Precise Timing and Phase-resolved Spectroscopy of the Young Pulsar J1617–5055 with NuSTAR

We report on a Nuclear Spectroscopic Telescope Array (NuSTAR) observation of the young, energetic pulsar PSR J1617–5055. Parkes Observatory 3 GHz radio observations of the pulsar (taken about 7 yr before the NuSTAR observations) are also reported here. NuSTAR detected pulsations at a frequency of f ≈ 14.4 Hz (P ≈ 69.44 ms) and, in addition, the observation was long enough to measure the source’s frequency derivative, f ̇ ≈ − 2.8 × 10 − 11 Hz s−1. We find that the pulsar shows one peak per period at both hard X-ray and radio wavelengths, but that the hard X-ray pulse is broader (having a duty cycle of ∼0.7), than the radio pulse (having a duty cycle of ∼0.08). Additionally, the radio pulse is strongly linearly polarized. J1617's phase-integrated hard X-ray spectrum is well fit by an absorbed power-law model, with a photon index Γ = 1.59 ± 0.02. The hard X-ray pulsations are well described by three Fourier harmonics, and have a pulsed fraction that increases with energy. We also fit the phase-resolved NuSTAR spectra with an absorbed power-law model in five phase bins and find that the photon index varies with phase from Γ = 1.52 ± 0.03 at phases around the flux maximum to Γ = 1.79 ± 0.06 around the flux minimum. Last, we compare our results with other pulsars whose magnetospheric emission is detected at hard X-ray energies and find that, similar to previous studies, J1617's hard X-ray properties are more similar to the MeV pulsars than the GeV pulsars.

Compton-thick AGN in the NuSTAR Era VI: The Observed Compton-thick Fraction in the Local Universe

We present the analysis of simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR) and XMM-Newton data of eight Compton-thick active galactic nuclei (CT-AGN) candidates selected in the Swift-BAT 100 month catalog. This work is part of an ongoing effort to find and characterize all CT-AGN in the Local (z ≤ 0.05) Universe. We used two physically motivated models, MYTorus and borus02, to characterize the sources in the sample, finding five of them to be confirmed CT-AGN. These results represent an increase of ∼19% over the previous NuSTAR-confirmed, BAT-selected CT-AGN at z ≤ 0.05, bringing the total number to 32. This corresponds to an observed fraction of ∼8% of all AGN within this volume-limited sample, although it increases to 20% ± 5% when limiting the sample to z ≤ 0.01. Out of a sample of 48 CT-AGN candidates, selected using BAT and soft (0.3−10 keV) X-ray data, only 24 are confirmed as CT-AGN with the addition of the NuSTAR data. This highlights the importance of NuSTAR when classifying local obscured AGN. We also note that most of the sources in our full sample of 48 Seyfert 2 galaxies with NuSTAR data have significantly different lines of sight and average torus column densities, favoring a patchy torus scenario.

Search for Very High-energy Emission from the Millisecond Pulsar PSR J0218+4232

PSR J0218+4232 is one of the most energetic millisecond pulsars known and has long been considered as one of the best candidates for very high-energy (VHE; >100 GeV) γ-ray emission. Using 11.5 yr of Fermi Large Area Telescope (LAT) data between 100 MeV and 870 GeV, and ∼90 hr of Major Atmospheric Gamma Imaging Cherenkov (MAGIC) observations in the 20 GeV to 20 TeV range, we searched for the highest energy γ-ray emission from PSR J0218+4232. Based on the analysis of the LAT data, we find evidence for pulsed emission above 25 GeV, but see no evidence for emission above 100 GeV (VHE) with MAGIC. We present the results of searches for γ-ray emission, along with theoretical modeling, to interpret the lack of VHE emission. We conclude that, based on the experimental observations and theoretical modeling, it will remain extremely challenging to detect VHE emission from PSR J0218+4232 with the current generation of Imaging Atmospheric Cherenkov Telescopes, and maybe even with future ones, such as the Cherenkov Telescope Array.

Comprehensive Broadband X-Ray and Multiwavelength Study of Active Galactic Nuclei in 57 Local Luminous and Ultraluminous Infrared Galaxies Observed with NuSTAR and/or Swift/BAT

