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, $\sim$2.7 $M_\odot$, 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 $10^{-3}$, for a dipole magnetic field with $3 \times 10^{11}$ G < $B$ < $10^{14}$ 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 $\sim$$10^2$ (to $\sim$$10^{52}$ 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 $\thicksim$ 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, $\propto t^{-0.81 \pm 0.03}$. 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 $+0.72 \pm 0.14$; 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 $A_\mathrm{v}^\mathrm{local}$ from $\thicksim$0.8 mag to 0.3 mag in $\thicksim$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