VLA radio detection of Nova Sagittae 2026 (V488 Sge)

ATel #18088; Kirill Sokolovsky, Justin Linford (NRAO), Laura Chomiuk, Peter Craig (MSU), Katie Barnhart, Darien Perla, Pragati Acharya, John Worley, Anthony Pearce, Vallia Antoniou, Elias Aydi (TTU), Jennifer Sokoloski (Columbia), Koji Mukai (NASA/GSFC)
on 3 Oct 2026; 19:36 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)

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Peaking at visual magnitude 7 around 2026-08-25.9 UT and being (so far) the brightest classical nova of the year, Nova Sagittae 2026 (V488 Sge, PNV J19450648+1822422) has been the target of optical photometric and spectroscopic (CBET #5729, ATel #18008, #18009, #18012, #18014, #18021, #18022, #18033, #18053) as well as X-ray observations (ATel #18028, #18084).

We report 2.6-35 GHz radio observations of V488 Sge with the Karl G. Jansky Very Large Array (VLA) in its most compact D configuration. The nova was not detected on 2026-09-03.04 (8 days after the optical peak), was detected at 31 and 35 GHz (~0.3 mJy) on 2026-09-08.99 (14 days), and was clearly detected at all frequencies on 2026-09-25.98 (31 days). The measured flux densities, their one-sigma errors and three-sigma upper limits are listed below:

 
# epoch 1  2026-09-03.04 
# nu(GHz) S(mJy) 
2.6      <0.177 
3.4      <0.102 
5.1      <0.069 
7.0      <0.069 
13.7     <0.078 
16.5     <0.084 
31.1     <0.207 
34.9     <0.201 
 
# epoch 2  2026-09-08.99 
# nu(GHz) S(mJy)  S_err(mJy) 
2.6      <0.165 
3.4      <0.102 
5.1      <0.063 
7.0      <0.060 
13.7     <0.087 
16.5     <0.093 
31.1      0.268   0.081 
34.9      0.306   0.081 
 
# epoch 3  2026-09-25.98 
# nu(GHz) S(mJy)  S_err(mJy) 
2.6       0.301   0.051 
3.4       0.408   0.040 
5.1       0.409   0.021 
7.0       0.482   0.023 
13.7      0.693   0.030 
16.5      0.902   0.050 
31.1      1.066   0.094 
34.9      0.885   0.095 

An extragalactic radio source 1932+204 was used as the phase referencing calibrator, while 3C286 was used to set the flux density scale.

The radio spectrum of V488 Sge on 2026-09-25.98 is inverted with a spectral index of +0.5. The shape of the spectrum is likely determined by free-free absorption in the nova ejecta and does not discriminate between thermal and synchrotron origin of the emission.

VLA spectrum of V488 Sge