Pub Date : 2024-05-19DOI: 10.1088/1674-4527/ad3dc5
Yang-Yang Deng and Zhong-Mu Li
Recent studies indicate that some Galactic open clusters (OCs) exhibit extended main-sequence turnoff (eMSTO) in their color–magnitude diagrams (CMDs). However, the number of Galactic OCs with eMSTO structures detected so far is limited, and the reasons for their formation are still unclear. This work identifies 26 Galactic OCs with undiscovered eMSTOs and investigates the causes of these features. Stellar population types and fundamental parameters of cluster samples are acquired using CMD fitting methods. Among them, the results of 11 OCs are reliable as the observed CMDs are well-reproduced. We propose the crucial role of stellar binarity and confirm the importance of stellar rotation in reproducing eMSTO morphologies. The results also show that the impact of age spread is important, as it can adequately explain the structure of young OCs and fit the observed CMDs of intermediate-age OCs better.
{"title":"Study of 26 Galactic Open Clusters with Extended Main-sequence Turnoffs","authors":"Yang-Yang Deng and Zhong-Mu Li","doi":"10.1088/1674-4527/ad3dc5","DOIUrl":"https://doi.org/10.1088/1674-4527/ad3dc5","url":null,"abstract":"Recent studies indicate that some Galactic open clusters (OCs) exhibit extended main-sequence turnoff (eMSTO) in their color–magnitude diagrams (CMDs). However, the number of Galactic OCs with eMSTO structures detected so far is limited, and the reasons for their formation are still unclear. This work identifies 26 Galactic OCs with undiscovered eMSTOs and investigates the causes of these features. Stellar population types and fundamental parameters of cluster samples are acquired using CMD fitting methods. Among them, the results of 11 OCs are reliable as the observed CMDs are well-reproduced. We propose the crucial role of stellar binarity and confirm the importance of stellar rotation in reproducing eMSTO morphologies. The results also show that the impact of age spread is important, as it can adequately explain the structure of young OCs and fit the observed CMDs of intermediate-age OCs better.","PeriodicalId":54494,"journal":{"name":"Research in Astronomy and Astrophysics","volume":"68 1","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-05-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141149821","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-19DOI: 10.1088/1674-4527/ad3dc2
Xiaopeng Liu, Hao Tian, Wenyuan Cui, Linlin Li, Jiaming Liu, Zhenyan Huo and Yawei Gao
Using 9943 OB-type stars from LAMOST DR7 in the solar neighborhood, we fit the vertical stellar density profile with the model including a single exponential distribution at different positions (R, Φ). The distributions of the scale heights and scale length show that the young disk traced by the OB-type stars is not axisymmetric. The scale length decreases versus the azimuthal angle Φ, i.e., from kpc with Φ = − 3° to kpc with Φ = 9°. Meanwhile we find signal of non-symmetry in the distribution of the scale height of the north and south of the disk plane. The scale height in the north side shows signal of flaring of the disk, while that of the south disk stays almost constant around hs = 130 pc. The distribution of the displacement of the disk plane Z0 also shows variance versus the azimuthal angle Φ, which displays significant differences with the warp model constrained by the Cepheid stars. We also test different values for the position of the Sun, and the distance between the Sun and the Galactic center affects the scale heights and the displacement of the disk significantly, but that does not change our conclusion that the disk is not axisymmetric.
