Skip to main content
New Swift-BAT/GUANO and IceCube Notice Types Available! See news and announcements

GCN Circular 27826

Subject
GRB 200522A: Hubble Space Telescope Near-IR F160W Observations
Date
2020-05-26T14:43:47Z (4 years ago)
From
Wen-fai Fong at Northwestern U <wfong@northwestern.edu>
W. Fong (Northwestern), E. Berger (Harvard), J. Rastinejad (Northwestern) and C. D. Kilpatrick (UCSC) report on behalf of a larger collaboration:

"We initiated Hubble Space Telescope (HST) observations of the field of GRB 200522A (Evans et al., GCN 27778; Beardmore et al., GCN 27780) under Program 15964 (PI: Berger). We obtained WFC3/IR imaging in the F160W band, at a mid-time on 2020 May 26.077 UT (3.6 days post-burst). A total of 5223-sec of exposure time was obtained.

Coincident with the XRT position (90% confidence), we detect two clearly extended sources, Sources A and B. We perform absolute astrometry with SDSS DR12 and use WFC3 tabulated zeropoints to determine the following:

Source A:
RA(J2000) = 00:22:43.72
Dec(J2000) = -00:16:57.46
m(F160W) = 20.7 AB mag

Source B:
RA(J2000) = 00:22:43.82
Dec(J2000) = -00:16:59.54
m(F160W) = 23.7 AB mag.

Source A is the catalogued SDSS galaxy (Fong et al., GCN 27786) and exhibits a disturbed morphology, while Source B is considerably fainter. The angular offsets from the XRT positional center are ~2.0" and ~2.1", and the light of both galaxies are ~50% encompassed by the XRT position (90% confidence). Using NIR number counts, we estimate Pchance ~ 0.01 and 0.11 for Sources A and B, respectively.

We do not detect any additional sources, point-like or extended, within the XRT position or at the position of the additional LCO optical source (Strausbaugh et al., GCN 27794) to a 3-sigma limiting magnitude of m(F160W)>27.2 mag.

Assuming an optical decline rate of F~t^-1 from the time of the LCO faint source detection (R~22.57; Strausbaugh et al., GCNs 27792, 27794) to 3.6 days, and typical afterglow colors, the expected afterglow magnitude is m(F160W)~23.6 mag, which is >3 mag brighter than the HST limit. If we assume that a jet break occurred at t~1 day, this still results in expected afterglow magnitudes of ~25.5 mag, >1 mag brighter than the HST limit. We thus conclude that either the LCO source is not real, or that the afterglow exhibited a very steep decline of t^-3.5 or steeper beyond ~1 day.

At the redshift of the putative host galaxy of z~0.4 (Fong et al., GCN 27786), F160W roughly corresponds to rest-frame J-band. Scaling the J-band kilonova light curve of GW170817 (Villar et al. 2017: ApJL, 851, L21) to z~0.4, we find that the HST limit is slightly deeper than the kilonova of GW170817 at the same time.

The results of WFC3/F125W observations, which have been taken but are not yet available, will be discussed in an upcoming circular. We thank the HST staff for quickly implementing these observations."
Looking for U.S. government information and services? Visit USA.gov