Brief comment: Dicke Superradiance and Superfluorescence Find Application for Remote Sensing in Air

This letter briefly introduces the concepts of Dicke superradiance (SR) and superfluorescence (SF), their difference to amplified spontaneous emission (ASE), and the hints for identifying them in experiment. As a typical example it analyzes the latest observations by Dogariu et al. (Science 331, 442, 2011), and clarifies that it is SR. It also highlights the revealed potential significant application of SR and SF for remote sensing in air.Comment: 1.5 pages, 1 illustration figure, manuscript finished in March 2011, declined by two journal

Selection and Estimation Optimality in High Dimensions with the TWIN Penalty

We introduce a novel class of variable selection penalties called TWIN, which provides sensible data-adaptive penalization. Under a linear sparsity regime and random Gaussian designs we show that penalties in the TWIN class have a high probability of selecting the correct model and furthermore result in minimax optimal estimators. The general shape of penalty functions in the TWIN class is the key ingredient to its desirable properties and results in improved theoretical and empirical performance over existing penalties. In this work we introduce two examples of TWIN penalties that admit simple and efficient coordinate descent algorithms, making TWIN practical in large data settings. We demonstrate in challenging and realistic simulation settings with high correlations between active and inactive variables that TWIN has high power in variable selection while controlling the number of false discoveries, outperforming standard penalties

Constraining Parameters in Pulsar Models of Repeating FRB 121102 with High-Energy Follow-up Observations

Recently, a precise (sub-arcsecond) localization of the repeating fast radio burst (FRB) 121102 has led to the discovery of persistent radio and optical counterparts, the identification of a host dwarf galaxy at a redshift of $z=0.193$, and several campaigns of searches for higher-frequency counterparts, which gave only upper limits on the emission flux. Although the origin of FRBs remains unknown, most of the existing theoretical models are associated with pulsars, or more specifically, magnetars. In this paper, we explore persistent high-energy emission from a rapidly rotating highly magnetized pulsar associated with FRB 121102 if internal gradual magnetic dissipation occurs in the pulsar wind. We find that the efficiency of converting the spin-down luminosity to the high-energy (e.g., X-ray) luminosity is generally much smaller than unity, even for a millisecond magnetar. This provides an explanation for the non-detection of high-energy counterparts to FRB 121102. We further constrain the spin period and surface magnetic field strength of the pulsar with the current high-energy observations. In addition, we compare our results with the constraints given by the other methods in previous works and would expect to apply our new method to some other open issues in the future.Comment: 6 pages, 5 figures, ApJ in press, minor changes due to proof correction

Neutrino Emission in Jet Propagation Process

Relativistic jets are universal in long-duration gamma-ray burst (GRB) models. Before breaking out, they must propagate in the progenitor envelope along with a forward shock and a reverse shock forming at the jet head. Both electrons and protons will be accelerated by the shocks. High energy neutrinos could be produced by these protons interacting with stellar materials and electron-radiating photons. The jet will probably be collimated, which may have a strong effect on the final neutrino flux. Under the assumption of a power-law stellar-envelope density profile $\rho \propto r^{-\alpha}$ with an index $\alpha$, we calculate this neutrino emission flux by these shocks for low-luminosity GRBs (LL-GRBs) and ultra-long GRBs (UL-GRBs) in different collimation regimes, using the jet propagation framework developed by \citet{bro11}. We find that LL-GRBs and UL-GRBs are capable for detectable high energy neutrinos up to $\sim {\rm PeV}$, and obtain the final neutrino spectrum. Besides, we conclude that larger $\alpha$ corresponds to greater neutrino flux at high energy end ($\sim {\rm PeV}$) and higher maximum neutrino energy as well. However, such differences are so small that it is not promising for us to distinguish from observations, given the energy resolution we have now.Comment: 21 pages, 4 figures, accepted for publication in Ap

TeV-PeV Neutrino Oscillation of Low-luminosity Gamma-ray Bursts

There is a sign that long-duration gamma-ray bursts (GRBs) originate from the core collapse of massive stars. During a jet puncturing through the progenitor envelope, high energy neutrinos can be produced by the reverse shock formed at the jet head. It is suggested that low-luminosity GRBs (LL-GRBs) are possible candidates of this high energy neutrino precursor up to $\sim {\rm PeV}$. Before leaving the progenitor, these high energy neutrinos must oscillate from one flavor to another with matter effect in the envelope. Under the assumption of a power-law stellar envelope density profile $\rho \propto r^{-\alpha}$ with an index $\alpha$, we study the properties of ${\rm TeV-PeV}$ neutrino oscillation. We find that adiabatic conversion is violated for these neutrinos so we do certain calibration of level crossing effect. The resonance condition is reached for different energies at different radii. We notice that the effective mixing angles in matter for ${\rm PeV}$ neutrinos are close to zero so the transition probabilities from one flavor to another are almost invariant for ${\rm PeV}$ neutrinos. We plot all the transition probabilities versus energy of ${\rm TeV-PeV}$ neutrinos from the birth place to the surface of the progenitor. With an initial flavor ratio $\phi_{\nu_e}^0:\phi_{\nu_\mu}^0:\phi_{\nu_\tau}^0=1:2:0$, we plot how the flavor ratio evolves with energy and distance when neutrinos are still in the envelope, and further get the ratio when they reach the Earth. For ${\rm PeV}$ neutrinos, the ratio is always $\phi_{\nu_e}:\phi_{\nu_\mu}:\phi_{\nu_\tau}\simeq0.30:0.37:0.33$ on Earth. In addition, we discuss the dependence of the flavor ratio on energy and $\alpha$ and get a pretty good result. This dependence may provide a promising probe of the progenitor structure.Comment: 18 pages, 7 figures, accepted for publication in Ap

