arXiv subjects

Y. L. Qiu

Publications and source records attributed to Y. L. Qiu.

33 records · Page 2Linked to original sources

arXiv2018

A Global Photoionization Response to Prompt Emission and Outliers: Different Origin of Long Gamma-ray Bursts?

By using the line ratio \ion{C}{4}$\lambda1549$/\ion{C}{2}$\lambda1335$ as a tracer of ionization ratio of the interstellar medium (ISM) illuminated by a long gamma-ray burst (LGRB), we identify a global photoionization response of the ionization ratio to the photon luminosity of the prompt emission assessed by either $L_{\mathrm{iso}}/E_{\mathrm{peak}}$ or $L_{\mathrm{iso}}/E^2_{\mathrm{peak}}$. The ionization ratio increases with both $L_{\mathrm{iso}}/E_{\mathrm{peak}}$ and $L_{\mathrm{iso}}/E^2_{\mathrm{peak}}$ for a majority of the LGRBs in our sample, although there are a few outliers. The identified dependence of \ion{C}{4}/\ion{C}{2} on $L_{\mathrm{iso}}/E^2_{\mathrm{peak}}$ suggests that the scatter of the widely accepted Amati relation is related with the ionization ratio in ISM. The outliers tend to have relatively high \ion{C}{4}/\ion{C}{2} values as well as relatively high \ion{C}{4}$\lambda1549$/\ion{Si}{4}$\lambda1403$ ratios, which suggests an existence of Wolf-Rayet stars in the environment of these LGRBs. We finally argue that the outliers and the LGRBs following the identified \ion{C}{4}/\ion{C}{2}$-L_{\mathrm{iso}}/E_{\mathrm{peak}}$ ($L_{\mathrm{iso}}/E^2_{\mathrm{peak}}$) correlation might come from different progenitors with different local environments.

astro-ph.HE↗

arXiv2017

Evidence for magnetar formation in broad-lined type Ic supernovae 1998bw and 2002ap

Broad-lined type Ic supernovae (SNe Ic-BL) are peculiar stellar explosions that distinguish themselves from ordinary SNe. Some SNe Ic-BL are associated with long-duration (\gtrsim 2 s) gamma-ray bursts (GRBs). Black holes and magnetars are two types of compact objects that are hypothesized to be central engines of GRBs. In spite of decades of investigations, no direct evidence for the formation of black holes or magnetars has been found for GRBs so far. Here we report the finding that the early peak (t \lesssim 50 days) and late-time (t \gtrsim 300 days) slow decay displayed in the light curves of both SNe 1998bw (associated with GRB 980425) and 2002ap (not GRB-associated) can be attributed to magnetar spin-down with initial rotation period P0 \sim 20 ms, while the intermediate-time (50 \lesssim t \lesssim 300 days) linear decline is caused by radioactive decay of 56Ni. The connection between the early peak and late-time slow decline in the light curves is unexpected in alternative models. We thus suggest that GRB 980425 and SN 2002ap were powered by magnetars.

astro-ph.HE↗

arXiv2015

18-Months Operation of Lunar-based Ultraviolet Telescope: A Highly Stable Photometric Performance

We here report the photometric performance of Lunar-based Ultraviolet telescope (LUT), the first robotic telescope working on the Moon, for its 18-months operation. In total, 17 IUE standards have been observed in 51 runs until June 2015, which returns a highly stable photometric performance during the past 18 months (i.e., no evolution of photometric performance with time). The magnitude zero point is determined to be $17.53\pm0.05$ mag, which is not only highly consistent with the results based on its first 6-months operation, but also independent on the spectral type of the standard from which the magnitude zero point is determined. The implications of this stable performance is discussed, and is useful for next generation lunar-based astronomical observations.

astro-ph.IM↗

arXiv2015

An Unprecedented Constraint on Water Content in the Sunlit Lunar Exosphere Seen by Lunar-Based Ultraviolet Telescope of Chang'e-3 Mission

