From AAS NOVA: “A Software Solution for Tracking Down Gravitational Wave Sources”

AASNOVA

From AAS NOVA

9.9.22
Kerry Hensley

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An illustration of two neutron stars approaching a merger. [L. Calçada/The European Southern Observatory [La Observatorio Europeo Austral] [Observatoire européen austral][Europaiche Sûdsternwarte] (EU)(CL)]

When racing to follow up on a new detection of gravitational waves, every second of telescope time is precious. A recent publication describes how a new algorithm for scheduling observations might improve our ability to track down transient events.

Seeking Gravitational Wave Sources

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Locations of the observatories that followed up on the detection of the gravitational wave signal GW170817. [LIGO-Virgo]

The search for the source of gravitational wave event GW170817 is an amazing success story. In the days following the initial detection, telescopes across the world pinpointed and monitored the resulting kilonova, leading to a deep understanding of the event — but since then, no other gravitational wave source has been definitively identified.

Searches for gravitational wave sources are challenging because the search areas are often large, telescope time is limited, and the events are transient. How can we track down the causes of gravitational wave signals in a way that makes the most efficient use of the available observing time? In a recent publication, B. Parazin (Northeastern University and University of Minnesota) put a new observation-scheduling algorithm to the test.

Scheduling Telescope Time

Parazin and collaborators tested a new algorithm optimized for the Zwicky Transient Facility (ZTF), which is designed to detect transient events.

The team aimed to maximize the odds of tracking down the source of a new gravitational wave signal while minimizing the amount of observing time needed. They also accounted for factors that are unique to the ZTF, such as the time needed to switch between filters.

In addition to the particulars of the ZTF observing setup, the algorithm takes as an input a map of the sky showing the probable locations of a gravitational wave source, which is released by gravitational wave observatories when a new signal is detected. From there, the algorithm identifies which out of the ZTF telescope’s 1,778 possible pointing directions are appropriate, groups pointings that are continuously observable during a selected length of time, and orders the pointings within each group so as to minimize the amount of time the telescope spends between observations.

Improving Efficiency

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Comparison of the probability coverage of the existing algorithm in use by the ZTF (gwemopt) to that of the new algorithm introduced in this work (MUSHROOMS). The new algorithm performs better than the existing algorithm for cases located under the yellow line. [Parazin et al. 2022]

To compare the new algorithm to the one ZTF currently uses, the team scheduled observations with each method for 951 simulated detections of binary neutron star mergers. Under the conditions best suited to compare the two methods, Parazin and coauthors find that their new algorithm improves upon the existing software by 5.8%, on average — in other words, the new observing schedules increased the probability of finding the source. Since the existing algorithm sometimes outperformed the new algorithm, a hybrid approach — running both algorithms and choosing the more efficient solution — was the best, netting an average 8.1% improvement.

A final wrinkle is the fact that transient sources can fade rapidly, making the order in which the observations are carried out important — reach a source too late, and it may have dimmed beyond detection. When testing both algorithms on finding rapidly fading synthetic kilonovae, the team found that 1) once again, the hybrid approach had the best performance, and 2) the new algorithm had an advantage over the existing software when the search area was large.

Citation

Foraging with MUSHROOMS: A Mixed-integer Linear Programming Scheduler for Multimessenger Target of Opportunity Searches with the Zwicky Transient Facility, B. Parazin et al 2022 ApJ 935 87.
https://iopscience.iop.org/article/10.3847/1538-4357/ac7fa2/pdf

See the full article here .


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The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.