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
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： 2024-05-10 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： We have conducted a comprehensive investigation into the bright single pulse emission from PSR B1133+16 using the Giant Metrewave Radio Telescope. High time resolution data (61 μs) were obtained at a center frequency of 322 MHz with a bandwidth of 32 MHz over a continuous observation period of 7.45 hr. A total of 1082 bright pulses were sporadically detected with peak flux densities ranging from 10 to 23 times stronger than the average pulse profile. However, no giant pulse-like emission with a relative pulse energy larger than 10 and extremely short duration was detected, indicating that these bright pulses cannot be categorized as giant pulse emission. The majority of these bright pulses are concentrated in pulse phases at both the leading and trailing windows of the average pulse profile, with an occurrence ratio of approximately 2.74. The pulse energy distribution for all individual pulses can be described by a combination of two Gaussian components and a cutoff power-law with an index of α = − 3.2. An updated nulling fraction of 15.35% ± 0.45% was determined from the energy distribution. The emission of individual pulses follows a log-normal distribution in peak flux density ratio. It is imperative that regular phase drifting in bright pulse sequence is identified in both the leading and trailing components for the first time. Possible physical mechanisms are discussed in detail to provide insights into these observations.
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.
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