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1. chinaXiv:202305.00221 [pdf]
Possible evidences from H(z) parameter data for physics beyond Lambda CDM
Yang, Rong-JiaSubjects: Astronomy >> Galaxy and Cosmology
| We analyse $H(z)$ parameter data with some conditions by using Lagrange mean value theorem in Calculus. We find that: (1) there exists at least one decelerated phase at 1 $ sigma$ confidence level in the redshift range $(0.38, 0.59)$; (2) the equation of motion of dark energy may be less than $-1$ at 1 $ sigma$ confidence level at some redshifts in the redshift range $(1.3, 1.53)$; (3) there exists at least one accelerated phase at 1 $ sigma$ confidence level in the redshift range $(1.037, 1.944)$. These results may provide possible evidences for physics beyond $ Lambda$CDM. |
2. chinaXiv:202305.00149 [pdf]
李子涵; 刘煜; 张雪飞; 梁红飞; 沙飞扬; 于晋; 敦金平
Comment：已被天文学报接收
Subjects: Astronomy >> Astrophysics
| 日冕是太阳大气活动的关键区域, 是日地空间天气的源头. 受观测限制, 人们对日冕低层大气等离子体结构和磁场状态的研究非常欠缺, 国际上对于可见光波段日冕低层大气的亮度分层研究很少. 本文利用丽江日冕仪YOGIS(Yunnan Green-line Imaging System) 的日冕绿线（FeXIV 5303 Å）观测资料, 对内日冕区域（1.03R⊙-1.25R⊙）亮结构及其中冕环进行了有效的强度衰减分析. 本文通过对亮结构的强度在太阳径向高度上进行了指数衰减拟合, 比较这些拟合结果发现所得到的静态内冕环的衰减指数在一固定值附近. 然后将比较明显的冕环提取出来, 通过对不同高度的强度进行相同的指数拟合, 得出的衰减指数与亮结构中也比较相近, 这对进一步研究日冕中的各项物理参数演化提供了参考. |
3. chinaXiv:202303.00096 [pdf]
林哲宇; 徐稚
Subjects: Astronomy >> Astrophysical processes
| 本文给出了在连续式旋转波片调制模式下的傅里叶分析的推导过程和解调公式,并利用理论偏振轮廓对公式的准确性进行了验证。分别采用了傅里叶分析和解调矩阵两种解调方法定量模拟了在连续式调制模式下波片的初始方位角误差、旋转定位误差以及探测器曝光过程中时间差占比三个因素对测量精度的影响。主要结论是：(1)简单的傅里叶分析不再适用于连续式调制的结果解调。文中给出的新傅里叶分析方法与解调矩阵方法在进行误差分析时，可以得到基本一致的结果。(2)考虑初始方位角误差引起的影响，我们发现对于线偏振信号来说，采用傅里叶分析和解调矩阵可得到非常一致的结果，而对于圆偏振来说，基于解调矩阵的方法得到的结果误差相对较小。但是两种解调方法都反映出初始方位角误差对圆偏振和线偏振产生的影响是一致，且相对误差的大小与偏振信号本身的强弱有关。初始方位角的误差要求在十几角秒量级才能满足结果的相对误差在10-3量级以下。(3)考虑旋转定位误差引起的影响时，我们发现采用傅里叶分析和解调矩阵得到的结果非常接近。两者同时都显示出旋转定位误差对线偏振信号造成的影响更为明显，且相对误差的大小也与信号的强弱有关。当波片的重复定位精度在10''左右时，对10-2量级的弱偏振信号来说，测量误差也能在10-3的量级左右。从这一点上，我们发现连续式调制模式对波片旋转的定位精度要求要明显高于步进式调制模式。(4)两种解调方法的结果均显示，在连续式调制模式下，波片的调制周期与探测器曝光时长的时间差(?)会造成线偏振信号之间的串扰，即时间差占比(?/T)对线偏振信号造成的影响比对圆偏振信号的影响更为明显。当?/T小于1%时，线偏振信号相对误差达到10-3量级。 |
submitted time 2023-03-13 Cooperative journals:《天文研究与技术》 Hits3387， Downloads178， Comment 0
4. chinaXiv:202303.00097 [pdf]
王恩旺; 陈晓林; 王恩达
Subjects: Astronomy >> Astrophysical processes
| 针对空间目标与恒星的近距离强干扰和瞬间遮挡干扰，不易精确捕获目标位置。提出用卡尔曼滤波预测目标位置并跟踪目标，跟踪波门用改进自适应的可变波门。同时设计新的强干扰和瞬间遮挡目标的预判和跟踪方法，当预判到此类目标时，将卡尔曼滤波的预测值作为观测值跟踪目标，并用目标预测质心对波门质心进行限定修正，从而捕获有用的观测数据。实验发现，该方法能稳健跟踪强干扰和瞬间遮挡目标，提升空间目标的跟踪精度，降低数据错误率，提高数据质量，为捕获轨道位置提供更多更有用的数据。该方法程序运行速率快，具有一定的适用性和科学价值。 |
submitted time 2023-03-13 Cooperative journals:《天文研究与技术》 Hits3237， Downloads172， Comment 0
5. chinaXiv:202303.00095 [pdf]
周嘉 ; 吴锋泉; 孙士杰; 索南本; 张骄; 陈学雷
Subjects: Astronomy >> Astrophysical processes
| 月面低频射电观测具有巨大科学发现潜力，有望揭开宇宙黑暗和黎明时代秘密。本文针对于月背低频观测的天线及其匹配电路提出了一种新的设计方案，利用非福斯特匹配电路，大大减小了天线的物理尺寸，使之结构轻巧便于月面部署。首先，设计了一种轻巧、宽温度范围、具有易延展性、可折叠性、便于在月面部署的电小薄膜天线，其具有很好的全向性，在4-8MHz内增益小于1.92dB，半波束宽度大于83°，然后利用加载非福斯特匹配电路来改善其阻抗性能，将天线的电抗从高达-985.3Ω优化到-16.5Ω以内，最后采用等效电路进行了阻抗和噪声实测，其噪声功率密度水平在绝大部分频率范围内小于-150dBm/Hz，证实了该方案的可行性。 |
submitted time 2023-03-13 Cooperative journals:《天文研究与技术》 Hits3347， Downloads164， Comment 0
6. chinaXiv:202303.00094 [pdf]
Xception-AS：一种基于Xception算法结构的天体目标自动分类算法
李馨; 屠良平; 李娟; 高翔; 冯雪琦; 仲峥迪Subjects: Astronomy >> Astrophysical processes
| 提出了一种基于Xception结构的天体目标自动分类算法，该算法可有效应用于星系、恒星和类星体的自动分类问题。算法以Xception为基础框架，通过选择最优激活函数，加入注意力机制等方式进行改进。随机选择SDSS-DR16测光图像数据中的11543个星系、10490个类星体和11967个恒星共34000个观测源g，r和i的3个波段的图像作为实验数据，并设计多组实验进行算法验证和测试，综合分析所有实验结果得出本文算法在准确率、精确率、召回率和F1分数等关键指标分别达到了90.26%，90.01%，89.86%和89.85%。相同数据集与其他13种经典和流行的卷积神经网络（Convolutional Neural Network, CNN）算法的实验测试结果对比表明，本文提出的Xception-AS算法具有更加优异的分类性能，证明本文算法在解决天体目标自动分类问题具有优越性。 |
submitted time 2023-03-13 Cooperative journals:《天文研究与技术》 Hits3398， Downloads172， Comment 0
