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GCN Circular 27904

GRB 200522A: Further HST F125W Observations
2020-06-08T02:28:35Z (4 years ago)
Charles Kilpatrick at UC Santa Cruz <>
C. D. Kilpatrick (UCSC), J. Rastinejad, W. Fong (Northwestern), and E. Berger (Harvard) report on behalf of a larger collaboration:

"We report on further HST/WFC3 IR observations (PI: Berger; Program 15964) of the short GRB 200522A (Evans et al., GCN 27778). Subsequent to the previous F125W observations obtained 3.6 days post-burst (Fong et al., GCN 27826), we initiated a second epoch in the F125W filter starting on 2020 June 7.805 UT. A total of 4823-sec of exposure time was obtained (approximately 7 minutes shallower than the previous epoch), at a mid-time of ~16.4 days.

The previously-identified point-like Source C (Fong et al., GCN 27827) has an estimated m_f125W ~ 26.8 AB mag, fully consistent with our previous estimate. This indicates that this source has not faded and is unlikely to be related to the GRB.

To constrain the presence of any transient sources, we performed image subtraction between the two F125W epochs using the HOTPANTS software (Becker 2015). The difference image reveals low significance (<3 sigma) residuals, the brightest of which is located at RA = 00:22:43.62, Dec = -00:16:58.90 (J2000) with m_f125w = 28.1 AB mag.  This position is close to the LCO candidate (e.g., Strausbaugh et al., GCN 27792) but inconsistent with the VLA candidate (Fong et al., GCN 27786).

There are otherwise no obvious high-significance residuals consistent with the VLA or LCO candidates, or around the XRT position. We caution that the difference image is contaminated by the center of the bright galaxy, and analysis is ongoing. Firm conclusions will require a deep template observation.

We thank the HST staff for quickly implementing these observations."
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