[vsnet-grb-info 19364] Swift XRT observations of GRB 170424A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21074
SUBJECT: Swift XRT observations of GRB 170424A 
DATE:    17/05/06 16:23:20 GMT
FROM:    Boris Sbarufatti at INAF-OAB/IASFPA  <boris.sbarufatti at brera.inaf.it>

B. Sbarufatti (INAF-OAB/PSU), P. A. Evans (U. Leicester) report on behalf of the Swift XRT team.

We report on Swift XRT observations of the field of the Fermi-LAT discovered GRB 170424A (N. Omodei et al. 2017, GCN 21032).
Swift performed an initial tiled observation of the LAT error circle (27 arcmin) using a 7-tile pattern (7-tile pattern 100% coverage radius: 24 arcmins, maximal coverage radius: 33 arcmins), 700 s of exposure/tile, on April 25th (P. A. Evans 2017, GCN 21034). 

Three uncatalogued sources were detected:

Source# RA             Dec          Rate              Exposure time 
2       22h 52m 53.04s -45d10m43.5s 1.5+/-0.5E-2 cps  684s
3       22h 53m 10.51s -45d29m11.5s 1.9+/-0.6E-2 cps  677s
5       22h 52m 09.64s -45d02m43.3s 1.5+/-0.7E-2 cps  684s

On May 3rd and 4th further observations were performed to check for fading of the sources.
Source 2 was still detected without showing any evidence of fading.
Sources 3 and 5 were no more detected, but the 3-sigma upper limits are consistent with the earlier detections, within errors.

Source# Rate              Exposure time 
2       1.1+/-0.2E-2 cps  2.8 ks
3       < 1.4E-2  cps     3.1 ks      
5       < 7.1E-3  cps     3.1 ks

We conclude that Source 2 is not the GRB afterglow, while the nature of Sources 3 and 5 remains uncertain.

All the quoted errors are at the 90% confidence level.

This circular is an official product of the Swift-XRT team.