المؤلفون: Zhang, S. B., Geng, J. J., Wang, J. S., Yang, X., Kaczmarek, J., Tang, Z. F., Johnston, S., Hobbs, G., Manchester, R., Wu, X. F., Jiang, P., Huang, Y. F., Zou, Y. C., Dai, Z. G., Zhang, B., Li, D., Yang, Y. P., Dai, S., Chang, C. M., Pan, Z. C., Lu, J. G., Wei, J. J., Li, Y., Wu, Q. W., Qian, L., Wang, P., Wang, S. Q., Feng, Y., Staveley-Smith, L.

مصطلحات موضوعية: Astrophysics - High Energy Astrophysical Phenomena

الوصف: Rotating Radio Transients (RRATs) are neutron stars that emit sporadic radio bursts. We detected 1955 single pulses from RRAT J1913+1330 using the 19-beam receiver of the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). These pulses were detected in 19 distinct clusters, with 49.4% of them occurring sequentially with a waiting time of one rotation period. The energy distribution of these individual pulses exhibited a wide range, spanning three orders of magnitude, reminiscent of repeating fast radio bursts (FRBs). Furthermore, we observed abrupt variations in pulse profile, width, peak flux, and fluence between adjacent sequential pulses. These findings suggest that this RRAT could be interpreted as pulsars with extreme pulse-to-pulse modulation. The presence of sequential pulse trains during active phases, along with significant pulse variations in profile, fluence, flux, and width, should be intrinsic to a subset of RRATs. Our results indicate that J1913+1330 represents a peculiar source that shares certain properties with populations of nulling pulsars, giant pulses, and FRBs from different perspectives. The dramatic pulse-to-pulse variation observed in J1913+1330 could be attributed to unstable pair creation above the polar cap region and the variation of the site where streaming pairs emit coherently. Exploring a larger sample of RRATs exhibiting similar properties to J1913+1330 has the potential to significantly advance our understanding of pulsars, RRATs, and FRBs.
Comment: 12 pages, 10 figures, 1 table

الوصول الحر: http://arxiv.org/abs/2306.02855Test

المؤلفون: Miao, C. C., Zhu, W. W., Li, D., Freire, P. C. C., Niu, J. R., Wang, P., Yuan, J. P., Xue, M. Y., Cameron, A. D., Champion, D. J., Cruces, M., Chen, Y. T., Chi, M. M., Cheng, X. F., Dang, S. J., Ding, M. F., Feng, Y., Gan, Z. Y., Hobbs, G., Kramer, M., Liu, Z. J., Li, Y. X., Luo, Z. K., Miao, X. L., Meng, L. Q., Niu, C. H., Pan, Z. C., Qian, L., Sun, Z. Y., Wang, N., Wang, S. Q., Wang, J. B., Wu, Q. D., Wang, Y. B., Wang, C. J., Wang, H. F., Wang, S., Xie, X. Y., Xie, M., Xiao, Y. F., Yuan, M., Yue, Y. L., Yao, J. M., Yan, W. M., You, S. P., Yu, X. H., Zhao, D., Zhao, R. S., Zhang, L.

مصطلحات موضوعية: Astrophysics - High Energy Astrophysical Phenomena

الوصف: We report the phase-connected timing ephemeris, polarization pulse profiles, Faraday rotation measurements, and Rotating-Vector-Model (RVM) fitting results of twelve millisecond pulsars (MSPs) discovered with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in the Commensal radio Astronomy FAST survey (CRAFTS). The timing campaigns were carried out with FAST and Arecibo over three years. Eleven of the twelve pulsars are in neutron star - white dwarf binary systems, with orbital periods between 2.4 and 100 d. Ten of them have spin periods, companion masses, and orbital eccentricities that are consistent with the theoretical expectations for MSP - Helium white dwarf (He WD) systems. The last binary pulsar (PSR J1912$-$0952) has a significantly smaller spin frequency and a smaller companion mass, the latter could be caused by a low orbital inclination for the system. Its orbital period of 29 days is well within the range of orbital periods where some MSP - He WD systems have shown anomalous eccentricities, however, the eccentricity of PSR J1912$-$0952 is typical of what one finds for the remaining MSP - He WD systems.
Comment: 11 pages, 5 figures, MNRAS accepted

الوصول الحر: http://arxiv.org/abs/2205.04232Test

المؤلفون: Bai, J. T., Dai, S., Zhi, Q. J., Coles, W. A., Li, D., Zhu, W. W., Hobbs, G., Qiao, G. J., Wang, N., Yuan, J. P., Filipovic, M. D., Wang, J. B., Pan, Z. C., Shang, L. H., Dang, S. J., Wang, S. Q., Miao, C. C.

