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GCN Circular 25822

LIGO/Virgo S190814bv: Chandra X-ray non-detection of ASKAP J005547-270433 / AT2019osy
2019-09-23T17:43:42Z (5 years ago)
Amruta Jaodand at Caltech <>
Amruta Jaodand (Caltech), Sergio Campana (INAF/Brera), Murray Brightman
(Caltech), Paolo D'Avanzo (INAF/Brera), Marianne Heida (Caltech), Fiona
Harrison (Caltech), Giancarlo Ghirlanda (INAF/Brera), Mansi Kasliwal
(Caltech), Kristin Madsen (Caltech), Kunal Mooley (Caltech), Maria Grazia
Bernardini (INAF/Brera), Andrea Melandri (INAF/Brera), Om Sharan Salafia
(INAF/Brera), Ruben Salvaterra (INAF/IASF Milano)

We report on the Chandra X-ray follow-up of ASKAP J005547-270433 /
AT2019osy, a candidate radio counterpart to GW190814bv (GCN 25324, 25621)
identified by Stewart et. al (GCN 25487) located at RA + 00:55:47.40  (13.948deg),
DEC: -27:04:33.00 (-27.076deg). We have observed the field of AT2019osy ~ days 
post merger starting at 2019-09-22T21:33:50 UT with the Chandra X-ray telescope.

Earlier, optical follow-up reported a source with i=22.3 (Andreoni et al.
GCN 25488), spatially coincident with the radio source, and Palomar
200-inch spectroscopic observations (Perley et al. GCN 25494) indicated
that the flux could be arising from AGN variability. Follow-up VLA and ATCA
radio observations (Mooley et al. GCN 25539; Dobie et al. 25691) showed
that the radio flux did not continue increasing. Recent follow-up
observations carried out with ALMA reported a detection at 109 GHz,
consistent with the (RA 00:55:47.417, DEC -27:04:33.14) location reported
by ASKAP, VLA and ATCA (Bauer et al. GCN 25801). An almost simultaneous HST
observation provided evidence for a small elongated nucleus at the host
center, but not for a point source (Bauer et al. GCN 25801).

The Chandra observation failed to detect any X-ray source at the ASKAP
J005547-270433 / AT2019osy position. No sources in the close vicinity are
also apparent. A cross-match with the 2MASS archive shows a source should
have been present at the location of the radio candidate. We derive a 95\%
(0.3-8 keV) upper limit of 2.85e-4 counts/s. This converts to a 0.3-8 keV
unabsorbed flux upper (nH=1.8e20 cm-2) limit of 3.2e-15 erg/cm2/s, assuming
a power law spectrum with photon index 1.66 (motivated by radio
observations, Dobie et al. GCN 25691), corresponding to a 0.3-8 keV
unabsorbed luminosity of 4.2e40 erg/s.

The lack of detection of any X-ray activity at such a low level, indicates
that the emission of ASKAP J005547-270433 / AT 2019osy might not be due to
the nucleus of the host galaxy.

We thank Belinda Wilkes and the entire CXC staff for scheduling and
enabling these observations at a rapid pace.

[GCN OPS NOTE(24sep19): The extra header field was eliminated; the RA,DEC
values were added into the first paragraph; and the signiture/contact block
at the bottom of the CIrcualr was elimianted.]
[GCN OPS NOTE(25sep19): Per author's request, the 25961 reference in the
third paragraph was changed from 25961 to 25691.]
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