South Pole Telescope Alert: Detection of an Unusually Long Millimeter-Band Stellar Flare from CD-55 8799

ATel #16138; Chris Tandoi (UIUC), SPT-3G Collaboration
on 18 Jul 2023; 18:36 UT
Credential Certification: Sam Guns (sguns@berkeley.edu)

Tweet

The South Pole Telescope Collaboration reports: The 3rd-generation receiver on the South Pole Telescope (SPT-3G) detects a flaring millimeter point source at RA = 320.18516d, DEC = -54.63147d (estimated positional uncertainty of 5 arcseconds), associated with star CD-55 8799. Peak emission is currently (as of the most recent observation ending on 2023-07-18) 60+-5 mJy (95 GHz) and 75+-5 mJy (150 GHz). The SPT has observed this source increase in brightness in 6 separate observations since 2023-07-14, with an average revisit time of 12 hours. The SPT has previously observed flaring events originating from CD-55 8799 on 8 separate occasions since 2019, with durations on the order of hours and peak flux as high as 359+-6 mJy (95 GHz) and 724+-7 mJy (150 GHz). The duration of the current flaring state is the longest yet observed by the SPT for a stellar source. At the time of this alert, emission from this source is still above quiescence. The average quiescent fluxes measured by the SPT at this position are < 2 mJy at 90GHz and 150GHz. SPT-3G will continue to monitor this star at hour- to day-long intervals. All flux calibrations quoted here are preliminary and are believed to be accurate to 20%. Further information including lightcurves and a catalog of past SPT ATels can be found at https://pole.uchicago.edu/public/data/transients/. The South Pole Telescope is a 10-meter telescope designed for observations of the cosmic microwave background located at Amundsen-Scott South Pole Station and supported by the National Science Foundation and the US Dept. of Energy. The SPT online transient program providing data in this telegram is supported by NSF grants AST-1716965 and OPP 1852617, and observes 1500 square degrees of the southern sky at 95, 150, and 220 GHz with an average revisit cadence of 12 hours. For more details on the SPT transient program and survey strategy, please see https://arxiv.org/abs/2103.06166.

SPT ATel lightcurves and data table