42 research outputs found
An Analysis of the Environment and Gas Content of Luminous Infrared Galaxies
Luminous and ultraluminous infrared galaxies (U/LIRGs) represent a population among the most extreme in our universe, emitting an extraordinary amount of energy at infrared wavelengths from dust heated by prolific star formation and/or an active galactic nucleus (AGN). We present three investigations of U/LIRGs to better understand their global environment, their interstellar medium properties, and their nuclear region where molecular gas feeds a starburst or AGN. To study the global environment, we compute the spatial cluster-galaxy amplitude, Bgc, for 76 z 1 Jy), and at moderately high elevation (> 45°). We map Arp 193 in 12CO(2-1) with CARMA, achieving 0.18'' x 0.12'' (~65 pc) resolution, and demonstrating an improvement with C-PACS. We compute a molecular gas mass of 2 x 109 Msun and find ~20% of the total mass is in the form of molecular gas out to a radius of 750 pc. In the inner 150 pc of the nucleus, N(H2) > 1025 cm-2
Detection of Radio Emission from the Hyperactive L Dwarf 2MASS J13153094-2649513AB
We report the detection of radio emission from the unusually active L5e + T7
binary 2MASS J13153094-2649513AB made with the Australian Telescope Compact
Array. Observations at 5.5 GHz reveal an unresolved source with a continuum
flux of 370+/-50 microJy, corresponding to a radio luminosity of L_rad = nuL_nu
= (9+/-3)x10^23 erg/s and log10(L_rad/L_bol) = -5.44+/-0.22. No detection is
made at 9.0 GHz to a 5 sigma limit of 290 microJy, consistent with a power law
spectrum S_nu ~ nu^-a with a > 0.5. The emission is quiescent, with no evidence
of variability or bursts over 3 hr of observation, and no measurable
polarization (V/I < 34%). 2MASS J1315-2649AB is one of the most radio-luminous
ultracool dwarfs detected in quiescent emission to date, comparable in strength
to other cool sources detected in outburst. Its detection indicates no decline
in radio flux through the mid-L dwarfs. It is unique among L dwarfs in having
strong and persistent Halpha and radio emission, indicating the coexistence of
a cool, neutral photosphere (low electron density) and a highly active
chromosphere (high electron density and active heating). These traits, coupled
with the system's mature age and substellar secondary, makes 2MASS J1315-2649AB
an important test for proposed radio emission mechanisms in ultracool dwarfs.Comment: 5 pages, 4 figures, accepted for publication in ApJ Letter
The Intermediate Mass Black Hole Candidate in the Center of NGC 404: New Evidence from Radio Continuum Observations
We present the results of deep, high-resolution, 5 GHz Expanded Very Large
Array (EVLA) observations of the nearby, dwarf lenticular galaxy and
intermediate mass black hole candidate (M ~4.5 x 10^5 M_sun), NGC 404. For the
first time, radio emission at frequencies above 1.4 GHz has been detected in
this galaxy. We found a modestly resolved source in the NGC 404 nucleus with a
total radio luminosity of 7.6 +/- 0.7 x 10^17 W/Hz at 5 GHz and a spectral
index from 5 to 7.45 GHz of alpha = -0.88 +/- 0.30. NGC 404 is only the third
central intermediate mass black hole candidate detected in the radio regime
with subarcsecond resolution. The position of the radio source is consistent
with the optical center of the galaxy and the location of a known, hard X-ray
point source (Lx ~1.2 x 10^37 erg/s). The faint radio and X-ray emission could
conceivably be produced by an X-ray binary, star formation, a supernova remnant
or a low-luminosity AGN powered by an intermediate mass black hole. In light of
our new EVLA observations, we find that the most likely scenario is an
accreting intermediate mass black hole, with other explanations incompatible
with the observed X-ray and/or radio luminosities or statistically unlikely.Comment: Accepted for publication to Ap
A VLA Study of High-redshift GRBs I - Multi-wavelength Observations and Modeling of GRB 140311A
We present the first results from a recently concluded study of GRBs at
with the Karl G. Jansky Very Large Array (VLA). Spanning to
GHz and 7 epochs from 1.5 to 82.3 d, our observations of GRB 140311A are
the most detailed joint radio and millimeter observations of a GRB afterglow at
to date. In conjunction with optical/near-IR and X-ray data, the
observations can be understood in the framework of radiation from a single
blast wave shock with energy erg
expanding into a constant density environment with density, . The X-ray and radio observations require a jet break at d, yielding an opening angle of and a beaming-corrected blast wave kinetic energy of
erg. The results from our radio follow-up
and multi-wavelength modeling lend credence to the hypothesis that detected
high-redshift GRBs may be more tightly beamed than events at lower redshift. We
do not find compelling evidence for reverse shock emission, which may be
related to fast cooling driven by the moderately high circumburst density.Comment: 16 pages, 13 figures, submitted to Ap
Radio Properties of Tidal Disruption Events
Radio observations of tidal disruption events (TDEs) probe material ejected
by the disruption of stars by supermassive black holes (SMBHs), uniquely
tracing the formation and evolution of jets and outflows, revealing details of
the disruption hydrodynamics, and illuminating the environments around
