ATLAS observations of the blue, featureless transient MASTER OT J034412.48-263556.5

ATel #10940; O. McBrien, K. W. Smith, S. J. Smartt (Queen's University Belfast) J. Tonry, L. Denneau, B. Stalder, A. Heinze, H. Weiland (IfA, University of Hawaii), A. Rest (STScI)
on 9 Nov 2017; 16:00 UT
Credential Certification: Stephen Smartt (s.smartt@qub.ac.uk)

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Lipunov et al. (Atel #10929) reported the discovery of MASTER OT J034412.48-263556.5 (0"W,21"S of PGC134086) on 2017-11-06.23799 (MJD = 58063.23799). They reported this as possibly spatially coincident with the short GRB171030A (GCN 22076), which was discovered at 2017-10-30 17:29:45 (MJD = 58056.728). Wang et al. (ATel #10935) reported two spectra, both of which were blue and featureless (one of them taken at 2017-11-08 12:58:44, or MJD=58065.54).

We have detected the source in ATLAS survey data, and have run forced photometry at the position. The object is detected on 58053.46 at 3 sigma, and is clearly visible on 3 images at 58055.45 at o = 19.2. The latter is 1.3 days before the GRB171030A discovery.

The blue and featureless spectra of the transient reported by Wang et al. (ATel 10935, GCN 22108) are unusual, given that the transient was 12 days old at the time of the spectrum. Given the detection a few days before the GRB, and the rising lightcurve, it is likely not associated. But further spectra of the unusual transient are encouraged. The host is redshift z=0.066926 +/- 0.000150, distance modulus mu=37.35 +/- 0.05. foreground extinction A_o = 0.02, which implies absolute magnitude M_o = -19.1 for the transient at peak (from o = 18.3 at peak).

For completeness, we report the full ATLAS detection information here:

The Asteroid Terrestrial-impact Last Alert System (ATLAS, see Tonry et al. 2011, PASP, 123, 58 and Tonry et al. ATel #8680) reports observations of a supernova candidate internally named as ATLAS17mzy. The object was detected by ATLAS on MJD 58055.4547042 (2017-10-29 UT) at (RA, Dec) = (56.05214 deg, -26.59936 deg) with discovery magnitude 19.12 +/- 0.22. The object is located 23 arcsec S and 0.4’’ E of host galaxy 2MASX J03441248-2635352. Repeat observations were made over subsequent nights. The corresponding magnitudes, sky locations and filters are as follows:

 
  
  
MJD            | RA             | Dec            | Magnitude       | Filter 
58053.4624     | 56.05214       | -26.59936      | 19.38           | ATLAS-o 
58055.4547     | 56.05199       | -26.59964      | 19.12           | ATLAS-o 
58055.4547     | 56.05197       | -26.59956      | 19.27           | ATLAS-o 
58055.46666    | 56.05227       | -26.59965      | 19.39           | ATLAS-o 
58055.46849    | 56.05211       | -26.59923      | 19.07           | ATLAS-o 
58059.46924    | 56.05239       | -26.59931      | 18.35           | ATLAS-o 
58063.45363    | 56.05214       | -26.59905      | 18.34           | ATLAS-o 
58063.45683    | 56.05211       | -26.59908      | 18.28           | ATLAS-o