114 research outputs found
The Non-homogeneous Poisson Process for Fast Radio Burst Rates
This paper presents the non-homogeneous Poisson process (NHPP) for modeling
the rate of fast radio bursts (FRBs) and other infrequently observed
astronomical events. The NHPP, well-known in statistics, can model changes in
the rate as a function of both astronomical features and the details of an
observing campaign. This is particularly helpful for rare events like FRBs
because the NHPP can combine information across surveys, making the most of all
available information. The goal of the paper is two-fold. First, it is intended
to be a tutorial on the use of the NHPP. Second, we build an NHPP model that
incorporates beam patterns and a power law flux distribution for the rate of
FRBs. Using information from 12 surveys including 15 detections, we find an
all-sky FRB rate of 586.88 events per sky per day above a flux of 1 Jy (95\%
CI: 271.86, 923.72) and a flux power-law index of 0.91 (95\% CI: 0.57, 1.25).
Our rate is lower than other published rates, but consistent with the rate
given in Champion et al. 2016.Comment: 19 pages, 2 figure
A VLBI Proper Motion Analysis of the Recoiling Supermassive Black Hole Candidate Mrk 1018
Mrk 1018 is a nearby changing-look AGN that has oscillated between spectral
Type 1.9 and Type 1 over a period of 40 years. Recently, a recoiling
supermassive black hole (rSMBH) scenario has been proposed to explain the
spectral and flux variability observed in this AGN. Detections of rSMBHs are
important for understanding the processes by which SMBH binaries merge and how
rSMBHs influence their galactic environment through feedback mechanisms.
However, conclusive identification of any rSMBHs has remained elusive to date.
In this paper, we present an analysis of 6.5 years of multi-frequency Very Long
Baseline Array (VLBA) monitoring of Mrk 1018. We find that the radio emission
is compact down to 2.4 pc, and displays flux density and spectral variability
over the length of our campaign, typical of a flat spectrum radio core. We
observe proper motion in RA of the radio core at -36.4 8.6 as
yr (4.2), or at the redshift of Mrk 1018. No
significant proper motion is found in DEC (31.3 25.1 as yr).
We discuss possible physical mechanisms driving the proper motion, including a
rSMBH. We conclude that the apparent velocity we observe of the VLBI radio core
is too high to reconcile with theoretical predictions of rSMBH velocities and
that the proper motion is most likely dominated by an unresolved, outflowing
jet component. Future observations may yet reveal the true nature of Mrk 1018.
However, our observations are not able to confirm it as a true rSMBH.Comment: 17 pages, 7 figures, 3 tables; accepted for publication in Ap
Supermassive Black-hole Demographics & Environments With Pulsar Timing Arrays
Precision timing of large arrays (>50) of millisecond pulsars will detect the
nanohertz gravitational-wave emission from supermassive binary black holes
within the next ~3-7 years. We review the scientific opportunities of these
detections, the requirements for success, and the synergies with
electromagnetic instruments operating in the 2020s.Comment: Submitted to the Astro2020 Decadal Survey. One of 5 core white-papers
authored by members of the NANOGrav Collaboration. 9 pages, 2 figure
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