Abstracts of Interest

Selected by: Rebecca Blackwell

Abstract: 1710.05832
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Title: GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral

Abstract: On August 17, 2017 at 12:41:04 UTC the Advanced LIGO and Advanced Virgo gravitational-wave detectors made their first observation of a binary neutron star inspiral. The signal, GW170817, was detected with a combined signal-to-noise ratio of 32.4 and a false-alarm-rate estimate of less than one per $8.0\times10^4$ years. We infer the component masses of the binary to be between 0.86 and 2.26 $M_\odot$, in agreement with masses of known neutron stars. Restricting the component spins to the range inferred in binary neutron stars, we find the component masses to be in the range 1.17 to 1.60 $M_\odot$, with the total mass of the system $2.74^{+0.04}_{-0.01}\,M_\odot$. The source was localized within a sky region of 28 deg$^2$ (90% probability) and had a luminosity distance of $40^{+8}_{-14}$ Mpc, the closest and most precisely localized gravitational-wave signal yet. The association with the gamma-ray burst GRB 170817A, detected by Fermi-GBM 1.7 s after the coalescence, corroborates the hypothesis of a neutron star merger and provides the first direct evidence of a link between these mergers and short gamma-ray bursts. Subsequent identification of transient counterparts across the electromagnetic spectrum in the same location further supports the interpretation of this event as a neutron star merger. This unprecedented joint gravitational and electromagnetic observation provides insight into astrophysics, dense matter, gravitation and cosmology.

Abstract: 1710.05833
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Title: Multi-messenger Observations of a Binary Neutron Star Merger

Authors: LIGO Scientific Collaboration, Virgo Collaboration, Fermi GBM, INTEGRAL, IceCube Collaboration, AstroSat Cadmium Zinc Telluride Imager Team, IPN Collaboration, The Insight-Hxmt Collaboration, ANTARES Collaboration, The Swift Collaboration, AGILE Team, The 1M2H Team, The Dark Energy Camera GW-EM Collaboration, the DES Collaboration, The DLT40 Collaboration, GRAWITA: GRAvitational Wave Inaf TeAm, The Fermi Large Area Telescope Collaboration, ATCA: Australia Telescope Compact Array, ASKAP: Australian SKA Pathfinder, Las Cumbres Observatory Group, OzGrav, DWF (Deeper, Wider, Faster Program), AST3, CAASTRO Collaborations, The VINROUGE Collaboration, MASTER Collaboration, J-GEM, GROWTH, JAGWAR, Caltech- NRAO, TTU-NRAO, NuSTAR Collaborations, Pan-STARRS, The MAXI Team, TZAC Consortium, KU Collaboration, et al. (26 additional authors not shown)
Abstract: On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of $\sim$1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg$^2$ at a luminosity distance of $40^{+8}_{-8}$ Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Msun. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at $\sim$40 Mpc) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over $\sim$10 days. Following early non-detections, X-ray and radio emission were discovered at the transient's position $\sim$9 and $\sim$16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. (Abridged)

Comments: This is a reproduction of the article published in the Astrophysical Journal Letters, under the terms of the Creative Commons Attribution 3.0 licence

Abstract: 1710.05834
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Title: Gravitational Waves and Gamma-rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A

Abstract: On 2017 August 17, the gravitational-wave event GW170817 was observed by the Advanced LIGO and Virgo detectors, and the gamma-ray burst (GRB) GRB 170817A was observed independently by the Fermi Gamma-ray Burst Monitor, and the Anticoincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory. The probability of the near-simultaneous temporal and spatial observation of GRB 170817A and GW170817 occurring by chance is $5.0\times 10^{-8}$. We therefore confirm binary neutron star mergers as a progenitor of short GRBs. The association of GW170817 and GRB 170817A provides new insight into fundamental physics and the origin of short gamma-ray bursts. We use the observed time delay of $(+1.74 \pm 0.05)\,$s between GRB 170817A and GW170817 to: (i) constrain the difference between the speed of gravity and the speed of light to be between $-3\times 10^{-15}$ and $+7\times 10^{-16}$ times the speed of light, (ii) place new bounds on the violation of Lorentz invariance, (iii) present a new test of the equivalence principle by constraining the Shapiro delay between gravitational and electromagnetic radiation. We also use the time delay to constrain the size and bulk Lorentz factor of the region emitting the gamma rays. GRB 170817A is the closest short GRB with a known distance, but is between 2 and 6 orders of magnitude less energetic than other bursts with measured redshift. A new generation of gamma-ray detectors, and subthreshold searches in existing detectors, will be essential to detect similar short bursts at greater distances. Finally, we predict a joint detection rate for the Fermi Gamma-ray Burst Monitor and the Advanced LIGO and Virgo detectors of 0.1--1.4 per year during the 2018-2019 observing run and 0.3--1.7 per year at design sensitivity.

