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  • The Impact of Bias Row Noise to Photometric Accuracy: Case Study Based on a Scientific CMOS Detector

    DOI:https://doi.org/10.1088/1674-4527/ad1793

    提交时间: 2024-02-28

    摘要:We tested a new model of CMOS detector manufactured by the Gpixel Inc, for potential space astronomical application. In laboratory, we obtain some bias images under the typical application environment. In these bias images, clear random row noise pattern is observed. The row noise also contains some characteristic spatial frequencies. We quantitatively estimated the impact of this feature to photometric measurements, by making simulated images. We compared different bias noise types under strict parameter control. The result shows the row noise will significantly deteriorate the photometric accuracy. It effectively increases the readout noise by a factor of 2–10. However, if it is properly removed, the image quality and photometric accuracy will be significantly improved.

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  • A New Method for Monitoring Scattered Stray Light of an Inner-occulted Coronagraph

    DOI:https://doi.org/10.1088/1674-4527/ad019c

    提交时间: 2024-02-28

    摘要:The scattered stray light of a coronagraph is a type of stray light that is generated by the objective lens as its surface defects are irradiated by sunlight. The defects mainly include dust and blemishes on the lens surface, microroughness of the lens surface, and impurity and inhomogeneity of the glass. Unlike the other types of relatively stable defects introduced when the objective lens is being manufactured, the scattered stray light caused by dusts on the lens surface is difficult to quantify accurately due to the disorder and randomness of the dust accumulation. The contribution of this type of stray light to the overall stray light level is difficult to determine through simulations and experiments. This can result in continuous deterioration of the stray light level of a coronagraph and thus affect the observation capabilities of the instrument. To solve this issue, through analyzing the forming mechanism of scattered stray light and ghost image generated by the inner-occulted coronagraph, we propose a novel method to monitor the scattered stray light from dusts by utilizing different stray light correlation coefficients. In this method, we first simulate and measure the level of stray light from the ghost image of the objective lens, and then determine the flux ratio of scattered light and ghost image on the conjugate plane. Although the flux ratio varies with the accumulation of dusts on the lens surface, it remains constant on the image plane. Therefore, the level of dust scattering light on the image plane can be obtained by using this ratio together with the level of ghost image stray light. The accuracy of this method has been validated in a laboratory by applying the objective lens with numerous surface cleanliness levels.

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  • The Precursor of GRB211211A: A Tide-induced Giant Quake?

    DOI:https://doi.org/10.1088/1674-4527/ad0825

    提交时间: 2024-02-28

    摘要:The equilibrium configuration of a solid strange star in the final inspiral phase with another compact object is generally discussed, and the starquake-related issue is revisited, for a special purpose to understand the precursor emission of binary compact star merger events (e.g., that of GRB211211A). As the binary system inspirals inward due to gravitational wave radiation, the ellipticity of the solid strangeon star increases due to the growing tidal field of its compact companion. Elastic energy is hence accumulated during the inspiral stage which might trigger a starquake before the merger when the energy exceeds a critical value. The energy released during such starquakes is calculated and compared to the precursor observation of GRB211211A. The result shows that the energy might be insufficient for binary strangeon-star case unless the entire solid strangeon star shatters, and hence favors a black hole-strangeon star scenario for GRB211211A. The timescale of the precursor as well as the frequency of the observed quasi-periodic-oscillation have also been discussed in the starquake model.

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  • Lobe-dominated γ-Ray Emission of Compact Symmetric Objects

    DOI:https://doi.org/10.1088/1674-4527/ad1c78

    提交时间: 2024-02-28

    摘要:The γ-ray emitting compact symmetric objects (CSOs) PKS 1718–649, NGC 3894, and TXS 0128+554 are lobe-dominated in the radio emission. In order to investigate their γ-ray radiation properties, we analyze the ∼14 yr Fermi/LAT observation data of the three CSOs. They all show the low luminosity (1041–1043 erg s−1) and no significant variability in the γ-ray band. Their γ-ray average spectra can be well fitted by a power-law function. These properties of γ-rays are clearly different from the γ-ray emitting CSOs CTD 135 and PKS 1413+135, for which the γ-rays are produced by a restarted aligned jet. In the Lγ − Γγ plane, the three CSOs are also located at the region occupied by radio galaxies (RGs) while CTD 135 and PKS 1413+135 display a similar feature to blazars. Together with a similar radio emission property to γ-ray emitting RGs Cen A and Fornax A, we speculate that the γ-rays of the three CSOs stem from their extended mini-lobes. The broadband spectral energy distributions of the three CSOs can be well explained by the two-zone leptonic model, where their γ-rays are produced by the inverse Compton process of the relativistic electrons in extended regions. By extrapolating the observed Fermi/LAT spectra to the very high energy band, we find that TXS 0128+554 among the three CSOs may be detected by the Cherenkov Telescope Array in the future.

