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In this study, we detected the horizontal ground strains induced by the atmospheric Lamb wave emitted from the 2022 eruption of the Tonga–Hunga Ha'apai undersea volcano, at an underground observatory in Kamioka, Japan. The observed strains were in the range of 10 - 11 – 10 - 10 and were measured precisely using a 1500-m laser strainmeter with a high resolution in the order of 10 - 12 . This was one of the first observations of a Lamb wave using a laser strainmeter. The strainmeter was constructed in a tunnel of the KAGRA gravitational-wave telescope. Our observations demonstrate that strain and atmospheric pressure were clearly correlated, resulting in a regression coefficient of - 2.3 - 3.7 × 10 - 10 strain/hPa. This finding was compared with the responses under regular pressure conditions and the estimations obtained using the local deformation and traveling wave models. The observed coefficients for the Lamb wave exhibited smaller magnitudes than those observed under regular conditions and take values between that of the two theoretical models. These results reflect the intermediate scale of the pressure distribution of the Lamb wave between the assumptions of the simple models. The strain variations were also found to have started earlier than the corresponding pressure changes at the observation site with characteristic time lags ranging from 25 to 155 s. In addition, several aspects related to the mechanism that created the time lags are discussed. [ABSTRACT FROM AUTHOR]

KAGRA uses cryogenics to cool its sapphire test masses down to 20 K to reduce the thermal noise. However, cryocooler vibration and structural resonances of the cryostat couple to the test mass and can contaminate the detector sensitivity. We performed vibration analysis of the cooling system at cryogenic temperature to study its impact on detector sensitivity. Our measurements show shield vibration below 1 Hz is not impacted by cryocooler operation or structural resonances and is dominated by ground motion. The noise floor of the shield in the range 1â€"100 Hz was observed to be 2â€"3 orders of magnitude larger than seismic motion even without cryocooler operation. The operation of cryocoolers does not change the noise floor, but 2 Hz peaks and their harmonics were observed over the entire spectrum (1â€"100 Hz). These results were used to calculate the coupling of cooling system vibration to the test mass. We conclude that vibration from the cooling system does not limit KAGRA design sensitivity. [ABSTRACT FROM AUTHOR]

The Hurst exponent was computed locally for three triaxial seismometers monitoring the KAGRA corner station and the two end stations of the interferometer allowing to estimate variability in the persistent behaviour of the seismometer time series. Results show that, in all the three cases considered, the vertical component of the seismometer has lower persistency compared to the horizontal degrees of freedom, as also confirmed by the low frequency region of the amplitude spectral density of the data. Furthermore, data of the horizontal components of the EXV end station, located in the direction of the X arm of the interferometer, exhibits lower values of seismic noise and of its Hurst exponent. This is possibly due to the lack of an exit point at this location, and hence to a reduced human activity, to the presence of water flow in the mine hosting the KAGRA detector or to differences in seismometers' self noise. [ABSTRACT FROM AUTHOR]

Zusammenfassung Seit 2015 wurden in bisher drei Beobachtungsläufen periodische Raumzeitkrümmungen von großen Laserinterferometern gemessen. Das Ergebnis: Fünfzig Gravitationswellensignale konnten in den Daten gefunden werden, die jeweils vom Umkreisen und Verschmelzen von kompakten Doppelsystemen ausgelöst wurden. Zwei dieser beobachteten Systeme bestanden dabei aus Neutronensternen, die anderen Signale entstammen der Verschmelzung von Schwarzen Löchern. Durch diese Messungen wird ein bisher kaum zugänglicher Bereich des Universums nach und nach sichtbar. Es zeichnet sich ab, dass auch in Zukunft die Signale vieler verschmelzender Schwarzer Löcher, die jeweils 10 bis 40 Sonnenmassen schwer sind, den Großteil der Beobachtungen ausmachen werden. Allerdings hat der erst kürzlich analysierte Beobachtungslauf auch einige überraschende Messungen beinhaltet. Doppelsysteme, in denen die Masse nicht symmetrisch auf beide Partner verteilt ist, wurden erstmals beobachtet und ihr „Klang" inklusive Obertöne analysiert. In zumindest einem Fall (GW190814) kann das kleine Objekt im System nicht zweifelsfrei identifiziert werden. Bei GW190521 sind die Schwarzen Löcher dagegen so massereich, dass deren Entstehung Rätsel aufgibt. Weitere Beobachtungsläufe, ebenso wie neuartige Gravitationswelleninstrumente, sind für die Zukunft geplant und werden weitere Einsichten zur Zusammensetzung, Entwicklung und Entstehung des Universums liefern. [ABSTRACT FROM AUTHOR]

A laser strainmeter with a 1500-m baseline was constructed at an underground site in Kamioka, Gifu Prefecture, Japan, and has been operating since August 2016. The laser interferometer measures the change in distance between two retroreflectors housed in two vacuum chambers with a separation of 1500 m. The retroreflectors are fixed to the ground in the tunnel of the KAGRA gravitational wave telescope. A high-frequency-stabilized laser is used as a light source; it achieves an Allan variance of 3 × 10. Since operations began, ground motions with large amplitude and timescale variations have been detected. The recorded tidal waveform almost agrees with the theoretical waveform; however, a slight difference of ~13% in amplitude is found, likely due to a topographic effect. The strain spectrum of the observed data for the 1500-m strainmeter indicates that the lowest background noise attained is less than 10 in the mHz band. Seismic waves up to 6 × 10 in amplitude have been observed without saturation or fringe steps. The strainmeter, with its excellent resolution, dynamic range, and bandwidth performance, provides a new method for observing low-frequency ground motion on seismic, geodetic, and intermediate timescales. [ABSTRACT FROM AUTHOR]

Future gravitational wave observatories will be realized underground in order to reduce external disturbances, such as seismic, Newtonian and environmental noises. The Japanese gravitational wave telescope KAGRA is under construction at the Kamioka site and the Einstein Telescope gravitational wave observatory is under study in Europe; the common aspects, the differences and the expected performances of these innovative machines are investigated. [ABSTRACT FROM AUTHOR]

Paramagnetic spin is investigated using electron spin resonance technique at room temperature for a pure sapphire, or single crystalline sapphire that is made without any intentional doping. In particular, the spin density of the pure sapphire is compared with that of a commercial available sapphire. Four kinds of signals are detected for commercially available sapphire, all of which have spin density on the order of 1015 cm-3. It is found that for the pure sapphire, one of them is missing and rest of the three have lower density on the order of 1014 cm-3 or lower. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]