VLA radio detection of Galactic novae V1674 Her and V1405 Cas

ATel #14731; Kirill Sokolovsky, Elias Aydi, Laura Chomiuk, Adam Kawash, Jay Strader (MSU), Aliya-Nur Babul, Jennifer Sokoloski (Columbia), Justin Linford (NRAO), Koji Mukai (NASA/GSFC), Kwan-Lok Li (NCKU)
on 21 Jun 2021; 22:06 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)

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Following Fermi/LAT detections of GeV gamma-rays from novae V1674 Her (ATel #14705, #14707) and V1405 Cas (ATel #14658), we initiated radio observations with the Karl G. Jansky Very Large Array (VLA) to search for synchrotron signatures of particle-accelerating shocks. The observations were performed at 2.6, 3.4, 5.1, 7.0, 13.7, 16.5, 31.1 and 34.9 GHz.

V1674 Her was detected on 2021-06-15, 16 and 17 with the 34.9 GHz flux density rising from 0.1 to 0.2 mJy over the three days. It was also marginally detected at 31.1 GHz (0.1 mJy), 16.5 and 13.7 GHz (~0.04 mJy) on the second and third epoch. If the distance to the nova is greater than 5 kpc and the expansion velocity is 5000 km/s (ATel #14710) starting on 2021-06-12.537 UT (ATel #14704), the measured 34.9 GHz flux density corresponds to the brightness temperature >10^4 K, indicating non-thermal emission.

V1405 Cas is clearly detected above 5 GHz on 2021-06-10, 12 and 17 having the inverted spectrum (positively defined spectral index 1.6) and the following flux densities:

 
# f(GHz) F(mJy) eF(mJy)  
2021-06-10 
05.1  0.166  0.021 
07.0  0.234  0.019 
13.7  0.682  0.018 
16.5  0.866  0.019 
31.1  2.550  0.047 
34.9  2.975  0.054 
 
2021-06-12       
05.1  0.223  0.026 
07.0  0.244  0.023 
13.7  0.675  0.020 
16.5  0.851  0.022 
31.1  2.274  0.047 
34.9  2.563  0.057 
 
2021-06-17 
05.1  0.178  0.022 
07.0  0.311  0.022 
13.7  0.842  0.019 
16.5  1.092  0.022 
31.1  3.183  0.051 
34.9  3.834  0.060 

Assuming the distance of 1.7 kpc (Bailer-Jones et al. 2018, AJ, 156, 58) and the expansion velocity of 1200 km/s starting on 2021-03-18.4236 (ATel #14530), the measured flux densities correspond to the brightness temperatures of a few thousand K, consistent with the radio emission of V1405 Cas being thermal.

The observations reported here were obtained with the National Radio Astronomy Observatory's Karl G. Jansky Very Large Array. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.