bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE IONIZED GAS IN NEARBY GALAXIES AS TRACED BY THE
122 AND 205 μm TRANSITIONS
Authors: Herrera-Camus R. , Bolatto A. , Smith J. D. , Draine B. , Pellegrini E. , Wolfire M. , Croxall K. , Looze I. de , Calzetti D. , Kennicutt R. , Crocker A. , Armus L. , van der Werf P. , Sandstrom K. , Galametz M. , Brandl B. , Groves B. , Rigopoulou D. , Walter F. , Leroy A. , Boquien M. , Tabatabaei F. S. , Beirao P. 
Published: July 2016

ABSTRACT
The [N ii] 122 and 205 μm transitions are powerful tracers of the ionized gas in the interstellar medium. By combining data from 21 galaxies selected from the Herschel KINGFISH and Beyond the Peak surveys, we have compiled 141 spatially resolved regions with a typical size of ∼1 kpc, with observations of both [N ii] far-infrared lines. We measure [N ii] 122/205 line ratios in the ∼0.6–6 range, which corresponds to electron gas densities of n
e ∼ 1–300 cm−3, with a median value of n
e = 30 cm−3. Variations in the electron density within individual galaxies can be as high as a factor of ∼50, frequently with strong radial gradients. We find that n
e increases as a function of infrared color, dust-weighted mean starlight intensity, and star-formation rate (SFR) surface density (ΣSFR). As the intensity of the [N ii] transitions is related to the ionizing photon flux, we investigate their reliability as tracers of the SFR. We derive relations between the [N ii] emission and SFR in the low-density limit and in the case of a log-normal distribution of densities. The scatter in the correlation between [N ii] surface brightness and ΣSFR can be understood as a property of the n
e distribution. For regions with n
e close to or higher than the [N ii] line critical densities, the low-density limit [N ii]-based SFR calibration systematically underestimates the SFR because the [N ii] emission is collisionally quenched. Finally, we investigate the relation between [N ii] emission, SFR, and n
e by comparing our observations to predictions from the MAPPINGS-III code.
THE BEAMING STRUCTURES OF JUPITER’S DECAMETRIC COMMON S-BURSTS OBSERVED FROM THE LWA1, NDA, AND URAN2 RADIO TELESCOPES
Authors: Imai Masafumi , Lecacheux Alain , Clarke Tracy E. , Higgins Charles A. , Panchenko Mykhaylo , Dowell Jayce , Imai Kazumasa , Brazhenko Anatolii I. , Frantsuzenko Anatolii V. , Konovalenko Alexandr A. 
Published: July 2016

ABSTRACT
On 2015 February 21, simultaneous observations of Jupiter's decametric radio emission between 10 and 33 MHz were carried out using three powerful low-frequency radio telescopes: the Long Wavelength Array Station One in the USA, the Nançay Decameter Array in France, and the URAN2 telescope in Ukraine. We measured the lag times of short-bursts (S-bursts) for 105 minutes of data over effective baselines of up to 8460 km by using cross-correlation analysis of the spectrograms from each instrument. Of particular interest is the measurement of the beaming thickness of S-bursts, testing if either flashlight- or beacon-like beaming is emanating from Jupiter. We find that the lag times for all pairs drift slightly as time elapses, in agreement with expectations from the flashlight-like beaming model. This leads to a new constraint of the minimum beaming thickness of 2.″66. Also, we find that most of the analyzed data abound with S-bursts, whose occurrence probability peaks at 17–18 MHz.
ASYMPTOTIC STEADY-STATE SOLUTION TO A BOW SHOCK WITH AN INFINITE MACH NUMBER
Authors: Yalinewich Almog , Sari Re’em 
Published: July 2016

