Neutrino Burst-Generated Gravitational Radiation From Collapsing Supermassive Stars [HEAP]

We estimate the gravitational radiation signature of the electron/positron annihilation-driven neutrino burst accompanying the asymmetric collapse of an initially hydrostatic, radiation-dominated supermassive object suffering the Feynman-Chandrasekhar instability. An object with a mass $5\times10^4M_\odot<M<5\times10^5M_\odot$, with primordial metallicity, is an optimal case with respect to the fraction of its rest mass emitted in neutrinos as it collapses to a black hole: lower initial mass objects will be subject to scattering-induced neutrino trapping and consequently lower efficiency in gravitational radiation generation; while higher masses will not get hot enough to radiate significant neutrino energy before producing a black hole. The optimal case collapse will radiate several percent of the star’s rest mass in neutrinos and, with an assumed small asymmetry in temperature at peak neutrino production, produces a characteristic linear memory gravitational wave burst signature. The timescale for this signature, depending on redshift, is $\sim1{\rm~s}$ to $10{\rm~s}$, optimal for proposed gravitational wave observatories like DECIGO. Using the response of that detector, and requiring a signal-to-noise ratio SNR $>$ 5, we estimate that collapse of a $\sim 10^5M_\odot$ supermassive star could produce a neutrino burst-generated gravitational radiation signature detectable to redshift $z\lesssim10$. These events could be detected to even higher redshifts with the ultimate DECIGO design sensitivity.

Read this paper on arXiv…

J. Li, G. Fuller and C. Kishimoto
Fri, 18 Aug 17

Comments: 9 pages, 6 figures, to be submitted to PRD

Jupiter's North Equatorial Belt expansion and thermal wave activity ahead of Juno's arrival [EPA]

The dark colors of Jupiter’s North Equatorial Belt (NEB, $7-17^\circ$N) appeared to expand northward into the neighboring zone in 2015, consistent with a 3-5 year cycle of activity in the NEB. Inversions of thermal-IR imaging from the Very Large Telescope revealed a moderate warming and reduction of aerosol opacity at the cloud tops at $17-20^\circ$N, suggesting subsidence and drying in the expanded sector. Two new thermal waves were identified during this period: (i) an upper tropospheric thermal wave (wavenumber 16-17, amplitude 2.5 K at 170 mbar) in the mid-NEB that was anti-correlated with haze reflectivity; and (ii) a stratospheric wave (wavenumber 13-14, amplitude 7.3 K at 5 mbar) at $20-30^\circ$N. Both were quasi-stationary, confined to regions of eastward zonal flow, and are morphologically similar to waves observed during previous expansion events.

Read this paper on arXiv…

L. Fletcher, G. Orton, J. Sinclair, et. al.
Fri, 18 Aug 17

Comments: 28 pages, 15 figures, published in Geophysical Research Letters

Correlated Signatures of Gravitational-Wave and Neutrino Emission in Three-Dimensional General-Relativistic Core-Collapse Supernova Simulations [HEAP]

We present results from general-relativistic (GR) three-dimensional (3D) core-collapse simulations with approximate neutrino transport for three non-rotating progenitors (11.2, 15, and 40 Msun) using different nuclear equations of state (EOSs). We find that the combination of progenitor’s higher compactness at bounce and the use of softer EOS leads to stronger activity of the standing accretion shock instability (SASI). We confirm previous predications that the SASI produces characteristic time modulations both in neutrino and gravitational-wave (GW) signals. By performing a correlation analysis of the SASI-modulated neutrino and GW signals, we find that the correlation becomes highest when we take into account the time-delay effect due to the advection of material from the neutrino sphere to the proto-neutron star core surface. Our results suggest that the correlation of the neutrino and GW signals, if detected, would provide a new signature of the vigorous SASI activity in the supernova core, which can be hardly seen if neutrino-convection dominates over the SASI.

Read this paper on arXiv…

T. Kuroda, K. Kotake, K. Hayama, et. al.
Fri, 18 Aug 17

Comments: 22 pages, 9 figures

Catching a star before explosion: the luminous blue variable progenitor of SN 2015bh [SSA]

In this paper we analyse the pre-explosion spectrum of SN2015bh by performing radiative transfer simulations using the CMFGEN code. This object has attracted significant attention due to its remarkable similarity to SN2009ip in both its pre- and post-explosion behavior. They seem to belong to a class of events for which the fate as a genuine core-collapse supernova or a non-terminal explosion is still under debate. Our CMFGEN models suggest that the progenitor of SN2015bh had an effective temperature between 8700 and 10000 K, luminosity ~2.7e6 Lsun, contained at least 25% H in mass at the surface, and half-solar Fe abundances. The results also show that the progenitor of SN2015bh generated an extended wind with a mass-loss rate of ~ 6e-4 to 1.5e-3 Msun/yr and a velocity of 1000 km/s. We determined that the wind extended to at least 7e14 cm and lasted for at least 81 days prior to the observations, releasing 2.2e-4 Msun into the circumstellar medium. In analogy to 2009ip, we propose that this is the material that the explosive ejecta will interact at late epochs. We conclude that the progenitor of SN2015bh was most likely a warm luminous blue variable of at least 60 Msun before the explosion. Considering the high wind velocity, we cannot exclude the possibility that the progenitor was a Wolf-Rayet star that inflated just before the 2013 eruption, similar to HD5980 during its 1994 episode. If the star survived, late-time spectroscopy may reveal either a similar LBV or a Wolf-Rayet star, depending on the mass of the H envelope before the explosion. If the star exploded as a genuine SN, 2015bh would be a remarkable case of a successful explosion after black-hole formation in a star with 60 Msun at the pre-SN stage.

