分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Blue large-amplitude pulsators (BLAPs) are a newly discovered type of variable star. Their typical pulsation periods are on the order of a few tens of minutes, with relatively large amplitudes of 0.2-0.4 mag in optical bands, and their rates of period changes are on the order of $10^{-7} yr^{-1}$ (both positive and negative). They are extremely rare objects and attempts to explain their origins and internal structures have attracted a great deal of attention. Previous studies have proposed that BLAPs may be pre-white dwarfs, with masses around $0.3M_\odot$, or core-helium-burning stars in the range of $\sim 0.7-1.1M_\odot$. In this work, we use a number of MESA models to compute and explore whether BLAPs could be explained as shell helium-burning subdwarfs type B (SHeB sdBs). The models that best match existing observational constraints have helium core masses in the range of $\sim 0.45-0.5M_\odot$. Our model predicts that the positive rate of period change may evolve to negative. The formation channels for SHeB sdBs involve binary evolution and although the vast majority of BLAPs do not appear to be binaries (with the exception of HD 133729), the observational constraints are still very poor. Motivated by these findings, we explored the Roche lobe overflow channel. Of the 304 binary evolution models we computed, about half of them are able to produce SHeB sdBs in long-period binaries that evade detection from the limited observations that are currently available.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
X. Zhang
A. Simionescu
C. Stuardi
R. J. van Weeren
H. T. Intema
H. Akamatsu
J. de Plaa
J. S. Kaastra
A. Bonafede
M. Brüggen
J. ZuHone
Y. Ichinohe
摘要： Knowledge of X-ray shock and radio relic connection in merging galaxy clusters has been greatly extended in terms of both observation and theory over the last decade. ZwCl 2341+0000 is a double-relic merging galaxy cluster; previous studies have shown that half of the S relic is associated with an X-ray surface brightness discontinuity, while the other half not. The discontinuity was believed to be a shock front. Therefore, it is a mysterious case of an only partial shock-relic connection. By using the 206.5 ks deep Chandra observations, we aim to investigate the nature of the S discontinuity. Meanwhile, we aim to explore new morphological and thermodynamical features. In addition, we utilize the GMRT and JVLA images to compute radio spectral index (SI) maps. In the deep observations, the previously reported S surface brightness discontinuity is better described as a sharp change in slope or as a kink, which is likely contributed by the disrupted core of the S subcluster. The radio SI maps show spectral flattening at the SE edge of the S relic, suggesting that the location of the shock front is 640 kpc away from the kink. We update the radio shock Mach number to be $2.2\pm0.1$ and $2.4\pm0.4$ for the S and N radio relics, respectively, based on the injection SI. We also put a 3 sigma lower limit on the X-ray Mach number of the S shock to be >1.6. Meanwhile, the deep observations reveal that the N subcluster is in a perfect cone shape, with a ~400 kpc linear cold front on each side. This type of conic subcluster has been predicted by simulations but is observed here for the first time. It represents a transition stage between a blunt-body cold front and a slingshot cold front. Strikingly, we found a 400 kpc long gas trail attached to the apex of the cone, which could be due to the gas stripping. In addition, an over-pressured hot region is found in the SW flank of the cluster.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
R. Cassano
V. Cuciti
G. Brunetti
A. Botteon
M. Rossetti
L. Bruno
A. Simionescu
F. Gastaldello
R. J. van Weeren
M. Brueggen
D. Dallacasa
X. Zhang
H. Akamatsu
A. Bonafede
G. Di Gennaro
T. W. Shimwell
F. de Gasperin
H. J. A. Roettgering
A. Jones
摘要： Diffuse cluster-scale synchrotron radio emission is discovered in an increasing number of galaxy clusters in the form of radio halos (RHs), probing the presence of relativistic electrons and magnetic fields in the intra-cluster medium. The favoured scenario to explain their origin is that they trace turbulent regions generated during cluster mergers where particles are re-accelerated. In this framework, RHs are expected to probe cluster dynamics and are predicted to be more frequent in massive systems. Statistical studies are important to study the connection of RHs with cluster dynamics and to constrain theoretical models. Furthermore, low-frequency surveys can shed light on the existence of RHs with very steep radio-spectra, a key prediction of turbulent models. We study the properties of RHs from clusters of the second catalog of Planck Sunyaev Zel'dovich detected sources that lie within the 5634 deg^2 covered by the second Data Release (DR2) of the LOFAR Two-meter Sky Survey. We find that the number of observed RHs, their radio flux density and redshift distributions are in line with what is expected in the framework of the re-acceleration scenario. In addition, the fraction of clusters with RHs increases with the cluster mass, confirming the leading role of the gravitational process of cluster formation in the generation of RHs. These models predict a large fraction of RHs with very steep spectrum in the DR2 Planck sample, this will be tested in future studies, yet a comparison of the occurrence of halos in GMRT and LOFAR samples indeed shows a larger occurrence of RHs at lower frequencies suggesting the presence of a number of very steep spectrum RH that is preferentially detected by LOFAR. Using morphological information we confirm that RHs are preferentially located in merging systems and that the fraction of newly LOFAR discovered RHs is larger in less disturbed systems.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