{"title":"An Asymmetric Galactic Stellar Disk Traced by OB-type Stars from LAMOST DR7","authors":"Xiaopeng Liu, Hao Tian, Wenyuan Cui, Linlin Li, Jiaming Liu, Zhenyan Huo and Yawei Gao","doi":"10.1088/1674-4527/ad3dc2","DOIUrl":"https://doi.org/10.1088/1674-4527/ad3dc2","url":null,"abstract":"Using 9943 OB-type stars from LAMOST DR7 in the solar neighborhood, we fit the vertical stellar density profile with the model including a single exponential distribution at different positions (R, Φ). The distributions of the scale heights and scale length show that the young disk traced by the OB-type stars is not axisymmetric. The scale length decreases versus the azimuthal angle Φ, i.e., from kpc with Φ = − 3° to kpc with Φ = 9°. Meanwhile we find signal of non-symmetry in the distribution of the scale height of the north and south of the disk plane. The scale height in the north side shows signal of flaring of the disk, while that of the south disk stays almost constant around hs = 130 pc. The distribution of the displacement of the disk plane Z0 also shows variance versus the azimuthal angle Φ, which displays significant differences with the warp model constrained by the Cepheid stars. We also test different values for the position of the Sun, and the distance between the Sun and the Galactic center affects the scale heights and the displacement of the disk significantly, but that does not change our conclusion that the disk is not axisymmetric.","PeriodicalId":54494,"journal":{"name":"Research in Astronomy and Astrophysics","volume":"47 1","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-05-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141149860","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-12DOI: 10.1088/1674-4527/ad3a2b
Zhong-Mu Li and Cai-Yan Mao
Open clusters (OCs) are common in the Milky Way, but most of them remain undiscovered. There are numerous techniques, including some machine-learning algorithms, available for the exploration of OCs. However, each method has its limitations and therefore, different approaches to discovering OCs hold significant values. We develop a comprehensive approach method to automatically explore the data space and identify potential OC candidates with relatively reliable membership determination. This approach combines the techniques of Hierarchical Density-Based Spatial Clustering of Applications with Noise, Gaussian mixture model, and a novel cluster member identification technique, color excess constraint. The new method exhibits efficiency in detecting OCs while ensuring precise determination of cluster memberships. Because the main feature of this technique is to add an extra constraint (EC) for the members of cluster candidates using the homogeneity of color excess, compared to typical blind search codes, it is called Blind Search-Extra Constraint (BSEC) method. It is successfully applied to the Gaia Data Release 3, and 83 new OCs are found, whose color–magnitude diagrams (CMDs) are fitted well to the isochrones. In addition, this study reports 621 new OC candidates with discernible main sequence or red giant branch. It is shown that BSEC technique can discard some false negatives of previous works, which takes about three percentage of known clusters. It shows that as an EC, the color excess (or two-color) constraint is useful for removing fake cluster member stars from the clusters that are identified from the positions and proper motions of stars, and getting more precise CMDs, when differential reddening of member stars of a cluster is not large (e.g., ΔE(GBP − GRP) < 0.5 mag). It makes the CMDs of 15% clusters clearer (in particular for the region near turnoff) and therefore is helpful for CMD and stellar population studies. Our result suggests that the color excess constraint is more appropriate for clusters with small differential reddening, such as globular clusters or older OCs, and clusters that the distances of member stars cannot be determined accurately.
{"title":"BSEC Method for Unveiling Open Clusters and its Application to Gaia DR3: 83 New Clusters","authors":"Zhong-Mu Li and Cai-Yan Mao","doi":"10.1088/1674-4527/ad3a2b","DOIUrl":"https://doi.org/10.1088/1674-4527/ad3a2b","url":null,"abstract":"Open clusters (OCs) are common in the Milky Way, but most of them remain undiscovered. There are numerous techniques, including some machine-learning algorithms, available for the exploration of OCs. However, each method has its limitations and therefore, different approaches to discovering OCs hold significant values. We develop a comprehensive approach method to automatically explore the data space and identify potential OC candidates with relatively reliable membership determination. This approach combines the techniques of Hierarchical Density-Based Spatial Clustering of Applications with Noise, Gaussian mixture model, and a novel cluster member identification technique, color excess constraint. The new method exhibits efficiency in detecting OCs while ensuring precise determination of cluster memberships. Because the main feature of this technique is to add an extra constraint (EC) for the members of cluster candidates using the homogeneity of color excess, compared to typical blind search codes, it is called Blind Search-Extra Constraint (BSEC) method. It is successfully applied to the Gaia Data Release 3, and 83 new OCs are found, whose color–magnitude diagrams (CMDs) are fitted well to the isochrones. In addition, this study reports 621 new OC candidates with discernible main sequence or red giant branch. It is shown that BSEC technique can discard some false negatives of previous works, which takes about three percentage of known clusters. It shows that as an EC, the color excess (or two-color) constraint is useful for removing fake cluster member stars from the clusters that are identified from the positions and proper motions of stars, and getting more precise CMDs, when differential reddening of member stars of a cluster is not large (e.g., ΔE(GBP − GRP) < 0.5 mag). It makes the CMDs of 15% clusters clearer (in particular for the region near turnoff) and therefore is helpful for CMD and stellar population studies. Our result suggests that the color excess constraint is more appropriate for clusters with small differential reddening, such as globular clusters or older OCs, and clusters that the distances of member stars cannot be determined accurately.","PeriodicalId":54494,"journal":{"name":"Research in Astronomy and Astrophysics","volume":"67 1","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-05-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140942447","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-10DOI: 10.1088/1674-4527/ad3c70
