A Hubble Space Telescope Survey for Novae in M87. III. Novae as Effective Standard Candles [SSA]


Ten weeks’ daily imaging of the giant elliptical galaxy M87 with the Hubble Space Telescope has yielded 41 nova light curves of unprecedented quality for extragalactic cataclysmic variables. We have recently used these light curves to demonstrate that the observational scatter in the so-called Maximum-Magnitude Rate of Decline (MMRD) relation for classical novae is so large as to render the nova-MMRD useless as a standard candle. Here we demonstrate that the Buscombe – de Vaucouleurs hypothesis, that all novae converge to nearly the same absolute magnitude about two weeks after maximum light, is strongly supported by our M87 nova data. For 24 novae in V-band (F606W filter) and I-band (F814W filter) light with daily-sampled light curves and well determined maxima, we find that the times of minimum scatter of nova absolute magnitude are, respectively, 17 and 20 days after maximum light. At those epochs novae display M_{V,17} = -6.06 +/- 0.23 and M_{I,20} = -6.11 +/- 0.34 . The distances of single novae in the Milky Way, sparse or elliptical galaxies, or free-floating in intergalactic space can be reasonably well-determined with the above calibrations.

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M. Shara, T. Doyle, A. Pagnotta, et. al.
Fri, 24 Feb 17

Comments: 11 pages, 4 figures, submitted to the Astrophysical Journal

Periodic optical variability of AGN [GA]


Here we present the evidence for periodicity of an optical emission detected in several AGN. Significant periodicity is found in light curves and radial velocity curves. We discuss possible mechanisms that could produce such periodic variability and their implications. The results are consistent with possible detection of the orbital motion in proximity of the AGN central supermassive black holes.

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E. Bon, P. Marziani and N. Bon
Fri, 24 Feb 17

Comments: 5 pages, 2 figures, in press

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-Scale Clustering as a Probe of the Origin and the Host Environment of Fast Radio Bursts [CEA]


We propose to use degree-scale angular clustering of fast radio bursts (FRBs) to identify their origin and the host galaxy population. We study the information content in auto-correlation of the angular positions and dispersion measures (DM) and in cross-correlation with galaxies. We show that the cross-correlation with Sloan Digital Sky Survey (SDSS) galaxies will place stringent constraints on the mean physical quantities associated with FRBs. If ~10,000 FRBs are detected with <deg resolution in the SDSS field, the clustering analysis can constrain the global abundance of free electrons at $z<1$, the bias factor of FRB host galaxies, and the mean near-source dispersion measure, with fractional errors (with a $68\%$ confidence level) of $\sim5 \%, \sim 20 \%$, and $\sim70 \%$, respectively. The delay time distribution of FRB sources can be also determined by combining the clustering and the probability distribution function of dispersion measure. Our approach will be complementary to high-resolution ($\ll {\rm deg}$) event localization using e.g., VLA and VLBI for identifying the origin of FRBs and the source environment. We strongly encourage future observational programs such as CHIME, UTMOST, HIRAX to survey FRBs in the SDSS field.

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M. Shirasaki, K. Kashiyama and N. Yoshida
Fri, 24 Feb 17

Comments: 14 pages, 8 figures, 2 tables, To be submitted to Phys. Rev. D