ABSTRACT
The problem of a cold gas flowing past a stationary obstacle is considered. We study the bow shock that forms around the obstacle and show that at large distances from the obstacle the shock front forms a parabolic solid of revolution. The profiles of the hydrodynamic variables in the interior of the shock are obtained by solution of the hydrodynamic equations in parabolic coordinates. The results are verified with a hydrodynamic simulation. The drag force on the obstacle is also calculated. Finally, we use these results to model the bow shock around an isolated neutron star.
EXPLAINING THE MOST ENERGETIC SUPERNOVAE WITH AN INEFFICIENT JET-FEEDBACK MECHANISM
Authors: Gilkis Avishai , Soker Noam , Papish Oded 
Published: July 2016

ABSTRACT
We suggest that the energetic radiation from core-collapse super-energetic supernovae (SESNe) is due to a long-lasting accretion process onto the newly born neutron star (NS), resulting from an inefficient operation of the jet-feedback mechanism (JFM). The jets that are launched by the accreting NS or black hole maintain their axis due to a rapidly rotating pre-collapse core and do not manage to eject core material from near the equatorial plane. The jets are able to eject material from the core along the polar directions and reduce the gravity near the equatorial plane. The equatorial gas expands, and part of it falls back over a timescale of minutes to days to prolong the jet-launching episode. According to the model for SESNe proposed in the present paper, the principal parameter that distinguishes between the different cases of core-collapse supernova (CCSN) explosions, such as between normal CCSNe and SESNe, is the efficiency of the JFM. This efficiency, in turn, depends on the pre-collapse core mass, envelope mass, core convection, and, most of all, the angular momentum profile in the core. One prediction of the inefficient JFM for SESNe is the formation of a slow equatorial outflow in the explosion. The typical velocity and mass of this outflow are estimated to be v
eq ≈ 1000 km s−1 and M
eq ≳ 1 M
⊙, respectively, though quantitative values will have to be checked in future hydrodynamic simulations.
THREE-DIMENSIONAL SIMULATIONS OF LONG DURATION GAMMA-RAY BURST JETS: TIMESCALES FROM VARIABLE ENGINES
Authors: López-Cámara D. , Lazzati Davide , Morsony Brian J. 
Published: July 2016

ABSTRACT
Gamma-ray burst (GRB) light curves are characterized by marked variability, each showing unique properties. The origin of this variability, at least for a fraction of long GRBs, may be the result of an unsteady central engine. It is thus important to study the effects that an episodic central engine has on the jet propagation and, eventually, on the prompt emission within the collapsar scenario. Thus, in this study we follow the interaction of pulsed outflows with their progenitor stars with hydrodynamic numerical simulations in both two and three dimensions. We show that the propagation of unsteady jets is affected by the interaction with the progenitor material well after the break-out time, especially for jets with long quiescent times comparable to or larger than a second. We also show that this interaction can lead to an asymmetric behavior in which pulse durations and quiescent periods are systematically different. After the pulsed jets drill through the progenitor and the interstellar medium, we find that, on average, the quiescent epochs last longer than the pulses (even in simulations with symmetrical active and quiescent engine times). This could explain the asymmetry detected in the light curves of long quiescent time GRBs.
RADIO PULSATION SEARCH AND IMAGING STUDY OF SGR J1935+2154
Authors: Surnis Mayuresh. P. , Joshi Bhal Chandra , Maan Yogesh , Krishnakumar M. A. , Manoharan P. K. , Naidu Arun 
Published: July 2016

ABSTRACT
We present the results obtained from imaging observations and a search for radio pulsations toward the magnetar SGR J1935+2154 made using the Giant Metrewave Radio Telescope and the Ooty Radio Telescope. We present the high-resolution radio image of the supernova remnant (SNR) G57.2+0.8, which is positionally associated with SGR J1935+2154. We did not detect significant periodic radio pulsations from the magnetar, with 8σ upper limits on its flux density of 0.4 and 0.2 mJy at 326.5 and 610 MHz, respectively, for an assumed duty cycle of 10%. The corresponding 6σ upper limits at the two frequencies for any burst emission with an assumed width of 10 ms are 0.5 Jy and 63 mJy, respectively. No continuum radio point source was detected at the position of SGR J1935+2154 with a 3σ upper limit of 1.2 mJy. We also did not detect significant diffuse radio emission in a radius of 70 arc s coinciding with the recently reported diffuse X-ray emission, with a 3σ upper limit of 4.5 mJy. Using the archival HI spectra, we estimate the distance of SNR G57.2+0.8 to be 11.7 ± 2.8 kpc. Based on the measured HI column density (N