7. chinaXiv:202302.00234 [pdf]
NuSTAR Observations of Intrinsically X-ray Weak Quasar Candidates: An Obscuration-Only Scenario
Chaojun Wang; B. Luo; W. N. Brandt; D. M. Alexander; F. E. Bauer; S. C. Gallagher; Jian Huang; Hezhen Liu; D. SternSubjects: Astronomy >> Astrophysics
| We utilize recent NuSTAR observations (co-added depth ≈55-120 ks) of PG 1001+054, PG 1254+047, and PHL 1811 to constrain their hard X-ray (?5 keV) weakness and spectral shapes, and thus to investigate the nature of their extreme X-ray weakness. These quasars showed very weak soft X-ray emission, and they were proposed to be intrinsically X-ray weak, with the X-ray coronae producing weak continuum emission relative to their optical/UV emission. However, the new observations suggest an alternative explanation. The NuSTAR 3-24 keV spectral shapes for PG 1001+054 and PHL 1811 are likely flat (effective power-law photon indices \Gamma_{\rm eff}=1.0^{+0.5}_{-0.6} and \Gamma_{\rm eff}=1.4^{+0.8}_{-0.7}, respectively), while the shape is nominal for PG 1254+047 (\Gamma_{\rm eff}=1.8\pm0.3). PG 1001+054 and PHL 1811 are significantly weak at hard X-ray energies (by factors of ≈26-74 at rest-frame 8 keV) compared to the expectations from their optical/UV emission, while PG 1254+047 is only hard X-ray weak by a factor of ≈3. We suggest that X-ray obscuration is present in all three quasars. We propose that, as an alternative to the intrinsic X-ray weakness + X-ray obscuration scenario, the soft and hard X-ray weakness of these quasars can be uniformly explained under an obscuration-only scenario. This model provides adequate descriptions of the multi-epoch soft and hard X-ray data of these quasars, with variable column density and leaked fraction of the partial-covering absorber. We suggest that the absorber is the clumpy dust-free wind launched from the accretion disk. These quasars probably have super-Eddington accretion rates that drive powerful and high-density winds. |
8. chinaXiv:202302.00235 [pdf]
Galaxy-galaxy strong lens perturbations: line-of-sight haloes versus lens subhaloes
Qiuhan He; Ran Li; Carlos S. Frenk; James Nightingale; Shaun Cole; Nicola C. Amorisco; Richard Massey; Andrew Robertson; Amy Etherington; Aristeidis Amvrosiadis; Xiaoyue CaoSubjects: Astronomy >> Galaxy and Cosmology
| We rederive the number density of intervening line-of-sight haloes relative to lens subhaloes in galaxy-galaxy strong lensing observations, where these perturbers can generate detectable image fluctuations. Previous studies have calculated the detection limit of a line-of-sight small-mass dark halo by comparing the lensing deflection angles it would cause, to those caused by a subhalo within the lens. However, this overly simplifies the difference in observational consequences between a subhalo and a line-of-sight halo. Furthermore, it does not take into account degeneracies between an extra subhalo and the uncertain properties of the main lens. More in keeping with analyses of real-world observations, we regard a line-of-sight halo as detectable only if adding it to a smooth model generates a statistically significant improvement in the reconstructed image. We find that the number density of detectable line-of-sight perturbers has been overestimated by as much as a factor of two in the previous literature. For typical lensing geometries and configurations, very deep imaging is sensitive to twice as many line-of-sight perturbers as subhaloes, but moderate depth imaging is sensitive to only slightly more line-of-sight perturbers than subhaloes. |
9. chinaXiv:202302.00237 [pdf]
