GRB 070208: Optical Decay

GCN Circular #6075 GRB 070208: MDM Optical Observations

N. Mirabal and J. P. Halpern (Columbia U.) report on behalf of the MDM Observatory GRB follow-up team: "We have observed the Swift BAT localization of GRB 070208 (Sato et al., GCN 6074) with the MDM 1.3m telescope starting on February 8 09:25. Within the XRT error box, we detect two extended sources (also seen in the DSS plates), which should be considered potential host galaxies for this short burst. Observations are continuing to determine optical variability. This message may be cited."

(J2000) 13h 11m 32.77s, +61° 57′ 55.2″ Swift XRT 5" radius (Sato et al., GCN 6074)

SDSS r' Pre-Burst (Cool et al., GCN 6080)

MDM 1.3m R-band Feb. 08.39 UT

MDM 1.3m R-band Feb. 08.46 UT

MDM 1.3m R-band Feb. 08.54 UT

GCN Circular #6082 GRB 070208: MDM Optical Decay

J. P. Halpern & N. Mirabal (Columbia U.) report on behalf of the MDM Observatory GRB follow-up team: "Monitoring of the afterglow of GRB 070208 (GCNs 6077, 6078, 6079) in the R-band on the MDM 1.3m telescope consisted of a series of 10-minute exposures beginning on Feb. 8 09:25 UT and ending at 13:12 UT, thus spanning the time 0.25-4 hours after the burst. Partly cloudy conditions, together with bright moonlight, resulted in images of highly variable quality. Nevertheless, we see the fading optical transient within the Swift XRT error circle (Sato et al., GCN 6074). In agreement with the GCNs listed above, we find the OT 3.0" west and 3.3" south of the center of a galaxy visible on the POSS (Mirabal & Halpern, GCN 6075) and in pre-burst SDSS images (Cool et al., GCN 6080). Preliminary magnitudes for the OT, calibrated with respect to USNO B1.0 magnitudes of nearby stars, are R=20.04+/-0.08 for the first exposure centered at 09:30 UT, and R=21.5+/-0.2 for a summed 30-minute exposure centered at 12:55 UT. Some contamination from the nearby galaxy is possible in this analysis. Quoted uncertainties are statistical only. This corresponds to a mean power-law decay index of -0.55. It is not yet clear from this collection of images, both SDSS and MDM, if the visible galaxy is the host, or if we should wait to see if a fainter galaxy underlies the OT of this judged long burst (Markwardt et al., GCN 6081). Images are posted at http://www.astro.columbia.edu/~jules/grb/070208/ This message may be cited."

MDM 1.3m R-band Feb. 09.50 UT

MDM 1.3m R-band Feb. 10.53 UT

Nestor Mirabal mirabal@astro.columbia.edu	Jules Halpern jules@astro.columbia.edu
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Last Modified: February 8, 2007	jules@astro.columbia.edu