arXiv subjects

Yulei Qiu

Publications and source records attributed to Yulei Qiu.

At least 19 recordsLinked to original sources

arXiv2026

Overview of Ground-based Wide-Angle Cameras array

As one of the key ground-based facilities of the Chinese-French SVOM mission, the main scientific objectives of the Ground-based Wide Angle Camera array (GWAC) are to detect prompt optical emission of gamma-ray bursts or other short duration astronomical transients on a second-scale temporal resolution. GWAC is located at Xinglong observatory, China, and consists of 10 mounts and 40 cameras, providing a joint field of view of about 3600 square degrees.The detection ability is 16 magnitude in 10 seconds of exposure time in the visual band under the condition of the new moon phase. Here, we give an overview of GWAC and introduce the science motivation of the project, as well as the performance of the hardware and the software. The observation strategies and the data processing are briefly presented. The early sciences in the last 5 years since the first light are summarized.

astro-ph.IM↗

arXiv2023

Robotic Fabric Flattening with Wrinkle Direction Detection

Deformable Object Manipulation (DOM) is an important field of research as it contributes to practical tasks such as automatic cloth handling, cable routing, surgical operation, etc. Perception is considered one of the major challenges in DOM due to the complex dynamics and high degree of freedom of deformable objects. In this paper, we develop a novel image-processing algorithm based on Gabor filters to extract useful features from cloth, and based on this, devise a strategy for cloth flattening tasks. We also evaluate the overall framework experimentally and compare it with three human operators. The results show that our algorithm can determine the direction of wrinkles on the cloth accurately in simulation as well as in real robot experiments. Furthermore, our dewrinkling strategy compares favorably to baseline methods. The experiment video is available on https://sites.google.com/view/robotic-fabric-flattening/home

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arXiv2023

The Teenager's Problem: Efficient Garment Decluttering as Probabilistic Set Cover

This paper addresses the "Teenager's Problem": efficiently removing scattered garments from a planar surface into a basket. As grasping and transporting individual garments is highly inefficient, we propose policies to select grasp locations for multiple garments using an overhead camera. Our core approach is segment-based, which uses segmentation on the overhead RGB image of the scene. We propose a Probabilistic Set Cover formulation of the problem, aiming to minimize the number of grasps that clear all garments off the surface. Grasp efficiency is measured by Objects per Transport (OpT), which denotes the average number of objects removed per trip to the laundry basket. Additionally, we explore several depth-based methods, which use overhead depth data to find efficient grasps. Experiments suggest that our segment-based method increases OpT by $50\%$ over a random baseline, whereas combined hybrid methods yield improvements of $33\%$. Finally, a method employing consolidation (with segmentation) is considered, which locally moves the garments on the work surface to increase OpT, when the distance to the basket is much greater than the local motion distances. This yields an improvement of $81\%$ over the baseline.

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arXiv2023

Prompt-to-afterglow transition of optical emission in a long gamma-ray burst consistent with a fireball

Long gamma-ray bursts (GRBs), which signify the end-life collapsing of very massive stars, are produced by extremely relativistic jets colliding into circumstellar medium. Huge energy is released both in the first few seconds, namely the internal dissipation phase that powers prompt emissions, and in the subsequent self-similar jet-deceleration phase that produces afterglows observed in broad-band electromagnetic spectrum. However, prompt optical emissions of GRBs have been rarely detected, seriously limiting our understanding of the transition between the two phases. Here we report detection of prompt optical emissions from a gamma-ray burst (i.e. GRB 201223A) using a dedicated telescope array with a high temporal resolution and a wide time coverage. The early phase coincident with prompt γ-ray emissions show a luminosity in great excess with respect to the extrapolation of γ-rays, while the later luminosity bump is consistent with onset of the afterglow. The clearly detected transition allows us to differentiate physical processes contributing to early optical emissions and to diagnose the composition of the jet

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arXiv2021

An Automatic Observation Management System of the GWAC Network I: System Architecture and Workflow

