86 research outputs found
Discovery and Monitoring of a new Black Hole Candidate XTE J1752-223 with RXTE: RMS spectrum evolution, BH mass and the source distance
We report on the discovery and monitoring observations of a new galactic
black hole candidate XTE J1752-223 by Rossi X-ray Timing Explorer (RXTE). The
new source appeared on the X-ray sky on October 21 2009 and was active for
almost 8 months. Phenomenologically, the source exhibited the
low-hard/high-soft spectral state bi-modality and the variability evolution
during the state transition that matches standard behavior expected from a
stellar mass black hole binary. We model the energy spectrum throughout the
outburst using a generic Comptonization model assuming that part of the input
soft radiation in the form of a black body spectrum gets reprocessed in the
Comptonizing medium. We follow the evolution of fractional root-mean-square
(RMS) variability in the RXTE/PCA energy band with the source spectral state
and conclude that broad band variability is strongly correlated with the source
hardness (or Comptonized fraction). We follow changes in the energy
distribution of rms variability during the low-hard state and the state
transition and find further evidence that variable emission is strongly
concentrated in the power-law spectral component. We discuss the implication of
our results to the Comptonization regimes during different spectral states.
Correlations of spectral and variability properties provide measurements of the
BH mass and distance to the source. The spectral-timing correlation scaling
technique applied to the RXTE observation during the hard-to-soft state
transition indicates a mass of the BH in XTE J1752-223 between 8 and 11 solar
masses and a distance to the source about 3.5 kiloparsec.Comment: Accepted for publication in The Astrophysical Journa
Diverse Long-Term Variability of Five Candidate High-Mass X-ray Binaries from Swift Burst Alert Telescope Observations
We present an investigation of long-term modulation in the X-ray light curves
of five little-studied candidate high-mass X-ray binaries using the Swift Burst
Alert Telescope. IGR J14488-5942 and AX J1700.2-4220 show strong modulation at
periods of 49.6 and 44 days, respectively, which are interpreted as orbital
periods of Be star systems. For IGR J14488-5942, observations with Swift X-ray
Telescope show a hint of pulsations at 33.4 s. For AX J1700.2-4220, 54 s
pulsations were previously found with XMM. Swift J1816.7-1613 exhibits
complicated behavior. The strongest peak in the power spectrum is at a period
near 150 days, but this conflicts with a determination of a period of 118.5
days by La Parola et al. (2014). AX J1820.5-1434 has been proposed to exhibit
modulation near 54 days, but the extended BAT observations suggest modulation
at slightly longer than double this at approximately 111 days. There appears to
be a long-term change in the shape of the modulation near 111 days, which may
explain the apparent discrepancy. The X-ray pulsar XTE J1906+090, which was
previously proposed to be a Be star system with an orbital period of ~30 days
from pulse timing, shows peaks in the power spectrum at 81 and 173 days. The
origins of these periods are unclear, although they might be the orbital period
and a superorbital period respectively. For all five sources, the long-term
variability, together with the combination of orbital and proposed pulse
periods, suggests that the sources contain Be star mass donors.Comment: Accepted for publication in The Astrophysical Journal. 15 pages, 27
figures. (v2 corrects citation
A Study of the 20 Day Superorbital Modulation in the High-Mass X-ray Binary IGR J16493-4348
We report on Nuclear Spectroscopic Telescope Array (NuSTAR), Neil Gehrels
Swift Observatory (Swift) X-ray Telescope (XRT) and Swift Burst Alert Telescope
(BAT) observations of IGR J16493-4348, a wind-fed Supergiant X-ray Binary
(SGXB) showing significant superorbital variability. From a discrete Fourier
transform of the BAT light curve, we refine its superorbital period to be
20.058 0.007 days. The BAT dynamic power spectrum and a fractional root
mean square analysis both show strong variations in the amplitude of the
superorbital modulation, but no observed changes in the period were found. The
superorbital modulation is significantly weaker between MJD 55,700 and MJD
56,300. The joint NuSTAR and XRT observations, which were performed near the
minimum and maximum of one cycle of the 20 day superorbital modulation, show
that the flux increases by more than a factor of two between superorbital
minimum and maximum. We find no significant changes in the 3-50 keV pulse
profiles between superorbital minimum and maximum, which suggests a similar
accretion regime. Modeling the pulse-phase averaged spectra we find a possible
Fe K emission line at 6.4 keV at superorbital maximum. The feature is
not significant at superorbital minimum. While we do not observe any
significant differences between the pulse-phase averaged spectral continua
apart from the overall flux change, we find that the hardness ratio near the
broad main peak of the pulse profile increases from superorbital minimum to
maximum. This suggests the spectral shape hardens with increasing luminosity.
We discuss different mechanisms that might drive the observed superorbital
modulation.Comment: 17 pages, 14 figures, 3 tables, accepted for publication in The
Astrophysical Journal on 2019 May 1
BatAnalysis -- A Comprehensive Python Pipeline for Swift BAT Survey Analysis
The Swift Burst Alert Telescope (BAT) is a coded aperture gamma-ray
instrument with a large field of view that primarily operates in survey mode
when it is not triggering on transient events. The survey data consists of
eighty-channel detector plane histograms that accumulate photon counts over
time periods of at least 5 minutes. These histograms are processed on the
ground and are used to produce the survey dataset between and keV.
Survey data comprises of all BAT data by volume and allows for the
tracking of long term light curves and spectral properties of cataloged and
uncataloged hard X-ray sources. Until now, the survey dataset has not been used
to its full potential due to the complexity associated with its analysis and
the lack of easily usable pipelines. Here, we introduce the BatAnalysis python
package which provides a modern, open-source pipeline to process and analyze
BAT survey data. BatAnalysis allows members of the community to use BAT survey
data in more advanced analyses of astrophysical sources including pulsars,
pulsar wind nebula, active galactic nuclei, and other known/unknown transient
events that may be detected in the hard X-ray band. We outline the steps taken
by the python code and exemplify its usefulness and accuracy by analyzing
survey data from the Crab Pulsar, NGC 2992, and a previously uncataloged MAXI
Transient. The BatAnalysis package allows for 18 years of BAT survey to
be used in a systematic way to study a large variety of astrophysical sources.Comment: 13 pages, 6 figures; Submitted to ApJ; BatAnalysis github link is:
https://github.com/parsotat/BatAnalysis, comments/suggestions are welcome
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