مصطلحات موضوعية: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics

الوصف: We present the first measurement of pulse scattering close to the eclipse region of PSR B1957+20, which is in a compact binary system with a low-mass star. We measured pulse scattering time-scales up to 0.2 ms close to the eclipse and showed that it scales with the dispersion measure (DM) excess roughly as $\tau\propto\Delta{\rm DM}^{2}$. Our observations provide the first evidence of strong scattering due to multi-path propagation effects in the eclipsing material. We show that Kolmogorov turbulence in the eclipsing material with an inner scale of $\sim100$ m and an outer scale of the size of the eclipse region can naturally explain the observation. Our results show that the eclipsing material in such systems can be highly turbulent and suggest that scattering is one of the main eclipsing mechanisms at around 1.4 GHz.
Comment: 8 pages, 4 figures, MNRAS accepted

الوصول الحر: http://arxiv.org/abs/2203.15134Test

المؤلفون: Cruces, M., Champion, D. J., Li, D., Kramer, M., Zhu, W. W., Wang, P., Cameron, A. D., Chen, Y. T., Hobbs, G., Freire, P. C. C., Graikou, E., Krco, M., Liu, Z. J., Miao, C. C., Niu, J., Pan, Z. C., Qian, L., Xue, M. Y., Xie, X. Y., You, S. P., Yu, X. H., Yuan, M., Yue, Y. L., Zhu, Y.

مصطلحات موضوعية: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics

الوصف: We report the follow-up of 10 pulsars discovered by the Five-hundred-meter Aperture Spherical radio-Telescope (FAST) during its commissioning. The pulsars were discovered at a frequency of 500-MHz using the ultra-wide-band (UWB) receiver in drift-scan mode, as part of the Commensal Radio Astronomy FAST Survey (CRAFTS). We carried out the timing campaign with the 100-m Effelsberg radio-telescope at L-band around 1.36 GHz. Along with 11 FAST pulsars previously reported, FAST seems to be uncovering a population of older pulsars, bordering and/or even across the pulsar death-lines. We report here two sources with notable characteristics. PSR J1951$+$4724 is a young and energetic pulsar with nearly 100% of linearly polarized flux density and visible up to an observing frequency of 8 GHz. PSR J2338+4818, a mildly recycled pulsar in a 95.2-d orbit with a Carbon-Oxygen white dwarf (WD) companion of $\gtrsim 1\rm{M}_{\odot}$, based on estimates from the mass function. This system is the widest WD binary with the most massive companion known to-date. Conspicuous discrepancy was found between estimations based on NE2001 and YMW16 electron density models, which can be attributed to under-representation of pulsars in the sky region between Galactic longitudes $70^o

الوصول الحر: http://arxiv.org/abs/2108.09121Test

المؤلفون: Li, D., Wang, P., Zhu, W. W., Zhang, B., Zhang, X. X., Duan, R., Zhang, Y. K., Feng, Y., Tang, N. Y., Chatterjee, S., Cordes, J. M., Cruces, M., Dai, S., Gajjar, V., Hobbs, G., Jin, C., Kramer, M., Lorimer, D. R., Miao, C. C., Niu, C. H., Niu, J. R., Pan, Z. C., Qian, L., Spitler, L., Werthimer, D., Zhang, G. Q., Wang, F. Y., Xie, X. Y., Yue, Y. L., Zhang, L., Zhi, Q. J., Zhu, Y.

