分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The microwave spectrum contains valuable information about solar flares. Yet, the present spectral coverage is far from complete and broad data gaps exist above 20 GHz. Here we report the first flare (the X2.2 flare on 2022 April 20) observation of the newly-built Chashan Broadband Solar millimeter spectrometer (CBS) working from 35 to 40 GHz. We use the CBS data of the new Moon to calibrate,and the simultaneous NoRP data at 35 GHz to cross-calibrate. The impulsive stage has three local peaks with the middle one being the strongest and the maximum flux density reaches 9300 SFU at 35-40 GHz. The spectral index of the CBS data (alpha_C) for the major peak is mostly positive, indicating the gyrosynchrotron turnover frequency (nu_t) goes beyond 35-40 GHz. The frequency nu_t is smaller yet still larger than 20 GHz for most time of the other two peaks according to the spectral fittings with NoRP-CBS data. The CBS index manifests the general rapid-hardening-then-softening trend for each peak and gradual hardening during the decay stage, agreeing with the fitted optically-thin spectral index (alpha_tn) for nu_t 20 GHz).
分类： 天文学 >> 天文学 提交时间： 2023-02-19
The LIGO Scientific Collaboration
the Virgo Collaboration
the KAGRA Collaboration
R. Abbott
H. Abe
F. Acernese
K. Ackley
S. Adhicary
N. Adhikari
R. X. Adhikari
V. K. Adkins
V. B. Adya
C. Affeldt
D. Agarwal
M. Agathos
O. D. Aguiar
L. Aiello
A. Ain
P. Ajith
T. Akutsu
摘要： We describe a search for gravitational waves from compact binaries with at least one component with mass 0.2 $M_\odot$ -- $1.0 M_\odot$ and mass ratio $q \geq 0.1$ in Advanced LIGO and Advanced Virgo data collected between 1 November 2019, 15:00 UTC and 27 March 2020, 17:00 UTC. No signals were detected. The most significant candidate has a false alarm rate of 0.2 $\mathrm{yr}^{-1}$. We estimate the sensitivity of our search over the entirety of Advanced LIGO's and Advanced Virgo's third observing run, and present the most stringent limits to date on the merger rate of binary black holes with at least one subsolar-mass component. We use the upper limits to constrain two fiducial scenarios that could produce subsolar-mass black holes: primordial black holes (PBH) and a model of dissipative dark matter. The PBH model uses recent prescriptions for the merger rate of PBH binaries that include a rate suppression factor to effectively account for PBH early binary disruptions. If the PBHs are monochromatically distributed, we can exclude a dark matter fraction in PBHs $f_\mathrm{PBH} \gtrsim 0.6$ (at 90% confidence) in the probed subsolar-mass range. However, if we allow for broad PBH mass distributions we are unable to rule out $f_\mathrm{PBH} = 1$. For the dissipative model, where the dark matter has chemistry that allows a small fraction to cool and collapse into black holes, we find an upper bound $f_{\mathrm{DBH}} < 10^{-5}$ on the fraction of atomic dark matter collapsed into black holes.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We identify substructures of the Galactic halo using 3,003 type $ab$ RR Lyraes (RRab) with 6D position-velocity information from the SDSS, LAMOST, and Gaia EDR3. Based on the information, we define the separation of any two of the stars in the integrals of motion space and identify substructures by utilizing the friends-of-friends algorithm. We identify members belonging to several known substructures: the Sagittarius stream, the Gaia-Enceladus-Sausage (GES), the Sequoia, and the Helmi streams. In addition to these known substructures, there are three other substructures possibly associated with globular clusters NGC 5272, NGC 6656, and NGC 5024, respectively. Finally, we also find three remaining unknown substructures and one of them has large angular momentum and a mean metallicity $\rm -2.13\,dex$ which may be a new substructure. As for GES, we find that it accounts for a large part of substructures in the inner halo and the range of apocenter distance is from 10 to $34\,\rm kpc$, which suggests that the GES is mainly distributed in the inner halo. The near one-third proportion of the GES and the peak value $20\,\rm kpc$ of the apocenter distances suggest that GES could account for the break in the density profile of the Galactic halo at Galactocentric distance ${\sim}20-25\,\rm kpc$. The similarity of comparing the kinematic properties of Gaia-Enceladus-Sausage with the Hercules-Aquila Cloud and Virgo Overdensity suggests that the three substructures may have similar origins.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Y. P. Peng
