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Choosing a Maximum Drift Rate: Astrophysical Considerations
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  • Sofia Sheikh,
  • Jason Wright,
  • Andrew Siemion,
  • Emilio Enriquez
Sofia Sheikh
Pennsylvania State University

Corresponding Author:[email protected]

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Jason Wright
Pennsylvania State University
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Andrew Siemion
University of California Berkeley
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Emilio Enriquez
University of California Berkeley, Radboud Universiteit Nijmegen
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A radio transmitter which is accelerating with a non-zero radial component with respect to a receiver will produce a signal that appears to change in frequency over time. This effect, commonly produced in astrophysical situations where orbital and rotational motions are ubiquitous, is called a drift rate. In radio SETI (Search for Extraterrestrial Intelligence) research, it is unknown a priori which frequency a signal is being sent at, or even if there will be any drift rate at all besides motions in the solar system. Therefore a range of potential drift rates need to be individually searched, and a maximum drift rate needs to be chosen. The middle of this range is zero, indicating no acceleration, but the absolute value for the limits remains unconstrained. A balance must be struck between computational time and the possibility of excluding a signal from ETI. In this work, we examine physical considerations that constrain a maximum drift rate and highlight the importance of this problem in any narrowband SETI search. We determine that a normalized drift rate of 200 nHz (e.g. 200 Hz/s at 1 GHz) is a generous, physically motivated guideline for the maximum drift rate that should be applied to future narrowband SETI projects if computational capabilities permit.