The first Earth-scale quantum sensor network based on optical atomic clocks is looking for dark matter candidates.

Following the recent discovery of γ rays from the radio-loud narrow-line Seyfert 1 galaxy PMN J0948+0022 (z = 0.5846), we started a multiwavelength campaign from radio to γ rays, which was carried out between the end of 2009 March and the beginning of July. The source displayed activity at all the observed wavelengths: a general decreasing trend from optical to γ -ray frequencies was followed by an increase of radio emission after less than two months from the peak of the γ -ray emission. The largest flux change, about a factor of about 4, occurred in the X-ray band. The smallest was at ultraviolet and near-infrared frequencies, where the rate of the detected photons dropped by a factor 1.6-1.9. At optical wavelengths, where the sampling rate was the highest, it was possible to observe day scale variability, with flux variations up to a factor of about 3. The behavior of PMN J0948+0022 observed in this campaign and the calculated power carried out by its jet in the form of protons, electrons, radiation, and magnetic field are quite similar to that of blazars, specifically of flat-spectrum radio quasars. These results confirm the idea that radio-loud narrow-line Seyfert 1 galaxies host relativistic jets with power similar to that of average blazars.

Context. There is growing evidence of relativistic jets in radio-loud narrow-line Seyfert 1 (RL-NLS1) galaxies. Aims. We constrain the observational properties of the radio emission in the first RL-NLS1 galaxy ever detected in gamma-rays, PMN J0948+0022, i.e., its flux density and structure in both total intensity and polarization, its compactness, and variability. Methods. We performed three real-time e-VLBI observations of PMN J0948+0022 at 22 GHz, using a global array including telescopes in Europe, East Asia, and Australia. These are the first e-VLBI science observations ever carried out with a global array, reaching a maximum baseline length of 12 458 km. The observations were part of a large multiwavelength campaign in 2009. Results. The source is detected at all three epochs. The structure is dominated by a bright component, more compact than 55 μas, with a fainter component at a position angle θ ∼ 35 • . Relativistic beaming is required by the observed brightness temperature of 3.4 × 10 11 K. Polarization is detected at a level of about 1%. Conclusions. The parameters derived by the VLBI observations, in addition to the broad-band properties, confirm that PMN J0948+0022 is similar to flat spectrum radio quasars. Global e-VLBI is a reliable and promising technique for future studies.

[1] Precise ionospheric total electron content (TEC) map of the Earth is useful, if it is available for calibration of ionospheric dispersive delay for space measurement techniques using microwave such as GPS, VLBI, and spacecraft navigation. Recent rapid development of GPS techniques is making it more realistic that Earth s ionosphere TEC map measured by GPS observation is practically applicable in those space measurements. For the purpose of evaluating the accuracy of the ionospheric TEC map produced from GPS measurements, two cases of TEC maps were compared with dual band VLBI TEC measurements. In one case, local TEC maps produced from observation data using TECMETERs, which are a kind of GPS receiver for TEC measurements, were compared with VLBI data. As the second case, Global Ionosphere Maps (GIMs) generated by the Center for Orbit determination in Europe (CODE) were compared with VLBI data from short baseline to intercontinental baseline. The ionospheric group delay derived from the local TEC map of the first case had about 80 % correlation with VLBI data on 109 km short baseline. Also the group delay computed by using the GIM data of the CODE (GIM/CODE) had about 90 % correlation with VLBI data on that baseline. In comparisons on intercontinental baselines, correlations between GIM/CODE data and TEC measured by VLBI indicated almost unity. Then it was found that more than 90 % of ionospheric TEC could be predictable with that TEC map. Through further statistical analysis of TEC comparison data, the error spectrum of GIM/CODE data was computed. Comparing the obtained error spectrum with error of the spherical harmonics component of the GIM/CODE data, the latter was always smaller than the former, and the error of GIM/CODE data is suspected to be underestimated, especially at low spatial frequency. It was inferred from the spectrum that more than 0.8 TECU of ionosphere perturbations remain in the higher spatial frequency region, which is not covered by the GIM/CODE model. Total accuracy of GIM/CODE data was evaluated around 3.7 -3.9 TECU. Also phase delay rates derived from the GIM/CODE were compared with VLBI data. It indicated correlation around 0.6 -0.8 on intercontinental baseline, but it is not enough accuracy for practical use in phase delay rate correction in VLBI observation. The reason for low coincidence is understood by the lack of small scale and short timescale TEC variation information in that TEC map model.

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.