D. Malesani (DARK/NBI), J. A. Kennea, D. N. Burrows (PSU), J. R.
Cummings (GSFC/UMBC), C. B. Markwardt, N. Gehrels (GSFC), T. N. Ukwatta
(MSU), B. Sbarufatti (PSU), C. J. Mountford (Leicester), H. A. Krimm
(GSFC/USRA), M. H. Siegel, M. M. Chester, D. Grupe (PSU), report:
The Swift team has carried out further analysis of trigger 569022
(Malesani et al., GCN 15157; Kennea et al., ATel 5354).
The BAT emission is extremely soft, and using the full data set the
spectrum is best fit with a black body function with a temperature of
2.57+-0.22 keV (reduced chi^2 = 0.79, where the small value is due to
allowances for systematic errors). The best fit simple power law
(reduced chi^2 = 0.93) has a photon index of 5.87+-0.43.
The X-ray light curve shows an initial decay with very prominent dips
(by a factor of 10 in flux), and is observed to rise starting around 60
ks after the trigger. The time-averaged spectrum during the first orbit
is not well fit by an absorbed power law, but can be described with an
absorbed black-body model with kT = 1.50+-0.02 keV and N_H =
(0.67+-0.05)*10^22 cm^-2. UVOT detected no bright counterpart, which is
expected given the large Galactic extinction towards this sightline.
Given the above properties, unusual among cosmic GRBs, and the position
2.8 deg away from the Galactic centre, we conclude that the trigger is
not due to a GRB, but is a new Galactic transient that we name Swift
J1734.5-3027 (Kennea et al., ATel 5354).
Automatic BAT and XRT products are available at the following URLs:
This circular is an official product of the Swift team.