179 research outputs found
Discovery of a Peculiar Dip from GX 301-2
We present temporal and spectral properties of a unique X-ray dip in GX 301-2
as seen with Rossi X-ray Timing Explorer in May 2010. The X-ray pulsation from
the source gradually declined prior to the dip, disappears for one spin cycle
during the dip and is abruptly restored in the spin cycle immediately after the
dip. Moreover, the phase-integrated spectrum of the source becomes softer
before and during the dip and it quickly hardens again following the dip. Our
findings indicate the fact that the mechanism for pulsations gradually turned
off briefly and underlying dim and softer emission likely from the accretion
column became observable in the brief absence of high level emission due to
wind accretion.Comment: Accepted for publication in A&A Letter
Detection of Very Low-Frequency Quasi-Periodic Oscillations in the 2015 Outburst of V404 Cygni
In June 2015, the black hole X-ray binary (BHXRB) V404 Cygni went into
outburst for the first time since 1989. Here, we present a comprehensive search
for quasi-periodic oscillations (QPOs) of V404 Cygni during its recent
outburst, utilizing data from six instruments on board five different X-ray
missions: Swift/XRT, Fermi/GBM, Chandra/ACIS, INTEGRAL's IBIS/ISGRI and JEM-X,
and NuSTAR. We report the detection of a QPO at 18 mHz simultaneously with both
Fermi/GBM and Swift/XRT, another example of a rare but slowly growing new class
of mHz-QPOs in BHXRBs linked to sources with a high orbital inclination.
Additionally, we find a duo of QPOs in a Chandra/ACIS observation at 73 mHz and
1.03 Hz, as well as a QPO at 136 mHz in a single Swift/XRT observation that can
be interpreted as standard Type-C QPOs. Aside from the detected QPOs, there is
significant structure in the broadband power, with a strong feature observable
in the Chandra observations between 0.1 and 1 Hz. We discuss our results in the
context of current models for QPO formation.Comment: 17 pages, 9 figures, published in Ap
SGR J1550-5418 bursts detected with the Fermi Gamma-ray Burst Monitor during its most prolific activity
We have performed detailed temporal and time-integrated spectral analysis of
286 bursts from SGR J1550-5418 detected with the Fermi Gamma-ray Burst Monitor
(GBM) in January 2009, resulting in the largest uniform sample of temporal and
spectral properties of SGR J1550-5418 bursts. We have used the combination of
broadband and high time-resolution data provided with GBM to perform
statistical studies for the source properties. We determine the durations,
emission times, duty cycles and rise times for all bursts, and find that they
are typical of SGR bursts. We explore various models in our spectral analysis,
and conclude that the spectra of SGR J1550-5418 bursts in the 8-200 keV band
are equally well described by optically thin thermal bremsstrahlung (OTTB), a
power law with an exponential cutoff (Comptonized model), and two black-body
functions (BB+BB). In the spectral fits with the Comptonized model we find a
mean power-law index of -0.92, close to the OTTB index of -1. We show that
there is an anti-correlation between the Comptonized Epeak and the burst
fluence and average flux. For the BB+BB fits we find that the fluences and
emission areas of the two blackbody functions are correlated. The
low-temperature BB has an emission area comparable to the neutron star surface
area, independent of the temperature, while the high-temperature blackbody has
a much smaller area and shows an anti-correlation between emission area and
temperature. We compare the properties of these bursts with bursts observed
from other SGR sources during extreme activations, and discuss the implications
of our results in the context of magnetar burst models.Comment: 13 pages, 10 figures, 2 tables; minor changes, ApJ in pres
Timing Noise in SGR 1806-20
We have phase connected a sequence of RXTE PCA observations of SGR 1806-20
covering 178 days. We find a simple secular spin-down model does not adequately
fit the data. The period derivative varies gradually during the observations
between 8.1 and 11.7 * 10^-11 s/s (at its highest, ~40% larger than the long
term trend), while the average burst rate as seen with BATSE drops throughout
the time interval. The phase residuals give no compelling evidence for
periodicity, but more closely resemble timing noise as seen in radio pulsars.
