Drastic Change in the Eclipse Cutoff Frequency for PSR J1544+4937 Observed with the GMRT

We report a very drastic change in the eclipse cut-off frequency for the black widow pulsar J1544+4937. Majority of such systems often exhibit relatively long duration (~ 15%) radio eclipses caused by ablated material from the companion stars. The eclipse observed in such systems are frequency dependent and are more pronounced at lower frequencies (< 1.5 MHz). The eclipse cutoff frequency has changed from 345 MHz to > 750 MHz. Such an intense change in the eclipse cutoff frequency is not observed and reported for any other spider MSPs before. This shows that PSR J1544+4937 is clearly undergoing some kind of transition, where the eclipse environment is dynamically evolving. Follow-up observations showed that the system is coming back to its normal state, where the eclipse cutoff frequency is < 550 MHz. This change in the eclipse cut-off frequency could depict changes of the magnetic field and drastic change in electron density in the eclipse region.