HST ACS Images of the Host of XRF/GRB 020903

The region surrounding the possible optical counterpart of XRF 020903. Showing the position and 1 sigma error for the position of the optical transient (when compared to ground based images obtained on the 4th and 9th Dec). Also showing the nearby interacting galaxy G2. At a redshift of 0.23 (Soderberg et al GCN 1554). North is up, and east to the left. The image is approximately 10" across and has been drizzled onto an output grid with pixels 0.66 times size of the native ACS pixel.

The candiate optical transient for XRF 020903 (Soderberg et al, GCN 1554) was imaged with HST/ACS in F606W on 3rd Dec 2002. 4 dithered exposures were obtained with a total exposure time of 1840s.

The candidate appears to be within an irregular galaxy with four (possibly interacting) components. Astrometry with images obtained with the CTIO 4-m telescope and Mosaic imager on Sept 4th and 9th 2002 (Fruchter et al, GCN 1558) shows that the transient source is located at a position coincident with the peak of the most western of these compact knots (with a positional accuracy of ~0".1). The knot has an F606W AB magnitude of 22.6 and a FWHM of ~0."14, greater than the PSF of ACS. Hence the source is resolved at this resolution, indicating that an AGN does not dominate the optical light from this object.

The galaxy, named G2 by Soderberg et al, (GCN 1554) is also clearly an interacting system. However, as noted by Soderberg et al the redshift difference (z=0.23 for G2 and z=0.25 for the candidate OT) indicate that the sytems are not associated.

Using a 1" aperture the magnitude of the entire system in F606W is approximately R=21, roughly consistent with the late time magnitudes determined by Gorosabel et al (GCN 1631).

Further observations will allow an image subtraction to search for any variability in this source, to help further establish its nature.

This result was reported as GCN 1671 .