Mysterious white dwarf pulsar discovered

An exotic binary star system 380 light-years away has been identified as an elusive white dwarf pulsar – the first of its kind ever to be discovered in the universe – thanks to research by the University of Warwick.

Professors Tom Marsh and Boris Gänsicke of the University of Warwick’s Astrophysics Group, with Dr David Buckley from the South African Astronomical Observatory, have identified the star AR Scorpii (AR Sco) as the first white dwarf version of a pulsar – objects found in the 1960s and associated with very different objects called neutron stars.

More…

an earlier article is dated from 01.02.08

White Dwarf Pulses Like a Pulsar
https://www.nasa.gov/centers/goddard/news/topstory/2007/whitedwarf_pulsar.html

First Article refers to AR Scorpii (AR Sco) as the first white dwarf version of a pulsar Submitted on 9 Dec 2016 https://arxiv.org/abs/1612.03185

Second article refers to AE Aquarii discovered with the Suzaku X-ray astronomy satellite in October 2005 and October 2006. https://www.nasa.gov/centers/goddard/news/topstory/2007/whitedwarf_pulsar.html

Tau.Neutrino said:

Mysterious white dwarf pulsar discovered

An exotic binary star system 380 light-years away has been identified as an elusive white dwarf pulsar – the first of its kind ever to be discovered in the universe – thanks to research by the University of Warwick.

Professors Tom Marsh and Boris Gänsicke of the University of Warwick’s Astrophysics Group, with Dr David Buckley from the South African Astronomical Observatory, have identified the star AR Scorpii (AR Sco) as the first white dwarf version of a pulsar – objects found in the 1960s and associated with very different objects called neutron stars.

an earlier article is dated from 01.02.08

White Dwarf Pulses Like a Pulsar
https://www.nasa.gov/centers/goddard/news/topstory/2007/whitedwarf_pulsar.html

First Article refers to AR Scorpii (AR Sco) as the first white dwarf version of a pulsar Submitted on 9 Dec 2016 https://arxiv.org/abs/1612.03185

Second article refers to AE Aquarii discovered with the Suzaku X-ray astronomy satellite in October 2005 and October 2006. https://www.nasa.gov/centers/goddard/news/topstory/2007/whitedwarf_pulsar.htm

Um, what!

Clearly they’re not talking about either white dwarf + neutron star binary or about a standard polsating white dwarf. So what are the talking about?

Wikipedia has this on AE Aquarii, (not to be confused with the famous EZ Aquarii).

AE Aquarii is a cataclysmic variable binary star of the DQ Herculis type. The AE Aquarii system consisting of an ordinary star in a close orbit around a magnetic white dwarf; the pair orbit each other with a period of 9.88 hours. The white dwarf primary has 63% of the Sun’s mass but a radius of only about 1% of the Sun. As of 2009, it has the shortest known spin period of any white dwarf, completing a full revolution every 33.08 seconds.

The X-ray luminosity is likely being caused by the accretion of mass onto the white dwarf,

So, what’s new?

There have been at least nine technical articles in the years 2014 to 2016 searching for hard X rays and gamma rays from ae aquarii. The conclusion, all papers agree that the spacecraft NuSTAR, Suzaku and Fermi can neither confirm nor deny the existence of hard X rays or gamma rays from this white dwarf.

In other words there may or may not be pulsar-like radiation from this star.

AR Scorpii, on the other hand, definitely gets referred to in the literature as a “pulsar white dwarf”. The pulsations are relatively weak, the X-ray excess above thermal radiation is also fairly weak. That said, AR Scorpii could definitely count as the first white dwarf to be confirmed as a pulsar.

Oh oh oh oh oh. I see now. The main pulsations in brightness are actually of the wrong period, of the orbital period rather than the rotational period. It was only when a high speed camera was used was it possible to separate out the pulsations due to the orbital period from those due to the rotational period. Pulsations at the rotational period were spotted using four different telescopes, including Hubble and the VLT. Fourier transforms of the rapid pulsations show two high frequency components, at 8.5 and 17 mHz. That gives a fundamental frequency corresponding to a period close to 118 seconds = 1.97 min.

eg. A radio pulsing white dwarf binary star

“The star, AR Scorpii (henceforth AR Sco), was classified in the early 1970s as a δ-Scuti star, a common variety of periodic variable star. Our observations reveal instead a 3.56 hr period close binary, pulsing in brightness on a period of 1.97 min. The pulses are so intense that AR Sco’s optical flux can increase by a factor of four within 30 s, and they are detectable at radio frequencies, the first such detection for any white dwarf system.”