Candidate 4471

The pipeline flagged it at 01:14 and Tomás almost didn't look, because the pipeline flagged things all night, every night, and 4,470 of them so far this year had been nothing. Candidate 4471 was narrowband. That was the first thing. Nature doesn't do narrowband; stars and gas emit across wide smeared swathes of the spectrum. A signal a few hertz wide is what a transmitter makes. It's what the pipeline was built to find and almost never did, because humans are everywhere and it had been taught to throw out all the usual ones. 4471 wasn't one of the usual ones. He pulled up the waterfall plot. A thin bright line, drifting slowly across the frequency axis the way a signal from something in orbit, or on a rotating planet, would drift. It had drift. It had the right drift. He checked the on-off: the telescope nodded between the target star and an empty patch of sky every five minutes, and the line was there when it looked at the star and gone when it looked away. On. Off. On. Off. Three cycles. He sat back. The control room at that hour was him and the hum of the racks and a mug that said WORLD'S OKAYEST ASTRONOMER that a previous night-shifter had left as a kind of inheritance. There's a protocol. Step one: don't tell anyone. Not yet. Step two: rule out everything you can rule out yourself. Step three: if it survives, get a second telescope to look. Step four is a lot of phone calls. He started on step two. Local interference: he checked the site log. Nothing scheduled, nobody on site but the security guard, asleep in a hut a kilometre away. Satellites: he ran the ephemeris. Nothing within ten degrees. Aircraft: none on the tracker. The drift rate was consistent with a body rotating at roughly the rate of a planet. He'd calculated that himself, twice. The star was a boring one, a K-dwarf forty light years out, on the target list because it was boring, because boring stars were where you'd want to live.

At 02:50 the signal was still there. Six on-off cycles now. He thought about calling Dr Achterberg, the PI. He didn't. Step one. He thought about his sister, who'd asked him at Christmas what he'd actually do if he ever found something, and he'd said "probably throw up", and she'd laughed, and he was now aware that it hadn't been a joke. At 03:20 he did the thing he'd been avoiding, which was to look at the other beam. The telescope had a multi-beam receiver: it looked at the target star and, simultaneously, at six patches of sky around it. A real signal from the star would be in the central beam and nowhere else. Interference from something on the ground would leak into all of them. He pulled up beam three. There it was. Fainter. But there. He pulled up beam five. There. Beam one. There. He sat for a while with all seven beams on the screen, seven thin lines drifting in step, and felt the floor of the last two hours go out from under him in a way that was, he'd think later, almost restful. The on-off pattern had been a coincidence of timing: something on site switching on and off on a cycle that happened to line up. The drift was a cheap oscillator warming up. It took him until 04:40 to find it, walking the site with a handheld spectrum analyser in the dark, and it was the microwave in the kitchen of the visitor centre, four hundred metres away, which had a faulty door interlock and had been cycling all night trying to finish reheating something nobody had come back for. He unplugged it. All seven beams went clean. He wrote it up, all of it, the two hours where it was real and the four minutes where it stopped being, with time stamps, because the next person who saw a narrowband line on a boring star at one in the morning would need to know about the door. At 06:00 his relief came in, saw the mug, saw his face, and said, "Rough night?"

"Candidate 4471," Tomás said. "Microwave." "Ah. Beam three?" "Beam three." "They always are." He drove home with the sun coming up. He felt, he was surprised to find, fine. He'd spent two hours as a person who might have found something, and he'd found out what that person was like, and that person had followed the protocol, and had not thrown up, and had unplugged the microwave. He'd be back at ten tonight. The target list had four hundred more stars on it. Boring ones.