29 research outputs found
A Search for Gamma-Ray Burst Optical Emission with the Automated Patrol Telescope
The Automated Patrol Telescope (APT) is a wide-field (5 X 5 deg.s), modified
Schmidt capable of covering large gamma-ray burst (GRB) localization regions to
produce a high rate of GRB optical emission measurements. Accounting for
factors such as bad weather and incomplete overlap of our field and large GRB
localization regions, we estimate our search will image the actual location of
20-41 BATSE GRB sources each year. Long exposures will be made for these
images, repeated for several nights, to detect delayed optical transients (OTs)
with light curves similar to those already discovered. The APT can also respond
within about 20 sec. to GRB alerts from BATSE to search for prompt emission
from GRBs. We expect to image more than 2.4 GRBs/yr. during gamma-ray emission.
More than 5.1 will be imaged/yr. within about 20 sec. of emission. The APT's 50
cm aperture is much larger than other currently operating experiments used to
search for prompt emission, and the APT is the only GRB dedicated telescope in
the Southern Hemisphere. Given the current rate of about 25% OTs per X/gamma
localization, we expect to produce a sample of about 10 OTs for detailed
follow-up observations in 1-2 years of operation.Comment: 4 pages latex + 3 ps figures. Download a single tar file of ps at
http://panisse.lbl.gov/public/bruce/optgrbsearch.tar.g
GW170817 Most Likely Made a Black Hole
There are two outstanding issues regarding the neutron-star merger event
GW170817: the nature of the compact remnant and the interstellar shock. The
mass of the remnant of GW170817, 2.7 , implies the remnant could
be either a massive, rotating, neutron star, or a black hole. We report Chandra
Director's Discretionary Time observations made in 2017 December and 2018
January, and we reanalyze earlier observations from 2017 August and 2017
September, in order to address these unresolved issues. We estimate the X-ray
flux from a neutron star remnant and compare that to the measured X-ray flux.
If we assume that the spin-down luminosity of any putative neutron star is
converted to pulsar wind nebula X-ray emission in the 0.5-8 keV band with an
efficiency of , for a dipole magnetic field with G
< < G, a rising X-ray signal would result and would be brighter
than that observed by day 107, we therefore conclude that the remnant of
GW170817 is most likely a black hole. Independent of any assumptions of X-ray
efficiency, however, if the remnant is a rapidly-rotating, magnetized, neutron
star, the total energy in the external shock should rise by a factor
(to erg) after a few years, therefore, Chandra
observations over the next year or two that do not show substantial brightening
will rule out such a remnant. The same observations can distinguish between two
different models for the relativistic outflow, either an angular or radially
varying structure.Comment: 10 pages, 4 figures, accepted to ApJ
Distinguishing Time Clustering of Astrophysical Bursts
Many astrophysical bursts can recur, and their time series structure or
pattern could be closely tied to the emission and system physics. While
analysis of periodic events is well established, some sources, e.g. some fast
radio bursts and soft gamma-ray emitters, are suspected of more subtle and less
explored periodic windowed behavior: the bursts themselves are not periodic,
but the activity only occurs during periodic windows. We focus here on
distinguishing periodic windowed behavior from merely clustered events through
time clustering analysis, using techniques analogous to spatial clustering,
demonstrating methods for identifying and characterizing the behavior. An
important aspect is accounting for the ``curious incident of the dog in the
night time'' - lack of bursts carries information. As a worked example, we
analyze six years of data from the soft gamma repeater SGR1935+2154, deriving a
window period of 231 days and 55% duty cycle; this has now successfully
predicted both active and inactive periods.Comment: 12 pages, 11 figures; v2 highlights successful burst prediction,
improves uncertainty quantification, adds comparison to other optimization
results, PRD accepte
Digital Complex Correlator for a C-band Polarimetry survey
The international Galactic Emission Mapping project aims to map and
characterize the polarization field of the Milky Way. In Portugal it will
cartograph the C-band sky polarized emission of the Northern Hemisphere and
provide templates for map calibration and foreground control of microwave space
probes like ESA Planck Surveyor mission. The receiver system is equipped with a
novel receiver with a full digital back-end using an Altera Field Programmable
Gate Array, having a very favorable cost/performance relation. This new digital