H
) along this line of sight, we argue that the magnetar could be physically associated with SNR G57.2+0.8. Based on the present data, we cannot rule out either a pulsar wind nebula or a dust-scattering halo origin for the diffuse X-ray emission seen around the magnetar.
EXTRAGALACTIC PLUS GALACTIC MODEL FOR ICECUBE NEUTRINO EVENTS
Authors: Palladino Andrea , Vissani Francesco 
Published: July 2016

ABSTRACT
The hypothesis that high-energy cosmic neutrinos are power law distributed is critically analyzed. We propose a model with two components that better explains the observations. The extragalactic component of the high-energy neutrino flux has a canonical

spectrum while the galactic component has a

spectrum; both of them are significant. This model has several implications, which can be tested by IceCube and ANTARES over the next several years. Moreover, the existence of a diffuse component, close to the Galactic plane and that yields (20–30)% of IceCube’s events, is interesting for the future km3 neutrino telescopes located in the Northern Hemisphere and for gamma-ray telescopes aiming to measure events up to a few 100 TeV from the southern sky.
TOWARD AN UNDERSTANDING OF CHANGING-LOOK QUASARS: AN ARCHIVAL SPECTROSCOPIC SEARCH IN SDSS
Authors: Ruan John J. , Anderson Scott F. , Cales Sabrina L. , Eracleous Michael , Green Paul J. , Morganson Eric , Runnoe Jessie C. , Shen Yue , Wilkinson Tessa D. , Blanton Michael R. , Dwelly Tom , Georgakakis Antonis , Greene Jenny E. , LaMassa Stephanie M. , Merloni Andrea , Schneider Donald P. 
Published: July 2016

ABSTRACT
The uncertain origin of the recently discovered “changing-look” quasar phenomenon—in which a luminous quasar dims significantly to a quiescent state in repeat spectroscopy over ∼10-year timescales—may present unexpected challenges to our understanding of quasar accretion. To better understand this phenomenon, we take a first step toward building a sample of changing-look quasars with a systematic but simple archival search for these objects in the Sloan Digital Sky Survey Data Release 12. By leveraging the >10-year baselines for objects with repeat spectroscopy, we uncover two new changing-look quasars and a third discovered previously. Decomposition of the multiepoch spectra and analysis of the broad emission lines suggest that the quasar accretion disk emission dims because of rapidly decreasing accretion rates (by factors of ≳2.5), while disfavoring changes in intrinsic dust extinction for the two objects where these analyses are possible. Broad emission line energetics also support intrinsic dimming of quasar emission as the origin for this phenomenon rather than transient tidal disruption events or supernovae. Although our search criteria included quasars at all redshifts and transitions from either quasar-like to galaxy-like states or the reverse, all of the clear cases of changing-look quasars discovered were at relatively low redshift (

) and only exhibit quasar-like to galaxy-like transitions.
THE GAMMA-RAY-EMITTING QUASAR 0202+149: A CSS REVISITED
Authors: An T. , Cui Y.-Z. , Baan W. A. , Wang W.-H. , Mohan P. 
Published: July 2016

