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Title: Real-time Recovery Efficiencies and Performance of the Palomar Transient Factory's Transient Discovery Pipeline

Abstract

In this paper, we present the transient source detection efficiencies of the Palomar Transient Factory (PTF), parameterizing the number of transients that PTF found versus the number of similar transients that occurred over the same period in the survey search area but were missed. PTF was an optical sky survey carried out with the Palomar 48 inch telescope over 2009–2012, observing more than 8000 square degrees of sky with cadences of between one and five days, locating around 50,000 non-moving transient sources, and spectroscopically confirming around 1900 supernovae. We assess the effectiveness with which PTF detected transient sources, by inserting $$\simeq 7$$ million artificial point sources into real PTF data. We then study the efficiency with which the PTF real-time pipeline recovered these sources as a function of the source magnitude, host galaxy surface brightness, and various observing conditions (using proxies for seeing, sky brightness, and transparency). The product of this study is a multi-dimensional recovery efficiency grid appropriate for the range of observing conditions that PTF experienced and that can then be used for studies of the rates, environments, and luminosity functions of different transient types using detailed Monte Carlo simulations. Finally, we illustrate the technique using the observationally well-understood class of type Ia supernovae.

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [2];  [3]
  1. Univ. of Southampton (United Kingdom)
  2. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  3. Stanford Univ., CA (United States)
Publication Date:
Research Org.:
Univ. of Southampton (United Kingdom); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR) (SC-21); European Research Council (ERC); Science and Technology Facilities Council (STFC) (United Kingdom)
OSTI Identifier:
1379822
Grant/Contract Number:
AC02-05CH11231; 615929
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
The Astrophysical Journal. Supplement Series (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal. Supplement Series (Online); Journal Volume: 230; Journal Issue: 1; Journal ID: ISSN 1538-4365
Publisher:
American Astronomical Society/IOP
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; data analysis methods; supernovae; surveys

Citation Formats

Frohmaier, C., Sullivan, M., Nugent, P. E., Goldstein, D. A., and DeRose, J. Real-time Recovery Efficiencies and Performance of the Palomar Transient Factory's Transient Discovery Pipeline. United States: N. p., 2017. Web. doi:10.3847/1538-4365/aa6d70.
Frohmaier, C., Sullivan, M., Nugent, P. E., Goldstein, D. A., & DeRose, J. Real-time Recovery Efficiencies and Performance of the Palomar Transient Factory's Transient Discovery Pipeline. United States. doi:10.3847/1538-4365/aa6d70.
Frohmaier, C., Sullivan, M., Nugent, P. E., Goldstein, D. A., and DeRose, J. Tue . "Real-time Recovery Efficiencies and Performance of the Palomar Transient Factory's Transient Discovery Pipeline". United States. doi:10.3847/1538-4365/aa6d70. https://www.osti.gov/servlets/purl/1379822.
@article{osti_1379822,
title = {Real-time Recovery Efficiencies and Performance of the Palomar Transient Factory's Transient Discovery Pipeline},
author = {Frohmaier, C. and Sullivan, M. and Nugent, P. E. and Goldstein, D. A. and DeRose, J.},
abstractNote = {In this paper, we present the transient source detection efficiencies of the Palomar Transient Factory (PTF), parameterizing the number of transients that PTF found versus the number of similar transients that occurred over the same period in the survey search area but were missed. PTF was an optical sky survey carried out with the Palomar 48 inch telescope over 2009–2012, observing more than 8000 square degrees of sky with cadences of between one and five days, locating around 50,000 non-moving transient sources, and spectroscopically confirming around 1900 supernovae. We assess the effectiveness with which PTF detected transient sources, by inserting $\simeq 7$ million artificial point sources into real PTF data. We then study the efficiency with which the PTF real-time pipeline recovered these sources as a function of the source magnitude, host galaxy surface brightness, and various observing conditions (using proxies for seeing, sky brightness, and transparency). The product of this study is a multi-dimensional recovery efficiency grid appropriate for the range of observing conditions that PTF experienced and that can then be used for studies of the rates, environments, and luminosity functions of different transient types using detailed Monte Carlo simulations. Finally, we illustrate the technique using the observationally well-understood class of type Ia supernovae.},
doi = {10.3847/1538-4365/aa6d70},
journal = {The Astrophysical Journal. Supplement Series (Online)},
number = 1,
volume = 230,
place = {United States},
year = {Tue May 09 00:00:00 EDT 2017},
month = {Tue May 09 00:00:00 EDT 2017}
}

