Unusually Bright Single Pulses from the Binary Pulsar B1744–24A: A Case of Strong Lensing?

Abstract

Abstract We present a study of unusually bright single pulses (BSPs) from a millisecond pulsar in an ablating binary system, B1744−24A, based on several multiorbit observations with the Green Bank Telescope. These pulses come predominantly in time near eclipse ingress and egress, have intensities up to 40 times the average pulse intensity, and pulse widths similar to that of the average pulse profile. The average intensity, spectral index of radio emission, and the dispersion measure do not vary in connection with BSP outbursts. The average profile obtained from BSPs has the same shape as the average profile from all pulses. These properties make it difficult to explain BSPs via scintillation in the interstellar medium, as a separate emission mode, or as conventional giant pulses. BSPs from B1744−24A have similar properties to the strong pulses observed from the Black Widow binary pulsar B1957+10, which were recently attributed to strong lensing by the intrabinary material. We argue that the strong lensing likely occurs in B1744−24A as well. For this system, the sizes and locations of the lenses are not well constrained by simple 1D lensing models from Cordes et al. and Main et al. This partly stems from the poor knowledge of several important physical parameters of the system.