including a foreword and
an executive summary in German), the original file is available via the MPIfR
homepag
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