Comments: 36 pages, 6 figures, 2 tables; ApJL, in press

Abstract: 1710.05839
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Abstract: 1710.05846
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Title: Follow up of GW170817 and its electromagnetic counterpart by Australian-led observing programs

Authors: I. Andreoni, K. Ackley, J. Cooke, A. Acharyya, J. R. Allison, G. E. Anderson, M. C. B. Ashley, D. Baade, M. Bailes, K. Bannister, A. Beardsley, M. S. Bessell, F. Bian, P. A. Bland, M. Boer, T. Booler, A. Brandeker, I. S. Brown, D. Buckley, S.-W. Chang, D. M. Coward, S. Crawford, H.Crisp, B. Crosse, A. Cucchiara, M. Cupák, J. S. de Gois, A. Deller, H. A. R. Devillepoix, D. Dobie, E. Elmer, D. Emrich, W. Farah, T. J. Farrell, T. Franzen, B. M. Gaensler, D. K. Galloway, B. Gendre, T. Giblin, A. Goobar, J. Green, P. J. Hancock, B. A. D. Hartig, E. J. Howell, L. Horsley, A. Hotan, R. M. Howie, L. Hu, Y. Hu, C. W. James, S. Johnston, M. Johnston-Hollitt, D. L. Kaplan, M. Kasliwal, E. F. Keane, D. Kenney, A. Klotz, R. Lau, R. Laugier, E. Lenc, X. Li, E. Liang, C. Lidman, L. C. Luvaul, C. Lynch, et al. (60 additional authors not shown)
(Submitted on 16 Oct 2017)
Abstract: The discovery of the first electromagnetic counterpart to a gravitational wave signal has generated follow-up observations by over 50 facilities world-wide, ushering in the new era of multi-messenger astronomy. In this paper, we present follow-up observations of the gravitational wave event GW170817 and its electromagnetic counterpart SSS17a/DLT17ck (IAU label AT2017gfo) by 14 Australian telescopes and partner observatories as part of Australian-based and Australian-led research programs. We report early- to late-time multi-wavelength observations, including optical imaging and spectroscopy, mid-infrared imaging, radio imaging, and searches for fast radio bursts. Our optical spectra reveal that the transient source afterglow cooled from approximately 6400K to 2100K over a 7-day period and produced no significant optical emission lines. The spectral profiles, cooling rate, and photometric light curves are consistent with the expected outburst and subsequent processes of a binary neutron star merger. Star formation in the host galaxy probably ceased at least a Gyr ago, although there is evidence for a galaxy merger. Binary pulsars with short (100 Myr) decay times are therefore unlikely progenitors, but pulsars like PSR B1534+12 with its 2.7 Gyr coalescence time could produce such a merger. The displacement (about 2.2 kpc) of the binary star system from the centre of the main galaxy is not unusual for stars in the host galaxy or stars originating in the merging galaxy, and therefore any constraints on the kick velocity imparted to the progenitor are poor.

Comments: 26 pages, 9 figures, 15 tables

Abstract: 1710.05862
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Title: TeV gamma-ray observations of the binary neutron star merger GW170817 with H.E.S.S

