104 research outputs found
AT 2017be - a new member of the class of Intermediate-Luminosity Red Transients
We report the results of our spectrophotometric monitoring campaign for
AT~2017be in NGC~2537. Its lightcurve reveals a fast rise to an optical
maximum, followed by a plateau lasting about 30 days, and finally a fast
decline. Its absolute peak magnitude ( 12 ) is
fainter than that of core-collapse supernovae, and is consistent with those of
supernova impostors and other Intermediate-Luminosity Optical Transients. The
quasi-bolometric lightcurve peaks at 2 10 erg s,
and the late-time photometry allows us to constrain an ejected Ni mass
of 8 10\msun. The spectra of AT~2017be show minor
evolution over the observational period, a relatively blue continuum showing at
early phases, which becomes redder with time. A prominent H emission
line always dominates over other Balmer lines. Weak Fe {\sc ii} features,
Ca~{\sc ii} HK and the Ca {\sc ii} NIR triplet are also visible, while
P-Cygni absorption troughs are found in a high resolution spectrum. In
addition, the [Ca~{\sc ii}] 7291,7324 doublet is visible in all
spectra. This feature is typical of Intermediate-Luminosity Red Transients
(ILRTs), similar to SN~2008S. The relatively shallow archival Spitzer data are
not particularly constraining. On the other hand, a non-detection in deeper
near-infrared HST images disfavours a massive Luminous Blue Variable eruption
as the origin for AT~2017be. As has been suggested for other ILRTs, we propose
that AT~2017be is a candidate for a weak electron-capture supernova explosion
of a super-asymptotic giant branch star, still embedded in a thick dusty
envelope.Comment: 21 pages, 15 figures, accepted by MNRA
Optical and near infrared observations of SN 2014ck: an outlier among the Type Iax supernovae
We present a comprehensive set of optical and near-infrared photometric and
spectroscopic observations for SN 2014ck, extending from pre-maximum to six
months later. These data indicate that SN 2014ck is photometrically nearly
identical to SN 2002cx, which is the prototype of the class of peculiar
transients named SNe Iax. Similar to SN 2002cx, SN 2014ck reached a peak
brightness mag, with a post-maximum decline-rate mag. However, the spectroscopic sequence shows
similarities with SN 2008ha, which was three magnitudes fainter and faster
declining. In particular, SN 2014ck exhibits extremely low ejecta velocities,
km s at maximum, which are close to the value measured for
SN 2008ha and half the value inferred for SN 2002cx. The bolometric light curve
of SN 2014ck is consistent with the production of of Ni. The spectral identification of several iron-peak
features, in particular Co II lines in the NIR, provides a clear link to SNe
Ia. Also, the detection of narrow Si, S and C features in the pre-maximum
spectra suggests a thermonuclear explosion mechanism. The late-phase spectra
show a complex overlap of both permitted and forbidden Fe, Ca and Co lines. The
appearance of strong [Ca~II] 7292, 7324 again mirrors the
late-time spectra of SN 2008ha and SN 2002cx. The photometric resemblance to SN
2002cx and the spectral similarities to SN 2008ha highlight the peculiarity of
SN 2014ck, and the complexity and heterogeneity of the SNe Iax class.Comment: MNRAS Accepted 2016 March 22. Received 2016 March
SN 2016coi (ASASSN-16fp): an energetic H-stripped core-collapse supernova from a massive stellar progenitor with large mass loss
We present comprehensive observations and analysis of the energetic
H-stripped SN 2016coi (a.k.a. ASASSN-16fp), spanning the -ray through
optical and radio wavelengths, acquired within the first hours to 420
days post explosion. Our campaign confirms the identification of He in the SN
ejecta, which we interpret to be caused by a larger mixing of Ni into the outer
ejecta layers. From the modeling of the broad bolometric light curve we derive
a large ejecta mass to kinetic energy ratio (, ). The small
[\ion{Ca}{ii}] \lam\lam7291,7324 to [\ion{O}{i}] \lam\lam6300,6364 ratio
(0.2) observed in our late-time optical spectra is suggestive of a large
progenitor core mass at the time of collapse. We find that SN 2016coi is a
luminous source of X-rays ( in the first
days post explosion) and radio emission ( at peak). These values are in line with those
of relativistic SNe (2009bb, 2012ap). However, for SN 2016coi we infer
substantial pre-explosion progenitor mass-loss with rate and a sub-relativistic shock
velocity , in stark contrast with relativistic SNe and similar
to normal SNe. Finally, we find no evidence for a SN-associated shock breakout
-ray pulse with energy . While we
cannot exclude the presence of a companion in a binary system, taken together,
our findings are consistent with a massive single star progenitor that
experienced large mass loss in the years leading up to core-collapse, but was
unable to achieve complete stripping of its outer layers before explosion.Comment: Submitted to ApJ. Main text: 21 pages; Appendix: 15 pages; 12 figure
A pulsation analysis of K2 observations of the subdwarf B star PG 1142-037 during Campaign 1 : A subsynchronously rotating ellipsoidal variable