Zhi-Chu Ma, Rui Niu, Wen Zhao
In this work, we consider a conventional test of gravitational wave (GW) propagation which is based on the phenomenological parameterized dispersion relation to describe potential departures from General Relativity (GR) along the propagation of GWs. But different from tests conventionally performed previously, we vary multiple deformation coefficients simultaneously and employ the principal component analysis (PCA) method to remedy the strong degeneracy among deformation coefficients and obtain informative posteriors. The dominant PCA components can be better measured and constrained, and thus are expected to be more sensitive to potential departures from the waveform model. Using this method we analyze ten selected events and get the result that the combined posteriors of the dominant PCA parameters are consistent with GR within 99.7% credible intervals. The standard deviation of the first dominant PCA parameter is three times smaller than that of the original dispersion parameter of the leading order. However, the multi-parameter test with PCA is more sensitive to not only potential deviations from GR but also systematic errors of waveform models. The difference in results obtained by using different waveform templates hints that the demands of waveform accuracy are higher to perform the multi-parameter test with PCA. Whereas, it cannot be strictly proven that the deviation is indeed and only induced by systematic errors. It requires more thorough research in the future to exclude other possible reasons in parameter estimation and data processing.
在这项工作中，我们考虑了引力波（GW）传播的传统测试，该测试基于现象学参数化色散关系来描述引力波传播过程中可能偏离广义相对论（GR）的情况。但与以往常规测试不同的是，我们同时改变多个形变系数，并采用主成分分析（PCA）方法来弥补形变系数之间的强退化性，从而获得信息丰富的后验。主成分分析法可以更好地测量和约束主成分，从而对波形模型的潜在偏差更加敏感。利用这种方法，我们分析了 10 个选定的事件，结果发现主要 PCA 参数的综合后验在 99.7% 的可信区间内与 GR 一致。第一个主要 PCA 参数的标准偏差是原始前序分散参数标准偏差的三倍。然而，用 PCA 进行多参数测试不仅对可能偏离 GR 的情况更敏感，而且对波形模型的系统误差也更敏感。使用不同波形模板得出的结果存在差异，这表明使用 PCA 进行多参数测试对波形精度的要求更高。不过，目前还不能严格证明偏差确实且仅由系统误差引起。今后还需要进行更深入的研究，以排除参数估计和数据处理中可能存在的其他原因。
{"title":"The Multi-parameter Test of Gravitational Wave Dispersion with Principal Component Analysis","authors":"Zhi-Chu Ma, Rui Niu, Wen Zhao","doi":"10.1088/1674-4527/ad3c70","DOIUrl":"https://doi.org/10.1088/1674-4527/ad3c70","url":null,"abstract":"In this work, we consider a conventional test of gravitational wave (GW) propagation which is based on the phenomenological parameterized dispersion relation to describe potential departures from General Relativity (GR) along the propagation of GWs. But different from tests conventionally performed previously, we vary multiple deformation coefficients simultaneously and employ the principal component analysis (PCA) method to remedy the strong degeneracy among deformation coefficients and obtain informative posteriors. The dominant PCA components can be better measured and constrained, and thus are expected to be more sensitive to potential departures from the waveform model. Using this method we analyze ten selected events and get the result that the combined posteriors of the dominant PCA parameters are consistent with GR within 99.7% credible intervals. The standard deviation of the first dominant PCA parameter is three times smaller than that of the original dispersion parameter of the leading order. However, the multi-parameter test with PCA is more sensitive to not only potential deviations from GR but also systematic errors of waveform models. The difference in results obtained by using different waveform templates hints that the demands of waveform accuracy are higher to perform the multi-parameter test with PCA. Whereas, it cannot be strictly proven that the deviation is indeed and only induced by systematic errors. It requires more thorough research in the future to exclude other possible reasons in parameter estimation and data processing.","PeriodicalId":54494,"journal":{"name":"Research in Astronomy and Astrophysics","volume":"25 1","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140940252","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-09DOI: 10.1088/1674-4527/ad3132
Wei Zhu
The correlation between close-in super Earths and distant cold Jupiters in planetary systems has important implications for their formation and evolution. Contrary to some earlier findings, a recent study conducted by Bonomo et al. suggests that the occurrence of cold Jupiter companions is not excessive in super-Earth systems. Here we show that this discrepancy can be seen as a Simpson’s paradox and is resolved once the metallicity dependence of the super-Earth–cold Jupiter relation is taken into account. A common feature is noticed that almost all the cold Jupiter detections with inner super-Earth companions are found around metal-rich stars. Focusing on the Sun-like hosts with super-solar metallicities, we show that the frequency of cold Jupiters conditioned on the presence of inner super Earths is 39−11+12%, whereas the frequency of cold Jupiters in the same metallicity range is no more than 20%. Therefore, the occurrences of close-in super Earths and distant cold Jupiters appear correlated around metal-rich hosts. The relation between the two types of planets remains unclear for stars with metal-poor hosts due to the limited sample size and the much lower occurrence rate of cold Jupiters, but a correlation between the two cannot be ruled out.