The content of $\mathrm{OH/H_2O}$ molecules in the tenuous exosphere of the Moon is still an open issue at present. We here report an unprecedented upper limit of the content of the OH radicals, which is obtained from the in-situ measurements carried out \rm by the Lunar-based Ultraviolet Telescope, a payload of Chinese Chang'e-3 mission. By analyzing the diffuse background in the images taken by the telescope, the column density and surface concentration of the OH radicals are inferred to be $<10^{11}\ \mathrm{cm^{-2}}$ and $<10^{4}\ \mathrm{cm^{-3}}$ (by assuming a hydrostatic equilibrium with a scale height of 100km), respectively, by assuming that the recorded background is fully contributed by their resonance fluorescence emission. The resulted concentration is lower than the previously reported value by about two orders of magnitude, and is close to the prediction of the sputtering model. In addition, the same measurements and method allow us to derive a surface concentration of $<10^{2}\ \mathrm{cm^{-3}}$ for the neutral magnesium, which is lower than the previously reported upper limit by about two orders of magnitude. These results are the best known of the OH (MgI) content in the lunar exosphere to date.

astro-ph.EP↗

arXiv2014

Photometric Calibration on Lunar-based Ultraviolet Telescope for Its First Six Months of Operation on Lunar Surface

We reported the photometric calibration of Lunar-based Ultraviolet telescope (LUT), the first robotic astronomical telescope working on the lunar surface, for its first six months of operation on the lunar surface. Two spectral datasets (set A and B) from near-ultraviolet (NUV) to optical band were constructed for 44 International Ultraviolet Explorer (IUE) standards, because of the LUT's relatively wide wavelength coverage. Set A were obtained by extrapolating the IUE NUV spectra ($λ<3200Å$) to optical band basing upon the theoretical spectra of stellar atmosphere models. Set B were exactly the theoretical spectra from 2000Å to 8000Å extracted from the same model grid. In total, seven standards have been observed in 15 observational runs until May 2014. The calibration results show that the photometric performance of LUT is highly stable in its first six months of operation. The magnitude zero points obtained from the two spectral datasets are also consistent with each other, i.e., $\mathrm{zp=17.54\pm0.09}$mag (set A) and $\mathrm{zp=17.52\pm0.07}$mag (set B).

astro-ph.IM↗

arXiv2012

Very Early Photometry of SN 1998S: Physical Parameters and Date of Explosion

Context. We present very early optical lightcurves beginning 10 days before maximum of the Type IIn supernova 1998S, covering the first four months after discovery. Aims. We examine the light evolution and try to compare the lightcurves to two analytical models(Nakar & Sari(2010) and Rabinak & Waxman(2011)) for a red supergiant star. Methods. The photometry was carried at the 60-cm telescope of the Xinglong Station of China. Broadband filters Johnsons B, V and Cousins R were used. Results. The magnitude rose for the first few days and then dropped slowly afterwards. The two different models we use can fit the early lightcurves very well. The explosion date derived from the models is within the range of 1998 March 1.34 - 2.64(JD 2450873.84 - JD 2450875.14.) The radius of the progenitor is found to be ~ 300 Rsun and ~ 2000 Rsun for the model of Nakar & Sari(2010) and Rabinak & Waxman(2011) respectively. The constraint on mass and energy is not strong. The ranges of these two parameters are within that of a red supergiant.

astro-ph.CO↗

arXiv2012

The shallow-decay phase in both optical and x-ray afterglows of Swift GRB 090529A: Energy injection into a wind-type medium?

The energy injection model is usually proposed to interpret the shallow-decay phase in Swift GRB X-ray afterglows. However, very few GRBs have simultaneous signatures of energy injection in their optical and X-ray afterglows. Here, we report optical observations of GRB 090529A from 2000 sec to $\sim10^6$ sec after the burst, in which an achromatic decay is seen at both wavelengths. The optical light curve shows a decay from 0.37 to 0.99 with a break at $\sim10^5$ sec. In the same time interval, the decay indices of the X-ray light curve changed from 0.04 to 1.2. Comparing these values with the closure relations, the segment after 3$\times10^{4}$ sec is consistent with the prediction of the forward shock in an ISM medium without any energy injection. The shallow-decay phase between 2000 to 3$\times10^{4}$ sec could be due to the external shock in a wind-type-like medium with an energy injection under the condition of $ν_o < ν_c < ν_x$. However, the constraint of the spectral region is not well consistent with the multi-band observations. For this shallow-decay phase, other models are also possible, such as energy injection with evolving microphysical parameters, or a jet viewed off-axis,etc.

