Optical study of LMXBs with high temporal resolution: Evidence for non-thermal flares from MXB 1735-44

BESKIN, G; NEIZVESTNY, S; PLOKHOTNICHENKO, V; ZHURAVKOV, A.; BENVENUTO, OMAR; FEINSTEIN, CARLOS; MÉNDEZ, MARIANO

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 1994 vol. 289 p. 141 - 147

0004-6361

We present a search for ultrafast optical variability among some low mass X-ray binaries (LMXBs) using the fast photometer Multichannel Analysis of Nanosecond Intensity Alterations (MANIA) complex attached to the 2.15 m telescope of CASLEO, Argentina. Two flares of approximately = 0.25 sec in duration were recorded from the MXB 1735-44 X-ray burster. Brightness of the object increased approximately = 15 - 30 times during these flares with very steep forward fronts (characteristic rising time being approximately = 50 - 60 msec), displaying a fine structure on timescales of approximately = 5 - 6 msec (confidence level greater than or = 95%). Brightness temperatures for different phases of the flares ranged from 5 107 K to 1010 K; this can only be explained by non-thermal processes, or by a highly unprobable coherent thermal mechanism. These results are also an evidence that, at least, in the case of MXB 1735-44, there should exist some departures from the standard model of accretion onto compact objects. On the other hand we have detected no stochastic variations on timescale from 10-7 to 10 sec for 4U1659-487, 4U1822-371, GX339-4, 4U1636-536 and 2S0921-630.