A Photometric Investigation of the GRB970228 Afterglow and the Associated Nebulosity

Abstract

We carefully analyze the WFPC2 and STIS images of GRB970228. We measure magnitudes for the GRB970228 point source component in the WFPC2 images of $V=26.20_{-0.13}^{+0.14}$, $I_c=23.94_{-0.09}^{+0.10}$ and $V=26.52_{-0.18}^{+0.16}$, $I_c=24.31_{-0.11}^{+0.15}$ on March 26 and April 7, respectively; and $R_c=27.09_{-0.14}^{+0.14}$ on September 4 in the STIS image. For the extended component, we measure magnitudes of $R_c=25.48_{-0.20}^{+0.22}$ in the combined WFPC2 images and $R_c=25.54_{-0.22}^{+0.33}$ in the STIS image, which are consistent with no variation. This value is fainter than previously reported (Galama et al. 98) and modifies the previously assumed magnitudes for the optical transient when it faded to a level where the extended source component contribution was not negligible, alleviating the discrepancy to a power-law temporal behavior. We also measure a color of $V_{606}-I_{814}=-0.18_{-0.61}^{+0.51}$ for the extended source component. Taking into account the extinction measured in this field (Castander & Lamb 1998), this color implies that the extended source is most likely a galaxy with ongoing star formation.

21 pages, including 8 figures. Submitted to ApJ

References in corpus (7)

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• The optical counterpart to gamma-ray burst GRB970228 observed using the Hubble Space Telescope
• The Fading Optical Counterpart of GRB~970228, Six Months and One Year Later
• The decay of optical emission from the Gamma-Ray Burst GRB 970228
• Observations and Theoretical Implications of GRB 970228
• Iron line signatures in X-ray afterglows of GRB by BeppoSAX
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