GCN Circular 25801
Subject
LIGO/Virgo S190814bv: HST and ALMA observations of the host galaxy of ASKAP J005547-270433 / AT 2019osy
Date
2019-09-21T18:03:22Z (5 years ago)
From
Daniele B Malesani at DTU Space <malesani@space.dtu.dk>
F. E. Bauer (PUC), A. S. Fruchter (STScI), J. Gonzalez Lopez (UDP), J.
Hjorth (DARK/NBI), T. Kangas (STScI), S. Kim (PUC), A. J. Levan (Radboud
Univ.), D. B. Malesani (DTU Space), M. J. Michalowski (AMU), B.
Milvang-Jensen (DAWN/NBI), R. Paladino (INAF/IRA), S. Schulze (WIS), A.
de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), report on behalf of the
ENGRAVE collaboration:
We observed the host galaxy of the radio transient ASKAP 005547-270433 /
AT 2019osy (Stewart et al., GCN 25487) on 2019 Sep 17.9 UT using the
F140W (1.4 micron) broadband filter of the Wide-Field Camera 3 on the
Hubble Space Telescope and at 109 and 242 GHz in the configuration C43-7
(beam size of 0.21'' at 100 GHz) with ALMA on 2019 Sep 5.2 UT.
A point source is detected by ALMA at 109 GHz consistent with the
location reported by ASKAP (Stewart et al., GCN 25496), for which we
measure these refined coordinates (~0.05" error):
RA(J2000) = 00:55:47.417
Dec(J2000) = -27:04:33.14
We aligned the HST data to the Gaia catalog (to be consistent with the
ALMA astrometry) using four stars in common inside the HST field of
view. While we resolve a small elongated nucleus at the center of the
host, we see no clear evidence of a point source superposed on the
apparently normal structure of an edge-on spiral. Nonetheless, the
position of the ALMA source aligns with the peak of the light in the
nucleus to within its positional error of ~0.05". This result agrees
with the finding of Mooley et al. (GCN 25539), who reported an alignment
between the optical centroid of the host obtained from ground-based
imaging and a VLA position at the 0.1" level.
While the galaxy nucleus is not detected by ALMA at 242 GHz, a separate
source is marginally detected approximately 1.5" away (not visible at
109 GHz), at a position still overlaying the stellar extent of the host
galaxy and consistent with the ASKAP position of AT 2019osy (Stewart et
al., GCNs 25487, 25496). The lack of detections by both ALMA at 109 GHz
and by the VLA at 1-10 GHz (on Aug 28; Mooley et al., GCN 25539) makes
it unlikely to be associated with AT 2019osy. It could be a noise peak,
an unrelated background source, or a star-forming region inside the galaxy.
Cutouts from the HST image, both wide-field and zoomed-in, can be seen
at http://www.engrave-eso.org/AT2019osy_host_images .
This circular is based on data collected under ALMA program
2018.1.01652.T, and on HST GO program #15664. We thank the staffs of
STScI (in particular Alison Vick) and of the ALMA observatory for their
assistance with these time-constrained observations. For further
information on ENGRAVE, see http://www.engrave-eso.org/.