Abstract We collect a sample of 42 Type Ia supernovae (SNe Ia) with Swift UV photometry and well-measured early time light-curve rises and find that 2002es-like and 2003fg-like SNe Ia have different ...prepeak UV color evolutions compared to normal SNe Ia and other spectroscopic subtypes. Specifically, 2002es-like and 2003fg-like SNe Ia are cleanly separated from other SNe Ia subtypes by UVM 2 − UVW 1 ≳ 1.0 mag at t = − 10 days relative to B -band maximum. Furthermore, the SNe Ia that exhibit nonmonotonic bumps in their rising light curves, to date, consist solely of 2002es-like and 2003fg-like SNe Ia. We also find that SNe Ia with two-component power-law rises are more luminous than SNe Ia with single-component power-law rises at prepeak epochs. Given the similar UV colors, along with other observational similarities, we discuss a possible progenitor scenario that places 2002es-like and 2003fg-like SNe Ia along a continuum and may explain the unique UV colors, early time bumps, and other observational similarities between these objects. Ultimately, further observations of both subtypes, especially in the near-infrared, are critical for constraining models of these peculiar thermonuclear explosions.
Abstract
We present the Spectroscopic Classification of Astronomical Transients (SCAT) survey, which is dedicated to spectrophotometric observations of transient objects such as supernovae and tidal ...disruption events. SCAT uses the SuperNova Integral-Field Spectrograph (SNIFS) on the University of Hawai’i 2.2 m (UH2.2m) telescope. SNIFS was designed specifically for accurate transient spectrophotometry, including absolute flux calibration and host-galaxy removal. We describe the data reduction and calibration pipeline including spectral extraction, telluric correction, atmospheric characterization, nightly photometricity, and spectrophotometric precision. We achieve ≲5% spectrophotometry across the full optical wavelength range (3500–9000 Å) under photometric conditions. The inclusion of photometry from the SNIFS multi-filter mosaic imager allows for decent spectrophotometric calibration (10%–20%) even under unfavorable weather/atmospheric conditions. SCAT obtained ≈640 spectra of transients over the first 3 yr of operations, including supernovae of all types, active galactic nuclei, cataclysmic variables, and rare transients such as superluminous supernovae and tidal disruption events. These observations will provide the community with benchmark spectrophotometry to constrain the next generation of hydrodynamic and radiative transfer models.
Abstract
We present optical and near-infrared photometric and spectroscopic observations of the fast-declining Type Ia supernova (SN) 2015bo. SN 2015bo is underluminous (
M
B
= −17.50 ± 0.15 mag) and ...has a fast-evolving light curve (Δm15(
B
) = 1.91 ± 0.01 mag and
s
BV
= 0.48 ± 0.01). It has a unique morphology in the observed
V
−
r
color curve, where it is bluer than all other supernovae (SNe) in the comparison sample. A
56
Ni mass of 0.17 ± 0.03
M
⊙
was derived from the peak bolometric luminosity, which is consistent with its location on the luminosity–width relation. Spectroscopically, SN 2015bo is a cool SN in the Branch classification scheme. The velocity evolution measured from spectral features is consistent with 1991bg-like SNe. SN 2015bo has a SN twin (similar spectra)
and
sibling (same host galaxy), SN 1997cn. Distance moduli of
μ
= 34.33 ± 0.01 (stat) ±0.11 (sys) mag and
μ
= 34.34 ± 0.04 (stat) ± 0.12 (sys) mag are derived for SN 2015bo and SN 1997cn, respectively. These distances are consistent at the 0.06
σ
level with each other, and they are also consistent with distances derived using surface-brightness fluctuations and redshift-corrected cosmology. This suggests that fast-declining SNe could be accurate distance indicators, which should not be excluded from future cosmological analyses.
Multiple flares in the changing-look AGN NGC 5273 Neustadt, J M M; Hinkle, J T; Kochanek, C S ...
Monthly notices of the Royal Astronomical Society,
03/2023, Letnik:
521, Številka:
3
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
NGC 5273 is a known optical and X-ray variable AGN. We analyse new and archival IR, optical, UV, and X-ray data in order to characterize its long-term variability from 2000–2022. At least ...one optical changing-look event occurred between 2011 and 2014 when the AGN changed from a Type 1.8/1.9 Seyfert to a Type 1. It then faded considerably at all wavelengths, followed by a dramatic but slow increase in UV/optical brightness between 2021 and 2022. Near-IR (NIR) spectra in 2022 show prominent broad Paschen lines that are absent in an archival spectrum from 2010, making NGC 5273 one of the few AGNs to be observed changing-look in the NIR. We propose that NGC 5273 underwent multiple changing-look events between 2000 and 2022 – starting as a Type 1.8/1.9, NGC 5273 changes-look to a Type 1 temporarily in 2002 and again in 2014, reverting back to a Type 1.8/1.9 by 2005 and 2017, respectively. In 2022, it is again a Type 1 Seyfert. We characterize the changing-look events and their connection to the dynamic accretion and radiative processes in NGC 5273 and propose that the variable luminosity (and thus, Eddington ratio) of the source is changing how the broad-line region (BLR) reprocesses the continuum emission.
