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GCN Circular 20510

GRB 170121B: Swift-XRT and UVOT observations
2017-01-23T14:53:39Z (7 years ago)
Paolo D'Avanzo at INAF-OAB <>
B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), A.P. Beardmore (U.
Leicester), S.L. Gibson (U. Leicester), A. D'Ai (INAF-IASFPA), A.
Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), A. Cholden-Brown (PSU),
P.A. Evans (U. Leicester) and A.A. Breeveld (UCL-MSSL) report on behalf
of the Swift team:

Swift-XRT has performed follow-up observations of the optical transient
reported by Lipunov et al. (GCN Circ. 20502) as a possible candidate
afterglow of the Fermi/GBM-detected burst GRB 170121B (Hamburg et al.
GCN Circ. 20505), collecting 4.5 ks of Photon Counting (PC) mode data
between T0+124.0 ks and T0+147.4 ks. 

No X-ray sources have been detected at the position of the optical
transient reported by Lipunov et al. (GCN Circ. 20502). 

An uncatalogued X-ray source is detected within the XRT field of view
at the position RA, Dec 72.6361, -9.2424 which is equivalent to:
   RA(J2000)  = 04h 50m 32.66s
   Dec(J2000) = -09d 14' 32.5"
with an uncertainty of 2.7 arcseconds (radius, 90% containment). The
source has a 0.3-10 keV count rate of about 9e-3 ct/sec. We cannot
determine fading at this time.

The 3-sigma upper limit in the field ranges from ~2e-3 to ~3e-3 ct
s^-1, corresponding to a 0.3-10 keV observed flux of 6.5e-14 to 1.0e-13
erg cm^-2 s^-1 (assuming a typical GRB spectrum).

The results of the XRT-team automatic analysis of the XRT observations,
including a position specific upper limit calculator, are available at

The Swift/UVOT began settled observations 124 ks after the trigger
(Hamburg et al, GCN Circ. 20505). Summing up the early white data at
the position of the OT found by Lipunov et al. (GCN Circ. 20502) we do
not find any source to an upper limit of 22.2 mags in 3430s.
At the position of the new uncatalogued XRT source described above we
do see a source already listed in the USNO-B1.0 catalogue and it is not

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