X. Zhang
A. Simionescu
F. Gastaldello
D. Eckert
L. Camillini
R. Natale
M. Rossetti
G. Brunetti
H. Akamatsu
A. Botteon
R. Cassano
V. Cuciti
L. Bruno
T. W. Shimwell
A. Jones
J. S. Kaastra
S. Ettori
M. Brüggen
F. de Gasperin
A. Drabent
摘要： The footprint of LoTSS-DR2 covers 309 PSZ2 galaxy clusters, 83 of which host a radio halo and 26 host a radio relic(s). It provides us an excellent opportunity to statistically study the properties of extended cluster radio sources, especially their connection with merging activities. We aim to quantify cluster dynamic states to investigate their relation with the occurrence of extended radio sources. We also search for connections between intracluster medium (ICM) turbulence and nonthermal characteristics of radio halos in the LoTSS-DR2. We analyzed XMM-Newton and Chandra archival X-ray data and computed concentration parameters and centroid shifts that indicate the dynamic states of the clusters. We also performed a power spectral analysis of the X-ray surface brightness (SB) fluctuations to investigate large-scale density perturbations and estimate the turbulent velocity dispersion. The power spectral analysis results in a large scatter density fluctuation amplitude. We therefore only found a marginal anticorrelation between density fluctuations and cluster relaxation state, and we did not find a correlation between density fluctuations and radio halo power. Nevertheless, the injected power for particle acceleration calculated from turbulent dissipation is correlated with the radio halo power, where the best-fit unity slope supports the turbulent (re)acceleration scenario. Two different acceleration models, transit-time damping and adiabatic stochastic acceleration, cannot be distinguished due to the large scatter of the estimated turbulent Mach number. We introduced a new quantity $[kT\cdot Y_X]_{r_\mathrm{RH}}$, which is proportional to the turbulent acceleration power assuming a constant Mach number. This quantity is strongly correlated with radio halo power, where the slope is also unity.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Blue large-amplitude pulsators (BLAPs) are a newly discovered type of variable star. Their typical pulsation periods are on the order of a few tens of minutes, with relatively large amplitudes of 0.2-0.4 mag in optical bands, and their rates of period changes are on the order of $10^{-7} yr^{-1}$ (both positive and negative). They are extremely rare objects and attempts to explain their origins and internal structures have attracted a great deal of attention. Previous studies have proposed that BLAPs may be pre-white dwarfs, with masses around $0.3M_\odot$, or core-helium-burning stars in the range of $\sim 0.7-1.1M_\odot$. In this work, we use a number of MESA models to compute and explore whether BLAPs could be explained as shell helium-burning subdwarfs type B (SHeB sdBs). The models that best match existing observational constraints have helium core masses in the range of $\sim 0.45-0.5M_\odot$. Our model predicts that the positive rate of period change may evolve to negative. The formation channels for SHeB sdBs involve binary evolution and although the vast majority of BLAPs do not appear to be binaries (with the exception of HD 133729), the observational constraints are still very poor. Motivated by these findings, we explored the Roche lobe overflow channel. Of the 304 binary evolution models we computed, about half of them are able to produce SHeB sdBs in long-period binaries that evade detection from the limited observations that are currently available.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
A. Jones
F. de Gasperin
V. Cuciti
A. Botteon
X. Zhang
F. Gastaldello
T. Shimwell
A. Simionescu
M. Rossetti
R. Cassano
H. Akamatsu
A. Bonafede
M. Brüggen
G. Brunetti
L. Camillini
G. Di Gennaro
A. Drabent
D. N. Hoang
K. Rajpurohit
R. Natale
摘要： Context. It is well-established that shock waves in the intracluster medium launched by galaxy cluster mergers can produce synchrotron emission, which is visible to us at radio frequencies as radio relics. However, the particle acceleration mechanism producing these relics is still not fully understood. It is also unclear how relics relate to radio halos, which trace merger-induced turbulence in the intracluster medium. Aims. We aim to perform the first statistical analysis of radio relics in a mass-selected sample of galaxy clusters, using homogeneous observations. Methods. We analysed all relics observed by the Low Frequency Array Two Metre Sky Survey Data Release 2 (LoTSS DR2) at 144 MHz, hosted by galaxy clusters in the second Planck catalogue of SZ sources (PSZ2). We measured and compared the relic properties in a uniform, unbiased