Authors: H.E.S.S. Collaboration: H. Abdalla, A. Abramowski, F. Aharonian, F. Ait Benkhali, E.O. Angüner, M. Arakawa, M. Arrieta, P. Aubert, M. Backes, A. Balzer, M. Barnard, Y. Becherini, J. Becker Tjus, D. Berge, S. Bernhard, K. Bernlöhr, R. Blackwell, M. Böttcher, C. Boisson, J. Bolmont, S. Bonnefoy, P. Bordas, J. Bregeon, F. Brun, P. Brun, M. Bryan, M. Büchele, T. Bulik, M. Capasso, S. Caroff, A. Carosi, S. Casanova, M. Cerruti, N. Chakraborty, R.C.G. Chaves, A. Chen, J. Chevalier, S. Colafrancesco, B. Condon, J. Conrad, I.D. Davids, J. Decock, C. Deil, J. Devin, P. deWilt, L. Dirson, A. Djannati-Ataï, A. Donath, L.O'C. Drury, K. Dutson, J. Dyks, T. Edwards, K. Egberts, G. Emery, J.-P. Ernenwein, S. Eschbach, C. Farnier, S. Fegan, M.V. Fernandes, A. Fiasson, G. Fontaine,
S. Funk, M. Füßling, S. Gabici, Y.A. Gallant, T. Garrigoux, F. Gaté, G. Giavitto, B. Giebels, D. Glawion, J.F. Glicenstein, D. Gottschall, M.-H. Grondin, J. Hahn, M. Haupt, J. Hawkes, G. Heinzelmann, G. Henri, G. Hermann, J.A. Hinton, W. Hofmann, C. Hoischen, T. L. Holch, M. Holler, D. Horns, A. Ivascenko, H. Iwasaki, A. Jacholkowska, M. Jamrozy, D. Jankowsky, F. Jankowsky, M. Jingo, L. Jouvin, I. Jung-Richardt, M.A. Kastendieck, K. Katarzyński, M. Katsuragawa, U. Katz, D. Kerszberg, D. Khangulyan, B. Khélifi, J. King, S. Klepser, D. Klochkov, W. Kluźniak, Nu. Komin, K. Kosack, S. Krakau, M. Kraus, P.P. Krüger, H. Laffon, G. Lamanna, J. Lau, J.-P. Lees, J. Lefaucheur, A. Lemière, M. Lemoine-Goumard, J.-P. Lenain, E. Leser, T. Lohse, M. Lorentz, R. Liu, R. López-Coto, I. Lypova, D. Malyshev, V. Marandon, A. Marcowith, C. Mariaud, R. Marx, G. Maurin, N. Maxted, M. Mayer, P.J. Meintjes, M. Meyer, A.M.W. Mitchell, R. Moderski, M. Mohamed, L. Mohrmann, K. Morå, E. Moulin, T. Murach, S. Nakashima, M. de Naurois, H. Ndiyavala, F. Niederwanger, J. Niemiec, L. Oakes, P. O'Brien, H. Odaka, S. Ohm, M. Ostrowski, I. Oya, M. Padovani, M. Panter, R.D. Parsons, N.W. Pekeur, G. Pelletier, C. Perennes, P.-O. Petrucci, B. Peyaud, Q. Piel, S. Pita, V. Poireau, H. Poon, D. Prokhorov, H. Prokoph, G. Pühlhofer, M. Punch, A. Quirrenbach, S. Raab, R. Rauth, A. Reimer, O. Reimer, M. Renaud, R. de los Reyes, F. Rieger, L. Rinchiuso, C. Romoli, G. Rowell, B. Rudak, C.B. Rulten, V. Sahakian, S. Saito, D.A. Sanchez, A. Santangelo, M. Sasaki, R. Schlickeiser, F. Schüssler, A. Schulz, U. Schwanke, S. Schwemmer, M. Seglar-Arroyo, M. Settimo, A.S. Seyffert, N. Shafi, I. Shilon, K. Shiningayamwe, R. Simoni, H. Sol, F. Spanier, M. Spir-Jacob, Ł. Stawarz, R. Steenkamp, C. Stegmann, C. Steppa, I. Sushch, T. Takahashi, J.-P. Tavernet, T. Tavernier, A.M. Taylor, R. Terrier, L. Tibaldo, D. Tiziani, M. Tluczykont, C. Trichard, M. Tsirou, N. Tsuji, R. Tuffs, Y. Uchiyama, D.J. van der Walt, C. van Eldik, C. van Rensburg, B. van Soelen, G. Vasileiadis, J. Veh, C. Venter, A. Viana, P. Vincent, J. Vink, F. Voisin, H.J. Völk, T. Vuillaume, Z. Wadiasingh, S.J. Wagner, P. Wagner, R.M. Wagner, R. White, A. Wierzcholska, P. Willmann, A. Wörnlein, D. Wouters, R. Yang, D. Zaborov, M. Zacharias, R. Zanin, A.A. Zdziarski, A. Zech, F. Zefi, A. Ziegler, J. Zorn, N. Żywucka
et al. (190 additional authors not shown)
(Submitted on 16 Oct 2017)
Abstract: We search for high-energy gamma-ray emission from the binary neutron star merger GW170817 with the H.E.S.S. Imaging Air Cherenkov Telescopes. The observations presented here have been obtained starting only 5.3h after GW170817. The H.E.S.S. target selection identified regions of high probability to find a counterpart of the gravitational wave event. The first of these regions contained the counterpart SSS17a that has been identified in the optical range several hours after our observations. We can therefore present the first data obtained by a ground-based pointing instrument on this object. A subsequent monitoring campaign with the H.E.S.S. telescopes extended over several days, covering timescales from 0.22 to 5.2 days and energy ranges between $270\,\mathrm{GeV}$ to $8.55\,\mathrm{TeV}$. No significant gamma-ray emission has been found. The derived upper limits on the very-high-energy gamma-ray flux for the first time constrain non-thermal, high-energy emission following the merger of a confirmed binary neutron star system.

Comments: submitted to ApJL

Abstract: 1710.05038
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Title: Time Evolution of Gamma Rays from Supernova Remnants

Authors: Daniele Gaggero, Fabio Zandanel, Pierre Cristofari, Stefano Gabici
(Submitted on 13 Oct 2017)
Abstract: We present a systematic phenomenological study focused on the time evolution of the non-thermal radiation - from radio waves to gamma rays - emitted by typical supernova remnants via hadronic and leptonic mechanisms, for two classes of progenitors: thermonuclear and core-collapse. To this aim, we develop a numerical tool designed to model the evolution of the cosmic-ray spectrum inside a supernova remnant, and compute the associated multi-wavelength emission. We demonstrate the potential of this tool in the context of future population studies based on large collection of high-energy gamma-ray data. We discuss and explore the relevant parameter space involved in the problem, and focus in particular on their impact on the maximum energy of accelerated particles, in order to study the effectiveness and duration of the PeVatron phase. We outline the crucial role of the ambient medium through which the shock propagates during the remnant evolution. In particular, we point out the role of dense clumps in creating a significant hardening in the hadronic gamma-ray spectrum.

