arXiv subjects

Jinlin Han

Publications and source records attributed to Jinlin Han.

27 records · Page 2Linked to original sources

arXiv2023

Three New Spiral Galaxies with Active Nuclei Producing Double Radio Lobes

Double radio lobes are generally believed to be produced by active nuclei of elliptical galaxies. However, several double-lobed radio sources have been solidly found to be associated with spiral galaxies. By cross-matching $\sim9\times10^5$ spiral galaxies selected from the Sloan Digital Sky Survey DR8 data with the full 1.4-GHz radio source catalogs of NRAO VLA Sky Survey and Faint Images of Radio Sky at Twenty-centimeters, we identify three new spiral galaxies: J0326$-$0623, J1110+0321 and J1134+3046 that produce double radio lobes, and five double-lobed spirals previously known. By combining the newly discovered and all the other known cases in literature, we confirm the relation that more massive spirals could produce more powerful large-scale radio jets. We find that most of these spiral galaxies are located in a galaxy group or a poor cluster, in which the environment is denser than in the field, and about half of them are the central brightest galaxies in their parent system. We therefore suggest that the environment is one of the key factors for a spiral to produce double radio lobes.

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arXiv2022

Peering into the Milky Way by FAST: III. Magnetic fields in the Galactic halo and farther spiral arms revealed by the Faraday effect of faint pulsars

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the most sensitive radio telescope for pulsar observations. We make polarimetric measurements of a large number of faint and distant pulsars using the FAST. We present the new measurements of Faraday rotation for 134 faint pulsars in the Galactic halo. Significant improvements are also made for some basic pulsar parameters for 15 of them. We analyse the newly determined rotation measures (RMs) for the Galactic magnetic fields by using these 134 halo pulsars, together with previously available RMs for pulsars and extragalactic radio sources and also the newly determined RMs for another 311 faint pulsars which are either newly discovered in the project of the Galactic Plane Pulsar Snapshot (GPPS) survey or previously known pulsars without RMs. The RM tomographic analysis in the first Galactic quadrant gives roughly the same field strength of around 2~$μ$G for the large-scale toroidal halo magnetic fields. The scale height of the halo magnetic fields is found to be at least 2.7$\pm$0.3~kpc. The RM differentiation of a large number of pulsars in the Galactic disk in the Galactic longitude range of $26^{\circ}<l<90^{\circ}$ gives evidence for the clockwise magnetic fields (viewed from the north Galactic pole) in two interarm regions inside the Scutum arm and between the Scutum and Sagittarius arm, and the clockwise fields in the Local-Perseus interarm region and field reversals in the Perseus arm and beyond.

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arXiv2017

Spectral indices for radio emission of 228 pulsars

We determine spectral indices of 228 pulsars by using Parkes pulsar data observed at 1.4 GHz, among which 200 spectra are newly determined. The indices are distributed in the range from -4.84 to -0.46.Together with known pulsar spectra from literature, we tried to find clues to the pulsar emission process. The weak correlations between the spectral index, the spin-down energy loss rate $\dot{E}$ and the potential drop in the polar gap $ΔΨ$ hint that emission properties are related to the particle acceleration process in a pulsar's magnetosphere.

astro-ph.HE↗

arXiv2012

AXPs & SGRs: Magnetar or Quarctar?

The concept of a "magnetar" was proposed mainly because of two factors. First, the X-ray luminosity of Anomalous X-ray Pulsars (AXPs) and Soft Gamma-Ray Repeaters (SGRs) is larger than the rotational energy loss rate, and second, the magnetic field strength calculated from "normal method" is super strong. It is proposed that the radiation energy of magnetar comes from its magnetic fields. Here it is argued that the magnetic field strength calculated through the normal method is incorrect when X-ray luminosity is larger than rotational energy loss rate, because the wind braking is not taken into account. Besides, the "anti-magnetar" and some other X-ray and radio observations are difficult to understand with a magnetar model. Instead of the magnetar, we propose a "quarctar", which is a crusted quark star in an accretion disk, to explain the observations. In this model, the persistent X-ray emission, burst luminosity, spectrum of AXPs and SGRs can be understood naturally. The radio-emitting AXPs, which are challenging the magnetar, can also be explained by the quarctar model.

