1,325 research outputs found
The Accretion Flow - Discrete Ejection Connection in GRS 1915+105
The microquasar GRS~1915+105 is known for its spectacular discrete ejections.
They occur unexpectedly, thus their inception escapes direct observation. It
has been shown that the X-ray flux increases in the hours leading up to a major
ejection. In this article, we consider the serendipitous interferometric
monitoring of a modest version of a discrete ejection described in Reid et al.
(2014) that would have otherwise escaped detection in daily radio light curves.
The observation begins hour after the onset of the ejection, providing
unprecedented accuracy on the estimate of the ejection time. The astrometric
measurements allow us to determine the time of ejection as , i.e., within a precision of 41 minutes (95\%
confidence). Just like larger flares, we find that the X-ray luminosity
increases in last 2 - 4 hours preceding ejection. Our finite temporal
resolution indicates that this elevated X-ray flux persists within
minutes of the ejection with 95\% confidence, the
highest temporal precision of the X-ray - superluminal ejection connection to
date. This observation provides direct evidence that the physics that launches
major flares occurs on smaller scales as well (lower radio flux and shorter
ejection episodes). The observation of a X-ray spike prior to a discrete
ejection, although of very modest amplitude suggests that the process linking
accretion behavior to ejection is general from the smallest scales to high
luminosity major superluminal flares.Comment: To appear in Ap
XMM-Newton observations of five INTEGRAL sources located towards the Scutum Arm
Results are presented for XMM-Newton observations of five hard X-ray sources
discovered by INTEGRAL in the direction of the Scutum Arm. Each source received
more than 20 ks of effective exposure time. We provide refined X-ray positions
for all five targets enabling us to pinpoint the most likely counterpart in
optical/infrared archives. Spectral and timing information (much of which are
provided for the first time) allow us to give a firm classification for IGR
J18462-0223 and to offer tentative classifications for the others. For IGR
J18462-0223, we discovered a coherent pulsation period of 997+-1 s which we
attribute to the spin of a neutron star in a highly-obscured (nH = 2e23 /cm2)
high-mass X-ray binary (HMXB). This makes IGR J18462-0223 the seventh
supergiant fast X-ray transient (SFXT) candidate with a confirmed pulsation
period. IGR J18457+0244 is a highly-absorbed (nH = 8e23 /cm2) source in which
the possible detection of an iron line suggests an active galactic nucleus
(AGN) of type Sey-2 situated at z = 0.07(1). A periodic signal at 4.4 ks could
be a quasi-periodic oscillation which would make IGR J18457+0244 one of a
handful of AGN in which such features have been claimed, but a slowly-rotating
neutron star in an HMXB can not be ruled out. IGR J18482+0049 represents a new
obscured HMXB candidate with nH = 4e23 /cm2. We tentatively propose that IGR
J18532+0416 is either an AGN or a pulsar in an HMXB system. The X-ray spectral
properties of IGR J18538-0102 are consistent with the AGN classification that
has been proposed for this source.Comment: 15 pages, 9 figures, 4 tables: accepted for publication in Ap
- …