The early ultraviolet, optical, and radio evolution of the soft X-ray transient GRO J0422+32

Details The early ultraviolet, optical, and radio evolution of the soft X-ray transient GRO J0422+32 The early ultraviolet, optical, and radio evolution of the soft X-ray transient GRO J0422+32

Oct 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...434..698s&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 434, no. 2, p. 698-706

Astronomy and Astrophysics

Astronomy

61

Carbon, Helium, Line Shape, Nitrogen, Novae, Radio Astronomy, Radio Spectra, Spectral Energy Distribution, Ultraviolet Astronomy, Ultraviolet Spectra, Visible Spectrum, X Ray Binaries, Astronomical Photometry, Astronomical Spectroscopy, Balmer Series, Distance, Gamma Ray Observatory, Iue, Light Curve, Sky Surveys (Astronomy), Stellar Luminosity, Very Large Array (Vla)

Scientific paper

We have monitored the evolution of the transient X-ray source GRO J0422+32 from approximately 2 weeks postdiscovery into its early decline phase at ultraviolet, optical, and radio wavelengths. Optical and ultraviolet spectra exhibit numerous, but relatively weak, high-excitation emission lines such as those arising from He II, N III, N V, and C IV superposed on an intrinsically blue continuum. High-resolution optical spectroscopy reveals line profiles which are double peaked, and in the case of the higher order Balmer lines, superposed on a broad absorption profile. The early outburst optical-ultraviolet continuum energy distribution is well represented by a two power-law fit with a break at approximately equal 4000 A. Radio observations with the Very Large Array (VLA) reveal a flat-spectrum source, slowly increasing in intensity at the earliest epochs observed, followed by an approximate power-law decay light curve with an index of -1. Light curves for each wavelength domain are presented and discussed. Notable are the multiple secondary outbursts seen in the optical more than 1 year postdiscovery, and spectral changes associated with secondary rises seen in the radio and UV. We find that the ultraviolet and optical characteristics of GRO J0422+32 as well as its radio evolution, are similar to other recent well-observed soft X-ray transients (also called X-ray novae) such as Cen X-4, A0620-00 (V616 Mon), and Nova Muscae 1991 (GS 1124-683), suggesting that GRO J0422+32 is also a member of that subclass of low-mass X-ray binaries. We present definitive astrometric determination of the source position, and place an upper limit of R approximately equals 20 from our analysis of the Palomar Observatory Sky Survey (POSS). Additionally, we derive distinct values for color excess from analysis of the optical (E(B-V) = 0.23) and ultraviolet (E(B-V) = 0.4) data, suggesting an intrinsic magnitude of 19-19.5 for the progenitor if it is mid-K dwarf. This leads to a likely range of 2.4-3.0 kpc for the source distance, which is consistent with our separate estimate of 2.4 +/- 0.4 kpc based on measurement of the NaD interstellar line profile. Adopting 2.4 kpc and E(B-V) = 0.23, the outburst absolute magnitude was M approximately equals 0.0, which is a typical value for this class of objects.

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