| 1. |
- Aharonian, Felix, et al.
(författare)
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Hitomi X-ray studies of giant radio pulses from the Crab pulsar
- 2018
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Ingår i: Publications of the Astronomical Society of Japan. - : Oxford University Press (OUP). - 0004-6264 .- 2053-051X. ; 70:2
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Tidskriftsartikel (refereegranskat)abstract
- To search for giant X-ray pulses correlated with the giant radio pulses (GRPs) from the Crab pulsar, we performed a simultaneous observation of the Crab pulsar with the X-ray satellite Hitomi in the 2-300 keV band and the Kashima NICT radio telescope in the 1.4-1.7 GHz band with a net exposure of about 2 ks on 2016 March 25, just before the loss of the Hitomi mission. The timing performance of the Hitomi instruments was confirmed to meet the timing requirement and about 1000 and 100 GRPs were simultaneously observed at the main pulse and inter-pulse phases, respectively, and we found no apparent correlation between the giant radio pulses and the X-ray emission in either the main pulse or inter-pulse phase. All variations are within the 2 sigma fluctuations of the X-ray fluxes at the pulse peaks, and the 3 sigma upper limits of variations of main pulse or inter-pulse GRPs are 22% or 80% of the peak flux in a 0.20 phase width, respectively, in the 2-300 keV band. The values for main pulse or inter-pulse GRPs become 25% or 110%, respectively, when the phase width is restricted to the 0.03 phase. Among the upper limits from the Hitomi satellite, those in the 4.5-10 keV and 70-300 keV bands are obtained for the first time, and those in other bands are consistent with previous reports. Numerically, the upper limits of the main pulse and inter-pulse GRPs in the 0.20 phase width are about (2.4 and 9.3) x 10(-11) erg cm(-2), respectively. No significant variability in pulse profiles implies that the GRPs originated from a local place within the magneto-sphere. Although the number of photon-emitting particles should temporarily increase to account for the brightening of the radio emission, the results do not statistically rule out variations correlated with the GRPs, because the possible X-ray enhancement may appear due to a > 0.02% brightening of the pulse-peak flux under such conditions.
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| 2. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Near real-time monitoring of UT1 with geodetic VLBI
- 2011
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Ingår i: Proceedings of the 20th Meeting of the European VLBI Group for Geodesy and Astrometry. - 1864-1113. ; , s. 64-66
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We give a short overview on the current status of near real-time monitoring of UT1 with geodetic VLBI. The use ofreal-time data transfer together with automated correlation and data analysis makes it possible to derive final dUT1-results with very low latency. The agreement with IERS C04 results is on the level of 30 msec. It is even possible to determine time series of dUT1 during ongoing 24 h IVS-sessions. The concept is highly relevant for future VLBI2010 operations.
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| 3. |
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| 4. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Ultra-Rapid DUT1-Observations with E-VLBI
- 2010
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Ingår i: Artificial Satellites. - : Walter de Gruyter GmbH. - 0208-841X .- 2083-6104. ; 45:2 / 2010, s. 75-79
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Konferensbidrag (refereegranskat)abstract
- We give a short overview about the achievements of the Fennoscandian- Japanese ultra-rapid dUT1-project that was initiated in early 2007. The combination of real-time data transfer, near real-time data conversion and correlation, together with near-real time data analysis allows to determine dUT1 with a very low latency of less than 5 minutes after the end of a VLBI-session. The accuracy of these ultra-rapid dUT1-results is on the same order than the results of the standard rapid-service of the International Earth Rotation and Reference Frame Service (IERS). The ultra-rapid approach is currently extended to 24 hour sessions and is expected to become an important contribution for the future next generation VLBI system called VLBI2010.
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| 5. |
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| 6. |
- Koyama, Yasuhiro, et al.
(författare)
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Ultra rapid dUT1 estimations from e-VLBI sessions
- 2010
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Ingår i: Advances in Geosciences: Volume 20: Solid Earth (SE); World Scientific Publishing Company. - : World Scientific Publishing Company. - 9789812838186 ; 20, s. 197-204
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Konferensbidrag (refereegranskat)abstract
- Promptness of the data processing of the international VLBI observations has been continuously improved in the past decades. In particular, e-VLBI technique has proved that it has a capability to shorten the latency by transferring the observed data to the correlator by using high speed communication networks. The method has been introduced to routine intensive VLBI sessions to monitor dUT1. To improve the promptness even further, we started an initiative to develop automated data transfer and data processing systems using Europe-Japan baselines. On February 21, 2008, we succeeded to demonstrate the effectiveness of the developed systems and estimated the dUT1 parameter 3 minutes 45 seconds after the last scan of the one hour intensive style e-VLBI session. This achievement was realized by the developments of the K5/VSSP32 data acquisition terminal, automated data processing and analysis software.
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| 7. |
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| 8. |
- Otsubo, Toshimichi, et al.
(författare)
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Effective expansion of satellite laser ranging network to improve global geodetic parameters
- 2016
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Ingår i: Earth, Planets and Space. - : Springer Science and Business Media LLC. - 1880-5981 .- 1343-8832. ; 68:1
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study is to find an effective way to expand the ground tracking network of satellite laser ranging on the assumption that a new station is added to the existing network. Realistic numbers of observations for a new station are numerically simulated, based on the actual data acquisition statistics of the existing stations. The estimated errors are compared between the cases with and without a new station after the covariance matrices are created from a simulation run that contains six-satellite-combined orbit determination. While a station placed in the southern hemisphere is found to be useful in general, it is revealed that the most effective place differs according to the geodetic parameter. The X and Y components of the geocenter and the sectoral terms of the Earth’s gravity field are largely improved by a station in the polar regions. A middle latitude station best contributes to the tesseral gravity terms, and, to a lesser extent, a low latitude station best performs for the Z component of the geocenter and the zonal gravity terms.
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