astro-ph.HE↗

arXiv2011

Lunar Exosphere Influence on Lunar-based Near-ultraviolet Astronomical Observations

The potential effect of the lunar exosphere on the near-ultraviolet sky background emission is predicted for Lunar-based Ultraviolet Telescope (LUT: a funded Chinese scientific payload for the Chang'e-III mission). Using the upper limit on the OH concentration inferred from the recent MIP CHACE results, our calculations show that the sky brightness due to the illuminated exosphere is $<8.7\ \mathrm{photon\ s^{-1}\ cm^{-2}\ arcsec^{-2}}$ within the wavelength range 245-340 nm. By evaluating the signal-to-noise ratios of observations of an AB=13 mag point source at a series of sky background levels, our analysis indicates that the detection performance of LUT can be moderately degraded by the lunar exosphere emission in most cases. An AB=13 mag point source can still be detected by the telescope at a signal-to-noise ratio more than 8 when the OH concentration is less than $2\times10^8\ \mathrm{molecules\ cm^{-3}}$. However, the effect on the performance is considerable when the exosphere is as dense as suggested by CHACE.

astro-ph.EP↗

arXiv2009

GRB 070518: A Gamma-ray Burst with Optically Dim Luminosity

We present our optical observations of {\em Swift} GRB 070518 afterglow obtained at the 0.8-m Tsinghua University-National Astronomical Observatory of China telescope (TNT) at Xinglong Observatory. Our follow-up observations were performed from 512 sec after the burst trigger. With the upper limit of redshift $\sim$0.7, GRB 070518 is found to be an optically dim burst. The spectra indices $β_{ox}$ of optical to X-ray are slightly larger than 0.5, which implies the burst might be a dark burst. The extinction $A_{V}$ of the host galaxy is 3.2 mag inferred from the X-ray hydrogen column density with Galactic extinction law, and 0.3 mag with SMC extinction law. Also, it is similar to three other low-redshift optically dim bursts, which belong to XRR or XRF, and mid-term duration($T_{90}<10$, except for GRB 070419A, $T_{90}$=116s). Moreover, its $R$ band afterglow flux is well fitted by a single power-law with an index of 0.87. The optical afterglow and the X-ray afterglow in the normal segment might have the same mechanism, as they are consistent with the prediction of the classical external shock model. Besides, GRB 070518 agrees with Amati relation under reasonable assumptions. The Ghirlanda relation is also tested with the burst.

astro-ph.HE↗

arXiv2006

Very early multi-color observations of the plateau phase of GRB 041006 afterglow

Observations of the optical afterglow of GRB 041006 with the Kiso Observatory 1.05 m Schmidt telescope, the Lulin Observatory 1.0 m telescope and the Xinglong Observatory 0.6 m telescope. Three-bands (B, V and R) of photometric data points were obtained on 2004 October 6, 0.025-0.329 days after the burst. These very early multi band light curves imply the existence of a color dependent plateau phase. The B-band light curve shows a clear plateau at around 0.03 days after the burst. The R band light curve shows the hint of a plateau, or a possible slope change, at around 0.1 days after the burst. The overall behavior of these multi-band light curves may be interpreted in terms of the sum of two separate components, one showing a monotonic decay the other exhibiting a rising and a falling phase, as described by the standard afterglow model.

astro-ph↗

arXiv2002

The Type Ic Hypernova SN 2002ap

Photometric and spectroscopic data of the energetic Type Ic supernova (SN) 2002ap are presented, and the properties of the SN are investigated through models of its spectral evolution and its light curve. The SN is spectroscopically similar to the "hypernova" SN 1997ef. However, its kinetic energy [$\sim (4-10) \times 10^{51}$ erg] and the mass ejected (2.5-5 $M_{\odot}$) are smaller, resulting in a faster-evolving light curve. The SN synthesized $\sim 0.07 M_{\odot}$ of $^{56}$Ni, and its peak luminosity was similar to that of normal SNe. Brightness alone should not be used to define a hypernova, whose defining character, namely very broad spectral features, is the result of a high kinetic energy. The likely main-sequence mass of the progenitor star was 20-25 $M_{\odot}$, which is also lower than that of both hypernovae SNe 1997ef and 1998bw. SN 2002ap appears to lie at the low-energy and low-mass end of the hypernova sequence as it is known so far. Observations of the nebular spectrum, which is expected to dominate by summer 2002, are necessary to confirm these values.