المصدر: Nature 598 (2021) 267-271

مصطلحات موضوعية: Astrophysics - High Energy Astrophysical Phenomena

الوصف: The event rate, energy distribution, and time-domain behaviour of repeating fast radio bursts (FRBs) contains essential information regarding their physical nature and central engine, which are as yet unknown. As the first precisely-localized source, FRB 121102 has been extensively observed and shows non-Poisson clustering of bursts over time and a power-law energy distribution. However, the extent of the energy distribution towards the fainter end was not known. Here we report the detection of 1652 independent bursts with a peak burst rate of 122~hr^{-1}, in 59.5 hours spanning 47 days. A peak in the isotropic equivalent energy distribution is found to be ~4.8 x 10^{37} erg at 1.25~GHz, below which the detection of bursts is suppressed. The burst energy distribution is bimodal, and well characterized by a combination of a log-normal function and a generalized Cauchy function. The large number of bursts in hour-long spans allow sensitive periodicity searches between 1 ms and 1000 s. The non-detection of any periodicity or quasi-periodicity poses challenges for models involving a single rotating compact object. The high burst rate also implies that FRBs must be generated with a high radiative efficiency, disfavoring emission mechanisms with large energy requirements or contrived triggering conditions.
Comment: 69 pages, 14 figures, 2 tables; Updates for author correction

الوصول الحر: http://arxiv.org/abs/2107.08205Test

المؤلفون: Zhang, C., Wang, C., Hobbs, G., Russell, C. J., Li, D., Zhang, S. -B., Dai, S., Wu, J. -W., Pan, Z. -C., Zhu, W. -W., Toomey, L., Ren, Z. -Y.

المصدر: A&A 642, A26 (2020)

مصطلحات موضوعية: Astrophysics - Instrumentation and Methods for Astrophysics

الوصف: To investigate the use of saliency-map analysis to aid in searches for transient signals, such as fast radio bursts and individual pulses from radio pulsars. We aim to demonstrate that saliency maps provide the means to understand predictions from machine learning algorithms and can be implemented in piplines used to search for transient events. We have implemented a new deep learning methodology to predict whether or not any segment of the data contains a transient event. The algorithm has been trained using real and simulated data sets. We demonstrate that the algorithm is able to identify such events. The output results are visually analysed via the use of saliency maps. We find that saliency maps can produce an enhanced image of any transient feature without the need for de-dispersion or removal of radio frequency interference. Such maps can be used to understand which features in the image were used in making the machine learning decision and to visualise the transient event. Even though the algorithm reported here was developed to demonstrate saliency-map analysis, we have detected, in archival data, a single burst event with dispersion measure of $41$\,cm$^{-3}$pc that is not associated with any currently known pulsar.
Comment: 16 pages, 6 figures, accepted for publication in A&A

الوصول الحر: http://arxiv.org/abs/2005.11066Test

المؤلفون: Cameron, A. D., Li, D., Hobbs, G., Zhang, L., Miao, C. C., Wang, J. B., Yuan, M., Wang, S., Corban, G. Jacobs, Cruces, M., Dai, S., Feng, Y., Han, J., Kaczmarek, J. F., Nui, J. R., Pan, Z. C., Qian, L., Tao, Z. Z., Wang, P., Wang, S. Q., Xu, H., Xu, R. X., Yue, Y. L., Zhang, S. B., Zhi, Q. J., Zhu, W. W., Champion, D. J., Kramer, M. K., Zhou, S. Q., Qiu, K. P., Zhu, M.

مصطلحات موضوعية: Astrophysics - High Energy Astrophysical Phenomena

الوصف: We present timing solutions and analyses of 11 pulsars discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). These pulsars were discovered using an ultra-wide bandwidth receiver in drift-scan observations made during the commissioning phase of FAST, and were then confirmed and timed using the 64-m Parkes Radio Telescope. Each pulsar has been observed over a span of at least one year. Highlighted discoveries include PSR J0344-0901, which displays mode-changing behaviour and may belong to the class of so-called `swooshing' pulsars (alongside PSRs B0919+06 and B1859+07); PSR J0803-0942, whose emission is almost completely linearly polarised; and PSRs J1900-0134 and J1945+1211, whose well defined polarisation angle curves place stringent constraints on their emission geometry. We further discuss the detectability of these pulsars by earlier surveys, and highlight lessons learned from our work in carrying out confirmation and monitoring observations of pulsars discovered by a highly sensitive telescope, many of which may be applicable to next-generation pulsar surveys. This paper marks one of the first major releases of FAST-discovered pulsars, and paves the way for future discoveries anticipated from the Commensal Radio Astronomy FAST Survey (CRAFTS).
Comment: 18 pages, 8 figures, 5 tables. Accepted for publication by MNRAS. Correcting error in the caption of Figure 8

الوصول الحر: http://arxiv.org/abs/2005.09171Test

المؤلفون: Laugesen, R. S., Pan, Z. C., Son, S. S.