astro-ph.HE↗

arXiv2011

Faraday Rotation in Pulsar Magnetosphere

The magnetosphere of a pulsar is composed of relativistic plasmas streaming along the magnetic field lines and corotating with the pulsar. We study the intrinsic Faraday rotation in the pulsar magnetosphere by critically examining the wave modes and the variations of polarization properties for the circularly polarized natural modes under various assumptions about the magnetosphere plasma properties. Since it is difficult to describe analytically the Faraday rotation effect in such a plasma, we use numerical integrations to study the wave propagation effects in the corotating magnetosphere. Faraday rotation effect is identified among other propagation effects, such as wave mode coupling and the cyclotron absorption. In a highly symmetrical electron-positron pair plasma, the Faraday rotation effect is found to be negligible. Only for asymmetrical plasmas, such as the electron-ion streaming plasma, can the Faraday rotation effect become significant, and the Faraday rotation angle is found to be approximately proportional to $λ^{0.5}$ instead of the usual $λ^2$-law. For such electrons-ion plasma of pulsar magnetosphere, the induced rotation measure becomes larger at higher frequencies, and should have opposite signs for the emissions from opposite magnetic poles.

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arXiv2010

A bipolar outflow from the massive protostellar core W51e2-E

We present high resolution images of the bipolar outflow from W51e2, which are produced from the Submillimeter Array archival data observed for CO(3-2) and HCN(4-3) lines with angular resolutions of 0.8" x 0.6" and 0.3" x 0.2", respectively. The images show that the powerful outflow originates from the protostellar core W51e2-E rather than from the ultracompact HII region W51e2-W. The kinematic timescale of the outflow from W51e2-E is about 1000 yr, younger than the age (~5000 yr) of the ultracompact HII region W51e2-W. A large mass loss rate of ~1 x 10^{-3} M_sun yr^{-1} and a high mechanical power of 120 L_sun are inferred, suggesting that an O star or a cluster of B stars are forming in W51e2-E. The observed outflow activity along with the inferred large accretion rate indicates that at present W51e2-E is in a rapid phase of star formation.

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arXiv2007

Magnetic fields of our Galaxy on large and small scales

Magnetic fields have been observed on all scales in our Galaxy, from AU to kpc. With pulsar dispersion measures and rotation measures, we can directly measure the magnetic fields in a very large region of the Galactic disk. The results show that the large-scale magnetic fields are aligned with the spiral arms but reverse their directions many times from the inner-most arm (Norma) to the outer arm (Perseus). The Zeeman splitting measurements of masers in HII regions or star-formation regions not only show the structured fields inside clouds, but also have a clear pattern in the global Galactic distribution of all measured clouds which indicates the possible connection of the large-scale and small-scale magnetic fields.

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arXiv2000

Magnetic fields in our Galaxy: How much do we know?

The large scale magnetic fields of our Galaxy have been mostly revealed by rotation measures ($RM$s) of pulsars and extragalactic radio sources. In the disk of our Galaxy, the average field strength over a few kpc scale is about 1.8 $μ$G, while the total field, including the random fields on smaller scales, has a strength of about 5 $μ$G. The local regular field, if it is part of the large scale field of a bisymmetric form, has a pitch angle of about $-8\degr$. There are at least three, and perhaps five, field reversals from the Norma arm to the outer skirt of our Galaxy.

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arXiv1994

A search for the associations of distant radio-bright quasars with Abell clusters: an effect of gravitational amplification bias ?

The theory predicts that the effect of gravitational lensing by the matter associated with clusters of galaxies can magnify background sources, leading to an enhancement of source number density around foreground clusters of galaxies. We conduct a search for the associations of distant radio-bright quasars with Abell clusters using the 1-Jy and 2-Jy all-sky catalogs. Statistics turns to be very poor on the basis of the 1-Jy sample, which shows no correlations between the distant radio quasars with the foreground Abell clusters above $1σ$ level. However, an apparent association ($>1σ$) of the 2-Jy radio sources with the foreground Abell clusters has been detected on scale of $\sim20$ arcminutes. We point out that this enhancement is unlikely to be produced by the statistical gravitational lensing hypothesis utilizing the matter associated with a population of isolated clusters unless (1)their velocity dispersion is a few times larger than the presently adopted value and/or (2)the intrinsic counts of the radio-bright sources with flux have a steeper slope than the presently observed ones. This indicates that (1)the observed associations, if real, can be the integrated result of all the matter along the line of sight to the distant quasars, namely, the weak lensing effect of clusters of galaxies that trace large-scale structures of the universe, and/or (2)the number counts of the radio-bright sources have been seriously contaminated by lensing.

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