Read this paper on arXiv…

I. Boian and J. Groh
Fri, 18 Aug 17

Comments: 12 Pages, 9 figures, submitted to A&A. Comments welcome

Cycles of Activity in the Jovian Atmosphere [EPA]

Jupiter’s banded appearance may appear unchanging to the casual observer, but closer inspection reveals a dynamic, ever-changing system of belts and zones with distinct cycles of activity. Identification of these long-term cycles requires access to datasets spanning multiple jovian years, but explaining them requires multi-spectral characterization of the thermal, chemical, and aerosol changes associated with visible color variations. The Earth-based support campaign for Juno’s exploration of Jupiter has already characterized two upheaval events in the equatorial and temperate belts that are part of long-term jovian cycles, whose underlying sources could be revealed by Juno’s exploration of Jupiter’s deep atmosphere.

Read this paper on arXiv…

L. Fletcher
Fri, 18 Aug 17

Comments: 9 pages, 1 figures, Commentary published in Geophysical Research Letters

DustPedia: Multiwavelength Photometry and Imagery of 875 Nearby Galaxies in 42 Ultraviolet–Microwave Bands [GA]

The DustPedia project is capitalising on the legacy of the Herschel Space Observatory, using cutting-edge modelling techniques to study dust in the 875 DustPedia galaxies – representing the vast majority of extended galaxies within 3000 km s$^{-1}$ that were observed by Herschel. This work requires a database of multiwavelength imagery and photometry that greatly exceeds the scope (in terms of wavelength coverage and number of galaxies) of any previous local-Universe survey. We constructed a database containing our own custom Herschel reductions, along with standardised archival observations from GALEX, SDSS, DSS, 2MASS, WISE, Spitzer, and Planck. Using these data, we performed consistent aperture-matched photometry, which we combined with external supplementary photometry from IRAS and Planck. We present our multiwavelength imagery and photometry across 42 UV-microwave bands for the 875 DustPedia galaxies. Our aperture-matched photometry, combined with the external supplementary photometry, represents a total of 21,857 photometric measurements. A typical DustPedia galaxy has multiwavelength photometry spanning 25 bands. We also present the Comprehensive & Adaptable Aperture Photometry Routine (CAAPR), the pipeline we developed to carry out our aperture-matched photometry. CAAPR is designed to produce consistent photometry for the enormous range of galaxy and observation types in our data. In particular, CAAPR is able to determine robust cross-compatible uncertainties, thanks to a novel method for reliably extrapolating the aperture noise for observations that cover a very limited amount of background. Our rich database of imagery and photometry is being made available to the community

Read this paper on arXiv…

C. Clark, S. Verstocken, S. Bianchi, et. al.
Fri, 18 Aug 17

Comments: Accepted for publication in Astronomy & Astrophysics

chemical abundances and ages of the bulge stars in APOGEE high-velocity peaks [GA]

A cold high-velocity (HV, $\sim$ 200 km/s) peak was first reported in several Galactic bulge fields based on the APOGEE commissioning observations. Both the existence and the nature of the high-velocity peak are still under debate. Here we revisit this feature with the latest APOGEE DR13 data. We find that most of the low latitude bulge fields display a skewed Gaussian distribution with a HV shoulder. However, only 3 out of 53 fields show distinct high-velocity peaks around 200 km/s. The velocity distribution can be well described by Gauss-Hermite polynomials, except the three fields showing clear HV peaks. We find that the correlation between the skewness parameter ($h_{3}$) and the mean velocity ($\bar{v}$), instead of a distinctive HV peak, is a strong indicator of the bar. It was recently suggested that the HV peak is composed of preferentially young stars. We choose three fields showing clear HV peaks to test this hypothesis using the metallicity, [$\alpha$/M] and [C/N] as age proxies. We find that both young and old stars show HV features. The similarity between the chemical abundances of stars in the HV peaks and the main component indicates that they are not systematically different in terms of chemical abundance or age. In contrast, there are clear differences in chemical space between stars in the Sagittarius dwarf and the bulge stars. The strong HV peaks off-plane are still to be explained properly, and could be different in nature.

Read this paper on arXiv…

Y. Zhou, J. Shen, C. Liu, et. al.
Fri, 18 Aug 17

Comments: 13 pages, 10 figures, submitted to ApJ