Chuanjun Wang

Early optical follow-up of the nearby active star DG CVn during its 2014 superflare

DG CVn is a binary system in which one of the components is an M type dwarf ultra fast rotator, only three of which are known in the solar neighborhood. Observations of DG CVn by the Swift satellite and several ground-based observatories during its super-flare event on 2014 allowed us to perform a complete hard X-ray - optical follow-up of a super-flare from the red-dwarf star. The observations support the fact that the super-flare can be explained by the presence of (a) large active region(s) on the surface of the star. Such activity is similar to the most extreme solar flaring events. This points towards a plausible extrapolation between the behaviour from the most active red-dwarf stars and the processes occurring in the Sun.

Polarized curvature radiation in pulsar magnetosphere

The propagation of polarized emission in pulsar magnetosphere is investigated in this paper. The polarized waves are generated through curvature radiation from the relativistic particles streaming along curved magnetic field lines and co-rotating with the pulsar magnetosphere. Within the 1/{\deg} emission cone, the waves can be divided into two natural wave mode components, the ordinary (O) mode and the extraord nary (X) mode, with comparable intensities. Both components propagate separately in magnetosphere, and are aligned within the cone by adiabatic walking. The refraction of O-mode makes the two components separated and incoherent. The detectable emission at a given height and a given rotation phase consists of incoherent X-mode and O-mode components coming from discrete emission regions. For four particle-density models in the form of uniformity, cone, core and patches, we calculate the intensities for each mode numerically within the entire pulsar beam. If the co-rotation of relativistic particles with magnetosphere is not considered, the intensity distributions for the X-mode and O-mode components are quite similar within the pulsar beam, which causes serious depolarization. However, if the co-rotation of relativistic particles is considered, the intensity distributions of the two modes are very different, and the net polarization of out-coming emission should be significant. Our numerical results are compared with observations, and can naturally explain the orthogonal polarization modes of some pulsars. Strong linear polarizations of some parts of pulsar profile can be reproduced by curvature radiation and subsequent propagation effect.

Prediction on the very early afterglow of X-ray flashes

In the past two years, tremendous progress in understanding X-ray flashes has been made. Now it is widely believed that X-ray flashes and gamma-ray bursts are intrinsically the same, and that their very different peak energy and flux may be merely due to our different viewing angles to them. Here we analytically calculate the very early afterglow of X-ray flashes, i.e. the reverse shock emission powered by the outflows interacting with the interstellar medium. Assuming z similar to 0.3, we have shown that typically the R-band flux of reverse shock emission can be bright to similar to16-17th magnitude (the actual values are model-dependent and sensitive to the initial Lorentz factor of the viewed ejecta). That emission is bright enough to be detected by the telescope on work today such as Robotic Optical Transient Search Experiment (ROTSE-III) or the upcoming Ultraviolet and Optical Telescope (UVOT) carried by the Swift satellite, planned for launch in late 2004.

A Luminous Peculiar Type Ia Supernova SN 2011hr: More Like SN 1991T or SN 2007if?

Photometric and spectroscopic observations of a slowly declining, luminous Type Ia supernova (SN Ia) SN 2011hr in the starburst galaxy NGC 2691 are presented. SN. 2011hr is found to peak at MB = -19.84 +/- 0.40 mag, with a postmaximum decline rate Delta(m15)(B) = 0.92. +/- 0.03 mag. From the maximum-light bolometric luminosity, L = (2.30 +/- 0.90) x 10(43) erg s(-1), we estimate the mass of synthesized Ni-56 in SN 2011hr to be M(Ni-56) = 1.11 +/- 0.43M(circle dot). SN 2011hr appears more luminous than SN 1991T at around maximum light, and the absorption features from its intermediate-mass elements (IMEs) are noticeably weaker than those of the latter at similar phases. Spectral modeling suggests that SN 2011hr has IMEs of similar to 0.07 M-circle dot in the outer ejecta, which is much lower than the typical value of normal SNe Ia (i.e., 0.3-0.4 M-circle dot) and is also lower than the value of SN 1991T (i.e., similar to 0.18 M-circle dot). These results indicate that SN. 2011hr may arise from a Chandrasekhar-mass white dwarf progenitor that experienced a more efficient burning process in the explosion. Nevertheless, it is still possible that SN. 2011hr may serve as a transitional object connecting the SN 1991T-like SNe Ia with a superluminous subclass like SN 2007if given that the latter also shows very weak IMEs at all phases.