{"title":"The Metallicity Dimension of the Super Earth-cold Jupiter Correlation","authors":"Wei Zhu","doi":"10.1088/1674-4527/ad3132","DOIUrl":"https://doi.org/10.1088/1674-4527/ad3132","url":null,"abstract":"The correlation between close-in super Earths and distant cold Jupiters in planetary systems has important implications for their formation and evolution. Contrary to some earlier findings, a recent study conducted by Bonomo et al. suggests that the occurrence of cold Jupiter companions is not excessive in super-Earth systems. Here we show that this discrepancy can be seen as a Simpson’s paradox and is resolved once the metallicity dependence of the super-Earth–cold Jupiter relation is taken into account. A common feature is noticed that almost all the cold Jupiter detections with inner super-Earth companions are found around metal-rich stars. Focusing on the Sun-like hosts with super-solar metallicities, we show that the frequency of cold Jupiters conditioned on the presence of inner super Earths is <inline-formula>\u0000<tex-math>\u0000<?CDATA ${39}_{-11}^{+12} % $?>\u0000</tex-math>\u0000<mml:math overflow=\"scroll\"><mml:msubsup><mml:mrow><mml:mn>39</mml:mn></mml:mrow><mml:mrow><mml:mo>−</mml:mo><mml:mn>11</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>12</mml:mn></mml:mrow></mml:msubsup><mml:mo>%</mml:mo></mml:math>\u0000<inline-graphic xlink:href=\"raaad3132ieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>, whereas the frequency of cold Jupiters in the same metallicity range is no more than 20%. Therefore, the occurrences of close-in super Earths and distant cold Jupiters appear correlated around metal-rich hosts. The relation between the two types of planets remains unclear for stars with metal-poor hosts due to the limited sample size and the much lower occurrence rate of cold Jupiters, but a correlation between the two cannot be ruled out.","PeriodicalId":54494,"journal":{"name":"Research in Astronomy and Astrophysics","volume":"33 1","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140615747","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-09DOI: 10.1088/1674-4527/ad2e4d
Alexander S. Kutsenko, Valentina I. Abramenko, Andrei A. Plotnikov
Using the data on magnetic field maps and continuum intensity for Solar Cycles 23 and 24, we explored 100 active regions (ARs) that produced M5.0 or stronger flares. We focus on the presence/absence of the emergence of magnetic flux in these ARs 2–3 days before the strong flare onset. We found that 29 ARs in the sample emerged monotonically amidst quiet-Sun. A major emergence of a new magnetic flux within a pre-existing AR yielding the formation of a complex flare-productive configuration was observed in another 24 cases. For 30 ARs, an insignificant (in terms of the total magnetic flux of pre-existing AR) emergence of a new magnetic flux within the pre-existing magnetic configuration was observed; for some of them the emergence resulted in a formation of a configuration with a small δ-sunspot; 11 out of 100 ARs exhibited no signatures of magnetic flux emergence during the entire interval of observation. In six cases the emergence was in progress when the AR appeared on the Eastern limb, so that the classification and timing of emergence were not possible. We conclude that the recent flux emergence is not a necessary and/or sufficient condition for strong flaring of an AR. The flux emergence rate of flare-productive ARs analyzed here was compared with that of flare-quiet ARs analyzed in our previous studies. We revealed that the flare-productive ARs tend to display faster emergence than the flare-quiet ones do.
