In the era of large photometric surveys, the importance of automated and accurate classification is rapidly increasing. Specifically, the separation of resolved and unresolved sources in astronomical ...imaging is a critical initial step for a wide array of studies, ranging from Galactic science to large scale structure and cosmology. Here, we present our method to construct a large, deep catalog of point sources utilizing Pan-STARRS1 (PS1) 3π survey data, which consists of ∼3 × 109 sources with m 23.5 mag. We develop a supervised machine-learning methodology, using the random forest (RF) algorithm, to construct the PS1 morphology model. We train the model using ∼5 × 104 PS1 sources with HST COSMOS morphological classifications and assess its performance using ∼4 × 106 sources with Sloan Digital Sky Survey (SDSS) spectra and ∼2 × 108 Gaia sources. We construct 11 "white flux" features, which combine PS1 flux and shape measurements across five filters, to increase the signal-to-noise ratio relative to any individual filter. The RF model is compared to three alternative models, including the SDSS and PS1 photometric classification models, and we find that the RF model performs best. By number the PS1 catalog is dominated by faint sources (m 21 mag), and in this regime the RF model significantly outperforms the SDSS and PS1 models. For time-domain surveys, identifying unresolved sources is crucial for inferring the Galactic or extragalactic origin of new transients. We have classified ∼1.5 × 109 sources using the RF model, and these results are used within the Zwicky Transient Facility real-time pipeline to automatically reject stellar sources from the extragalactic alert stream.
Thin-film electronics intimately laminated onto the skin imperceptibly equip the human body with electronic components for health-monitoring and information technologies. When electronic devices are ...worn, the mechanical flexibility and/or stretchability of thin-film devices helps to minimize the stress and discomfort associated with wear because of their conformability and softness. For industrial applications, it is important to fabricate wearable devices using processing methods that maximize throughput and minimize cost. We demonstrate ultraflexible and conformable three-color, highly efficient polymer light-emitting diodes (PLEDs) and organic photodetectors (OPDs) to realize optoelectronic skins (oe-skins) that introduce multiple electronic functionalities such as sensing and displays on the surface of human skin. The total thickness of the devices, including the substrate and encapsulation layer, is only 3 μm, which is one order of magnitude thinner than the epidermal layer of human skin. By integrating green and red PLEDs with OPDs, we fabricate an ultraflexible reflective pulse oximeter. The device unobtrusively measures the oxygen concentration of blood when laminated on a finger. On-skin seven-segment digital displays and color indicators can visualize data directly on the body.
Deep Modeling of Quasar Variability Tachibana, Yutaro; Graham, Matthew J.; Kawai, Nobuyuki ...
The Astrophysical journal,
11/2020, Letnik:
903, Številka:
1
Journal Article
Recenzirano
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Quasars have long been known as intrinsically variable sources, but the physical mechanism underlying the temporal optical/UV variability is still not well understood. We propose a novel ...nonparametric method for modeling and forecasting the optical variability of quasars utilizing an AE neural network to gain insight into the underlying processes. The AE is trained with ∼15,000 decade-long quasar light curves obtained by the Catalina Real-time Transient Survey selected with negligible flux contamination from the host galaxy. The AE's performance in forecasting the temporal flux variation of quasars is superior to that of the damped random walk process. We find a temporal asymmetry in the optical variability and a novel relation-the amplitude of the variability asymmetry decreases as luminosity and/or black hole mass increases-is suggested with the help of autoencoded features. The characteristics of the variability asymmetry are in agreement with those from the self-organized disk instability model, which predicts that the magnitude of the variability asymmetry decreases as the ratio of the diffusion mass to inflow mass in the accretion disk increases.
Organic electronic devices implemented on flexible thin films are attracting increased attention for biomedical applications because they possess extraordinary conformity to curved surfaces. A ...neuronal device equipped with an organic light-emitting diode (OLED), used in combination with animals that are genetically engineered to include a light-gated ion channel, would enable cell type-specific stimulation to neurons as well as conformal contact to brain tissue and peripheral soft tissue. This potential application of the OLEDs requires strong luminescence, well over the neuronal excitation threshold in addition to flexibility. Compatibility with neuroimaging techniques such as MRI provides a method to investigate the evoked activities in the whole brain. Here, we developed an ultrathin, flexible, MRI-compatible OLED device and demonstrated the activation of channelrhodopsin-2–expressing neurons in animals. Optical stimulation from the OLED attached to nerve fibers induced contractions in the innervated muscles. Mechanical damage to the tissues was significantly reduced because of the flexibility. Owing to the MRI compatibility, neuronal activities induced by direct optical stimulation of the brain were visualized using MRI. The OLED provides an optical interface for modulating the activity of soft neuronal tissues.
Machine Learning for the Zwicky Transient Facility Mahabal, Ashish; Rebbapragada, Umaa; Walters, Richard ...
Publications of the Astronomical Society of the Pacific,
03/2019, Letnik:
131, Številka:
997
Journal Article
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The Zwicky Transient Facility is a large optical survey in multiple filters producing hundreds of thousands of transient alerts per night. We describe here various machine learning (ML) ...implementations and plans to make the maximal use of the large data set by taking advantage of the temporal nature of the data, and further combining it with other data sets. We start with the initial steps of separating bogus candidates from real ones, separating stars and galaxies, and go on to the classification of real objects into various classes. Besides the usual methods (e.g., based on features extracted from light curves) we also describe early plans for alternate methods including the use of domain adaptation, and deep learning. In a similar fashion we describe efforts to detect fast moving asteroids. We also describe the use of the Zooniverse platform for helping with classifications through the creation of training samples, and active learning. Finally we mention the synergistic aspects of ZTF and LSST from the ML perspective.
