Joint analysis of TeV blazar light curves with FACT and HAWC [HEAP]

Probing the high energy emission processes of blazars through their variability relies crucially on long-term monitoring. We present unprecedented light curves from unbiased observations of very high energy fluxes from the blazars Mrk 421 and Mrk 501 based on a joint analysis of data from the First G-APD Cherenkov Telescope (FACT) and the High Altitude Water Cherenkov (HAWC) Observatory. Thanks to an offset of 5.3 hours of the geographic locations, a complementary coverage of up to 12 hours of observation per day allows us to track variability on time scales of hours to days in more detail than with single-instrument analyses. Complementary features, such as better sensitivity thanks to a lower energy threshold with FACT and more regular coverage throughout the year with HAWC, provide valuable cross checks and extensions to the individual analyses. Daily flux comparisons for both Mrk 421 and Mrk 501 show largely correlated variations with a few significant exceptions. These deviations between measurements can be explained through fast variability within a few hours and will be discussed in detail.

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D. Dorner, FACT. Collaboration, R. Lauer, et. al.
Mon, 21 Aug 17

Comments: Presented at the 35th International Cosmic Ray Conference (ICRC2017), Bexco, Busan, Korea. See arXiv:1708.02572 for all HAWC contributions

DES Science Portal: II- Creating Science-Ready Catalogs [IMA]

We present a novel approach for creating science-ready catalogs through a software infrastructure developed for the Dark Energy Survey (DES). We integrate the data products released by the DES Data Management and additional products created by the DES collaboration in an environment known as DES Science Portal. Each step involved in the creation of a science-ready catalog is recorded in a relational database and can be recovered at any time. We describe how the DES Science Portal automates the creation and characterization of lightweight catalogs for DES Year 1 Annual Release, and show its flexibility in creating multiple catalogs with different inputs and configurations. Finally, we discuss the advantages of this infrastructure for large surveys such as DES and the Large Synoptic Survey Telescope. The capability of creating science-ready catalogs efficiently and with full control of the inputs and configurations used is an important asset for supporting science analysis using data from large astronomical surveys.

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A. Neto, L. Costa, A. Rosell, et. al.
Mon, 21 Aug 17

Comments: The second paper of the series about the DES Science Portal, submitted to the Astronomy & Computing journal. It shows the infrastructure to create science-ready catalogs from DES photometric data and ancillary maps

How cores grow by pebble accretion [EPA]

Context: Planet formation by pebble accretion is an alternative to classical core accretion. One of the main differences with classical core accretion is the increased thermal ablation rate experienced by pebbles. This changes the process of core growth. Aims: To describe and compute core growth in the pebble accretion model. We aim to predict core masses and compositions that can form by pebble accretion and compare them to the case of planetesimals. Methods: We have written a code containing both an impact and a planet evolution model to simulate the early growth of a proto-planet self-consistently. The region where high-Z material can exist in vapor form is determined by the temperature-dependent vapor pressure. We include enrichment effects by locally modifying the mean molecular weight of the envelope and determine when direct core growth of the planet terminates. Results: We have identified three phases of core growth in pebble accretion. In the first phase, pebbles impact the core without significant ablation. During the second phase, ablation becomes increasingly severe. A layer of high-Z vapor starts to form around the core that absorbs a small fraction of the ablated mass. The rest of the material either rains out to the core or mixes outwards instead, slowing core growth. In the third phase, the high-Z inner region expands outwards, absorbing an increasing fraction of the ablated material as vapor. Rainout ends before the core mass reaches 0.6 M_Earth, terminating direct core growth. Conclusions: Our results indicate that pebble accretion can directly form rocky cores up to only 0.6 M_Earth, and is unable to form icy cores. This result contrasts classical core accretion models, which can directly form massive cores of both rocky and icy compositions. Subsequent core growth can proceed indirectly when the planet cools, provided it is able to retain its high-Z material.