利用太阳周期 23 和 24 的磁场图和波连续强度数据，我们探索了 100 个产生 M5.0 或更强耀斑的活动区（ARs）。我们重点研究了这些活动区在强耀斑发生前2-3天是否出现磁通。我们发现，样本中有29个AR是在静日中单调出现的。在另外24个样本中，我们观测到在一个已经存在的AR中出现了新的磁通量，并形成了一个复杂的产生耀斑的构型。在 30 个 AR 中，观测到在原已存在的磁构型中出现了微不足道的新磁通量（就原已存在的 AR 的总磁通量而言）；其中一些新磁通量的出现导致形成了一个带有小型 δ 太阳黑子的构型；在 100 个 AR 中，有 11 个在整个观测期间没有显示出磁通量出现的迹象。在 6 个案例中，当 AR 出现在东侧边缘时，磁通出现正在进行中，因此无法对磁通出现的分类和时间进行确定。我们的结论是，最近出现的磁通量并不是 AR 强烈耀斑的必要和/或充分条件。我们将这里分析的产生耀斑的AR的流量出现率与之前研究中分析的平静耀斑AR的流量出现率进行了比较。我们发现，产生耀斑的AR往往比平静耀斑的AR显示出更快的涌现速度。
{"title":"A Statistical Study of Magnetic Flux Emergence in Solar Active Regions Prior to Strongest Flares","authors":"Alexander S. Kutsenko, Valentina I. Abramenko, Andrei A. Plotnikov","doi":"10.1088/1674-4527/ad2e4d","DOIUrl":"https://doi.org/10.1088/1674-4527/ad2e4d","url":null,"abstract":"Using the data on magnetic field maps and continuum intensity for Solar Cycles 23 and 24, we explored 100 active regions (ARs) that produced M5.0 or stronger flares. We focus on the presence/absence of the emergence of magnetic flux in these ARs 2–3 days before the strong flare onset. We found that 29 ARs in the sample emerged monotonically amidst quiet-Sun. A major emergence of a new magnetic flux within a pre-existing AR yielding the formation of a complex flare-productive configuration was observed in another 24 cases. For 30 ARs, an insignificant (in terms of the total magnetic flux of pre-existing AR) emergence of a new magnetic flux within the pre-existing magnetic configuration was observed; for some of them the emergence resulted in a formation of a configuration with a small <italic toggle=\"yes\">δ</italic>-sunspot; 11 out of 100 ARs exhibited no signatures of magnetic flux emergence during the entire interval of observation. In six cases the emergence was in progress when the AR appeared on the Eastern limb, so that the classification and timing of emergence were not possible. We conclude that the recent flux emergence is not a necessary and/or sufficient condition for strong flaring of an AR. The flux emergence rate of flare-productive ARs analyzed here was compared with that of flare-quiet ARs analyzed in our previous studies. We revealed that the flare-productive ARs tend to display faster emergence than the flare-quiet ones do.","PeriodicalId":54494,"journal":{"name":"Research in Astronomy and Astrophysics","volume":"16 1","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140615745","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-27DOI: 10.1088/1674-4527/ad2b39
Xue-Mei Ye, Da-Ming Wei, Yi-Ming Zhu, Zhi-Ping Jin
AT2021lfa, also known as ZTF21aayokph, was detected by the Zwicky Transient Facility on 2021 May 4, at 05:34:48 UTC. Follow-up observations were conducted using a range of ground-based optical telescopes, as well as Swift/XRT and VLA instruments. AT2021lfa is classified as an “orphan afterglow” candidate due to its rapid flux decline and its reddened color (g − r = 0.17 ± 0.14 mag). For an optical transient source without prompt gamma-ray detection, one key point is to determine its burst time. Here we measure the burst time through fitting the initial bump feature of AT2021lfa and obtain its burst time as 2021 May 3, at 22:09:50 UTC. Using afterglowpy, we model the multi-band afterglow of AT2021lfa and find that the standard model cannot reproduce the late radio observations well. Considering that the microphysical parameters ϵe, ϵB (the energy fraction given to electrons and magnetic field), and ξN (the fraction of accelerated electrons) may vary with time, we then model the afterglow of AT2021lfa taking into account the temporal evolution of the physical parameters ϵe, ϵB, and ξN and find in this case the multi-wavelength observations can be reproduced well. The initial Lorentz factor of AT2021lfa can be estimated from the peak time of the early afterglow, which yields a value of about 18, suggesting that AT2021lfa should be classified as a “dirty fireball.” From the upper limit for the prompt emission energy of AT2021lfa, we obtain that the radiation efficiency is less than 0.02%, which is much smaller than that of ordinary gamma-ray bursts (GRBs). It is also interesting that the fitted values of jet angle and viewing angle are very large, θc ∼ 0.66 rad, θv ∼ 0.53 rad, which may lead to the low Lorentz factor and radiation efficiency. When compared with GRB afterglow samples, it is evident that the onset bump timescale of AT2021lfa satisfies the empirical relationships observed in GRB samples. Additionally, the luminosity of AT2021lfa falls within the range of observations for GRB samples; however, approximately 1 day after the burst, its luminosity exceeds that of the majority of GRB samples.
