High energy properties of the flat spectrum radio quasar 4C 50.11

We investigate the gamma-ray and X-ray properties of the flat spectrum radio quasar (FSRQ) \4c50 at redshift z= 1.517. The Fermi Large Area Telescope (LAT) data indicate that this source was in an active state since 2013 July. During the active period, the gamma-ray flux increased by more than a factor of three and two distinct flares were detected with the variability timescale as short as several hours. The gamma-ray spectra can be well fitted by a log-parabola. From the fitting, we find a correlation between the peak energy and spectral curvature for the gamma-ray spectra, which is the first time seen in gamma-ray emission from a blazar. The Swift X-ray Telescope (XRT) data show that the source was variable at X-ray energies, but no evidence shows flux or spectral changes related to the gamma-ray activity. The broad-band X-ray spectrum obtained with Swift XRT and NuSTAR is well described by a broken PL model, with an extremely hard spectrum (Γ_1 ~ 0.1) below the break energy, E_(break) ~ 2.1 keV, and Γ_2 ~ 1.5 above the break energy. The spectral steepening below ~ 3 keV is likely due to the low energy cut-off in the energy distribution of the photon-emitting electron population. Both the gamma-ray and X-ray emission appear harder when brighter. The broad-band spectral energy distribution (SED) is constructed for the source, and we provide a model fit to the SED. Our modeling suggests that the emission region should be outside the broad line region, and the properties of the region indicate a jet with 42% of the Eddington power during the active state

Open-Set Object Detection Using Classification-free Object Proposal and Instance-level Contrastive Learning with Appendix

Detecting both known and unknown objects is a fundamental skill for robot manipulation in unstructured environments. Open-set object detection (OSOD) is a promising direction to handle the problem consisting of two subtasks: objects and background separation, and open-set object classification. In this paper, we present Openset RCNN to address the challenging OSOD. To disambiguate unknown objects and background in the first subtask, we propose to use classification-free region proposal network (CF-RPN) which estimates the objectness score of each region purely using cues from object's location and shape preventing overfitting to the training categories. To identify unknown objects in the second subtask, we propose to represent them using the complementary region of known categories in a latent space which is accomplished by a prototype learning network (PLN). PLN performs instance-level contrastive learning to encode proposals to a latent space and builds a compact region centering with a prototype for each known category. Further, we note that the detection performance of unknown objects can not be unbiasedly evaluated on the situation that commonly used object detection datasets are not fully annotated. Thus, a new benchmark is introduced by reorganizing GraspNet-1billion, a robotic grasp pose detection dataset with complete annotation. Extensive experiments demonstrate the merits of our method. We finally show that our Openset RCNN can endow the robot with an open-set perception ability to support robotic rearrangement tasks in cluttered environments. More details can be found in https://sites.google.com/view/openest-rcnn/Comment: Submit to IEEE Robotics and Automation Letter

A 34.5 day quasi-periodic oscillation in gamma-ray emission from the blazar PKS 2247-131

Since 2016 October, the active galaxy PKS 2247-131 has undergone a gamma-ray outburst, which we studied using data obtained with the Fermi Gamma-ray Space Telescope. The emission arises from a relativistic jet in PKS 2247-131, as an optical spectrum only shows a few weak absorption lines, typical of the BL Lacertae sub-class of the blazar class of active galactic nuclei. Here we report a ~34.5 day quasi-periodic oscillation (QPO) in the emission after the initial flux peak of the outburst. Compared to one-year time-scale QPOs, previously identified in blazars in Fermi energies, PKS 2247-131 exhibits the first clear case of a relatively short, month-like oscillation. We show that this QPO can be explained in terms of a helical structure in the jet, where the viewing angle to the dominant emission region in the jet undergoes periodic changes. The time scale of the QPO suggests the presence of binary supermassive black holes in PKS 2247-131.Comment: 6 pages, 4 figure

Realization of corner and helical edge states in topologically trivial band gap by twig edge

The twig edge states in graphene-like structures are viewed as the fourth states complementary to their zigzag, bearded, and armchair counterparts. In this work, we study a rod-in-plasma system in honeycomb lattice with twig edges under external magnetic fields and lattice scaling and show that twig edge states can exist in different phases of the system, such as quantum Hall phase, quantum spin Hall phase and insulating phase. The twig edge states in the quantum Hall phase exhibit robust one-way transmission property immune to backscattering and thus provide a novel avenue for solving the plasma communication blackout problem. Moreover, we demonstrate that corner and edge states can exist within the trivial band gap of the insulating phase by modulating the on-site potential of the twig edges. Especially, helical edge states with the unique feature of pseudospin-momentum locking that could be exited by chiral sources are demonstrated at the twig edges within the trivial band gap. Our results show that many topological-like behaviors of electromagnetic waves are not necessarily tied to the exact topology of the systems and the twig edges and interface engineering can bring new opportunities for more flexible manipulation of electromagnetic waves