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M. Brouwers, A. Vazan and C. Ormel
Mon, 21 Aug 17

Comments: 10 pages, 10 figures. Submitted to A&A. Comments welcome

Triggering Active Galactic Nuclei in galaxy clusters [GA]

We model the triggering of Active Galactic Nuclei (AGN) in galaxy clusters using the semi- analytic galaxy formation model SAGE (?). We prescribe triggering methods based on the ram pressure galaxies experience as they move throughout the intracluster medium, which is hypothesized to trigger star formation and AGN activity. The clustercentric radius and velocity distribution of the simulated active galaxies produced by these models are compared with that of AGN and galaxies with intense star formation from a sample of low-redshift, relaxed clusters from the Sloan Digital Sky Survey. The ram pressure triggering model that best explains the clustercentric radius and velocity distribution of these observed galaxies has AGN and star formation triggered if $2.5\times10^{-14} < P_{ram} < 2.5\times10^{-13}$ Pa and $P_{ram} > 2P_{internal}$; this is consistent with expectations from hydrodynamical simulations of ram-pressure induced star formation. Our results show that ram pressure is likely to be an important mechanism for triggering star formation and AGN activity in clusters.

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M. Marshall, S. Shabala, M. Krause, et. al.
Mon, 21 Aug 17

Comments: Submitted to MNRAS, updated following referee’s comments. 14 pages, 10 figures

Superflare UV flashes impact on Kepler-96 system: a glimpse of habitability when the ozone layer first formed on Earth [EPA]

Kepler-96 is an active solar-type star harbouring a Super-Earth planet in close orbit. Its age of 2.3 Gyr is the same as the Sun when there was a considerable increase of oxygen in Earth’s atmosphere due to micro-organisms living under the sea. We present the analysis of superflares seen on the transit lightcurves of Kepler-96b. The model used here simulates the planetary transit in a flaring star. By fitting the observational data with this model, it is possible to infer the physical properties of the flares, such as their duration and the energy released. We found 3 flares within the energy range of superflares, where the biggest superflare observed was found to have an energy of 1.81$\times$10$^{35}$ ergs. The goal is to analyse the biological impact of these superflares on the close by planet and also on a hypothetical Earth assuming the planets have protection via various atmospheres scenarios: an Archean atmosphere and Present-day atmospheres with and without oxygen. Also, we verify the attenuation of the UV radiation produced by the flares through an Archean ocean. The conclusion is that only extremophile life could survive on the surface of Kepler-96b, and if there was an ozone layer present on the planet atmosphere. However, under the Archean conditions lifeforms as \textit{E. Coli} could support the effects of the strongest superflare in this planet if it was at a depth of 48m below the ocean surface. For a hypothetical Earth, depending on the superflare size and on the resistance of the micro-organism, life could be sustained in the surface even in an Archean atmosphere or in an 8-20m ocean depth.

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R. Estrela and A. Valio
Mon, 21 Aug 17

Comments: 12 pages, 8 figures, under review at Astrobiology

A. G. W. Cameron 1925-2005, Biographical Memoir, National Academy of Sciences [CL]

Alastair Graham Walker Cameron was an astrophysicist and planetary scientist of broad interests and exceptional originality. A founder of the field of nuclear astrophysics, he developed the theoretical understanding of the chemical elements’ origins and made pioneering connections between the abundances of elements in meteorites to advance the theory that the Moon originated from a giant impact with the young Earth by an object at least the size of Mars. Cameron was an early and persistent exploiter of computer technology in the theoretical study of complex astronomical systems—including nuclear reactions in supernovae, the structure of neutron stars, and planetary collisions.

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D. Arnett
Mon, 21 Aug 17

Comments: 12 pages, I picture

A Theoretical Model of X-ray Jets from Young Stellar Objects [SSA]

There is a subclass of the X-ray jets from young stellar objects which are heated very close to the footpoint of the jets, particularly DG Tau jets. Previous models attribute the strong heating to shocks in the jets. However, the mechanism that localizes the heating at the footpoint remains puzzling. We presented a different model of such X-ray jets, in which the disk atmosphere is magnetically heated. Our disk corona model is based on the so-called nanoflare model for the solar corona. We show that the magnetic heating near the disks can result in the formation of a hot corona with a temperature of > 10^6 K even if the average field strength in the disk is moderately weak, > 1 G. We determine the density and the temperature at the jet base by considering the energy balance between the heating and cooling. We derive the scaling relations of the mass loss rate and terminal velocity of jets. Our model is applied to the DG Tau jets. The observed temperature and estimated mass loss rate are consistent with the prediction of our model in the case of the disk magnetic field strength of ~20 G and the heating region of < 0.1 au. The derived scaling relation of the temperature of X-ray jets could be a useful tool to estimate the magnetic field strength. We also found that the jet X-ray can have a significant impact on the ionization degree near the disk surface and the dead-zone size.

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S. Takasao, T. Suzuki and K. Shibata
Mon, 21 Aug 17

Comments: 31 pages (single column), 5 figures, Accepted to be published in ApJ