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Register a new userAnalyses of Laser Propagation Noises for TianQin Gravitational Wave Observatory Based on the Global Magnetosphere MHD Simulations
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TianQin is a proposed space-borne gravitational wave (GW) observatory composed of three identical satellites orbiting around the geocenter with a radius of $10^5$ km. It aims at detecting GWs in the frequency range of 0.1 mHz -- 1 Hz. The detection of GW relies on the high precision measurement of optical path length at $10^{-12}$~m level. The dispersion of space plasma can lead to the optical path difference (OPD, $Delta l$) along the propagation of laser beams between any pair of satellites. Here, we study the OPD noises for TianQin. The Space Weather Modeling Framework is used to simulate the interaction between the Earth magnetosphere and solar wind. From the simulations, we extract the magnetic field and plasma parameters on the orbits of TianQin at four relative positions of the satellite constellation in the Earth magnetosphere. We calculate the OPD noise for single link, Michelson combination, and Time-Delay Interferometry (TDI) combinations ($alpha$ and $X$). For single link and Michelson interferometer, the maxima of $|Delta l|$ are on the order of 1 pm. For the TDI combinations, these can be suppressed to about 0.004 and 0.008 pm for $alpha$ and $X$. The OPD noise of the Michelson combination is colored in the concerned frequency range; while the ones for the TDI combinations are approximately white. Furthermore, we calculate the ratio of the equivalent strain of the OPD noise to that of TQ, and find that the OPD noises for the TDI combinations can be neglected in the most sensitive frequency range of TQ.
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The TianQin space Gravitational Waves (GW) observatory will contain 3 geocentric and circularly orbiting spacecraft with an orbital radius of 10^5 km, to detect the GW in the milli-hertz frequency band. Each spacecraft pair will establish a 1.7*10^5 km-long laser interferometer immersed in the solar wind and the magnetospheric plasmas to measure the phase deviations induced by the GW. GW detection requires a high-precision measurement of the laser phase. The cumulative effects of the long distance and the periodic oscillations of the plasma density may induce an additional phase noise. This paper aims to model the plasma induced phase deviation of the inter-spacecraft laser signals, using a realistic orbit simulator and the Space Weather Modeling Framework (SWMF) model. Preliminary results show that the plasma density oscillation can induce the phase deviations close to 2*10^-6 rad/Hz^1/2 or 0.3pm/Hz^1/2 in the milli-hertz frequency band and it is within the error budget assigned to the displacement noise of the interferometry. The amplitude spectrum density of phases along three arms become more separated when the orbital plane is parallel to the Sun-Earth line or during a magnetic storm. Finally, the dependence of the phase deviations on the orbital radius is examined.
TianQin is a proposed space-based gravitational wave observatory. It is designed to detect the gravitational wave signals in the frequency range of 0.1 mHz -- 1 Hz. At a geocentric distance of $10^5$ km, the plasma in the earth magnetosphere will contribute as the main source of environmental noises. Here, we analyze the acceleration noises that are caused by the magnetic field of space plasma for the test mass of TianQin. The real solar wind data observed by the Advanced Composition Explorer are taken as the input of the magnetohydrodynamic simulation. The Space Weather Modeling Framework is used to simulate the global magnetosphere of the earth, from which we obtain the plasma and magnetic field parameters on the detectors orbits. We calculate the time series of the residual accelerations and the corresponding amplitude spectral densities on these orbit configurations. We find that the residual acceleration produced by the interaction between the TMs magnetic moment induced by the space magnetic field and the spacecraft magnetic field ($bm{a}_{rm M1}$) is the dominant term, which can approach $10^{-15}$ m/s$^2$/Hz$^{1/2}$ at $f approx$ 0.2 mHz for the nominal values of the magnetic susceptibility ($chi_{rm m} = 10^{-5}$) and the magnetic shielding factor ($xi_{rm m} = 10$) of the test mass. The ratios between the amplitude spectral density of the acceleration noise caused by the space magnetic field and the preliminary goal of the inertial sensor are 0.38 and 0.08 at 1 mHz and 10 mHz, respectively. We discuss the further reduction of this acceleration noise by decreasing $chi_{rm m}$ and/or increasing $xi_{rm m}$ in the future instrumentation development for TianQin.
Gravitational waves from coalescing neutron stars encode information about nuclear matter at extreme densities, inaccessible by laboratory experiments. The late inspiral is influenced by the presence of tides, which depend on the neutron star equation of state. Neutron star mergers are expected to often produce rapidly-rotating remnant neutron stars that emit gravitational waves. These will provide clues to the extremely hot post-merger environment. This signature of nuclear matter in gravitational waves contains most information in the 2-4 kHz frequency band, which is outside of the most sensitive band of current detectors. We present the design concept and science case for a neutron star extreme matter observatory (NEMO): a gravitational-wave interferometer optimized to study nuclear physics with merging neutron stars. The concept uses high circulating laser power, quantum squeezing and a detector topology specifically designed to achieve the high-frequency sensitivity necessary to probe nuclear matter using gravitational waves. Above one kHz, the proposed strain sensitivity is comparable to full third-generation detectors at a fraction of the cost. Such sensitivity changes expected event rates for detection of post-merger remnants from approximately one per few decades with two A+ detectors to a few per year, and potentially allows for the first gravitational-wave observations of supernovae, isolated neutron stars, and other exotica.
In this work, we study the prospect of detecting the stochastic gravitational-wave background with the TianQin observatory. We consider both astrophysical-origin and cosmological-origin sources, including stellar-mass binary black holes, binary neutron stars, Galactic white dwarves, inflation, first order phase transition, and cosmic defects. For the detector configurations, we considered TianQin, TianQin I+II and TianQin + LISA. We studied the detectability of stochastic gravitational-wave backgrounds with the assumed methods of both cross-correlation and null channel, and present the corresponding power-law integrated sensitivity curves. We introduce the definition of the joint foreground with a network of detectors. With the joint foreground, the number of resolved double white dwarves in the Galaxy will be increased by 5% $sim$ 22% compared with simple combination of individual detectors. The astrophysical background from the binary black holes and the binary neutron stars under the theoretical models are predicted to be detectable with signal-to-noise ratio of around 10 after five years operation. As for the cosmological sources, their models are highly uncertain, and we only roughly estimate the detection capability under certain cases.
We describe an atom interferometric gravitational wave detector design that can operate in a resonant mode for increased sensitivity. By oscillating the positions of the atomic wavepackets, this resonant detection mode allows for coherently enhanced, narrow-band sensitivity at target frequencies. The proposed detector is flexible and can be rapidly switched between broadband and narrow-band detection modes. For instance, a binary discovered in broadband mode can subsequently be studied further as the inspiral evolves by using a tailored narrow-band detector response. In addition to functioning like a lock-in amplifier for astrophysical events, the enhanced sensitivity of the resonant approach also opens up the possibility of searching for important cosmological signals, including the stochastic gravitational wave background produced by inflation. We give an example of detector parameters which would allow detection of inflationary gravitational waves down to $Omega_text{GW} sim 10^{-14}$ for a two satellite space-based detector.
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