22 research outputs found
Timescale-dependent X-ray to UV time lags of NGC 4593 using high-intensity XMM-Newton observations with Swift and AstroSat
We present a 140ks observation of NGC 4593 with XMM-Newton providing
simultaneous and continuous PN X-ray and OM UV (UVW1 2910\AA) lightcurves which
sample short-timescale variations better than previous observations. These
observations were simultaneous with 22d of Swift X-ray and UV/optical
monitoring, reported previously, and 4d of AstroSat X-ray (SXT), far (FUV
1541\AA), and near (NUV 2632\AA) UV allowing lag measurements between them and
the highly-sampled XMM. From the XMM we find that UVW1 lags behind the X-rays
by 29.51.3ks, half the lag previously determined from the Swift
monitoring. Re-examination of the \textit{Swift} data reveals a bimodal lag
distribution, with evidence for both the long and short lags. However if we
detrend the Swift lightcurves by LOWESS filtering with a 5d width, only the
shorter lag (23.821.2ks) remains. The NUV observations, compared to PN and
SXT, confirm the 30ks lag found by XMM and, after 4d filtering is applied
to remove the long-timescale component, the FUV shows a lag of 23ks. The
resultant new UVW1, FUV, and NUV lag spectrum extends to the X-ray band without
requiring additional X-ray to UV lag offset, which if the UV arises from
reprocessing of X-rays, implies direct illumination of the reprocessor. By
referencing previous Swift and HST lag measurements, we obtain an X-ray to
optical lag spectrum which agrees with a model using the KYNreverb
disc-reprocessing code, assuming the accepted mass of
and a spin approaching maximum. Previously noted
lag contribution from the BLR in the Balmer and Paschen continua are still
prominent.Comment: 13 pages, 23 figure
Contrasting X-ray/UV time-lags in Seyfert 1 galaxies NGC 4593 and NGC 7469 using AstroSat observations
We study accretion disk-corona connection in Seyfert 1 galaxies using
simultaneous UV/X-ray observations of NGC 4593 (July 14-18, 2016) and NGC 7469
(October 15-19, 2017) performed with AstroSat. We use the X-ray (0.5-7.0 keV)
data acquired with the Soft X-ray Telescope (SXT) and the UV (FUV: 130-180 nm,
NUV: 200-300 nm) data obtained with the Ultra-Violet Imaging Telescope (UVIT).
We also use the contemporaneous Swift observations of NGC 4593 and demonstrate
AstroSat's capability for X-ray/UV correlation studies. We performed UV/X-ray
cross-correlation analysis using the Interpolated and the Discrete
Cross-Correlation Functions and found similar results. In the case of NGC 4593,
we found that the variations in the X-rays lead to those in the FUV and NUV
bands by ~ 38 ks and ~ 44 ks, respectively. These UV lags favour the disk
reprocessing model, they are consistent with the previous results within
uncertainties. In contrast, we found an opposite trend in NGC 7469 where the
soft X-ray variations lag those in the FUV and NUV bands by ~ 41 ks and ~ 49
ks, respectively. The hard lags in NGC 7469 favour the Thermal Comptonization
model. Our results may provide direct observational evidence for the variable
intrinsic UV emission from the accretion disk which acts as the seed for
thermal Comptonization in a hot corona in a lamp-post like geometry. The
non-detection of disk reverberation photons in NGC 7469, using AstroSat data,
is most likely due to a high accretion rate resulting in a hot accretion disk
and large intrinsic emission.Comment: 14 pages, 20 figures, Accepted for publication in MNRA
The impact of surgical delay on resectability of colorectal cancer: An international prospective cohort study
AIM: The SARS-CoV-2 pandemic has provided a unique opportunity to explore the impact of surgical delays on cancer resectability. This study aimed to compare resectability for colorectal cancer patients undergoing delayed versus non-delayed surgery. METHODS: This was an international prospective cohort study of consecutive colorectal cancer patients with a decision for curative surgery (January-April 2020). Surgical delay was defined as an operation taking place more than 4 weeks after treatment decision, in a patient who did not receive neoadjuvant therapy. A subgroup analysis explored the effects of delay in elective patients only. The impact of longer delays was explored in a sensitivity analysis. The primary outcome was complete resection, defined as curative resection with an R0 margin. RESULTS: Overall, 5453 patients from 304 hospitals in 47 countries were included, of whom 6.6% (358/5453) did not receive their planned operation. Of the 4304 operated patients without neoadjuvant therapy, 40.5% (1744/4304) were delayed beyond 4 weeks. Delayed patients were more likely to be older, men, more comorbid, have higher body mass index and have rectal cancer and early stage disease. Delayed patients had higher unadjusted rates of complete resection (93.7% vs. 91.9%, P = 0.032) and lower rates of emergency surgery (4.5% vs. 22.5%, P < 0.001). After adjustment, delay was not associated with a lower rate of complete resection (OR 1.18, 95% CI 0.90-1.55, P = 0.224), which was consistent in elective patients only (OR 0.94, 95% CI 0.69-1.27, P = 0.672). Longer delays were not associated with poorer outcomes. CONCLUSION: One in 15 colorectal cancer patients did not receive their planned operation during the first wave of COVID-19. Surgical delay did not appear to compromise resectability, raising the hypothesis that any reduction in long-term survival attributable to delays is likely to be due to micro-metastatic disease