Talk detail

Participant	Mukhopadhyay, Banibrata
Institution	Indian Institute of Science - C. V. Raman Avenue - Bangalore - Karnataka - India

Session	WD2	Accepted		Order	Time
Talk	Oral abstract	Title	Possible formation of lowly luminous highly magnetized white dwarfs by accretion leading to SGRs/AXPs
Coauthors
Abstract	We sketch a possible evolutionary scenario by which a highly magnetized super-Chandrasekhar white dwarf could be formed by accretion on to a commonly observed magnetized white dwarf. This is an exploratory study, when the physics in CVs is very rich and complex. Based on this, we also explore the possibility that the white dwarf pulsar AR Sco acquired its high spin and magnetic field due to repeated episodes of accretion and spin-down. We show that strong magnetic field dramatically decreases the luminosity of these highly magnetized white dwarf (B-WD), letting them below the current detection limit. The repetition of this cycle can eventually lead to a B-WD, recently postulated to be the reason for over-luminous type Ia supernovae. This evolution leading to a spinning B-WD could also be an ideal source for soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs). SGRs/AXPs are generally believed to be highly magnetized, but observationally not confirmed yet, neutron stars. Invoking B-WDs to explain them does not require the magnetic field to be as high as for neutron star based model, however reproducing other observed properties intact.
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Session	GW1	Accepted		Order	Time
Talk	Poster abstract	Title	Plausible emission of gravitational wave from highly magnetized and/or modified gravity induced white dwarfs
Coauthors
Abstract	Since last half a decade of so, we have initiated exploring possible existence of highly magnetized white dwarfs (B-WDs) and also white dwarfs in modified gravity (MG-WD), with a new super-Chandrasekhar mass-limit. It has many implications including observed over-luminous type Ia supernovae, white dwarf pulsars, soft gamma-ray repeaters and anomalous X-ray pulsars. In the talk, we however show that these spinning B-WDs and MG-WDs are attractive sites for gravitational radiation. The amplitude of gravitational wave produced by a B-WD/MG-WD with mass of the order of 2 solar mass, polar radius 700 km, rotational period about 1 sec with oblateness parameter 1/10000 and at 100 pc away from us is within the sensitivity of the Einstein@Home search for early LIGO. If the B-WD/MG-WD’s polar radius is 2000 km, rotational period 10 sec and other parameters intact as above, a firm confirmation of gravitational wave emission can be provided by DECIGO/BBO. Nevertheless, high magnetic field rotating white dwarfs approaching a B-WD would be common and it is possible that such white dwarfs of radius about 7000 km, period 20 sec, at a distance 10 pc will is detectable by LISA.
Pdf file

Session	AC1	Accepted		Order	Time
Talk	Oral abstract	Title	ULXs as magnetized sub-Eddington advective accretion flows around stellar mass black holes
Coauthors
Abstract	Ultra-luminous X-ray (ULX) sources have been puzzling us with a debate whether they consist of intermediate mass black holes or super-Eddington accretion by stellar mass black holes. Here we suggest that in the presence of large scale strong magnetic fields and non-negligible vertical motion, the luminosity of ULXs, particularly in their hard states, can be explained with sub-Eddington accretion by stellar mass black holes. In this framework of 2.5D magnetized advective accretion flows, magnetic tension plays the role of transporting matter (equivalent to viscous shear via turbulent viscosity) and we neither require to invoke intermediate mass black holes nor super-Eddington accretion. Our model explains the sources, like, NGC 5775 X1/X2, M82 X42.3+59, M99 X1 etc. which are in their hard power-law dominated states.
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