We present optical photometry and spectroscopy of SN 2016iet, an unprecedented Type I supernova (SN) at \(z=0.0676\) with no obvious analog in the existing literature. The peculiar light curve has ...two roughly equal brightness peaks (\(\approx -19\) mag) separated by 100 days, and a subsequent slow decline by 5 mag in 650 rest-frame days. The spectra are dominated by emission lines of calcium and oxygen, with a width of only \(3400\) km s\(^{-1}\), superposed on a strong blue continuum in the first year, and with a large ratio of \(L_{\rm Ca\,II}/L_{\rm O\,I}\approx 4\) at late times. There is no clear evidence for hydrogen or helium associated with the SN at any phase. We model the light curves with several potential energy sources: radioactive decay, central engine, and circumstellar medium (CSM) interaction. Regardless of the model, the inferred progenitor mass near the end of its life (i.e., CO core mass) is \(\gtrsim 55\) M\(_\odot\) and up to \(120\) M\(_\odot\), placing the event in the regime of pulsational pair instability supernovae (PPISNe) or pair instability supernovae (PISNe). The models of CSM interaction provide the most consistent explanation for the light curves and spectra, and require a CSM mass of \(\approx 35\) M\(_\odot\) ejected in the final decade before explosion. We further find that SN 2016iet is located at an unusually large offset (\(16.5\) kpc) from its low metallicity dwarf host galaxy (\(Z\approx 0.1\) Z\(_\odot\), \(M\approx 10^{8.5}\) M\(_\odot\)), supporting the PPISN/PISN interpretation. In the final spectrum, we detect narrow H\(\alpha\) emission at the SN location, likely due to a dim underlying galaxy host or an H II region. Despite the overall consistency of the SN and its unusual environment with PPISNe and PISNe, we find that the inferred properties of SN\,2016iet challenge existing models of such events.
The broad-line radio galaxy 3C120 is a powerful source of both X-ray and radio emission including superluminal jet outflows. We report on our reanalysis of 160 ks of Suzaku data taken in 2006, ...previously examined by Kataoka et al. (2007). Spectral fits to the XIS and HXD/PIN data over a range of 0.7-45 keV reveal a well-defined iron K line complex with a narrow Ka core and relativistically broadened features consistent with emission from the inner regions of the accretion disk. Furthermore, the inner region of the disk appears to be truncated with an inner radius of r_in = 11.7^{+3.5}_{-5.2} r_g. If we assume that fluorescent iron line features terminate at the inner-most stable circular orbit (ISCO), we measure a black hole spin of a < -0.1 at a 90% confidence level. A rapidly spinning prograde black hole (a > 0.8) can be ruled out at the 99% confidence level. Alternatively, the disk may be truncated well outside of the ISCO of a rapid prograde hole. The most compelling scenario is the possibility that the inner regions of the disk were destroyed/ejected by catastrophic instabilities just prior to the time these observations were made.
We present nearly 500 days of observations of the tidal disruption event ASASSN-18pg, spanning from 54 days before peak light to 441 days after peak light. Our dataset includes X-ray, UV, and optical ...photometry, optical spectroscopy, radio observations, and the first published spectropolarimetric observations of a TDE. ASASSN-18pg was discovered on 2018 July 11 by the All-Sky Automated Survey for Supernovae (ASAS-SN) at a distance of \(d=78.6\) Mpc, and with a peak UV magnitude of \(m\simeq14\) it is both one of the nearest and brightest TDEs discovered to-date. The photometric data allow us to track both the rise to peak and the long-term evolution of the TDE. ASASSN-18pg peaked at a luminosity of \(L\simeq2.2\times10^{44}\) erg s\(^{-1}\), and its late-time evolution is shallower than a flux \(\propto t^{-5/3}\) power-law model, similar to what has been seen in other TDEs. ASASSN-18pg exhibited Balmer lines and spectroscopic features consistent with Bowen fluorescence prior to peak which remained detectable for roughly 225 days after peak. Analysis of the two-component H\(\alpha\) profile indicates that, if they are the result of reprocessing of emission from the accretion disk, the different spectroscopic lines may be coming from regions between \(\sim10\) and \(\sim60\) light-days from the black hole. No X-ray emission is detected from the TDE and there is no evidence of a jet or strong outflow detected in the radio. Our spectropolarimetric observations give no strong evidence for significant asphericity in the emission region, with the emission region having an axis ratio of at least \(\sim0.65\).
