The phase of the radio and X-ray pulses of PSR B1937+21

We present some results of an RXTE observation on PSR B1937+21, the fastest known millisecond pulsar (P≃1.56 ms). The pulse profile, detected up to ∼20 keV, shows a double peak, with the main component much stronger than the other. The peak phase separation is 0.526±0.002 and the pulsed spectrum over the energy range 2-25 keV is well described by a power law with a photon index equal to 1.14±0.07. We find that the X-ray pulses are closely aligned in phase with the giant pulses observed in the radio band. This result suggest that giant radio pulses and X-ray pulses originate in the same region of the magnetosphere due to a high and fluctuating electron density that occasionally emits coherently in the radio band. The X-ray events, however, do not show any clustering in time indicating that no X-ray flares are produced. © 2004 Elsevier B.V. All rights reserved.