分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jumei Yao
William A. Coles
Richard N. Manchester
Daniel R. Stinebring
Michael Kramer
Na Wang
Di Li
Weiwei Zhu
Yi Feng
Jianping Yuan
Pei Wang
摘要： High sensitivity interstellar scintillation and polarization observations of PSR~B0656+14 made at three epochs over a year using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) show that the scattering is dominated by two different compact regions. We identify the one nearer to the pulsar with the shell of the Monogem Ring, thereby confirming the association. The other is probably associated with the Local Bubble. We find that the observed position angles of the pulsar spin axis and the space velocity are significantly different, with a separation of $19\fdg3\pm$0\fdg8, inconsistent with a previously published near-perfect alignment of $1\degr\pm 2\degr$. The two independent scattering regions are clearly defined in the secondary spectra which show two strong forward parabolic arcs. The arc curvatures imply that the scattering screens corresponding to the outer and inner arcs are located approximately 28~pc from PSR B0656+14 and 185~pc from the Earth, respectively. Comparison of the observed Doppler profiles with electromagnetic simulations shows that both scattering regions are mildly anisotropic. For the outer arc, we estimate the anisotropy $A_R$ to be approximately 1.3, with the scattering irregularities aligned parallel to the pulsar velocity. For the outer arc, we compare the observed delay profiles with delay profiles computed from a theoretical strong-scattering model. Our results suggest that the spatial spectrum of the scattering irregularities in the Monogem Ring is flatter than Kolmogorov, but further observations are required to confirm this.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Timing observations from the Nanshan 26-m radio telescope for nine pulsars between 2000 and 2014 have been used to search for glitches. The data span for nine pulsars ranges from 11.6 to 14.2 years. From the total of 114 yr of pulsar rotational history, 16 new glitches were identified in 9 pulsars. Glitch parameters were measured by fitting the timing residuals data. All 16 glitches have a small fractional size. Six new glitches have been detected in PSR J1833-0827, making it another frequent glitching pulsar. Some of the 16 glitches may experience exponential or linear recovery, but it is unlikely for us to make further analyses with the large gap in the data set. All the glitch rates obtained from Nanshan are higher than that from Jodrell Bank Observatory. The small glitch size and high glitch rate could possibly attribute to the high observation cadence.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Cheng-Min Zhang
Xiang-Han Cui
Di Li
De-Hua Wang
Shuang-Qiang Wang
Na Wang
Jian-Wei Zhang
Bo Peng
Wei-Wei Zhu
Yi-Yan Yang
Yuan-Yue Pan
摘要： The evolutions of a neutron star's rotation and magnetic field (B-field) have remained unsolved puzzles for over half a century. We ascribe the rotational braking torques of pulsar to both components, the standard magnetic dipole radiation (MDR) and particle wind flow ( MDR + Wind, hereafter named MDRW), which we apply to the Crab pulsar (B0531 + 21), the only source with a known age and long-term continuous monitoring by radio telescope. Based on the above presumed simple spin-down torques, we obtain the exact analytic solution on the rotation evolution of the Crab pulsar, together with the related outcomes as described below: (1) unlike the constant characteristic B-field suggested by the MDR model, this value for the Crab pulsar increases by a hundred times in 50~kyr while its real B-field has no change; (2) the rotational braking index evolves from $\sim$3 to 1 in the long-term, however, it drops from 2.51 to 2.50 in $\sim$45 years at the present stage, while the particle flow contributes approximately 25% of the total rotational energy loss rate; (3) strikingly, the characteristic age has the maximum limit of $\sim$10 kyr, meaning that it is not always a good indicator of real age. Furthermore, we discussed the evolutionary path of the Crab pulsar from the MDR to the wind domination by comparing it with the possible wind braking candidate pulsar PSR J1734-3333.