17 research outputs found
Detection of anti-correlated hard X-ray time lag in Cygnus X-3
The wide-band X-ray spectra of the high mass X-ray binary Cygnus X-3 exhibits
a pivoting behavior in the `low' (as well as `hard') state, correlated to the
radio emission. The time scale of the soft and hard X-rays' anti-correlation,
which gave rise to the pivoting feature, was found to be less than a day from
the monitoring observations by RXTE--ASM and CGRO--BATSE. In this Letter we
report the detection of a lag of 1000s in the anti-correlation of
the hard X-ray emission (20--50 keV) to that of the soft X-ray emission (2--7
keV), which may be attributed to the viscous time scale of flow of matter in
the accretion disk. This suggests the geometrical picture of a truncated
accretion disc with a Compton cloud inside the disc, the relative sizes of
which determine the spectral shape. Any change in the disc structure will take
place in a viscous time scale, with corresponding anti-correlated change in the
Compton cloud. We also report the pivoting in the spectra in one span of a
pointed observation when an episode of the rearranging of the accretion system
is serendipitously observed. This is the first such observation of hard X-ray
delay seen in the persistent Galactic microquasars, within the precincts of the
hard state.Comment: Accepted in The Astrophysical Journal (Letters): in pres
Low frequency radio spectrum and spectral turnover of LS 5039
LS 5039, a possible black hole x-ray binary, was recently observed with Giant
Meterwave Radio Telescope. The observed spectrum presented here shows that the
spectrum is inverted at the low frequency. When combined with the archival data
with orbital phase similar to the present observations, it shows a clear
indication of a spectral turnover. The combined data are fitted with a broken
power-law and the break frequency signifies a possible spectral turnover of the
spectrum around 964 MHz. Truly simultaneous observations in radio wavelength
covering a wide range of frequencies are required to fix the spectrum and the
spectral turn over which will play a crucial role in developing a deeper
understanding of the radio emitting jet in LS 5039.Comment: Accepted for publication in MNRAS Letter
XMM-Newton view of the ultra-luminous X-ray sources in M51
(Abridged) We present results based on XMM-Newton observation of the nearby
spiral galaxy M51 (NGC5194 and NGC5195). Two ULXs in NGC5194 show evidence for
short-term variability, and all but two ULXs vary on long time scales (over a
baseline of 2.5 years), providing strong evidence that these are accreting
sources. One ULX in NGC5194, source 69, shows possible periodic behavior in its
X-ray flux. We derive a period of 5925\pm200s at a confidence level of 95%,
based on three cycles. This period is lower than the period of 7620\pm500s
derived from a Chandra observation in 2000. The higher effective area of
XMM-Newton enables us to identify multiple components in the spectra of ULXs.
Most ULXs require at least two components -- a power law and a soft X-ray
excess component which is modeled by an optically thin plasma or multicolor
disk blackbody (MCD). However, the soft excess emission, inferred from all ULXs
except source 69, are unlikely to be physically associated with the ULXs as
their strengths are comparable to that of the surrounding diffuse emission. The
soft excess emission of source 69 is well described either by a two temperature
mekal plasma or a single temperature mekal plasma kT~690eV) and an MCD
(kT~170eV). The MCD component suggests a cooler accretion disks compared to
that in Galactic X-ray binaries and consistent with that expected for
intermediate mass black holes (IMBHs). An iron line (EW 700eV) or K absorption
edge at 7.1keV is present in the EPIC PN spectrum of source 26. The spectrum of
the ULX in NGC5195, source 12, is consistent with a simple power law.Comment: 20 pages, To appear in Ap