arXiv subjects

L. Xiao

Publications and source records attributed to L. Xiao.

At least 37 records · Page 2Linked to original sources

arXiv2013

GSH 90-28-17: a Possible Old Supernova Remnant

GSH 90-28-17 is a high-latitude galactic HI supershell, identified in the HI supershell catalogs with a velocity of $v_{lsr}\sim-17$ \kms. We used the new Arecibo GALFA-HI survey data which have much higher resolution and sensitivity than what were previously available to re-examine the properties of the supershell. We derived a new distance of 400 pc for GSH 90-28-17 and suggested that it is related to the Lac OB1 association. The radius of GSH 90-28-17 is 66.0$\pm$3.5 pc. The HI mass of the shell is (3.1$\pm0.1)\times10^{4}$ M$_{\odot}$. It has an age of $\sim4.5$ Myr and a total kinetic energy of (8.2$\pm0.3)\times10^{48}$ ergs. We extracted radio continuum data for the GSH 90-28-17 region from the 408 MHz all-sky Survey and Bonn 1420 MHz survey, and filtered the diffuse background Galactic emission. A radio loop-like ridge is found to be associated with the HI shell at both frequencies, and shows a nonthermal origin with a TT-plot index of $α$=-1.35$\pm$0.69. In addition, the pulsar J2307+2225 with a similar distance is found in the shell region. We conclude that GSH 90-28-17 is probably an old, type II supernova remnant in the solar neighborhood.

astro-ph.GA↗

arXiv2013

A Sino-German 6cm polarisation survey of the Galactic plane - VIII. Small-diameter sources

Information of small-diameter sources is extracted from the Sino-German 6cm polarisation survey of the Galactic plane carried out with the Urumqi 25-m telescope. We performed two-dimensional elliptical Gaussian fits to the 6cm maps to obtain a list of sources with total-intensity and polarised flux densities. The source list contains 3832 sources with a fitted diameter smaller than 16 arcmin and a peak flux density exceeding 30 mJy, so about 5 times the rms noise, of the total-intensity data. The cumulative source count indicates completeness for flux densities exceeding about 60 mJy. We identify 125 linearly polarised sources at 6cm with a peak polarisation flux density greater than 10 mJy, so about 3 times the rms noise, of the polarised-intensity data. Despite lacking compact steep spectrum sources, the 6cm catalogue lists about 20 percent more sources than the Effelsberg 21cm source catalogue at the same angular resolution and for the same area. Most of the faint 6cm sources must have a flat spectrum and are either HII regions or extragalactic. When compared with the Green Bank 6cm (GB6) catalogue, we obtain higher flux densities for a number of extended sources with complex structures. Polarised 6cm sources density are uniformly distributed in Galactic latitude. Their number density decreases towards the inner Galaxy. More than 80 percent of the polarised sources are most likely extragalactic. With a few exceptions, the sources have a higher percentage polarisation at 6cm than at 21cm. Depolarisation seems to occur mostly within the sources with a minor contribution from the Galactic foreground emission.

astro-ph.GA↗

arXiv2013

Properties of the UCHII region G25.4NW and its associated molecular cloud

UCHII G25.4NW is a bright IR source in the inner Galaxy region. New HI images from the VLA Galactic Plane Survey (VGPS) show clear absorption features associated with the UCHII region up to 95 km s$^{-1}$, and there is not any other absorptions up to the tangential velocity. It reveals that G25.4NW is at a near-side distance of 5.7 kpc, and it is located in the inner Galactic molecular ring region. Using the new distance, the bolometric luminosity of G25.4NW is estimated as $10^{5.6} L_{\odot}$, which corresponds to an O6 star. It contains 460 $M_{\odot}$ of ionized gas. High-resolution $^{13}$CO image from the Galactic Ring Survey (GRS) reveals that G25.4NW is part of a more extended star-formation complex with about $10^{4} M_{\odot}$ molecular gas.