Production of the Extreme-Ultraviolet Late Phase of an X Class Flare in a Three-Stage Magnetic Reconnection Process

We report observations of an X class flare on 2011 September 6 by the instruments onboard the Solar Dynamics Observatory (SDO). The flare occurs in a complex active region with multiple polarities. The Extreme-Ultraviolet (EUV) Variability Experiment (EVE) observations in the warm coronal emission reveal three enhancements, of which the third one corresponds to an EUV late phase. The three enhancements have a one-to-one correspondence to the three stages in flare evolution identified by the spatially-resolved Atmospheric Imaging Assembly (AIA) observations, which are characterized by a flux rope eruption, a moderate filament ejection, and the appearance of EUV late phase loops, respectively. The EUV late phase loops are spatially and morphologically distinct from the main flare loops. Multi-channel analysis suggests the presence of a continuous but fragmented energy injection during the EUV late phase resulting in the warm corona nature of the late phase loops. Based on these observational facts, We propose a three-stage magnetic reconnection scenario to explain the flare evolution. Reconnections in different stages involve different magnetic fields but show a casual relationship between them. The EUV late phase loops are mainly produced by the least energetic magnetic reconnection in the last stage.Comment: 6 pages, 4 figures, 1 table. Accepted for Publication in ApJ

Two-dimensional Fourier-transform Spectroscopy of Potassium Vapor

Optical two-dimensional Fourier-transformed (2DFT) spectroscopy is used to study the coherent optical response of potassium vapor in a thin transmission cell. Rephasing and non-rephasing spectra of the D1 and D2 transitions are obtained and compared to numerical simulations. Calculations using the optical Bloch equations gives very good agreement with the experimental peak strengths and line shapes. Non-radiative Raman-like coherences are isolated using a different 2DFT projection. Density-dependent measurements show distortion of 2DFT spectra due to pulse propagation effects

SN2002bu -- Another SN2008S-like Transient

We observed SN2002bu in the near-IR with the Hubble Space Telescope, the mid-IR with the Spitzer Space Telescope and in X-rays with Swift 10 years after the explosion. If the faint L_H\sim100 Lsun HST near-IR source at the transient position is the near-IR counterpart of SN2002bu, then the source has dramatically faded between 2004 and 2012, from L\sim10^6.0 Lsun to L\sim10^4.5 Lsun. It is still heavily obscured, tau_V\sim5 in graphitic dust models, with almost all the energy radiated in the mid-IR. The radius of the dust emission is increasing as R\simt^(0.7+/-0.4) and the optical depth is dropping as tau_V\simt^(-1.3+/-0.4). The evolution expected for an expanding shell of material, tau_V\sim1/t^2, is ruled out at approximately 2 sigma while the tau_V\simt^(-0.8) to t^(-1) optical depth scaling for a shock passing through a pre-existing wind is consistent with the data. If the near-IR source is a chance superposition, the present day source can be moderately more luminous, significantly more obscured and evolving more slowly. While we failed to detect X-ray emission, the X-ray flux limits are consistent with the present day emissions being powered by an expanding shock wave. SN2002bu is clearly a member of the SN2008S class of transients, but continued monitoring of the evolution of the spectral energy distribution is needed to conclusively determine the nature of the transient.Comment: Submitted to Ap

Determining the locations visited by GPS users: a clustering approach

The aim of our research is to use the GPS log captured over 2 days from a PDA and try to extract locations the user have visited. For this research, we have logged GPS data over two days when the user was moving at least 2 miles per hour. To achieve this we cluster the information using data mining clustering software and then analyse the results to see which locations represent a place the user has spent his time

Can Gamma-Ray Bursts Be Used to Measure Cosmology? A Further Analysis

Three different methods of measuring cosmology with gamma-ray bursts (GRBs) have been proposed since a relation between the $\gamma$-ray energy $E_{\gamma}$ of a GRB jet and the peak energy $E_p$ of the $\nu F_{\nu}$ spectrum in the burst frame was reported by Ghirlanda and coauthors. In Method I, to calculate the probability for a favored cosmology, only the contribution of the $E_\gamma-E_p$ relation that is already best fitted for this cosmology is considered. We apply this method to a sample of 17 GRBs, and obtain the mass density $\Omega_M=0.15^{+0.45}_{-0.13}$ ($1\sigma$) for a flat $\Lambda$CDM universe. In Method II, to calculate the probability for some certain cosmology, contributions of all the possible $E_\gamma-E_p$ relations that are best fitted for their corresponding cosmologies are taken into account. With this method, we find a constraint on the mass density $0.14<\Omega_M<0.69$ ($1 \sigma$) for a flat universe. In Method III, to obtain the probability for some cosmology, contributions of all the possible $E_\gamma-E_p$ relations associated with their unequal weights are considered. With this method, we obtain an inspiring constraint on the mass density $0.16<\Omega_M<0.45$ ($1 \sigma$) for a flat universe, and a $\chi^2_{dof}=19.08/15=1.27$ for the concordance model of $\Omega_M=0.27$. (abridged)Comment: 26 pages including 6 figures, different methods compared, accepted for publication in Ap