Recently AstroSat, India's multi-wavelength space telescope, had measured the X-ray polarisation of the Crab pulsar (star) in the Taurus constellation. The telescope measured the variations of polarisation as the magnetised object (pulsar) spins 30 times per second. Taurus is the second astrological sign in the present zodiac. It spans the 30-60th degree of the zodiac.
Astrosat is India's first dedicated multi-wavelength space observatory. It was launched on a PSLV-XL in 2015. Astrosat is a proposal-driven general purpose observatory, with main scientific focus on:
- Simultaneous multi-wavelength monitoring of intensity variations in a broad range of cosmic sources
- Monitoring the X-ray sky for new transients
- Sky surveys in the hard X-ray and UV bands
- Broadband spectroscopic studies of X-ray binaries, AGN, SNRs, clusters of galaxies, and stellar coronae
- Studies of periodic and non-periodic variability of X-ray sources
Astrosat performs multi-wavelength observations covering spectral bands from radio, optical, IR, UV, and X-ray wavelengths. The observatory will also carry out:
- Low- to moderate-resolution spectroscopy over a wide energy band with the primary emphasis on studies of X-ray-emitting objects
- Timing studies of periodic and aperiodic phenomena in X-ray binaries
- Studies of pulsations in X-ray pulsars
- Quasi-periodic oscillations, flickering, flaring, and other variations in X-ray binaries
- Short- and long-term intensity variations in active galactic nuclei
- Time-lag studies in low/hard X-rays and UV/optical radiation
- Detection and study of X-ray transients.
A pulsar is a highly magnetized, rotating neutron star or white dwarf, that emits a beam of electromagnetic radiation. This radiation can be observed only when the beam of emission is pointing toward Earth and is responsible for the pulsed appearance of emission. Neutron stars are very dense, and have short, regular rotational periods. This produces a very precise interval between pulses that range from milliseconds to seconds for an individual pulsar. Pulsars are believed to be one of the candidates of the observed ultra-high-energy cosmic rays (see also Centrifugal mechanism of acceleration).
A neutron star is the collapsed core of a large star which before collapse had a total of between 10 and 29 solar masses. Neutron stars are the smallest and densest stars known to exist. Though neutron stars typically have a radius on the order of 10 kilometres (6.2 mi), they can have masses of about twice that of the Sun. They result from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past the white dwarf star density to that of atomic nuclei. Once formed, they no longer actively generate heat, and cool over time; however, they may still evolve further through collision or accretion. Most of the neutron stars are composed almost entirely of neutrons (subatomic particles with no net electrical charge and with slightly larger mass than protons); the electrons and protons present in normal matter combine to produce neutrons at the conditions in a neutron star.