108 research outputs found
Statement of James Perley and Mary Burgan Before the Commission on the Future of Worker-Management Relations
Testimony_Perley_and_Burgan_081094.pdf: 197 downloads, before Oct. 1, 2020
The Use of an Enzyme Electrode in the Analysis of Indole-3-acetic Acid Oxidase Activity in Avena
Statistical Properties of Radio Emission from the Palomar Seyfert Galaxies
We have carried out an analysis of the radio and optical properties of a
statistical sample of 45 Seyfert galaxies from the Palomar spectroscopic survey
of nearby galaxies. We find that the space density of bright galaxies (-22 mag
<= M_{B_T} <= -18 mag) showing Seyfert activity is (1.25 +/- 0.38) X 10^{-3}
Mpc^{-3}, considerably higher than found in other Seyfert samples. Host galaxy
types, radio spectra, and radio source sizes are uncorrelated with Seyfert
type, as predicted by the unified schemes for active galaxies. Approximately
half of the detected galaxies have flat or inverted radio spectra, more than
expected based on previous samples. Surprisingly, Seyfert 1 galaxies are found
to have somewhat stronger radio sources than Seyfert 2 galaxies at 6 and 20 cm,
particularly among the galaxies with the weakest nuclear activity. We suggest
that this difference can be accommodated in the unified schemes if a minimum
level of Seyfert activity is required for a radio source to emerge from the
vicinity of the active nucleus. Below this level, Seyfert radio sources might
be suppressed by free-free absorption associated with the nuclear torus or a
compact narrow-line region, thus accounting for both the weakness of the radio
emission and the preponderance of flat spectra. Alternatively, the flat spectra
and weak radio sources might indicate that the weak active nuclei are fed by
advection-dominated accretion disks.Comment: 18 pages using emulateapj5, 13 embedded figures, accepted by Ap
Evidence for dust destruction from the early-time colour change of GRB 120119A
We present broad-band observations and analysis of Swift gamma-ray burst (GRB) 120119A. Our early-time afterglow detections began under 15âs after the burst in the host frame (redshift z = 1.73), and they yield constraints on the burst energetics and local environment. Late-time afterglow observations of the burst show evidence for a moderate column of dust (AV â 1.1âmag) similar to, but statistically distinct from, dust seen along Small Magellanic Cloud sightlines. Deep late-time observations reveal a dusty, rapidly star-forming host galaxy. Most notably, our early-time observations exhibit a significant red-to-blue colour change in the first âŒ200âs after the trigger at levels heretofore unseen in GRB afterglows. This colour change, which is coincident with the final phases of the prompt emission, is a hallmark prediction of the photodestruction of dust in GRB afterglows. We test whether dust-destruction signatures are significantly distinct from other sources of colour change, namely a change in the intrinsic spectral index ÎČ. We find that a time-varying power-law spectrum alone cannot adequately describe the observed colour change, and allowing for dust destruction (via a time-varying AV) significantly improves the fit. While not definitively ruling out other possibilities, this event provides the best support yet for the direct detection of dust destruction in the local environment of a GRB
GRB 071028B, a burst behind large amounts of dust in an unabsorbed galaxy
We report on the discovery and properties of the fading afterglow and
underlying host galaxy of GRB 071028B, thereby facilitating a detailed
comparison between these two. Observations were performed with the Gamma-ray
Burst Optical and Near-infrared Detector at the 2.2 m telescope on the La Silla
Paranal Observatory in Chile. We conducted five observations from 1.9 d to
227.2 d after the trigger and obtained deep images in the g'r'i'z' and JHKs
bands. Based on accurate seven-channel photometry covering the optical to
near-infrared wavelength range, we derive a photometric redshift of z = 0.94
+0.05 -0.10 for the unabsorbed host galaxy of GRB 071028B. In contrast, we show
that the afterglow with an intrinsic extinction of AV(SB) = (0.70 +/- 0.11) mag
is moderately absorbed and requires a relatively flat extinction curve.
