The Ohio State University Big Ear radio telescope detected in 1977 the Wow! Signal, one of the most famous and intriguing signals of extraterrestrial origin.

Arecibo Wow! is a project that aims to find similar signals in archived data from the Arecibo Observatory. From 2017 to 2020, they observed many targets of interest at 1 to 10 GHz with the 305-meter telescope. Here are the first results of drift scans made between February and May 2020 at 1420 MHz presented. The methods, frequency, and bandwidth of these observations are similar to those used to detect the Wow! Signal. However, the observations are more sensitive, have better temporal resolution, and include polarization measurements. They report the detection of narrowband signals (10 kHz) near the hydrogen line similar to the Wow! Signal, although two-orders of magnitude less intense and in multiple locations. Despite the similarities, these signals are easily identifiable as due to interstellar clouds of cold hydrogen (HI) in the galaxy. They hypothesize that the Wow! Signal was caused by sudden brightening from stimulated emission of the hydrogen line due to a strong transient radiation source, such as a magnetar flare or a soft gamma repeater (SGR). These are very rare events that depend on special conditions and alignments, where these clouds might become much brighter for seconds to minutes. The original source or the cloud might not be detectable, depending on the sensitivity of the telescope. The precise location of the Wow! Signal might be determined by searching for transient radio sources behind the cold hydrogen clouds in the corresponding region. The hypothesis explains all observed properties of the Wow! Signal, proposes a new source of false positives in technosignature searches, and suggests that the Wow! Signal could be the first recorded event of an astronomical maser flare in the hydrogen line.

An approximation to determine the source of the WOW! Signal – publication

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