We present detailed observations of ZTF18abukavn (SN2018gep), discovered in high-cadence data from the Zwicky Transient Facility as a rapidly rising (1.4 0.1 mag hr−1) and luminous ( mag) transient. ...It is spectroscopically classified as a broad-lined stripped-envelope supernova (Ic-BL SN). The high peak luminosity ( ), the short rise time ( in g band), and the blue colors at peak ( ) all resemble the high-redshift Ic-BL iPTF16asu, as well as several other unclassified fast transients. The early discovery of SN2018gep (within an hour of shock breakout) enabled an intensive spectroscopic campaign, including the highest-temperature ( ) spectra of a stripped-envelope SN. A retrospective search revealed luminous ( mag) emission in the days to weeks before explosion, the first definitive detection of precursor emission for a Ic-BL. We find a limit on the isotropic gamma-ray energy release , a limit on X-ray emission , and a limit on radio emission . Taken together, we find that the early ( ) data are best explained by shock breakout in a massive shell of dense circumstellar material (0.02 ) at large radii ( ) that was ejected in eruptive pre-explosion mass-loss episodes. The late-time ( ) light curve requires an additional energy source, which could be the radioactive decay of Ni-56.
We report X-ray, optical, and near-infrared monitoring of the new X-ray transient MAXI J1820+070 discovered with MAXI on 2018 March 11. Its X-ray intensity reached ∼2 crab at 2-20 keV at the end of ...March, and then gradually decreased until the middle of June. In this period, the X-ray spectrum was described by Comptonization of the disk emission, with a photon index of ∼1.5 and an electron temperature of ∼50 keV, which is consistent with a black hole X-ray binary in the low/hard state. The electron temperature was slightly decreased, and the photon index increased, with increasing flux. The source showed significant X-ray flux variation on a timescale of seconds. This short-term variation was found to be associated with changes in the spectral shape, and the photon index became slightly harder at higher fluxes. This suggests that the variation was produced by a change in the properties of the hot electron cloud responsible for the strong Comptonization. Modeling a multi-wavelength spectral energy distribution around the X-ray flux peak at the end of March, covering the near-infrared to X-ray bands, we found that the optical and near-infrared fluxes were likely contributed substantially by the jet emission. Before this outburst, the source was never detected in the X-ray band with MAXI (with a 3 upper limit of ∼0.2 mcrab at 4-10 keV, obtained from seven years of data from 2009 to 2016), whereas weak optical and infrared activity was found at flux levels ∼3 orders of magnitude lower than the peak fluxes in the outburst.
ABSTRACT A bright long gamma-ray burst GRB 141207A was observed by the Fermi Gamma-ray Space Telescope and detected by both instruments onboard. The observations show that the spectrum in the prompt ...phase is not well described by the canonical empirical Band function alone, and that an additional power-law component is needed. In the early phase of the prompt emission, a modified blackbody with a hard low-energy photon index ( = +0.2 to +0.4) is detected, which suggests a photospheric origin. In a finely time-resolved analysis, the spectra are also well fitted by the modified blackbody combined with a power-law function. We discuss the physical parameters of the photosphere such as the bulk Lorentz factor of the relativistic flow and the radius. We also discuss the physical origin of the extra power-law component observed during the prompt phase in the context of different models such as leptonic and hadronic scenarios in the internal shock regime and synchrotron emission in the external forward shock. In the afterglow phase, the temporal and spectral behaviors of the temporally extended high-energy emission and the fading X-ray emission detected by the X-Ray Telescope on-board Swift are consistent with synchrotron emission in a radiative external forward shock.
Abstract
We report on the X-ray spectral analysis and time evolution of GRS 1739−278 during its 2014 outburst, based on MAXI/GSC and Swift/XRT observations. Over the course of the outburst, a ...transition from the low/hard state to the high/soft state and then back to the low/hard state was seen. During the high/soft state, the innermost disk temperature mildly decreased, while the innermost radius estimated with the multi-color disk model remained constant at ∼18 (D/8.5 kpc)(cos i/cos 30°)−1/2 km, where D is the source distance and i is the inclination of observation. This small innermost radius of the accretion disk suggests that the central object is more likely to be a Kerr black hole rather than a Schwardzschild black hole. Applying a relativistic disk emission model to the high/soft state spectra, a mass upper limit of 18.3 M⊙ was obtained based on the inclination limit i < 60° for an assumed distance of 8.5 kpc. Using the empirical relation of the transition luminosity to the Eddington limit, the mass is constrained to 4.0–18.3 M⊙ for the same distance. The mass can be further constrained to be no larger than 9.5 M⊙ by adopting the constraints based on the fits to the NuSTAR spectra with relativistically blurred disk reflection models (Miller et al. 2015, ApJ, 799, L6).
We report on the detection and follow-up multi-wavelength observations of the new X-ray transient MAXI J1807+132 with the MAXI/GSC, Swift, and ground-based optical telescopes. The source was first ...recognized with the MAXI/GSC on 2017 March 13. About a week later, it reached maximum intensity (∼10 mCrab in 2-10 keV), and then gradually faded in ∼10 days by more than one order of magnitude. Time-averaged Swift/X-ray Telescope spectra in the decaying phase can be described by a blackbody with a relatively low temperature (0.1-0.5 keV), plus a hard power-law component with a photon index of ∼2. These spectral properties are similar to those of neutron star low-mass X-ray binaries (LMXBs) in their dim periods. The blackbody temperature and the radius of the emission region varied in a complex manner as the source became dimmer. The source was detected in the optical wavelength on March 27-31 as well. The optical flux decreased monotonically as the X-ray flux decayed. The correlation between the X-ray and optical fluxes is found to be consistent with those of known neutron star LMXBs, supporting the idea that the source is likely to be a transient neutron star LMXB.
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