MAXI J1543-564: optical-nearIR observations with GROND

ATel #3365; Arne Rau, Jochen Greiner, Jonny Elliott, Felipe Olivares E. (all MPE Garching)
on 20 May 2011; 05:15 UT
Credential Certification: Arne Rau (arau@mpe.mpg.de)

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GROND (Greiner et al. 2008, PASP 120, 405), the 7-channel imager mounted at the 2.2m MPI/ESO telescope at La Silla Observatory (Chile) started follow-up observations of the transient source MAXI J1543-564 (Negoro et al. 2011, ATEL #3330) on 10 May 2011, 05:06 UT simultaneously in the g'r'i'z'JHK bands and continued for four nights. Within the 1.8 arcsec Swift/XRT error circle (Kennea et al. 2011, ATEL #3331) we detect the source (henceforth called source A) reported by Russel et al. (2011, ATEL #3359) at

A: RA(2000.0) = 15:43:17.37, Decl.(2000.0) = -56:24:49.1

The localization uncertainty is 0.4 arcsec in both coordinates. This position is ~1.7 arcsec from the center of the ATCA radio position (Miller-Jones et al., ATEL #3364), thus formally inconsistent with the ATCA radio source.

We measure the following magnitudes (all in AB system), not corrected for Galactic foreground reddening of E(B-V)~3.5mag (Schlegel et al. 1998):

g' = >22.8
r' = 20.7 +/- 0.1
i' = 19.4 +/- 0.1
z' = 18.7 +/- 0.1
J = 17.1 +/- 0.2
H = 16.8 +/- 0.2
K = 17.0 +/- 0.2

These magnitudes were derived by calibrating the images against GROND zero-points and 2MASS field stars and are consistent with the i'-band magnitude reported by Russel et al. (2011, ATEL #3359) and with the upper limit derived from Swift/UVOT (Kennea et al. 2011, ATEL #3336). No flux variation has been found between observations taken over four nights.

Assuming E(B-V)=3.5mag, the spectral energy distribution is best fit with a power law consistent with the Rayleigh-Jeans tail of a black body, or the outer part of an accretion disk. Note however, that the uncertainty in the Galactic foreground extinction leads to a wide range of possible spectral energy distributions.

We detect two additional, faint sources, one within the Swift/XRT error circle and 2.0 arcsec from the ATCA position at

B: RA(2000.0) = 15:43:17.35, Decl.(2000.0) = -56:24:48.1

and the other slightly outside the Swift/XRT error circle and 1.2 arcsec from the ATCA location at

C: RA(2000.0) = 15:43:17.22, Decl.(2000.0) = -56:24:48.5

We estimate z' band magnitudes of ~20.7mag (source B) and ~20.5mag (source C). These sources are not detected in the g', r', and i' bands and measurements in the J, H, and K_s bands are strongly affected by blending of both sources with source A. Variable seeing conditions prevent us from making proper statements about flux variations at this point.

No source is detected within the ATCA radio ellipse (Miller-Jones et al. 2011, ATEL #3364) to 3-sigma limiting AB magnitudes of

r'=23.4
i'=22.7
z'=22.1.

A GROND z'-band image is available at http://www.mpe.mpg.de/~jcg/xrt/MAXIJ1543m564.html

Observations are continuing.