The Late-time Afterglow Evolution of Long Gamma-Ray Bursts GRB 160625B and GRB 160509A

We present post-jet-break Hubble Space Telescope, Very Large Array, and Chandra observations of the afterglow of the long γ-ray bursts GRB 160625B (between 69 and 209 days) and GRB 160509A (between 35 and 80 days). We calculate the post-jet-break decline rates of the light curves and find the afterglow of GRB 160625B is inconsistent with a simple t −3/4 steepening over the break, expected from the geometric effect of the jet edge entering our line of sight. However, the favored optical post-break decline (${f}_{\nu }\propto {t}^{-1.96\pm 0.07}$) is also inconsistent with the f ν ∝ t −p decline (where p ≈ 2.3 from the pre-break light curve), which is expected from exponential lateral expansion of the jet; perhaps suggesting lateral expansion that only affects a fraction of the jet. The post-break decline of GRB 160509A is consistent with both the t −3/4 steepening and with f ν ∝ t −p . We also use boxfit to fit afterglow models to both light curves and find both to be energetically consistent with a millisecond magnetar central engine, but the magnetar parameters need to be extreme (i.e., E ~ 3 × 1052 erg). Finally, the late-time radio light curves of both afterglows are not reproduced well by boxfit and are inconsistent with predictions from the standard jet model; instead, both are well represented by a single power-law decline (roughly f ν ∝ t −1) with no breaks. This requires a highly chromatic jet break (${t}_{j,\mathrm{radio}}\gt 10\times {t}_{j,\mathrm{optical}}$) and possibly a two-component jet for both bursts

The Environment of the Binary Neutron Star Merger GW170817

We present Hubble Space Telescope (HST) and Chandra imaging, combined with Very Large Telescope MUSE integral field spectroscopy of the counterpart and host galaxy of the first binary neutron star merger detected via gravitational-wave emission by LIGO and Virgo, GW170817. The host galaxy, NGC 4993, is an S0 galaxy at z = 0.009783. There is evidence for large, face-on spiral shells in continuum imaging, and edge-on spiral features visible in nebular emission lines. This suggests that NGC 4993 has undergone a relatively recent ($\lesssim 1$ Gyr) "dry" merger. This merger may provide the fuel for a weak active nucleus seen in Chandra imaging. At the location of the counterpart, HST imaging implies there is no globular or young stellar cluster, with a limit of a few thousand solar masses for any young system. The population in the vicinity is predominantly old with lesssim1% of any light arising from a population with ages $\lt 500\,\mathrm{Myr}$. Both the host galaxy properties and those of the transient location are consistent with the distributions seen for short-duration gamma-ray bursts, although the source position lies well within the effective radius (${r}_{e}\sim 3$ kpc), providing an r e -normalized offset that is closer than $\sim 90 \%$ of short GRBs. For the long delay time implied by the stellar population, this suggests that the kick velocity was significantly less than the galaxy escape velocity. We do not see any narrow host galaxy interstellar medium features within the counterpart spectrum, implying low extinction, and that the binary may lie in front of the bulk of the host galaxy

Spatial and Sex-Specific Variation in Growth of Albacore Tuna (Thunnus alalunga) across the South Pacific Ocean

Spatial variation in growth is a common feature of demersal fish populations which often exist as discrete adult sub-populations linked by a pelagic larval stage. However, it remains unclear whether variation in growth occurs at similar spatial scales for populations of highly migratory pelagic species, such as tuna. We examined spatial variation in growth of albacore Thunnus alalunga across 90° of longitude in the South Pacific Ocean from the east coast of Australia to the Pitcairn Islands. Using length-at-age data from a validated ageing method we found evidence for significant variation in length-at-age and growth parameters (L∞ and k) between sexes and across longitudes. Growth trajectories were similar between sexes up until four years of age, after which the length-at-age for males was, on average, greater than that for females. Males reached an average maximum size more than 8 cm larger than females. Length-at-age and growth parameters were consistently greater at more easterly longitudes than at westerly longitudes for both females and males. Our results provide strong evidence that finer spatial structure exists within the South Pacific albacore stock and raises the question of whether the scale of their “highly migratory” nature should be re-assessed. Future stock assessment models for South Pacific albacore should consider sex-specific growth curves and spatial variation in growth within the stock

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

The Benefits to Children of being a Co-Researcher: Evidence from a PhD Thesis.