مصطلحات موضوعية: Mathematics - Analysis of PDEs, Mathematical Physics, 35P15

الوصف: We prove that among all triangles of given diameter, the equilateral triangle minimizes the sum of the first $n$ eigenvalues of the Neumann Laplacian, when $n \geq 3$. The result fails for $n=2$, because the second eigenvalue is known to be minimal for the degenerate acute isosceles triangle (rather than for the equilateral) while the first eigenvalue is 0 for every triangle. We show the third eigenvalue is minimal for the equilateral triangle.
Comment: 12 pages, 2 figures, 2 tables

الوصول الحر: http://arxiv.org/abs/1102.0071Test

المؤلفون: Li, D., Wang, P., Zhu, W. W., Zhang, B., Zhang, X. X., Duan, R., Zhang, Y. K., Feng, Y., Tang, N. Y., Chatterjee, S., Cordes, J. M., Cruces, M., Dai, S., Gajjar, V., Hobbs, G., Jin, C., Kramer, M., Lorimer, D. R., Miao, C. C., Niu, C. H., Niu, J. R., Pan, Z. C., Qian, L., Spitler, L., Werthimer, D., Zhang, G. Q., Wang, F. Y., Xie, X. Y., Yue, Y. L., Zhang, L., Zhi, Q. J., Zhu, Y.

المصدر: Nature ; volume 601, issue 7891, page E1-E1 ; ISSN 0028-0836 1476-4687

مصطلحات موضوعية: Multidisciplinary

الإتاحة: https://doi.org/10.1038/s41586-021-04178-8Test
https://www.nature.com/articles/s41586-021-04178-8.pdfTest
https://www.nature.com/articles/s41586-021-04178-8Test

المؤلفون: Wu, Q D, Yuan, J P, Wang, N, Li, D, Wang, P, Xue, M Y, Zhu, W W, Miao, C C, Yan, W M, Wang, J B, Yao, J M, Wang, S Q, Sun, S N, Kou, F F, Tu, Z Y, Xie, J T, Pan, Z C, Zhao, D, Chen, Y T, Dang, S J, Feng, Y, Liu, Z J, Miao, X L, Meng, L Q, Yuan, M, Niu, C H, Niu, J R, Qian, L, Wang, S, Xie, X Y, Xiao, Y F, Yue, Y L, You, S P, Yu, X H, Zhao, R S, Zhang, L, Yuen, R, Wen, Z G, Tedila, H M

المساهمون: National Key Research and Development Program of China, National Natural Science Foundation of China, Youth Innovation Promotion Association CAS

المصدر: Monthly Notices of the Royal Astronomical Society ; volume 522, issue 4, page 5152-5164 ; ISSN 0035-8711 1365-2966

مصطلحات موضوعية: Space and Planetary Science, Astronomy and Astrophysics

الوصف: The follow-up timing observations were carried out for 24 pulsars discovered with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in Commensal Radio Astronomy FAST Survey. We report their phase-connected timing ephemeris, polarization pulse profiles, and Faraday rotation measurements. With their spin periods spanning from 2.995 ms to 4.34 s, their period derivatives were determined to spread between 7.996(8) × 10−21 and 9.83(3) × 10−15 s s−1, which imply that they have characteristic ages from 1.97 × 106 to 5.93 × 109 yr. It is inferred that PSRs J0211+4235 and J0518+2431 are beyond the ‘traditional death line’. PSR J0211+4235 is beyond the ‘death valley’. The death line model of Zhang et al. also cannot explain the radio presence of PSR J0211+4235. This suggests that radiation theory needs to be improved. Besides, ten of the 22 canonical pulsars show nulling phenomena. Moreover, PSR J1617+1123 exhibits variation of emission and J0540+4542 shows subpulse drifting. The DM of five pulsars is larger than the estimated by the YMW16 electron density model, which could suggest that electron density models need updates for higher Galactic latitude regions. PSRs J0447+2447 and J1928−0548 are isolated millisecond pulsars. With their flux densities spanning from 5(1)–553(106) μJy, some of these new pulsars found by FAST are distant, dim, and low-$\dot{E}$ ones and are suitable for testing pulsar emission theories.

الإتاحة: https://doi.org/10.1093/mnras/stad1323Test
https://academic.oup.com/mnras/article-pdf/522/4/5152/50311090/stad1323.pdfTest