AstroSat observation of the Be/X-ray binary Pulsar 3A 0726-260 (4U 0728-25)

Results on timing and spectral properties of the Be/X-ray binary pulsar 3A 0726-260 (4U 0728-25) are presented. The binary was observed on 2016 May 6-7 with the Large Area X-ray Proportional Counter (LAXPC) and Soft X-ray Telescope (SXT) instruments onboard the AstroSat satellite. During this observation, the source was in non-flaring persistent state at a flux level of ∼ 8.6 ± 0.3 ×10^-11 erg cm^-2 s^-1 in 0.4-20 keV. Strong X-ray pulsations with a period of 103.144±0.001 s are detected in 0.3-7 keV with the SXT and in 3-40 keV with the LAXPC. The pulse profile is energy dependent, and there is an indication that the pulse shape changes from a broad single pulse to a double pulse at higher energy. At energies above 20 keV, we report the first time detection of pulsation period 103.145±0.001 s and the double peaked pulse profile from the source. The energy spectrum of the source is derived from the combined analysis of the SXT and LAXPC spectral data in 0.4-20 keV. The best spectral fit is obtained by a power law model with a photon index (1.7±0.03) with high energy spectral cut-off at 12.9 ± 0.7 keV. A broad iron line at ∼ 6.3 keV is detected in the energy spectrum. We briefly discuss the implications of these results.