The Redshift of the Optical Transient Associated with GRB 010222

Abstract

The gamma-ray burst (GRB) 010222 is the brightest GRB detected to date by the BeppoSAX satellite. Prompt identification of the associated optical transient (OT) allowed for spectroscopy with the Tillinghast 1.5m telescope at F. L. Whipple Observatory while the source was still relatively bright (R ~ 18.6 mag), within five hours of the burst. The OT shows a blue continuum with many superimposed absorption features corresponding to metal lines at z = 1.477, 1.157, and possibly also at 0.928. The redshift of GRB 010222 is therefore unambiguously placed at z >= 1.477. The high number of Mg II absorbers and especially the large equivalent widths of the Mg II, Mg I, and Fe II absorption lines in the z = 1.477 system further argue either for a very small impact parameter or that the z = 1.477 system is the GRB host galaxy itself. The spectral index of the OT is relatively steep, beta = 0.89 +/- 0.03, and this cannot be caused by dust with a standard Galactic extinction law in the z = 1.477 absorption system. This spectroscopic identification of the redshift of GRB 010222 shows that prompt and well-coordinated followup of bright GRBs can be successful even with telescopes of modest aperture.Comment: 12 pages, 3 figures; ApJ Letters accepted version, only minor change

RapidUBVRIFollow‐up of the Highly Collimated Optical Afterglow of GRB 010222

“…The spectrum is Ðtted reasonably well by a single power law with l~1.07B0.09, somewhat steeper than the spectral slope derived from our low-resolution spectrum ([0.89^0.03 : Jha et al 2001b), although there is a hint of slight downward curvature toward the blue end of the FLWO 1.5 m spectrum overplotted in Figure 2. Indeed, when we Ðt using only our BV RI data, we obtain a slope of l~0.88B0.10, in excellent agreement with Jha et al (2001b). Also, the g@r@i@z@ spectral slope of [0.90^0.03 found by Lee et al (2001) agrees very well with Jha et al We agree as well with Lee et al in the slopes derived when also using U/u@ data.…”

“…The OT declined by D0.2 mag during about 2 hr of the Ðrst nightÏs observations (Henden & Vrba 2001 ;Stanek et al 2001a). Absorption-line systems at z \ 1.477, 1.157 and possibly also at 0.928 were seen in the optical spectrum of GRB 010222 taken within 5 hr of the burst with the FLWO 1.5 m telescope (Garnavich et al 2001 ;Jha et al 2001a), providing a lower limit to the redshift of the GRB source. The BeppoSAX NFI follow-up of GRB 010222 started about 9 hr after the burst (GandolÐ 2001) and detected a strong X-ray afterglow with a position consistent with the optical transient.…”

Hubble Space Telescopeand Ground‐based Optical and Ultraviolet Observations of GRB 010222

“…Absorption lines yielded a redshift of z ¼ 1:4768AE 0:0002 (Garnavich et al 2001;Jha et al 2001;Bloom et al 2001;Castro et al 2001;Masetti et al 2001) for the highest redshift absorber. This system shows kinematic substructure, with two distinct systems at z 1 ¼ 1:47667 AE 0:00005 and z 2 ¼ 1:47755 AE 0:00005, corresponding to a rest-frame velocity separation of 106 km s À1 , typical for internal motions in galaxies .…”

“…The highest redshift absorber is therefore likely the host galaxy of the GRB itself (Jha et al 2001). In addition, two foreground absorbing systems are detected (Bloom et al 2001;Castro et al 2001).…”

Optical Spectropolarimetry of the GRB 020813 Afterglow

“…Figure 1 displays the total flux spectrum of the OT from all exposures combined. Numerous metal absorption lines are superposed on a featureless continuum, as is typical for GRB afterglow spectra (e.g., Metzger et al 1997;Kulkarni et al 1999;Vreeswijk et al 2001;Jha et al 2001). Two distinct absorption systems are present in the spectrum (Table 1).…”