astro-ph.GA↗

arXiv2012

Radio perspectives on the Monoceros SNR G205.5+0.5

The Monoceros Loop (SNR G205.5+0.5) is a large shell-type supernova remnant located in the Rosette Complex region. It was suggested to be interacting with the Rosette Nebula. We aim to re-examine the radio spectral index and its spatial variation over the Monoceros SNR, and study its properties of evolution within the complex interstellar medium. We extracted radio continuum data for the Monoceros complex region from the Effelsberg 21 cm and 11 cm surveys and the Urumqi 6 cm polarization survey. We used the new Arecibo GALFA-HI survey data with much higher resolution and sensitivity than that previously available to identify the HI shell related with the SNR. Multi-wavelengths data are included to investigate the properties of the SNR. The spectral index $α$ ($S_ν\proptoν^α$) averaged over the SNR is $-0.41 \pm$0.16. The TT-plots and the distribution of $α$ over the SNR show spatial variations which steepen towards the inner western filamentary shell. Polarized emission is prominent on the western filamentary shell region. The RM there is estimated to be about 30$\pm$77n rad m$^{-2}$, where the n=1 solution is preferred, and the magnetic field has a strength of about 9.5 $μ$G. From the HI channel maps, further evidence is provided for an interaction between the Monoceros SNR and the Rosette Nebula. We identify partial neutral hydrogen shell structures in the northwestern region at LSR velocities of +15 km s$^{-1}$ circumscribing the continuum emission. The HI shell has swept up a mass of about 4000 M$_{\odot}$ for a distance of 1.6 kpc. The western HI shell, well associated with the dust mission, is found to lie outside of the radio shell. We suggest that the Monoceros SNR is evolving within a cavity blown-out by the progenitor, and has triggered part of the star formation in the Rosette Nebula.

astro-ph.GA↗

arXiv2012

The sino-german 6cm polarization survey of the galactic plane: A summary

We have finished the 6cm polarization survey of the Galactic plane using the Urumqi 25m radio telescope. It covers 10deg<l<230deg in Galactic longitude and |b| <5deg in Galactic latitude. The new polarization maps not only reveal new properties of the diffuse magnetized interstellar medium, but also are very useful for studying individual objects such as Hii regions, which may act as Faraday screens with strong regular magnetic fields inside, and supernova remnants for their polarization properties and spectra. The high sensitivity of the survey enables us to discover two new SNRs G178.2-4.2 and G25.3-2.1 and a number of Hii regions.

astro-ph.GA↗

arXiv2011

A Sino-German 6cm polarization survey of the Galactic plane VII. Small supernova remnants

We study the spectral and polarization properties of supernova remnants (SNRs) based on our 6cm survey data. The observations were taken from the Sino-German 6cm polarization survey of the Galactic plane. By using the integrated flux densities at 6cm together with measurements at other wavelengths from the literature we derive the global spectra of 50 SNRs. In addition, we use the observations at 6cm to present the polarization images of 24 SNRs. We derived integrated flux densities at 6cm for 51 small SNRs with angular sizes less than 1 degree. Global radio spectral indices were obtained in all the cases except for Cas A. For SNRs G15.1-1.6, G16.2-2.7, G16.4-0.5, G17.4-2.3, G17.8-2.6, G20.4+0.1, G36.6+2.6, G43.9+1.6, G53.6-2.2, G55.7+3.4, G59.8+1.2, G68.6-1.2, and G113.0+0.2, the spectra have been significantly improved. From our analysis we argue that the object G16.8-1.1 is probably an HII region instead of a SNR. Cas A shows a secular decrease in total intensity, and we measured a flux density of 688+/-35 Jy at 6cm between 2004 and 2008. Polarized emission from 25 SNRs were detected. For G16.2-2.7, G69.7+1.0, G84.2-0.8 and G85.9-0.6, the polarized emission is detected for the first time confirming them as SNRs. High frequency observations of SNRs are rare but important to establish their spectra and trace them in polarization in particular towards the inner Galaxy where Faraday effects are important.

astro-ph.GA↗

arXiv2011

A Sino-German $λ$6\ cm polarization survey of the Galactic plane. V. Large supernova remnants