Comments: 10 pages, 6 figures. Submitted to MNRAS

Abstract: 1710.05517
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Title: Anisotropies of Ultra-high Energy Cosmic Rays Dominated by a Single Source in the Presence of Deflections

Authors: Andrej Dundović, Günter Sigl
(Submitted on 16 Oct 2017)
Abstract: This work presents a scenario of ultra-high energy cosmic ray source distribution where a nearby source is solely responsible for the anisotropies in arrival directions of cosmic rays while the rest of the sources contribute only isotropically. An analytical approach focused on large-scale anisotropies, which are influenced by deflections in a Kolmogorov-type turbulent magnetic field, is employed to give more general results. When the recent Pierre Auger Observatory angular power spectrum above 8 EeV is used the model gives two solutions: weaker RMS deflections $\delta_\mathrm{rms}^+ = (95\pm 36)^\circ$ with the lower relative flux from the single source $\eta^+=0.38\pm 0.18$, or stronger RMS deflections $\delta_\mathrm{rms}^- = (113\pm 24)^\circ$ with the higher relative flux $\eta^-=0.49\pm 0.23$. It is shown that the first solution predicts a lower dipole amplitude at higher energies compared to the second solution. Furthermore, these solutions can be translated into constraints on the source distance, luminosity, and extragalactic magnetic field strength. For Centaurus A and Virgo cluster the required relation between the coherence length and the RMS magnetic field strength is obtained: a coherence length of $~\sim 10\,\mathrm{kpc}$ would imply RMS field strengths above $1\,\mathrm{nG}$ for iron dominated and above $10\,\mathrm{nG}$ for proton dominated composition. A comparison of the model with advanced Monte Carlo techniques is performed to show its applicability in a realistic, structured magnetic field and to analyze structured field effects on the anisotropies. The result of the comparison shows a tendency of structured fields to suppress large scale anisotropies, especially the dipole, compared to those anisotropies of smaller scales.

Comments: 22 pages, 11 figures

Abstract: 1710.05617
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Title: On the anisotropy in the arrival directions of ultra-high-energy cosmic rays

Authors: David Wittkowski, Karl-Heinz Kampert
(Submitted on 16 Oct 2017)
Abstract: We present results of elaborate four-dimensional simulations of the propagation of ultra-high-energy cosmic rays (UHECR), which are based on a realistic astrophysical scenario. The distribution of the arrival directions of the UHECR is found to have a pronounced dipolar anisotropy and rather weak higher-order contributions to the angular power spectrum. This finding agrees well with the recent observation of a dipolar anisotropy for UHECR with arrival energies above 8 EeV by the Pierre Auger Observatory and constitutes an important prediction for other energy ranges and higher-order angular contributions for which sufficient experimental data are not yet available. Since our astrophysical scenario enables simulations that are completely consistent with the available data, this scenario will be a very useful basis for related future studies.

Comments: 6 pages, 1 figure

Abstract: 1710.05721
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Title: Galactocentric variation of the gas-to-dust ratio and its relation with metallicity

Authors: A. Giannetti, S. Leurini, C. Koenig, J. S. Urquhart, T. Pillai, J. Brand, J. Kauffmann, F. Wyrowski, K. M. Menten
(Submitted on 16 Oct 2017)
Abstract: (Abridged) Context: The assumption of a gas-to-dust mass ratio (\gamma) is a common approach to estimate the basic properties of molecular clouds, such as total mass and column density of molecular hydrogen, from (sub)mm continuum observations of the dust. In the Milky Way a single value is used at all galactocentric radii, independently of the observed metallicity gradients. Both models and extragalactic observations suggest that this quantity increases for decreasing metallicity Z, typical of the outer regions in disks, where fewer heavy elements are available to form dust grains.
Aims: We aim to investigate the variation of the gas-to-dust ratio as a function of galactocentric radius and metallicity, to allow a more accurate characterisation of the quantity of molecular gas across the galactic disk, as derived from observations of the dust.
Methods: Observations of the optically thin C\$^{18}\$O (2-1) transition were obtained with the APEX telescope for a sample of 23 massive and dense star-forming regions in the far outer Galaxy (galactocentric distance greater than 14 kpc). From the modelling of this line and of the spectral energy distribution of the selected clumps we computed the gas-to-dust ratio and compared it to that of well-studied sources from the ATLASGAL TOP100 sample in the inner galactic disk.
Results: The gradient in gas-to-dust ratio is found to be 0.087 dex/kpc (or equivalently \gamma\ proportional to Z\$^{-1.4}\$). The dust-to-metal ratio, decreases with galactocentric radius, which is the most common situation also for external late-type galaxies. This suggests that grain growth dominates over destruction. The predicted gas-to-dust ratio is in excellent agreement with the estimates in Magellanic clouds, for the appropriate value of Z.

Comments: Accepted for publication on A&A

Abstract: 1710.05940
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Title: Astrochemistry: overview and challenges

Authors: Ewine F. van Dishoeck
(Submitted on 16 Oct 2017)
Abstract: This paper provides a brief overview of the journey of molecules through the Cosmos, from local diffuse interstellar clouds and PDRs to distant galaxies, and from cold dark clouds to hot star-forming cores, protoplanetary disks, planetesimals and exoplanets. Recent developments in each area are sketched and the importance of connecting astronomy with chemistry and other disciplines is emphasized. Fourteen challenges for the field of Astrochemistry in the coming decades are formulated.

