Signatures of Einstein-Maxwell dilaton-axion gravity from the observed jet power and the radiative efficiency. (arXiv:2007.03947v2 [gr-qc] UPDATED)
<a href="http://arxiv.org/find/gr-qc/1/au:+Banerjee_I/0/1/0/all/0/1">Indrani Banerjee</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Mandal_B/0/1/0/all/0/1">Bhaswati Mandal</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+SenGupta_S/0/1/0/all/0/1">Soumitra SenGupta</a>
The Einstein-Maxwell dilaton-axion (EMDA) gravity arises in the low energy
effective action of the heterotic string theory and provides a simple framework
to explore the signatures of the same. The dilaton and the axion fields
inherited in the action from string compactifications have interesting
consequences in inflationary cosmology and in explaining the present
accelerated expansion of the universe. It is therefore worthwhile to search for
the footprints of these fields in the available astrophysical observations.
Since Einstein gravity is expected to receive quantum corrections in the high
curvature domain, the near horizon regime of black holes seems to be the ideal
astrophysical laboratory to test these deviations from general relativity.
Exact, stationary and axisymmetric black hole solution in EMDA gravity
corresponds to the Kerr-Sen spacetime which carries dilaton charge, while the
angular momentum is sourced by the axion field. The ballistic jets and the peak
emission of the continuum spectrum from the accretion disk are believed to be
launched very close to the event horizon and hence should bear the imprints of
the background spacetime. We compute the jet power and the radiative efficiency
derived from the continuum spectrum in the Kerr-Sen background and compare them
with the corresponding observations of microquasars. Our analysis reveals that
Kerr black holes are more favored compared to Kerr-Sen black holes with dilaton
charges.
The Einstein-Maxwell dilaton-axion (EMDA) gravity arises in the low energy
effective action of the heterotic string theory and provides a simple framework
to explore the signatures of the same. The dilaton and the axion fields
inherited in the action from string compactifications have interesting
consequences in inflationary cosmology and in explaining the present
accelerated expansion of the universe. It is therefore worthwhile to search for
the footprints of these fields in the available astrophysical observations.
Since Einstein gravity is expected to receive quantum corrections in the high
curvature domain, the near horizon regime of black holes seems to be the ideal
astrophysical laboratory to test these deviations from general relativity.
Exact, stationary and axisymmetric black hole solution in EMDA gravity
corresponds to the Kerr-Sen spacetime which carries dilaton charge, while the
angular momentum is sourced by the axion field. The ballistic jets and the peak
emission of the continuum spectrum from the accretion disk are believed to be
launched very close to the event horizon and hence should bear the imprints of
the background spacetime. We compute the jet power and the radiative efficiency
derived from the continuum spectrum in the Kerr-Sen background and compare them
with the corresponding observations of microquasars. Our analysis reveals that
Kerr black holes are more favored compared to Kerr-Sen black holes with dilaton
charges.
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