VLA resolved radio shell of the slow Galactic nova V1405 Cas (2021)

ATel #15518; Kirill Sokolovsky, Elias Aydi, Laura Chomiuk, Adam Kawash, Jay Strader, Sarah Watson, Caitlyn Emma Gerhard, David-Michael Peterson (MSU), Jennifer Sokoloski (Columbia), Justin Linford (NRAO), Koji Mukai (NASA/GSFC), Kwan-Lok Li (NCKU), Tim O'Brien (JBCA/Manchester), Michael Rupen (NRC)
on 19 Jul 2022; 10:06 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)

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Following the fast optical rise to V=7.5 discovered by Y. Nakamura on 2021-03-18.4236 UT the nova V1405 Cas showed a series of optical flares with the brightest one reaching V=5.1 around 2021-05-10 followed by a slow decline to V=11.3 by 2022-07-10 (CBET #4945, ATel #14471, #14472, #14476, #14478, #14482, #14530, #14577, #14614, #14620, #14622, #14665, #14704, #14794, #15093, #15111). The GeV emission from V1405 Cas was detected with Fermi/LAT (ATel #14658). The rising radio emission from V1405 Cas was followed with the Karl G. Jansky Very Large Array (VLA; ATel #14731, #15150) and the upgraded Giant Metrewave Radio Telescope (uGMRT; ATel #15383).

Our latest VLA epoch firmly places V1405 Cas among the five brightest novae ever observed in the radio band (cf. Chomiuk et al., 2021, ApJS, 257, 49). The following flux densities were measured on 2022-07-04:

 
f(GHz) S(mJy) err(mJy)   
 2.6    9.803  0.044 
 3.4   12.200  0.022 
 5.1   19.529  0.016 
 7.0   28.938  0.027 
13.7   84.482  0.030 
16.5  100.844  0.032 
31.1  175.838  0.065 
34.9  191.004  0.075 

The quoted uncertainties correspond to the RMS noise of the residual map after CLEANing. No self-calibration was applied at frequencies below 10 GHz and the flux densities were obtained from peaks of naturally-weighted CLEAN images of the unresolved nova emission. We used 3C147 to set the absolute flux density scale (Perley & Butler, 2017, ApJS, 230, 7) with expected uncertainties of 15% at 35 GHz and 5% at lower frequencies. The source J2339+6010 (TXS 2336+598) was used as the phase calibrator. The VLA was in its extended A configuration resulting in the naturally weighted beam sizes from 0.73"x1.06" at PA=103 deg. to 0.06"x0.07" at PA=122 deg. at 2.6 and 34.9 GHz, respectively.

The nova shell is clearly resolved in 13.7 to 34.9 GHz images. The reported flux densities correspond to the sum of all CLEAN components within the visual extent of the shell. Phase-only self-calibration was applied for measuring the total flux density and amplitude self-calibration was applied to produce the final images.

The 31.1 and 34.9 GHz images show an elliptical edge-brightened shell extending about 220 mas in the north-east to south-west direction crossed by a bright band of emission extending about 120 mas along the minor axis of the shell. The 13.7 and 16.5 GHz images show a center-brightened emission with the extent matching that at the higher-frequency images.

The VLA images of V1405 Cas may be found here