188 research outputs found
Multi-wavelength analysis of the Galactic supernova remnant MSH 11-61A
Due to its centrally bright X-ray morphology and limb brightened radio
profile, MSH 11-61A (G290.1-0.8) is classified as a mixed morphology supernova
remnant (SNR). H\textsc{i} and CO observations determined that the SNR is
interacting with molecular clouds found toward the north and southwest regions
of the remnant. In this paper we report on the detection of -ray
emission coincident with MSH 11-61A, using 70 months of data from the Large
Area Telescope on board the \textit{Fermi Gamma-ray Space Telescope}. To
investigate the origin of this emission, we perform broadband modelling of its
non-thermal emission considering both leptonic and hadronic cases and
concluding that the -ray emission is most likely hadronic in nature.
Additionally we present our analysis of a 111 ks archival \textit{Suzaku}
observation of this remnant. Our investigation shows that the X-ray emission
from MSH 11-61A arises from shock-heated ejecta with the bulk of the X-ray
emission arising from a recombining plasma, while the emission towards the east
arises from an ionising plasma.Comment: 12 Pages, 8 figures. Accepted for publication in the Astrophysical
Journa
Is the high-energy neutrino event IceCube-200530A associated with a hydrogen-rich superluminous supernova?
The Zwicky Transient Facility (ZTF) follow-up campaign of alerts released by
the IceCube Neutrino Observatory has led to the likely identification of the
transient AT2019fdr as the source of the neutrino event IC200530A. AT2019fdr
was initially suggested to be a tidal disruption event in a Narrow-Line Seyfert
1 galaxy. However, the combination of its spectral properties, color evolution,
and feature-rich light curve suggests that AT2019fdr may be a Type IIn
superluminous supernova. In the latter scenario, IC200530A may have been
produced via inelastic proton-proton collisions between the relativistic
protons accelerated at the forward shock and the cold protons of the
circumstellar medium. Here, we investigate this possibility and find that at
most muon neutrino and antineutrino events are expected to
be detected by the IceCube Neutrino Observatory within days of discovery
in the case of excellent discrimination of the atmospheric background. After
correcting for the Eddington bias, which occurs when a single cosmic neutrino
event is adopted to infer the neutrino emission at the source, we conclude that
IC200530A may originate from the hydrogen-rich superluminous supernova
AT2019fdr.Comment: 16 pages, including 10 figures. Improved modeling for neutrino
production, conclusions unchanged, matches version accepted for publication
in Ap
The broad-line type Ic SN 2020bvc: signatures of an off-axis gamma-ray burst afterglow
Long-duration gamma-ray bursts (GRBs) are almost unequivocally associated
with very energetic, broad-lined supernovae (SNe) of Type Ic-BL. While the
gamma-ray emission is emitted in narrow jets, the SN emits radiation
isotropically. Therefore, some SN Ic-BL not associated with GRBs have been
hypothesized to arise from events with inner engines such as off-axis GRBs or
choked jets. Here we present observations of the nearby ( Mpc) SN
2020bvc (ASAS-SN 20bs) which support this scenario. \textit{Swift} UVOT
observations reveal an early decline (up to two days after explosion) while
optical spectra classify it as a SN Ic-BL with very high expansion velocities
( 70,000 km/s), similar to that found for the jet-cocoon emission in
SN 2017iuk associated with GRB 171205A. Moreover, \textit{Swift} X-Ray
Telescope and \textit{CXO} X-ray Observatory detected X-ray emission only three
days after the SN and decaying onwards, which can be ascribed to an afterglow
component. Cocoon and X-ray emission are both signatures of jet-powered GRBs.
In the case of SN 2020bvc, we find that the jet is off axis (by 23
degrees), as also indicated by the lack of early ( day) X-ray
emission which explains why no coincident GRB was detected promptly or in
archival data. These observations suggest that SN 2020bvc is the first orphan
GRB detected through its associated SN emission.Comment: 9 pages, 6 figures, 5 tables. Accepted for publication in A&
An asymmetric electron-scattering photosphere around optical tidal disruption events
A star crossing the tidal radius of a supermassive black hole will be
spectacularly ripped apart with an accompanying burst of radiation. A few tens
of such tidal disruption events (TDEs) have now been identified in the optical
wavelengths, but the exact origin of the strong optical emission remains
inconclusive. Here we report polarimetric observations of three TDEs. The
continuum polarization is independent of wavelength, while emission lines are
partially depolarized. These signatures are consistent with optical photons
being scattered and polarized in an envelope of free electrons. An almost
axisymmetric photosphere viewed from different angles is in broad agreement
with the data, but there is also evidence for deviations from axial symmetry
before the peak of the flare and significant time evolution at early times,
compatible with the rapid formation of an accretion disk. By combining a
super-Eddington accretion model with a radiative transfer code we generate
predictions for the degree of polarization as a function of disk mass and
viewing angle, and we show that the predicted levels are compatible with the
observations, for extended reprocessing envelopes of 1000 gravitational
radii. Spectropolarimetry therefore constitutes a new observational test for
TDE models, and opens an important new line of exploration in the study of
TDEs.Comment: Author's version of paper to appear in Nature Astronomy. In the
journal version the detailed discussion on the ISP determination will be
moved from the Methods section to a Supplementary Information section. 58
