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GROND followup of ASASSN-17gu/AT2017eip

ATel #10435; Ting-Wan Chen, Tau Chen (MPE)
on 29 May 2017; 07:43 UT
Credential Certification: Ting-Wan Chen (jchen@mpe.mpg.de)

Subjects: Infra-Red, Optical, Supernovae, Transient

Referred to by ATel #: 10510

We observed the field of ASASSN-17gu/AT2017eip (Stone et al, ATel #10431) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG telescope at the ESO La Silla Observatory (Chile).

Observations started at 00:52 UT on 2017-05-28 (MJD = 57901.036), 4 days after the ASASSN pre-discovery image. We derive the following preliminary magnitudes (all in the AB system):

g' = 16.9 +/- 0.1 mag,
r' = 16.9 +/- 0.1 mag,
i' = 17.2 +/- 0.1 mag,
z' = 17.3 +/- 0.1 mag,
J = 17.7 +/- 0.1 mag,
H = 18.1 +/- 0.1 mag, and
K = 18.8 +/- 0.3 mag.

Given magnitudes are calibrated against SDSS field stars as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.03 mag in the direction of the transient (Schlafly & Finkbeiner 2011).

We fitted our colour SED assuming a black body, which indicates a temperature of 10400 K. If ASASSN-17gu/AT2017eip is associated with the elliptical galaxy (UGC 06831 at z=0.021), and thus an absolute r-band magnitude is about -17.8 mag (without any extinction correction).

We acknowledge excellent help in obtaining these data from the observer and supporting astronomer on La Silla, Simona Ciceri and Sam Kim.