South Pole Telescope Alert : Detection of a Currently Flaring Millimeter-Band Source

ATel #15400; A. Foster on behalf of the SPT Collaboration
on 25 May 2022; 23:53 UT
Credential Certification: Sam Guns (sguns@berkeley.edu)

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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 = 0.23494d, DEC = -60.82318d (estimated positional uncertainty of 10 arcseconds). Millimeter emission from this source has increased by a factor of ~3 over the past 6 months, and a factor of ~10 over the past 3 years. Peak emission is currently (as of the most recent observing day on May 23rd) 25.9 +/- 4.1 mJy (95 GHz), and 34.0 +/- 5.0 mJy (150 GHz). At the time of this alert, emission from this source shows signs of decreasing. SPT-3G will continue to monitor this source at hour- to day-long intervals. Average quiescent flux at this position has increased from 3.8+/-1.2 mJy (95GHz), and 3.1+/-1.4 mJy (150GHz) in 2019 to 7.7+/-1.0 mJy (95GHz), and 8.0+/-1.3 mJy (150GHz) in 2020, and to 9.3+/-1.0 mJy (95GHz), and 9.2+/-1.3 mJy (150GHz) in 2021 as measured by SPT-3G, suggesting a factor of ~3 increase in millimeter-band luminosity from 2019-2021 and a further increase of ~3x over the past 6 months. This source may be associated with SPT-S J000056-6049.0, which is located at a distance of <5 arcseconds from the SPT-3G source and measured by SPT-SZ to have average flux densities 11.3 +/- 2.1 mJy (95 GHz) and 6.3 +/- 1.3 mJy (150 GHz) between Sept 2010 and October 2011. There is also a nearby (few arcseconds) X-ray source 4XMM J000055.9-604924, optical source DES J000055.83-604926.0 and radio source RACS J000055.9-604926. All flux calibrations quoted here are preliminary and are believed to be accurate to 20%. Further information including lightcurves and an updated catalog of SPT transient detections 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 transient detections