The GWAC-N is an observation network composed of multi-aperture and multi-field of view robotic optical telescopes. The main instruments are the GWAC-A. Besides, several robotic optical telescopes with narrower field of views provide fast follow-up multi-band capabilities to the GWAC-N. The primary scientific goal of the GWAC-N is to search for the optical counterparts of GRB that will be detected by the SVOM. The GWAC-N performs many other observing tasks including the follow-ups of ToO and both the detection and the monitoring of variable/periodic objects as well as optical transients. To handle all of those scientific cases, we designed 10 observation modes and 175 observation strategies, especially, a joint observation strategy with multiple telescopes of the GWAC-N for the follow-up of GW events. To perform these observations, we thus develop an AOM system in charge of the object management, the dynamic scheduling of the observation plan and its automatic broadcasting to the network management and finally the image management. The AOM combines the individual telescopes into a network and smoothly organizes all the associated operations. The system completely meets the requirements of the GWAC-N on all its science objectives. With its good portability, the AOM is scientifically and technically qualified for other general purposed telescope networks. As the GWAC-N extends and evolves, the AOM will greatly enhance the discovery potential for the GWAC-N. In the first paper of a series of publications, we present the scientific goals of the GWAC-N as well as the hardware, the software and the strategy setup to achieve the scientific objectives. The structure, the technical design, the implementation and performances of the AOM will be also described in details. In the end, we summarize the current status of the GWAC-N and prospect for the development plan in the near future.

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arXiv2020

The GWAC Data Processing and Management System

GWAC will have been built an integrated FOV of 5,000 $degree^2$ and have already built 1,800 square $degree^2$. The limit magnitude of a 10-second exposure image in the moonless night is 16R. In each observation night, GWAC produces about 0.7TB of raw data, and the data processing pipeline generates millions of single frame alerts. We describe the GWAC Data Processing and Management System (GPMS), including hardware architecture, database, detection-filtering-validation of transient candidates, data archiving, and user interfaces for the check of transient and the monitor of the system. GPMS combines general technology and software in astronomy and computer field, and use some advanced technologies such as deep learning. Practical results show that GPMS can fully meet the scientific data processing requirement of GWAC. It can online accomplish the detection, filtering and validation of millions of transient candidates, and feedback the final results to the astronomer in real-time. During the observation from October of 2018 to December of 2019, we have already found 102 transients.

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arXiv2020

A Real-time Automatic Validation System for Optical Transients detected by GWAC

The ground-based wide-angle camera array (GWAC) generates millions of single frame alerts per night. After the complicated and elaborate filters by multiple methods, a couple of dozens of candidates are still needed to be confirmed by follow-up observations in real-time. In order to free scientists from the complex and high-intensity follow-up tasks, we developed a Real-time Automatic transient Validation System (RAVS), and introduce here its system architecture, data processing flow, database schema, automatic follow-up control flow, and mobile message notification solution. This system is capable of automatically carrying out all operations in real-time without human intervention, including the validation of transient candidates, the adaptive light-curve sampling for identified targets in multi-band, and the pushing of observation results to the mobile client. The running of RAVS shows that an M-type stellar flare event can be well sampled by RAVS without a significant loss of the details, while the observing time is only less than one-third of the time coverage. Because the control logic of RAVS is designed to be independent of the telescope hardware, RAVS can be conveniently transplanted to other telescopes, especially the follow-up system of SVOM. Some future improvements are presented for the adaptive light-curve sampling, after taking into account both the brightness of sources and the evolution trends of the corresponding light-curves.

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arXiv2016

Perspectives on Gamma-Ray Burst Physics and Cosmology with Next Generation Facilities

High-redshift Gamma-Ray Bursts (GRBs) beyond redshift $\sim6$ are potentially powerful tools to probe the distant early Universe. Their detections in large numbers and at truly high redshifts call for the next generation of high-energy wide-field instruments with unprecedented sensitivity at least one order of magnitude higher than the ones currently in orbit. On the other hand, follow-up observations of the afterglows of high-redshift GRBs and identification of their host galaxies, which would be difficult for the currently operating telescopes, require new, extremely large facilities of at multi-wavelengths. This chapter describes future experiments that are expected to advance this exciting field, both being currently built and being proposed. The legacy of Swift will be continued by SVOM, which is equipped with a set of space-based multi-wavelength instruments as well as and a ground segment including a wide angle camera and two follow-up telescopes. The established Lobster-eye X-ray focusing optics provides a promising technology for the detection of faint GRBs at very large distances, based on which the {THESEUS}, {Einstein Probe} and other mission concepts have been proposed. Follow-up observations and exploration of the reionization era will be enabled by large facilities such as {SKA} in the radio, the 30m class telescopes in the optical/near-IR, and the space-borne {WFIRST} and {JWST} in the optical/near-IR/mid-IR. In addition, the X-ray and $γ$-ray polarization experiment POLAR is also introduced.

