Millimeter flaring in LEDA 66480/ESO 145-001

ATel #17839; Thomas Maccarone (Texas Tech University) on behalf of the South Pole Telescope consortium
on 8 Jun 2026; 19:02 UT
Credential Certification: Tom Maccarone (thomas.maccarone@ttu.edu)

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The South Pole Telescope collaboration report millimeter flaring from SPT-SV J211659.7-592000. The source at this position has been marginally detected in SPT data since 2021, with a mean flux density of 1.6+-0.5mJy at 90 GHz and 1.9+-0.4 mJy at 150 GHz, and with ASKAP at about 9 mJy.. In the period from 5/10-5/31, the source is at 5.8+-0.9 mJy with a highest measured value in an individual epoch of 17 mJy and a test-statistic for variability of 51.2, corresponding to a >7-sigma variability detection. The 150 GHz measurements yield 6.7+-1.2 mJy over the same timespan, indicating a flat-to-mildly inverted spectrum.

The source is associated with the nearby merging galaxy pair LEDA 66480/ESO 145-001, which is at redshift z=0.0605 (Jones et al. 2009MNRAS.399..683J), or about 270 Mpc, assuming H0=70 km/sec/Mpc, but it is not clear which member of the pair is the location of the flaring activity. A ToO observation on the Australia Telescope Compact Array has been triggered, but additional follow-up at other wavelengths is encouraged.

The object has previously been seen in X-rays with eROSITA at a flux of 3.9e-14 erg/sec/cm^2(Merloni et al. 2024A&A...682A..34M ) and in the 4XMM catalog with a flux of 5.5e-13 erg/sec/cm^2 (Webb et al. 2020A&A...641A.136W). The spectrum appears to be strongly absorbed, so the difference between the two values is likely to be at least partially because of the different bandpasses. Regardless, X-ray variability measurements would help understand the source flaring, and the X-ray measurements suggest that the object is a low luminosity AGN.