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GCN Circular 32208

GRB 220611A: Gemini Ks counterpart detection
2022-06-17T17:37:14Z (a year ago)
Jillian Rastinejad at Northwestern Univ. <>
J. Rastinejad (Northwestern), A. J. Levan (Radboud), D. B. Malesani (Radboud and DAWN/NBI), B. P. Gompertz (Birmingham), W. Fong, C. D. Kilpatrick (Northwestern) report on behalf of a larger collaboration:

We observed the location of GRB 220611A (Cenko et al., GCN 32191) with the FLAMINGOS-2 instrument mounted on the Gemini-South 8-meter telescope on Cerro Pachon, Chile. At a mid-time of 2022 Jun 17.43 UT (~5.7 days post-burst), we obtained 48 x 11 s of K-band imaging at a median airmass of 2.15 and seeing of 1.1 arcsec. A K-band source is detected at the location reported by O'Connor et al. (GCN 32203). Based on calibration to 2MASS, we estimate a preliminary magnitude for the source of K_AB ~ 21.1 +/- 0.2 mag. Compared to the measurement reported by O'Connor et al. (K_AB = 20.0 +/- 0.3 mag), our value is indicative of fading, though we note that the strong, non-uniform background due to the nearby galaxy MCG-06-10-007 and the lack of a common set of calibrators prevent a definitive statement. Furthermore, the source is not detected in archival imaging from the VISTA Hemisphere Survey (VHS; Cross et al. 2012), from which we measure a limiting magnitude K_AB > 20.5 mag. If confirmed, the fading and the non-detection in the VHS images would indicate that this object is transient, thus likely associated with GRB 220611A. 

We also note that a faint optical source is visible in r-band Legacy Source imaging (Dey et al. 2019) at the location reported by O'Connor et al. (GCN 32203). We measure a preliminary magnitude of r_AB ~ 24.5 +/- 0.3 mag for this source (again, uncertain due to the strong, non-uniform background). At present, it is not possible to discern if this source is associated with the z = 0.049 galaxy, or is a fainter, background galaxy. 

Further observations are planned. We thank Jen Andrews, German Gimeno and Ricardo Salinas at Gemini for the rapid planning and execution of these observations.
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