New ULX in M101
ATel #271; K. D.Kuntz (GSFC & UMBC) and the M101 Megasecond Collaboration
on 17 Apr 2004; 01:12 UT
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)
Subjects: X-ray, Binary, Transient
A new ultraluminous X-ray source has been detected in M101 (NGC 5457)
during a recent 142 ks observation by the Chandra X-ray Observatory
on 14 March 2004 and 19 March 2004. The source is tentatively labeled
CXO M101K J140314.27+541806, although the astrometry is still somewhat
uncertain.
The source was listed in the catalogue of Pence et al (2001, ApJ 561, 189)
as source 51, where it was noted that the flux might be variable within
their 92 ks observation. Pence et al also identified this object with
H25 of Wang et al (1999, ApJ 523:121), which is only marginally resolved
from two other sources in that catalogue.
The spectrum during the new observation is tolerably fit with an
absorbed power law, with strong residuals in the 0.85-1.1 keV region,
suggestive of Ne or Fe line emission. The fit parameters are an
absorbing column of (1.3+/-0.09)e21 cm^-2, a power law index of
2.45+/-0.05 (1 sigma uncertainties), and an unabsorbed luminosity
of roughly 2e39 ergs s^{-1} in the 0.5-8.0 keV band. The Pence et al.
fits found an absorbing column of 8e21 cm^-2, an index of 2.08,
and a luminosity of 5e37 ergs s^{-1}. The lightcurve during the March
2004 observations shows no sign of non-statistical variation.
Before the current outburst, the object seems to have maintained
a relatively steady mean flux in the 0.5-8.0 keV band:
8.2e-15 ergs/cm^2/s (2000-03-26, Chandra obsid 934, marginally variable),
8.1e-15 ergs/cm^2/s (2000-10-29, Chandra obsid 2065),
2.0e-14 ergs/cm^2/s (2004-01-19, Chandra obsid 4731, strongly variable),
2.7e-13 ergs/cm^2/s (2004-03-14, the current observation).
This light curve may be extended using ROSAT data;
the mean 0.5-2.0 keV band flux measured by the HRI over the 1992-1996
period is 0.65e-14 ergs/cm^2/s (Wang et al), compared to the 0.36e-14
ergs/cm^2/s recorded by Pence et al in the same band.