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arXiv2011

The Most Slowly Declining Type Ia Supernova 2001ay

We present optical and near-infrared photometry, as well as ground-based optical spectra and Hubble Space Telescope ultraviolet spectra, of the Type Ia supernova (SN) 2001ay. At maximum light the Si II and Mg II lines indicated expansion velocities of 14,000 km/sec, while Si III and S II showed velocities of 9,000 km/sec There is also evidence for some unburned carbon at 12,000 km/sec. SN 2001ay exhibited a decline-rate parameter Delta m_15(B) = 0.68 \pm 0.05 mag; this and the B-band photometry at t > +25 d past maximum make it the most slowly declining Type Ia SN yet discovered. Three of four super-Chandrasekhar-mass candidates have decline rates almost as slow as this. After correction for Galactic and host-galaxy extinction, SN 2001ay had M_B = -19.19 and M_V = -19.17 mag at maximum light; thus, it was not overluminous in optical bands. In near-infrared bands it was overluminous only at the 2-sigma level at most. For a rise time of 18 d (explosion to bolometric maximum) the implied Ni-56 yield was (0.58 \pm 0.15)/alpha M_Sun, with alpha = L_max/E_Ni probably in the range 1.0 to 1.2. The Ni-56 yield is comparable to that of many Type Ia supernovae. The "normal" Ni-56 yield and the typical peak optical brightness suggest that the very broad optical light curve is explained by the trapping of the gamma rays in the inner regions.

astro-ph.CO↗

arXiv2010

Probing the Nature of High-z Short GRB 090426 with Its Early Optical and X-ray Afterglows

GRB 090426 is a short duration burst detected by Swift ($T_{90}\sim 1.28$ s in the observer frame, and $T_{90}\sim 0.33$ s in the burst frame at $z=2.609$). Its host galaxy properties and some $γ$-ray related correlations are analogous to those seen in long duration GRBs, which are believed to be of a massive-star origin (so-called Type II GRBs). We present the results of its early optical observations with the 0.8-m TNT telescope at Xinglong observatory, and the 1-m LOAO telescope at Mt. Lemmon Optical Astronomy Observatory in Arizona. Our well-sampled optical afterglow lightcurve covers from $\sim 90$ seconds to $\sim 10^4$ seconds post the GRB trigger. It shows two shallow decay episodes that are likely due to energy injection, which end at $\sim 230$ seconds and $\sim 7100$ seconds, respectively. The decay slopes post the injection phases are consistent with each other ($α\simeq 1.22$). The X-ray afterglow lightcurve appears to trace the optical, although the second energy injection phase was missed due to visibility constraints introduced by the {\em Swift} orbit. The X-ray spectral index is $β_X\sim 1.0$ without temporal evolution. Its decay slope is consistent with the prediction of the forward shock model. Both X-ray and optical emission is consistent with being in the same spectral regime above the cooling frequency ($ν_c$). The fact that $ν_c$ is below the optical band from the very early epoch of the observation provides a constraint on the burst environment, which is similar to that seen in classical long duration GRBs. We therefore suggest that death of a massive star is the possible progenitor of this short burst.

astro-ph.HE↗

arXiv2009

Swifts GRB GRB071010B : outlier of the $\rm E^{src}_{peak} - E_γ$ and ${\rm E_{iso}-E^{src}_{peak}-t^{src}_{jet}}$ correlations

