Optical polarimetry of the soft-state low-mass X-ray binary MAXI J0637-430

ATel #13291; V. Kravtsov, A. Berdyugin, A. Veledina, J. Poutanen, V. Piirola (University of Turku, Finland), S. Berdyugina (Kiepenheuer-Institute für Sonnenphysik, Freiburg, Germany), T. Sakanoi, M. Kagitani (Tohoku University, Sendai, Japan).
on 14 Nov 2019; 18:08 UT
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Credential Certification: Andrei Berdyugin (andber@utu.fi)

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We report optical polarimetric observations of the new soft-state low-mass X-ray binary MAXI J0637-430 (ATel #13256, #13257, #13270). We observed the source with the Dipol-2 BVR-polarimeter using the remotely controlled Tohoku 0.60 m (T60) telescope at Haleakala Observatory, Hawaii, for 3 nights (UT 2019 Nov 5.6, 7.6 and 9.6). Due to the very blue spectrum of the source (see also ATel #13260) and very low flux at the V and R passbands, only the data in the B-band are useful. Each night we obtained up to 24 independent measurements of Stokes parameters q and u for MAXI J0637-430 and for 3 field stars. Below we list nightly average values of Stokes parameters (q) and (u), polarization (P) and polarization angle (PA) for the source and 3-nights averages for the field stars (ref1-3). ID q (%) u (%) P(%) PA(deg) ref1 0.11 0.56 0.57 +/- 0.08 39 +/- 4 ref2 -0.10 0.10 0.14 +/- 0.07 67 +/- 14 ref3 0.10 0.41 0.42 +/- 0.08 38 +/- 6 maxi (051119) -0.21 0.59 0.63 +/- 0.29 55 +/- 13 maxi (071119) 0.22 0.19 0.29 +/- 0.24 21 +/- 20 maxi (091119) 0.17 0.002 0.17 +/- 0.26 0.3+/- 29 The polarization of MAXI J0637-430 is within 2-sigma errorbar from the interstellar value, the latter estimated using the field stars.