The Be/X-ray binary system A0535+262 underwent a giant outburst in May-June 2005 , followed by a dimmer outburst in August-September 2005 .
This increased intensity provided an opportunity to search for redshifted neutron-capture lines from the surface of the neutron star .
If discovered , such lines would constrain the neutron star equation of state , providing the motivation of this search .
The spectrometer ( SPI ) on board the INTEGRAL satellite observed the dimmer outburst and provided the data for this research .
We have not detected a line with enough significance , with the width-dependent upper limits on the broadened and redshifted neutron capture line in the range of ( 2 – 11 ) \times 10 ^ { -4 } photons cm ^ { -2 } s ^ { -1 } .
To our knowledge , these are the strongest upper limits on the redshifted 2.2 MeV emission from an accreting neutron star .
Our analysis of the transparency of the neutron star surface for 2.2 MeV photons shows that photons have a small but finite chance of leaving the atmosphere unscattered , which diminishes the possibility of detection .