According to the reported Swift/BAT observations, the energetics yield an
isotropic energy release of E(gamma,iso.,rest) = (1.4 +2.4 -0.7) x 10^51 erg.Comment: 8 pages, 5 figures, accepted for publication in A&
The Fast, Luminous Ultraviolet Transient AT2018cow: Extreme Supernova, or Disruption of a Star by an Intermediate-Mass Black Hole?
Wide-field optical surveys have begun to uncover large samples of fast (t_(rise) âČ 5 d), luminous (M_(peak) 10 days. The spectrum remains extremely hot throughout its evolution, and the photospheric radius contracts with time (receding below R < 10^(14) cm after 1 month). This behaviour does not match that of any known supernova, although a relativistic jet within a fallback supernova could explain some of the observed features. Alternatively, the transient could originate from the disruption of a star by an intermediate-mass black hole, although this would require long-lasting emission of highly super-Eddington thermal radiation. In either case, ATâ2018cow suggests that the population of fast luminous transients represents a new class of astrophysical event. Intensive follow-up of this event in its late phases, and of any future events found at comparable distance, will be essential to better constrain their origins
Deep VLA Observations of the Cluster 1RXS J0603.3+4214 in the Frequency Range of 1â2 GHz
We report L-band VLA observations of 1RXS J0603.3+4214, a cluster that hosts
a bright radio relic, known as the Toothbrush, and an elongated giant radio
halo. These new observations allow us to study the surface brightness
distribution down to one arcsec resolution with very high sensitivity. Our
images provide an unprecedented detailed view of the Toothbrush, revealing
enigmatic filamentary structures. To study the spectral index distribution, we
complement our analysis with published LOFAR and GMRT observations. The bright
`brush' of the Toothbrush shows a prominent narrow ridge to its north with a
sharp outer edge. The spectral index at the ridge is in the range
. We suggest that the ridge is caused by projection
along the line of sight. With a simple toy model for the smallest region of the
ridge, we conclude that the magnetic field is below and varies
significantly across the shock front. Our model indicates that the actual Mach
number is higher than that obtained from the injection index and agrees well
with the one derived from the overall spectrum, namely . The radio halo shows an average spectral index of
and a slight gradient from north to south. The
southernmost part of the halo is steeper and possibly related to a shock front.
Excluding the southernmost part, the halo morphology agrees very well with the
X-ray morphology. A power-law correlation is found between the radio and X-ray
surface brightnessComment: 23 pages, 21 figures, accepted for publication in Ap
Berkeley Supernova Ia Program I: Observations, Data Reduction, and Spectroscopic Sample of 582 Low-Redshift Type Ia Supernovae
In this first paper in a series we present 1298 low-redshift (z\leq0.2)
optical spectra of 582 Type Ia supernovae (SNe Ia) observed from 1989 through
2008 as part of the Berkeley SN Ia Program (BSNIP). 584 spectra of 199 SNe Ia
have well-calibrated light curves with measured distance moduli, and many of
the spectra have been corrected for host-galaxy contamination. Most of the data
were obtained using the Kast double spectrograph mounted on the Shane 3 m
telescope at Lick Observatory and have a typical wavelength range of
3300-10,400 Ang., roughly twice as wide as spectra from most previously
published datasets. We present our observing and reduction procedures, and we
describe the resulting SN Database (SNDB), which will be an online, public,
searchable database containing all of our fully reduced spectra and companion
photometry. In addition, we discuss our spectral classification scheme (using
the SuperNova IDentification code, SNID; Blondin & Tonry 2007), utilising our
newly constructed set of SNID spectral templates. These templates allow us to
accurately classify our entire dataset, and by doing so we are able to
reclassify a handful of objects as bona fide SNe Ia and a few other objects as
members of some of the peculiar SN Ia subtypes. In fact, our dataset includes
spectra of nearly 90 spectroscopically peculiar SNe Ia. We also present
spectroscopic host-galaxy redshifts of some SNe Ia where these values were
previously unknown. [Abridged]Comment: 34 pages, 11 figures, 11 tables, revised version, re-submitted to
MNRAS. Spectra will be released in January 2013. The SN Database homepage
(http://hercules.berkeley.edu/database/index_public.html) contains the full
tables, plots of all spectra, and our new SNID template
Rapid, Machine-Learned Resource Allocation: Application to High-redshift GRB Follow-up
As the number of observed Gamma-Ray Bursts (GRBs) continues to grow,
follow-up resources need to be used more efficiently in order to maximize
science output from limited telescope time. As such, it is becoming
increasingly important to rapidly identify bursts of interest as soon as
possible after the event, before the afterglows fade beyond detectability.
