arXiv subjects

Bo Xia

Publications and source records attributed to Bo Xia.

39 records · Page 3Linked to original sources

arXiv2015

Generic ill-posedness for wave equation of power type on 3D torus

In this article, we prove that the equation \begin{equation*} \left\{\begin{split} &(\partial^2_t-Δ)u+|u|^{p-1}u=0,\ \ \ 3\leq p<5 &\big(u(0),\partial_tu(0)\big)=(u_0,u_1)\in H^{s}(\mathbb{T}^3)\times H^{s-1}(\mathbb{T}^3)=:\mathcal{H}^s(\mathbb{T}^3) \end{split}\right. \end{equation*} with $s<\frac{3}{2}-\frac{2}{p-1}$ is everywhere ill-posed. This work also indicates that, only properly regularizing the initial data can we smoothly approximate the solutions constructed in \cite{BT14} and \cite{Xia14}.

math.AP↗

arXiv2013

Observations of 6.7 GHz Methanol Masers with EAVN I: VLBI Images of the first Epoch of Observations

Very long baseline interferometry (VLBI) monitoring of the 6.7 GHz methanol maser allows us to measure the internal proper motions of the maser spots and therefore study the gas motion around high-mass young stellar objects. To this end, we have begun monitoring observations with the East-Asian VLBI Network. In this paper we present the results of the first epoch observation for 36 sources, including 35 VLBI images of the methanol maser. Since two independent sources were found in three images, respectively, images of 38 sources were obtained. In 34 sources, more than or equal to 10 spots were detected. The observed spatial scale of the maser distribution was from 9 to 4900 astronomical units, and the following morphological categories were observed: elliptical, arched, linear, paired, and complex. The position of the maser spot was determined to an accuracy of approximately 0.1 mas, sufficiently high to measure the internal proper motion from two years of monitoring observations. The VLBI observation, however, detected only approximately 20% of all maser emission, suggesting that the remaining 80% of the total flux was spread into an undetectable extended distribution. Therefore, in addition to high-resolution observations, it is important to observe the whole structure of the maser emission including extended low-brightness structures, to reveal the associated site of the maser and gas motion.

astro-ph.SR↗

arXiv2012

VLBI detection of the Galactic black hole binary candidate MAXI J1836-194

The X-ray transient MAXI J1836-194 is a newly-identified Galactic black hole binary candidate. As most X-ray transients, it was discovered at the beginning of an X-ray outburst. After the initial canonical X-ray hard state, the outburst evolved into a hard intermediate state and then went back to the hard state. The existing RATAN-600 radio monitoring observations revealed that it was variable on a timescale of days and had a flat or inverted spectrum, consistent with optically thick synchrotron emission, possibly from a self-absorbed jet in the vicinity of the central compact object. We observed the transient in the hard state near the end of the X-ray outburst with the European VLBI Network (EVN) at 5 GHz and the Chinese VLBI Network (CVN) at 2.3 and 8.3 GHz. The 8.3 GHz observations were carried out at a recording rate of 2048 Mbps using the newly-developed Chinese VLBI data acquisition system (CDAS), twice higher than the recording rate used in the other observations. We successfully detected the low-declination source with a high confidence level in both observations. The source was unresolved (<=0.5 mas), which is in agreement with an AU-scale compact jet.

astro-ph.HE↗