ABSTRACT
PKS 0202+149 is a low-power radio source with blazar-like, γ-ray active galactic nucleus (AGN) characteristics. We investigate its properties and classification in relation to its γ-ray characteristics. This source shows a hint of low-frequency turnover at about 200 MHz. Radio imaging data of 0202+149 at different frequencies show differing morphologies on both kiloparsec (kpc) and parsec (pc) scales. The overall source shows a triple structure of a core and double lobes with a total projected size of ∼1.3 kpc. The compact source structure of 0202+149 is reminiscent of a compact steep spectrum (CSS) source. At pc scales, a core-jet structure extends ∼25 pc (in projection) at a position angle perpendicular to the kpc-scale structure. The curved pc-scale structure with a jet and inner lobe suggests that the CSS nuclear activity has recently re-started, although its power has been decreasing, while the kpc-scale lobes are relics of earlier activity. A maximum apparent superluminal motion of

is detected in the jet components, indicating a highly relativistic jet flow. The brightness temperature of the core is lower than the average value found for highly beamed, γ-ray AGNs, indicating a lower radio power and a relatively lower Doppler boosting factor. The CSS radio classification indicates that blazar-like γ-ray properties can also be manifested in low-power CSS radio sources with the appropriate jet and beaming properties.
THE INTRINSIC ABUNDANCE RATIO AND X-FACTOR OF CO ISOTOPOLOGUES IN L 1551 SHIELDED FROM FUV PHOTODISSOCIATION
Authors: Lin 林聖鈞 Sheng-Jun , Shimajiri Yoshito , Hara Chihomi , Lai 賴詩萍 Shih-Ping , Nakamura Fumitaka , Sugitani Koji , Kawabe Ryohei , Kitamura Yoshimi , Yoshida Atsushi , Tatei Hidefumi , Akashi Toshiya , Higuchi Aya E. , Tsukagoshi Takashi 
Published: July 2016

ABSTRACT
We investigate the intrinsic abundance ratio of 13CO to C18O and the X-factor in L 1551 using the Nobeyama Radio Observatory (NRO) 45 m telescope. L 1551 is chosen because it is relatively isolated in the Taurus molecular cloud shielded from FUV photons, providing an ideal environment for studying the target properties. Our observations cover

with a resolution of

which make up maps with the highest spatial dynamical range to date. We derive the

value on the sub-parsec scales in the range of ∼3–27 with a mean value of 8.0 ± 2.8. Comparing to the visual extinction map derived from the Herschel observations, we found that the abundance ratio reaches its maximum at low

(i.e.,

∼ 1–4 mag), and decreases to the typical solar system value of 5.5 inside L 1551 MC. The high

value at the boundary of the cloud is most likely due to the selective FUV photodissociation of C18O. This is in contrast with Orion-A where internal OB stars keep the abundance ratio at a high level, greater than ∼10. In addition, we explore the variation of the X-factor, because it is an uncertain, but widely used, quantity in extragalactic studies. We found that the X-factor

, which is consistent with previous simulations. Excluding the high density region, the average X-factor is similar to the Milky Way average value.
THE IBEX RIBBON AND THE PICKUP ION RING STABILITY IN THE OUTER HELIOSHEATH. I. THEORY AND HYBRID SIMULATIONS
Authors: Florinski V. , Heerikhuisen J. , Niemiec J. , Ernst A. 
Published: July 2016