Observations of large supernova remnants (SNRs) at high frequencies are rare, but provide valuable information about their physical properties. The total intensity and polarization properties of 16 large SNRs in the Galactic plane were investigated based on observations of the Urumqi $λ$6\ cm polarization survey of the Galactic plane with an angular resolution of 9$\farcm$5. We extracted total intensity and linear polarization maps of large SNRs from the Urumqi $λ$6\ cm survey, obtained their integrated flux densities, and derived the radio spectra in context with previously published flux densities at various frequencies. In particular, Effelsberg $λ$11\ cm and $λ$21\ cm survey data were used for calculating integrated flux densities. The $λ$6\ cm polarization data also delineate the magnetic field structures of the SNRs. We present the first total intensity maps at $λ$6\ cm for SNRs G106.3+2.7, G114.3+0.3, G116.5+1.1, G166.0+4.3 (VRO 42.05.01), G205.5+0.5 (Monoceros Nebula) and G206.9+2.3 (PKS 0646+06) and the first polarization measurements at $λ$6\ cm for SNRs G82.2+5.3 (W63), G106.3+2.7, G114.3+0.3, G116.5+1.1, G166.0+4.3 (VRO 42.05.01), G205.5+0.5 (Monoceros Nebula) and G206.9+2.3 (PKS 0646+06). Most of the newly derived integrated radio spectra are consistent with previous results. The new flux densities obtained from the Urumqi $λ$6\ cm, Effelsberg $λ$11\ cm and $λ$21\ cm surveys are crucial to determine the spectra of SNR G65.1+0.6, G69.0+2.7 (CTB 80), G93.7-0.2 and G114.3+0.3. We find that G192.8$-$1.1 (PKS 0607+17) consists of background sources, \ion{H}{II} regions and the extended diffuse emission of thermal nature, and conclude that G192.8$-$1.1 is not a SNR.

astro-ph.GA↗

arXiv2011

A Sino-German 6cm polarization survey of the Galactic plane IV. The region from 60deg to 129deg longitude

Linear polarization of diffuse Galactic emission is a signature of magnetic fields in the interstellar medium of our Galaxy. Observations at high frequencies are less affected by Faraday depolarization than those at lower frequencies and are able to detect polarized emission from more distant Galactic regions. We attempt to perform a sensitive survey of the polarized emission from the Galactic disk at 6 cm wavelength. We made polarization observations of the Galactic plane using the Urumqi 25-m telescope at 6 cm covering the area of 60deg< l <129deg and |b|<5deg. Missing large-scale structures in polarization were restored by extrapolation of the WMAP polarization data. We present the 6cm total intensity and linear polarization maps of the surveyed region. We identify two new extended HII regions G98.3-1.6 and G119.6+0.4 in this region. Numerous polarized patches and depolarization structures are visible in the polarization maps. Depolarization along the periphery of a few HII complexes was detected and can be explained by a Faraday screen model. We discuss some prominent depolarization HII regions, which have regular magnetic fields of several $μ$G. Structure functions of U, Q and PI images of the entire 6cm survey region of 10deg< l < 230deg exhibit much larger fluctuation power towards the inner Galaxy, which suggests a higher turbulence in the arm regions of the inner Galaxy. The Sino-German 6cm survey reveals new properties of the diffuse magnetized interstellar medium. The survey is also very useful for studying individual objects such as HII regions, which act as Faraday screens and have high rotation measures and therefore strong regular magnetic fields inside the regions.

astro-ph.GA↗

arXiv2010

A Sino-German 6 cm polarization survey of the Galactic plane II. The region from 129 degree to 230 degree longitude

Linearly polarized Galactic synchrotron emission provides valuable information about the properties of the Galactic magnetic field and the interstellar magneto-ionic medium, when Faraday rotation along the line of sight is properly taken into account. We aim to survey the Galactic plane at 6 cm including linear polarization. At such a short wavelength Faraday rotation effects are in general small and the Galactic magnetic field properties can be probed to larger distances than at long wavelengths. The Urumqi 25-m telescope is used for a sensitive 6 cm survey in total and polarized intensities. WMAP K-band (22.8 GHz) polarization data are used to restore the absolute zero-level of the Urumqi U and Q maps by extrapolation. Total intensity and polarization maps are presented for a Galactic plane region of 129 degree < l < 230 degree and |b| < 5 degree in the anti-centre with an angular resolution of 9'5 and an average sensitivity of 0.6 mK and 0.4 mK Tb in total and polarized intensity, respectively. We briefly discuss the properties of some extended Faraday Screens detected in the 6 cm polarization maps. The Sino-German 6 cm polarization survey provides new information about the properties of the magnetic ISM. The survey also adds valuable information for discrete Galactic objects and is in particular suited to detect extended Faraday Screens with large rotation measures hosting strong regular magnetic fields.

