Detection of persistent gamma-ray emission toward SS433/W50

The microquasar SS433 features the most energetic jets known in our Galaxy. A large fraction of the jet kinetic power is delivered to the surrounding W50 nebula at the jet termination shock, from which high-energy emission and cosmic-ray production have been anticipated. Here we report on the detection of a persistent gamma-ray signal from the direction of SS433/W50 with the Fermi Large Area Telescope. The steady flux and a narrow spectral energy distribution with a maximum around 250 MeV suggest that gamma-rays are rendered by the bulk jet kinetic power through proton-proton collisions at the SS433/W50 interaction regions. If the same mechanism is operating in other baryon-loaded microquasar jets, their collective contribution may represent a significant fraction of the total galactic cosmic-ray flux at GeV energies.Comment: Accepted for publication in ApJ

Massive Stars as Major Factories of Galactic Cosmic Rays

The identification of major contributors to the locally observed fluxes of Cosmic Rays (CRs) is a prime objective towards the resolution of the long-standing enigma of CRs. We report on a compelling similarity of the energy and radial distributions of multi-TeV CRs extracted from observations of very high energy (VHE) $\gamma$-rays towards the Galactic Center (GC) and two prominent clusters of young massive stars, Cyg~OB2 and Westerlund~1. This resemblance we interpret as a hint that CRs responsible for the diffuse VHE $\gamma$-ray emission from the GC are accelerated by the ultracompact stellar clusters located in the heart of GC. The derived $1/r$ decrement of the CR density with the distance from a star cluster is a distinct signature of continuous, over a few million years, CR injection into the interstellar medium. The lack of brightening of the $\gamma$-ray images toward the stellar clusters excludes the leptonic origin of $\gamma$-radiation. The hard, $\propto E^{-2.3}$ type power-law energy spectra of parent protons continues up to $\sim$ 1 PeV. The efficiency of conversion of kinetic energy of stellar winds to CRs can be as high as 10 percent implying that the young massive stars may operate as proton PeVatrons with a dominant contribution to the flux of highest energy galactic CRs.Comment: minor revisions have been applied to address the referees' comments, conclusion unchange

High-resolution, large field-of-view label-free imaging via aberration-corrected, closed-form complex field reconstruction

Computational imaging methods empower modern microscopy with the ability of producing high-resolution, large field-of-view, aberration-free images. One of the dominant computational label-free imaging methods, Fourier ptychographic microscopy (FPM), effectively increases the spatial-bandwidth product of conventional microscopy by using multiple tilted illuminations to achieve high-throughput imaging. However, its iterative reconstruction method is prone to parameter selection, can be computationally expensive and tends to fail under excessive aberrations. Recently, spatial Kramers-Kronig methods show it is possible to analytically reconstruct complex field but lacks the ability of correcting aberrations or providing extended resolution enhancement. Here, we present a closed-form method, termed APIC, which weds the strengths of both methods. A new analytical phase retrieval framework is established in APIC, which demonstrates, for the first time, the feasibility of analytically reconstructing the complex field associated with darkfield measurements. In addition, APIC can analytically retrieve complex aberrations of an imaging system with no additional hardware. By avoiding iterative algorithms, APIC requires no human designed convergence metric and always obtains a closed-form complex field solution. The faithfulness and correctness of APIC's reconstruction are guaranteed due to its analytical nature. We experimentally demonstrate that APIC gives correct reconstruction result while FPM fails to do so when constrained to the same number of measurements. Meanwhile, APIC achieves 2.8 times faster computation using image tile size of 256 (length-wise). We also demonstrate APIC is unprecedentedly robust against aberrations compared to FPM - APIC is capable of addressing aberration whose maximal phase difference exceeds 3.8${\pi}$ when using a NA 0.25 objective in experiment.Comment: 13 pages, 5 figure

Diffuse gamma-ray emission around the Rosette Nebula

The Rosette Nebula is a young stellar cluster and molecular cloud complex, located at the edge of the southern shell of a middle-aged SNR Monoceros Loop (G205.5+0.5). We revisited the GeV gamma-ray emission towards the Rosette Nebula using more than 13 years of Fermi-LAT data. We tested several spatial models and found that compared to the result using the CO gas template only, the inclusion of the HII gas template can significantly improve the likelihood fit. We performed spectral analysis using the new spatial template. With both the gamma-ray observation and CO+HII gas data, we derived the cosmic ray spectrum of different components in the vicinity of the Rosette Nebula. We found the gamma-ray emissions from Rosette Nebula are substantially harder than previously reported, which may imply that Rosette Nebula is another example of a gamma-ray emitting young massive star cluster.Comment: 6 pages, 5 figures, published in MNRA

Cross-Channel Integration and Customer Retention in Omnichannel Retailing: The Role of Retailer Image and Alternative Attractiveness

Cross-channel integration (CCI) is increasingly considered as an important driver of customer retention in omnichannel retailing. However, the existing findings about the relationship between CCI and customer retention are contradictory, wherein both positive and non-significant findings exist. This study aims to explore the contingency role of retailer image and alternative attractiveness for the above relationship. Specifically, both two-way and three-way interaction effects of retailer image and alternative attractiveness were tested. Our survey finding confirmed the positive relationship between CCI and customer retention. We also found that the positive relationship was negatively moderated by retailer image, while positively moderated by alternative attractiveness. This study further uncovered that alternative attractiveness can weaken the negative moderating effect of retailer image. Implications and limitations of the study are discussed

Analysis of the Gravitational Wave Background Using Gamma-Ray Pulsar Timing Arrays with Next-Generation Detectors

In this work, we investigate the potential of gamma-ray pulsar time array (PTA) on gravitational waves background (GWB) using future gamma-ray detectors with larger effective areas. We consider both spaceborne detectors and ground-based imaging air Cherenkov telescope arrays (IACTs). We simulated the detected photons from pulsars using the response of hypothetical detectors taking into account the backgrounds and analyzed the sensitivities. Our results showed that thanks to the higher statistics of IACTs, the PTA using IACTs can improve significantly the performance compared with the PTA using Fermi-LAT data.Comment: 6 pages, 5 figures, Accepted for publication in PR