分类: 天文学 >> 天体物理学 提交时间: 2023-07-29
摘要: The pulsar radio emission mechanism remains an enigma since its discovery in 1967. The critical issue of origin of coherent emission is usually investigated separately from the micro-structure of individual pulses and characteristic emission frequency of pulsars... In this letter, these issues are interpreted in an unified scenario. The pulsar spin piles up magnetic field at the apex of last closed field line triggering magnetic reconnection. The resultant Alfven wave interacts with open field lines giving rise to coherent maser curvature and cyclotron emission. Such a scenario of coherent emission not only imposes new limit to emission site, nanoburst, and characteristic frequency, but also affects polarization and pair production required in maintaining a marginal stable circuit in radio emission of pulsars.
分类: 物理学 >> 核物理学 提交时间: 2016-09-02
摘要: The maximum frequency of gravitational waves (GWs) detectable with traditional pulsar timing methods is set by the Nyquist frequency (fNy) of the observation. Beyond this frequency, GWs leave no temporal-correlated signals; instead, they appear as white noise in the timing residuals. The variance of the GW-induced white noise is a function of the position of the pulsars relative to the GW source. By observing this unique functional form in the timing data, we propose that we can detect GWs of frequency > fNy (super-Nyquist frequency GWs; SNFGWs). We demonstrate the feasibility of the proposed method with simulated timing data. Using a selected dataset from the Parkes Pulsar Timing Array data release 1 and the North American Nanohertz Observatory for Gravitational Waves publicly available datasets, we try to detect the signals from single SNFGW sources. The result is consistent with no GW detection with 65.5\% probability. An all-sky map of the sensitivity of the selected pulsar timing array to single SNFGW sources is generated, and the position of the GW source where the selected pulsar timing array is most sensitive to is λs=−0.82, βs=−1.03 (rad); the corresponding minimum GW strain is h=6.31×10−11 at f=1×10−5 Hz.
分类: 天文学 >> 天体物理学 提交时间: 2024-01-16
摘要: The pulsar radio emission mechanism remains an enigma since over half a century. A radiation process requires not only to explain the coherency and high degree of polarization of the emission, but also nanobursts, characteristic frequency of emission, and problems like death line, which can#2;not be well understood in the context of long standing cap models and recent models of magnetic reconnection. This article proposes a dynamo process in pulsar magnetosphere. Through centrifu#2;gal force the last closed magnetic field lines can be amplified to a critical value of, BT 104T, which triggers magnetic reconnection responsible for the instability required in coherent curvature radiation, so that a number of problems can be interpreted. The time scale of magnetic field pile up and relaxation can be short or long for young or old pulsars respectively, which naturally account for the diverse intermittencies exhibited in pulsars and FRBs.
分类: 物理学 >> 核物理学 提交时间: 2016-09-01
摘要: Context: The LIGO consortium announced the first direct detection of gravitation wave event GW150914 from two merging black holes; however the nature of the black holes are still not clear. Aims: We study whether electromagnetic radiation can be detected from merging stellar mass black binaries like GW150914. Methods: We briefly investigate the possible growth and merging processes of the two stellar mass black holes in the merging event of GW150914 detected by aLIGO, as clocked by a distant external observer. Our main results are: (1) The description of the black hole growth using stationary metric of a pre-existing black hole predicts strong electromagnetic radiation from merging black holes, which is inconsistent with GW150914; (2) Only gravitational wave radiation can be produced in the coalescence of two black holes such as that in the GW150914 event, if the black hole growth is described using time-dependent metric considering the influence of the in-falling matter onto a pre-existing black hole, as clocked by a distant external observer. Conclusions: Future high sensitivity detections of gravitational waves from merging black holes might be used to probe matter distribution and space-time geometry in the vicinity of the horizon. Perhaps the GW150914-like events can be identified with traditional astronomy observations only if the black holes are embedded in extremely dense medium before their final merge, when very strong electromagnetic radiation is produced and can escape from the system.
分类: 天文学 >> 天体物理学 提交时间: 2023-12-04
摘要: The pulsar radio emission mechanism remains an enigma over half a century.A successful radiation process requires not only to explain the coherency and high degree of polarization of the emission, but alsomicrostructures, characteristic frequency of emission, and the death line problem, etc. These issues challenge both the long standing cap models and recent models of magnetic reconnection assuming stationary magnetosphere of a pulsar.This article proposes a radio emission through global-local interaction of pulsar magnetosphere. The centrifugal force at the light cylinder leads to the concentration of both field lines and plasma in an equatorial layer much less than that of a pulsar magnetosphere.The resultant magnetic reconnection with chain of plasmoids interprets not only the above problems in a simple and unified way, but also Rotating Radio Transients (RRATs) and Fast Radio Bursts (FRBs).
分类: 物理学 >> 核物理学 分类: 物理学 >> 地球物理学、天文学和天体物理学 提交时间: 2024-05-29
摘要: It is hypothesized that, though atomic nuclei are made of nucleons, strongly interacting matter with baryon number from $A simeq 10^{3-9}$ to $ sim 10^{57}$ would be composed of strangeons if Nature favors always the flavor symmetry of quarks.According to that logic, strangeon matter with $A sim 10^{57}$ could manifest in the form of pulsar-like compact stars, and multi-messenger observations with advanced facilities (e.g., China’s FAST) could eventually provide a disproof/proof.It is worth emphasizing that this point of view, based on established “old physics”, may have particular consequences for understanding our material world, for both normal luminous matter and the dark sector.
分类: 天文学 >> 天文学 提交时间: 2016-05-23
摘要: The Five-hundred-meter Aperture Spherical radio Telescope (FAST) will begin its early-science operations during 2016. Drift-scan pulsar surveys will be carried out during this period using an ultra-wide-band receiver system (covering ∼ 270 to 1620 MHz). We describe a method for accounting for the changes in the telescope beam shape and the pulsar parameters when searching for pulsars over such a wide bandwidth. We applied this method to simulated data sets of pulsars in globular clusters that are visible to FAST and found that a representative observation would have a sensitivity of ∼ 40 µJy. Our results showed that a single drift-scan (lasting less than a minute) is likely to find at least one pulsar for observations of four globular clusters. Repeated observations will increase the likely number of detections. We found that pulsars in ∼16 clusters are likely to be found if the data from 100 drift-scan observations of each cluster are incoherently combined.
分类: 物理学 >> 地球物理学、天文学和天体物理学 提交时间: 2023-07-25
摘要: Strong evidence for a gravitational-wave background (GWB) has been reported in the nano-Hertz band. Interpreting the origin of this background to be scalar-induced gravitational waves (SIGWs), we explore the equation of state (EoS) of the early universe by performing Bayes parameter inferences across the big-bang nucleosynthesis (BBN), cosmic microwave background (CMB), and pulsar timing array (PTA) joint observations for the first time. Assuming a monochromatic power spectrum for primordial curvature perturbations, we obtain the spectral amplitude $A\sim10^{-3}-10^{-1}$ and spectral peak frequency $f_\ast\sim10^{-7}-10^{-6}$ Hz. We find that the radiation domination with EoS $w=1/3$ is compatible with the current observational data, the kination domination with EoS $w=1$ is not forbidden, while the early matter domination with EoS $w=0$ is excluded at more than $2\sigma$ confidence level. These results can be tested with future observations.