Ultra-high-energy cosmic rays from tidally-ignited stars [HEAP]


Ultra-high-energy cosmic rays (UHECRs) can be accelerated by tidal disruption events of stars by black holes. Encounters between white dwarfs with intermediate-mass black holes (IMBHs) provide a natural environment for acceleration, as tidal forces can ignite nuclear burn and lead to a supernova explosion. The numbers of IMBHs may be substantially augmented once account is taken of their likely presence in dwarf galaxies. In this Letter we show that this kind of tidal disruption event naturally provides an intermediate/heavy composition for the inferred UHECR composition. We further argue that this mechanism is virtually model-independent, as it does not rely on any specific acceleration model. Finally, we point out a possible link between ultra-luminous x-ray and UHECR sources.

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R. Batista and J. Silk
Fri, 24 Feb 17

Comments: 5 pages, 1 figure

Outflow-Driven Transients from the Birth of Binary Black Holes [HEAP]


We consider the electromagnetic radiation from newborn binary black holes (BBHs) formed by the evolution of isolated massive stellar binaries. Before the formation of a BBH, the binary consists of a primary black hole (BH) and a secondary Wolf-Rayet star. We investigate two types of transients from the birth of a secondary BH: one powered by the Bondi-Hoyle-Lyttleton accretion onto the primary BH, and the other induced by accretion onto the secondary BH. In the former scenario, when the secondary collapses to a BH, it may eject a fraction of its outer material, which forms a disk around the primary BH and induces an ultrafast outflow. This companion-induced outflow can lead to week-scale optical transients with a kinetic energy of $\sim10^{47}$ — $3\times10^{48}$~erg, ejecta velocity of $10^8$ — $10^9\rm~cm~s^{-1}$, and absolute magnitude ranging from about $-10$ to $-12$. In the latter scenario, assuming that the tidal torque synchronizes the spin period of the secondary to the orbital period of the primary, the accretion of the stellar material is expected to form a disk around a newborn BH, following its core-collapse. This disk may produce an energetic outflow with a kinetic energy of $\sim10^{52}$~erg and the outflow velocity of $\sim10^{10}\rm~cm~s^{-1}$, resulting in an optical transient of absolute magnitude from $\sim -13$ to $\sim-14$ with a duration of a few days. While dimmer than ordinary supernovae, their light curves and late-time spectra are distinctive, and dedicated optical transient surveys could detect these two types of transients, the second type also leading to detectable radio signals.

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S. Kimura and P. Meszaros
Fri, 24 Feb 17

Comments: 11 pages, 3 figures

Radio Follow-up on all Unassociated Gamma-ray Sources from the Third Fermi Large Area Telescope Source Catalog [HEAP]


The third Fermi Large Area Telescope (LAT) $\gamma$-ray source catalog (3FGL) contains over 1000 objects for which there is no known counterpart at other wavelengths. The physical origin of the $\gamma$-ray emission of those objects is unknown. Such objects are commonly referred to as unassociated and mostly do not exhibit significant $\gamma$-ray flux variability. We performed a survey of all unassociated $\gamma$-ray sources found in 3FGL using the Australia Telescope Compact Array and Very Large Array in the range of 4.0-10.0 GHz. We found 2097 radio candidates for association with $\gamma$-ray sources. The follow-up with very long baseline interferometry for a subset of those candidates yielded 142 new AGN associations with $\gamma$-ray sources, provided alternative associations for 7 objects, and improved positions for another 144 known associations to the milliarcsecond level of accuracy. In addition, for 245 unassociated $\gamma$-ray sources we did not find a single compact radio source above 2 mJy within 3$\sigma$ of their $\gamma$-ray localization. A significant fraction of these empty fields, 39%, are located away from the galactic plane. We also found 36 extended radio sources that are candidates for association with a corresponding $\gamma$-ray object, 19 of which are most likely supernova remnants or HII regions, whereas 17 could be radio galaxies.

