//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 26966 SUBJECT: ZTF Discovery of ZTF20aajnksq: a Rapidly Fading Luminous Transient in the GRB 200128A Localiziation Region DATE: 20/02/02 21:53:10 GMT FROM: Anna Ho at Caltech The Zwicky Transient Facility (ZTF; ATel #11266) reports the discovery of ZTF20aajnksq, a rapidly fading red transient located at 12:47:04.87 +45:12:02.3 (J2000) 191.770292 +45.200626 (J2000) and detected as part of the ZTF Uniform Depth Survey (Goldstein et al. in prep). The source was discovered on UT 2020-01-28T06:43:20.640 at r=19.6 mag, which was 0.74 days after the last non-detection. Follow-up photometry with the IO:O optical imager on the Liverpool Telescope (PI: D. Perley) and the Wafer-Scale Imager for Prime (WASP) on the 200-inch Hale telescope (PI: I. Andreoni) at Palomar Observatory established a rapid fade rate of 2.5 magnitudes in 1.25 days as well as red colors (g-r=+0.65, from the WASP observation). We obtained a target-of-opportunity (PI: M. M. Kasliwal) spectrum with the Low Resolution Imaging Spectrometer (LRIS) on the Keck I 10-m telescope, which showed features consistent with the Lyman break and Lyman alpha absorption at z=2.9. We obtained a target-of-opportunity observation with the Neil Gehrels Swift Observatory (Swift) and detected X-ray emission at 0.0039 ct/s. Assuming a neutral hydrogen column density n_H = 1.77E20/cm2 and a power-law spectrum with photon index 2, the unabsorbed flux is 1.5E-13 erg/cm^2/s, corresponding to a luminosity of 1.1E46 erg/s. We searched the Fermi/GBM catalog and identified a reported likely short GRB 24 degrees away: GRB 200128A (GCN #26909). ZTF20aajnksq is located along the 90% contour of the localization region. The trigger time of GRB 200128A is three hours before the first optical detection. We are grateful to the staff of Palomar and Keck for rapidly scheduling our observations, and to M. Heida (ESO Garching) and J. Rhoads (Goddard) for accommodating the interruption to their scheduled programs. Thank you to the Swift team for rapidly scheduling and executing our observations. ZTF is a project led by PI S. R. Kulkarni at Caltech (see ATEL #11266), and includes IPAC; WIS, Israel; OKC, Sweden; JSI/UMd, USA; UW,USA; DESY, Germany; NRC, Taiwan; UW Milwaukee, USA and LANL USA. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. Alert distribution service provided by DIRAC@UW. Alert filtering is being undertaken by the GROWTH marshal system, supported by NSF PIRE grant 1545949. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 26968 SUBJECT: ZTF20aajnksq: Gemini-North r-band photometry DATE: 20/02/03 02:54:07 GMT FROM: Leo Singer at GSFC ZTF20aajnksq: Gemini-North optical photometry Leo P. Singer (NASA/GSFC), Tomas Ahumada (UMD), Anna Y. Q. Ho (Caltech) report on behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: Starting at 2020-02-01T12:25:57 UTC, we imaged ZTF20aajnksq/AT2020blt (Ho et al., ATel #13429, GCN 26966) using the Gemini Multi-Object Spectrograph (GMOS) mounted on the Gemini North 8-meter telescope on Mauna Kea. We combined 8 r-band 200s exposures using DRAGONS, a Python-based data reduction platform provided by the Gemini Observatory. We detect a source at the location of the transient. The aperture photometry calibrated against Pan-STARRS DR1 magnitudes (Chambers et al., 2016) of the object is r = 25.2 +- 0.05 AB mag. We note that for the redshift (z = 2.9) and apparent magnitude (r = 19.6 AB mag) reported in GCN 26966, the absolute magnitude of the source (M_r = -27.4) would be significantly brighter than afterglows of short GRBs at one day: short GRBs are typically M_B = -17.34 +- 0.50 AB mag whereas long GRBs are typically M_B = -23.17 +- 0.21 AB mag (Kann et al., 2011). We therefore suggest three alternative interpretations: (a) GRB 200128A is not a typical short GRB, (b) ZTF20aajnksq is the afterglow of a different (long) GRB, or (c) ZTF20aajnksq is an orphan afterglow. We thank S. Stewart and the Gemini North staff for executing these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 26970 SUBJECT: ZTF20aajnksq: Occulted by Earth at the time of GRB 200128A DATE: 20/02/03 04:40:02 GMT FROM: Rachel Hamburg at UAH R. Hamburg (UAH) reports on behalf of the Fermi-GBM Team: The newly discovered transient ZTF20aajnksq (GCN 26966) was found within the 3-sigma localization contour of GRB 200128A (GCN 26909) approximately 3 hours after the GBM trigger time. However the reported position of ZTF20aajnksq: 12:47:04.87 +45:12:02.3 (J2000) 191.770292 +45.200626 (J2000) was occulted by the Earth for Fermi-GBM from approximately 25.3 minutes prior until 1.8 minutes after the GRB trigger time. The position was also occulted 18.0 minutes prior until 8.8 minutes after the ZTF20aajnksq detection time. Therefore, we consider it unlikely that GRB 200128A is associated with ZTF20aajnksq. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27039 SUBJECT: ZTF20aajnksq: Upper limits from Konus-Wind observations DATE: 20/02/12 13:04:21 GMT FROM: Anna Ridnaia at Ioffe Institute A. Ridnaia, S. Golenetskii, R.Aptekar, D. Frederiks, M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline, on behalf of the Konus-Wind team, report: Konus-Wind (KW) was observing the whole sky between the last non-detection and the first detection of ZTF20aajnksq (2020-01-28 06:43:20 UTC, hereafter T0; Anna Ho, GCN Circ. 26966). Two waiting-mode KW events were detected during ~18-hour (~0.74 days) interval before T0. The burst localizations are inconsistent with the ZTF20aajnksq. For the interval excluding the KW events, we estimate an upper limit (90% conf.) on the 20 - 1500 keV fluence to 6.1x10^-7 erg/cm^2 for a burst lasting less than 2.944 s and having a typical KW short GRB spectrum (an exponentially cut off power law with alpha =-0.5 and Ep=500 keV). For a typical long GRB spectrum (the Band function with alpha=-1, beta=-2.5, and Ep=300 keV), the corresponding limiting peak flux is 1.7x10^-7 erg/cm^2/s (20 - 1500 keV, 2.944 s scale). All the quoted values are preliminary.