ESnet Links NERSC to HPWREN to Help in Exposing Cosmic Transients

An innovative new sky survey, called the Palomar Transient Factory (PTF), will utilize the unique tools and services offered by the Department of Energy's (DOE) National Energy Research Scientific Computing Center (NERSC) at the Lawrence Berkeley National Lab (Berkeley Lab) to expose relatively rare and fleeting cosmic events, like supernovae and gamma ray bursts.

In fact, during the commissioning phase alone, the survey has already uncovered more than 40 supernovae, or stellar explosions, and astronomers expect to discover thousands more each year. Such events occur about once a century in our own Milky Way galaxy and are visible for only a few months.

Finding fleeting cosmic events not only requires the right kind of telescope and camera, it depends on high-performance computing to pinpoint objects of interest among thousands of images while there’s still time for follow-up observations. Caltech and NERSC join forces in just such a search, the Palomar Transient Factory.

“This survey is a trail blazer in many ways," says Shrinivas Kulkarni, who is professor of astronomy and planetary science at the California Institute of Technology (Caltech), director of Caltech Optical Observatories, and principal investigator of PTF. "It is the first project dedicated solely to finding transient events, and as part of this mission we've worked with NERSC to develop an automated system that will sift through terabytes of astronomical data every night to find interesting events, and have secured time on some of the world's most powerful ground-based telescopes to conduct immediate follow up observations as events are identified.”

“This truly novel survey combines the power of a wide-field telescope, a high-resolution camera, high-performance network and computing, as well as the ability to conduct rapid follow-up observations with telescopes around the globe for the first time,” says Peter Nugent, a staff scientist in Berkeley Lab’s Computational Research Division (CRD) and the NERSC Analytics Group. Nugent is also the Real-time Transient Detection Lead for the PTF project.

Every night the PTF camera — a 100-megapixel machine mounted on the 48-inch Samuel Oschin Telescope at Palomar Observatory in Southern California — will automatically snap pictures of the sky, then send those images to NERSC for archiving via high-speed networks provided by the DOE's Energy Sciences Network (ESnet) and the National Science Foundation's High Performance Wireless Research and Education Network (HPWREN).

At NERSC, computers running machine learning algorithms in the Real-time Transient Detection pipeline scour the PTF observations for "transient” sources, or cosmic objects that change in brightness or position, by comparing the new observations with all of the data collected from previous nights. Once an interesting even is discovered, machines at NERSC will, within minutes, send its coordinates to Palomar's 60-inch telescope and others for follow-up observations.

“PTF is an example of the growing need to provide data services for science. It combines automated, real-time analysis with high end systems and networks in a way that changes the way the scientific community works,” says NERSC Director Kathy Yelick.

“We are currently uncovering one event every 12 minutes. This project will be keeping the astronomical community busy for quite a while,” says Kulkarni.

“These tools are extremely valuable because they not only help us identify supernovae, they uncover them while the star is in the act of exploding,” says Robert Quimby of Caltech, who is the software lead for the PTF program. “This gives us valuable information about how cosmic dust is spread across the universe.”

Quimby notes that all chemical elements in the universe besides hydrogen and helium are created inside stars. When massive stars die in fiery explosions, or supernovae, they blast these chemical creations out into space. This cosmic dust will eventually come together to become stars, planets, comets, and even humans. Everything around us is made of stardust.

In addition to spreading stardust across the cosmos, some species of supernovae also play a vital role in helping us understand the nature of the universe. For example, because Type Ia supernovae are relatively uniform in brightness, they act as cosmic lighthouses, helping astronomers judge distance. Many astronomers participating in the PTF survey will specifically be searching for these cosmic markers.

“It is very exciting to find so many supernovae, so early in the project. It's like we've just turned on the spigot and are now waiting for the fire hose to blast,” says Quimby.

Palomar Transient Factory/ Dovi Poznanski (Berkeley Lab) These four images reveal how astronomers using NERSC's Real-Time Detection pipeline uncovered supernova SN2009av-1a in the act of exploding. (1) This portrait of a galaxy located 800 million light-years away was created by layering a variety of observations taken by the Palomar Transient Factory camera (PTF) from February 23–27. (2) Image captured by the PTF camera on February 28. (3) By digitally subtracting the earlier image from the new one, using NERSC's pipeline, scientists can expose cosmic transients like supernovae. This is essentially like subtracting the haystack to find the needle inside. (4) Subtraction of an image taken on March 2 showed that the source got brighter within a few days. Follow-up observations revealed that this new source is a Type Ia supernova caught at peak brightness. It is now called SN2009av.

PTF is a collaboration of Berkeley Lab, Caltech, Columbia University, the NSF's HPWREN, the Infrared Processing and Analysis Center, Las Cumbres Observatory Global Telescope Network, Oxford University, University of California, Berkeley, and the Weizmann Institute of Science, Israel. PTF is partly supported by DOE's Scientific Discovery through Advanced Computing program, and NERSC provided the storage and systems infrastructure. NERSC and ESnet are managed by the Berkeley Lab on behalf of DOE.