Weicheng Zang; Youn Kil Jung; Hongjing Yang; Xiangyu Zhang; Andrzej Udalski; Jennifer C. Yee; Andrew Gould; Shude Mao
Subjects: Astronomy >> Astrophysics
| We present the analysis of seven microlensing planetary events with planet/host mass ratios q < 10^{-4}: KMT-2017-BLG-1194, KMT-2017-BLG-0428, KMT-2019-BLG-1806, KMT-2017-BLG-1003, KMT-2019-BLG-1367, OGLE-2017-BLG-1806, and KMT-2016-BLG-1105. They were identified by applying the Korea Microlensing Telescope Network (KMTNet) AnomalyFinder algorithm to 2016--2019 KMTNet events. A Bayesian analysis indicates that all the lens systems consist of a cold super-Earth orbiting an M or K dwarf. Together with 17 previously published and three that will be published elsewhere, AnomalyFinder has found a total of 27 planets that have solutions with q < 10^{-4} from 2016--2019 KMTNet events, which lays the foundation for the first statistical analysis of the planetary mass-ratio function based on KMTNet data. By reviewing the 27 planets, we find that the missing planetary caustics problem in the KMTNet planetary sample has been solved by AnomalyFinder. We also find a desert of high-magnification planetary signals (A?65), and a follow-up project for KMTNet high-magnification events could detect at least two more q < 10^{-4} planets per year and form an independent statistical sample. |
10. chinaXiv:202302.00236 [pdf]
Gravitational signal propagation in the Double Pulsar studied with the MeerKAT telescope
H. Hu; M. Kramer; D. J. Champion; N. Wex; A. Parthasarathy; T. T. Pennucci; N. K. Porayko; W. van Straten; V. Venkatraman Krishnan; M. Burgay; P. C. C. Freire; R. N. Manchester; A. Possenti; I. H. Stairs; M. Bailes; S. Buchner; A. D. Cameron; F. Camilo; M. SerylakSubjects: Astronomy >> Astrophysics
| The Double Pulsar, PSR J0737-3039A/B, has offered a wealth of gravitational experiments in the strong-field regime, all of which GR has passed with flying colours. In particular, among current gravity experiments that test photon propagation, the Double Pulsar probes the strongest spacetime curvature. Observations with MeerKAT and, in future, the SKA can greatly improve the accuracy of current tests and facilitate tests of NLO contributions in both orbital motion and signal propagation. We present our timing analysis of new observations of PSR J0737-3039A, made using the MeerKAT telescope over the last 3 years. The increased timing precision offered by MeerKAT yields a 2 times better measurement of Shapiro delay parameter s and improved mass measurements compared to previous studies. In addition, our results provide an independent confirmation of the NLO signal propagation effects and already surpass the previous measurement from 16-yr data by a factor of 1.65. These effects include the retardation effect due to the movement of B and the deflection of the signal by the gravitational field of B. We also investigate novel effects which are expected. For instance, we search for potential profile variations near superior conjunctions caused by shifts of the line-of-sight due to latitudinal signal deflection and find insignificant evidence with our current data. With simulations, we find that the latitudinal deflection delay is unlikely to be measured with timing because of its correlation with Shapiro delay. Furthermore, although it is currently not possible to detect the expected lensing correction to the Shapiro delay, our simulations suggest that this effect may be measured with the full SKA. Finally, we provide an improved analytical description for the signal propagation in the Double Pulsar system that meets the timing precision expected from future instruments such as the full SKA. |
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