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  • GRB 200612A: An Ultralong Gamma-Ray Burst Powered by Magnetar Spinning Down

    DOI:https://doi.org/10.1088/1674-4527/ad1d2a

    提交时间: 2024-02-28

    摘要:GRB 200612A could be classified as an ultralong gamma-ray burst due to its prompt emission lasting up to ∼1020 s and the true timescale of the central engine activity tburst ≥ 4 × 104 s. The late X-ray light curve with a decay index of α = 7.53 is steeper than the steepest possible decay from an external shock model. We propose that this X-ray afterglow can be driven by dipolar radiation from the magnetar spindown during its early stage, while the magnetar collapsed into the black hole before its spindown, resulting in a very steep decay of the late X-ray light curve. The optical data show that the light curve is still rising after 1.1 ks, suggesting a late onset. We show that GRB 200612A's optical afterglow light curve is fitted with the forward shock model by Gaussian structured off-axis jet. This is a special case among GRBs, as it may be an ultralong gamma-ray burst powered by a magnetar in an off-axis observation scenario.

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  • Relations between the Fractional Variation of the Ionizing Continuum and C iv Broad Absorption Lines with Different Ionization Levels

    DOI:https://doi.org/10.1088/1674-4527/ad057c

    提交时间: 2024-02-28

    摘要:This paper explores the correlation between the fractional variation of the ionizing continuum and C iv broad absorption lines (BALs) with different ionization levels. Our results reveal anti-correlations between fractional variation of the continuum and fractional equivalency width (EW) variation of the C iv BALs without Al iii BAL/mini-BALs at corresponding velocities, providing evidence for the widespread influence of the ionizing continuum variability on the variation of HiBALs. Conversely, for C iv BALs accompanied by Al iii BAL/mini-BALs (LoBAL groups), no significant correction is detected. The absence of such a correlation does not rule out the possibility that variations in these low-ionization lines are caused by ionizing continuum variability, but rather suggests the influence of BAL saturation to some extent. This saturation effect is reflected in the distribution of the fractional EW variation, where the C iv BAL group accompanied by Al iii BAL has a smaller standard deviation for the best-fitting Gaussian component than the two BAL groups without Al iii BAL. However, the distribution of fractional variation of their continuum does not show any significant difference. Besides the saturation influence, another potential explanation for the lack of correlations in the LoBAL groups may be the effects of other variability mechanisms besides the ionization change, such as clouds transiting across the line of sight.

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  • Dreicer Electric Field Definition and Runaway Electrons in Solar Flares

    DOI:https://doi.org/10.1088/1674-4527/ad1bd5

    提交时间: 2024-02-28

    摘要:We analyze electron acceleration by a large-scale electric field E in a collisional hydrogen plasma under the solar flare coronal conditions based on approaches proposed by Dreicer and Spitzer for the dynamic friction force of electrons. The Dreicer electric field EDr is determined as a critical electric field at which the entire electron population runs away. Two regimes of strong (E ≲ EDr) and weak (E ≪ EDr) electric field are discussed. It is shown that the commonly used formal definition of the Dreicer field leads to an overestimation of its value by about five times. The critical velocity at which the electrons of the "tail" of the Maxwell distribution become runaway under the action of the sub-Dreiser electric fields turns out to be underestimated by  times in some works because the Coulomb collisions between runaway and thermal electrons are not taken into account. The electron acceleration by sub-Dreicer electric fields generated in the solar corona faces difficulties.

