680 research outputs found
Autonomous Spacecraft Navigation With Pulsars
An external reference system suitable for deep space navigation can be
defined by fast spinning and strongly magnetized neutron stars, called pulsars.
Their beamed periodic signals have timing stabilities comparable to atomic
clocks and provide characteristic temporal signatures that can be used as
natural navigation beacons, quite similar to the use of GPS satellites for
navigation on Earth. By comparing pulse arrival times measured on-board a
spacecraft with predicted pulse arrivals at a reference location, the
spacecraft position can be determined autonomously and with high accuracy
everywhere in the solar system and beyond. The unique properties of pulsars
make clear already today that such a navigation system will have its
application in future astronautics. In this paper we describe the basic
principle of spacecraft navigation using pulsars and report on the current
development status of this novel technology.Comment: 22 pages, 12 figures, 2 tables, to be published in the proceedings of
the workshop "Relativistic Positioning Systems and their Scientific
Applications", held on 19-21 Sept. 2012, Brdo near Kranj, Sloveni
Comparison of giant radio pulses in young pulsars and millisecond pulsars
Pulse-to-pulse intensity variations are a common property of pulsar radio
emission. For some of the objects single pulses are often 10-times stronger
than their average pulse. The most dramatic events are so-called giant radio
pulses (GRPs). They can be thousand times stronger than the regular single
pulses from the pulsar. Giant pulses are a rare phenomenon, occurring in very
few pulsars which split into two groups. The first group contains very young
and energetic pulsars like the Crab pulsar, and its twin (PSR B0540-69) in the
Large Magellanic Cloud (LMC), while the second group is represented by old,
recycled millisecond pulsars like PSR B1937+21, PSR B1821-24, PSR B1957+20 and
PSR J0218+4232 (the only millisecond pulsar detected in gamma-rays). We compare
the characteristics of GRPs for these two pulsar groups. Moreover, our latest
findings of new features in the Crab GRPs are presented. Analysis of our
Effelsberg data at 8.35 GHz shows that GRPs do occur in all phases of its
ordinary radio emission, including the phases of the two high frequency
components (HFCs) visible only between 5 and 9 GHz.Comment: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and
Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany,
May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.64-6
Polarization characteristics of the Crab pulsar's giant radio pulses at HFCs phases
We discuss our recent discovery of the giant radio emission from the Crab
pulsar at its high frequency components (HFCs) phases and show the polarization
characteristic of these pulses. This leads us to a suggestion that there is no
difference in the emission mechanism of the main pulse (MP), interpulse (IP)
and HFCs. We briefly review the size distributions of the Crab giant radio
pulses (GRPs) and discuss general characteristics of the GRP phenomenon in the
Crab and other pulsars.Comment: AIP Conference Proceedings "Astrophysical Sources of High Energy
Particles and Radiation", eds. T. Bulik et al. (NY:AIP), Volume 801, 2005,
pp. 324-32
An Experimental Investigation of the Dead Time of Geiger-Mueller Counters
As ever more sensitive and precise experiments are being performed with Geiger Counters, especially in cosmic ray research, the resolving power of these instruments assumes an ever increasing importance. With the present perfection of electronic circuitry, this resolving time has become largely a function of the dead time of the Geiger counter tube itself. It was therefore proposed to investigate methods of reducing this dead time. Only self-quenching counter tubes had to be considered in this connection since the dead time of all other types of Geiger counters is inherently longer
- …