RXTE Observes MAXI J0556-332
ATel #3106; T. E. Strohmayer (NASA/GSFC), E. A. Smith (GSFC/Wyle IS)
on 13 Jan 2011; 19:56 UT
Credential Certification: Tod Strohmayer (tod.strohmayer@nasa.gov)
Subjects: X-ray, Transient
RXTE observed the new transient MAXI J0556-332 for about 3 ksec
beginning on January 13 at 12:29:42.00 (UTC). The spectrum is soft,
and can be modeled as a sum of black body and power-law components,
both modified by absorption. The 2 - 10 keV flux is 1.77 x 10-9
erg/cm^2/s (approximately 90 mCrab). The best-fit black body has kT =
1.1 +- 0.02 keV, but contributes only about 20% of the flux. The
power-law is steep, with an index of 5.5 +- 0.2, and makes up the
majority (80%) of the total flux. The inferred absorption column is
also large, at 7.8 +- 0.6 x 10^22 cm^-2. A power spectral analysis
shows only modest broad-band variability, and no evidence for significant QPOs.
The flux varies in the last third of the observation in a manner that
is perhaps suggestive of a dipping or absorption phenomena. The soft
spectrum and relatively low rms variability are suggestive of thermal
state black holes, but the relatively small fraction of black body to
total flux is then unusual. Alternatively, the soft spectrum and high
inferred absorption might be indicative of emission from an optically
thick outflow. Further RXTE observations are planned. We encourage
additional observations in other wave-bands.