way. In particular, we developed a method to describe the characteristic downstream width in a statistical manner. Additionally, we searched for differences between radio relic-hosting clusters with and without radio halos. Results. We find that, in our sample, $\sim$ 10% of galaxy clusters host at least one radio relic. We confirm previous findings, at higher frequencies, of a correlation between the relic-cluster centre distance and the longest linear size, as well as the radio relic power and cluster mass. However, our findings suggest that we are still missing a population of low-power relics. We also find that relics are wider than theoretically expected, even with optimistic downstream conditions. Finally, we do not find evidence of a single property that separates relic-hosting clusters with and without radio halos.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Z. Rustamkulov
D. K. Sing
S. Mukherjee
E. M. May
J. Kirk
E. Schlawin
M. R. Line
C. Piaulet
A. L. Carter
N. E. Batalha
J. M. Goyal
M. López-Morales
J. D. Lothringer
R. J. MacDonald
S. E. Moran
K. B. Stevenson
H. R. Wakeford
N. Espinoza
J. L. Bean
N. M. Batalha
摘要： Transmission spectroscopy of exoplanets has revealed signatures of water vapor, aerosols, and alkali metals in a few dozen exoplanet atmospheres. However, these previous inferences with the Hubble and Spitzer Space Telescopes were hindered by the observations' relatively narrow wavelength range and spectral resolving power, which precluded the unambiguous identification of other chemical species$-$in particular the primary carbon-bearing molecules. Here we report a broad-wavelength 0.5-5.5 $\mu$m atmospheric transmission spectrum of WASP-39 b, a 1200 K, roughly Saturn-mass, Jupiter-radius exoplanet, measured with JWST NIRSpec's PRISM mode as part of the JWST Transiting Exoplanet Community Early Release Science Team program. We robustly detect multiple chemical species at high significance, including Na (19$\sigma$), H$_2$O (33$\sigma$), CO$_2$ (28$\sigma$), and CO (7$\sigma$). The non-detection of CH$_4$, combined with a strong CO$_2$ feature, favours atmospheric models with a super-solar atmospheric metallicity. An unanticipated absorption feature at 4$\mu$m is best explained by SO$_2$ (2.7$\sigma$), which could be a tracer of atmospheric photochemistry. These observations demonstrate JWST's sensitivity to a rich diversity of exoplanet compositions and chemical processes.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
A. Liu
E. Bulbul
M. E. Ramos-Ceja
J. S. Sanders
V. Ghirardini
Y. E. Bahar
M. Yeung
E. Gatuzz
M. Freyberg
C. Garrel
X. Zhang
A. Merloni
K. Nandra
摘要： SMACS~J0723.3-7327 is the first galaxy cluster lens observed by JWST. Based on the ERO data from JWST, several groups have reported the results on strong lensing analysis and mass distribution of this cluster. However, limited by the angular coverage of the JWST data, the strong lensing models only cover the central region. X-ray analysis on the hot ICM is necessary to obtain a more complete constraint on the mass distribution in this very massive cluster. In this work, we aim to perform a comprehensive X-ray analysis of J0723 to obtain accurate ICM hydrostatic mass measurements, using the X-ray data from SRG/eROSITA and Chandra X-ray observatories. By comparing the hydrostatic mass profile with the strong lensing model, we aim to provide the most reliable constraint on the distribution of mass up to R500. Thanks to the eROSITA all-sky survey and Chandra data, which provide high S/N and high angular resolution respectively, we are able to constrain the ICM gas density profile and temperature profile with good accuracy both in the core and to the outskirts. With the density and temperature profiles, we compute the hydrostatic mass profile, which is then projected along the line of sight to compare with the mass distribution obtained from the recent strong lensing analysis based on JWST data. We also deproject the strong lensing mass distribution using the hydrostatic mass profile we obtained in this work. The X-ray results obtained from eROSITA and Chandra agree very well with each other. The hydrostatic mass profiles we measured in this work, both projected and deprojected, are in good agreement with recent strong lensing results based on JWST data, at all radii. We also find that the radial acceleration relation in J0723 is inconsistent with the RAR for spiral galaxies, implying that the latter is not a universal property of gravity across all mass scales.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
J. ZuHone
Y. E. Bahar
V. Biffi
K. Dolag
J. Sanders
E. Bulbul
T. Liu
T. Dauser
O. König
X. Zhang
V. Ghirardini
