Optical spectroscopy of MAXI J0637-430 confirms a new low-mass X-ray binary
ATel #13260; J Strader, E Aydi, K Sokolovsky, L Shishkovsky (Michigan St)
on 4 Nov 2019; 16:37 UT
Credential Certification: Jay Strader (strader@pa.msu.edu)
Subjects: Optical, Binary, Black Hole, Neutron Star, Transient
On 2019 Nov 3, the new soft X-ray transient MAXI J0637-430 was announced (ATel #13256), with a bright candidate optical counterpart was identified in Swift data (ATel #13257). We obtained spectroscopy of this source on UT 2019 Nov 4.2 with the Goodman Spectrograph on the SOAR telescope. We took both a low resolution spectrum (wavelength range 3800-7800 A, resolution 5.6 A) and a moderate resolution spectrum (5500-6750 A, resolution 1.7 A). The low resolution spectrum shows strong, broad, clearly double-peaked H-alpha and He II 4686 emission at Galactic velocities, with weaker emission from H-beta, H-gamma, and He I 5875 and 6678. The Bowen blend is not visible. In the medium resolution spectrum, the H-alpha has a FWHM of about 1740 km/s and an equivalent width of about 5 Ang. No absorption lines conceivably associated with the binary are seen.
The spectrum is very blue, with a spectral slope (in lambda--f_lambda) of ~ -3.22 after correcting for the modest foreground reddening of E(B-V) ~ 0.064 (Schlafly & Finkbeiner, 2011, ApJ, 737, 103). Consistent with this low reddening, no clear interstellar absorption lines are present in the spectra, other than perhaps a hint of Na D.
These spectroscopic properties provide strong evidence that MAXI J0637-430 is a new low-mass X-ray binary in outburst.