ABSTRACT
The nearly circular band of energetic neutral atom emission dominating the field of view of the Interplanetary Boundary Explorer (IBEX ) satellite, is most commonly attributed to the effect of charge exchange of secondary pickup ions (PUIs) gyrating about the magnetic field in the outer heliosheath and the interstellar space beyond. Several models for the PUI dynamics of this mechanism have been proposed, each requiring either strong or weak scattering of the initial pitch angle. Conventional wisdom states that ring distributions tend to generate waves and scatter onto a shell on timescales too short for charge exchange to occur. We performed a careful study of ring and thin shell proton distribution stability using theoretical tools and hybrid plasma simulations. We show that the kinetic behavior of a freshly injected proton ring is a far more complicated process than previously thought. In the presence of a warm Maxwellian core, narrower rings could be more stable than broader toroidal distributions. The scattered rings possess a fine structure that can only be revealed using very large numbers of macroparticles in a simulation. It is demonstrated that a “stability gap” in ring temperature exists where the protons could retain large gyrating anisotropies for years, and the wave activity could remain below the level of the ambient magnetic fluctuations in interstellar space. In the directions away from the ribbon, however, a partial shell distribution is more likely to be unstable, leading to significant scattering into one hemisphere in velocity space. The process is accompanied by turbulence production, which is puzzling given the very low level of magnetic fluctuations measured in the outer heliosheath by Voyager 1.
DDO 68: A FLEA WITH SMALLER FLEAS THAT ON HIM PREY
Authors: Annibali Francesca , Nipoti Carlo , Ciotti Luca , Tosi Monica , Aloisi Alessandra , Bellazzini Michele , Cignoni Michele , Cusano Felice , Paris Diego , Sacchi Elena 
Published: July 2016

ABSTRACT
We present new photometry of the dwarf irregular galaxy DDO 68, one of the most metal-poor and least massive dwarfs, located in the Lynx-Cancer Void. The images were acquired with the Large Binocular Telescope in the g and r passbands and show unequivocally that DDO 68 has previously unknown stellar streams related to the accretion of at least two smaller companions: a flea with smaller fleas biting it, to put it in Jonathan Swift’s words (from Jonathan Swift’s On Poetry: a Rhapsody: So, naturalists observe, a flea/has smaller fleas that on him prey/and these have smaller still to bite em/and so proceed ad infinitum). Our data provide direct observational evidence of multiple galaxy merging occurring at very low galactic mass scales. We present the results of an N-body simulation of the interaction of three dwarf galaxies that reproduce well the main morphological features of DDO 68.
A DECAM SEARCH FOR AN OPTICAL COUNTERPART TO THE LIGO GRAVITATIONAL-WAVE EVENT GW151226
Authors: Cowperthwaite P. S. , Berger E. , Soares-Santos M. , Annis J. , Brout D. , Brown D. A. , Buckley-Geer E. , Cenko S. B. , Chen H. Y. , Chornock R. , Diehl H. T. , Doctor Z. , Drlica-Wagner A. , Drout M. R. , Farr B. , Finley D. A. , Foley R. J. , Fong W. , Fox D. B. , Frieman J. , Garcia-Bellido J. , Gill M. S. S. , Gruendl R. A. , Herner K. , Holz D. E. , Kasen D. , Kessler R. , Lin H. , Margutti R. , Marriner J. , Matheson T. , Metzger B. D. , Neilsen Jr. E. H. , Quataert E. , Rest A. , Sako M. , Scolnic D. , Smith N. , Sobreira F. , Strampelli G. M. , Villar V. A. , Walker A. R. , Wester W. , Williams P. K. G. , Yanny B. , Abbott T. M. C. , Abdalla F. B. , Allam S. , Armstrong R. , Bechtol K. , Benoit-Lévy A. , Bertin E. , Brooks D. , Burke D. L. , Rosell A. Carnero , Kind M. Carrasco , Carretero J. , Castander F. J. , Cunha C. E. , D’Andrea C. B. , Costa L. N. da , Desai S. , Dietrich J. P. , Evrard A. E. , Neto A. Fausti , Fosalba P. , Gerdes D. W. , Giannantonio T. , Goldstein D. A. , Gruen D. , Gutierrez G. , Honscheid K. , James D. J. , Johnson M. W. G. , Johnson M. D. , Krause E. , Kuehn K. , Kuropatkin N. , Lima M. , Maia M. A. G. , Marshall J. L. , Menanteau F. , Miquel R. , Mohr J. J. , Nichol R. C. , Nord B. , Ogando R. , Plazas A. A. , Reil K. , Romer A. K. , Sanchez E. , Scarpine V. , Sevilla-Noarbe I. , Smith R. C. , Suchyta E. , Tarle G. , Thomas D. , Thomas R. C. , Tucker D. L. , Weller J. ,   (The DES Collaboration)
Published: July 2016

