ZTF20aajnksq
GCN Circular 26968
Subject
ZTF20aajnksq: Gemini-North r-band photometry
Date
2020-02-03T02:54:07Z (5 years ago)
From
Leo Singer at GSFC <leo.p.singer@nasa.gov>
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.
GCN Circular 26970
Subject
ZTF20aajnksq: Occulted by Earth at the time of GRB 200128A
Date
2020-02-03T04:40:02Z (5 years ago)
From
Rachel Hamburg at UAH <rkh0007@uah.edu>
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.
GCN Circular 27039
Subject
ZTF20aajnksq: Upper limits from Konus-Wind observations
Date
2020-02-12T13:04:21Z (5 years ago)
From
Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>
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.