1,052 research outputs found
Identification of a Likely Radio Counterpart of the Rapid Burster
We have identified a likely radio counterpart to the low-mass X-ray binary
MXB 1730-335 (the Rapid Burster). The counterpart has shown 8.4 GHz radio
on/off behavior correlated with the X-ray on/off behavior as observed by the
RXTE/ASM during six VLA observations. The probability of an unrelated, randomly
varying background source duplicating this behavior is 1-3% depending on the
correlation time scale. The location of the radio source is RA 17h 33m 24.61s;
Dec -33d 23' 19.8" (J2000), +/- 0.1". We do not detect 8.4 GHz radio emission
coincident with type II (accretion-driven) X-ray bursts. The ratio of radio to
X-ray emission during such bursts is constrained to be below the ratio observed
during X-ray persistent emission at the 2.9-sigma level. Synchrotron bubble
models of the radio emission can provide a reasonable fit to the full data set,
collected over several outbursts, assuming that the radio evolution is the same
from outburst to outburst, but given the physical constraints the emission is
more likely to be due to ~hour-long radio flares such as have been observed
from the X-ray binary GRS 1915+105.Comment: 28 pages, 4 figures; accepted for publication in ApJ (no changes
Quiescent Thermal Emission from the Neutron Star in Aql X-1
We report on the quiescent spectrum measured with Chandra/ACIS-S of the
transient, type-I X-ray bursting neutron star Aql X-1, immediately following an
accretion outburst. The neutron star radius, assuming a pure hydrogen
atmosphere and hard power-law spectrum, is =13.4{+5}{-4} (d/5 \kpc)
km. Based on the historical outburst record of RXTE/ASM, the quiescent
luminosity is consistent with that predicted by Brown, Bildsten and Rutledge
from deep crustal heating, lending support to this theory for providing a
minimum quiescent luminosity of transient neutron stars. While not required by
the data, the hard power-law component can account for 18+/-8% of the 0.5-10
keV thermal flux. Short-timescale intensity variability during this observation
is less than 15% rms (3 sigma; 0.0001-1 Hz, 0.2-8 keV). Comparison between the
Chandra spectrum and three X-ray spectral observations made between Oct 1992
and Oct 1996 find all spectra consistent with a pure H atmosphere, but with
temperatures ranging from 145--168 eV, spanning a factor of 1.87+/-0.21 in
observed flux. The source of variability in the quiescent luminosity on long
timescales (greater than years) remains a puzzle. If from accretion, then it
remains to be explained why the quiescent accretion rate provides a luminosity
so nearly equal to that from deep crustal heating.Comment: 15 pages, 1 figure, 2 tables; ApJ, accepte
Work-related psychological health and psychological type among lead elders within the Newfrontiers network of churches in the United Kingdom
Building on a series of recent studies concerned with assessing work-related psychological health and psychological type among various groups of church leaders, this study reports new data provided by 134 Lead Elders within the Newfrontiers network of churches in the United Kingdom who completed the Francis Psychological Type Scales (FPTS) together with the two scales of the Francis Burnout Inventory (FBI) concerned with emotional exhaustion and satisfaction in ministry. Compared with other groups of church leaders, Lead Elders within the Newfrontiers network of churches reported lower levels of emotional exhaustion and higher levels of satisfaction in ministry. Compared with other groups of church leaders, there was a higher proportion of extraverts among Lead Elders within the Newfrontiers network of churches. There was only a weak association between psychological type and burnout
Further X-ray observations of EXO 0748-676 in quiescence: evidence for a cooling neutron star crust
In late 2008, the quasi-persistent neutron star X-ray transient and eclipsing
binary EXO 0748-676 started a transition from outburst to quiescence, after it
had been actively accreting for more than 24 years. In a previous work, we
discussed Chandra and Swift observations obtained during the first five months
after this transition. Here, we report on further X-ray observations of EXO
0748-676, extending the quiescent monitoring to 1.6 years. Chandra and
XMM-Newton data reveal quiescent X-ray spectra composed of a soft, thermal
component that is well-fitted by a neutron star atmosphere model. An additional
hard powerlaw tail is detected that changes non-monotonically over time,
contributing between 4 and 20 percent to the total unabsorbed 0.5-10 keV flux.
