arXiv subjects

Jiguang Lu

Publications and source records attributed to Jiguang Lu.

40 records · Page 3Linked to original sources

arXiv2017

The optical/UV excess of X-ray dim isolated neutron star: I. bremsstrahlung emission from a strangeon star plasma atmosphere

X-ray dim isolated neutron stars (XDINSs) are characterized by Planckian spectra in X-ray bands, but show optical/ultraviolet(UV) excesses which are the measured photometry exceeding that is extrapolated from X-ray spectra. To solve this problem, a radiative model of bremsstrahlung emission from a plasma atmosphere is established in the regime of strangeon star. A strangeon star atmosphere could simply be regarded as the upper layer of a normal neutron star. This plasma atmosphere, formed and maintained by the ISM-accreted matter due to the so-called strangeness barrier, is supposed to be of two-temperature. All the seven XDINS spectra could be well fitted by the radiative model, from optical/UV to X-ray bands. The fitted radiation radii of XDINSs are from 7 to 13km, while the modelled electron temperatures are between 50 and 250eV, except RX J0806.4-4123 with a radiation radius ~3.5km, indicating that this source could be a low-mass strangeon star candidate. This strangeon star model could further be tested by soft X-ray polarimetry, such as the Lightweight Asymmetry and Magnetism Probe which is expected to work on Chinese space station around 2020.

astro-ph.HE↗

arXiv2015

Two types of glitches in a solid quark star model

TThe glitch of anomalous X-ray pulsars \& soft gamma repeaters (AXP/SGRs) usually accompanied with detectable energy releases manifesting as X-ray bursts or outbursts, while the glitch of some pulsars like Vela release negligible energy. We find that these two types of glitches can naturally correspond to two types of starquake of solid strange stars. By applying the EoS of quark cluster star and some realistic pulsar parameters, we can reproduce consistent results compared with previous constraints and observations.

astro-ph.HE↗

arXiv2014

Two types of glitches in a solid quark star model

Glitch (sudden spinup) is a common phenomenon in pulsar observations. However, the physical mechanism of glitch is still a matter of debate because it depends on the puzzle of pulsar's inner structure, i.e., the equation of state of dense matter. Some pulsars (e.g., Vela-like) show large glitches (Δν/ν~10^-6) but release negligible energy, whereas the large glitches of AXPs/SGRs (anomalous X-ray pulsars/soft gamma repeaters) are usually (but not always) accompanied with detectable energy releases manifesting as X-ray bursts or outbursts. We try to understand this aspect of glitches in a starquake model of solid quark stars. There are actually two kinds of glitches in this scenario: bulk-invariable (Type I) and bulk-variable (Type II) ones. The total stellar volume changes (and then energy releases) significantly for the latter but not for the former. Therefore, glitches accompanied with X-ray bursts (e.g., that of AXP/SGRs) could originate from Type II starquakes induced probably by accretion, while the others without evident energy release (e.g., that of Vela pulsar) would be the result of Type I starquakes due to, simply, a change of stellar ellipticity.

astro-ph.HE↗

arXiv2013

To differentiate neutron star models by X-ray polarimetry

The nature of pulsar is still unknown because of non-perturbative effects of the fundamental strong interaction, and different models of pulsar inner structures are then suggested, either conventional neutron stars or quark stars. Additionally, a state of quark-cluster matter is conjectured for cold matter at supranuclear density, as a result pulsars could thus be quark-cluster stars. Besides understanding different manifestations, the most important issue is to find an effective way to observationally differentiate those models. X-ray polarimetry would play an important role here. In this letter, we focus on the thermal X-ray polarization of quark/quark-cluster stars. While the thermal X-ray linear polarization percentage is typically higher than ~10% in normal neutron star models, the percentage of quark/quark-cluster stars is almost zero. It could then be an effective method to identify quark/quark-cluster stars by soft X-ray polarimetry. We are therefore expecting to detect thermal X-ray polarization in the coming decades.

astro-ph.HE↗