Adaptive ADMM in Distributed Radio Interferometric Calibration [IMA]

Distributed radio interferometric calibration based on consensus optimization has been shown to improve the estimation of systematic errors in radio astronomical observations. The intrinsic continuity of systematic errors across frequency is used by a consensus polynomial to penalize traditional calibration. Consensus is achieved via the use of alternating direction method of multipliers (ADMM) algorithm. In this paper, we extend the existing distributed calibration algorithms to use ADMM with an adaptive penalty parameter update. Compared to a fixed penalty, its adaptive update has been shown to perform better in diverse applications of ADMM. In this paper, we compare two such popular penalty parameter update schemes: residual balance penalty update and spectral penalty update (Barzilai-Borwein). We apply both schemes to distributed radio interferometric calibration and compare their performance against ADMM with a fixed penalty parameter. Simulations show that both methods of adaptive penalty update improve the convergence of ADMM but the spectral penalty parameter update shows more stability.

Read this paper on arXiv…

S. Yatawatta, F. Diblen and H. Spreeuw
Tue, 17 Oct 17

Comments: Draft, to be published in the Proceedings of the 7th International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP) (IEEE CAMSAP 2017), published by IEEE

Space telescope designed for accurate measurements [IMA]

A modified version of the folded aplanatic Gregory telescope equipped with a spherical two-lens corrector is proposed for observations requiring a high signal-to-noise ratio. The basic telescope model has an aperture of 400 mm (f/3.0), its field of view is 3.0 degrees, the linear obscuration is 0.12, the distortion is less than 0.5%. The focal surface has a spherical shape; the achieving of a plane field requires an increase in the number of lenses in the corrector. The images of stars in the integrated wavelength range 0.35 – 1.0 mcm are close to the diffraction-limited ones (D_{80} = 5.9 – 8.2 mcm = 1.0 – 1.4 arc seconds). The system is free from direct background illumination; both the lens corrector and the light detector are protected from cosmic particles.

Read this paper on arXiv…

V. Terebizh
Tue, 17 Oct 17

Comments: Accepted for publication in the Astronomical Journal

How Many Kilonovae Can Be Found in Past, Present, and Future Survey Datasets? [IMA]

The discovery of a kilonova (KN) associated with the Advanced LIGO (aLIGO)/Virgo event GW170817 opens up new avenues of multi-messenger astrophysics. Here, using realistic simulations, we provide estimates of the number of KNe that could be found in data from past, present and future surveys without a gravitational-wave trigger. For the simulation, we construct a spectral time-series model based on the DES-GW multi-band light-curve from the single known KN event, and we use an average of BNS rates from past studies of $10^3 \rm{Gpc}^{-3}/\rm{year}$, consistent with the $1$ event found so far. Examining past and current datasets from transient surveys, the number of KNe we expect to find for ASAS-SN, SDSS, PS1, SNLS, DES, and SMT is between 0 and $0.3$. We predict the number of detections per future survey to be: 8.3 from ATLAS, 10.6 from ZTF, 5.5/69 from LSST (the Deep Drilling / Wide Fast Deep), and 16.0 from WFIRST. The maximum redshift of KNe discovered for each survey is z = 0.8 for WFIRST, z = 0.25 for LSST and z = 0.04 for ZTF and ATLAS. For the LSST survey, we also provide contamination estimates from Type Ia and Core-collapse supernovae: after light-curve and template-matching requirements, we estimate a background of just 2 events. More broadly, we stress that future transient surveys should consider how to optimize their search strategies to improve their detection efficiency, and to consider similar analyses for GW follow-up programs.

Read this paper on arXiv…

D. Scolnic, R. Kessler, D. Brout, et. al.
Tue, 17 Oct 17

Comments: Submitted to ApJL

Development of the LAGO Project in Chiapas-Mexico [CL]

The Latin American Giant Observatory (LAGO) is an extended astroparticle observatory with the goal of studying Gamma Ray Bursts (among other extreme universe phenomena), space weather and atmospheric radiation at ground level. It consists of a network of several Water Cherenkov Detectors (WCD) located at different sites and different latitudes along the American Continent (from Mexico up to the Antarctic region). Another interest of LAGO is to encourage and support the development of experimental basic research in Latin America, mainly with low cost equipment. In the case of Chiapas, Mexico, the experimental astroparticle physics activity was limited, up to now, to data analysis from other detectors located far away from the region. Thanks to the collaboration within LAGO, the deployment of one WCD is ongoing at the Universidad Aut\’onoma de Chiapas (UNACH). This will allow, for the first time in the region, to train students and researchers in the deployment processes. Till now the setup of the signal-processing electronics has been performed and the characterization of the photomultiplier tube is currently being done. The main, short-term goal is to install one WCD on top of the Tacan\’a volcano in Chiapas in a short term. The status of the work is presented.

