TITLE: GCN CIRCULAR NUMBER: 30995 SUBJECT: GRB 211024B: CAHA 2.2m Detection; ultra-long DATE: 21/10/25 15:45:51 GMT FROM: Alexander Kann at IAA-CSIC <kann@iaa.es> Return-Path: <kann@iaa.es> Received: from smtp.iaa.es (smtp.iaa.csic.es [193.146.145.11]) by capella2.gsfc.nasa.gov (8.15.2/8.15.2) with ESMTPS id 19PFjnvS028149 (version=TLSv1.2 cipher=AES128-GCM-SHA256 bits=128 verify=NO) for <gcncirc@capella.gsfc.nasa.gov>; Mon, 25 Oct 2021 11:45:51 -0400 DKIM-Filter: OpenDKIM Filter v2.11.0 capella2.gsfc.nasa.gov 19PFjnvS028149 Received: from webmail.iaa.csic.es (webmail.iaa.csic.es [193.146.145.15]) by smtp.iaa.es (Postfix) with ESMTPSA id 7385432909; Mon, 25 Oct 2021 17:45:48 +0200 (CEST) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Mon, 25 Oct 2021 17:45:48 +0200 From: David Alexander Kann <kann@iaa.es> To: gcncirc@capella.gsfc.nasa.gov, scott@milkyway.gsfc.nasa.gov Subject: GRB 211024B: CAHA 2.2m Detection; ultra-long =?UTF-8?Q?GRB=3F?= Message-ID: <279ca387cd388a654a4db43b3ea668ce@iaa.es> X-Sender: kann@iaa.es User-Agent: Roundcube Webmail/1.0.9 D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH, DARK/NBI), C. C. Thoene, M. Blazek, J. F. Agui Fernandez (all HETH/IAA-CSIC), A. Guijarro, and P. Martin-Fernandez (both CAHA) report: We observed the optical afterglow of the very long Swift GRB 211024B (Gropp et al., GCN #30980; Zhu et al., GCN #30984) with CAFOS mounted on the 2.2m Telescope at Calar Alto, Almeria, Spain. We obtained 30 x 90 s in the SDSS i' band under mediocre conditions. At the position of the GRB afterglow discovered by Nanshan/NEXT (Zhu et al., GCN #30984), we detect a source. Against one Pan-STARRS comparison star, we measure: i' = 20.27 +\- 0.05 mag (AB) at 0.2485 d after the GRB. We note the XRT light curve at time of writing (https://www.swift.ac.uk/xrt_curves/01081073/ Evans et al., GCN #30994) shows a certain resemblance to that of the ultra-long GRB 111209A, being relatively flat until 10 ks before dropping off very steeply. The lack of early data prevents further conclusions for now. Further follow-up is warranted.