MAXIJ1727-203: GROND discovery of a candidate optical/NIR counterpart

ATel #11690; Arne Rau & Tassilo Schweyer (both MPE Garching)
on 6 Jun 2018; 08:13 UT
Credential Certification: Arne Rau (arau@mpe.mpg.de)

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The new transient MAXI J1727-203 (Yoneyama et al. 2018, ATel #11683) was observed simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) at the MPG 2.2m telescope at the ESO La Silla Observatory (Chile). Observations were obtained on June 6th 06:!2 UT with integrations of ~7.3min in the four optical bands and ~10.7min in the three NIR bands.

Within the 1.5' NICER positional uncertainty (Ludlum et al. 2018, ATel #11689), we find a bright new source located at

RA(J2000) = 17:28:29.92 (262.12466deg)
Dec(J2000) = -20:22:56.2 (-20.3823deg)
with an astrometric uncertainty of 0.02" in RA and 0.04" in Dec calibrated against PanSTARRS DR1 (https://panstarrs.stsci.edu).

We measure the following AB magnitudes (calibrated against PanSTARRS DR1 in griz and against 2MASS in JHK, not corrected for Galactic foreground reddening):

Source A:
g' = 16.91 +/- 0.01
r' = 16.53 +/- 0.01
i' = 16.39 +/- 0.01
z' = 16.26 +/- 0.01
J = 16.19 +/- 0.05
H = 16.38 +/- 0.12
K = 16.33 +-/ 0.06

The source is not detected in the PanSTARRS DR1 images.