The Discovery of an X-ray/UV Stellar Flare from the Late-K/Early-M Dwarf LMC 335

We report the discovery of an X-ray/UV stellar flare from the source LMC 335, captured by XMM-Newton in the field of the Large Magellanic Cloud. The flare event was recorded continuously in X-ray for its first 10 hours from the precursor to the late decay phases. The observed fluxes increased by more than two orders of magnitude at its peak in X-ray and at least one in the UV as compared to quiescence. The peak 0.1-7.0 keV X-ray flux is derived from the two-temperature APEC model to be ~(8.4 +/- 0.6) x 10^-12 erg cm-2 s-1. Combining astrometric information from multiple X-ray observations in the quiescent and flare states, we identify the NIR counterpart of LMC 335 as the 2MASS source J05414534-6921512. The NIR color relations and spectroscopic parallax characterize the source as a Galactic K7-M4 dwarf at a foreground distance of (100 - 264) pc, implying a total energy output of the entire event of ~(0.4 - 2.9) x 10^35 erg. This report comprises detailed analyses of this late-K / early-M dwarf flare event that has the longest time coverage yet reported in the literature. The flare decay can be modeled with two exponential components with timescales of ~28 min and ~4 hours, with a single component decay firmly ruled out. The X-ray spectra during flare can be described by two components, a dominant high temperature component of ~40-60MK and a low temperature component of ~10MK, with a flare loop length of about 1.1-1.3 stellar radius.Comment: 35 pages, 6 figures, 5 tables, accepted for publication in Ap

Nickel Mixing in the Outer Layers of SN 1987A

Supernova 1987A remains the most well-observed and well-studied supernova to date. Observations produced excellent broad-band photometric and spectroscopic coverage over a wide wavelength range at all epochs. Here, we focus on the very early spectroscopic observations. Only recently have numerical models been of sufficient detail to accurately explain the observed spectra. In SN 1987A, good agreement has been found between observed and synthetic spectra for day one, but by day four, the predicted Balmer lines become much weaker than the observed lines. We present the results of work based on a radiation-hydrodynamic model by Blinnikov and collaborators. Synthetic non-LTE spectra generated from this model by the general radiation transfer code PHOENIX strongly support the theory that significant mixing of nickel into the outer envelope is required to maintain strong Balmer lines. Preliminary results suggest a lower limit to the average nickel mass of 1.0 \times 10^{-5} solar masses is required above 5000 \kmps by day four. PHOENIX models thus have the potential to be a sensitive probe for nickel mixing in the outer layers of a supernova.Comment: 16 pages, 7 figures, ApJ, v556 2001 (in press

Challenges of Using Google Sites in Education and How Students Perceive Using It

ABSTRACT This paper describes an on-going project which is about how Google Sites, which is a type of wiki, applied in the implementation of Inquiry project based learning (PjBL). Teachers and students from a local school being anonymous as KS shared the first hand experience and positive comment on using Web 2.0 technologies in education and learning. This paper reveals the finding of the project and states out the school encountered the challenges from students" parent because of misunderstanding the nature of on-line project, and also from the students due to not being familiar with using Google Sites. This paper also includes how the school IT teacher dealt with those challenges with probable solutions, and he perceived an improvement of the students" performance in this General Studies group project facilitated by using Google Sites

Application of fuzzy integrated FMEA with product lifetime consideration for new product development in flexible electronics industry

Purpose: the aim of this paper is to minimize the risks of new product development and shorten time-to-market, particularly for high-tech enterprise where the complexity of the product generates vast amount of failure mode. Design/methodology/approach: first, the concept of Critical Consideration Factor (CCF) is introduced based on product-specific technical characteristics, expected lifetime, and yield requirement to identify and prioritize the critical failure mode in the subsequent Failure Mode and Effect Analysis (FMEA), followed by process characterization on the high-risk failure mode and Critical Parameter Management (CPM) practice to realize a robust mass production system of the developed technology. The application on the development of advanced flexible substrate and surface finishes fabrication technique is presented. Findings: through the proposed methodology, the risk level of each potential failure mode can be accurately quantified to identify the critical variables. With process characterization, reliability of the product is ensured. Consequently, significant reduction in development resources and time-to-market can be achieved. Practical implications: the development strategy allows high tech enterprises to achieve a balanced ecosystem in which value created through adaption of new technology/product can be thoroughly captured through commercialization in a timely manner with no field failure. Originality/value: the proposed development strategy utilizes a unique approach with thorough considerations that enables high tech enterprise to deliver new product with rapid time-to-market without sacrificing product lifetime reliability, which is key to achieve competitive advantage in the highly dynamic market.Peer Reviewe

