5,010 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
Vom Wunder der Freiheit
In the course of the history of democratic voting rights a remarkable development has taken place: collective privileges to vote were completely replaced by a personalisation of voting rights. Today, it is perceived as self-evident that every adult citizen has the right to vote. But neither the classical forms of democracy acknowledged such a right nor is it promoted by the conditions of modern mass society. Therefore, its emergence and dissemination is a historic 'miracle' and an achievement that is based on the fundamental political concept of a 'person'. This concept has to be protected at all tim - and today afresh - against the ever-present dangers of erosion and neglect.democratic voting, individual voting rights, freedom, democracy
HST Proper Motion confirms the optical identification of the nearby pulsar PSR 1929+10
We report on the proper motion measurement of the proposed optical
counterpart of the X-ray/radio pulsar PSR 1929+10. Using images obtained with
the HST/STIS (average epoch 2001.73) we computed a yearly displacement of +97
+/- 1 mas yr^{-1} in RA and +46 +/- 1 mas yr^{-1} in Dec since the epoch
(1994.52) of the original HST/FOC detection. Both the magnitude and direction
of the optical proper motion components are found to be fully consistent with
the most recent VLBA radio measurements. This result provides an unambiguous
confirmation of the pulsar optical identification. In addition, we have used
the combined STIS/FOC datasets to derive information on the pulsar spectrum,
which seems characterized by a power law component, apparently unrelated to the
X-ray emission.Comment: 12 pages, 3 figures, submitted to ApJ Letter
A multiwavlength study of PSR B0628-28: The first overluminous rotation-powered pulsar?
The ROSAT source RX J0630.8-2834 was suggested by positional coincidence to
be the X-ray counterpart of the old field pulsar PSR B0628-28. This
association, however, was regarded to be unlikely based on the computed
energetics of the putative X-ray counterpart. In this paper we report on
multiwavelength observations of PSR B0628-28 made with the ESO/NTT observatory
in La Silla, the Jodrell Bank radio observatory and XMM-Newton. Although the
optical observations do not detect any counterpart of RX J0630.8-2834 down to a
limiting magnitude of V=26.1 mag and B=26.3 mag, XMM-Newton observations
finally confirmed it to be the pulsar's X-ray counterpart by detecting X-ray
pulses with the radio pulsar's spin-period. The X-ray pulse profile is
characterized by a single broad peak with a second smaller peak leading the
main pulse component by ~144 degree. The fraction of pulsed photons is (38 +-
7)% with no strong energy dependence in the XMM-Newton bandpass. The pulsar's
X-ray spectrum is well described by a single component power law with photon
index 2.63^{+0.23}_{-0.15}, indicating that the pulsar's X radiation is
dominated by non-thermal emission processes. A low level contribution of
thermal emission from residual cooling or from heated polar caps, cannot be
excluded. The pulsar's spin-down to X-ray energy conversion efficiency is
obtained to be ~16% for the radio dispersion measure inferred pulsar distance.
If confirmed, PSR B0628-28 would be the first X-ray overluminous
rotation-powered pulsar identified among all ~1400 radio pulsars known today.Comment: Accepted for publication in ApJ. Find a paper copy with higher
resolution images at
ftp://ftp.xray.mpe.mpg.de/people/web/astro-ph-0505488_rev2.pd
X-Rays from the Nearby Solitary Millisecond Pulsar PSR J0030+0451 - the Final ROSAT Observations
We report on X-ray observations of the solitary 4.8 ms pulsar PSR J0030+0451.
The pulsar was one of the last targets observed in DEC-98 by the ROSAT PSPC.
X-ray pulses are detected on a level and make the source the
millisecond pulsar detected in the X-ray domain. The pulsed fraction
is found to be . The X-ray pulse profile is characterized by two
narrow peaks which match the gross pulse profile observed at 1.4 GHz. Assuming
a Crab-like spectrum the X-ray flux is in the range
erg s cm ( keV), implying an X-ray efficiency of
.Comment: Accepted for publication in Ap
One Step Forward, One Step Back: Shale Gas in Denmark and Sweden
Denmark and Sweden take two-fold positions on the question whether shale gas should be developed. At first sight, it appears the governments are supportive by licencing exploration to domestic and foreign companies. However, Denmark has suspended issuance of new licenses as doubts of extraction activities have risen. Sweden was forced to give landowners and municipalities a say in decision-making, and there is a larger context of mining minerals policy controversy. Even though both countries only have exploration activities at the moment, and the economic promise is yet unclear, public awareness and attention are increasing and cause difficulties for governments and industry to proceed without open discussions and debates. Scandinavia’s green image is at stake as the new fossil fuel opportunities are in conflict with the ambitious goals for renewable energy development. Both countries now have to prioritise energy self-sufficiency and industrial economics versus ecological consciousness
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