previously-dormant SMBHs. To date, observations reveal a surprisingly diverse
population. A small fraction of TDEs (at most a few percent) have been observed
to produce radio-luminous mildly relativistic jets. The remainder of the
population are radio quiet, producing less luminous jets, non-relativistic
outflows or, possibly, no radio emission at all. Here, we review the radio
observations that have been made of TDEs to date and discuss possible
explanations for their properties, focusing on detected sources and, in
particular, on the two best-studied events: Sw J1644+57 and ASASSN-14li. We
also discuss what we have learned about the host galaxies of TDEs from radio
observations and review constraints on the rates of bright and faint radio
outflows in TDEs. Upcoming X-ray, optical, near-IR, and radio surveys will
greatly expand the sample of TDEs, and technological advances open the exciting
possibility of discovering a sample of TDEs in the radio band unbiased by host
galaxy extinction.Comment: Resubmitted for publication in Springer Space Science Reviews
following referee comments. Chapter in ISSI review "The Tidal Disruption of
Stars by Massive Black Holes" vol. 79. Table 2 is available in
machine-readable format upon reques
Short GRB 130603B: Discovery of a jet break in the optical and radio afterglows, and a mysterious late-time X-ray excess
We present radio, optical/NIR, and X-ray observations of the afterglow of the
short-duration 130603B, and uncover a break in the radio and optical bands at
0.5 d after the burst, best explained as a jet break with an inferred jet
opening angle of 4-8 deg. GRB 130603B is only the third short GRB with a radio
afterglow detection to date, and the first time that a jet break is evident in
the radio band. We model the temporal evolution of the spectral energy
distribution to determine the burst explosion properties and find an
isotropic-equivalent kinetic energy of (0.6-1.7) x 10^51 erg and a circumburst
density of 5 x 10^-3-30 cm^-3. From the inferred opening angle of GRB 130603B,
we calculate beaming-corrected energies of Egamma (0.5-2) x 10^49 erg and EK
(0.1-1.6) x 10^49 erg. Along with previous measurements and lower limits we
find a median short GRB opening angle of 10 deg. Using the all-sky observed
rate of 10 Gpc^-3 yr^-1, this implies a true short GRB rate of 20 yr^-1 within
200 Mpc, the Advanced LIGO/VIRGO sensitivity range for neutron star binary
mergers. Finally, we uncover evidence for significant excess emission in the
X-ray afterglow of GRB 130603B at >1 d and conclude that the additional energy
component could be due to fall-back accretion or spin-down energy from a
magnetar formed following the merger.Comment: Submitted to ApJ; emulateapj style; 10 pages, 1 table, 3 figure
A Resolved Ring of Debris Dust around the Solar Analog HD 107146
We present resolved images of the dust continuum emission from the debris disk around the young (80-200 Myr) solar-type star HD 107146 with CARMA at λ = 1.3 mm and the CSO at λ = 350 μ. Both images show that the dust emission extends over an approximately 10" diameter region. The high-resolution (3") CARMA image further reveals that the dust is distributed in a partial ring with significant decrease in a flux inward of 97 AU. Two prominent emission peaks appear within the ring separated by ~140° in the position angle. The morphology of the dust emission is suggestive of dust captured into a mean motion resonance, which would imply the presence of a planet at an orbital radius of ~45-75 AU
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Energy Injection in Gamma-Ray Burst Afterglows
We present multi-wavelength observations and modeling of Gamma-ray Bursts (GRBs) that exhibit a simultaneous re-brightening in their X-ray and optical light curves, and are also detected at radio wavelengths. We show that the re-brightening episodes can be modeled by injection of energy into the blastwave and that in all cases the energy injection rate falls within the theoretical bounds expected for a distribution of energy with ejecta Lorentz factor. Our measured values of the circumburst density, jet opening angle, and beaming corrected kinetic energy are consistent with the distribution of these parameters for long-duration GRBs at both z ∼ 1 and z & 6, suggesting that the jet launching mechanism and environment of these events are similar to that of GRBs that do not have bumps in their light curves. However, events exhibiting re-brightening episodes have lower radiative efficiencies than average, suggesting that a majority of the kinetic energy of the outflow is carried by slow-moving ejecta, which is further supported by steep measured distributions of the ejecta energy as a function of Lorentz factor. We do not find evidence for reverse shocks over the energy injection period, implying that the onset of energy injection is a gentle process. We further show that GRBs exhibiting simultaneous X-ray and optical re-brightenings are likely the tail of a distribution of events with varying rates of energy injection, forming the most extreme events in their class. Future X-ray observations of GRB afterglows with Swift and its successors will thus likely discover several more such events, while radio follow-up and multi-wavelength modeling of similar events will unveil the role of energy injection in GRB afterglows.Astronom