Michelle Buxton - Yale

Michelle Buxton
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Michelle Buxton

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High Energy Astrophysical Phenomena (8)
Astrophysics (5)
Solar and Stellar Astrophysics (4)
Cosmology and Nongalactic Astrophysics (1)
Astrophysics of Galaxies (1)

Publications Authored By Michelle Buxton

We investigated the relation between compact jet emission and X-ray variability properties of all black hole transients with multiwavelength coverage during their outburst decays. We studied the evolution of all power spectral components (including low frequency quasi-periodic oscillations), and related this evolution to changes in jet properties tracked by radio and infrared observations. We grouped sources according to their tracks in radio/X-ray luminosity relation, and show that the standards show stronger broadband X-ray variability than outliers at a given X-ray luminosity when the compact jet turned on. Read More

We perform time-dependent, spatially-resolved simulations of blazar emission to evaluate several flaring scenarios related to magnetic-field amplification and enhanced particle acceleration. The code explicitly accounts for light-travel-time effects and is applied to flares observed in the flat spectrum radio quasar (FSRQ) PKS 0208-512, which show optical/{\gamma}-ray correlation at some times, but orphan optical flares at other times. Changes in both the magnetic field and the particle acceleration efficiency are explored as causes of flares. Read More

We analyze a large set of new and archival photometric and spectroscopic observations of LMC X-3 to arrive at a self-consistent dynamical model for the system. Using echelle spectra obtained with the MIKE instrument on the 6.5m Magellan Clay telescope and the UVES instrument on the second 8. Read More

The X-ray persistence and characteristically soft spectrum of the black hole X-ray binary LMC X-3 make this source a touchstone for penetrating studies of accretion physics. We analyze a rich, 10-year collection of optical/infrared (OIR) time-series data in conjunction with all available contemporaneous X-ray data collected by the ASM and PCA detectors aboard the Rossi X-ray Timing Explorer. A cross-correlation analysis reveals an X-ray lag of ~2 weeks. Read More

We examine ~10 years of photometric data and find that the black hole X-ray binary V4641 Sgr has two optical states, passive and active, during X-ray quiescence. The passive state is dominated by ellipsoidal variations and is stable in the shape and variability of the light curve. The active state is brighter and more variable. Read More

Compact, steady jets are observed in the near infrared and radio bands in the hard state of Galactic black hole transients as their luminosity decreases and the source moves towards a quiescent state. Recent radio observations indicate that the jets turn off completely in the soft state, therefore multiwavelength monitoring of black hole transients are essential to probe the formation of jets. In this work we conducted a systematic study of all black hole transients with near infrared and radio coverage during their outburst decays. Read More

We report multiwavelength observations of the black hole transient GX 339-4 during its outburst decay in 2011 using the data from RXTE, Swift and SMARTS. Based on the X-ray spectral, temporal, and the optical/infrared (OIR) properties, the source evolved from the soft-intermediate to the hard state. Twelve days after the start of the transition towards the hard state, a rebrightening was observed simultaneously in the optical and the infrared bands. Read More

We present the optical/infra-red lightcurve (O/IR) of the black hole X-ray binary GX 339-4 collected at the SMARTS 1.3m telescope from 2002 to 2010. During this time the source has undergone numerous state transitions including hard-to-soft state transitions when we see large changes in the near-IR flux accompanied by modest changes in optical flux, and three rebrightening events in 2003, 2005 and 2007 after GX 339-4 transitioned from the soft state to the hard. Read More

We present an improved method for determining the mass of neutron stars in eclipsing X-ray pulsar binaries and apply the method to six systems, namely Vela X-1, 4U 1538-52, SMC X-1, LMC X-4, Cen X-3, and Her X-1. In previous studies to determine neutron star mass, the X-ray eclipse duration has been approximated analytically by assuming the companion star is spherical with an effective Roche lobe radius. We use a numerical code based on Roche geometry with various optimizers to analyze the published data for these systems, which we supplement with new spectroscopic and photometric data for 4U 1538-52. Read More

A 24 day period for the low-mass X-ray binary GX 13+1 was previously proposed on the basis of 7 years of RXTE ASM observations (Corbet 2003) and it was suggested that this was the orbital period of the system. This would make it the one of the longest known orbital periods for a Galactic low-mass X-ray binary powered by Roche lobe overflow. We present here the results of: (i) K-band photometry obtained with the SMARTS Consortium CTIO 1. Read More

Affiliations: 1San Diego State, 2University of Warwick, 3CfA, 4CfA, 5CfA, 6CfA, 7CfA, 8Cal-Poly Pomona, 9MIT, 10MIT, 11Yale, 12Yale, 13Yale
Category: Astrophysics

We present a dynamical model of the high mass X-ray binary LMC X-1 based on high-resolution optical spectroscopy and extensive optical and near-infrared photometry. From our new optical data we find an orbital period of P=3.90917 +/- 0. Read More

Affiliations: 1SSL/UCB, 2Sabanci Univ., 3Univ. of Iowa, 4Univ. of Amsterdam, 5AIM - Univ. Paris VII and CEA Saclay, 6CASS/UCSD, 7Univ. of Southampton, 8Yale Univ., 9Yale Univ.
Category: Astrophysics

A major question in the study of black hole binaries involves our understanding of the accretion geometry when the sources are in the hard state. In this state, the X-ray energy spectrum is dominated by a hard power-law component and radio observations indicate the presence of a steady and powerful compact jet. Although the common hard state picture is that the accretion disk is truncated, perhaps at hundreds of gravitational radii from the black hole, recent results for the recurrent transient GX 339-4 by Miller and co-workers show evidence for optically thick material very close to the black hole's innermost stable circular orbit. Read More

(Abridged) We report on RXTE and optical/near-infrared (nIR) observations of the black hole transient GX 339-4, made over a time span of 8 months in 2002 and covering the initial rise and transition from a hard to a soft spectral state. Two patterns of correlated X-ray-optical/nIR behavior were found. During the hard state the optical/nIR and X-ray fluxes correlated well, with a nIR vs. Read More

Optical spectroscopic observations of GX 339-4 were carried out between 1998 May (X-ray high state) and 1999 May (X-ray low state) over 7 epochs. The equivalent width of Halpha increased during the high state then decreased during the low state. The equivalent width of HeII 4686 decreased over both states. Read More

We have examined the success rates of 19 American, Canadian, Australian, and Dutch graduate programs in producing astronomers. A 20-year baseline was considered (1975-1994), incorporating 897 PhD recipients. The major conclusion from our study is that the fraction of PhD graduates still involved in astronomical research is surprisingly insensitive to the institutional source of one's PhD. Read More