1,319 research outputs found
Broad Band Photometric Reverberation Mapping of NGC 4395
We present results of broad band photometric reverberation mapping (RM) to
measure the radius of the broad line region, and subsequently the black hole
mass (M), in the nearby, low luminosity active galactic nuclei (AGN)
NGC 4395. Using the Wise Observatory's 1m telescope equipped with the SDSS
g, r and i broad band filters, we monitored NGC 4395 for 9 consecutive
nights and obtained 3 light curves each with over 250 data points. The g and
r bands include time variable contributions from H and H
(respectively) plus continuum. The i band is free of broad lines and covers
exclusively continuum. We show that by looking for a peak in the difference
between the cross-correlation and the auto-correlation functions for all
combinations of filters, we can get a reliable estimate of the time lag
necessary to compute M. We measure the time lag for H to be
hours, comparable to previous studies using the line resolved
spectroscopic RM method. We argue that this lag implies a black hole mass of
M \Msun
Constraining Jupiter's internal flows using Juno magnetic and gravity measurements
Deciphering the flow below the cloud-level of Jupiter remains a critical milestone in understanding Jupiter's internal structure and dynamics. The expected high-precision Juno measurements of both the gravity field and the magnetic field might help to reach this goal. Here we propose a method that combines both fields to constrain the depth-dependent flow field inside Jupiter. This method is based on a mean-field electrodynamic balance that relates the flow field to the anomalous magnetic field, and geostrophic balance that relates the flow field to the anomalous gravity field. We find that the flow field has two distinct regions of influence: an upper region in which the flow affects mostly the gravity field and a lower region in which the flow affects mostly the magnetic field. An optimization procedure allows to reach a unified flow structure that is consistent with both the gravity and the magnetic fields
The `Periodic Nulls' of Radio Pulsar J1819+1305
We present a single-pulse study of the four-component pulsar J1819+1305,
whose ``null'' pulses bunch at periodic intervals of around 57 times the
rotation period. The emission bursts between the null bunches exhibit
characteristic modulations at two shorter periodicities of approximately 6.2
and 3 times the rotation period, the former found largely in the two outer
components, and the latter only in the first component. Many bursts commence
with bright emission in second component, exhibit positive six-period drift
across the full profile width, and end with 3-period modulation in the leading
component. The 57-period cycle can be modelled geometrically as a sparsely
filled subbeam carousel with nulls appearing whenever our line of sight
intersects a circulating empty region. This interpretation is compatible with
other recent evidence for periodic, carousel-related nulling and appears to
support the physics of a polar-gap emission model for ``drifting'' subpulses,
but the subtle structure of the emission bursts defies an easy explanation.Comment: 8 pages, 9 figure
The GBT350 Survey of the Northern Galactic Plane for Radio Pulsars and Transients
Using the Green Bank Telescope (GBT) and Pulsar Spigot at 350MHz, we have
surveyed the Northern Galactic Plane for pulsars and radio transients. This
survey covers roughly 1000 square degrees of sky within 75 deg < l < 165 deg
and |b| < 5.5 deg, a region of the Galactic Plane inaccessible to both the
Parkes and Arecibo multibeam surveys. The large gain of the GBT along with the
high time and frequency resolution provided by the Spigot make this survey more
sensitive by factors of about 4 to slow pulsars and more than 10 to millisecond
pulsars (MSPs), compared with previous surveys of this area. In a preliminary,
reduced-resolution search of all the survey data, we have discovered 33 new
pulsars, almost doubling the number of known pulsars in this part of the
Galaxy. While most of these sources were discovered by normal periodicity
searches, 5 of these sources were first identified through single, dispersed
bursts. We discuss the interesting properties of some of these new sources.
Data processing using the data's full-resolution is ongoing, with the goal of
uncovering MSPs missed by our first, coarse round of processing.Comment: To appear in the proceedings of "Forty Years of Pulsars: Millisecond
Pulsars, Magnetars and More" held in Montreal, Canada, August 12-17, 2007. 3
pages, 2 figure
Radio Properties of Low Redshift Broad Line Active Galactic Nuclei
The question as to whether the distribution of radio-loudness in active
galactic nuclei (AGN) is actually bimodal has been discussed extensively in the
literature. Futhermore, there have been claims that radio-loudness depends on
black hole mass and Eddington ratio. We investigate these claims using the low
redshift broad line AGN sample of Greene & Ho (2007), which consists of 8434
objects at z < 0.35 from the Sloan Digital Sky Survey Fourth Data Release (SDSS
DR4). We obtained radio fluxes from the Very Large Array Faint Images of the
Radio Sky at Twenty-Centimeters (FIRST) survey for the SDSS AGN. Out of the
8434 SDSS AGN, 821 have corresponding observed radio fluxes in the FIRST
survey. We calculated the radio-loudness parameter (R) for all objects above
the FIRST detection limit (1 mJy), and an upper limit to R for the undetected
objects. Using these data, the question of radio bimodality is investigated for
different subsets of the total sample. We find no clear demarcation between the
radio-loud (RL, R > 10) and radio-quiet (RQ, R < 10) objects, but instead fill
in a more radio-intermediate population in a continuous fashion for all
subsamples. We find that 4.7% of the AGN in the flux-limited subsample are RL
based on core radio emission alone. We calculate the radio-loud fraction (RLF)
as both a function of black hole mass and Eddington ratio. The RLF decreases
(from 13% to 2%) as Eddington ratio increases over 2.5 order of magnitude. The
RLF is nearly constant (~5%) over 4 decades in black hole mass, except for an
increase at masses greater than 10^8 solar masses. We find for the FIRST
detected subsample that 367 of the RL AGN have black hole masses less than 10^8
solar masses, a large enough number to indicate that RL AGN are not a product
of only the most massive black holes in the local universe.Comment: 28 pages, 14 figures, accepted to A
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