LOFAR 144-MHz follow-up observations of GW170817. Issue 4 (14th April 2020)

• Record Type: Journal Article
• Authors: Broderick, J W; Shimwell, T W; Gourdji, K; Rowlinson, A; Nissanke, S; Hotokezaka, K; Jonker, P G; Tasse, C; Hardcastle, M J; Oonk, J B R; Fender, R P; Wijers, R A M J; Shulevski, A; Stewart, A J; ter Veen, S; Moss, V A; van der Wiel, M H D; Nichols, D A; Piette, A; Bell, M E; Carbone, D; Corbel, S; Eislöffel, J; Grießmeier, J-M; Keane, E F; Law, C J; Muñoz-Darias, T; Pietka, M; Serylak, M; van der Horst, A J; van Leeuwen, J; Wijnands, R; Zarka, P; Anderson, J M; Bentum, M J; Blaauw, R; Brouw, W N; Brüggen, M; Ciardi, B; de Vos, M; Duscha, S; Fallows, R A; Franzen, T M O; Garrett, M A; Gunst, A W; Hoeft, M; Hörandel, J R; Iacobelli, M; Jütte, E; Koopmans, L V E; Krankowski, A; Maat, P; Mann, G; Mulder, H; Nelles, A; Paas, H; Pandey-Pommier, M; Pekal, R; Reich, W; Röttgering, H J A; Schwarz, D J; Smirnov, O; Soida, M; Toribio, M C; van Haarlem, M P; van Weeren, R J; Vocks, C; Wucknitz, O; Zucca, P;
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 494:Issue 4(2020)
• Page Start: 5110
• Page End: 5117
• Publication Date: 2020-04-14
• Subjects: gravitational waves -- stars: neutron -- radio continuum: stars; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa950
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We present low-radio-frequency follow-up observations of AT 2017gfo, the electromagnetic counterpart of GW170817, which was the first binary neutron star merger to be detected by Advanced LIGO–Virgo. These data, with a central frequency of 144 MHz, were obtained with LOFAR, the Low-Frequency Array. The maximum elevation of the target is just 13${_{.}^{\circ}}$ 7 when observed with LOFAR, making our observations particularly challenging to calibrate and significantly limiting the achievable sensitivity. On time-scales of 130–138 and 371–374 d after the merger event, we obtain 3σ upper limits for the afterglow component of 6.6 and 19.5 mJy beam −1, respectively. Using our best upper limit and previously published, contemporaneous higher frequency radio data, we place a limit on any potential steepening of the radio spectrum between 610 and 144 MHz: the two-point spectral index $\alpha ^{610}_{144} \gtrsim$ −2.5. We also show that LOFAR can detect the afterglows of future binary neutron star merger events occurring at more favourable elevations.