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： PSR J$1946+3417$ is a millisecond pulsar (MSP) with a spin period $P\simeq3.17\rm~ms$. Harbored in a binary with an orbital period $P_{\rm b}\simeq27$ days, the MSP is accompanied by a white dwarf (WD). The masses of the MSP and the WD were determined to be $1.83\rm~M_\odot$ and $0.266\rm~M_\odot$, respectively. Specially, its orbital eccentricity is $e\simeq0.134$, which is challenging the recycling model of MSPs. Assuming that the neutron star in a binary may collapse to a strange star when its mass reaches a critical limit, we propose a phase transition (PT) scenario to account for the origin of the system. The sudden mass loss and the kick induced by asymmetric collapse during the PT may result in the orbital eccentricity. If the PT event takes place after the mass transfer ceases, the eccentric orbit can not be re-circularized in the Hubble time. Aiming at the masses of both components, we simulate the evolution of the progenitor of PSR J$1946+3417$ via \texttt{MESA}. The simulations show that a NS / main sequence star binary with initial masses of $1.4+1.6\rm~M_\odot$ in an initial orbit of 2.59 days will evolve into a binary consisting of a $2.0\rm~M_\odot$ MSP and a $0.27\rm~M_\odot$ WD in an orbit of $\sim21.5$ days. Assuming that the gravitational mass loss fraction during PT is $10\%$, we simulate the effect of PT via the kick program of \texttt{BSE} with a velocity of $\sigma_{\rm PT}=60~{\rm km~s}^{-1}$. The results show that the PT scenario can reproduce the observed orbital period and eccentricity with higher probability then other values.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jumei Yao
William A. Coles
Richard N. Manchester
Daniel R. Stinebring
Michael Kramer
Na Wang
Di Li
Weiwei Zhu
Yi Feng
Jianping Yuan
Pei Wang
摘要： High sensitivity interstellar scintillation and polarization observations of PSR~B0656+14 made at three epochs over a year using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) show that the scattering is dominated by two different compact regions. We identify the one nearer to the pulsar with the shell of the Monogem Ring, thereby confirming the association. The other is probably associated with the Local Bubble. We find that the observed position angles of the pulsar spin axis and the space velocity are significantly different, with a separation of $19\fdg3\pm$0\fdg8, inconsistent with a previously published near-perfect alignment of $1\degr\pm 2\degr$. The two independent scattering regions are clearly defined in the secondary spectra which show two strong forward parabolic arcs. The arc curvatures imply that the scattering screens corresponding to the outer and inner arcs are located approximately 28~pc from PSR B0656+14 and 185~pc from the Earth, respectively. Comparison of the observed Doppler profiles with electromagnetic simulations shows that both scattering regions are mildly anisotropic. For the outer arc, we estimate the anisotropy $A_R$ to be approximately 1.3, with the scattering irregularities aligned parallel to the pulsar velocity. For the outer arc, we compare the observed delay profiles with delay profiles computed from a theoretical strong-scattering model. Our results suggest that the spatial spectrum of the scattering irregularities in the Monogem Ring is flatter than Kolmogorov, but further observations are required to confirm this.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Cheng-Min Zhang
Xiang-Han Cui
Di Li
De-Hua Wang
Shuang-Qiang Wang
Na Wang
Jian-Wei Zhang
Bo Peng
Wei-Wei Zhu
Yi-Yan Yang
Yuan-Yue Pan
摘要： The evolutions of a neutron star's rotation and magnetic field (B-field) have remained unsolved puzzles for over half a century. We ascribe the rotational braking torques of pulsar to both components, the standard magnetic dipole radiation (MDR) and particle wind flow ( MDR + Wind, hereafter named MDRW), which we apply to the Crab pulsar (B0531 + 21), the only source with a known age and long-term continuous monitoring by radio telescope. Based on the above presumed simple spin-down torques, we obtain the exact analytic solution on the rotation evolution of the Crab pulsar, together with the related outcomes as described below: (1) unlike the constant characteristic B-field suggested by the MDR model, this value for the Crab pulsar increases by a hundred times in 50~kyr while its real B-field has no change; (2) the rotational braking index evolves from $\sim$3 to 1 in the long-term, however, it drops from 2.51 to 2.50 in $\sim$45 years at the present stage, while the particle flow contributes approximately 25% of the total rotational energy loss rate; (3) strikingly, the characteristic age has the maximum limit of $\sim$10 kyr, meaning that it is not always a good indicator of real age. Furthermore, we discussed the evolutionary path of the Crab pulsar from the MDR to the wind domination by comparing it with the possible wind braking candidate pulsar PSR J1734-3333.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yuzhu Cui
Kazuhiro Hada
Motoki Kino
Bong Won Sohn
Jongho Park
Hyun Wook Ro
Satoko Sawada-Satoh
Wu Jiang
Lang Cui
Mareki Honma
Zhi Qiang Shen
Fumie Tazaki
Tao An
Ilje Cho
Guang Yao Zhao
Xiao Peng Cheng
Kotaro Niinuma
Kiyoaki Wajima
Ying Kang Zhang
Noriyuki Kawaguchi
