On the patchiness of the individual pulse spectra at the very low radio frequencies [HEAP]


We have used sensitive LOw Frequency ARray (LOFAR) observations of PSR B0809+74 at 15–62 MHz to study the anomalously intensive pulses, first reported by Ulyanov et al. (2006) at 18–30MHz. Similarly to Ulyanov et al., we found that the spectra of strong pulses consist of distinct bright patches. Moreover, these spectral patches were spotted to drift upwards in frequency over the course of several pulse sequences. We established that this drift is not pulsar-intrinsic, but is caused by the broadband ~20 second-long enhancements of recorded signal, which influenced the dispersed tracks of several pulses at once. We speculate on the cause of such enhancements (i.e. propagation or telescope-related) and the ramifications they bring to the single-pulse studies at the very low radio frequencies. Depending on the origin, the phenomenon may also affect the analysis of highly dispersed single pulses at higher radio frequencies, e.g. Fast Radio Bursts.

Read this paper on arXiv…

X. Song, V. Kondratiev and A. Bilous
Tue, 21 Nov 17

Comments: 2 pages, 2 figures, to appear in the proceedings of “IAUS 337: Pulsar Astrophysics – The Next 50 Years” eds: P. Weltevrede, B.B.P. Perera, L. Levin Preston & S. Sanidas. Poster available at: this http URL

Prompt emission from the counter jet of a short gamma-ray burst [HEAP]


The counter jet of a short gamma-ray burst (sGRB) has not been observed yet, while recent discoveries of gravitational waves (GWs) from a binary neutron star (NS) merger GW170817 and the associated sGRB 170817A have demonstrated that off-axis sGRB jets are detectable. We calculate the prompt emission from the counter jet of an sGRB and show that it is typically 23-26 magnitude in the optical-infrared band 10-10^3 sec after the GWs for an sGRB 170817A-like event, which is brighter than the early macronova (or kilonova) emission and detectable by LSST in the near future. We also propose a new method to constrain the unknown jet properties, such as the Lorentz factor, opening angle, emission radii and jet launch time, by observing both the forward and counter jets. To scrutinize the counter jets, space GW detectors like DECIGO is powerful by forecasting the merger time (<~ 1 sec) and position (<~1 arcmin) (~ a week) before the merger.

Read this paper on arXiv…

R. Yamazaki, K. Ioka and T. Nakamura
Tue, 21 Nov 17

Comments: 13 pages, 3 figures, 1 table

Methodology study of machine learning for the neutron star equation of state [CL]


We discuss a methodology of the machine learning to deduce the neutron star equation of state from a set of mass-radius observational data. We propose an efficient procedure to deal with a mapping from finite data points with observational errors onto an equation of state. We generate training data and optimize the neural network. Using independent validation data (mock observational data) we confirm that the equation of state is correctly reconstructed with precision surpassing observational errors.

Read this paper on arXiv…

Y. Fujimoto, K. Fukushima and K. Murase
Tue, 21 Nov 17

Comments: 5 pages, 4 figures

The high brightness temperature of B0529+483 revealed by RadioAstron and implications for interstellar scattering [HEAP]


The high brightness temperatures, $T_\mathrm{b}\gtrsim 10^{13}$ K, detected in several active galactic nuclei by RadioAstron space VLBI observations challenge theoretical limits. Refractive scattering by the interstellar medium may affect such measurements. We quantify the scattering properties and the sub-mas scale source parameters for the quasar B0529+483. Using RadioAstron correlated flux density measurements at 1.7, 4.8, and 22 GHz on projected baselines up to 240,000 km we find two characteristic angular scales in the quasar core, about 100 $\mu$as and 10 $\mu$as. Some indications of scattering substructure are found. Very high brightness temperatures, $T_\mathrm{b}\geq 10^{13}$ K, are estimated at 4.8 GHz and 22 GHz even taking into account the refractive scattering. Our findings suggest a clear dominance of the particle energy density over the magnetic field energy density in the core of this quasar.

Read this paper on arXiv…

S. Pilipenko, Y. Kovalev, A. Andrianov, et. al.
Tue, 21 Nov 17

Comments: 14 pages, 9 figures

Central Compact Objects in Supernova Remnants [HEAP]


Central Compact Objects (CCOs) are a handful of sources located close to the geometrical center of young supernova remnants. They only show thermal-like, soft X-ray emission and have no counterparts at any other wavelength. While the first observed CCO turned out to be a very peculiar magnetar, discovery that three members of the family are weakly magnetised Isolated Neutron Stars (INSs) set the basis for an interpretation of the class. However, the phenomeology of CCOs and their relationship with other classes of INSs, possibly ruled by supernova fall-back accretion, are still far from being well understood.

Read this paper on arXiv…

A. Luca
Tue, 21 Nov 17

Comments: 7 pages, to appear in the proceedings of “Physics of Neutron Stars – 2017” Conference (July 10-14, Saint Petersburg), JPCS, eds. G.G. Pavlov, J.A. Pons, P.S. Shternin & D.G. Yakovlev

An HLLC Riemann Solver for Resistive Relativistic Magnetohydrodynamics [IMA]


We present a new approximate Riemann solver for the augmented system of equations of resistive relativistic magnetohydrodynamics (RRMHD) that belongs to the family of Harten-Lax-van Leer contact wave (HLLC) solvers. In HLLC solvers, the solution is approximated by two constant states flanked by two shocks separated by a contact wave. The accuracy of the new approximate solver is calibrated through one- and two-dimensional test problems.

Read this paper on arXiv…

S. Miranda-Aranguren, M. Aloy and T. Rembiasz
Tue, 21 Nov 17

Comments: 23 pages, 20 figures, 3 tables, submitted for publication in MNRAS

Host galaxies and relativistic ejecta of compact binary mergers in the ngVLA era [IMA]


We present the results of a community study aimed at exploring some of the scientific opportunities that the next generation Very Large Array (ngVLA) could open in the field of multi-messenger time-domain astronomy. We focus on compact binary mergers, golden astrophysical targets of ground-based gravitational wave (GW) detectors such as advanced LIGO. A decade from now, a large number of these mergers is likely to be discovered by a world-wide network of GW detectors. This will enable the identification of host galaxies, either directly through detection of electromagnetic (EM) counterparts, or indirectly by probing potential anisotropies in the spatial distribution of mergers. Identifying the host galaxy population of GW mergers would provide a way to constrain the efficiency of various binary neutron star (NS) or black hole (BH) formation scenarios, and the merger timescale distributions as linked to merger rates in early- and late-type galaxies. We discuss how a radio array with ~10x the sensitivity of the current Karl G. Jansky VLA and ~10x the resolution, would enable resolved radio continuum studies of binary merger hosts, probing regions of the galaxy undergoing star formation (which can be heavily obscured by dust and gas), AGN components, and mapping the offset distribution of the mergers with respect to the host galaxy light. For compact binary mergers containing at least one NS and with associated EM counterparts, we show how the ngVLA would enable direct size measurements of the relativistic merger ejecta and probe, for the first time directly, their dynamics.

Read this paper on arXiv…

A. Corsi, D. Frail, B. Owen, et. al.
Tue, 21 Nov 17

Comments: 8 pages, 5 figures, 1 Table, published as an ngVLA memo at this https URL