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F. Schinzel, L. Petrov, G. Taylor, et. al.
Fri, 24 Feb 17

Comments: 14 pages, 9 figures, 6 tables, 5 machine readable tables, accepted for publication in ApJS

Enforcing causality in nonrelativistic equations of state at finite temperature [HEAP]


We present a thermodynamically consistent method by which equations of state based on nonrelativistic potential models can be modified so that they respect causality at high densities, both at zero and finite temperature (entropy). We illustrate the application of the method using the high density phase parametrization of the well known APR model in its pure neutron matter configuration as an example. We also show that, for models with only contact interactions, the adiabatic speed of sound is independent of the temperature in the limit of very large temperature. This feature is approximately valid for models with finite-range interactions as well, insofar as the temperature dependence they introduce to the Landau effective mass is weak. In addition, our study reveals that in first principle nonrelativistic models of hot and dense matter, contributions from higher than two-body interactions must be screened at high density to preserve causality.

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C. Constantinou and M. Prakash
Fri, 24 Feb 17

Comments: 12 pages, 12 figures

Large Decay of X-ray Flux in 2XMM J123103.2+110648: Evidence for a Tidal Disruption Event [HEAP]


The X-ray source 2XMM J123103.2+110648 was previously found to show pure thermal X-ray spectra and a ~3.8 hr periodicity in three XMM-Newton X-ray observations in 2003-2005, and the optical spectrum of the host galaxy suggested it as a type 2 active galactic nucleus candidate. We have obtained new X-ray observations of the source, with Swift and Chandra in 2013-2016, in order to shed new light on its nature based on its long-term evolution property. We found that the source could be in an X-ray outburst, with the X-ray flux decreasing by an order of magnitude in the Swift and Chandra observations, compared with the XMM-Newton observations ten years ago. There seemed to be significant spectral softening associated with the drop of X-ray flux (disk temperature kT ~ 0.16-0.2 keV in XMM-Newton observations versus kT~0.09+-0.02 keV in the Chandra observation. Therefore the Swift and Chandra follow-up observations support our previous suggestion that the source could be a tidal disruption event (TDE), though it seems to evolve slower than most of the other TDE candidates. The apparent long duration of this event could be due to the presence of a long super-Eddington accretion phase and/or slow circularization.

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D. Lin, O. Godet, L. Ho, et. al.
Fri, 24 Feb 17

Comments: Accepted for publication in MNRAS. 8 pages, 5 figures

The effect upon neutrinos of core-collapse supernova accretion phase turbulence [HEAP]


During the accretion phase of a core-collapse supernovae, large amplitude turbulence is generated by the combination of the standing accretion shock instability and convection driven by neutrino heating. The turbulence directly affects the dynamics of the explosion, but there is also the possibility of an additional, indirect, feedback mechanism due to the effect turbulence can have upon neutrino flavor evolution and thus the neutrino heating. In this paper we consider the effect of turbulence during the accretion phase upon neutrino evolution, both numerically and analytically. Adopting representative supernova profiles taken from the accretion phase of a supernova simulation, we find the numerical calculations exhibit no effect from turbulence. We explain this absence using two analytic descriptions: the Stimulated Transition model and the Distorted Phase Effect model. In the Stimulated Transition model turbulence effects depend upon six different lengthscales, and three criteria must be satisfied between them if one is to observe a change in the flavor evolution due to Stimulated Transition. We further demonstrate that the Distorted Phase Effect depends upon the presence of multiple semi-adiabatic MSW resonances or discontinuities that also can be expressed as a relationship between three of the same lengthscales. When we examine the supernova profiles used in the numerical calculations we find the three Stimulated Transition criteria cannot be satisfied, independent of the form of the turbulence power spectrum, and that the same supernova profiles lack the multiple semi-adiabatic MSW resonances or discontinuities necessary to produce a Distorted Phase Effect. Thus we conclude that even though large amplitude turbulence is present in supernova during the accretion phase, it has no effect upon neutrino flavor evolution.

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J. Kneller and M. Reyes
Fri, 24 Feb 17

Comments: N/A

Mass of the compact object in the Be/gamma-ray binaries LSI+61303 and MWC 148 [HEAP]


We estimate the mass of the compact object in the gamma-ray binaries LSI+61303 and MWC 148, using the latest data for the inclination, orbital motion and assuming that the orbital plane coincides with the equatorial plane of the Be star. For LSI+61303 we find the mass of the compact object to be most likely in the range 1.3 M_sun < M_2 < 2.0 M_sun, which means that it is probably a neutron star. For MWC 148, we find the mass of the compact object in a higher range, 2.1 M_sum < M_2 < 7.3 M_sun, which increases the chances for this system to host a black hole companion.

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R. Zamanov, J. Marti and M. Garcia-Hernandez
Fri, 24 Feb 17

Comments: 4 pages, submitted