We perform a systematic X-ray spectroscopic analysis of 57 local luminous and ultraluminous infrared galaxy systems (containing 84 individual galaxies) observed with the Nuclear Spectroscopic Telescope Array and/or Swift/BAT. Combining soft X-ray data obtained with Chandra, XMM-Newton, Suzaku, and/or Swift/XRT, we identify 40 hard (>10 keV) X-ray–detected active galactic nuclei (AGNs) and constrain their torus parameters with the X-ray clumpy torus model XCLUMPY. Among the AGNs at z < 0.03, for which sample biases are minimized, the fraction of Compton-thick (N H ≥ 1024 cm−2) AGNs reaches 64 − 15 + 14 % (6/9 sources) in late mergers, while it is 24 − 10 + 12 % (3/14 sources) in early mergers, consistent with the tendency reported by Ricci et al. We find that the bolometric AGN luminosities derived from the infrared data increase but the X-ray to bolometric luminosity ratios decrease with merger stage. The X-ray-weak AGNs in late mergers ubiquitously show massive outflows at subparsec to kiloparsec scales. Among them, the most luminous AGNs (L bol,AGN ∼ 1046 erg s−1) have relatively small column densities of ≲1023 cm−2 and almost super-Eddington ratios (λ Edd ∼ 1.0). Their torus covering factors (C T (22) ∼ 0.6) are larger than those of Swift/BAT-selected AGNs with similarly high Eddington ratios. These results suggest a scenario where, in the final stage of mergers, multiphase strong outflows are produced due to chaotic quasi-spherical inflows, and the AGN becomes extremely X-ray weak and deeply buried due to obscuration by inflowing and/or outflowing material.

Constraints on heavy decaying dark matter with current gamma-ray measurements

Among the several strategies for indirect searches of dark matter, a very promising one is to look for the gamma-rays from decaying dark matter. Here we use the most up-to-date upper bounds on the gamma-ray flux from 105 to 1011 GeV, obtained from CASA-MIA, KASCADE, KASCADE-Grande, Pierre Auger Observatory, Telescope Array and EAS-MSU. We obtain global limits on dark matter lifetime in the range of masses m DM = [107-1015] GeV. We provide the bounds for a set of decay channels chosen as representatives. The constraints derived here are new and cover a region of the parameter space not yet explored. We compare our results with the projected constraints from future neutrino telescopes, in order to quantify the improvement that will be obtained by the complementary high-energy neutrino searches.

Developments of Space Debris Laser Ranging Technology Including the Applications of Picosecond Lasers

Debris laser ranging (DLR) is receiving considerable attention as an accurate and effective method of determining and predicting the orbits of space debris. This paper reports some technologies of DLR, such as the high pulse repetition frequency (PRF) laser pulse, large-aperture telescope, telescope array, multi-static stations receiving signals. DLR with a picosecond laser at the Shanghai Astronomical Observatory is also presented. A few hundred laps of space debris laser-ranging measurements have been made. A double-pulse picosecond laser with an average power of 4.2 W, a PRF of 1 kHz, and a wavelength of 532 nm has been implemented successfully in DLR, it’s the first time that DLR technology has reached a ranging precision at the sub-decimeter level. In addition, the characteristics of the picosecond-pulse-width laser transmission with the advantages of transmission in laser ranging were analyzed. With a mode of the pulse-burst picosecond laser having high average power, the DLR system has tracked small debris with a radar cross-section (RCS) of 0.91 m2 at a ranging distance up to 1726.8 km, corresponding to an RCS of 0.1 m2 at a distance of 1000 km. These works are expected to provide new technologies to further improve the performance of DLR.

THE CHANGING EVENT SURVEY: TRANSIENTS, SPACE DEBRIS & NEOs

Motivated by the promising era of time-domain and multi-messenger astronomy, CHanging Event Survey (CHES) is designed to join the ongoing campaign with a powerful wide-field optical telescope array. CHES project aims to monitor the transient universe, including gamma-ray bursts, fast radio bursts, the electromagnetic counterpart of gravitational waves events (kilonova), supernova, variable stars, near-earth objects, and space debris. The array consists of 12 individual wide field refractors with aperture 280 mm, covering 600 square degrees in total. In the same project, two 800 mm prime focus telescopes can be triggered for follow-up observation. Furthermore, CHES can effectively monitor 300 square deg in a dual band simultaneously, which enable the array to do candidate identification and follow-up for the triggers from LIGO/Virgo collaboration, Fermi, Swift, GECam and SVOM satellites.

Mass Composition of UHECRs from Xmax Distributions Recorded by the Pierre Auger and Telescope Array Observatories

In this paper we infer the mass composition of the ultra high energy cosmic rays (UHECRs) from measurements of Xmax distributions recorded at the Pierre Auger (2014) and Telescope Array (TA) (2016) Observatories, by fitting them with all possible combinations of Monte Carlo (MC) templates from a large set of primary species (p, He, C, N, O, Ne, Si and Fe), as predicted by EPOS-LHC, QGSJETII-04 and Sibyll 2.1 hadronic interaction models. We use the individual fractions of nuclei reconstructed from one experiment in each energy interval to build equivalent MC Xmax distributions, which we compare with the experimental Xmax distributions of the other experiment, applying different statistical tests of compatibility. The results obtained from both experiments confirm that the mass composition of the UHECRs is dominated (≳70%) by protons and He nuclei in the energy range investigated lgE(eV) = [17.8–19.3] (Auger) and lgE(eV) = [18.2–19.0] (TA). The indirect comparisons between the Xmax distributions recorded by the two experiments show that the degree of compatibility of the two datasets is good, even excellent in some high energy intervals, especially above the ankle (lgE(eV)∼18.7). However, our study reveals that, at low energies, further effort in data analysis is required in order to harmonize the results of the two experiments.