pages in double spacing format, including 5 Figures, 10 Extended Data Figures
and 2 Table
Seeing Double: ASASSN-18bt Exhibits a Two-component Rise in the Early-time K2 Light Curve
On 2018 February 4.41, the All-Sky Automated Survey for SuperNovae (ASAS-SN) discovered ASASSN-18bt in the K2 Campaign 16 field. With a redshift of z = 0.01098 and a peak apparent magnitude of B max = 14.31, ASASSN-18bt is the nearest and brightest SNe Ia yet observed by the Kepler spacecraft. Here we present the discovery of ASASSN-18bt, the K2 light curve, and prediscovery data from ASAS-SN and the Asteroid Terrestrial-impact Last Alert System. The K2 early-time light curve has an unprecedented 30-minute cadence and photometric precision for an SN Ia light curve, and it unambiguously shows a ∼4 day nearly linear phase followed by a steeper rise. Thus, ASASSN-18bt joins a growing list of SNe Ia whose early light curves are not well described by a single power law. We show that a double-power-law model fits the data reasonably well, hinting that two physical processes must be responsible for the observed rise. However, we find that current models of the interaction with a nondegenerate companion predict an abrupt rise and cannot adequately explain the initial, slower linear phase. Instead, we find that existing published models with shallow 56Ni are able to span the observed behavior and, with tuning, may be able to reproduce the ASASSN-18bt light curve. Regardless, more theoretical work is needed to satisfactorily model this and other early-time SNe Ia light curves. Finally, we use Swift X-ray nondetections to constrain the presence of circumstellar material (CSM) at much larger distances and lower densities than possible with the optical light curve. For a constant-density CSM, these nondetections constrain ρ < 4.5 × 105 cm−3 at a radius of 4 × 1015 cm from the progenitor star. Assuming a wind-like environment, we place mass loss limits of \\dot{M}< 8× {10}-6 {M}ȯ {yr}}-1 for v w = 100 km s−1, ruling out some symbiotic progenitor systems. This work highlights the power of well-sampled early-time data and the need for immediate multiband, high- cadence follow-up for progress in understanding SNe Ia
Discovery and Early Evolution of ASASSN-19bt, the First TDE Detected by TESS
We present the discovery and early evolution of ASASSN-19bt, a tidal
disruption event (TDE) discovered by the All-Sky Automated Survey for
Supernovae (ASAS-SN) at a distance of Mpc and the first TDE to be
detected by TESS. As the TDE is located in the TESS Continuous Viewing Zone,
our dataset includes 30-minute cadence observations starting on 2018 July 25,
and we precisely measure that the TDE begins to brighten days before
its discovery. Our dataset also includes 18 epochs of Swift UVOT and XRT
observations, 2 epochs of XMM-Newton observations, 13 spectroscopic
observations, and ground data from the Las Cumbres Observatory telescope
network, spanning from 32 days before peak through 37 days after peak.
ASASSN-19bt thus has the most detailed pre-peak dataset for any TDE. The TESS
light curve indicates that the transient began to brighten on 2019 January 21.6
and that for the first 15 days its rise was consistent with a flux power-law model. The optical/UV emission is well-fit by a blackbody SED,
and ASASSN-19bt exhibits an early spike in its luminosity and temperature
roughly 32 rest-frame days before peak and spanning up to 14 days that has not
been seen in other TDEs, possibly because UV observations were not triggered
early enough to detect it. It peaked on 2019 March 04.9 at a luminosity of
ergs s and radiated
ergs during the 41-day rise to peak. X-ray observations after peak indicate a
softening of the hard X-ray emission prior to peak, reminiscent of the
hard/soft states in X-ray binaries.Comment: 23 pages, 14 figures, 5 tables. A machine-readable table containing
the host-subtracted photometry presented in this manuscript is included as an
ancillary fil
A Cool and Inflated Progenitor Candidate for the Type Ib Supernova 2019yvr at 2.6 Years Before Explosion
We present Hubble Space Telescope imaging of a pre-explosion counterpart to
SN 2019yvr obtained 2.6 years before its explosion as a type Ib supernova (SN
Ib). Aligning to a post-explosion Gemini-S/GSAOI image, we demonstrate that
there is a single source consistent with being the SN 2019yvr progenitor
system, the second SN Ib progenitor candidate after iPTF13bvn. We also analyzed
pre-explosion Spitzer/IRAC imaging, but we do not detect any counterparts at
the SN location. SN 2019yvr was highly reddened, and comparing its spectra and
photometry to those of other, less extinguished SNe Ib we derive
mag for SN 2019yvr. Correcting photometry
of the pre-explosion source for dust reddening, we determine that this source
is consistent with a and K star. This relatively cool photospheric
temperature implies a radius of 320, much larger
than expectations for SN Ib progenitor stars with trace amounts of hydrogen but
in agreement with previously identified SN IIb progenitor systems. The
photometry of the system is also consistent with binary star models that
undergo common envelope evolution, leading to a primary star hydrogen envelope
mass that is mostly depleted but seemingly in conflict with the SN Ib
classification of SN 2019yvr. SN 2019yvr had signatures of strong circumstellar
interaction in late-time (150 day) spectra and imaging, and so we consider
eruptive mass loss and common envelope evolution scenarios that explain the SN
Ib spectroscopic class, pre-explosion counterpart, and dense circumstellar
material. We also hypothesize that the apparent inflation could be caused by a
quasi-photosphere formed in an extended, low-density envelope or circumstellar
matter around the primary star.Comment: 22 pages, 9 figures, submitted to MNRA
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