VizieR Online Data Catalog: LRIS sp. of SDSSJ143359.16+400636.0 nucleus (Brightman+, 2021)

In addition to the initial detection in the first XRT observation (ObsID 00032818012), Swift has observed and detected the transient in X-rays 27 times, all in photon counting mode. Previous to this, Swift observed the position of the source 17 times, 12 times in 2013 and 5 times in 2016 where the source was not detected in X-rays. In addition to the XRT data, Swift also observed the source with its UVOT instrument, which has six filters, UVW2 (central wavelength λ=1928Å), UVM2 (λ=2246Å), UVW1 (λ=2600Å), U (λ=3465Å), B (λ=4392Å), and V (λ=5468Å). While a UVOT source was clearly seen prior to the 2020 observations, likely emission from the host galaxy, a small increase in brightness measured by UVOT can be seen in the 2020 observations, though it is much weaker than seen in the X-rays. See Section 2.1.

In order to study the hard X-ray emission from the transient, we obtained Director's Discretionary Time observation on the Nuclear Spectroscopic Telescope Array (NuSTAR, ObsID 90601606002), which took place on 2020 February 13, 8 days after the X-ray transient was first detected by Swift.

On 2020 February 16 and 29, 11 and 24 days after the initial Swift detection, respectively, SDSS J143359.16+400636.0 was also serendipitously observed by Chandra (ObsIDs 23171 and 23172DR) for 10ks each exposure with ACIS-S at the aim point.

Khabibullin+ (2020ATel13494....1K) reported via The Astronomer's Telegram the detection by Spectrum-Roentgen-Gamma (SRG)/eROSITA of a very bright X-ray source, SRGet J143359.25+400638.5, centered on SDSSJ143359.16+400636.0 on 2019 December 27, 40 days prior to the detection of the transient with Swift/XRT. See Section 2.4.

As described in Section 2.3, the candidate optical transient ZTF19acymzwg was detected in the g, r, and i bands by ZTF on 2019 December 14, 53 days before the detection with Swift/XRT. Previous to this date, the field was observed on 2019 October 5 and the transient was not detected in any filter. Once we obtained the position of the transient, we produced ZTF light curves to produce difference-imaging photometry at the best-fit transient position across all ZTF images of the field taken between 2018 March 21 and 2020 May 11. We found no evidence for nuclear activity before the flare. See Section 3.

We obtained an optical spectrum of the host galaxy nucleus with Keck/LRIS on 2020 February 18, 13 days after the initial Swift detection. The data were acquired using a standard long-slit mode using a 1" slit on both the red and blue sides when the seeing was 101 in i band. See Section 4.

We carried out radio observations with the Karl G. Jansky Very Large Array (VLA) through Director's Discretionary Time (project code VLA/20A-579, PI: Mooley) on 2020 August 2, 180 days after the detection by Swift. Data were obtained at C band in the 3-bit mode of the WIDAR correlator to get a contiguous frequency coverage between 4 and 8GHz. We did not detect any radio source at the location of the transient. See Section 5.

(1 data file).