Read this paper on arXiv…

K. Mora, H. Hidalgo, E. Barbosa, et. al.
Tue, 17 Oct 17

Comments: International Cosmic Ray Conference, Busan, Korea, 10-20 July, 2017 this https URL

Performance of the extreme-AO instrument VLT/SPHERE and dependence on the atmospheric conditions [IMA]

SPHERE is the high-contrast exoplanet imager and spectrograph installed at the Unit Telescope 3 of the Very Large Telescope. After more than two years of regular operations, we analyse statistically the performance of the adaptive optics system and its dependence on the atmospheric conditions above the Paranal observatory, as measured by the suite of dedicated instruments which are part of the Astronomical Site Monitor and as estimated by the SPHERE real-time calculator. We also explain how this information can be used to schedule the observations in order to yield the best data quality and to guide the astronomer when processing his/her data.

Read this paper on arXiv…

J. Milli, D. Mouillet, T. Fusco, et. al.
Tue, 17 Oct 17

Comments: 13 pages, 10 figures, AO4ELT 2017 conference proceeding

High resolution observations of Cen A: Yellow and red supergiants in a region of jet-induced star formation? [GA]

We present the analysis of near infrared (NIR), adaptive optics (AO) Subaru and archived HST imaging data of a region near the northern middle lobe (NML) of the Centaurus A (Cen A) jet, at a distance of $\sim15$ kpc north-east (NE) from the center of NGC5128. Low-pass filtering of the NIR images reveals strong — $>3\sigma$ above the background mean — signal at the expected position of the brightest star in the equivalent HST field. Statistical analysis of the NIR background noise suggests that the probability to observe $>3\sigma$ signal at the same position, in three independent measurements due to stochastic background fluctuations alone is negligible ($\leq10^{-7}\%$) and, therefore, that this signal should reflect the detection of the NIR counterparts of the brightest HST star. An extensive photometric analysis of this star yields $V-I$, visual-NIR, and NIR colors expected from a yellow supergiant (YSG) with an estimated age $\sim10^{+4}{-3}$ Myr. Furthermore, the second and third brighter HST stars are, likely, also supergiants in Cen A, with estimated ages $\sim16^{+6}{-3}$ Myr and $\sim25^{+15}_{-9}$ Myr, respectively. The ages of these three supergiants are in good agreement with the ages of the young massive stars that were previously found in the vicinity and are thought to have formed during the later phases of the jet-HI cloud interaction that appears to drive the star formation (SF) in the region for the past $\sim100$ Myr.

Read this paper on arXiv…

K. Markakis, A. Eckart, N. Castro, et. al.
Tue, 17 Oct 17

Comments: 11 pages, 6 figures, 2 tables, accepted for publication in ApJ

MARXS: A modular software to ray-trace X-ray instrumention [IMA]

To obtain the best possible scientific result, astronomers must understand the properties of the available instrumentation well. This is important both when designing new instruments and when using existing instruments close to the limits of their specified capabilities or beyond. Ray-tracing is a technique for numerical simulations where the path of many light rays is followed through the system to understand how individual system components influence the observed properties, such as the shape of the point-spread-function (PSF). In instrument design, such simulations can be used to optimize the performance. For observations with existing instruments this helps to discern instrumental artifacts from a true signal. Here, we describe MARXS, a new python package designed to simulate X-ray instruments on satellites and sounding rockets. MARXS uses probability tracking of photons and has polarimetric capabilities.

Read this paper on arXiv…

H. Gunther, J. Frost and A. Theriault-Shay
Tue, 17 Oct 17

Comments: 8 pages, 4 figures (two of which have interactive versions available at external URLs)