astro-ph.GA↗

arXiv2009

Radio properties of the low surface brightness SNR G65.2+5.7

Many physical properties of this SNR such as spectrum and polarization can only be investigated by radio observations. The $λ$11 cm and $λ$6\ cm continuum and polarization observations of SNR G65.2+5.7 were made with the Effelsberg 100-m and the Urumqi 25-m telescopes, respectively, to investigate the integrated spectrum, the spectral index distribution, and the magnetic field properties. $λ$21 cm archival data from the Effelsberg 100-m telescope have been also used. The integrated flux densities of G65.2+5.7 at $λ11$ cm and $λ6$ cm are $21.9\pm3.1$ Jy and 16.8$\pm$1.8 Jy, respectively. The power-law spectrum ($S\simν^α$) is well fitted by $α= -0.58\pm0.07$ from 83 MHz to 4.8 GHz. Spatial spectral variations are small. Along the northern shell strong depolarizion is observed at both wavelengths. The southern filamentary shell of SNR G65.2+5.7 is polarized up to 54% at $λ6$ cm. There is significant depolarization at $λ11$ cm and confusion with diffuse polarized Galactic emission. Using equipartition principle, we estimated the magnetic field strength for the southern filamentary shell about 20 $μ$G (filling factor 1) to 50 $μ$G (filling factor 0.1). A faint HI shell may be associated with the SNR. Despite its unusual strong X-ray and optical emission and its very low surface brightness, the radio properties of SNR G65.2+5.7 are found to be typical for evolved shell type SNRs. SNR G65.2+5.7 may be expanding in a preblown cavity as indicated by a deficit of HI gas and a possible HI-shell.

astro-ph.GA↗

arXiv2008

Crab cavities for linear colliders

Crab cavities have been proposed for a wide number of accelerators and interest in crab cavities has recently increased after the successful operation of a pair of crab cavities in KEK-B. In particular crab cavities are required for both the ILC and CLIC linear colliders for bunch alignment. Consideration of bunch structure and size constraints favour a 3.9 GHz superconducting, multi-cell cavity as the solution for ILC, whilst bunch structure and beam-loading considerations suggest an X-band copper travelling wave structure for CLIC. These two cavity solutions are very different in design but share complex design issues. Phase stabilisation, beam loading, wakefields and mode damping are fundamental issues for these crab cavities. Requirements and potential design solutions will be discussed for both colliders.

physics.acc-ph↗

arXiv2008

The radio spectrum and magnetic field structure of SNR HB3

Evidence for a spectral flattening of the supernova remnant (SNR) HB3 (G132.7+1.3) was recently claimed in literature based on previously published total flux density data, and the flattening was further interpreted as the discovery of thermal bremsstrahlung emission in the shell of HB3. A spectral flattening has never been observed from any SNR before. Reliable observations of HB3 at frequencies above 3000 MHz are crucial to confirm such a spectral behaviour. We extracted 4800 MHz total intensity and polarisation data of HB3 from the Sino-German 6 cm polarisation survey of the Galactic plane made with the Urumqi 25 m telescope, and analysed the spectrum of HB3, together with Effelsberg data at 1408 MHz and 2675 MHz. We found an overall spectral index of HB3 of alpha=-0.61+-0.06 between 1408 MHz and 4800 MHz, similar to the index at lower frequencies. There is no spectral flattening at high frequencies. We detected strong polarised emission from HB3 at 4800 MHz. Our 4800 MHz data show a tangential field orientation in the HB3 shell.