backend comprises a base-band complex cross-correlator outputting the four
Stokes parameters of the incoming polarized radiation. In this document we
describe the design and implementation of the complex correlator using COTS
components and a processing FPGA, detailing the method applied in the several
algorithm stages and suitable for large sky area surveys.Comment: 15 pages, 10 figures; submitted to Experimental Astronomy, Springe
Evolution of the afterglow optical spectral shape of GRB 201015A in the first hour: evidence for dust destruction
Instruments such as the ROTSE, TORTORA, Pi of the Sky, MASTER-net, and others
have recorded single-band optical flux measurements starting as early as
10 seconds after a gamma-ray burst trigger. The earliest
measurements of optical spectral shape have been made only much later,
typically on hour time scales, never starting less than a minute after trigger,
until now. Beginning only 58 seconds after the Swift BAT triggerred on
GRB201015A, we observed a sharp rise in flux to a peak, followed by an
approximate power law decay light curve, . Flux was
measured simultaneously in three optical filter bands, g', r', and i', using
our unique instrument mounted on the Nazarbayev University Transient Telescope
at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO). Our simultaneous
multi-band observations of the early afterglow show strong colour evolution
from red to blue, with a change in the optical log slope (after correction for
Milky Way extinction) of ; during this time the X-ray log slope
remained constant. We did not find evidence for a two-component jet structure
or a transition from reverse to forward shock that would explain this change in
slope. We find that the majority of the optical spectral slope evolution is
consistent with a monotonic decay of extinction, evidence of dust destruction.
If we assume that the optical log slope is constant throughout this period,
with the value given by the late-time slope, and we further assume an SMC-like
extinction curve, we derive a change in the local extinction
from 0.8 mag to 0.3 mag in
2500 s. This work shows that significant information about the early
emission phase (and possibly prompt emission, if observed early enough) is
being missed without such early observations with simultaneous multi-band
instruments.Comment: 7 pages, 3 figures. Submitted to MNRA
An IR Search for Extinguished Supernovae in Starburst Galaxies
IR and Radio band observations of heavily extinguished regions in starburst
galaxies suggest a very high SN rate associated with such regions. Optically
measured supernova (SN) rates may therefore underestimate the total SN rate by
factors of up to 10, due to the high extinction to SNe in starburst regions.
The IR/radio SN rates come from a variety of indirect means, however, which
suffer from model dependence and other problems.
We describe a direct measurement of the SN rate from a regular patrol of
starburst galaxies done with K' band imaging to minimize the effects of
extinction. A collection of K' measurements of core-collapse SNe near maximum
light is presented. Results of a preliminary SN search using the MIRC camera at
the Wyoming IR Observatory (WIRO), and an improved search using the ORCA optics
are described. A monthly patrol of starburst galaxies within 25 Mpc should
yield 1.6 - 9.6 SNe/year. Our MIRC search with low-resolution (2.2" pixels)
failed to find extinguished SNe, limiting the SN rate outside the nucleus (at >
15" radius) to less than 3.8 Supernova Rate Units (SRU or SNe/century/10^10
L(solar); 90% confidence). The MIRC camera had insufficient resolution to
search nuclear starburst regions, where SN activity is concentrated, explaining
why we found no heavily obscured SNe. We conclude that high-resolution, small
field SN searches in starburst nuclei are more productive than low resolution,
large-field searches, even for our large galaxies. With our ORCA
high-resolution optics, we could limit the total SN rate to < 1.3 SRU at 90%
confidence in 3 years of observations, lower than the most pessimistic
estimate.Comment: AJ Submitted 1998 Dec. 13. View figures and download all as one file
at http://panisse.lbl.gov/public/bruce/irs
The cryogenic detector for cosmology observation
https://iopscience.iop.org/article/10.1088/1757-899X/502/1/012060/pdfThis paper will present the implementation of the Microwave Kinetic Inductance Detectors (MKID) for mm/submm astronomy purposes in our cryocooler at the Energetic Cosmos Laboratory (ECL). Authors have used the robust cryocooler 106 Shasta from HPD Company. The refrigerator can cool down the temperature to 30 millikelvin. In this report, authors describe our experiences about millikelvin refrigerator, implementation challenges of MKIDs in refrigerator and the evaluation results