The combined set of Chandra, XMM-Newton and Swift data reveals that the thermal
bolometric luminosity fades from ~1E34 to 6E33 (D/7.4 kpc)^2 erg/s, whereas the
inferred neutron star effective temperature decreases from ~124 to 109 eV. We
interpret the observed decay as cooling of the neutron star crust and show that
the fractional quiescent temperature change of EXO 0748-676 is markedly smaller
than observed for three other neutron star X-ray binaries that underwent
prolonged accretion outbursts.Comment: Moderate textual revisions according to referee report, accepted for
publication in MNRA
Chandra X-Ray Observatory Observations of the Globular Cluster M71
We observed the nearby, low-density globular cluster M71 (NGC 6838) with the
Chandra X-ray Observatory to study its faint X-ray populations. Five X-ray
sources were found inside the cluster core radius, including the known
eclipsing binary millisecond pulsar (MSP) PSR J1953+1846A. The X-ray light
curve of the source coincident with this MSP shows marginal evidence for
periodicity at the binary period of 4.2 h. Its hard X-ray spectrum and
luminosity resemble those of other eclipsing binary MSPs in 47 Tuc, suggesting
a similar shock origin of the X-ray emission. A further 24 X-ray sources were
found within the half-mass radius, reaching to a limiting luminosity of 1.5
10^30 erg/s (0.3-8 keV). From a radial distribution analysis, we find that
18+/-6 of these 29 sources are associated with M71, somewhat more than
predicted, and that 11+/-6 are background sources, both galactic and
extragalactic. M71 appears to have more X-ray sources between L_X=10^30--10^31
erg/s than expected by extrapolating from other studied clusters using either
mass or collision frequency. We explore the spectra and variability of these
sources, and describe the results of ground-based optical counterpart searches.Comment: 36 pages including 7 figures and 8 tables, accepted by The
Astrophysical Journa
XMM-Newton observations of two black hole X-ray transients in quiescence
We report on XMM-Newton observations of GRO J1655-40 and GRS 1009-45, which
are two black hole X-ray transients currently in their quiescent phase. GRO
J1655-40 was detected with a 0.5 - 10 keV luminosity of 5.9 10^{31} erg/s. This
luminosity is comparable to a previous Chandra measurement, but ten times lower
than the 1996 ASCA value, most likely obtained when the source was not yet in a
true quiescent state. Unfortunately, XMM-Newton failed to detect GRS 1009-45. A
stringent upper limit of 8.9 10^{30} erg/s was derived by combining data from
the EPIC-MOS and PN cameras.
The X-ray spectrum of GRO J1655-40 is very hard as it can be fitted with a
power law model of photon index ~ 1.3 +/- 0.4. Similarly hard spectra have been
observed from other systems; these rule out coronal emission from the secondary
or disk flares as the origin of the observed X-rays. On the other hand, our
observations are consistent with the predictions of the disc instability model
in the case that the accretion flow forms an advection dominated accretion flow
(ADAF) at distances less than a fraction ~ 0.1 - 0.3) of the circularization
radius. This distance corresponds to the greatest extent of the ADAF that is
thought to be possible.Comment: 6 pages, 4 figures. Submitted to Astronomy and Astrophysic
A Keck/DEIMOS spectroscopic survey of faint Galactic satellites: searching for the least massive dwarf galaxies
[abridged] We present the results of a spectroscopic survey of the recently
discovered faint Milky Way satellites Boo, UMaI, UMaII and Wil1. Using the
DEIMOS spectrograph on Keck, we have obtained samples that contain from 15 to
85 probable members of these satellites for which we derive radial velocities
precise to a few km/s down to i~21-22. About half of these stars are observed
with a high enough S/N to estimate their metallicity to within \pm0.2 dex. From
this dataset, we show that UMaII is the only object that does not show a clear
radial velocity peak. However, the measured systemic radial velocity
(v_r=115\pm5 km/s) is in good agreement with recent simulations in which this
object is the progenitor of the recently discovered Orphan Stream. The three
other satellites show velocity dispersions that make them highly dark-matter
