A Hydrogen Atmosphere Spectral Model Applied to the Neutron Star X7 in 47 Tuc

New article on ApJ:

Heinke, Craig O.; Rybicki, George B.; Narayan, Ramesh; Grindlay, Jonathan E.
“A Hydrogen Atmosphere Spectral Model Applied to the Neutron Star X7 in the Globular Cluster 47 Tucanae”

Current X-ray missions are providing high-quality X-ray spectra from neutron stars (NSs) in quiescent low-mass X-ray binaries (qLMXBs). This has motivated us to calculate new hydrogen atmosphere models, including opacity due to free-free absorption and Thomson scattering, thermal electron conduction, and self-irradiation by photons from the compact object. We have constructed a self-consistent grid of neutron star models covering a wide range of surface gravities, as well as effective temperatures, which we make available to the scientific community. We present multiepoch Chandra X-ray observations of the qLMXB X7 in the globular cluster 47 Tuc, which is remarkably nonvariable on timescales from minutes to years. Its high-quality X-ray spectrum is adequately fitted by our hydrogen atmosphere model without any hard power-law component or narrow spectral features. If a mass of 1.4 Msolar is assumed, our spectral fits require that its radius be in the range Rns=14.5+1.8-1.6 km (90% confidence), which is larger than that expected from currently preferred models of NS interiors. If its radius is assumed to be 10 km, then a mass of Mns=2.20+0.03-0.16 Msolar is required. Using models with the appropriate surface gravity for each value of the mass and radius becomes important for interpretation of the highest quality data.

ADS link

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s