Phase shift during an X-ray burst in GRO J1744-28
ATel #5910; A. Sanna, F. Pintore, A. Riggio, L. Burderi (University of Cagliari), T. Di Salvo, A. D'Ai, R. Iaria, N. R. Robba (University of Palermo)
on 20 Feb 2014; 19:11 UT
Credential Certification: Alessandro Riggio (riggio@dsf.unica.it)
Subjects: X-ray, Binary, Transient, Pulsar
Referred to by ATel #: 5963
We report the detection of coherent pulsations during an X-ray burst of the accreting Neutron Star GRO J1744-28, observed during its ongoing outburst (ATel #5790, #5810, #5845, #5858, #5883).
We analyzed all the available Swift observations between February the 2nd and February the 18th 2014. In accordance with previous findings (Atel #5883), we detected 8 X-ray bursts within 5 Swift/XRT observations. The X-ray bursts duration is, on average, 25 seconds, with a mean counts of ~2000 counts.
Time of arrival (ToA) of the photons detected during the X-ray bursts were referred to the Solar system barycenter, using the source coordinates reported by Wijnands & Wang 2002, ApJ, 568, L93. ToAs were subsequently corrected for orbital delays using the orbital parameters of the source provided by Atel #5901.
We then epoch-folded the ToAs adopting spin frequency and time derivative of the spin frequency reported in Atel #5091. We found evidence of pulsations during one of the X-ray bursts (EPOCH 56701.45129 MJD). We also epoch-folded the ToAs right before this X-ray burst (~140 seconds of data). Both pulse profiles are shown in figure 1. Interestingly, the two pulsations are shifted in phase by 0.19(5) (1 sigma error). We note that, in all the other X-ray bursts the statistic was too low to allow a secure detection of the pulsations.