ABSTRACT We report the All-Sky Automated Survey for SuperNovae discovery of the tidal disruption event (TDE) ASASSN-23bd (AT 2023clx) in NGC 3799, a LINER galaxy with no evidence of strong active ...galactic nucleus (AGN) activity over the past decade. With a redshift of z = 0.01107 and a peak ultraviolet (UV)/optical luminosity of (5.4 ± 0.4) × 1042 erg s−1, ASASSN-23bd is the lowest-redshift and least-luminous TDE discovered to date. Spectroscopically, ASASSN-23bd shows H α and He i emission throughout its spectral time series, there are no coronal lines in its near-infrared spectrum, and the UV spectrum shows nitrogen lines without the strong carbon and magnesium lines typically seen for AGN. Fits to the rising ASAS-SN light curve show that ASASSN-23bd started to brighten on MJD 59988$^{+1}_{-1}$, ∼9 d before discovery, with a nearly linear rise in flux, peaking in the g band on MJD $60 \, 000^{+3}_{-3}$. Scaling relations and TDE light curve modelling find a black hole mass of ∼106 M⊙, which is on the lower end of supermassive black hole masses. ASASSN-23bd is a dim X-ray source, with an upper limit of $L_{0.3-10\, \mathrm{keV}} \lt 1.0\times 10^{40}$ erg s−1 from stacking all Swift observations prior to MJD 60061, but with soft (∼0.1 keV) thermal emission with a luminosity of $L_{0.3-2 \, \mathrm{keV}}\sim 4\times 10^{39}$ erg s−1 in XMM-Newton observations on MJD 60095. The rapid (t < 15 d) light curve rise, low UV/optical luminosity, and a luminosity decline over 40 d of ΔL40 ≈ −0.7 dex make ASASSN-23bd one of the dimmest TDEs to date and a member of the growing ‘Low Luminosity and Fast’ class of TDEs.
The aim of this study was to investigate the signal‐to‐noise ratio (SNR) gain in early‐stage cervical cancer at ultrahigh‐field MRI (e.g. 7 T) using a combination of multiple external antennas and a ...single endorectal antenna. In particular, we used an endorectal monopole antenna to increase the SNR in cervical magnetic resonance imaging (MRI). This should allow high‐resolution, T2‐weighted imaging and magnetic resonance spectroscopy (MRS) for metabolic staging, which could facilitate the local tumor status assessment. In a prospective feasibility study, five healthy female volunteers and six patients with histologically proven stage IB1–IIB cervical cancer were scanned at 7 T. We used seven external fractionated dipole antennas for transmit–receive (transceive) and an endorectally placed monopole antenna for reception only. A region of interest, containing both normal cervix and tumor tissue, was selected for the SNR measurement. Separated signal and noise measurements were obtained in the region of the cervix for each element and in the near field of the monopole antenna (radius < 30 mm) to calculate the SNR gain of the endorectal antenna in each patient. We obtained high‐resolution, T2‐weighted images with a voxel size of 0.7 × 0.8 × 3.0 mm3. In four cases with optimal placement of the endorectal antenna (verified on the T2‐weighted images), a mean gain of 2.2 in SNR was obtained at the overall cervix and tumor tissue area. Within a radius of 30 mm from the monopole antenna, a mean SNR gain of 3.7 was achieved in the four optimal cases. Overlap between the two different regions of the SNR calculations was around 24%. We have demonstrated that the use of an endorectal monopole antenna substantially increases the SNR of 7‐T MRI at the cervical anatomy. Combined with the intrinsically high SNR of ultrahigh‐field MRI, this gain may be employed to obtain metabolic information using MRS and to enhance spatial resolutions to assess tumor invasion.
The combination of an endorectally inserted ultrathin monopole antenna for receive only at 7 T, with seven external fractionated dipole antennas for transmit and receive, boosts the signal‐to‐noise ratio (SNR) in the cervix by a mean factor of two. This results in high‐resolution. T2‐weighted imaging in the cervix, cervical tumor and surrounding tissue (parametria).
Proton MRS of cervical cancer at 7 T Arteaga de Castro, C.S.; Hoogendam, J.P.; Kalleveen, I.M.L. ...
NMR in biomedicine,
January 2019, Letnik:
32, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The differentiation grade of cervical cancer is histologically assessed by examining biopsies or surgical specimens.
MRS is a highly sensitive technique that images tissue metabolism and can be used ...to increase the specificity of tissue characterization in a non‐invasive manner. We aim to explore the feasibility of using in vivo 1H‐MRS at 7 T in women with cervical cancer to study tissue fatty acid composition.
