{
  "subject": "GRB 210112A: LBT host detection and correction to GCN 29319 (CAHA observations)",
  "eventId": "GRB 210112A",
  "bibcode": "2021GCN.29456....1R",
  "createdOn": 1612969955000,
  "circularId": 29456,
  "submitter": "Alexander Kann at IAA-CSIC  <kann@iaa.es>",
  "email": "kann@iaa.es",
  "body": "A. Rossi (INAF-OAS), on behalf of the CIBO collaboration, and D. A. Kann \n(HETH/IAA-CSIC) report:\n\nWe observed the field of GRB210112A (Ambrosi et al., GCN #29289; Ursi et \nal., GCN #29293; Svinkin et al., GCN #29315) simultaneously in the r' \nand z' bands with the LBC imager mounted on the Large Binocular \nTelescope (LBT, Mt. Graham, AZ, USA). We obtained 20 min of imaging on \n2021-02-05, 24.3 days after the burst trigger. Observations were \nperformed under mediocre seeing conditions and reached a depth of r' ~ \n26 mag.\n\nAt the position of the afterglow (Ambrosi et al., GCN #29289), we \nclearly detect the host galaxy in both filters and we measure the \nfollowing AB magnitudes:\n\nr' = 23.96 +/- 0.15 mag,\nz' = 23.38 +/- 0.15 mag.\n\ncalibrated against SDSS field stars.\n\nTherefore, we confirm that the flattening observed by Kann et al. (GCN \n#29319) was due to the host component.\n\nHowever, we do not see the faint object detected by Kann et al. at RA, \nDec. = 14:36:01.453, +33:03:13.40 (J2000). We have investigated the CAHA \nand OSN (Kann et al., GCN 29296) images and found that the source \ndetected by Kann et al., GCN 29319, which should have been \"South\" of \nthe afterglow position, not \"East\", is the actual afterglow (with the \nfainter, northern extension possibly stemming from image distortion or a \nslight mismatch when co-adding frames), the offset stemming from a small \narcsecond-scale astrometry mismatch. For the afterglow position, we \nmeasure Ic = 23.52 �� 0.19 mag (AB), replacing the value given in GCN \n#29319. We estimate the underlying host to be Ic ~ 23.7 mag (AB) from \nthe LBT photometry.\n\nCorrelating the OSN image with the LBT image, we find an afterglow \nposition of RA, Dec. = 14:36:01.492 +33:03:14.945 (J2000), with errors \nof 0\".2 in each coordinate, calibrated against Gaia DR2, in good \nagreement with the UVOT position (Ambrosi et al., GCN #29289).\n\nIn the LBT image, we furthermore detect a second, fainter, but probably \nalso extended source just 2\" north-north-east of the host (at RA, Dec. \n=14:36:01.54 +33:03:18.7; J2000) with r' = 24.5 �� 0.2 mag. It is unclear \nif this likely galaxy is related to the host galaxy.\n\nWe acknowledge the excellent support from the LBTO and LBT-INAF staff, \nparticularly B. Rothberg and D. Paris, in obtaining these observations."
}