We present multi-band results for GRB071010B based on \Swift, \Suzaku, and ground-based optical observations. This burst is an ideal target to evaluate the robustness of the ${\rm E^{src}_{peak}-E_{iso}}$ and ${\rm E^{src}_{peak}-E_γ}$ relations, whose studies have been in stagnation due to the lack of the combined estimation of $\rm E^{src}_{peak}$ and long term optical monitoring. The joint prompt spectral fitting using \Swift/Burst Alert Telescope and \Suzaku/Wide-band All sky Monitor data yielded the spectral peak energy as E$^{src}_{peak}$ of $86.5^{+6.4}_{-6.3}$ keV and E$_{iso}$ of $2.25^{+0.19}_{-0.16}\times10^{52}$ erg with $z=0.947$. The optical afterglow light curve is well fitted by a simple power law with temporal index $α=-0.60\pm0.02$. The lower limit of temporal break in the optical light curve is 9.8 days. Our multi-wavelength analysis reveals that GRB071010B follows ${\rm E^{src}_{peak}-E_{iso}}$ but violates the ${\rm E^{src}_{peak}-E_γ}$ and ${\rm E_{iso}-E^{src}_{peak}-t^{src}_{jet}}$ at more than the 3$σ$ level.

astro-ph.CO↗

arXiv2008

The Rapidly Flaring Afterglow of the Very Bright and Energetic GRB 070125

We report on multi-wavelength observations, ranging from the X-ray to radio wave bands, of the IPN-localized gamma-ray burst GRB 070125. Spectroscopic observations reveal the presence of absorption lines due to O I, Si II, and C IV, implying a likely redshift of z = 1.547. The well-sampled light curves, in particular from 0.5 to 4 days after the burst, suggest a jet break at 3.7 days, corresponding to a jet opening angle of ~7.0 degrees, and implying an intrinsic GRB energy in the 1 - 10,000 keV band of around E = (6.3 - 6.9)x 10^(51) erg (based on the fluences measured by the gamma-ray detectors of the IPN network). GRB 070125 is among the brightest afterglows observed to date. The spectral energy distribution implies a host extinction of Av < 0.9 mag. Two rebrightening episodes are observed, one with excellent time coverage, showing an increase in flux of 56% in ~8000 seconds. The evolution of the afterglow light curve is achromatic at all times. Late-time observations of the afterglow do not show evidence for emission from an underlying host galaxy or supernova. Any host galaxy would be subluminous, consistent with current GRB host-galaxy samples. Evidence for strong Mg II absorption features is not found, which is perhaps surprising in view of the relatively high redshift of this burst and the high likelihood for such features along GRB-selected lines of sight.

astro-ph↗

arXiv2007

Optical and Near-Infrared Observations of the Highly Reddened, Rapidly Expanding Type Ia Supernova 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 R_V = 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 a 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 near-infrared 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 to 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 72.7+/-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.

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arXiv2007

Testing the External Shock Model of Gamma-Ray Bursts using the Late-Time Simultaneous Optical and X-ray Afterglows

We study the ``normal'' decay phase of the X-ray afterglows of gamma-ray bursts (GRBs), which follows the shallow decay phase, using the events simultaneously observed in the R-band. The classical external shock model -- in which neither the delayed energy injection nor time-dependency of shock micro-physics is considered -- shows that the decay indices of the X-ray and R-band light curves, $α_{\rm X}$ and $α_{\rm O}$, obey a certain relation, and that in particular, $α_{\rm O}-α_{\rm X}$ should be larger than -1/4 unless the ambient density increases with the distance from the central engine. For our selected 14 samples, we have found that 4 events violate the limit at more than the 3$σ$ level, so that a fraction of events are outliers of the classical external shock model at the ``normal'' decay phase.

astro-ph↗

arXiv2007

A multi band study of the optically dark GRB 051028

Observations were made of the optical afterglow of GRB 051028 with the Lulin observatory's 1.0 m telescope and the WIDGET robotic telescope system. R band photometric data points were obtained on 2005 October 28 (UT), or 0.095-0.180 days after the burst. There is a possible plateau in the optical light curve around 0.1 days after the burst; the light curve resembles optically bright afterglows (e.g. GRB 041006, GRB 050319, GRB060605) in shape of the light curve but not in brightness. The brightness of the GRB 051028 afterglow is 3 magnitudes fainter than that of one of the dark events, GRB 020124. Optically dark GRBs have been attributed to dust extinction within the host galaxy or high redshift. However, the spectrum analysis of the X-rays implies that there is no significant absorption by the host galaxy. Furthermore, according to the model theoretical calculation of the Ly$α$ absorption to find the limit of GRB 051028's redshift, the expected $R$ band absorption is not high enough to explain the darkness of the afterglow. While the present results disfavor either the high-redshift hypothesis or the high extinction scenario for optically dark bursts, they are consistent with the possibility that the brightness of the optical afterglow, intrinsically dark.