摘要： The number density of galaxy clusters as a function of mass and redshift is a sensitive function of the cosmological parameters. To use clusters for cosmological parameter studies, it is necessary to determine their masses as accurately as possible, which is typically done via mass-observable scaling relations. X-ray observables can be biased by multiphase gas and projection effects, especially in the case where cluster temperatures and luminosities are estimated from single-model fits to all of the emission with a given radius. Using simulated galaxy clusters from a realistic cosmological simulation, we seek to determine the importance of these biases in the context of Spectrum-Roentgen-Gamma/eROSITA observations of clusters. We extract clusters from the Magneticum suite, and simulate eROSITA observations of these clusters using PHOX and SIXTE. We compare the fitted observables from these observations to those derived from the simulations. We fitted an intrinsically scattered $L_{\rm X}-T$ scaling relation to these measurements following a Bayesian approach with which we fully took into account the selection effects and the mass function. The largest biases on the cluster observables come from the inadequacy of single-temperature model fits to represent emission from multiphase gas, as well as a bias arising from cluster emission within the projected $r_{500c}$ along the line of sight but outside of the spherical $r_{500c}$. We find that the biases on temperature and luminosity due to the projection of emission from other clusters within $r_{500c}$ is small. We find that our simulated clusters follow a $L_{\rm X}-T$ scaling relation that has a broadly consistent but slightly shallower slope compared to the literature, and that the intrinsic scatter of $L_{\rm X}$ at given T is lower compared to the recent observational results where the selection effects are fully considered.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Ultra-high-Q resonators are fundamentally important to optics and microwave photonics. Up to now, it is still very challenging to boost the Q factor while maintaining a compact size for a resonator. Herein, we proposed and demonstrated an ultra-high-Q silicon-nitride (Si3N4) racetrack resonator with uniform multi-mode Si3N4 photonic waveguides. It consists of two multi-mode straight waveguides connected by two multi-mode waveguide bends (MWBs). In particular, the MWBs are based on modified Euler curves, and a multi-mode straight waveguide directional coupler is used for the fundamental mode coupling and avoid exciting higher-order modes in the racetrack. In this way, the fundamental mode is excited and propagates in the multi-mode racetrack resonator with ultra-low loss. Meanwhile, it helps to achieve a compact 180{\deg} bend to reduce the chip footprint. In this paper, the propagation loss of the fundamental mode is significantly reduced with standard fabrication process by broadening the waveguides width to as wide as 3{\mu}m. Results show that an ultra-high-Q resonator with an intrinsic Q of TE mode is 4.57*10^7, and the corresponding propagation loss of the waveguide is only 1.80 dB/m. To the best of our knowledge, this is the highest Q value of the ring resonator with only 2.226 mm ring length reported so far. The proposed ultra-high-Q Si3N4 resonator can be used to microwave photonic filters and optoelectronic oscillators with large operation bandwidth.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Maxwell fisheye lens was proposed to pinpoint super-resolution with the addition of wave drain and the interaction of multiple drains is theoretically predicted to improve subwavelength resolution further. In this paper we discuss the role played by port drains in optical absolute instruments, and verify by full-wave simulation that coupling nature for wave source and drain applies correctly in the picture of scanning imaging for absolute instrument. This work prospects for scanning near fields shaped from far-field wave propagation.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： We report in detail the design process and performance of an auto-locking ultra-stable laser with sub-hertz linewidth at the first time. The laser frequency is automatically stabilized to an optical reference cavity with a home-made controller, which is based on a combination of digital circuit and analog circuit. The digital circuit is used for diagnosing and manipulating the state of the ultra-stable laser, and the analog circuit is used for demodulating the discriminate signal and servo control. A method of searching the transmission signal in the closed-loop state instead of the open-loop state is proposed to reduce the locking time and improve the reliable of the auto-locking ultra-stable laser. The median time of 16.6s is obtained after 157 times of relocking, and the probability of less than 20 s is more than 86%. The median linewidth of 1.08 Hz is obtained, and the fractional frequency instability is less than 3.4E-15 at integration time between 0.1 and 100 s. The performance of this system demonstrates that will be used as an important subsystem to transfer the optical clock signal.
分类： 物理学 >> 凝聚态:结构、力学和热性能 提交时间： 2017-03-26
摘要： The effect of Cu content on the evolution of defects in Fe-x%Cu alloys (x= 0.15, 0.3, and 0.6) were investigated using Positron Annihilation Lifetime Spectroscopy. The vacancy-type and Cu-vacancy complexes defects were respectively produced by quenching from 1173 K and cold-rolled deformation followed by isochronal annealing. The isochronal annealing results obtained by PALS showed that Cu-vacancy complexes delayed the complete recovery of vacancy-type defects and the complete recovery temperature increased with the content of Cu in 30% deformed Fe-Cu alloys. The increment of Cu content also restrained the migration of vacancies in as-quenched Fe-Cu alloys.
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