astro-ph↗

arXiv2000

A High Intrinsic Peculiarity Rate Among Type Ia Supernovae

We have compiled a sample of 45 Type Ia supernovae (SNe Ia) discovered by the Lick Observatory Supernova Search (LOSS) and the Beijing Astronomical Observatory Supernova Survey (BAOSS), and determined the rate of spectroscopically peculiar SNe Ia (i.e., SN 1986G-like, SN 1991bg-like, and SN 1991T-like objects) and the luminosity function of SNe Ia. Because of the nature of the two surveys (distance-limited with small baselines and deep limiting magnitudes), nearly all SNe Ia have been discovered in the sample galaxies of LOSS and BAOSS; thus, the observed peculiarity rate and luminosity function of SNe Ia are intrinsic. We find that 36$\pm$9% of nearby SNe Ia are peculiar; specifically, the luminosity function of SNe Ia consists of 20% SN 1991T-like, 64% normal, and 16% SN 1991bg-like objects. We have compared our results to those found by earlier studies, and to those found at high redshift. The apparent dearth of SN 1991T-like objects at high redshift may be due to extinction, and especially to the difficulty of recognizing them from spectra obtained past maximum brightness or from spectra with low signal-to-noise ratios. Implications of the high peculiarity rate for the progenitor systems of SNe Ia are also briefly discussed.

astro-ph↗

arXiv2000

Spectrum Analysis of the Type Ib Supernova 1999dn: Probable Identifications of C II and H-alpha

Low resolution spectra of SN 1999dn at early times are presented and compared with synthetic spectra generated with the parameterized supernova synthetic-spectrum code SYNOW. We find that the spectra of SN 1999dn strongly resemble those of SN 1997X and SN 1984L, and hence we classify it as a Type Ib event. Line-identifications are established through spectrum synthesis. Strong evidence of both H-alpha and C II 6580 is found. We infer that H-alpha appears first, before the time of maximum brightness, and then is blended with and finally overwhelmed by the C II line after maximum; this favors a thin high-velocity hydrogen skin in this Type Ib supernova.

astro-ph↗

arXiv1999

A High Peculiarity Rate for Type Ia SNe

We have compiled a sample of 90 SNe Ia from 1997 to 1999 (up to SN 1999da) and studied the peculiarity rate of SN 1991T, SN 1991bg and SN 1986G-like objects. A Monte Carlo code is written to study the observational biases involved in the evaluation of the intrinsic peculiarity rate of SNe Ia. We found that the peculiarity rate of SNe Ia is higher than 30% and the luminosity function of SNe Ia is flat.

astro-ph↗

arXiv1999

The Type Ia Supernova 1997br in ESO 576-G40

The peculiar type Ia supernova SN 1997br in ESO 576-G40 was extensively observed at Beijing Astronomical Observatory and Lick Observatory. In this paper, we present and discuss the BVRI photometry and the spectra collected over 3 months, beginning 9 days before maximum brightness. The light curves of SN 1997br are similar to those of SN 1991T, with slow decline rates after the B maximum. Well-sampled data before the B maximum show unambiguously that SN 1997br rises more slowly and has a wider peak than normal type Ia supernovae. The optical color evolution of SN 1997br is also similar to that of SN 1991T. We estimate the extinction of SN 1997br to be E(B-V) = 0.35+/-0.10 mag by comparing its BVRI light curves with those of SN 1991T and by measureing the equivalent width of interstellar Na I D absorption lines. We have conducted a thorough comparison of the spectroscopic evolution of SN 1997br, SN 1991T, and SN 1994D. Although SN 1997br is generally very similar to SN 1991T, it shows some interesting differences at various epoches. Spectra of SN 1997br seem to indicate an earlier transition to the dominant phase of Fe-peak elements after the B maximum. Si II lines in SN 1997br show a very short duration after the B maximum. We discuss the implications of our observations of SN 1997br for models of type Ia supernovae. Specifically, we suggest that some SNe Ia may result from decelerated detonations of white dwarfs.

astro-ph↗