Talk detail

Participant	Mukhopadhyay, Banibrata
Institution	Indian Institute of Science - Department of Physics, Indian Institute of Science - Bangalore - Karnataka - India

Session	WD2	Accepted		Order	Time
Talk	Oral abstract	Title	SOFT GAMMA-RAY REPEATERS AND ANOMALOUS X-RAY PULSARS AS HIGHLY MAGNETIZED WHITE DWARFS
Coauthors
Abstract	We show that the soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) can be explained as recently proposed highly magnetized white dwarfs (B-WDs). The radius and magnetic field of B-WDs are perfectly adequate to explain energies in SGRs/AXPs as the rotationally powered energy. While the highly magnetized neutron stars require an extra, observationally not well established yet, source of energy, the magnetized white dwarfs, yet following Chandrasekhar's theory, exhibit large ultra-violet luminosity which is observationally constrained from a strict upper limit.
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Session	AC2	Accepted		Order	Time
Talk	Oral abstract	Title	Removal of angular momentum by strong magnetic field stresses in advective accretion flows around black holes
Coauthors
Abstract	We show that the removal of angular momentum is possible in the presence of large scale magnetic stresses, arisen by fields much stronger than that for MRI, in geometrically thick, advective, sub-Keplerian accretion flows around black holes in steady-state, in the complete absence of alpha-viscosity. The efficiency of matter infall and hence an angular momentum transfer in such disks could be equivalent to that of alpha-viscosity with alpha=0.01-0.08. Nevertheless, required field is well below its equipartition value, leading to a magnetically stable disk flow. This is essentially important in order to describe the hard spectral state of the sources. We show in our simpler 1.5-dimensional, vertically averaged disk model that larger the vertical-gradient of azimuthal component of magnetic field, stronger the rate of angular momentum transfer is, which in turn may lead to a faster rate of outflowing matter.
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Session	AT1	Accepted		Order	Time
Talk	Oral abstract	Title	Exploring a missing link between peculier, sub- and super-Chandrasekhar type Ia supernovae by modifying EInstein's gravity
Coauthors
Abstract	Observations of several peculiar, under- and over-luminous type Ia supernovae (SNeIa) argue for exploding masses widely different from the Chandrasekhar-limit. We explore the modification to Einstein's gravity in white dwarfs for the first time in the literature, to the best of our knowledge, to resolve the issue. We show that modified gravity induced white dwarfs' limiting masses could be significantly sub- and super-Chandrasekhar, depending on a single model parameter, and hence result in under- and over-luminous SNeIa respectively. Thus a single theory unifies these two apparently disjoint sub-classes of SNeIa and, hence, serving as a missing link. Our discovery raises two fundamental questions. Is the Chandrasekhar limit unique? Is Einstein's gravity the ultimate theory for understanding astronomical phenomena? Both the answers appear to be no.
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Session	GN2	Accepted		Order	Time
Talk	Oral abstract	Title	A search for chaos in the blazar: W2R 1926+42 and its possible consequence
Coauthors
Abstract	By using publicly available data, we search for signatures of low-dimensional chaos in the temporal behavior of the Kepler-field blazar W2R 1946+42. We use an ~160000 points long and mostly equally spaced light curve and apply the correlation integral method to both -- real datasets and phase randomized "surrogates". However, we are not able to confirm the presence of low-dimensional chaos in the light curve. Although not entirely conclusive, these results may suggest for the mechanism of particle acceleration. Models, based on a ”single engine”, operating perhaps close to the jet base seem unlikely. Models, relying on the presence of many independent active zones, like multiple magnetic reconnections or turbulence within the jet, are more plausible.
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