Optical observations of an SN 2002cx-like peculiar supernova SN 2013en in UGC 11369

We present optical observations of an SN 2002cx-like supernova SN 2013en in UGC 11369, spanning from a phase near maximum light (t = +1d) to t = +60 d with respect to the R-band maximum. Adopting a distance modulus of mu = 34.11 +/- 0.15 mag and a total extinction (host galaxy+Milky Way) of A(V) approximate to 1.5 mag, we found that SN 2013en peaked at M-R approximate to -18.6 mag, which is underluminous compared to the normal SNe Ia. The near maximum spectra show lines of Si II, Fe II, Fe III, Cr II, Ca II and other intermediate-mass and iron group elements which all have lower expansion velocities (i.e. similar to 6000 km s(-1)). The photometric and spectroscopic evolution of SN 2013en is remarkably similar to those of SN 2002cx and SN 2005hk, suggesting that they are likely to be generated from a similar progenitor scenario or explosion mechanism.

Rapid instrument exchanging system for the Cassegrain focus of the Lijiang 2.4-m Telescope

As a facility used for astronomical research, the Lijiang 2.4-m telescope of Yunnan Astronomical Observatories, requires the ability to change one auxiliary instrument with another in as short a time as possible. This arises from the need to quickly respond to scientific programs (e.g. transient observation, time domain studies) and changes in observation conditions (e.g. seeing and weather conditions). In this paper, we describe the design, construction and test of hardware and software in the rapid instrument exchange system (RIES) for the Cassegrain focal station of this telescope, which enables instruments to be quickly changed at night without much loss of observing time. Tests in the laboratory and at the telescope show that the image quality and pointing accuracy of RIES are satisfactory. With RIES, we observed the same Landolt standard stars almost at the same time with the Princeton Instruments VersArray 1300B Camera (PICCD) and the Yunnan Faint Object Spectrograph and Camera (YFOSC), while both were mounted at the Cassegrain focus. A quasi-simultaneous comparison shows that the image quality of the optical system inside the YFOSC is comparable with that provided by the PICCD.

On the frequency dependence of pulsar linear polarization

Frequency dependence of pulsar linear polarization is investigated by simulations of emission and propagation processes. Linearly polarized waves are generated through curvature radiation by relativistic particles streaming along curved magnetic field lines, which have ordinary mode (O-mode) and extra-ordinary mode (X-mode) components. As emitted waves propagate outwards, two mode components are separated due to re- fraction of the O mode, and their polarization states are also modified. According to the radius to frequency mapping, low frequency emission is generated from higher magnetosphere, where significant rotation effect leads the X and O modes to be sepa- rated. Hence, the low frequency radiation has a large fraction of linear polarization. As the frequency increases, emission is generated from lower heights, where the rotation effect becomes weaker and the distribution regions of two modes are more overlapped. Hence, more significant depolarization appears for emission at higher frequencies. In addition, refraction effect of the O mode becomes serious in very deep magnetosphere, which bends the O mode emission towards outer parts of a pulsar beam and also causes the separation of mode distribution regions and hence the fractional linear polariza- tion increasing with frequency. If emission of different frequencies is generated from a region of the same height, serious O mode refraction can result in the decrease of both profile width and fractional linear polarization. The observed frequency dependence of linear polarization for some pulsars can be naturally explained within the scope of our scenario.

Optical Observations of the Young Type Ic Supernova SN 2014L in M99

We present optical spectroscopic and photometric observations of the nearby type Ic supernova (SN Ic) SN 2014L. This SN was discovered by the Tsinghua-NAOC Transient Survey (TNTS) in the nearby type-Sc spiral galaxy M99((NGC 4254). Fitting to the early-time light curve indicates that SN 2014L was detected at only a few hours after the shock breakout, and it reached a peak brightness of M-V = -17.73 +/- 0.28 mag (L = [2.06 +/- 0.50] x 10(42) erg s(-1)) approximately 13 days later. SN 2014L shows a close resemblance to SN 2007gr in the photometric evolution, while it shows stronger absorption features of intermediate-mass elements (especially Ca II) in the early-time spectra. Based on simple modeling of the observed light curves, we derived the mass of synthesized Ni-56 as M-Ni = 0.075 +/- 0.025 M-circle dot, and the mass and total energy of the ejecta as M-ej = 1.00 +/- 0.20 M-circle dot and E-ej = 1.45 +/- 0.25 foe, respectively. Given these typical explosion parameters, the early detection, and the extensive observations, we suggest that SN 2014L could be a template sample for the investigation of SNe Ic.

Design and Implement of Astronomical Cloud Computing Environment In China-VO.

Astronomy cloud computing environment is a cyber-Infrastructure for Astronomy Research initiated by Chinese Virtual Observatory (China-VO) under funding support from NDRC (National Development and Reform commission) and CAS (Chinese Academy of Sciences). Based on virtualization technology, astronomy cloud computing environment was designed and implemented by China-VO team. It consists of five distributed nodes across the mainland of China. Astronomer can get compuitng and storage resource in this cloud computing environment. Through this environments, astronomer can easily search and analyze astronomical data collected by different telescopes and data centers , and avoid the large scale dataset transportation.