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ATEL # 1893; H. A. Krimm (CRESST/USRA/NASA/GSFC), J. A. Kennea (PSU), P. Schady (MSSL-UCL), P. A. Evans (Univ. Leicester)
on 7 Jan 2009; 21:12 UT
Password Certification: Hans A. Krimm (Hans.Krimm@nasa.gov)
Subjects: Ultra-Violet, X-ray, Binaries, Transients
We report on Swift observations of the newly discovered galactic transient Swift J1539.2-6227 (Krimm et al, ATel #1855). Observations were made with the Swift satellite between 2008-12-25 03:15 UT and 2008-12-26 22:25 UT for a total exposure of 7263 seconds.
The spectrum derived for the Swift/X-Ray Telescope (XRT) data, correcting for pile up, is well fit by a power-law model with a photon index of 2.15 ± 0.1, and a N_H of (4.49 ± 0.05) x 10^21 cm^-2. Flux values are F(0.3-10 keV; observed) = (2.500 ± 0.015) x 10^-9 erg cm^-2 s^-1 and Flux(0.3-10 keV; unabsorbed) = 4.8 x 10^-9 erg cm^-2 s^-1. The source remained at constant intensity during the observations.
In observations with the Swift UltraViolet/Optical Telescope (UVOT), a bright source was found in a 3906-s co-added uvw2 exposure at the location:
RA (J2000) = 15:39:11.963 (234.79985 degs)
Dec (J2000) = -62:28:02.30 (-62.46731 degs)
with a positional uncertainty of 0.5" (90% confidence). There are no known sources coincident with this position found in the USNO-B1, USNO-A2 or 2MASS catalogs. The derived magnitudes are:
Exposure (filter) Magnitude
3906 s (uvw2) 18.07 ± 0.03
3259 s (uvm2) 17.96 ± 0.04
At the time of these observations the source was detected in the Swift/Burst Alert Telescope (BAT) at a level of 0.013 ± 0.001 ct s-1 cm-2 (15-50 keV), or ~55 mcrab. The BAT spectrum is best fit by a power-law model with a photon index of 1.92 ± 0.16 and a flux (15-150 keV) = (1.05 ± 0.03) X 10^-9 erg cm^-2 s^-1. Since the time of the joint observations, the source has declined in intensity and on 2009-01-06, was at 0.006 ± 0.001 ct s^-1 cm^-2.
BAT Transient Monitor observations of Swift J1539.2-6227