astro-ph↗

arXiv2008

Radio spectral properties and the magnetic field of the SNR S147

(Abridged) S147 is a large faint shell-type supernova remnant (SNR). Its remarkable spectral break at cm-wavelengths is an important physical property to characterize the SNR evolution. However, the spectral break is based on radio observations with limited precision. We made new radio continuum and polarization observations of S147 at 11cm and at 6cm with the Effelsberg 100-m telescope and the Urumqi 25-m telescope, respectively. These new data were combined with published lower frequency data from the Effelsberg 100-m telescope and very high frequency data from WMAP to investigate the spectral turnover and polarization properties of S147. S147 consists of numerous filaments embedded in diffuse emission. We found that the integrated flux densities of S147 are 34.8+/-4.0 Jy at 11cm and 15.4+/-3.0Jy at 6cm. These new measurements confirm the known spectral turnover at ~1.5GHz, which can be entirely attributed to the diffuse emission component. The spectral index above the turnover is -1.35+/-0.20. The filamentary emission component has a constant spectral index over the entire wavelength range up to 40.7GHz of -0.35+/-0.15. The weak polarized emission of S147 is at the same level as the ambient diffuse Galactic polarization. The rotation measure of the eastern filamentary shell is about -70 rad/m2. The filamentary and diffuse emission components of S147 have different physical properties, which make S147 outstanding among shell type SNRs.The weak polarization of S147 at 11cm and at 6cm can be attributed to a section of the S147 shell showing a tangential magnetic field direction.

astro-ph↗

arXiv2007

Polarization observations of SNR G156.2+5.7 at lambda 6cm

G156.2+5.7 is a large supernova remnant (SNR) first discovered in the ROSAT X-ray survey but radio observations are rare because of its low surface brightness and large size. Radio continuum and polarization images of the SNR G156.2+5.7 at lambda 6 cm are presented for the first time to be discussed in the context with available data to investigate its physical properties. We obtained an integrated flux density for G156.2+5.7 of S6cm= 2.5+-0.5Jy. The spectral index of the integrated emission is alpha=-0.48+-0.08 between lambda 74 cm and 6 cm excluding compact radio sources. We also obtained a spectral index map, which shows little variation between the shells and the central area of the SNR. This is consistent with the constant integrated flux density spectrum. Highly polarized radio emission has been detected from the SNR shell, but also from a central patch, which probably originates in the front part of the spherical SNR shell. We derived the distribution of rotation measure from polarization data at 11 cm and 6 cm and found RM gradients of opposite direction in the SNR shell. The SNR G156.2+5.7 is unusual by its exceptionally high X-ray brightness and very low surface-brightness in the radio range. The magnetic field is very well ordered along the shell periphery as expected for a compressed ambient magnetic field. A toroidal magnetic field component is indicated by the RM distribution. (abridged)

astro-ph↗

arXiv2004

Practical Implementations of Twirl Operations

Twirl operations, which convert impure singlet states into Werner states, play an important role in many schemes for entanglement purification. In this paper we describe strategies for implementing twirl operations, with an emphasis on methods suitable for ensemble quantum information processors such as nuclear magnetic resonance (NMR) quantum computers. We implement our twirl operation on a general two-spin mixed state using liquid state NMR techniques, demonstrating that we can obtain the singlet Werner state with high fidelity.

quant-ph↗

arXiv2003

Effect of magnetization process on levitation force between a superconducting disk and a permanent magnet

The levitation forces between a permanent magnet and a coaxial superconducting disk after different magnetization processes are measured. Significant effect of the magnetization process on the levitation force is observed. Theoretical calculations of levitation force based on the critical state model with temperature and field-dependent critical current density, and the heat dissipation due to the flux motion are in perfect agreement with the experimental data.

cond-mat.supr-con↗

arXiv2001

Fetching marked items from an unsorted database in NMR ensemble computing

Searching a marked item or several marked items from an unsorted database is a very difficult mathematical problem. Using classical computer, it requires $O(N=2^n)$ steps to find the target. Using a quantum computer, Grover's algorithm uses $O(\sqrt{N=2^n})$ steps. In NMR ensemble computing, Brushweiler's algorithm uses $\log N$ steps. In this Letter, we propose an algorithm that fetches marked items in an unsorted database directly. It requires only a single query. It can find a single marked item or multiple number of items.

quant-ph↗

arXiv2001

Experimental NMR Realization of A Generalized Quantum Search Algorithm

A generalized quantum search algorithm, where phase inversions for the marked state and the prepared state are replaced by $π/2$ phase rotations, is realized in a 2-qubit NMR heteronuclear system. The quantum algorithm searches a marked state with a smaller step compared to standard Grover algorithm. Phase matching requirement in quantum searching is demonstrated by comparing it with another generalized algorithm where the two phase rotations are $π/2$ and $3π/2$ respectively. Pulse sequences which include non 90 degree pulses are given.

quant-ph↗