10 women with histologically proven Stage IB1‐IIB cervical cancer were scanned with a whole‐body 7 T MR system with a multi‐transmit system and an internal receive only monopole antenna. A STEAM sequence was used to obtain 1H‐MRS data. Fatty acid resonances were fitted with Lorentzian curves and the 2.1 ppm/1.3 ppm ratios were calculated.
1H‐MRS data showed fatty acid signals resonating at 2.1 ppm, 1.9 ppm, 1.5 ppm, 1.3 ppm and 0.9 ppm. Mean 2.1/1.3 ppm ratios were 0.019 ± 0.01, 0.021 ± 0.006, 0.12 ± 0.089 and 0.39 ± 0.27 for normal, Grade I, Grade II and Grade III groups respectively. Poorly differentiated tumor tissue (Grade III) showed elevated fatty acid ratios when compared with the well differentiated tumor (Grade I) or normal tissue.
1H‐MRS in cervical cancer at 7 T is feasible and individual fatty acid signals were detected. In addition, poorly differentiated tumors show more fatty acid unsaturation. The 2.1 ppm/1.3 ppm ratio has potential for tumor characterization in a non‐invasive manner for uterine cervical cancer.
The feasibility of fatty acid characterization was investigated at ultra‐high field. Fatty acids in uterine cervix were measured in a single voxel with MRS at 7 T in 10 patients with cervical cancer and 5 healthy volunteers. Fatty acids were fitted and the 2.1 ppm/1.3 ppm ratios were calculated for each subject. These showed a trend towards unsaturation of the fatty acids in poorly differentiated tumors, when compared with well differentiated tumors or normal tissue.
The aim of this study was to investigate the signal-to-noise ratio (SNR) gain in early-stage cervical cancer at ultrahigh-field MRI (e.g. 7 T) using a combination of multiple external antennas and a ...single endorectal antenna. In particular, we used an endorectal monopole antenna to increase the SNR in cervical magnetic resonance imaging (MRI). This should allow high-resolution, T
-weighted imaging and magnetic resonance spectroscopy (MRS) for metabolic staging, which could facilitate the local tumor status assessment. In a prospective feasibility study, five healthy female volunteers and six patients with histologically proven stage IB1-IIB cervical cancer were scanned at 7 T. We used seven external fractionated dipole antennas for transmit-receive (transceive) and an endorectally placed monopole antenna for reception only. A region of interest, containing both normal cervix and tumor tissue, was selected for the SNR measurement. Separated signal and noise measurements were obtained in the region of the cervix for each element and in the near field of the monopole antenna (radius < 30 mm) to calculate the SNR gain of the endorectal antenna in each patient. We obtained high-resolution, T
-weighted images with a voxel size of 0.7 × 0.8 × 3.0 mm
. In four cases with optimal placement of the endorectal antenna (verified on the T
-weighted images), a mean gain of 2.2 in SNR was obtained at the overall cervix and tumor tissue area. Within a radius of 30 mm from the monopole antenna, a mean SNR gain of 3.7 was achieved in the four optimal cases. Overlap between the two different regions of the SNR calculations was around 24%. We have demonstrated that the use of an endorectal monopole antenna substantially increases the SNR of 7-T MRI at the cervical anatomy. Combined with the intrinsically high SNR of ultrahigh-field MRI, this gain may be employed to obtain metabolic information using MRS and to enhance spatial resolutions to assess tumor invasion.
We report a case of a young woman presenting with abdominal pain due to a rare and recurrent herniation of the ovary, to a retroperitoneal location lateral to the external iliac artery and directly ...dorsal to the iliopsoas muscle. Correlation between computed tomography, magnetic resonance imaging and laparoscopy is presented. The patient’s complaints subsided after right oophoropexy. When aware, this diagnosis is easy to make and may allow symptomatic patients to be treated with laparoscopic oophoropexy.
Accurate automated brain structure segmentation methods facilitate the analysis of large-scale neuroimaging studies. This work describes a novel method for brain structure segmentation in magnetic ...resonance images that combines information about a structure's location and appearance. The spatial model is implemented by registering multiple atlas images to the target image and creating a spatial probability map. The structure's appearance is modeled by a classifier based on Gaussian scale-space features. These components are combined with a regularization term in a Bayesian framework that is globally optimized using graph cuts. The incorporation of the appearance model enables the method to segment structures with complex intensity distributions and increases its robustness against errors in the spatial model. The method is tested in cross-validation experiments on two datasets acquired with different magnetic resonance sequences, in which the hippocampus and cerebellum were segmented by an expert. Furthermore, the method is compared to two other segmentation techniques that were applied to the same data. Results show that the atlas- and appearance-based method produces accurate results with mean Dice similarity indices of 0.95 for the cerebellum, and 0.87 for the hippocampus. This was comparable to or better than the other methods, whereas the proposed technique is more widely applicable and robust.
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