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  • The Palomar Transient Factory (PTF) is an optical wide-field variability survey carried out using a camera with a 7.8 deg{sup 2} field of view mounted on the 48 inch Oschin Schmidt telescope at Palomar Observatory. One of the key goals of this survey is to conduct high-cadence monitoring of the sky in order to detect optical transient sources shortly after they occur. Here, we describe the real-time capabilities of the PTF and our related rapid multiwavelength follow-up programs, extending from the radio to the {gamma}-ray bands. We present as a case study observations of the optical transient PTF10vdl (SN 2010id),more » revealed to be a very young core-collapse (Type II-P) supernova having a remarkably low luminosity. Our results demonstrate that the PTF now provides for optical transients the real-time discovery and rapid-response follow-up capabilities previously reserved only for high-energy transients like gamma-ray bursts.« less
  • A fast-turnaround pipeline for realtime data reduction plays an essential role in discovering and permitting followup observations to young supernovae and fast-evolving transients in modern time-domain surveys. In this paper, we present the realtime image subtraction pipeline in the intermediate Palomar Transient Factory. By using highperformance computing, efficient databases, and machine-learning algorithms, this pipeline manages to reliably deliver transient candidates within 10 minutes of images being taken. Our experience in using high-performance computing resources to process big data in astronomy serves as a trailblazer to dealing with data from large-scale time-domain facilities in the near future.
  • Many photometric time-domain surveys are driven by specific goals, such as searches for supernovae or transiting exoplanets, which set the cadence with which fields are re-imaged. In the case of the Palomar Transient Factory (PTF), several sub-surveys are conducted in parallel, leading to non-uniform sampling over its ∼20,000 deg{sup 2} footprint. While the median 7.26 deg{sup 2} PTF field has been imaged ∼40 times in the R band, ∼2300 deg{sup 2} have been observed >100 times. We use PTF data to study the trade off between searching for microlensing events in a survey whose footprint is much larger than thatmore » of typical microlensing searches, but with far-from-optimal time sampling. To examine the probability that microlensing events can be recovered in these data, we test statistics used on uniformly sampled data to identify variables and transients. We find that the von Neumann ratio performs best for identifying simulated microlensing events in our data. We develop a selection method using this statistic and apply it to data from fields with >10 R-band observations, 1.1 × 10{sup 9} light curves, uncovering three candidate microlensing events. We lack simultaneous, multi-color photometry to confirm these as microlensing events. However, their number is consistent with predictions for the event rate in the PTF footprint over the survey's three years of operations, as estimated from near-field microlensing models. This work can help constrain all-sky event rate predictions and tests microlensing signal recovery in large data sets, which will be useful to future time-domain surveys, such as that planned with the Large Synoptic Survey Telescope.« less
  • We present observations of two new hydrogen-poor superluminous supernovae (SLSN-I), iPTF15esb and iPTF16bad, showing late-time Hα emission with line luminosities ofmore » $$(1\mbox{-}3)\times {10}^{41}$$ erg s -1 and velocity widths of (4000-6000) km s -. Including the previously published iPTF13ehe, this makes up a total of three such events to date. iPTF13ehe is one of the most luminous and the slowest evolving SLSNe-I, whereas the other two are less luminous and fast decliners. We interpret this as a result of the ejecta running into a neutral H-shell located at a radius of ~10 16 cm. This implies that violent mass loss must have occurred several decades before the supernova explosion. Such a short time interval suggests that eruptive mass loss could be common shortly before core collapse, and more importantly helium is unlikely to be completely stripped off the progenitor and could be present in the ejecta. It is a mystery why helium features are not detected, even though nonthermal energy sources, capable of ionizing He, may exist as suggested by the O ii absorption series in the early-time spectra. Our late-time spectra (+240 days) appear to have intrinsically lower [O i] 6300 Å luminosities than that of SN2015bn and SN2007bi, which is possibly an indication of less oxygen (<10 M ). The blueshifted Hα emission relative to the hosts for all three events may be in tension with the binary model proposed for iPTF13ehe. Lastly, iPTF15esb has a peculiar light curve (LC) with three peaks separated from one another by ~22 days. The LC undulation is stronger in bluer bands. One possible explanation is ejecta-circumstellar medium interaction.« less
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