RXTE detection of Rapidly Varying Transient Swift J164449.3+573451
ATel #3251; C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC), E. A. Smith (Wyle IS & NASA/GSFC), T. S. Strohmayer (NASA/GSFC), J. H. Swank (NASA/GSFC)
on 30 Mar 2011; 20:43 UT
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)
Subjects: X-ray, Gamma Ray, AGN, Black Hole, Blazar, Gamma-Ray Burst, Neutron Star, Transient, Pulsar
RXTE observed of the X-ray source Swift J164449.3+573451 / GRB 110328A (GCN Circ. 11823, 11824, 11842; ATEL #3242, #3244, #3250) on 2011-03-30 at 04:55 UTC for an exposure of 1.8 ksec.
The PCA light curve is characterized by strong variations on a time scale of hundreds of seconds. Variations are a factor of ~2.5x peak to peak (50-125 mCrab 2-10 keV), with r.m.s. variability of 30%. A power spectrum shows red noise stochastic variability (power law with index f-2), although the mHz end of the spectrum is poorly characterized. If pulsations are present, then the period must be larger than the observation exposure, 1800 sec. We searched for rapid variability, but none was detected at the >1% level.
The spectrum is consistent with a power law, photon index -1.73, and neutral absorption fixed by Swift XRT (ATEL #3242). The average fluxes in the 2-10, 10-20 and 20-40 keV bands are 10.5, 6.1, 7.3 in units of
1 x 10-10 erg/s/cm2. This spectral shape is consistent with Swift BAT (GCN Circ 11842) and Swift XRT (ATEL #3242) shapes.
The properties measured by RXTE are comparable to those seen by other X-ray and gamma-ray observatories. If the source were a galactic black hole in the hard power law state, then we would typically expect to detect QPOs, which are not in fact detected. If the source were a galactic X-ray pulsar, we would typically expect to detect X-ray pulsations, were are not in fact detected. The source has also been classified as a potential SFXT (ATEL #3242). If the source were extragalactic, then the luminosity is large enough (>5 x 1048 erg/s) that beaming is required (GCN #11843).
While we cannot rule out either a galactic or extragalactic interpretations with the RXTE data, the source appears to be unique.