{"title":"Optical Transient Source AT2021lfa: A Possible “Dirty Fireball”","authors":"Xue-Mei Ye, Da-Ming Wei, Yi-Ming Zhu, Zhi-Ping Jin","doi":"10.1088/1674-4527/ad2b39","DOIUrl":"https://doi.org/10.1088/1674-4527/ad2b39","url":null,"abstract":"AT2021lfa, also known as ZTF21aayokph, was detected by the Zwicky Transient Facility on 2021 May 4, at 05:34:48 UTC. Follow-up observations were conducted using a range of ground-based optical telescopes, as well as Swift/XRT and VLA instruments. AT2021lfa is classified as an “orphan afterglow” candidate due to its rapid flux decline and its reddened color (<italic toggle=\"yes\">g</italic> − <italic toggle=\"yes\">r</italic> = 0.17 ± 0.14 mag). For an optical transient source without prompt gamma-ray detection, one key point is to determine its burst time. Here we measure the burst time through fitting the initial bump feature of AT2021lfa and obtain its burst time as 2021 May 3, at 22:09:50 UTC. Using <monospace>afterglowpy</monospace>, we model the multi-band afterglow of AT2021lfa and find that the standard model cannot reproduce the late radio observations well. Considering that the microphysical parameters <italic toggle=\"yes\">ϵ</italic>\u0000<sub>\u0000<italic toggle=\"yes\">e</italic>\u0000</sub>, <italic toggle=\"yes\">ϵ</italic>\u0000<sub>\u0000<italic toggle=\"yes\">B</italic>\u0000</sub> (the energy fraction given to electrons and magnetic field), and <italic toggle=\"yes\">ξ</italic>\u0000<sub>\u0000<italic toggle=\"yes\">N</italic>\u0000</sub> (the fraction of accelerated electrons) may vary with time, we then model the afterglow of AT2021lfa taking into account the temporal evolution of the physical parameters <italic toggle=\"yes\">ϵ</italic>\u0000<sub>\u0000<italic toggle=\"yes\">e</italic>\u0000</sub>, <italic toggle=\"yes\">ϵ</italic>\u0000<sub>\u0000<italic toggle=\"yes\">B</italic>\u0000</sub>, and <italic toggle=\"yes\">ξ</italic>\u0000<sub>\u0000<italic toggle=\"yes\">N</italic>\u0000</sub> and find in this case the multi-wavelength observations can be reproduced well. The initial Lorentz factor of AT2021lfa can be estimated from the peak time of the early afterglow, which yields a value of about 18, suggesting that AT2021lfa should be classified as a “dirty fireball.” From the upper limit for the prompt emission energy of AT2021lfa, we obtain that the radiation efficiency is less than 0.02%, which is much smaller than that of ordinary gamma-ray bursts (GRBs). It is also interesting that the fitted values of jet angle and viewing angle are very large, <italic toggle=\"yes\">θ</italic>\u0000<sub>\u0000<italic toggle=\"yes\">c</italic>\u0000</sub> ∼ 0.66 rad, <italic toggle=\"yes\">θ</italic>\u0000<sub>\u0000<italic toggle=\"yes\">v</italic>\u0000</sub> ∼ 0.53 rad, which may lead to the low Lorentz factor and radiation efficiency. When compared with GRB afterglow samples, it is evident that the onset bump timescale of AT2021lfa satisfies the empirical relationships observed in GRB samples. Additionally, the luminosity of AT2021lfa falls within the range of observations for GRB samples; however, approximately 1 day after the burst, its luminosity exceeds that of the majority of GRB samples.","PeriodicalId":54494,"journal":{"name":"Research in Astronomy and Astrophysics","volume":"21 1","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140314088","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-27DOI: 10.1088/1674-4527/ad2ee0
Rai Yuen