Comments: 20 pages, 5 figures, to appear in IAU Symposium 332 "Astrochemistry VII: Through the Cosmos from Galaxies to Planets", eds. M. Cunningham, T.J. Millar, Y. Aikawa

Abstract: 1710.06101
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Title: Probing The Local Environment of the Supernova Remnant HESS J1731$-$347 with CO and CS Observations

Authors: Nigel Maxted, Michael Burton, Catherine Braiding, Gavin Rowell, Hidetoshi Sano, Fabien Voisin, Massimo Capasso, Gerd Pühlhofer, Yasuo Fukui
(Submitted on 17 Oct 2017)
Abstract: The shell-type supernova remnant HESS J1731$-$347 emits TeV gamma-rays, and is a key object for the study of the cosmic ray acceleration potential of supernova remnants. We use 0.5-1 arcminute Mopra CO/CS(1-0) data in conjunction with HI data to calculate column densities towards the HESS J1731$-$347 region. We trace gas within at least four Galactic arms, typically tracing total (atomic+molecular) line-of-sight H column densities of 2-3$\times$10$^{22}$ cm$^{-2}$. Assuming standard X-factor values and that most of the HI/CO emission seen towards HESS J1731$-$347 is on the near-side of the Galaxy, X-ray absorption column densities are consistent with HI+CO-derived column densities foreground to, but not beyond, the Scutum-Crux Galactic arm, suggesting a kinematic distance of $\sim$3.2 kpc for HESS J1731$-$347. At this kinematic distance, we also find dense, infrared-dark gas traced by CS(1-0) emission coincident with the north of HESS J1731$-$347, the nearby HII region G353.43$-$0.37 and the nearby unidentified gamma-ray source HESS J1729$-$345. This dense gas lends weight to the idea that HESS J1729$-$345 and HESS J1731-347 are connected, perhaps via escaping cosmic-rays.

Comments: 16 pages, 13 figures, Accepted for publication in MNRAS

Abstract: 1710.06489
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Title: Mapping Spiral Structure on the far side of the Milky Way

Authors: Alberto Sanna, Mark J. Reid, Thomas M. Dame, Karl M. Menten, Andreas Brunthaler
(Submitted on 17 Oct 2017)
Abstract: Little is known about the portion of the Milky Way lying beyond the Galactic center at distances of more than 9 kilo-parsec from the Sun. These regions are opaque at optical wavelengths due to absorption by interstellar dust, and distances are very large and hard to measure. We report a direct trigonometric parallax distance of 20.4_{-2.2}^{+2.8} kilo-parsec obtained with the Very Long Baseline Array to a water maser source in a region of active star formation. These measurements allow us to shed light on Galactic spiral structure by locating the Scutum-Centaurus spiral arm as it passes through the far side of the Milky Way, and to validate a kinematic method for determining distances in this region based on transverse motions.

Comments: 21 pages, 5 figures, 4 tables, published in Science, October 13 issue

Abstract: 1710.07391
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Title: Design & development of position sensitive detector for hard X-ray using SiPM and new generation scintillators

Authors: S. K. Goyal, Amisha P. Naik, Mithun N. P. S., S. V. Vadawale, Neeraj K. Tiwari, T. Chattopadhyay, N. Nagrani, S. Madhavi, T. ladiya, A. R. Patel, M. Shanmugam, H. L. Adalja, V. R. patel, G. P. Ubale
(Submitted on 20 Oct 2017)
Abstract: There is growing interest in high-energy astrophysics community for the development of sensitive instruments in the hard X-ray energy extending to few hundred keV. This requires position sensitive detector modules with high efficiency in the hard X-ray energy range. Here, we present development of a detector module, which consists of 25 mm x 25 mm CeBr3 scintillation detector, read out by a custom designed two dimensional array of Silicon Photo-Multipliers (SiPM). Readout of common cathode of SiPMs provides the spectral measurement whereas the readout of individual SiPM anodes provides measurement of interaction position in the crystal. Preliminary results for spectral and position measurements with the detector module are presented here.

Comments: Published in SPIE Proceedings Vol. 10392

Abstract: 1710.06971
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Title: Simulation of Near Horizontal Muons and Muon Bundles for the HAWC Observatory with CORSIKA

Authors: Ahron S. Barber, David B. Kieda, R. Wayne Springer (for the HAWC Collaboration)
(Submitted on 19 Oct 2017)
Abstract: The HAWC (High Altitude Water Cerenkov) gamma ray observatory observes muons with nearly-horizontal trajectories corresponding to zenith angles greater than $80^{0}$. HAWC is located at an altitude of 4100 meters a.s.l. (70 deg. atmospheric depth of 2400 g/cm$^{2}$) on the extinct volcano, Sierra Negra in Mexico. In this poster, we summarize the CORSIKA and GEANT4 as well as toy-model based simulations performed to determine the effective area of HAWC to muons from high zenith angle cosmic ray primaries. We are developing an updated GEANT4 based detector response simulation that includes a model of the volcanoes that are located near HAWC. These simulations are investigating the capability to use muon multiplicity and rates to differentiate between the primary particle composition (proton or iron) and measure the primary energy.

