9 research outputs found
Gravitational waves from an SMBH binary in M87
In this paper, we study gravitational-wave (GW) emission from a hypothetical
supermassive black-hole (SMBH) binary at the center of M87. The existence of a
SMBH other than that usually identified with the central AGN is a possible
explanation for the observed displacement () between the
AGN and the galactic centroid, and it is reasonable to assume consid- ering the
evolution of SMBHs through galaxy mergers. Because the period of the binary and
the resulting GWs is much longer than the observational time span, we calculate
the variation of the GW amplitude, rather than the amplitude itself. We
investigate the dependence on the orbital elements and the second BH mass
taking the observational constraints into account. The frequency of the GWs is
too low to be detected with the conventional pulsar timing array and we propose
a new method to detect such low-frequency GWs with the distribution func- tion
of pulsar spin-down rates. Although the GWs from a SMBH binary which explains
the observed displacement is extremely hard to be detected even with the new
method, GWs are still a useful way to probe the M87 center.Comment: 5 pages, 6 figures. Accepted for Publications of the Astronomical
Society of Japa
Artificial neural networks for selection of pulsar candidates from the radio continuum surveys
Pulsar search with time-domain observation is very computationally expensive
and data volume will be enormous with the next generation telescopes such as
the Square Kilometre Array. We apply artificial neural networks (ANNs), a
machine learning method, for efficient selection of pulsar candidates from
radio continuum surveys, which are much cheaper than time-domain observation.
With observed quantities such as radio fluxes, sky position and compactness as
inputs, our ANNs output the "score" that indicates the degree of likeliness of
an object to be a pulsar. We demonstrate ANNs based on existing survey data by
the TIFR GMRT Sky Survey (TGSS) and the NRAO VLA Sky Survey (NVSS) and test
their performance. Precision, which is the ratio of the number of pulsars
classified correctly as pulsars to that of any objects classified as pulsars,
is about 96. Finally, we apply the trained ANNs to unidentified radio
sources and our fiducial ANN with five inputs (the galactic longitude and
latitude, the TGSS and NVSS fluxes and compactness) generates 2,436 pulsar
candidates from 456,866 unidentified radio sources. These candidates need to be
confirmed if they are truly pulsars by time-domain observations. More
information such as polarization will narrow the candidates down further.Comment: 11 pages, 13 figures, 3 tables, accepted for publication in MNRA