We investigate the population and several properties of radio pulsars whose emission does not null (non-nulling) through simulation of a large pulsar sample. Emission from a pulsar is identified as non-nulling if (i) the emission does not cease across the whole pulse profile, and (ii) the emission is detectable. For (i), we adopt a model for switching in the plasma charge density, and emission persists if the charge density is non-zero. For (ii), we assume that detectable emission originates from source points where it is emitted tangentially to the magnetic field-line and parallel to the line-of-sight. We find that pulsars exhibiting non-nulling emission possess obliquity angles with an average of 42.°5, and almost half the samples maintain a duty cycle between 0.05 and 0.2. Furthermore, the pulsar population is not fixed but dependent on the obliquity angle, with the population peaking at 20°. In addition, three evolutionary phases are identified in the pulsar population as the obliquity angle evolves, with the majority of samples having an obliquity angle between 20° and 65°. Our results also suggest that emission from a pulsar may evolve between nulling and non-nulling during its lifetime.
{"title":"Characteristics of Emission Non-nulling Pulsars Through Simulation","authors":"Rai Yuen","doi":"10.1088/1674-4527/ad2ee0","DOIUrl":"https://doi.org/10.1088/1674-4527/ad2ee0","url":null,"abstract":"We investigate the population and several properties of radio pulsars whose emission does not null (non-nulling) through simulation of a large pulsar sample. Emission from a pulsar is identified as non-nulling if (i) the emission does not cease across the whole pulse profile, and (ii) the emission is detectable. For (i), we adopt a model for switching in the plasma charge density, and emission persists if the charge density is non-zero. For (ii), we assume that detectable emission originates from source points where it is emitted tangentially to the magnetic field-line and parallel to the line-of-sight. We find that pulsars exhibiting non-nulling emission possess obliquity angles with an average of 42.°5, and almost half the samples maintain a duty cycle between 0.05 and 0.2. Furthermore, the pulsar population is not fixed but dependent on the obliquity angle, with the population peaking at 20°. In addition, three evolutionary phases are identified in the pulsar population as the obliquity angle evolves, with the majority of samples having an obliquity angle between 20° and 65°. Our results also suggest that emission from a pulsar may evolve between nulling and non-nulling during its lifetime.","PeriodicalId":54494,"journal":{"name":"Research in Astronomy and Astrophysics","volume":"56 1","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140313913","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-27DOI: 10.1088/1674-4527/ad2edf
Lei Wang, Huanyuan Shan, Lin Nie, Dezi Liu, Zhaojun Yan, Guoliang Li, Cheng Cheng, Yushan Xie, Han Qu, Wenwen Zheng, Xi Kang
We have developed a novel method for co-adding multiple under-sampled images that combines the iteratively reweighted least squares and divide-and-conquer algorithms. Our approach not only allows for the anti-aliasing of the images but also enables Point-Spread Function (PSF) deconvolution, resulting in enhanced restoration of extended sources, the highest peak signal-to-noise ratio, and reduced ringing artefacts. To test our method, we conducted numerical simulations that replicated observation runs of the China Space Station Telescope/ the VLT Survey Telescope (VST) and compared our results to those obtained using previous algorithms. The simulation showed that our method outperforms previous approaches in several ways, such as restoring the profile of extended sources and minimizing ringing artefacts. Additionally, because our method relies on the inherent advantages of least squares fitting, it is more versatile and does not depend on the local uniformity hypothesis for the PSF. However, the new method consumes much more computation than the other approaches.