Whether supernovae are a significant source of dust has been a long-standing debate. The large quantities of dust observed in high-redshift galaxies raise a fundamental question as to the origin of ...dust in the Universe since stars cannot have evolved to the AGB dust-producing phase in high-redshift galaxies. In contrast, supernovae occur within several millions of years after the onset of star formation. This white paper focuses on dust formation in supernova ejecta with US-Extremely Large Telescope (ELT) perspective during the era of JWST and LSST.
astroquery is a collection of tools for requesting data from databases hosted on remote servers with interfaces exposed on the internet, including those with web pages but without formal application ...program interfaces (APIs). These tools are built on the Python requests package, which is used to make HTTP requests, and astropy, which provides most of the data parsing functionality. astroquery modules generally attempt to replicate the web page interface provided by a given service as closely as possible, making the transition from browser-based to command-line interaction easy. astroquery has received significant contributions from throughout the astronomical community, including several significant contributions from telescope archives. astroquery enables the creation of fully reproducible workflows from data acquisition through publication. This paper describes the philosophy, basic structure, and development model of the astroquery package. The complete documentation for astroquery can be found at http://astroquery.readthedocs.io/.
We present the first effort to aggregate, homogenize, and uniformly model the combined ultraviolet, optical, and near-infrared dataset for the electromagnetic counterpart of the binary neutron star ...merger GW170817. By assembling all of the available data from 18 different papers and 46 different instruments, we are able to identify and mitigate systematic offsets between individual datasets, and to identify clear outlying measurements, with the resulting pruned and adjusted dataset offering an opportunity to expand the study of the kilonova. The unified dataset includes 647 individual flux measurements, spanning 0.45 to 29.4 days post-merger, and thus has greater constraining power for physical models than any single dataset. We test a number of semi-analytical models and find that the data are well modeled with a three-component kilonova model: a "blue" lanthanide-poor component with Mej~0.020 Msol and vej~0.27c; an intermediate opacity "purple" component with Mej~0.047 Msol and vej~0.15c; and a "red" lanthanide-rich component with Mej~0.011 Msol and vej~0.14c. We further explore the possibility of ejecta asymmetry and its impact on the estimated parameters. From the inferred parameters we draw conclusions about the physical mechanisms responsible for the various ejecta components, the properties of the neutron stars, and, combined with an up-to-date merger rate, the implications for r-process enrichment via this channel. To facilitate future studies of this keystone event we make the unified dataset and our modeling code public.
This report provides an overview of recent work that harnesses the Big Data Revolution and Large Scale Computing to address grand computational challenges in Multi-Messenger Astrophysics, with a ...particular emphasis on real-time discovery campaigns. Acknowledging the transdisciplinary nature of Multi-Messenger Astrophysics, this document has been prepared by members of the physics, astronomy, computer science, data science, software and cyberinfrastructure communities who attended the NSF-, DOE- and NVIDIA-funded "Deep Learning for Multi-Messenger Astrophysics: Real-time Discovery at Scale" workshop, hosted at the National Center for Supercomputing Applications, October 17-19, 2018. Highlights of this report include unanimous agreement that it is critical to accelerate the development and deployment of novel, signal-processing algorithms that use the synergy between artificial intelligence (AI) and high performance computing to maximize the potential for scientific discovery with Multi-Messenger Astrophysics. We discuss key aspects to realize this endeavor, namely (i) the design and exploitation of scalable and computationally efficient AI algorithms for Multi-Messenger Astrophysics; (ii) cyberinfrastructure requirements to numerically simulate astrophysical sources, and to process and interpret Multi-Messenger Astrophysics data; (iii) management of gravitational wave detections and triggers to enable electromagnetic and astro-particle follow-ups; (iv) a vision to harness future developments of machine and deep learning and cyberinfrastructure resources to cope with the scale of discovery in the Big Data Era; (v) and the need to build a community that brings domain experts together with data scientists on equal footing to maximize and accelerate discovery in the nascent field of Multi-Messenger Astrophysics.
If the influence of national cultures on the implementation of global standards is not taken into account, the result will be inconsistent implementation at best and outright failure at worst. The ...experiences in fields such as medicine, peacekeeping, aviation, and environmental protection offer insight into possible difficulties with the implementation, beginning in 2010, of International Standards on Auditing (ISAs) by members of the International Federation of Accountants. Some countries may have difficulty with implementation because of the differences between their cultural assumptions and those embodied in the standards to be adopted. It is too soon to know if and where that will happen, especially because the data on first experiences will not begin to be available until 2013. However, cultural‐comparison data can be used to foresee which countries may have difficulty with implementation. But if unintended consequences do become evident, it will be important not to assume that the standards and the standard‐setting process are defective; it is more likely that practitioners will need help in interpreting the ISAs in light of their local culture. A useful first step would be for standard‐setting bodies to identify explicitly the cultural assumptions inherent in the standards they produce. The standard setters can then give that information to those responsible for standards implementation at the practitioner level to help promote consistent application of the standards globally.
