Temperature measurement during thermonuclear X-ray bursts with BeppoSAX

•Temperature measurement of thermonuclear X-ray bursts using hardness ratio.•Observation with BeppoSAX show temperatures as high as 3 keV in different spectral states.•High temperatures indicate the possibility of deviation from a true blackbody.

We have carried out a study of temperature evolution during thermonuclear bursts in LMXBs using broad band data from two instruments onboard BeppoSAX, the MECS and the PDS. However, instead of applying the standard technique of time resolved spectroscopy, we have determined the temperature in small time intervals using the ratio of count rates in the two instruments assuming a blackbody nature of burst emission and different interstellar absorption for different sources. Data from a total of twelve observations of six sources were analyzed during which 22 bursts were detected. We have obtained temperatures as high as ∼3.0 keV, even when there is no evidence of photospheric radius expansion. These high temperatures were observed in the sources within different broadband spectral states (soft and hard).