{"title":"How to Coadd Images. II. Anti-aliasing and PSF Deconvolution","authors":"Lei Wang, Huanyuan Shan, Lin Nie, Dezi Liu, Zhaojun Yan, Guoliang Li, Cheng Cheng, Yushan Xie, Han Qu, Wenwen Zheng, Xi Kang","doi":"10.1088/1674-4527/ad2edf","DOIUrl":"https://doi.org/10.1088/1674-4527/ad2edf","url":null,"abstract":"We have developed a novel method for co-adding multiple under-sampled images that combines the iteratively reweighted least squares and divide-and-conquer algorithms. Our approach not only allows for the anti-aliasing of the images but also enables Point-Spread Function (PSF) deconvolution, resulting in enhanced restoration of extended sources, the highest peak signal-to-noise ratio, and reduced ringing artefacts. To test our method, we conducted numerical simulations that replicated observation runs of the China Space Station Telescope/ the VLT Survey Telescope (VST) and compared our results to those obtained using previous algorithms. The simulation showed that our method outperforms previous approaches in several ways, such as restoring the profile of extended sources and minimizing ringing artefacts. Additionally, because our method relies on the inherent advantages of least squares fitting, it is more versatile and does not depend on the local uniformity hypothesis for the PSF. However, the new method consumes much more computation than the other approaches.","PeriodicalId":54494,"journal":{"name":"Research in Astronomy and Astrophysics","volume":"416 1","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140314068","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Rotating Radio Transients (RRATs) are a relatively new subclass of pulsars that emit detectable radio bursts sporadically. We analyzed 10 RRATs observed using the Parkes telescope, with eight of these observed via the ultra-wide-bandwidth low-frequency (UWL) receiver. We measured the burst rate and produced integrated profiles spanning multiple frequency bands for three RRATs. We also conducted a spectral analysis on both integrated pulses and individual pulses of three RRATs. All of their integrated pulses follow a simple power law, consistent with the known range of pulsar spectral indices. Their average spectral indices of single pulses are −0.9, −1.2, and −1.0 respectively, which are within the known range of pulsar spectral indices. Additionally, we find that the spreads of single-pulse spectral indices for these RRATs (ranging from −3.5 to +0.5) are narrower compared to what has been observed in other RRATs. Notably, the average spectral index and scatter of single pulses are both relatively small. For the remaining five RRATs observed at the UWL receiver, we also provide the upper limits on fluence and flux density. In addition, we obtain the timing solution of PSR J1709-43. Our analysis shows that PSRs J1919+1745, J1709-43, and J1649-4653 are potentially nulling pulsars or weak pulsars with sparse strong pulses.
{"title":"A Study of 10 Rotating Radio Transients Using Parkes Radio Telescope","authors":"Xinhui Ren, Jingbo Wang, Wenming Yan, Jintao Xie, Shuangqiang Wang, Yirong Wen, Yong Xia","doi":"10.1088/1674-4527/ad2dbe","DOIUrl":"https://doi.org/10.1088/1674-4527/ad2dbe","url":null,"abstract":"Rotating Radio Transients (RRATs) are a relatively new subclass of pulsars that emit detectable radio bursts sporadically. We analyzed 10 RRATs observed using the Parkes telescope, with eight of these observed via the ultra-wide-bandwidth low-frequency (UWL) receiver. We measured the burst rate and produced integrated profiles spanning multiple frequency bands for three RRATs. We also conducted a spectral analysis on both integrated pulses and individual pulses of three RRATs. All of their integrated pulses follow a simple power law, consistent with the known range of pulsar spectral indices. Their average spectral indices of single pulses are −0.9, −1.2, and −1.0 respectively, which are within the known range of pulsar spectral indices. Additionally, we find that the spreads of single-pulse spectral indices for these RRATs (ranging from −3.5 to +0.5) are narrower compared to what has been observed in other RRATs. Notably, the average spectral index and scatter of single pulses are both relatively small. For the remaining five RRATs observed at the UWL receiver, we also provide the upper limits on fluence and flux density. In addition, we obtain the timing solution of PSR J1709-43. Our analysis shows that PSRs J1919+1745, J1709-43, and J1649-4653 are potentially nulling pulsars or weak pulsars with sparse strong pulses.","PeriodicalId":54494,"journal":{"name":"Research in Astronomy and Astrophysics","volume":"29 1","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140314064","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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