The magnitude of the timing noise, however, is large relative to the noise
level typically found in radio pulsars. Combining these results with the noise
levels measured for some AXPs, we find all magnetar candidates have \Delta_8
values larger than those expected from a simple extrapolation of the
correlation found in radio pulsars. We find that the timing noise in SGR
1806-20 is greater than or equal to the levels found in some accreting systems
(e.g., Vela X-1, 4U 1538-52 and 4U 1626-67), but the spin-down of SGR 1806-20
has thus far maintained coherence over 6 years. Alternatively, an orbital model
with a period P_orb = 733 days provides a statistically acceptable fit to the
data. If the phase residuals are created by Doppler shifts from a
gravitationally bound companion, then the allowed parameter space for the mass
function (small) and orbital separation (large) rule out the possibility of
accretion from the companion sufficient to power the persistent emission from
the SGR.Comment: 11 pages, accepted for publication in ApJ Letter
Statistical properties of SGR 1900+14 bursts
We study the statistics of soft gamma repeater (SGR) bursts, using a data
base of 187 events detected with BATSE and 837 events detected with RXTE PCA,
all from SGR 1900+14 during its 1998-1999 active phase. We find that the
fluence or energy distribution of bursts is consistent with a power law of
index 1.66, over 4 orders of magnitude. This scale-free distribution resembles
the Gutenberg-Richter Law for earthquakes, and gives evidence for
self-organized criticality in SGRs. The distribution of time intervals between
successive bursts from SGR 1900+14 is consistent with a log-normal
distribution. There is no correlation between burst intensity and the waiting
times till the next burst, but there is some evidence for a correlation between
burst intensity and the time elapsed since the previous burst. We also find a
correlation between the duration and the energy of the bursts, but with
significant scatter. In all these statistical properties, SGR bursts resemble
earthquakes and solar flares more closely than they resemble any known
accretion-powered or nuclear-powered phenomena. Thus our analysis lends support
to the hypothesis that the energy source for SGR bursts is internal to the
neutron star, and plausibly magnetic.Comment: 11 pages, 4 figures, accepted for publication in ApJ
Sedoanalgesia Administration with Propofol and Ketamine for Minor Urologic Interventions
Aim: In this study we aimed to administer sedoanalgesia with propofol and ketamine combination in patients undergoing planned minor urologic interventions with limited anesthesia. By combining these two medications, lower doses may be used, and we aimed to provide sufficient sedation, analgesia and amnesia without disrupting hemodynamic and respiratory stability and to increase patient and surgeon satisfaction. Material-Method: The study included 53 patients with planned minor urologic interventions aged from 19 to 85 years and physical situation ASA I-III. After six hours starvation, patients were taken to the surgery. Patients were monitored for electrocardiography (ECG), oxygen saturation (SPO2 ) and non-invasive blood pressure. For use if necessary a nasal O2 cannula was inserted. A vein in the back of the left hand was opened and 5 ml/min isotonic sodium chloride infusion was begun. Patient heart rate (HR), systolic arterial pressure (SAP), diastolic arterial pressure (DAP), mean arterial pressure (MAP) and oxygen saturation (SpO2 ) values were measured and a 5 point sedation scale (Table 1) was used to measure sedation scores. Basal values were recorded (0 min). Later patients were randomly divided into two groups with Group I administered intraurethral lidocaine gel for local anesthesia by the surgeon, while Group II were administered intravenous 0.015 mg/kg midazolam, 0.5 mg/kg 1% ketamine and 0.5 mg/kg 1% propofol by the authors for sedoanalgesia. At five minute intervals the HR, SAP, DAP, MAP, SpO2 values and sedation scores were measured and recorded. Results: Statistical evaluation found a statistically significant increase in SAP, DAP and MAP values measured at the 5th minute in Group I patients compared to preoperative values. In Group I patients, when the heart rate measured in the 1st and 5th minutes are compared with preoperative values there was a statistically significant increase identified. In Group II patients, there was a statistically significant fall in SpO2 values in the 1st and 5th minutes compared with preoperative values. When patient and surgeon satisfaction are compared with Group I, Group II was found to be statistically significantly higher. Though the blood pressure and heart rate increases in Group I patients were statistically significant, they were not at levels that required clinical intervention and/or treatment. Similarly the SpO2 decrease observed in Group II patients did not fall below 90% in any patient in spite of being statistically significant and rose again without clinical intervention and/or treatment. Conclusion: In this study we showed that sedoanalgesia administration with propofol and ketamine may be an alternative method for patients undergoing minor urology interventions that does not disrupt hemodynamic and respiratory stability, does not delay patient discharge, has low side effect incidence and has high patient and surgeon satisfaction
Transit Timing Analysis in the HAT-P-32 system
We present the results of 45 transit observations obtained for the transiting
exoplanet HAT-P-32b. The transits have been observed using several telescopes
mainly throughout the YETI network. In 25 cases, complete transit light curves
with a timing precision better than min have been obtained. These light
curves have been used to refine the system properties, namely inclination ,
planet-to-star radius ratio , and the ratio between
the semimajor axis and the stellar radius . First analyses by
Hartman et al. (2011) suggest the existence of a second planet in the system,
thus we tried to find an additional body using the transit timing variation
(TTV) technique. Taking also literature data points into account, we can
explain all mid-transit times by refining the linear ephemeris by 21ms. Thus we
can exclude TTV amplitudes of more than min.Comment: MNRAS accepted; 13 pages, 10 figure
Hard X-Ray flux upper limits of central compact objects in supernova remnants
We searched for hard X-ray (20–300 keV) emission from nine central compact
objects (CCOs) 1E 1207.4−5209, 1WGA J1713−3949, J082157.5−430017,
J085201.4−461753, J1601−5133, J1613483−5055, J181852.0−150213,
J185238.6+004020, and J232327.9+584843 with the INTEGRAL observatory.
We applied spectral imaging analysis and did not detect any of the sources
with luminosity upper limits in the range of 1033-1034 ergs/s in the 20-75 keV
band. For nearby CCOs (< 4 kpc) the upper limit luminosities are an order
of magnitude lower than the measured persistent hard X-ray luminosities of
AXPs. This may indicate that the central compact objects are low magnetic
field systems with fallback disks around them
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