22,266 research outputs found
Discovery of an X-ray Nebula associated with PSR J2124-3358
We report the discovery of an X-ray nebula associated with the nearby
millisecond pulsar PSR J2124-3358. This is the first time that extended
emission from a solitary millisecond pulsar is detected. The emission extends
from the pulsar to the northwest by ~ 0.5 arcmin. The spectrum of the nebular
emission can be modeled by a power law spectrum with photon index of 2.2
+/-0.4. This is inline with the emission being originated from accelerated
particles in the post shock flow.Comment: roceedings 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.13-1
Resolving the bow-shock nebula around the old pulsar PSR B1929+10 with multi-epoch Chandra observations
We have studied the nearby old pulsar PSR B1929+10 and its surrounding
interstellar medium utilizing the sub-arcsecond angular resolution of the
Chandra X-ray Observatory. The Chandra data are found to be fully consistent
with the results obtained from deep XMM-Newton observations as far as the
pulsar is concerned. We confirm the non-thermal emission nature of the pulsar's
X-radiation. In addition to the X-ray trail already seen in previous
observations by the ROSAT and XMM-Newton X-ray observatories, we discovered an
arc-like nebula surrounding the pulsar. We interpret the feature as a bow-shock
nebula and discuss its energetics in the context of standard shock theory.Comment: Accepted by A&A, revised in accordance with referee's comment
Adaptive reference model predictive control for power electronics
An adaptive reference model predictive control (ARMPC) approach is proposed as an alternative means of controlling power converters in response to the issue of steady-state residual errors presented in power converters under the conventional model predictive control (MPC). Differing from other methods of eliminating steady-state errors of MPC based control, such as MPC with integrator, the proposed ARMPC is designed to track the so-called virtual references instead of the actual references. Subsequently, additional tuning is not required for different operating conditions. In this paper, ARMPC is applied to a single-phase full-bridge voltage source inverter (VSI). It is experimentally validated that ARMPC exhibits strength in substantially eliminating the residual errors in environment of model mismatch, load change, and input voltage change, which would otherwise be present under MPC control. Moreover, it is experimentally demonstrated that the proposed ARMPC shows a consistent erasion of steady-state errors, while the MPC with integrator performs inconsistently for different cases of model mismatch after a fixed tuning of the weighting factor
Multiwavelength properties of a new Geminga-like pulsar: PSR J2021+4026
In this paper, we report a detailed investigation of the multiwavelength
properties of a newly detected gamma-ray pulsar, PSR J2021+4026, in both
observational and theoretical aspects. We firstly identify an X-ray source in
the XMM-Newton serendipitous source catalogue, 2XMM J202131.0+402645, located
within the 95% confidence circle of PSR J2021+4026. With an archival Chandra
observation, this identification provides an X-ray position with arcsecond
accuracy which is helpful in facilitating further investigations. Searching for
the pulsed radio emission at the position of 2XMM J202131.0+402645 with a 25-m
telescope at Urumqi Astronomical Observatory resulted in null detection and
places an upper-limit of 0.1~mJy for any pulsed signal at 18~cm. Together with
the emission properties in X-ray and gamma-ray, the radio quietness suggests
PSR J2021+4026 to be another member of Geminga-like pulsars. In the radio sky
survey data, extended emission features have been identified in the gamma-ray
error circle of PSR J2021+4026. We have also re-analyzed the gamma-ray data
collected by FERMI's Large Area Telescope. We found that the X-ray position of
2XMM J202131.0+402645 is consistent with that of the optimal gamma-ray timing
solution. We have further modeled the results in the context of outer gap model
which provides us with constraints for the pulsar emission geometry such as
magnetic inclination angle and the viewing angle. We have also discussed the
possibility of whether PSR J2021+4026 has any physical association with the
supernova remnant G78.2+2.1 (gamma-Cygni).Comment: 11 pages, 14 figure
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