//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29508 SUBJECT: ZTF21aakruew/AT2021cwd: ZTF and LT discovery of a hostless, red, and rapidly fading optical transient DATE: 21/02/14 00:31:34 GMT FROM: Anna Ho at UC Berkeley Yuhan Yao (Caltech), Daniel Perley (LJMU), Anna Ho (UCB) on behalf of the Zwicky Transient Facility (ZTF) collaboration: We report the discovery two nights ago of the fast optical transient ZTF21aakruew/AT2021cwd in Zwicky Transient Facility (ZTF, Bellm et al. 2019, Graham et al. 2019) data at coordinates (J2000): RA = 10:24:42.16 (156.17566 deg) Dec = +11:36:40.98 (+11.61138 deg) ZTF21aakruew was first detected at g=19.64+/-0.10 mag in an image obtained at 2021-02-12 08:52.4 UT as part of the 2-day cadence public survey, and passed a filter designed to find fast transients (Ho et al. 2020, ApJ, 905, 2). The most recent upper limit was one night prior: r > 20.93 mag on 2021-02-11 07:59.6 UT in an image obtained for reference construction. Liverpool Telescope (LT) follow-up photometry showed that the source faded by ~2.1 mag in r-band in the next 0.9 days. The transient was most recently detected in an LT image on 2021-02-13 22:49 UT at r = 22.42 +/- 0.21 mag. The color appears to be red, with g-r~0.9 on 2021-02-13 and low extinction along the line of sight (E(B-V)=0.04 mag; Planck Collaboration et al., 2015). There do not appear to be any reported GRBs consistent with the position of ZTF21aakruew during the interval between the last non-detection and the first detection. No counterpart is visible in deep Legacy Survey pre-imaging (>24 mag; Dey et al. 2019, ApJ, 157, 5). We encourage spectroscopic classification and multi-wavelength follow-up of ZTF21aakruew. ZTF is supported by the National Science Foundation under Grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, and IN2P3, France. Operations are conducted by COO, IPAC, and UW. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert database searches are performed using Kowalski (Duev et al. 2019). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29511 SUBJECT: IPN triangulation of GRB 210212B (consistent with ZTF21aakruew/AT2021cwd) DATE: 21/02/15 18:35:45 GMT FROM: Dmitry Svinkin at Ioffe Institute D. Svinkin, S. Golenetskii, D. Frederiks, A. Ridnaia, A. Lysenko, and T. Cline on behalf of the Konus-Wind team, K. Hurley, on behalf of the IPN, A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team, and S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, and A. Tohuvavohu on behalf of the Swift-BAT team, report: The long-duration GRB 210212B has been detected by Konus-Wind, in the waiting mode, INTEGRAL (SPI-ACS), and Swift (BAT), so far, at about 9477 s UT (02:37:57). The burst was likely outside the coded field of view of the BAT. We have triangulated it to a preliminary, error box whose coordinates are: --------------------------------- RA(2000), deg Dec(2000), deg --------------------------------- Corners: 159.26 +24.95 100.54 +38.07 96.30 +19.08 163.83 +2.39 --------------------------------- This box may be improved. The optical transient ZTF21aakruew/AT2021cwd (Yao et al., GCN Circ. 29508) is inside the box, lending support to the association of the transient and the burst. A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB210212_T09477/IPN/ The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29514 SUBJECT: Konus-Wind detection of GRB 210212B / ZTF21aakruew DATE: 21/02/16 16:15:34 GMT FROM: Dmitry Svinkin at Ioffe Institute D. Svinkin, S. Golenetskii, D. Frederiks, M. Ulanov, A. Tsvetkova, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 210212B (ZTF OT detection: Yao et al., GCN Circ. 29508; IPN triangulation: Svinkin et al., GCN Circ. 29511) was detected by Konus-Wind (KW) in the waiting mode. The burst light curve shows a single emission episode which starts at about T0=9479 s UT (02:37:59) and has the total duration of ~48 s. The K-W light curve of this burst is available at http://www.ioffe.ru/LEA/GRBs/GRB210212_T09477/ As observed by Konus-Wind, the burst had a fluence of 8.7(-1.1,+1.7)x10^-6 erg/cm2 and a 2.944-s peak flux, measured from ~T0, of 6.7(-1.6,+4.8)x10^-7 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The K-W 3-channel time-integrated spectrum (from T0 to T0+48 s) is well described by a cutoff power-law model with alpha = -1.24(-0.23,+0.33) and Ep = 208(-46,+84) keV. All the quoted errors are estimated at the 1 sigma confidence level. All the presented results are preliminary. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29528 SUBJECT: Subject: ZTF21aakruew/AT2021cwd: GROND observations DATE: 21/02/18 12:18:01 GMT FROM: Ana Nicuesa at TLS Tautenburg A. Nicuesa Guelbenzu and S. Klose (both TLS Tautenburg) report: We observed the field of the optical transient ZTF21aakruew/AT2021cwd (Yao et al., GCN 29508) that was located inside the error box of GRB 210212B (Svinkin et al., GCN 29511) with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG telescope at the ESO La Silla Observatory (Chile). Observations were performed at 5:00 UT (midtime) on February 15, 2021, about 3.1 days after the GRB 210212B trigger. They were executed at an average seeing of 1.15 arcsec and at an average airmass of 1.3. The optical transient is detected in the optical but not in the NIR bands. Based on a 33 min exposure in g'r'i'z' and 30 min in JHK, and we measure the following preliminary AB magnitudes and upper limits (3 sigma): g' = 24.16 +/- 0.14, r' = 23.63 +/- 0.12, i' = 23.41 +/- 0.21, z' > 23.3, J > 21.7, H > 21.1, K > 18.1, calibrated against SDSS and 2MASS field stars. The observed r'-band magnitude is formally consistent with the observations reported by Pozanenko et al. (GCN 29512). After correction for Galactic extinction (E(B-V)=0.04 mag; Ho et al., GCN 29508), the data are in agreement with an SED that follows a power law. We consider this as evidence that the transient was indeed afterglow light, confirming its suggested association with GRB 210212B (Svinkin et al., GCN 29511; Svinkin et al., GCN 29514). We thank R. Lechaume (PUC) for performing the observations.