Article Title
Affiliation & Organization
Author: Joel Dombek
Published: 24 October 2020
Link Citation: Effects of science on the religious mind.New 2nd Success Danger
The questions and hypotheses that initiate an investigation, the resultant data gathered, and the background information obtained by reading the literature will lead to conclusions. Your research paper presents these conclusions and the appropriate evidence (data and relevant literature). Before writing your report, construct an outline that logically presents the information to support your conclusions. Organize the data into tables and figures to present the evidence in a logical order. Many authors prefer to construct a draft by rapidly putting down ideas with little regard to sentence structure, and to make corrections later. Others prefer to make revisions as they proceed. Write the report with a target audience of other students with experience in biology equivalent to that of the class for which the report is written.
Proper use of English is considered paramount in grading. Your major responsibility is to make the reader understand exactly what you mean by using words with precision, clarity, and economy. Every sentence should be exact and say something of importance (no "padding"). Economy and accuracy require using straightforward English sentences (subject, verb, and object). Follow a consistent pattern of tenses. Although it is acceptable to write in either the active or passive voice, you should write in the active voice unless you have good reason to usethe passive voice. Different biological fields and faculty may have specific requirements for tense or voice and students should consult specific course instructions or instructors for these assignment details.
The discovery of gravitational waves (GWs) from coalescing binary black holes by the Laser Interferometer Gravitational Wave Observatory (LIGO) has transformed the study of compact objects in the universe (1, 2). Unlike black holes, merging neutron stars are expected to produce electromagnetic radiation. The electromagnetic signature of such an event can provide more information than the GW signal alone: constraining location of the source, reducing the degeneracies in GW parameter estimation (3), probing the expansion rate of the universe (4, 5), and producing a more complete picture of the merger process (6, 7).
Short gamma-ray bursts (GRBs) have long been expected to result from neutron star mergers (8, 9), and therefore would be a natural electromagnetic counterpart to GWs (10).
Unfortunately, their emission is beamed, so that it may not intersect our line of sight (11). The possibility that only a small fraction of GRBs may be detectable has motivated theoretical and observational searches for more-isotropic electromagnetic signatures, such as an astronomical transient powered by the radioactive decay of neutron-rich ejecta from the merger (12–17). Referred to as a macronova or kilonova, the detection of these events would provide information on the origin of many of the heaviest elements in the periodic table (18).
It has long been realized that approximately half of the elements heavier than iron are created via r-process nucleosynthesis—the capture of neutrons onto lighter seed nuclei on a time scale more rapid than β-decay pathways (19, 20). However, it is less clear where the r-process predominantly occurs, namely whether the primary sources of these elements are core-collapse supernovae or compact binary mergers (black hole–neutron star or neutron star–neutron star) (21, 22). For supernovae, direct detection of the electromagnetic signatures from r-process nucleosynthesis is obscured by the much larger luminosity originating from hydrogen recombination (for hydrogen-rich supernovae) or nickel-56 and cobalt-56 decay (for hydrogen-poor supernovae). By contrast, it may be possible to measure the r-process nucleosynthesis after a compact object merger from the associated transient, based on its radioactive decay. Such a measurement would demonstrate directly that r-process elements are produced in compact mergers, and provide an estimate of the r-process yield. While there has been some tentative evidence for kilonovae following short gamma-ray bursts (23, 24), no conclusive event has yet been observed.
On 17 August 2020, LIGO and Virgo detected the gravitational wave source GW170817, which was identified as a binary neutron star merger based on the waveform (25–27). At 23:33 UTC on 17 August 2020 (10.86 hours post-merger), an optical transient, Swope Supernova Survey 2020a (SSS17a), was identified in the galaxy NGC 4993 by the 1M2H collaboration and was determined to be associated with this event (28, 29). Within an hour of the identification, we began observing the spectral energy distribution (SED) of SSS17a from the g- to K-bands with the Magellan telescopes (30). Early spectra of the source, also obtained within an hour of the optical discovery, were blue and smooth, indicating that the transient event was initially very hot (31, 32). Over the following weeks, we acquired optical and near-infrared (near-IR) imaging of SSS17a at Las Campanas Observatory and W. M. Keck Observatory with the Swope, du Pont, Magellan, and Keck-I telescopes, which are analyzed below (33). A companion paper presents optical spectroscopy of SSS17a for an overlapping time period (32). Figure 1A shows the discovery image, composed of g-, i-, and H-band Magellan/Swope imaging from the night of August 17. For comparison, Fig. 1B shows a color image from observations obtained 4 days later. The change in color of SSS17a between these images demonstrates the rapid evolution of this transient.
Evolution of the ultraviolet to near-infrared spectral energy distribution (SED) of SSS17a.
(A) The vertical axis, log Fλ,o, is the logarithm of the observed flux. Fluxes have been corrected for foreground Milky Way extinction (33). Detections are plotted as filled symbols and upper limits for the third epoch (1.0 days post-merger) as downward pointing arrows. Less-constraining upper limits at other epochs are not plotted for clarity. Between 0.5 and 8.5 days after the merger, the peak of the SED shifts from the near-UV (<4500 Å) to the near-IR (>1 μm), and fades by a factor >70. The SED is broadly consistent with a thermal distribution and the colored curves represent best-fitting blackbody models at each epoch. In 24 hours after the discovery of SSS17a, the observed color temperature falls from Embedded Image10,000 K to ~5000 K. The epoch and best-fitting blackbody temperature (rounded to 100 K) are listed. SEDs for each epoch are also plotted individually in fig. S2 and described in (33). (B) Filter transmission functions for the observed photometric bands.
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