SWIFT XRT Observations of the ULX M81 X-9
ATel #1505; S. B. Moore, J. M. Miller (University of Michigan)
on 2 May 2008; 18:44 UT
Credential Certification: Jon Miller (jonmm@umich.edu)
Subjects: X-ray, Binary, Black Hole
We report on the well-known ultra-luminous X-ray (ULX) source M81 X-9 using several
SWIFT XRT observations. These observations occurred on 2006 July 7, July 8, October
14, October 18, October 19, and November 22, and 2007 March 25. Using XSPEC v11 and
fitting the spectra with a power-law model in the 0.3-10.0 keV band (and freezing the
absorbing column density along the long of sight at 2.1 E+21 cm^-2), we obtained
power-law indices ranging from 1.6 +/- 0.2 to 1.9 +/- 0.1 (90 percent confidence
errors). The flux values ranged from 1.01 +/- 0.06 E+11 cgs to 1.71 +/- 0.04 E+11
cgs. Thus, while evidence for spectral variability is marginal, the evidence for
flux variability is significant. There is no significant relation between the flux
and the power-law indices. The calculated luminosity (assuming a distance of 3.4 Mpc)
ranged from 1.2 +/- 0.1 E +40 erg/s to 2.5 +/- 0.2 E+40 erg/s. These luminosity
values are consistent with prior observations of M81 X-9 (La Parola et al.
2001, Miller, Fabian, & Miller 2004), and demonstrate that even short observations
with Swift can provide useful long-term flux monitoring of ULXs.
