Hintze Centre for Astrophysical Surveys: publications

Modelling the spectra of the kilonova AT2017gfo – I. The photospheric epochs

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 515:1 (2022) 631-651

Authors:

JH Gillanders, SJ Smartt, SA Sim, A Bauswein, S Goriely

Abstract:

ABSTRACT The kilonova (KN) associated with the binary neutron star (BNS) merger GW170817 is the only known electromagnetic counterpart to a gravitational wave source. Here we produce a sequence of radiative transfer models (using tardis) with updated atomic data, and compare them to accurately calibrated spectra. We use element compositions from nuclear network calculations based on a realistic hydrodynamical simulation of a BNS merger. We show that the blue spectrum at +1.4 d after merger requires a nucleosynthetic trajectory with a high electron fraction. Our best-fitting model is composed entirely of first r-process peak elements (Sr and Zr) and the strong absorption feature is reproduced well by Sr ii absorption. At this epoch, we set an upper limit on the lanthanide mass fraction of $X_{{\small LN}} \lesssim 5 \times 10^{-3}$. In contrast, all subsequent spectra from +2.4 to 6.4 d require the presence of a modest amount of lanthanide material ($X_{{\small LN}} \simeq 0.05^{+0.05}_{-0.02}$), produced by a trajectory with Ye = 0.29. This produces lanthanide-induced line blanketing below 6000 Å, and sufficient light r-process elements to explain the persistent strong feature at ∼0.7–1.0 $\mu$m (Sr ii). The composition gives good matches to the observed data, indicating that the strong blue flux deficit results in the near-infrared (NIR) excess. The disjoint in composition between the first epoch and all others indicates either ejecta stratification, or the presence of two distinct components of material. This further supports the ‘two-component’ KN model, and constrains the element composition from nucleosynthetic trajectories. The major uncertainties lie in availability of atomic data and the ionization state of the expanding material.

A multi-wavelength study of GRS 1716-249 in outburst : constraints on its system parameters

(2022)

Authors:

Payaswini Saikia, David M Russell, MC Baglio, DM Bramich, Piergiorgio Casella, M Diaz Trigo, Poshak Gandhi, Jiachen Jiang, Thomas Maccarone, Roberto Soria, Hind Al Noori, Aisha Al Yazeedi, Kevin Alabarta, Tomaso Belloni, Marion Cadolle Bel, Chiara Ceccobello, Stephane Corbel, Rob Fender, Elena Gallo, Jeroen Homan, Karri Koljonen, Fraser Lewis, Sera B Markoff, James CA Miller-Jones, Jerome Rodriguez, Thomas D Russell, Tariq Shahbaz, Gregory R Sivakoff, Vincenzo Testa, Alexandra J Tetarenko

On the robustness of triaxial Schwarzschild modelling: The effects of correcting the orbit mirroring

ArXiv 2205.04165 (2022)

Authors:

Sabine Thater, Prashin Jethwa, Behzad Tahmasebzadeh, Ling Zhu, Mark den Brok, Giulia Santucci, Yuchen Ding, Adriano Poci, Edward Lilley, P Tim de Zeeuw, Alice Zocchi, Thomas I Maindl, Fabio Rigamonti, Glenn van de Ven, Meng Yang, Katja Fahrion

Long-term radio monitoring of the neutron star X-ray binary Swift J1858.6-0814

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 513:2 (2022) 2708-2718

Authors:

L Rhodes, RP Fender, S Motta, J van den Eijnden, DRA Williams, J Bright, GR Sivakoff

Jet-cocoon geometry in the optically dark, very high energy gamma-ray burst 201216C

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 513:2 (2022) 1895-1909

Authors:

L Rhodes, AJ van der Horst, R Fender, DR Aguilera-Dena, JS Bright, S Vergani, DRA Williams

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