We report a new subdwarf B pulsator, PG 1142-037, discovered during the first full-length campaign of K2, the two-gyro mission of the Kepler space telescope. 14 periodicities have been detected between 0.9 and 2.5 hr with amplitudes below 0.35 parts-per-thousand. We have been able to associate all of the pulsations with low-degree, 1Peer reviewe
The long-lived Type IIn SN 2015da: Infrared echoes and strong interaction within an extended massive shell star star star
In this paper we report the results of the first similar to four years of spectroscopic and photometric monitoring of the Type IIn supernova SN 2015da (also known as PSN J13522411+3941286, or iPTF16tu). The supernova exploded in the nearby spiral galaxy NGC 5337 in a relatively highly extinguished environment. The transient showed prominent narrow Balmer lines in emission at all times and a slow rise to maximum in all bands. In addition, early observations performed by amateur astronomers give a very well-constrained explosion epoch. The observables are consistent with continuous interaction between the supernova ejecta and a dense and extended H-rich circumstellar medium. The presence of such an extended and dense medium is difficult to reconcile with standard stellar evolution models, since the metallicity at the position of SN 2015da seems to be slightly subsolar. Interaction is likely the mechanism powering the light curve, as confirmed by the analysis of the pseudo bolometric light curve, which gives a total radiated energy greater than or similar to 10(51) erg. Modeling the light curve in the context of a supernova shock breakout through a dense circumstellar medium allowed us to infer the mass of the prexisting gas to be similar or equal to 8 M-circle dot, with an extreme mass-loss rate for the progenitor star similar or equal to 0.6 M-circle dot yr(-1), suggesting that most of the circumstellar gas was produced during multiple eruptive events. Near- and mid-infrared observations reveal a fluxexcess in these domains, similar to those observed in SN 2010jl and other interacting transients, likely due to preexisting radiatively heated dust surrounding the supernova. By modeling the infrared excess, we infer a mass greater than or similar to 0.4 x 10(-3) M-circle dot for the dustSpanish MICINN gran
A SEARCH for AN OPTICAL COUNTERPART to the GRAVITATIONAL-WAVE EVENT GW151226
We present a search for an electromagnetic counterpart of the gravitational-wave source GW151226. Using the Pan-STARRS1 telescope we mapped out 290 square degrees in the optical filter, starting 11.5 hr after the LIGO information release and lasting for an additional 28 days. The first observations started 49.5 hr after the time of the GW151226 detection. We typically reached sensitivity limits of = 20.3–20.8 and covered 26.5% of the LIGO probability skymap. We supplemented this with ATLAS survey data, reaching 31% of the probability region to shallower depths of 19. We found 49 extragalactic transients (that are not obviously active galactic nuclei), including a faint transient in a galaxy at 7 Mpc (a luminous blue variable outburst) plus a rapidly decaying M-dwarf flare. Spectral classification of 20 other transient events showed them all to be supernovae. We found an unusual transient, PS15dpn, with an explosion date temporally coincident with GW151226, that evolved into a type Ibn supernova. The redshift of the transient is secure at = 0.1747 ± 0.0001 and we find it unlikely to be linked, since the luminosity distance has a negligible probability of being consistent with that of GW151226. In the 290 square degrees surveyed we therefore do not find a likely counterpart. However we show that our survey strategy would be sensitive to NS–NS mergers producing kilonovae at 100 Mpc, which is promising for future LIGO/Virgo searches.NASA (Grant IDs: NNX08AR22G, NNX12AR65G, NNX14AM74G, NNX12AR55G), EU/FP7-ERC (Grant IDs: 291222, 307260, 320360, 615929), a Weizmann-UK Making Connections Grant, STFC (Ernest Rutherford Fellowship), Alexander von Humboldt Foundation (Sofia Kovalevskaja Award), National Science Foundation (Grant ID: AST-1238877)This is the final version of the article. It first appeared from Institute of Physics Publishing via http://dx.doi.org/10.3847/2041-8205/827/2/L4
The Early Detection and Follow-up of the Highly Obscured Type II Supernova 2016ija/DLT16am
We present our analysis of the Type II supernova DLT16am (SN 2016ija). The object was discovered during theongoing D < 40 Mpc (DLT40) one-day cadence supernova search at r ∼ 20.1 mag in the edge-on nearby(D = 20.0 ± 4.0 Mpc) galaxy NGC 1532. The subsequent prompt and high-cadenced spectroscopic andphotometric follow-up revealed a highly extinguished transient, with E(B - V) = 1.95 ±0.15 mag, consistentwith a standard extinction law with RV=3.1 and a bright (MV = -18.48 ±0.77 mag) absolute peak magnitude. Acomparison of the photometric features with those of large samples of SNe II reveals a fast rise for the derivedluminosity and a relatively short plateau phase, with a slope of S50V = 0.84 ±0.04 mag 50 days, consistent withthe photometric properties typical of those of fast-declining SNe II. Despite the large uncertainties on the distance andthe extinction in the direction of DLT16am, the measured photospheric expansion velocity and the derived absoluteV-band magnitude at ~50 days after the explosion match the existing luminosity-velocity relation for SNe II