T. Liu
S. -L. Qin
T. Baug
H. -L. Liu
K. Wang
G. Garay
C. Zhang
L. -F. Chen
C. W. Lee
M. Juvela
D. L. Li
K. Tatematsu
X. -C. Liu
J. -E. Lee
G. Luo
L. Dewangan
Y. -F. Wu
L. Zhang
L. Bronfman
摘要： Investigating the physical and chemical structures of massive star-forming regions is critical for understanding the formation and the early evolution of massive stars. We performed a detailed line survey toward six dense cores named as MM1, MM4, MM6, MM7, MM8, and MM11 in G9.62+0.19 star-forming region resolved in ALMA band 3 observations. Toward these cores, about 172 transitions have been identified and attributed to 16 species including organic Oxygen-, Nitrogen-, Sulfur-bearing molecules and their isotopologues. Four dense cores MM7, MM8, MM4, and MM11 are line rich sources. Modeling of these spectral lines reveals the rotational temperature in a range of 72$-$115~K, 100$-$163~K, 102$-$204~K, and 84$-$123~K for the MM7, MM8, MM4, and MM11, respectively. The molecular column densities are 1.6 $\times$ 10$^{15}$ $-$ 9.2 $\times$ 10$^{17}$~cm$^{-2}$ toward the four cores. The cores MM8 and MM4 show chemical difference between Oxygen- and Nitrogen-bearing species, i.e., MM4 is rich in oxygen-bearing molecules while nitrogen-bearing molecules especially vibrationally excited HC$_{3}$N lines are mainly observed in MM8. The distinct initial temperature at accretion phase may lead to this N/O differentiation. Through analyzing column densities and spatial distributions of O-bearing Complex Organic Molecules (COMs), we found that C$_{2}$H$_{5}$OH and CH$_{3}$OCH$_{3}$ might have a common precursor, CH$_{3}$OH. CH$_{3}$OCHO and CH$_{3}$OCH$_{3}$ are likely chemically linked. In addition, the observed variation in HC$_{3}$N and HC$_{5}$N emission may indicate that their different formation mechanism at hot and cold regions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
J. C. Hood
A. Simpson
A. McDaniel
A. Foster
P. A. R. Ade
M. Ajello
A. J. Anderson
J. E. Austermann
J. A. Beall
A. N. Bender
B. A. Benson
F. Bianchini
L. E. Bleem
J. E. Carlstrom
C. L. Chang
P. Chaubal
H. C. Chiang
T-L. Chou
R. Citron
C. Corbett Moran
摘要： Including millimeter-wave (mm-wave) data in multi-wavelength studies of the variability of active galactic nuclei (AGN) can provide insights into AGN physics that are not easily accessible at other wavelengths. We demonstrate in this work the potential of cosmic microwave background (CMB) telescopes to provide long-term, high-cadence mm-wave AGN monitoring over large fractions of sky. We report on a pilot study using data from the SPTpol instrument on the South Pole Telescope (SPT), which was designed to observe the CMB at arcminute and larger angular scales. Between 2013 and 2016, SPTpol was used primarily to observe a single 500 deg^2 field, covering the entire field several times per day with detectors sensitive to radiation in bands centered at 95 and 150 GHz. We use SPT 150 GHz observations to create AGN light curves, and we compare these mm-wave light curves to those at other wavelengths, in particular gamma-ray and optical. In this Letter, we focus on a single source, PKS 2326-502, which has extensive, day-timescale monitoring data in gamma-ray, optical, and now mm-wave between 2013 and 2016. We find PKS 2326-502 to be in a flaring state in the first two years of this monitoring, and we present a search for evidence of correlated variability between mm-wave, optical R band, and gamma-ray observations. This pilot study is paving the way for AGN monitoring with current and upcoming CMB experiments such as SPT-3G, Simons Observatory, and CMB-S4, including multi-wavelength studies with facilities such as VRO-LSST.