dc.contributor.author |
Lin, Dacheng |
|
dc.contributor.author |
Irwin, Jimmy A. |
|
dc.contributor.author |
Webb, Natalie A. |
|
dc.contributor.author |
Didier, Barret |
|
dc.contributor.author |
Remillard, Ronald A. |
|
dc.date.accessioned |
2018-09-12T19:38:48Z |
|
dc.date.available |
2018-09-12T19:38:48Z |
|
dc.date.issued |
2013-12-20 |
|
dc.identifier.citation |
Lin, D., Irwin, J., Webb, N., Barret, D., Remillard, R. (2013): Discovery of a Highly
Variable Dipping Ultraluminous X-Ray Source in M94. The Astrophysical Journal,
779(2). |
en_US |
dc.identifier.uri |
http://ir.ua.edu/handle/123456789/3841 |
|
dc.description.abstract |
We report the discovery of a new ultraluminous X-ray source (ULX) 2XMM J125048.6+410743 within the spiral
galaxy M94. The source has been observed by ROSAT, Chandra, and XMM-Newton on several occasions, exhibiting
as a highly variable persistent source or a recurrent transient with a flux variation factor of 100, a high duty cycle (at
least ∼70%), and a peak luminosity of LX ∼ 2 × 1039 erg s−1 (0.2–10 keV, absorbed). In the brightest observation,
the source is similar to typical low-luminosity ULXs, with the spectrum showing a high-energy cutoff but harder
than that from a standard accretion disk. There are also sporadical short dips, accompanied by spectral softening. In
a fainter observation with LX ∼ 3.6×1038 erg s−1, the source appears softer and is probably in the thermal state seen
in Galactic black hole X-ray binaries (BHBs). In an even fainter observation (LX ∼ 9×1037 erg s−1), the spectrum is
harder again, and the source might be in the steep-power-law state or the hard state of BHBs. In this observation, the
light curve might exhibit ∼7 hr (quasi-)periodic large modulations over two cycles. The source also has a possible
point-like optical counterpart from Hubble Space Telescope images. In terms of the colors and the luminosity,
the counterpart is probably a G8 supergiant or a compact red globular cluster containing ∼2 × 105 K dwarfs,
with some possible weak UV excess that might be ascribed to accretion activity. Thus, our source is a candidate
stellar-mass BHB with a supergiant companion or with a dwarf companion residing in a globular cluster. Our study
supports that some low-luminosity ULXs are supercritically accreting stellar-mass BHBs. |
en_US |
dc.format.mimetype |
application/pdf |
en_US |
dc.subject |
accretion, accretion disks |
en_US |
dc.subject |
black hole physics |
en_US |
dc.subject |
X-rays: binaries |
en_US |
dc.subject |
X-rays: individual: 2XMM J125048.6+410743 |
en_US |
dc.title |
Discovery of a Highly Variable Dipping Ultraluminous X-Ray Source in M94 |
en_US |
dc.type |
text |
en_US |