Ti-Pei Li

OPTICAL AND NEAR-INFRARED OBSERVATIONS OF THE HIGHLY REDDENED, RAPIDLY EXPANDING TYPE Ia SUPERNOVA SN 2006X IN M100

We present extensive optical (UBVRI), near-infrared (JK) light curves and optical spectroscopy of the Type Ia supernova SN 2006X in the nearby galaxy NGC 4321 (M100). Our observations suggest that either SN 2006X has an intrinsically peculiar color evolution or it is highly reddened [E(B − V)host = 1.42 ± 0.04 mag ] with RV = 1.48 ± 0.06, much lower than the canonical value of 3.1 for the average Galactic dust. SN 2006X also has one of the highest expansion velocities ever published for an SN Ia. Compared with the other SNe Ia we analyzed, SN 2006X has a broader light curve in the U band, a more prominent bump/shoulder feature in the V and R bands, a more pronounced secondary maximum in the I and NIR bands, and a remarkably smaller late-time decline rate in the B band. The B − V color evolution shows an obvious deviation from the Lira-Phillips relation at 1-3 months after maximum brightness. At early times, optical spectra of SN 2006X displayed strong, high-velocity features of both intermediate-mass elements (Si, Ca, and S) and iron peak elements, while at late times they showed a relatively blue continuum, consistent with the blue U − B and B − V colors at similar epochs. A light echo and/or the interaction of the SN ejecta and its circumstellar material may provide a plausible explanation for its late-time photometric and spectroscopic behavior. Using the Cepheid distance of M100, we derive a Hubble constant of 72.8 ± 8.2 km s−1 Mpc−1 (statistical) from the normalized dereddened luminosity of SN 2006X. We briefly discuss whether abnormal dust is a universal signature for all SNe Ia and whether the most rapidly expanding objects form a subclass with distinct photometric and spectroscopic properties.

The Golden Standard Type Ia Supernova 2005cf: Observations from the Ultraviolet to the Near-Infrared Wavebands

We present extensive photometry at ultraviolet (UV), optical, and near-infrared (NIR) wavelengths, as well as dense sampling of optical spectra, for the normal Type Ia supernova (SN Ia) 2005cf. The optical photometry, performed at eight different telescopes, shows a 1σ scatter of ≾0.03 mag after proper corrections for the instrument responses. From the well-sampled light curves, we find that SN 2005cf reached a B-band maximum at 13.63 ± 0.02 mag, with an observed luminosity decline rate Δm _(15)(B) = 1.05 ± 0.03 mag. The correlations between the decline rate and various color indexes, recalibrated on the basis of an expanded SN Ia sample, yield a consistent estimate for the host-galaxy reddening of SN 2005cf, E(B – V)_(host) = 0.10 ± 0.03 mag. The UV photometry was obtained with the Hubble Space Telescope and the Swift Ultraviolet/Optical Telescope, and the results match each other to within 0.1-0.2 mag. The UV light curves show similar evolution to the broadband U, with an exception in the 2000-2500 A spectral range (corresponding to the F220W/uvm2 filters), where the light curve appears broader and much fainter than that on either side (likely owing to the intrinsic spectral evolution). Combining the UV data with the ground-based optical and NIR data, we establish the generic UV-optical-NIR bolometric light curve for SN 2005cf and derive the bolometric corrections in the absence of UV and/or NIR data. The overall spectral evolution of SN 2005cf is similar to that of a normal SN Ia, but with variety in the strength and profile of the main feature lines. The spectra at early times displayed strong, high-velocity (HV) features in the Ca II H&K doublet and NIR triplet, which were distinctly detached from the photosphere (v ≈ 10,000 km s^(–1)) at a velocity ranging from 20,000 to 25,000 km s^(–1). One interesting feature is the flat-bottomed absorption observed near 6000 A in the earliest spectrum, which rapidly evolved into a triangular shape and then became a normal Si II λ6355 absorption profile at about one week before maximum brightness. This premaximum spectral evolution is perhaps due to the blending of the Si IIλ6355 at photospheric velocity and another HV absorption component (e.g., an Si II shell at a velocity ~18,000 km s^(–1)) in the outer ejecta, and may be common in other normal SNe Ia. The possible origin of the HV absorption features is briefly discussed.

An antimatter spectrometer in space

Abstract We discuss a simple magnetic spectrometer to be installed on a satellite or space station. The purpose of this spectrometer is to search for primordial antimatter to the level of antimatter/matter ≈10 −9 , improving the existing limits obtained with balloon flights by a factor of 10 4 to 10 5 . The design of the spectrometer is based on an iron-free, NdFeB permanent magnet, scintillation counters, drift tubes, and silicon or time projection chambers. Different design options are discussed. Typically, the spectrometer has a weight of about 2 tons and an acceptance of about 1.0 m 2 sr. The availability of the new NdFeB material makes it possible for the first time to put a magnet into space economically and reliably.

Orbital Period and Outburst Luminosity of Transient Low Mass X-ray Binaries

In this paper we investigate the relation between the maximal luminosity of X-ray outburst and the orbital period in transient low mass X-ray binaries (or soft X-ray transients) observed by the Rossi X-ray Timing Explorer (RXTE) in the past decade. We find that the maximal luminosity (3-200 keV) in Eddington unit generally increases with increasing orbital period, which does not show a luminosity saturation but in general agrees with theoretical prediction. The peak luminosities in ultra-compact binaries might be higher than those with orbital period of 2-4 h, but more data are needed to make the claim. We also find that there is no significant difference in the 3-200 keV outburst peak luminosity between neutron star systems and black hole systems with orbital periods above 4 h; however, there might be significant difference at smaller orbital period where only neutron star systems are observed and radiatively ineffcient accretion flow is expected to work at the low luminosities for black hole accreters.