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The microwave spectrum contains valuable information about solar flares. Yet, the present spectral coverage is far from complete and broad data gaps exist above 20 GHz. Here we report the first flare (the X2.2 flare on 2022 April 20) observation of the newly-built Chashan Broadband Solar millimeter spectrometer (CBS) working from 35 to 40 GHz. We use the CBS data of the new Moon to calibrate,and the simultaneous NoRP data at 35 GHz to cross-calibrate. The impulsive stage has three local peaks with the middle one being the strongest and the maximum flux density reaches 9300 SFU at 35-40 GHz. The spectral index of the CBS data (alpha_C) for the major peak is mostly positive, indicating the gyrosynchrotron turnover frequency (nu_t) goes beyond 35-40 GHz. The frequency nu_t is smaller yet still larger than 20 GHz for most time of the other two peaks according to the spectral fittings with NoRP-CBS data. The CBS index manifests the general rapid-hardening-then-softening trend for each peak and gradual hardening during the decay stage, agreeing with the fitted optically-thin spectral index (alpha_tn) for nu_t 20 GHz).
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We reinvestigate the Cosmic Lens All-Sky Survey (CLASS) gravitational lens B1152+199 using archived Hubble Space Telescope (HST) data and Very Long Baseline Interferometry (VLBI) data. A consistent luminosity ratio within effective radius between the host galaxy and the X-galaxy is measured from HST tri-band images, which leads to a mass ratio between the two galaxies as $r_b\sim 2$. To determine the role of the X-galaxy in the lens system, we modelled the dual-lens system with constraints from the VLBI-resolved jet components and the HST images. The 8.4-GHz global-VLBI data currently provide the most stringent constraints to the mass model, especially to the radial power-law slope. The optimized models for this two-image three-component radio lens favour a steeper-than-isothermal inner slope. The jet bending in image B was also investigated and it turned out to be rather a misalignment than a curvature. The goodness of fit indicates that the role of the X-galaxy is crucial in the lens system if three pairs of resolved jet components are to be fitted. When we imported the optimal model from radio constraints to optical modelling with the HST tri-band data, the optimization kept the consistency of the optimal model and successfully reproduced the features observed in the HST images. This implies that the diffuse emission discovered in the HST images is actually a detection of the secondary lensing effects from the companion lens.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
S. Dai
Y. Feng
Y. P. Yang
Y. K. Zhang
D. Li
C. H. Niu
P. Wang
M. Y. Xue
B. Zhang
S. Burke-Spolaor
C. J. Law
R. S. Lynch
L. Connor
R. Anna-Thomas
L. Zhang
R. Duan
J. M. Yao
C. W. Tsai
W. W. Zhu
M. Cruces
摘要： The environment of actively repeating fast radio bursts (FRBs) has been shown to be complex and varying. The recently localized FRB 20190520B is extremely active, has the largest confirmed host dispersion measure, and is only the second FRB source associated with a compact, persistent radio source (PRS). The main tracer of the magneto-ionic environments is the rotation measure (RM), a path-integral of the line-of-sight component of magnetic field strength (B) and electron density, which does not allow a direct probe of the B-field configuration. Here we report direct evidence for a B-field reversal based on the observed sign change and extreme variation of FRB 20190520B's RM, which changed from $\sim10000$ rad m$^{-2}$ to $\sim-16000$ rad m$^{-2}$ between June 2021 and January 2022. Such extreme RM reversal has never been observed before in any FRB nor in any astronomical object. The implied short-term change of the B-field configuration in or around the FRB could be due to the vicinity of massive black holes, or a magnetized companion star in binary systems, or a young supernova remnant along the line of sight.
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