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

Abstract: 1710.06980
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Title: Nature of the low-energy, γ-like background for the Cherenkov Telescope Array

Authors: Julian Sitarek, Dorota Sobczyńska, Michał Szanecki, Katarzyna Adamczyk, Paolo Cumani, Abelardo Moralejo
(Submitted on 19 Oct 2017)
Abstract: The upcoming Cherenkov Telescope Array (CTA) project is expected to provide unprecedented sensitivity in the low-energy (<~100 GeV) range for Cherenkov telescopes. Most of the remaining background in this energy range results from misidentified hadron showers. In order to fully exploit the potential of the telescope systems it is worthwhile to look for ways to further improve the available analysis methods for {\gamma}/hadron separation. We study the composition of the background for the planned CTA-North array by identifying events composed mostly of a single electromagnetic subcascade or double subcascade from a {\pi}0 (or another neutral meson) decay. We apply the standard simulation chain and state-of-the-art analysis chain of CTA to evaluate the potential of the standard analysis to reject such events. Simulations show a dominant role of such single subcascade background for CTA up to energies ~70 GeV. We show that a natural way of rejection of such events stems from a shifted location of the shower maximum, and that the standard stereo reconstruction method used by CTA already exploits most of expected separation.

Comments: 11 pages, 13 figures, accepted for publication in Astroparticle Physics

Abstract: 1710.07117
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Title: The Graphical User Interface of the Operator of the Cherenkov Telescope Array

Authors: Iftach Sadeh, Igor Oya, Joseph Schwarz, Emmanuel Pietriga, Dejan Dezman (the CTA Consortium)
(Submitted on 19 Oct 2017)
Abstract: The Cherenkov Telescope Array (CTA) is the next generation gamma-ray observatory. CTA will incorporate about 100 imaging atmospheric Cherenkov telescopes (IACTs) at a southern site, and about 20 in the north. Previous IACT experiments have used up to five telescopes. Subsequently, the design of a graphical user interface (GUI) for the operator of CTA poses an interesting challenge. In order to create an effective interface, the CTA team is collaborating with experts from the field of Human-Computer Interaction. We present here our GUI prototype. The back-end of the prototype is a Python Web server. It is integrated with the observation execution system of CTA, which is based on the Alma Common Software (ACS). The back-end incorporates a redis database, which facilitates synchronization of GUI panels. redis is also used to buffer information collected from various software components and databases. The front-end of the prototype is based on Web technology. Communication between Web server and clients is performed using Web Sockets, where graphics are generated with the d3.js Javascript library.

Comments: To appear in the proceedings of the 2017 ICALEPCS conference

Abstract: 1710.05350
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Title: Information Retrieval and Recommendation System for Astronomical Observatories

Authors: Nikhil Mukund, Saurabh Thakur, Sheelu Abraham, A. K. Aniyan, Sanjit Mitra, Ninan Sajeeth Philip, Kaustubh Vaghmare, D. P. Acharjya
(Submitted on 15 Oct 2017)
Abstract: We present a machine learning based information retrieval system for astronomical observatories that tries to address user defined queries related to an instrument. In the modern instrumentation scenario where heterogeneous systems and talents are simultaneously at work, the ability to supply with the right information helps speeding up the detector maintenance operations. Enhancing the detector uptime leads to increased coincidence observation and improves the likelihood for the detection of astrophysical signals. Besides, such efforts will efficiently disseminate technical knowledge to a wider audience and will help the ongoing efforts to build upcoming detectors like the LIGO-India etc even at the design phase to foresee possible challenges. The proposed method analyses existing documented efforts at the site to intelligently group together related information to a query and to present it on-line to the user. The user in response can further go into interesting links and find already developed solutions or probable ways to address the present situation optimally. A web application that incorporates the above idea has been implemented and tested for LIGO Livingston, LIGO Hanford and Virgo observatories.

Comments: 14 pages, 7 figures

Abstract: 1710.07249
Full Text: [ PostScript, PDF]

Title: Inferences on Mass Composition and Tests of Hadronic Interactions from 0.3 to 100 EeV using the water-Cherenkov Detectors of the Pierre Auger Observatory

