VLA Observations Of T CrB Reveal Increase in Radio Flux Density Between 2014 and 2016

ATel #9153; J. Linford (Michigan State), J. Weston (NRAO), L. Chomiuk (Michigan State), J. Sokoloski (Columbia), T. Nelson (U. Pittsburgh), K. Mukai (UMBC/NASA GSFC), T. Finzell (Michigan State), M. Rupen (NRC-HIA) and A. Mioduszewski (NRAO)
on 14 Jun 2016; 20:36 UT
Credential Certification: Justin Linford (jlinford@msu.edu)

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We report new observations of the symbiotic binary and known recurrent nova T Coronae Borealis (T CrB) with the Karl G. Janksy Very Large Array (VLA). We recently began monitoring T CrB in 2016 May after reports that it was in a super-active state at other wavelengths (Munari, Dallaporta, & Cherini 2016, NewA, 47, 7; ATEL #8675; AAVSO Special Notice 415). We have observations from 2016 May 04.4 and 2016 June 04.3. We also observed it on 2014 October 2, prior to the transition to the super-active state.

All reported uncertainties are the Gaussian fit errors from the AIPS task JMFIT and do not include uncertainty in the absolute flux density calibration. All non-detections are 3-sigma upper limits.

The pre-super-active state observation of T CrB on 2014 October 2 was at a frequency of 10 GHz. The flux density at that time was 0.040 +/- 0.004 mJy. The in-band spectral index (8--12 GHz) was consistent with a flat spectrum.

Below are the tabulated results from the two 2016 epochs.

 
      | 2016-05-04.4   | 2016-06-04.3   | 
Freq. | Flux density   | Flux density   | 
[GHz] | [mJy]          | [mJy]          | 
1.26  | <0.61          | <0.57          | 
1.77  | <0.33          | <0.22          | 
5.0   | <0.05          | 0.04 +/- 0.01  | 
7.0   | 0.08 +/- 0.01  | 0.04 +/- 0.01  | 
9.0   | 0.13 +/- 0.01  | 0.15 +/- 0.01  | 
11.0  | 0.15 +/- 0.01  | 0.18 +/- 0.01  | 
13.5  | 0.19 +/- 0.01  | 0.22 +/- 0.01  | 
16.5  | 0.22 +/- 0.01  | 0.25 +/- 0.01  | 
29.5  | 0.40 +/- 0.03  | 0.44 +/- 0.03  | 
35.0  | 0.44 +/- 0.03  | 0.49 +/- 0.03  | 

Clearly, the source is currently in a higher flux state than in 2014. The spectral shape of the radio emission has also changed from flat in 2014 to the flux density rising toward higher frequencies now. The current spectral shape is consistent with optically thick thermal emission. There also appears to be some variability in the radio emission in the source's current state.

We currently plan monthly VLA observations of T CrB through 2016 September. We encourage others to monitor it at other wavelengths.