GAMMA-RAY BURSTS ARE PRODUCED PREDOMINATELY IN THE EARLY UNIVERSE

It is known that some observed gamma-ray bursts (GRBs) are produced at cosmological distances and that the GRB production rate may follow the star formation rate. We model the BATSE-detected intensity distribution of long GRBs in order to determine their space density distribution and opening angle distribution. Our main results are: the lower and upper distance limits to the GRB production are z approximate to 0.24 and > 10, respectively; the GRB opening angle follows an exponential distribution and the mean opening angle is about 0.03 radians; and the peak luminosity appears to be a better standard candle than the total energy of a GRB.

RECONSTRUCTION OF OBJECTS BY DIRECT DEMODULATION

High resolution reconstruction of complicated objects from incomplete and noisy data can be achieved by solving modulation equations iteratively under physical constraints. This direct demodulation method is a powerful technique for dealing with inverse problem in general case. Spectral and image restorations and computerized tomography are only particular cases of general demodulation. It is possible to reconstruct an object in higher dimensional space from observations by a simple lower dimensional instrument through direct demodulation. Our simulations show that wide field and high resolution images of space hard X-rays and softγ-rays can be obtained by a collimated non-position-sensitive detector without coded aperture masks.

MODEL-INDEPENDENT DETERMINATION OF CURVATURE PARAMETER USING H(z) AND D-A (z) DATA PAIRS FROM BAO MEASUREMENTS

We present a model-independent determination of the curvature parameter Omega(k) using the Hubble parameter H(z) and the angular diameter distance D-A(z) from recent baryon acoustic oscillation (BAO) measurements. Each H(z) and D-A(z) pair from a BAO measurement can constrain a curvature parameter. The accuracy of the curvature measurement improves with increased redshift of H(z) and D-A(z) data. By using the H(z) and D-A(z) pair derived from a BAO Lyman a forest measurement at z = 2.36, the Omega(k) is confined to be -0.05 +/- 0.06, which is consistent with the curvature of -0.037(-0.042) (+0.044) constrained by the nine year Wilkinson Microwave Anisotropy Probe data only. Considering future BAOmeasurements, at least one order of magnitude improvement of this curvature measurement can be expected.

A DIRECT RESTORATION METHOD FOR SPECTRAL AND IMAGE-ANALYSIS

Physical constraints to directly control the output restoration are introduced in each iteration of solving the spectral or image formation equation. For the purpose of increasing the restoration sensitivity and the capability of smoothing noises, the fitting technique is used to reform the resolved equation. Our reconstruction results for Monte Carlo samples and observation data from space high energy astronomy show that, in comparison with traditional restorations, the direct method has high sensitivity, high resolution ability and capability of effectively reducing the effect of statistical fluctuation in data and can be used in the case of poor statistics. This method is model independent and has the capability to simultaneously represent both the extended and discrete features in object.

The cross spectra of Circinus X-1: Evolution of time lags

Earlier work showed that the track in the X-ray hardness-intensity diagram of Cir X-1 corresponds to a Z track in its color-color diagram. In this paper, we study the cross spectrum of Cir X-1 in different regions of the hardness-intensity diagram with RXT E/PCA data. Comparing the light curves of Cir X-1 for the energy band 1.8-5.1 keV with those for 5.1-13.1 keV, we find that Cir X-1 exhibits a hard time lag on the horizontal branch and a soft time lag on both the normal and the flaring branches. This indicates that Cir X-1 is similar to GX 5-1 and Cyg X-2 on the horizontal branch but is different from them on the normal branch. We briefly discuss the mechanism of the time lags in the context of Comptonization models.

The 2009 outburst of H 1743-322 as observed by RXTE

Context. Six outbursts have been observed by RXTE from the source since 2003. Following “a failed outburst” with a missing high/soft state in 2008, the most recent one occurred in 2009, exhibiting all spectral transitions. Aims. An outburst was observed by RXTE from the black hole candidate H 1743-322 in 2009. We investigate this particular outburst in the context of the source outburst history. Methods. We analyze the RXTE observations of the 2009 outburst of H 1743-322, as well as the observations of the previous five outbursts for comparison. All available RXTE observations taken since 2003 sum up to a total exposure of ∼1200 ks. Results. The hardness-intensity diagram (HID) shows a complete counter-clockwise q-track for the 2009 outburst. It leaves the low/hard state but does not reach the leftmost edge of the overall HID. Near maximum, the X-ray spectra show a power law with photon index <2.4; the peak luminosity during the whole outburst reached only 20% of the Eddington luminosity. The highest disk fractional luminosity is about 0.75 for the 2009 outburst, which is close to the lower limit observed from the black hole XRB sample in their state transitions from the intermediate to the high/soft state. While the lowest hardness (6–19 keV/3–6 keV) values in the HID is about 0.3–0.4 for the 2009 outburst, the timing analysis shows that a transition to the high soft state occurred. During the low/hard state of the 2009 outburst, the inner radius of the accretion disk is found to be closer to the central black hole and anti-correlated with the disk temperature implying reprocessing of the hot corona on the disk’s soft X-rays. In the luminosity diagram of the corona versus the disk, the tracks of the outbursts in 2003 and 2009 cross the line which represents a roughly equal contribution to the emission from the thermal and the non-thermal components; the track of the 2008 outburst has its turn-over falling on this line. This may indicate an emission balance between the corona and the disk that prevents the state transition from going further than the low/hard state.