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.

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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.

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

Comments: 13 pages, 3 figures, 1 table

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.

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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.

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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

Tidal double detonation: a new mechanism for a thermonuclear explosion of a white dwarf induced by a tidal disruption event [HEAP]


We suggest “tidal double detonation”: a new mechanism for a thermonuclear explosion of a white dwarf (WD) induced by a tidal disruption event (TDE). Tidal detonation is also a WD explosion induced by a TDE. In this case, helium (He) and carbon-oxygen (CO) detonation waves incinerate He~WD and CO~WD, respectively. On the other hand, for tidal double detonation, He detonation is first excited in the He shell of a CO~WD, and drives CO detonation in the CO core. We name this mechanism after the double detonation scenario in the context of type Ia supernovae. In this paper, we show tidal double detonation occurs in shallower encounter of a CO~WD with an intermediate mass black hole (IMBH) than simple tidal detonation, performing numerical simulations for CO~WDs with $0.60M_\odot$ with and without a He shell. We expect tidal double detonation spreads opportunity to WD~TDEs illuminating IMBHs.

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A. Tanikawa
Tue, 21 Nov 17

Comments: 5 pages, 3 figures

Absence of reflection features in NuSTAR spectra of the luminous neutron star X-ray binary GX 5-1 [HEAP]


We present NuSTAR observations of the luminous neutron star low-mass X-ray binary (NS LMXB) and Z source GX 5-1. During our three observations, made with separations of roughly two days, the source traced out an almost complete Z track. We extract spectra from the various branches and fit them with a continuum model that has been successfully applied to other Z sources. Surprisingly, and unlike most of the (luminous) NS-LMXBs observed with NuSTAR, we do not find evidence for reflection features in any of the spectra of GX 5-1. We discuss several possible explanations for the absence of reflection features. Based on a comparison with other accreting neutron-star systems and given the high luminosity of GX 5-1 (~1.6-2.3 times the Eddington luminosity, for a distance of 9 kpc), we consider a highly ionized disk the most likely explanation for the absence of reflection features in GX 5-1.

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J. Homan, J. Steiner, D. Lin, et. al.
Tue, 21 Nov 17

Comments: Submitted to ApJ Letters

Host galaxy identification for binary black hole mergers with long baseline gravitational wave detectors [HEAP]


The detection of three black hole binary coalescence events by Advanced LIGO allows the science benefits of future detectors to be evaluated. In this paper we report the science benefits of one or two 8km arm length detectors based on the doubling of key parameters in an advanced LIGO type detector, combined with realisable enhancements. It is shown that the total detection rate for sources similar to those already detected, would increase to $\sim$ 10$^{3}$–10$^{5}$ per year. Within 0.4Gpc we find that around 10 of these events would be localizable to within $\sim 10^{-1}$ deg$^2$. This is sufficient to make unique associations or to rule out a direct association with the brightest galaxies in optical surveys (at r-band magnitudes of 17 or above) or for deeper limits (down to r-band magnitudes of 20) yield statistically significant associations. The combination of angular resolution and event rate would benefit precision testing of formation models, cosmic evolution and cosmological studies.

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E. Howell, M. Chan, Q. Chu, et. al.
Tue, 21 Nov 17

Comments: Accepted to MNRAS with minor revisions