Eclipses of the moon and the sun have always been popular celestial events, attracting astronomy and science enthusiasts of all ages, world over.
In a latest international research led from Pune using the upgraded Giant Metrewave Radio Telescope (uGMRT), a group of scientists has tried to understand how and why the low-frequency radio signals emerging from spider millisecond pulsars get eclipsed.
Researchers from TIFR – National Centre for Radio Astrophysics (NCRA) and Jordell Bank Centre for Astrophysics, University of Manchester, studied J1544+4937, a spider milli second pulsar system that was discovered in 2013 using the GMRT.
Unlike solid objects like the moon or the earth that cause the solar and lunar eclipse, respectively, there is no solid object involved in eclipsing the low frequency radio signals, said Devojyoti Kansabanik, lead author of the paper published in Astrophysical Journal.
He said, “It is the material in the medium and plasma which block the low frequency radio signals.”
Milli second pulsars flash radio signals at regular intervals, and hence are often compared to atomic clocks. These have an orbiting partner, often a star, and take less than 10 hours to complete one rotation. The distance between such pulsars and their respective partner stars is less than that which exists between the earth and moon. Due to this relative closeness, charged radiations emitted from the milli second pulsars often result in material from the companion star blowing away. These blown-off ejectiles then surround the low frequency radio emissions, staging an eclipse. In this study, the eclipse was found to last for anywhere between 10 and 13 minutes.
Even though researchers studying spider millisecond pulsars have known since the 1980s the eclipsing phenomenon of radio signals emerging from the millisecond pulsars, the exact reason was still a mystery. The speculations have been on possible refraction, scattering and a number of types of absorption of radio emissions from the pulsar by the materials ejected from the companion star.
“Absorption by the magnetised materials that ejected from the companion star was found to be causing the eclipse in case of J1544+4937. The absorption coefficient, which gives the exact amount of absorption, is frequency dependent. A coefficient value associated with the low frequency radio signals was large, signalling its eclipse phase. The coefficient value of high frequency radio signals was small, meaning it was getting eclipsed,” added Kansabanik, a fourth-year PhD student at NCRA.
Such detailed observations in low bandwidth would not have been possible without uGMRT, said the scientists.
“Due to the wide bandwidth offered by uGMRT, we could study the frequency-dependent eclipse with 20 times better accuracy than previous estimations. It also allowed us to study for the first time the cause of eclipsing,” said Bhaswati Bhattacharya, a senior scientist at NCRA.
The telescope’s sensitivity will further enable the team to apply this method while studying other compact binary systems and decipher eclipse mechanisms, said Jayanta Roy, another co-author and NCRA scientist.