Optical follow-up of the tidal disruption event iPTF16fnl: new insights from X-shooter observations
We present the results from Nordic Optical Telescope and X-shooter follow-up campaigns of the tidal disruption event (TDE) iPTF16fnl, covering the first similar to 100 d after the transient discovery. We followed the source photometrically until the TDE emission was no longer detected above the host galaxy light. The bolometric luminosity evolution of the TDE is consistent with an exponential decay with e-folding constant t(0) = 17.6 +/- 0.2 d. The early-time spectra of the transient are dominated by broad He II lambda 4686, H beta, H alpha, and N III lambda 4100 emission lines. The latter is known to be produced together with the N III lambda 4640 in the Bowen fluorescence mechanism. Due to the medium-resolution X-shooter spectra we have been able to separate the Bowen blend contribution from the broad He II emission line. The detection of the Bowen fluorescence lines in iPTF16fnl place this transient among the N-rich TDE subset. In the late-time X-shooter spectra, narrow emission lines of [O III] and [N II] originating from the host galaxy are detected, suggesting that the host galaxy harbours a weak active galactic nucleus in its core. The properties of all broad emission lines evolve with time. The equivalent widths follow an exponential decay compatible with the bolometric luminosity evolution. The full width at half-maximum of the broad lines decline with time and the line profiles develop a narrow core at later epochs. Overall, the optical emission of iPTF16fnl can be explained by being produced in an optically thick region in which high densities favour the Bowen fluorescence mechanism and where multiple electron scatterings are responsible for the line broadening
A population of highly energetic transient events in the centres of active galaxies
Recent all-sky surveys have led to the discovery of new types of transients. These include stars disrupted by the central supermassive black hole, and supernovae that are 10–100 times more energetic than typical ones. However, the nature of even more energetic transients that apparently occur in the innermost regions of their host galaxies is hotly debated1,2,3. Here we report the discovery of the most energetic of these to date: PS1-10adi, with a total radiated energy of ~2.3 × 1052 erg. The slow evolution of its light curve and persistently narrow spectral lines over ∼ 3 yr are inconsistent with known types of recurring black hole variability. The observed properties imply powering by shock interaction between expanding material and large quantities of surrounding dense matter. Plausible sources of this expanding material are a star that has been tidally disrupted by the central black hole, or a supernova. Both could satisfy the energy budget. For the former, we would be forced to invoke a new and hitherto unseen variant of a tidally disrupted star, while a supernova origin relies principally on environmental effects resulting from its nuclear location. Remarkably, we also discover that PS1-10adi is not an isolated case. We therefore surmise that this new population of transients has previously been overlooked due to incorrect association with underlying central black hole activity
Dead or Alive? Long-term evolution of SN 2015bh (SNhunt275)
This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stw2253Supernova (SN) 2015bh (or SNhunt275) was discovered in NGC 2770 on 2015 February with an absolute magnitude of M ~ −13.4 mag, and was initially classified as an SN impostor. Here, we present the photometric and spectroscopic evolution of SN 2015bh from discovery to late phases (~1 yr after). In addition, we inspect archival images of the host galaxy up to ~21 yr before discovery, finding a burst ~1 yr before discovery, and further signatures of stellar instability until late 2014. Later on, the luminosity of the transient slowly increases, and a broad light-curve peak is reached after about three months. We propose that the transient discovered in early 2015 could be a core-collapse SN explosion. The pre-SN luminosity variability history, the long-lasting rise and faintness first light-curve peak suggests that the progenitor was a very massive, unstable and blue star, which exploded as a faint SN because of severe fallback of material. Later on, the object experiences a sudden brightening of 3 mag, which results from the interaction of the SN ejecta with circumstellar material formed through repeated past mass-loss events. Spectroscopic signatures of interaction are however visible at all epochs. A similar chain of events was previously proposed for the similar interacting SN 2009ip.European Research Council under the European Union's Seventh Framework Programme, Science and Technology Facilities Counci
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