GRB 070125: Optical Monitoring

(J2000) 07h 51m 17.77s, +31° 09′ 04.1″

MDM 2.4m - I - Jan. 27.30 UT	MDM 2.4m - I - Jan. 28.28 UT

MDM 2.4m - R - Jan. 27.27 UT	MDM 2.4m - R - Jan. 28.30 UT

MDM 2.4m - R - Jan. 29.35 UT	MDM 2.4m - V - Jan. 28.31 UT

MDM 1.3m - R - Feb 06.31 UT

GCN Circular #6096 GRB 070125: Break in Optical Decay

N. Mirabal, J. Halpern (Columbia U.), & J. R. Thorstensen (Dartmouth) report on behalf of the MDM Observatory GRB follow-up team: "We obtained several observations of the afterglow of GRB 070125 (Cenko & Fox, GCN 6028) between 2 and 12 days after the burst using the MDM 2.4m and 1.3m telescopes. Results in the R-band are summarized as follows: --------------------------------------- Date(UT) t-t0(days) R(mag) +/- --------------------------------------- Jan 27.270 1.964 19.71 0.02 Jan 28.299 2.993 20.44 0.03 Jan 29.346 4.040 21.07 0.07 Feb 6.307 12.001 >23.8 --------------------------------------- Calibration was performed with Landolt standard stars. In addition, we compiled data from the GCN circulars, and placed them on a common scale using their stated calibrators. MDM images and the compiled R-band light curve are shown at: http://www.astro.columbia.edu/~jules/grb/070125/ The light curve shows an apparent plateau or rise at about 1 day. Between 1 and 4 days, it is well described by a power law of slope -1.6. Our upper limit at 12 days implies that a break occurred after 4 days, and that the slope became steeper than -2.2. At redshift z=1.55 (Fox et al., GCN 6071) and fluence 1.5x10^-4 erg cm^-2 (Bellm et al., GCN 6025), the assumed isotropic energy is 9x10^53 erg. If we treat 4 days as a lower limit on the time of any "jet break", then the jet opening angle is of order 6 degrees or greater, and the beamed energy is 6x10^51 erg or greater. This message may be cited."

Last Modified: February 10, 2007	jules@astro.columbia.edu