The Atacama Cosmology Telescope: Detection of Millimeter-wave Transient Sources
Hilton, Matt; Choi, Steve K.; Dünner, Rolando; Gallardo, Patricio A.; Gralla, Megan; Huffenberger, Kevin M.; Koopman, Brian J.; Madhavacheril, Mathew S.; McMahon, Jeff; Nati, Federico; Niemack, Michael D.; Partridge, Bruce; Wollack, Edward J.; Halpern, Mark; Guan, Yilun; Naess, Sigurd; Duell, Cody J.; Calabrese, Erminia; Cothard, Nicholas F.; Devlin, Mark; Duivenvoorden, Adriaan J.; Dunkley, Jo; Kosowsky, Arthur B.; Salatino, Maria; Sehgal, Neelima; Staggs, Suzanne; Xu, Zhilei; Page, Lyman; Battaglia, Nick; Richard Bond, J.; Colin Hill, J.; Spergel, David
United States, Canada, United Kingdom, Chile, South Africa, Italy
Abstract
We report on the serendipitous discovery of three transient millimeter-wave sources using data from the Atacama Cosmology Telescope. The first, detected at R.A. = 273.8138, decl. = -49.4628 at ~50σ total, brightened from less than 5 mJy to at least 1100 mJy at 150 GHz with an unknown rise time shorter than 13 days, during which the increase from 250 mJy to 1100 mJy took only 8 minutes. Maximum flux was observed on 2019 November 8. The source's spectral index in flux between 90-150 GHz was positive, α = 1.5 ± 0.2. The second, detected at R.A. = 105.1584, decl. = -11.2434 at ~20σ total, brightened from less than 20 mJy to at least 300 mJy at 150 GHz with an unknown rise time shorter than 8 days. Maximum flux was observed on 2019 December 15. Its spectral index was also positive, α = 1.8 ± 0.2. The third, detected at R.A. = 301.9952, decl. = 16.1652 at ~40σ total, brightened from less than 8 mJy to at least 300 mJy at 150 GHz over a day or less but decayed over a few days. Maximum flux was observed on 2018 September 11. Its spectrum was approximately flat, with a spectral index of α = -0.2 ± 0.1. None of the sources were polarized to the limits of these measurements. The two rising-spectrum sources are coincident in position with M and K stars, while the third is coincident with a G star.