ABSTRACT
We report the results of a Dark Energy Camera optical follow-up of the gravitational-wave (GW) event GW151226, discovered by the Advanced Laser Interferometer Gravitational-wave Observatory detectors. Our observations cover 28.8 deg2 of the localization region in the i and z bands (containing 3% of the BAYESTAR localization probability), starting 10 hr after the event was announced and spanning four epochs at 2–24 days after the GW detection. We achieve

5
σ

point-source limiting magnitudes of

i
≈
21.7

and

z
≈
21.5

, with a scatter of 0.4 mag, in our difference images. Given the two-day delay, we search this area for a rapidly declining optical counterpart with

≳
3
σ

significance steady decline between the first and final observations. We recover four sources that pass our selection criteria, of which three are cataloged active galactic nuclei. The fourth source is offset by 5.8 arcsec from the center of a galaxy at a distance of 187 Mpc, exhibits a rapid decline by 0.5 mag over 4 days, and has a red color of

i
−
z
≈
0.3

mag. These properties could satisfy a set of cuts designed to identify kilonovae. However, this source was detected several times, starting 94 days prior to GW151226, in the Pan-STARRS Survey for Transients (dubbed as PS15cdi) and is therefore unrelated to the GW event. Given its long-term behavior, PS15cdi is likely a Type IIP supernova that transitioned out of its plateau phase during our observations, mimicking a kilonova-like behavior. We comment on the implications of this detection for contamination in future optical follow-up observations.
STATISTICAL MEASUREMENT OF THE GAMMA-RAY SOURCE-COUNT DISTRIBUTION AS A FUNCTION OF ENERGY
Authors: Zechlin Hannes-S. , Cuoco Alessandro , Donato Fiorenza , Fornengo Nicolao , Regis Marco 
Published: July 2016

ABSTRACT
Statistical properties of photon count maps have recently been proven as a new tool to study the composition of the gamma-ray sky with high precision. We employ the 1-point probability distribution function of six years of Fermi-LAT data to measure the source-count distribution dN/dS and the diffuse components of the high-latitude gamma-ray sky as a function of energy. To that aim, we analyze the gamma-ray emission in five adjacent energy bands between 1 and 171 GeV. It is demonstrated that the source-count distribution as a function of flux is compatible with a broken power law up to energies of ∼50 GeV. The index below the break is between 1.95 and 2.0. For higher energies, a simple power-law fits the data, with an index of

2.2

−
0.3

+
0.7

in the energy band between 50 and 171 GeV. Upper limits on further possible breaks as well as the angular power of unresolved sources are derived. We find that point-source populations probed by this method can explain

83

−
13

+
7

% (

81

−
19

+
52

%) of the extragalactic gamma-ray background between 1.04 and 1.99 GeV (50 and 171 GeV). The method has excellent capabilities for constraining the gamma-ray luminosity function and the spectra of unresolved blazars.
Les concentrations hivernales : une pratique touristique originale des motocyclistes européens à la recherche du froid et de la neige
Authors: Scol Jean 
Published: July 2016

La concentration est une forme de tourisme très développée dans le monde de la moto. Parmi les presque 3 500 concentrations de moto organisées chaque année en Europe environ dix pour-cent le sont au cœur de l'hiver. Ces concentrations dites hivernales répondent à des critères tout à fait spécifiques. Leur réussite et réputation dépendent pour une grande part de conditions météorologiques paradoxalement peu adaptées à la moto! Elles sont donc de préférence organisées dans des régions qui promettent des conditions hivernales les plus rudes : (très) loin vers le nord ou vers l'est du continent ou bien à des altitudes parfois très élevées. Des localisations à l'origine d'une véritable hiérarchie établie entre les hivernales elles-mêmes mais aussi entre les motocyclistes qui y participent.