[Paper Review] Morphology of the Light Curves for the X-ray Novae H1743-322 and GX339-4 during their Outbursts in 2005-2019

A. S. Grebenev, Yu. A. Dvorkovich+5 more|arXiv (Cornell University)|Sep 19, 2020

Astrophysical Phenomena and ObservationsPhysics and Astronomy43 references3 citations

TL;DR

This study analyzes X-ray light curves of the black hole X-ray novae H1743-322 and GX339-4 from 2005 to 2019 using SWIFT, RXTE, and MAXI data, identifying two primary outburst types—hard (H) and soft (S)—with subtypes including ultrabright (U) and intermediate (I). The authors demonstrate that these morphological differences are explained by the truncated accretion disk model, where the presence or absence of a cold, opaque outer disk determines spectral state transitions and light curve shape.

ABSTRACT

Based on long-term SWIFT, RXTE, and MAXI observations of the X-ray novae H1743-322 (IGR J17464-3213) and GX339-4, we have investigated the morphology and classified the light curves of their X-ray outbursts. In particular, we have confirmed the existence of two radically different types of outbursts, soft (S) and hard (H), in both sources and revealed their varieties, ultrabright (U) and intermediate (I). The properties and origin of the differences in the light curves of these outbursts are discussed in terms of the truncated accretion disk model.

Motivation & Objective

• . To classify the morphology of X-ray outbursts in H1743-322 and GX339-4 over a 15-year period.
• . To investigate the physical origin of distinct light curve shapes—particularly fast rise-exponential decay (FRED) versus symmetric profiles—across different outburst types.
• . To test the validity of the truncated accretion disk model in explaining spectral state transitions and light curve morphology in X-ray novae.
• . To determine whether outburst type (hard vs. soft) is determined by accretion rate and disk truncation radius dynamics.

Proposed method

• . Analyzed long-term X-ray light curves from SWIFT, RXTE, and MAXI observations of H1743-322 and GX339-4.
• . Classified outbursts into five types: hard (H), soft (S), ultrabright (U), intermediate (I), and possible micro-outbursts (M) based on light curve shape and spectral evolution.
• . Applied the truncated accretion disk model to interpret differences in light curve morphology, focusing on the boundary between cold, thin, opaque outer disk and hot, thick, optically thin inner disk.
• . Tracked spectral state transitions (hard, intermediate hard, soft, intermediate soft, two-component) across outbursts to correlate with light curve evolution.
• . Compared soft (2–4 keV) and hard (15–50 keV) band light curves to identify spectral component shifts, such as the emergence of a blackbody component during soft state.
• . Evaluated the role of Thomson scattering opacity and accretion rate in shaping symmetric versus asymmetric light curves, particularly in GX339-4 vs. H1743-322.

Experimental results

Research questions

• RQ1 . What are the dominant morphological types of X-ray outbursts in H1743-322 and GX339-4 from 2005 to 2019, and how do they differ?
• RQ2 . How do the light curve shapes (e.g., FRED vs. symmetric) relate to the accretion rate and disk truncation radius in the truncated disk model?
• RQ3 . Why do some outbursts show a sharp dip in the soft band during the transition from hard to soft state, and what causes the faint hard X-ray burst during the soft state?
• RQ4 . What determines whether an outburst is hard (H) or soft (S/U/I), and is this determined by the peak accretion rate or disk history?
• RQ5 . How does the presence or absence of a cold, opaque outer disk affect the spectral and light curve evolution of X-ray novae?

Key findings

• . The study confirms two primary outburst types—hard (H) and soft (S)—with subtypes ultrabright (U) and intermediate (I), observed in both H1743-322 and GX339-4.
• . Light curve morphology is explained by the truncated accretion disk model: soft outbursts (S, U, I) feature a cold, opaque outer disk that emits a blackbody component, while hard outbursts (H) lack this component.
• . The appearance of the soft blackbody component during phase II of soft outbursts is linked to a sharp drop in hard X-ray flux, indicating inward migration of the disk's inner edge.
• . In the hard spectral state (phases I and III), the soft X-ray component is not from the cold disk but is an extension of the hard power-law spectrum via Comptonization in the hot inner disk, as shown by spectral similarity between soft and hard bands.
• . GX339-4 exhibits nearly symmetric light curves due to higher outburst intensity and dominant Thomson scattering opacity, contrasting with H1743-322’s fast-rise-slow-decay (FRED) profiles.
• . A faint hard X-ray burst in the 15–50 keV band during phase II of soft outbursts in GX339-4 may result from increased temperature near the disk's inner edge or a transient hot corona, suggesting complex inner disk dynamics.