16,405 research outputs found
Swift J1734.5-3027: a new long type-I X-ray bursting source
Swift J1734.5-3027 is a hard X-ray transient discovered by Swift while
undergoing an outburst in September 2013. Archival observations showed that
this source underwent a previous episode of enhanced X-ray activity in May-June
2013. In this paper we report on the analysis of all X-ray data collected
during the outburst in September 2013, the first that could be intensively
followed-up by several X-ray facilities. Our data-set includes INTEGRAL, Swift,
and XMM-Newton observations. From the timing and spectral analysis of these
observations, we show that a long type-I X-ray burst took place during the
source outburst, making Swift J1734.5-3027 a new member of the class of
bursting neutron star low-mass X-ray binaries. The burst lasted for about 1.9
ks and reached a peak flux of (6.01.8)10 erg cm
s in the 0.5-100 keV energy range. The estimated burst fluence in the
same energy range is (1.100.10)10 erg cm. By
assuming that a photospheric radius expansion took place during the first
200 s of the burst and that the accreted material was predominantly
composed by He, we derived a distance to the source of 7.21.5 kpc.Comment: Accepted for publication on A&
Two years of monitoring Supergiant Fast X-ray Transients with Swift
We present two years of intense Swift monitoring of three SFXTs, IGR
J16479-4514, XTE J1739-302, and IGR J17544-2619 (since October 2007).
Out-of-outburst intensity-based X-ray (0.3-10keV) spectroscopy yields absorbed
power laws with by hard photon indices (G~1-2). Their outburst broad-band
(0.3-150 keV) spectra can be fit well with models typically used to describe
the X-ray emission from accreting NSs in HMXBs. We assess how long each source
spends in each state using a systematic monitoring with a sensitive instrument.
These sources spend 3-5% of the total in bright outbursts. The most probable
flux is 1-2E-11 erg cm^{-2} s^{-1} (2-10 keV, unabsorbed), corresponding to
luminosities in the order of a few 10^{33} to 10^{34} erg s^{-1} (two orders of
magnitude lower than the bright outbursts). The duty-cycle of inactivity is 19,
39, 55%, for IGR J16479-4514, XTE J1739-302, and IGR J17544-2619, respectively.
We present a complete list of BAT on-board detections further confirming the
continued activity of these sources. This demonstrates that true quiescence is
a rare state, and that these transients accrete matter throughout their life at
different rates. X-ray variability is observed at all timescales and
intensities we can probe. Superimposed on the day-to-day variability is
intra-day flaring which involves variations up to one order of magnitude that
can occur down to timescales as short as ~1ks, and whichcan be explained by the
accretion of single clumps composing the donor wind with masses
M_cl~0.3-2x10^{19} g. (Abridged)Comment: Accepted for publication in MNRAS. 17 pages, 11 figures, 8 table
Coarse-grained simulations of DNA overstretching
We use a recently developed coarse-grained model to simulate the
overstretching of duplex DNA. Overstretching at 23C occurs at 74 pN in the
model, about 6-7 pN higher than the experimental value at equivalent salt
conditions. Furthermore, the model reproduces the temperature dependence of the
overstretching force well. The mechanism of overstretching is always
force-induced melting by unpeeling from the free ends. That we never see S-DNA
(overstretched duplex DNA), even though there is clear experimental evidence
for this mode of overstretching under certain conditions, suggests that S-DNA
is not simply an unstacked but hydrogen-bonded duplex, but instead probably has
a more exotic structure.Comment: 11 pages, 11 figure
The effect of topology on the structure and free energy landscape of DNA kissing complexes
We use a recently developed coarse-grained model for DNA to study kissing
complexes formed by hybridization of complementary hairpin loops. The binding
of the loops is topologically constrained because their linking number must
remain constant. By studying systems with linking numbers -1, 0 or 1 we show
that the average number of interstrand base pairs is larger when the topology
is more favourable for the right-handed wrapping of strands around each other.
The thermodynamic stability of the kissing complex also decreases when the
linking number changes from -1 to 0 to 1. The structures of the kissing
complexes typically involve two intermolecular helices that coaxially stack
with the hairpin stems at a parallel four-way junction
The 2015 outburst of the accreting millisecond pulsar IGR J17511-3057 as seen by INTEGRAL, Swift and XMM-Newton
We report on INTEGRAL, Swift and XMM-Newton observations of IGR J17511-3057
performed during the outburst that occurred between March 23 and April 25,
2015. The source reached a peak flux of 0.7(2)E-9 erg/cm/s and decayed to
quiescence in approximately a month. The X-ray spectrum was dominated by a
power-law with photon index between 1.6 and 1.8, which we interpreted as
thermal Comptonization in an electron cloud with temperature > 20 keV . A broad
({\sigma} ~ 1 keV) emission line was detected at an energy (E =
6.9 keV) compatible with the K{\alpha} transition of ionized
Fe, suggesting an origin in the inner regions of the accretion disk. The
outburst flux and spectral properties shown during this outburst were
remarkably similar to those observed during the previous accretion event
detected from the source in 2009. Coherent pulsations at the pulsar spin period
were detected in the XMM-Newton and INTEGRAL data, at a frequency compatible
with the value observed in 2009. Assuming that the source spun up during the
2015 outburst at the same rate observed during the previous outburst, we derive
a conservative upper limit on the spin down rate during quiescence of 3.5E-15
Hz/s. Interpreting this value in terms of electromagnetic spin down yields an
upper limit of 3.6E26 G/cm to the pulsar magnetic dipole (assuming a
magnetic inclination angle of 30{\deg}). We also report on the detection of
five type-I X-ray bursts (three in the XMM-Newton data, two in the INTEGRAL
data), none of which indicated photospheric radius expansion.Comment: 10 pages, 7 figures, accepted for publication in A&
New generation B-Field and RAD-tolerant DCDC power converter for on-detector operation
The increase in the number of readout channels in new detectors, like the
Micro Pattern Gas Detectors (MPGD), in the order of several millions, requires
a large amount of electrical power to supply the front-end electronics, up to
hundreds kW. If this power is generated at long distances from the detector,
the voltage drop on the connection cables puts serious constraints to the
supply current, to the wire cross-section and to the power distribution. A
large amount of voltage drop on the cables, apart an increased power
dissipation on wire resistance, determines regulation issues on the load in
case of current transients. To mitigate these problems, a new generation DC/DC
converter, working in a heavily hostile environment and with a power density
greater than 200 W/dm3, was developed. It is modular, with up to four
independent modules, eight channels each, collected in a water-cooled crate,
and can supply the load with an adjustable 10 to 12 V output up to 170 W per
channel. In this contribution, the design constraints of such a converter are
analysed, taking as a basis the environmental, electrical and mechanical
requirements of the ATLAS New Small Wheel (NSW) project. Thermal considerations
require the converter to be water-cooled, and the dimensional constraints
impose the adoption of an innovative design to convey the dissipated heat
towards the heat exchanger. The control and monitoring system allows for the
full remote management of the converter. Main electrical parameters were
measured and are reported. The converter was also characterized in a harsh
working environment, with radiation tests in the CERN CHARM facility beyond the
limits estimated for ten years operation in ATLAS, and with magnetic field
tests in various orientations, using different magnets at CERN up to 1.3 T.Comment: (7 pages, 10 figures, TWEPP 2023 conference
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