Authors: The Pierre Auger Collaboration: A. Aab, P. Abreu, M. Aglietta, I. Al Samarai, I.F.M. Albuquerque, I. Allekotte, A. Almela, J. Alvarez Castillo, J. Alvarez-Muñiz, G.A. Anastasi, L. Anchordoqui, B. Andrada, S. Andringa, C. Aramo, F. Arqueros, N. Arsene, H. Asorey, P. Assis, J. Aublin, G. Avila, A.M. Badescu, A. Balaceanu, F. Barbato, R.J. Barreira Luz, J.J. Beatty, K.H. Becker, J.A. Bellido, C. Berat, M.E. Bertaina, X. Bertou, P.L. Biermann, J. Biteau, S.G. Blaess, A. Blanco, J. Blazek, C. Bleve, M. Boháčová, D. Boncioli, C. Bonifazi, N. Borodai, A.M. Botti, J. Brack, I. Brancus, T. Bretz, A. Bridgeman, F.L. Briechle, P. Buchholz, A. Bueno, S. Buitink, M. Buscemi, K.S. Caballero-Mora, L. Caccianiga, A. Cancio, F. Canfora, L. Caramete, R. Caruso, A. Castellina, F. Catalani,
G. Cataldi, L. Cazon, A.G. Chavez, J.A. Chinellato, J. Chudoba, R.W. Clay, A. Cobos, R. Colalillo, A. Coleman, L. Collica, M.R. Coluccia, R. Conceição, G. Consolati, F. Contreras, M.J. Cooper, S. Coutu, C.E. Covault, J. Cronin, S. D'Amico, B. Daniel, S. Dasso, K. Daumiller, B.R. Dawson, R.M. de Almeida, S.J. de Jong, G. De Mauro, J.R.T. de Mello Neto, I. De Mitri, J. de Oliveira, V. de Souza, J. Debatin, O. Deligny, M.L. Díaz Castro, F. Diogo, C. Dobrigkeit, J.C. D'Olivo, Q. Dorosti, R.C. dos Anjos, M.T. Dova, A. Dundovic, J. Ebr, R. Engel, M. Erdmann, M. Erfani, C.O. Escobar, J. Espadanal, A. Etchegoyen, H. Falcke, J. Farmer, G. Farrar, A.C. Fauth, N. Fazzini, F. Fenu, B. Fick, J.M. Figueira, A. Filipčič, O. Fratu, M.M. Freire, T. Fujii, A. Fuster, R. Gaior, B. García, D. Garcia-Pinto, F. Gaté, H. Gemmeke, A. Gherghel-Lascu, P.L. Ghia, U. Giaccari, M. Giammarchi, M. Giller, D. Głas, C. Glaser, G. Golup, M. Gómez Berisso, P.F. Gómez Vitale, N. González, A. Gorgi, P. Gorham, A.F. Grillo, T.D. Grubb, F. Guarino, G.P. Guedes, R. Halliday, M.R. Hampel, P. Hansen, D. Harari, T.A. Harrison, J.L. Harton, A. Haungs, T. Hebbeker, D. Heck, P. Heimann, A.E. Herve, G.C. Hill, C. Hojvat, E. Holt, P. Homola, J.R. Hörandel, P. Horvath, M. Hrabovský, T. Huege, J. Hulsman, A. Insolia, P.G. Isar, I. Jandt, J.A. Johnsen, M. Josebachuili, J. Jurysek, A. Kääpä, O. Kambeitz, K.H. Kampert, B. Keilhauer, N. Kemmerich, E. Kemp, J. Kemp, R.M. Kieckhafer, H.O. Klages, M. Kleifges, J. Kleinfeller, R. Krause, N. Krohm, D. Kuempel, G. Kukec Mezek, N. Kunka, A. Kuotb Awad, B.L. Lago, D. LaHurd, R.G. Lang, M. Lauscher, R. Legumina, M.A. Leigui de Oliveira, A. Letessier-Selvon, I. Lhenry-Yvon, K. Link, D. Lo Presti, L. Lopes, R. López, A. López Casado, R. Lorek, Q. Luce, A. Lucero, M. Malacari, M. Mallamaci, D. Mandat, P. Mantsch, A.G. Mariazzi, I.C. Mariş, G. Marsella, D. Martello, H. Martinez, O. Martínez Bravo, J.J. Masías Meza, H.J. Mathes, S. Mathys, J. Matthews, J.A.J. Matthews, G. Matthiae, E. Mayotte, P.O. Mazur, C. Medina, G. Medina-Tanco, D. Melo, A. Menshikov, K.-D. Merenda, S. Michal, M.I. Micheletti, L. Middendorf, L. Miramonti, B. Mitrica, D. Mockler, S. Mollerach, F. Montanet, C. Morello, M. Mostafá, A.L. Müller, G. Müller, M.A. Muller, S. Müller, R. Mussa, I. Naranjo, L. Nellen, P.H. Nguyen, M. Niculescu-Oglinzanu, M. Niechciol, L. Niemietz, T. Niggemann, D. Nitz, D. Nosek, V. Novotny, L. Nožka, L.A. Núñez, L. Ochilo, F. Oikonomou, A. Olinto, M. Palatka, J. Pallotta, P. Papenbreer, G. Parente, A. Parra, T. Paul, M. Pech, F. Pedreira, J. Pękala, R. Pelayo, J. Peña-Rodriguez, L. A. S. Pereira, M. Perlin, L. Perrone, C. Peters, S. Petrera, J. Phuntsok, R. Piegaia, T. Pierog, M. Pimenta, V. Pirronello, M. Platino, M. Plum, C. Porowski, R.R. Prado, P. Privitera, M. Prouza, E.J. Quel, S. Querchfeld, S. Quinn, R. Ramos-Pollan, J. Rautenberg, D. Ravignani, J. Ridky, F. Riehn, M. Risse, P. Ristori, V. Rizi, W. Rodrigues de Carvalho, G. Rodriguez Fernandez, J. Rodriguez Rojo, D. Rogozin, M.J. Roncoroni, M. Roth, E. Roulet, A.C. Rovero, P. Ruehl, S.J. Saffi, A. Saftoiu, F. Salamida, H. Salazar, A. Saleh, F. Salesa Greus, G. Salina, F. Sánchez, P. Sanchez-Lucas, E.M. Santos, E. Santos, F. Sarazin, R. Sarmento, C. Sarmiento-Cano, R. Sato, M. Schauer, V. Scherini, H. Schieler, M. Schimp, D. Schmidt, O. Scholten, P. Schovánek, F.G. Schröder, S. Schröder, A. Schulz, J. Schumacher, S.J. Sciutto, A. Segreto, A. Shadkam, R.C. Shellard, G. Sigl, G. Silli, O. Sima, A. Śmiałkowski, R. Šmída, G.R. Snow, P. Sommers, S. Sonntag, R. Squartini, D. Stanca, S. Stanič, J. Stasielak, P. Stassi, M. Stolpovskiy, F. Strafella, A. Streich, F. Suarez, M. Suarez Durán, T. Sudholz, T. Suomijärvi, A.D. Supanitsky, J. Šupík, J. Swain, Z. Szadkowski, A. Taboada, O.A. Taborda, V.M. Theodoro, C. Timmermans, C.J. Todero Peixoto, L. Tomankova, B. Tomé, G. Torralba Elipe, P. Travnicek, M. Trini, R. Ulrich, M. Unger, M. Urban, J.F. Valdés Galicia, I. Valiño, L. Valore, G. van Aar, P. van Bodegom, A.M. van den Berg, A. van Vliet, E. Varela, B. Vargas Cárdenas, G. Varner, R.A. Vázquez, D. Veberič, C. Ventura, I.D. Vergara Quispe, V. Verzi, J. Vicha, L. Villaseñor, S. Vorobiov, H. Wahlberg, O. Wainberg, D. Walz, A.A. Watson, M. Weber, A. Weindl, L. Wiencke, H. Wilczyński, M. Wirtz, D. Wittkowski, B. Wundheiler, L. Yang, A. Yushkov, E. Zas, D. Zavrtanik, M. Zavrtanik, A. Zepeda, B. Zimmermann, M. Ziolkowski, Z. Zong, F. Zuccarello
et al. (347 additional authors not shown)
(Submitted on 19 Oct 2017)
Abstract: We present a new method for probing the hadronic interaction models at ultra-high energy and extracting details about mass composition. This is done using the time profiles of the signals recorded with the water-Cherenkov detectors of the Pierre Auger Observatory. The profiles arise from a mix of the muon and electromagnetic components of air-showers. Using the risetimes of the recorded signals we define a new parameter, which we use to compare our observations with predictions from simulations. We find, firstly, inconsistencies between our data and predictions over a greater energy range and with substantially more events than in previous studies. Secondly, by calibrating the new parameter with fluorescence measurements from observations made at the Auger Observatory, we can infer the depth of shower maximum for a sample of over 81,000 events extending from 0.3 EeV to over 100 EeV. Above 30 EeV, the sample is nearly fourteen times larger than currently available from fluorescence measurements and extending the covered energy range by half a decade. The energy dependence of the average depth of shower maximum is compared to simulations and interpreted in terms of the mean of the logarithmic mass. We find good agreement with previous work and extend the measurement of the mean depth of shower maximum to greater energies than before, reducing significantly the statistical uncertainty associated with the inferences about mass composition.

