Burst-induced coronal cooling in GS 1826-24

The X-ray burster GS 1826-24 remained persistently in the hard state and presented regular bursting properties over the period 2003-2008. Given the stable properties of the system, we stacked the spectra of the X-ray bursts detected during that period by INTEGRAL (JEM-X and ISGRI) and XMM-Newton (RGS) to study the effect of the burst photons on the properties of the corona. The extended energy range provided by these instruments allows the simultaneous observation of the burst and persistent emission spectra. We detect an overall change in the shape of the persistent emission spectrum in response to the burst photon shower, consistent with a burst-induced cooling of the corona. Additionally, we observe an excess in soft X-rays that can be described by fitting the burst emission with an atmosphere model, instead of a simple blackbody model. Traditionally, the persistent emission was assumed to be invariant during X-ray bursts, and more recently to change only in normalization but not in spectral shape. Our results may trigger the revision of existing neutron star mass-radius constraints, as the derived values rely on the assumption that the persistent emission does not change during X-ray bursts.