dominated systems. In particular the Willman 1 object is not a globular cluster
given its metallicity scatter over -2.0<[Fe/H]<-1.0 and is therefore almost
certainly a dwarf galaxy or dwarf galaxy remnant. We measure a radial velocity
dispersion of only 4.3_{-1.3}^{+2.3} km/s around a systemic velocity of
-12.3\pm2.3 km/s which implies a mass-to-light ratio of ~700 and a total mass
of ~5x10^5 Msun for this satellite, making it the least massive satellite
galaxy known to date. Such a low mass could mean that the 10^7 Msun limit that
had until now never been crossed for Milky Way and Andromeda satellite galaxies
may only be an observational limit and that fainter, less massive systems exist
within the Local Group. However, more modeling and an extended search for
potential extra-tidal stars are required to rule out the possibility that these
systems have not been significantly heated by tidal interaction.Comment: 24 pages, 11 figures, MNRAS accepte
The X-ray spectrum of a disk illuminated by ions
The X-ray spectrum from a cool disk embedded in an ion supported torus is
computed. The interaction of the hot ions with the disk increases the hard
X-ray luminosity of the system}. A surface layer of the disk is heated by the
protons from the torus. The Comptonized spectrum produced by this layer has a
shape that depends only weakly on the incident energy flux and the distance
from the accreting compact object. It consists of a `blue bump' of
unComptonized soft photons and a flat high energy tail, reminiscent of the
observed spectra. The hard tail becomes flatter as the thermalization depth in
the cool disk is increased. Further evidence for ion illumination are the Li
abundance in the secondaries of low mass X-ray binaries and the 450 keV lines
sometimes seen in black-hole transient spectra.Comment: 7p, to appear in Monthly Notice
Evidence for crust cooling in the transiently accreting 11-Hz X-ray pulsar in the globular cluster Terzan 5
The temporal heating and subsequent cooling of the crusts of transiently
accreting neutron stars carries unique information about their structure and a
variety of nuclear reaction processes. We report on a new Chandra Director's
Discretionary Time observation of the globular cluster Terzan 5, aimed to
monitor the transiently accreting 11-Hz X-ray pulsar IGR J17480-2446 after the
cessation of its recent 10-week long accretion outburst. During the
observation, which was performed ~125 days into quiescence, the source displays
a thermal spectrum that fits to a neutron star atmosphere model with a
temperature for an observer at infinity of kT~92 eV. This is ~10% lower than
found ~75 days earlier, yet ~20% higher than the quiescent base level measured
prior to the recent outburst. This can be interpreted as cooling of the
accretion-heated neutron star crust, and implies that crust cooling is
observable after short accretion episodes. Comparison with neutron star thermal
evolution simulations indicates that substantial heat must be released at
shallow depth inside the neutron star, which is not accounted for in current
nuclear heating models.Comment: 5 pages, 3 figures, 1 table. Minor changes according to referee
report. MNRAS Letters in pres
INTEGRAL discovery of a bright highly obscured galactic X-ray binary source IGR J16318-4848
INTEGRAL regularly scans the Galactic plane to search for new objects and in
particular for absorbed sources with the bulk of their emission above 10-20
keV. The first new INTEGRAL source was discovered on 2003 January 29, 0.5
degree from the Galactic plane and was further observed in the X-rays with
XMM-Newton. This source, IGR J16318-4848, is intrinsically strongly absorbed by
cold matter and displays exceptionally strong fluorescence emission lines. The
likely infrared/optical counterpart indicates that IGR J16318-4848 is probably
a High Mass X-Ray Binary neutron star or black hole enshrouded in a Compton
thick environment. Strongly absorbed sources, not detected in previous surveys,
could contribute significantly to the Galactic hard X-ray background between 10
and 200 keV.Comment: 6 pages, 4 figures (fig 1 quality lowered), accepted for publication
in A&A letters (INTEGRAL special issue
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