摘要： The East Asian very-long-baseline interferometry (VLBI) Network (EAVN) is a rapidly evolving international VLBI array that is currently promoted under joint efforts among China, Japan, and Korea. EAVN aims at forming a joint VLBI Network by combining a large number of radio telescopes distributed over East Asian regions. After the combination of the Korean VLBI Network (KVN) and the VLBI Exploration of Radio Astrometry (VERA) into KaVA, further expansion with the joint array in East Asia is actively promoted. Here we report the first imaging results (at 22 and 43 GHz) of bright radio sources obtained with KaVA connected to Tianma 65-m and Nanshan 26-m Radio Telescopes in China. To test the EAVN imaging performance for different sources, we observed four active galactic nuclei (AGN) having different brightness and morphology. As a result, we confirmed that Tianma 65-m Radio Telescope (TMRT) significantly enhances the overall array sensitivity, a factor of 4 improvement in baseline sensitivity and 2 in image dynamic range compared to the case of KaVA only. The addition of Nanshan 26-m Radio Telescope (NSRT) further doubled the east-west angular resolution. With the resulting high-dynamic-range, high-resolution images with EAVN (KaVA+TMRT+NSRT), various fine-scale structures in our targets, such as the counter-jet in M87, a kink-like morphology of the 3C273 jet and the weak emission in other sources, are successfully detected. This demonstrates the powerful capability of EAVN to study AGN jets and to achieve other science goals in general. Ongoing expansion of EAVN will further enhance the angular resolution, detection sensitivity and frequency coverage of the network.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Nobuyuki Sakai
Bo Zhang
Shuangjing Xu
Daisuke Sakai
Yoshiaki Tamura
Takaaki Jike
Taehyun Jung
Chungsik Oh
Jeong-Sook Kim
Noriyuki Kawaguchi
Hiroshi Imai
Wu Jiang
Lang Cui
Soon-Wook Kim
Pengfei Jiang
Tomoharu Kurayama
Jeong Ae Lee
Kazuya Hachisuka
Dong-Kyu Jung
Bo Xia
摘要： We aim to reveal the structure and kinematics of the Outer-Scutum-Centaurus (OSC) arm located on the far side of the Milky Way through very long baseline interferometry (VLBI) astrometry using KaVA, which is composed of KVN (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). We report the proper motion of a 22 GHz H$_{2}$O maser source, which is associated with the star-forming region G034.84$-$00.95, to be ($\mu_{\alpha} \rm{cos}\delta$, $\mu_{\delta}$) = ($-$1.61$\pm$0.18, $-$4.29$\pm$0.16) mas yr$^{-1}$ in equatorial coordinates (J2000). We estimate the 2D kinematic distance to the source to be 18.6$\pm$1.0 kpc, which is derived from the variance-weighted average of kinematic distances with LSR velocity and the Galactic-longitude component of the measured proper motion. Our result places the source in the OSC arm and implies that G034.84$-$00.95 is moving away from the Galactic plane with a vertical velocity of $-$38$\pm$16 km s$^{-1}$. Since the H I supershell GS033+06$-$49 is located at a kinematic distance roughly equal to that of G034.84$-$00.95, it is expected that gas circulation occurs between the outer Galactic disk around G034.84$-$00.95 with a Galactocentric distance of 12.8$^{+1.0}_{-0.9}$ kpc and halo. We evaluate possible origins of the fast vertical motion of G034.84$-$00.95, which are (1) supernova explosions and (2) cloud collisions with the Galactic disk. However, neither of the possibilities are matched with the results of VLBI astrometry as well as spatial distributions of H II regions and H I gas.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Kazunori Akiyama
Juan-Carlos Algaba
Tao An
Keiichi Asada
Kitiyanee Asanok
Do-Young Byun
Thanapol Chanapote
Wen Chen
Zhong Chen
Xiaopeng Cheng
James O. Chibueze
Ilje Cho
Se-Hyung Cho
Hyun-Soo Chung
Lang Cui
Yuzhu Cui
Akihiro Doi
Jian Dong
Kenta Fujisawa
Wei Gou
摘要： The East Asian VLBI Network (EAVN) is an international VLBI facility in East Asia and is operated under mutual collaboration between East Asian countries, as well as part of Southeast Asian and European countries. EAVN currently consists of 16 radio telescopes and three correlators located in China, Japan, and Korea, and is operated mainly at three frequency bands, 6.7, 22, and 43 GHz with the longest baseline length of 5078 km, resulting in the highest angular resolution of 0.28 milliarcseconds at 43 GHz. One of distinct capabilities of EAVN is multi-frequency simultaneous data reception at nine telescopes, which enable us to employ the frequency phase transfer technique to obtain better sensitivity at higher observing frequencies. EAVN started its open-use program in the second half of 2018, providing a total observing time of more than 1100 hours in a year. EAVN fills geographical gap in global VLBI array, resulting in enabling us to conduct contiguous high-resolution VLBI observations. EAVN has produced various scientific accomplishments especially in observations toward active galactic nuclei, evolved stars, and star-forming regions. These activities motivate us to initiate launch of the 'Global VLBI Alliance' to provide an opportunity of VLBI observation with the longest baselines on the earth.
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