This project arose as a detailed part of a longitudinal study on the changing attitude to science of children from years 5 to 9 (age 10 – 14) in the UK. At the start of the project the pupils had experienced 2 years of data collection at timed intervals that was fully supported by the school. In this way these potential co-researchers were already familiar with the idea of research being conducted within their school. The project enabled them to participate at a collaborative level (Hanley, Bradburn et al. 2004) throughout, with elements of full participation as defined as the supporting level by (Wilcox 1994) in their own research. The research took the form of a small scale, participant observer case study working with a final group of 8 children as co-researchers. The research question therefore was: “How does working as a co-researcher affect children’s attitudes to their own learning in science, their confidence and skills.” I worked as a social constructionist within an interpretivist framework. Radnor suggests that ‘all social research is a form of participant observation because we cannot study social life without being part of it.’ p49 (Radnor 2001) and this view is supported widely (Wenger 1998; Scott and Usher 2000; Brewer and Hunter 2006) The nature of participation in any social setting has its impact on both the participator and the community within which they participate (Wenger 1998). In the case of my research, my involvement with the co-researchers is multi layered; leading the interventions, supporting their own research, mentoring and facilitating and over-viewing their progress. It would be impossible to assess the project without assessing the effect of my part in it. Working with Children in research has undergone considerable evolution over recent years, in this project I define them as experts in their own world (Grover 2004). Working in this way children should have more say in what should be researched and how that research should be conducted. The literature generally categorises positive outcomes of children working as researchers into two main areas : Benefits to the research process in terms of accessing children’s expertise their insights into what might be the most meaningful studies and their contribution to disseminating the outcomes in powerful ways. (Edwards 2004, McLaughlin 2006) Benefits to the children in terms of accessing their rights to have their say and be heard, gaining confidence and esteem, developing relationships with peers, adults and schools, developing particular generic personal and specific skills, and attaining perspective and reflection on their lives, learning and the value of research. (Alderson 2001; Griesel, Swart-Kruger et al. 2004). I was also mindful of potential negative impacts, particularly on the children and these will be discussed in more detail in the paper. However, the general findings included that Co-researchers attitude to science became more positive about science overall over the course of the project in comparison to other groups where attitudes were declining. This could be linked to ideas about the impact of significant others as described in a Norwegian study (Sjaastad 2013). The co-researchers also exhibited enhanced: ontological understanding; reflection on their own learning; confidence in expressing and arguing for their own ideas and confidence in their own skills in analysing data. From my reading of literature from around the world this study will contribute to our understandings around this area. This a case study in that there are clear boundaries to the project both in terms of the timescale of initiation, interventions, co-researcher research, write up and dissemination and also in terms of the children’s engagement in the project as distinct from their school and social life. 'Though social actors within these boundaries also have experience outside them, the boundaries are well enough understood to constitute the object of enquiry as a 'case'. p87 .(Scott and Usher 2000) Additionally, the multi method approach to data collection is designed to capture the experience from the viewpoint of the co-researchers in the main part with triangulation from other actors in the immediate social setting. The use of a range of such qualitative methods as primary data collection techniques is also characteristic of a case study approach. (Scott and Usher 2000; Cohen, Manion et al. 2007) Brewer and Hunter (Brewer and Hunter 2006) advocate a multi method approach to social research which they call a fifth research style. In this way, Brewer and Hunter argue the differing strengths of individual methods overlap and compensate for individual weaknesses. ‘employing different types of methods helps to guard against and to correct for inherent methodological biases, p37 (Brewer and Hunter 2006). This study differs from the personal approach Brewer and Hunter describe in that it does not derive from a positivist stance but combines case study with participatory research. Additionally, the study employs grounded theory which Glaser and Strauss (Glaser and Strauss 2009) describe as ‘discovery of theory from data’ using comparative analysis as a key strategy . I am also influenced by Charmaz’s perspective that 'neither data nor theories are discovered. Rather, we are part of the world we study and the data we collect. We construct our grounded theories through our past and present involvements and interactions with people, perspectives, and research practices.' p10 (Charmaz 2006). The simultaneous analysis and data collection, the use of coding to develop themes from the data itself and the development of theory during analysis are hallmarks of the grounded theory approach p5 (Charmaz 2006). Alderson, P. (2001). "Research by children." International Journal of Social Research Methodology 4(2): 139-153. Edwards, A. (2004). Education. Doing Research with Children and Young People. S. Fraser, V. Lewis, S. Ding, M. Kellett and C. Robinson. London, Sage: 255-269. Griesel, D., J. Swart-Kruger, et al. (2004). Children in South Africa can make a difference: An Assessment of 'Growing Up in Cities' in Johannesburg. The Reality of Research with Children and Young People. V. Lewis, M. Kellett, C. Robinson, S. Fraser and S. Ding. London, Sage: 277-301. Grover, S. (2004). "Why Won't They Listen to Us? On Giving Power and Poice to Children Participating in Social Research." Childhood 11(1): 81-93. Hassan, G. (2008). "Attitudes toward science among australian tertiary and secondary school students." Research in Science & Technological Education 26(2): 129 - 147. Sjaastad, J. (2013). "Measuring the Ways Significant Persons Influence Attitudes Towards Science and Mathematics." International Journal of Science Education 35(2): 192 - 212. van Aalderen-Smeets, S. and J. W. van der Moden (2013). "Measuring Primary Teachers' Attitidues Toward Teaching Science: Development of the Dimensions of Attitude Toward Science (DAS) Instrument." International Journal of Science Education 35(4): 577 - 600