The Ultraluminous X-ray Sources near the Center of M82

We report the identification of a recurrent ultraluminous X-ray source (ULX), a highly absorbed X-ray source (possibly a background AGN), and a young supernova remnant near the center of the starburst galaxy M82. From a series of Chandra observations taken from 1999 to 2005, we found that the transient ULX first appeared in 1999 October. The source turned off in 2000 January, but later reappeared and has been active since then. The X-ray luminosity of this source varies from below the detection level (~2.5e38 erg/s) to its active state in between ~7e39 erg/s and 1.3e40 erg/s (in the 0.5-10 keV energy band) and shows unusual spectral changes. The X-ray spectra of some Chandra observations are best fitted with an absorbed power-law model with photon index ranging from 1.3 to 1.7. These spectra are similar to those of Galactic black hole binary candidates seen in the low/hard state except that a very hard spectrum was seen in one of the observations. By comparing with near infrared images taken with the Hubble Space Telescope, the ULX is found to be located within a young star cluster. Radio imaging indicates that it is associated with a H II region. We suggest that the ULX is likely to be a > 100 solar mass intermediate-mass black hole in the low/hard state. In addition to the transient ULX, we also found a highly absorbed hard X-ray source which is likely to be an AGN and an ultraluminous X-ray emitting young supernova remnant which may be related to a 100-year old gamma-ray burst event, within 2 arcsec of the transient ULX.Comment: 9 pages, 8 figures. Accepted for publication in Ap

A Chandra View of The Morphological And Spectral Evolution of Supernova Remnant 1987A

We present an update on the results of our monitoring observations of the X-ray remnant of supernova (SN) 1987A with the {\it Chandra X-Ray Observatory}. As of 2002 December, we have performed a total of seven observations of SN 1987A. The high angular resolution images from the latest data reveal developments of new X-ray bright spots in the northwestern and the southwestern portions of the remnant as well as changes on the eastern side. The latest 0.5-2 keV band flux ($f_X$ $\sim$ 6 $\times$ 10$^{-13}$ ergs cm$^{-2}$ s$^{-1}$) is four times brighter than three years earlier. The overall X-ray emission is primarily from the blast wave shock with $kT$ $\sim$ 2.4 keV. As the blast wave approaches the dense circumstellar material, the contribution from the decelerated slow shock ($kT$ $\sim$ 0.22 keV) to the observed X-ray emission is becoming significant. The increase of this slow shock contribution over the last two years is particularly noticeable in the western half of the remnant. These results indicate that the shock front is now reaching the main body of the inner circumstellar ring. Based on the best-fit two-shock spectral model, we derive approximate densities of the X-ray-emitting regions ($n_e$ $\sim$ 235 cm$^{-3}$ for the fast shock and $n_e$ $\sim$ 7500 cm$^{-3}$ for the slow shock). We obtain an upper limit on the observed X-ray luminosity of any embedded point source ($L_X$ $\le$ 1.5 $\times$ 10$^{34}$ ergs s$^{-1}$) in the 2$-$10 keV band. The X-ray remnant continues to expand linearly at a rate of 4167 km s$^{-1}$.Comment: 22 pages (ApJ preprint style), 7 Figures, Accepted by ApJ (scheduled on July 20, 2004), for high-quality Fig 1 and Fig 2, please contact [email protected]