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  • Electromagnetic Ion Beam Instability in the Solar Corona

    DOI:https://doi.org/10.1088/1674-4527/ad1bd6

    提交时间: 2024-02-28

    摘要:Remote-sensing measurements indicate that heavy ions in the corona undergo an anisotropic and mass-charge dependent energization. A popular explanation to this phenomenon is the damping of the Alfvén/ion cyclotron waves. In this paper, we propose that the ion beam instability can be an important source of the Alfvén/ion cyclotron waves, and we study the excitation of the ion beam instability in the corona at the heliocentric distance ∼3R⊙ and the corresponding energy transfer process therein based on plasma kinetic theory. The results indicate that the existence of the motionless heavy ions inhibits the ion beam instability. However, the anisotropic beams of heavy ions promote the excitation of the ion beam instability. Besides, the existence of α beams can provide a second energy source for exciting beam instability. However, when both the proton beam and the α beam reach the instability excitation threshold, the proton beam driven instability excites preferentially. Moreover, the excitation threshold of the Alfvén/ion cyclotron instability driven by ion beam is of the local Alfvén speed or even less in the corona.

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  • Analysis of Bright Source Hardness Ratios in the 4 yr Insight-HXMT Galactic Plane Scanning Survey Catalog

    DOI:https://doi.org/10.1088/1674-4527/ad18a3

    提交时间: 2024-02-28

    摘要:We conduct a statistical analysis of the hardness ratio (HR) for bright sources in the 4 yr Galactic Plane Scanning Survey catalog of Insight-HXMT. Depending on the stable (variable) flux Fs (Fv) or spectrum Ss(Sv) of each source, the bright sources are classified into three groups: Fv&Sv, Fv&Ss, and Fs&Ss. Our study of the HR characteristics in different types of sources reveals that accretion-powered neutron star (NS) low-mass X-ray binaries (LMXBs) exhibit softer energy spectra than NS high-mass X-ray binaries (HMXBs), but harder energy spectra than black hole binaries in most cases. This difference is probably due to their different magnetic field strengths. Additionally, Fv&Sv LMXBs tend to be harder than Fv&Ss LMXBs below 7 keV, while the opposite is true for HMXBs. Our results suggest that LMXBs may dominate unclassified sources, and NS binaries are likely to be the primary type of X-ray binaries with ambiguous compact stars. By comparing the HR of transient sources in their outburst and low-flux states, it is found that the averaged HR of four sources in the two states are roughly comparable within uncertainties. We also investigate the spatial properties of the three groups and find that Fv&Sv sources are mainly located in the longitude of −20° < l < 9°, Fv&Ss sources cross the Galactic Plane, and Fs&Ss sources are predominantly concentrated in 19° < l < 42°. In addition, analyzing the HR spatial distributions shows the absorption of soft X-rays (primarily below 2 keV) in the Galactic Plane.

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  • Variation in the Flaring Potential of Different Sunspot Groups During Different Phases of Solar Cycles 23 and 24

    DOI:https://doi.org/10.1088/1674-4527/ad1922

    提交时间: 2024-02-28

    摘要:In this present study, we have analyzed different types of X-ray solar flares (C, M, and X classes) coming out from different classes of sunspot groups (SSGs). The data which we have taken under this study cover the duration of 24 yr from 1996 to 2019. During this, we observed a total of 15015 flares (8417 in SC-23 and 6598 in SC-24) emitted from a total of 33780 active regions (21746 in SC-23 and 12034 in SC-24) with sunspot only. We defined the flaring potential or flare-production potential as the ratio of the total number of flares produced from a particular type of SSG to the total number of the same-class SSGs observed on the solar surface. Here we studied yearly changes in the flaring potential of different McIntosh class groups of sunspots in different phases of SC-23 and 24. In addition, we investigated yearly variations in the potential of producing flares by different SSGs (A, B, C, D, E, F, and H) during different phases (ascending, maximum, descending, and minimum) of SC-23 and 24. These are our findings: (1) D, E, and F SSGs have the potential of producing flares ≥8 times greater than A, B, C and H SSGs; (2) The larger and more complex D, E, and F SSGs produced nearly 80% of flares in SC-23 and 24; (3) The A, B, C and H SSGs, which are smaller and simpler, produced only 20% of flares in SC-23 and 24; (4) The biggest and most complex SSGs of F-class have flaring potential 1.996 and 3.443 per SSG in SC-23 and 24, respectively. (5) The potential for producing flares in each SSG is higher in SC-24 than in SC-23, although SC-24 is a weaker cycle than SC-23. (6) The alterations in the number of flares (C+M+X) show different time profiles than the alterations in sunspot numbers during SC-23 and 24, with several peaks. (7) The SSGs of C, D, E, and H-class have the highest flaring potential in the descending phase of both SC-23 and 24. (8) F-class SSGs have the highest flaring potential in the descending phase of SC-23 but also in the maximum phase of SC-24.

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