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arXiv2003

Optical and Infrared Photometry of the Nearby Type Ia Supernovae 1999ee, 2000bh, 2000ca, and 2001ba

We present near infrared photometry of the Type Ia supernova 1999ee; also, optical and infrared photometry of the Type Ia SNe 2000bh, 2000ca, and 2001ba. For SNe 1999ee and 2000bh we present the first-ever SN photometry at 1.035 microns (the Y-band). We present K-corrections which transform the infrared photometry in the observer's frame to the supernova rest frame. Using our infrared K-corrections and stretch factors derived from optical photometry, we construct JHK templates which can be used to determine the apparent magnitudes at maximum if one has some data in the window -12 to +10 d with respect to T(B_max). Following up previous work on the uniformity of V minus IR loci of Type Ia supernovae of mid-range decline rates, we present unreddened loci for slow decliners. We also discuss evidence for a continuous change of color at a given epoch as a function of decline rate.

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arXiv2002

A Hubble Space Telescope Snapshot Survey of Nearby Supernovae

We present photometry of 12 recent supernovae (SNe) recovered in a {\it Hubble Space Telescope} Snapshot program, and tie the measurements to earlier ground-based observations, in order to study the late-time evolution of the SNe. Many of the ground-based measurements are previously unpublished, and were made primarily with a robotic telescope, the Katzman Automatic Imaging Telescope. Evidence for circumstellar interaction is common among the core-collapse SNe. Late-time decline rates for Type IIn SNe are found to span a wide range, perhaps due to differences in circumstellar interaction. An extreme case, SN IIn 1995N, declined by only 1.2 mag in $V$ over about 4 years following discovery. Template images of some SNe must therefore be obtained many years after the explosion, if contamination from the SN itself is to be minimized. Evidence is found against a previous hypothesis that the Type IIn SN 1997bs was actually a superoutburst of a luminous blue variable star. The peculiar SN Ic 1997ef, a "hypernova," declined very slowly at late times. The decline rate of the SN Ia 2000cx decreased at late times, but this is unlikely to have been caused by a light echo.

astro-ph↗

arXiv2001

Spectrum Analysis of Type IIb Supernova 1996cb

We analyze a time series of optical spectra of SN 1993J-like supernova 1996cb, from 14 days before maximum to 86 days after that, with a parameterized supernova synthetic-spectrum code SYNOW. Detailed line identification are made through fitting the synthetic spectra to observed ones. The derived photospheric velocity, decreasing from 11,000 km/s to 3,000 km/s, gives a rough estimate of the ratio of explosion kinetic energy to ejecta mass, i.e. E/M_ej \sim 0.2-0.5 \times 10^51 ergs / M_ej(M_\sun). We find that the minimum velocity of hydrogen is about 10,000 km/s, which suggests a small hydrogen envelope mass of \sim 0.02-0.1 M_ej, or 0.1-0.2 M_\sun if E is assumed 1 \times 10^51 ergs. A possible Ni II absorption feature near 4000 Åis identified throughout the epochs studied here and is most likely produced by primordial nickel. Unambiguous Co II features emerge from 16 days after maximum onward, which suggests that freshly synthesized radioactive material has been mixed outward to a velocity of at least 7,000 km/s as a result of hydrodynamical instabilities. Although our synthetic spectra show that the bulk of the blueshift of [O I] 5577 net emission, as large as \sim 70 Åat 9 days after maximum, is attributed to line blending, a still considerable residual \sim 20 Åremains till the late phase. It may be evidence of clumpy or large-scale asymmetric nature of oxygen emission region.

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