Question de culture : en quoi la culture influe sur l’audit
Résumé
Si l’on ne tient pas compte de l’influence des cultures nationales sur la mise en œuvre de normes internationales, les résultatsde l’exercice seront incohérents, au mieux, ouse solderont par un échec pur et simple, au pire. Les expériences dans des domaines comme la médecine, le maintien de la paix, l’aviation et la protection de l’environnement nous livrent des indications quant aux problèmes que pourrait présenter la conversion, à compter de 2010, aux normes internationales d’audit et de certification établies par les membres de l’International Federation of Accountants (IFAC). Certains pays pourraient éprouver de la difficultéà instaurer ces normes en raison des différences entre leurs a priori culturels et ceux que véhiculent les normes devant être adoptées. Il est trop tôt pour dire si ces difficultés se manifesteront et à quel moment, notamment du fait que les données relatives aux premières expériences ne seront accessibles qu’à compter de 2013. Toutefois, des donnéesculturelles comparatives peuvent être utilisées pour prévoir quels pays risquent defaire face à des embûches dans la mise en œuvre de ces normes. Toutefois, s’il émergedu processus des conséquences non souhaitées évidentes, il importera de ne pas en conclure que les normes et les processus de normalisation sont défectueux, mais plutôt que les professionnels en exerciceont besoin d’assistance pour interpréter les normes internationales à la lumière de leur culture nationale. Les organismes de normalisation pourraient faire un premier pas dans ce sens en définissant explicitement les a priori culturels inhérents aux normes qu’ils produisent. Les normalisateurs pourraient ensuite communiquer cette information aux responsables de la mise en œuvre des normes chez lesprofessionnels en exercice et contribuer ainsi à promouvoir la cohérence dans l’application des normes à l’échelle mondiale.
Blazars are a highly-variable, radio-loud subclass of active galactic nuclei (AGN). In order to better understand such objects we must be able to easily identify candidate blazars from the growing ...population of unidentified sources. Working towards this goal we attempt to identify new gamma-ray blazar candidates from a sample of 102 previously unidentified sources. These sources are selected from Astronomer's Telegrams and the literature on the basis of non-periodic variability and multi-wavelength behavior. We then attempt to associate these objects to an IR counterpart in the WISE all-sky survey. We are able to identify sixteen candidate sources whose IR colors are consistent with those of the blazar population. Of those sixteen, thirteen sources have IR colors indicative of being gamma-ray emitting blazar candidates. These sources all possess archival multi-wavelength observations that support their blazar-like nature.
The direct detection of gravitational waves from the inspiral and merger of compact object binaries by the Advanced LIGO and Virgo interferometers has ushered in an exciting new era of astronomy. ...Analysis of this gravitational wave data provides fundamental insight into GR in a strong gravity regime not normally accessible and allows the detection of binary systems not visible via electromagnetic observations. However, truly maximizing the science gains from these events requires the joint detection of a coincident electromagnetic counterpart. Doing so will provide new insight into the environment and host galaxy of the merger, an accurate determination of distance and energy scales, and insight into the hydrodynamics of the merger. The most promising counterpart for this task is a "kilonova," an optical/NIR transient powered by the radioactive decay of heavy r-process elements synthesized in the merger ejecta. In this thesis, I present a series of studies that culminate in the first joint detection of gravitational waves and electromagnetic radiation from the merger of a binary neutron star system.First, I present studies of observational strategies to detect kilonovae and reject contaminating false-positives from unrelated transients. Using simulated observations, I show that efficient kilonova detection requires nightly observations achieving depths of i = 24 mag and z = 23 mag, ideally starting within twelve hours of a gravitational wave trigger. Furthermore, I show that kilonovae are well separated from other unrelated transients (e.g., supernovae) on the basis of their red i-z colors and shorter timescales. I confirm these results with an empirical study of contamination using data taken with the Dark Energy Camera (DECam). I show that the expected contamination rate for kilonova-like transients is low with Rred = 0.16 events per sq. deg at a limiting magnitude of i < 22.5 mag.Second, I present results from optical follow-up observations of gravitational wave events conducted with DECam. I discuss follow-up of GW151226, the second binary black hole merger detected by the Advanced LIGO interferometers. I show that while our DECam program did not identify an electromagnetic counterpart to this event, the presence of an errant Type II-P Supernova in these observations highlights the unique challenge faced in rejecting false-positives. I then discuss follow-up of the first binary neutron star merger detected by Advanced LIGO and Virgo, GW170817, including an independent discovery of the optical counterpart by our DECam program. I present modeling of the broadband optical/NIR photometry and show that this optical emission is consistent with expectations for a kilonova. I also show that the amount of material ejected during the merger is sufficient to suggest that binary neutron star mergers are a dominant site of cosmic r-process nucleosynthesis.