Comments: 21 pages; 18 figures; version accepted for publication in Phys. Rev. D

Abstract: 1710.06902
Full Text: [ PostScript, PDF]

Title: The Survey of Water and Ammonia in the Galactic Center (SWAG): Molecular Cloud Evolution in the Central Molecular Zone

Authors: Nico Krieger, Jürgen Ott, Henrik Beuther, Fabian Walter, J. M. Diederik Kruijssen, David S. Meier, Elisabeth A. C. Mills, Yanett Contreras, Phil Edwards, Adam Ginsburg, Christian Henkel, Jonathan Henshaw, James Jackson, Jens Kauffmann, Steven Longmore, Sergio Martin, Mark R. Morris, Thushara Pillai, Matthew Rickert, Erik Rosolowsky, Hiroko Shinnaga, Andrew Walsh, Farhad Yusef-Zadeh, Qizhou Zhang
(Submitted on 18 Oct 2017)
Abstract: The Survey of Water and Ammonia in the Galactic Center (SWAG) covers the Central Molecular Zone (CMZ) of the Milky Way at frequencies between 21.2 and 25.4 GHz obtained at the Australia Telescope Compact Array at $\sim 0.9$ pc spatial and $\sim 2.0$ km s$^{-1}$ spectral resolution. In this paper, we present data on the inner $\sim 250$ pc ($1.4^\circ$) between Sgr C and Sgr B2. We focus on the hyperfine structure of the metastable ammonia inversion lines (J,K) = (1,1) - (6,6) to derive column density, kinematics, opacity and kinetic gas temperature. In the CMZ molecular clouds, we find typical line widths of $8-16$ km s$^{-1}$ and extended regions of optically thick ($\tau > 1$) emission. Two components in kinetic temperature are detected at $25-50$ K and $60-100$ K, both being significantly hotter than dust temperatures throughout the CMZ. We discuss the physical state of the CMZ gas as traced by ammonia in the context of the orbital model by Kruijssen et al. (2015) that interprets the observed distribution as a stream of molecular clouds following an open eccentric orbit. This allows us to statistically investigate the time dependencies of gas temperature, column density and line width. We find heating rates between $\sim 50$ and $\sim 100$ K Myr$^{-1}$ along the stream orbit. No strong signs of time dependence are found for column density or line width. These quantities are likely dominated by cloud-to-cloud variations. Our results qualitatively match the predictions of the current model of tidal triggering of cloud collapse, orbital kinematics and the observation of an evolutionary sequence of increasing star formation activity with orbital phase.

Comments: 68 pages, 44 figures, accepted for publication in ApJS; slightly compressed images due to file size limitations, high resolution available at this http URL

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