High Resolution X-Ray Imaging of the Center of IC342

We presented the result of a high resolution (FWHM~0.5'') 12 ks Chandra HRC-I observation of the starburst galaxy IC342 taken on 2 April 2006. We identified 23 X-ray sources within the central 30' x 30' region of IC342. Our HRC-I observation resolved the historical Ultraluminous X-ray sources (ULX), X3, near the nucleus into 2 sources, namely C12 and C13, for the first time. The brighter source C12, with L(0.08-10keV)=(6.66\pm0.45)\times10^{38}ergs^-1, was spatially extended (~82 pc x 127 pc). From the astrometric registration of the X-ray image, C12 was at R.A.=03h:46m:48.43s, decl.=+68d05m47.45s, and was closer to the nucleus than C13. Thus we concluded that source was not an ULX and must instead be associated with the nucleus. The fainter source C13, with L(0.08-10keV)=(5.1\pm1.4) x 10^{37}ergs^-1 was consistent with a point source and located $6.51'' at P.A. 240 degree of C12. We also analyzed astrometrically corrected optical Hubble Space Telescope and radio Very Large Array images, a comparison with the X-ray image showed similarities in their morphologies. Regions of star formation within the central region of IC342 were clearly visible in HST H alpha image and this was the region where 3 optical star clusters and correspondingly our detected X-ray source C12 were observed. We found that a predicted X-ray emission from starburst was very close to the observed X-ray luminosity of C12, suggesting that nuclear X-ray emission in IC342 was dominated by starburst. Furthermore, we discussed the possibility of AGN in the nucleus of IC342. Although our data was not enough to give a firm existence of an AGN, it could not be discarded.Comment: 29 page, 8 figures, accepted by Ap

Thin accretion disks in f(R) modified gravity models

We consider the basic physical properties of matter forming a thin accretion disc in the static and spherically symmetric space-time metric of the vacuum $f(R)$ modified gravity models. The Lagrangian of the generalized gravity theory is also obtained in a parametric form, and the conditions of the viability of the model are discussed. The exact Schwarzschild type solution of the gravitational field equations in the $f(R)$ gravity contains a linearly increasing term, as well as a logarithmic correction, as compared to the standard Schwarzschild solution of general relativity, and it depends on four arbitrary integration constants. The energy flux and the emission spectrum from the accretion disk around the $f(R)$ gravity black holes are obtained, and they are compared to the general relativistic case. Particular signatures can appear in the electromagnetic spectrum, thus leading to the possibility of directly testing modified gravity models by using astrophysical observations of the emission spectra from accretion disks.Comment: 21 pages, 3 figures, accepted for publication in PR

Observations of the Crab Nebula and its pulsar in the far-ultraviolet and in the optical

We present HST/STIS far-UV observations of the Crab nebula and its pulsar. Broad, blueshifted absorption arising in the nebula is seen in C IV 1550, reaching about 2500 km/s. This can be interpreted as evidence for a fast outer shell, and we adopt a spherically symmetric model to constrain the properties of this. We find that the density appears to decrease outward in the shell. A lower limit to the mass is 0.3 solar masses with an accompanying kinetic energy of 1.5EE{49} ergs. A massive 10^{51} erg shell cannot be excluded, but is less likely if the density profile is much steeper than R^{-4} and the velocity is <6000 km/s. The observations cover the region 1140-1720 A. With the time-tag mode of the spectrograph we obtain the pulse profile. It is similar to that in the near-UV, although the primary peak is marginally narrower. Together with the near-UV data, and new optical data from NOT, our spectrum of the pulsar covers the entire region from 1140-9250 A. Dereddening the spectrum gives a flat spectrum for E(B-V)=0.52, R=3.1. This dereddened spectrum of the Crab pulsar can be fitted by a power law with spectral index alpha_{\nu} = 0.11 +/- 0.04. The main uncertainty is the amount and characteristics of the interstel- lar reddening, and we have investigated the dependence of \alpha_{\nu} on E(B-V) and R. In the extended emission covered by our 25" x 0.5" slit in the far-UV, we detect C IV 1550 and He II 1640 emission lines from the Crab nebula. Several interstellar absorption lines are detected toward the pulsar. The Ly alpha absorption indicates a column density of 3.0+/-0.5\EE{21} cm^{-2} of neutral hydrogen, which agrees well with our estimate of E(B-V)=0.52 mag. Other lines show no evidence of severe depletion of metals in atomic gas.Comment: 18 pages emulateapj style, including 10 figures. ApJ, accepte