The unblinking eye on the sky

From near-Earth asteroids to superluminous supernovae and counterparts to gravitational wave sources, the Zwicky Transient Facility will soon scan the night sky for transient phenomena.Comment: Author's version of "Mission Control" profile published in Nature Astronomy. 3 pages, 1 figure. https://www.nature.com/articles/s41550-017-007

Volumetric Survey Speed: A Figure of Merit for Transient Surveys

Time-domain surveys can exchange sky coverage for revisit frequency, complicating the comparison of their relative capabilities. By using different revisit intervals, a specific camera may execute surveys optimized for discovery of different classes of transient objects. We propose a new figure of merit, the instantaneous volumetric survey speed, for evaluating transient surveys. This metric defines the trade between cadence interval and snapshot survey volume and so provides a natural means of comparing survey capability. The related metric of areal survey speed imposes a constraint on the range of possible revisit times: we show that many modern time-domain surveys are limited by the amount of fresh sky available each night. We introduce the concept of "spectroscopic accessibility" and discuss its importance for transient science goals requiring followup observing. We present an extension of the control time algorithm for cases where multiple consecutive detections are required. Finally, we explore how survey speed and choice of cadence interval determine the detection rate of transients in the peak absolute magnitude–decay timescale phase space

Volumetric Survey Speed: A Figure of Merit for Transient Surveys

Time-domain surveys can exchange sky coverage for revisit frequency, complicating the comparison of their relative capabilities. By using different revisit intervals, a specific camera may execute surveys optimized for discovery of different classes of transient objects. We propose a new figure of merit, the instantaneous volumetric survey speed, for evaluating transient surveys. This metric defines the trade between cadence interval and snapshot survey volume and so provides a natural means of comparing survey capability. The related metric of areal survey speed imposes a constraint on the range of possible revisit times: we show that many modern time-domain surveys are limited by the amount of fresh sky available each night. We introduce the concept of "spectroscopic accessibility" and discuss its importance for transient science goals requiring followup observing. We present an extension of the control time algorithm for cases where multiple consecutive detections are required. Finally, we explore how survey speed and choice of cadence interval determine the detection rate of transients in the peak absolute magnitude–decay timescale phase space

Origins of the 1/4 keV Soft X-Ray Background

Snowden and coworkers have presented a model for the 1/4 keV soft X-ray diffuse background in which the observed flux is dominated by a ~ 10^6 K thermal plasma located in a 100-300 pc diameter bubble surrounding the Sun, but has significant contributions from a very patchy Galactic halo. Halo emission provides about 11% of the total observed flux and is responsible for half of the H I anticorrelation. The remainder of the anticorrelation is presumably produced by displacement of disk H I by the varying extent of the local hot bubble (LHB). The ROSAT R1 and R2 bands used for this work had the unique spatial resolution and statistical precision required for separating the halo and local components, but provide little spectral information. Some consistency checks had been made with older observations at lower X-ray energies, but we have made a careful investigation of the extent to which the model is supported by existing sounding rocket data in the Be (73-111 eV) and B bands (115-188 eV) where the sensitivities to the model are qualitatively different from the ROSAT bands. We conclude that the two-component model is well supported by the low-energy data. We find that these combined observations of the local component may be consistent with single-temperature thermal emission models in collisional ionization equilibrium if depleted abundances are assumed. However, different model implementations give significantly different results, offering little support for the conclusion that the astrophysical situation is so simple.Comment: 17 pages, 6 figures, accepted by the Astrophysical Journa

RHESSI Spectral Fits of Swift GRBs

One of the challenges of the Swift era has been accurately determining Epeak for the prompt GRB emission. RHESSI, which is sensitive from 30 keV to 17 MeV, can extend spectral coverage above the Swift-BAT bandpass. Using the public Swift data, we present results of joint spectral fits for 26 bursts co-observed by RHESSI and Swift-BAT through May 2007. We compare these fits to estimates of Epeak which rely on BAT data alone. A Bayesian Epeak estimator gives better correspondence with our measured results than an estimator relying on correlations with the Swift power law indices.Comment: 4 pages, 1 figure. To appear in the proceedings of Gamma Ray Bursts 2007, Santa Fe, New Mexico, November 5-9 200

Identification of Stellar Flares Using Differential Evolution Template Optimization

We explore methods for the identification of stellar flare events in irregularly sampled data of ground-based time domain surveys. In particular, we describe a new technique for identifying flaring stars, which we have implemented in a publicly available Python module called "PyVAN". The approach uses the Differential Evolution algorithm to optimize parameters of empirically derived light-curve templates for different types of stars to fit a candidate light-curve. The difference of the likelihoods that these best-fit templates produced the observed data is then used to delineate targets that are well explained by a flare template but simultaneously poorly explained by templates of common contaminants. By testing on light-curves of known identity and morphology, we show that our technique is capable of recovering flaring status in $69\%$ of all light-curves containing a flare event above thresholds drawn to include $\lt1\%$ of any contaminant population. By applying to Palomar Transient Factory data, we show consistency with prior samples of flaring stars, and identify a small selection of candidate flaring G-type stars for possible follow-up.Comment: 15 figures, 24 page