Studying the most distant (highest redshift) events, for instance, remains a
primary goal for many in the field. Here we present our Random forest Automated
Triage Estimator for GRB redshifts (RATE GRB-z) for rapid identification of
high-redshift candidates using early-time metrics from the three telescopes
onboard Swift. While the basic RATE methodology is generalizable to a number of
resource allocation problems, here we demonstrate its utility for
telescope-constrained follow-up efforts with the primary goal to identify and
study high-z GRBs. For each new GRB, RATE GRB-z provides a recommendation -
based on the available telescope time - of whether the event warrants
additional follow-up resources. We train RATE GRB-z using a set consisting of
135 Swift bursts with known redshifts, only 18 of which are z > 4.
Cross-validated performance metrics on this training data suggest that ~56% of
high-z bursts can be captured from following up the top 20% of the ranked
candidates, and ~84% of high-z bursts are identified after following up the top
~40% of candidates. We further use the method to rank 200+ Swift bursts with
unknown redshifts according to their likelihood of being high-z.Comment: 44 pages, 11 figures, 6 tables, Accepted to Ap
ZTF20aajnksq (AT 2020blt): A Fast Optical Transient at z â 2.9 with No Detected Gamma-Ray Burst Counterpart
We present ZTF20aajnksq (AT 2020blt), a fast-fading (Îr = 2.3 mag in Ît = 1.3 days) red (g â r â 0.6 mag) and luminous (M_(1626 Ă
) = â25.9 mag) optical transient at z = 2.9 discovered by the Zwicky Transient Facility (ZTF). AT 2020blt shares several features in common with afterglows to long-duration gamma-ray bursts (GRBs): (1) an optical light curve well-described by a broken power law with a break at t_j = 1 d (observer frame); (2) a luminous (L_(0.3â10 KeV) = 10âŽâ¶ erg sâ»Âč) X-ray counterpart; and (3) luminous (L_(10 GHz) = 4 Ă 10ÂłÂč erg sâ»Âč Hzâ»Âč) radio emission. However, no GRB was detected in the 0.74 days between the last ZTF nondetection (r > 21.36 mag) and the first ZTF detection (r = 19.60 mag), with an upper limit on the isotropic-equivalent gamma-ray energy release of E_(Îł,iso) < 7 Ă 10â”ÂČ erg. AT 2020blt is thus the third afterglow-like transient discovered without a detected GRB counterpart (after PTF11agg and ZTF19abvizsw) and the second (after ZTF19abvizsw) with a redshift measurement. We conclude that the properties of AT 2020blt are consistent with a classical (initial Lorentz factor Îâ âł 100) on-axis GRB that was missed by high-energy satellites. Furthermore, by estimating the rate of transients with light curves similar to that of AT 2020blt in ZTF high-cadence data, we agree with previous results that there is no evidence for an afterglow-like phenomenon that is significantly more common than classical GRBs, such as dirty fireballs. We conclude by discussing the status and future of fast-transient searches in wide-field high-cadence optical surveys
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