[en] This work proposes a thermophysical model for realistic surface layers on airless small bodies (RSTPM) for the use of interpreting their multiepoch thermal light curves (e.g., WISE/NEOWISE). RSTPM considers the real orbital cycle, rotation cycle, rough surface, temperature-dependent thermal parameters, as well as contributions of sunlight reflection to observations. It is thus able to produce a precise temperature distribution and thermal emission of airless small bodies regarding the variations on orbital timescales. Details of the physics, mathematics, and numerical algorithms of RSTPM are presented. When used to interpret multiepoch thermal light curves by WISE/NEOWISE, RSTPM can give constraints on the spin orientation and surface physical properties, such as the mean thermal inertia or the mean size of dust grains, the roughness fraction, and the albedo via a radiometric procedure. As an application example, we apply this model to the main-belt object (24) Themis, the largest object of the Themis family, which is believed to be the source region of many main-belt comets. We find multiepoch (2010, 2014–2018) observations of Themis by WISE/NEOWISE, yielding 18 thermal light curves. By fitting these data with RSTPM, the best-fit spin orientation of Themis is derived to be (λ = 137°, β = 59°) in ecliptic coordinates, and the mean radius of dust grains on the surface is estimated to be $\stackrel{~<!--\; ~\; -->}{b}={140}_{-<!--\; ???\; -->114}^{+500}(6\sim <!--\; ???\; -->640)$ μm, indicating that the surface thermal inertia varies from ∼3 Jm⁻² s^−0.5 K⁻¹ to ∼60 Jm⁻² s ^−0.5 K⁻¹ due to seasonal temperature variation. A more detailed analysis found that the thermal light curves of Themis show a weak feature that depends on the rotation phase, which is indicative of heterogeneous thermal properties or imperfections of the light-curve inversion shape model.

[en] We investigate the surface thermophysical properties (thermal emissivity, thermal inertia, roughness fraction and geometric albedo) of asteroid (99942) Apophis, using the currently available mid-infrared observations from CanariCam on Gran Telescopio CANARIAS and far-infrared data from PACS on Herschel, based on the Advanced Thermophysical Model. We show that the thermal emissivity of Apophis should be wavelength dependent from 8.70 μm to 160 μm, and the maximum emissivity may appear around 20 μm, similar to that of Vesta. Moreover, we further derive the thermal inertia, roughness fraction, geometric albedo and effective diameter of Apophis within a possible 1$\mathrm{\sigma <!--\; ??\; -->}$ scale of $\mathrm{\Gamma <!--\; ??\; -->}={100}_{-<!--\; ???\; -->52}^{+100}{\mathrm{J}\mathrm{m}}^{-<!--\; ???\; -->2}{\mathrm{s}}^{-<!--\; ???\; -->0.5}{\mathrm{K}}^{-<!--\; ???\; -->1}$, $f_{\mathrm{r}}=0.78\sim <!--\; ???\; -->1.0$, $p_{\mathrm{v}}={0.286}_{-<!--\; ???\; -->0.026}^{+0.030}$ and $D_{\mathrm{e}\mathrm{f}\mathrm{f}}={378}_{-<!--\; ???\; -->25}^{+19}\mathrm{m}$, and 3$\mathrm{\sigma <!--\; ??\; -->}$ scale of $\mathrm{\Gamma <!--\; ??\; -->}={100}_{-<!--\; ???\; -->100}^{+240}{\mathrm{J}\mathrm{m}}^{-<!--\; ???\; -->2}{\mathrm{s}}^{-<!--\; ???\; -->0.5}{\mathrm{K}}^{-<!--\; ???\; -->1}$, $f_{\mathrm{r}}=0.2\sim <!--\; ???\; -->1.0$, $p_{\mathrm{v}}={0.286}_{-<!--\; ???\; -->0.029}^{+0.039}$ and $D_{\mathrm{e}\mathrm{f}\mathrm{f}}={378}_{-<!--\; ???\; -->29}^{+27}\mathrm{m}$. The derived low thermal inertia but high roughness fraction may imply that Apophis could have regolith on its surface, where stronger space weathering but weaker regolith migration has happened in comparison with asteroid Itokawa. Our results show that small-size asteroids could also have fine regolith on the surface, and further infer that Apophis may have been delivered from the Main Belt by the Yarkovsky effect. (paper)

[en] Supernova remnants (SNRs) are the most attractive candidates for the acceleration sites of Galactic cosmic rays. We report the detection of GeV γ-ray emission with the Pass 8 events recorded by the Fermi Large Area Telescope (Fermi-LAT) in the vicinity of the shell-type SNR CTB 37B that is likely associated with the TeV γ-ray source HESS J1713–381. The photon spectrum of CTB 37B is consistent with a power law with an index of 1.89 ± 0.08 in the energy range of 0.5–500 GeV, and the measured flux connects smoothly with that of HESS J1713–381 at a few hundred GeV. No significant spatial extension and time variation are detected. The multi-wavelength data can be well fitted with either a leptonic model or a hadronic one. However, parameters of both models suggest more efficient particle acceleration than typical SNRs. Meanwhile, the X-ray and γ-ray spectral properties of CTB 37B show that it is an interesting source bridging young SNRs dominated by non-thermal emission and old SNRs interacting with molecular clouds