Gamma-ray bursts (GRBs) are divided into two populations
; long GRBs that derive from the core collapse of massive stars (for example, ref.
) and short GRBs that form in the merger of two compact ...objects
. Although it is common to divide the two populations at a gamma-ray duration of 2 s, classification based on duration does not always map to the progenitor. Notably, GRBs with short (≲2 s) spikes of prompt gamma-ray emission followed by prolonged, spectrally softer extended emission (EE-SGRBs) have been suggested to arise from compact object mergers
. Compact object mergers are of great astrophysical importance as the only confirmed site of rapid neutron capture (r-process) nucleosynthesis, observed in the form of so-called kilonovae
. Here we report the discovery of a possible kilonova associated with the nearby (350 Mpc), minute-duration GRB 211211A. The kilonova implies that the progenitor is a compact object merger, suggesting that GRBs with long, complex light curves can be spawned from merger events. The kilonova of GRB 211211A has a similar luminosity, duration and colour to that which accompanied the gravitational wave (GW)-detected binary neutron star (BNS) merger GW170817 (ref.
). Further searches for GW signals coincident with long GRBs are a promising route for future multi-messenger astronomy.
Abstract We present rest-frame UV Hubble Space Telescope imaging of the largest and most complete sample of 23 long-duration gamma-ray burst (GRB) host galaxies between redshifts 4 and 6. Of these ...23, we present new WFC3/F110W imaging for 19 of the hosts, which we combine with archival WFC3/F110W and WFC3/F140W imaging for the remaining four. We use the photometry of the host galaxies from this sample to characterize both the rest-frame UV luminosity function (LF) and the size–luminosity relation of the sample. We find that when assuming the standard Schechter-function parameterization for the UV LF, the GRB host sample is best fit with α = − 1.30 − 0.25 + 0.30 and M * = − 20.33 − 0.54 + 0.44 mag, which are consistent with results based on z ∼ 5 Lyman-break galaxies. We find that ∼68% of our size–luminosity measurements fall within or below the same relation for Lyman-break galaxies at z ∼ 4. This study observationally confirms expectations that at z ∼ 5 Lyman-break and GRB host galaxies should trace the same population and demonstrates the utility of GRBs as probes of hidden star formation in the high-redshift Universe. Under the assumption that GRBs unbiasedly trace star formation at this redshift, our nondetection fraction of 7/23 is consistent at the 95% confidence level with 13%–53% of star formation at redshift z ∼ 5 occurring in galaxies fainter than our detection limit of M 1600Å ≈ −18.3 mag.
Abstract
The detonation of a thin (≲0.03
M
⊙
) helium shell (He-shell) atop a ∼1
M
⊙
white dwarf (WD) is a promising mechanism to explain normal Type Ia supernovae (SNe Ia), while thicker He-shells ...and less massive WDs may explain some recently observed peculiar SNe Ia. We present observations of SN 2020jgb, a peculiar SN Ia discovered by the Zwicky Transient Facility (ZTF). Near maximum brightness, SN 2020jgb is slightly subluminous (ZTF
g
-band absolute magnitude −18.7 mag ≲
M
g
≲ −18.2 mag depending on the amount of host-galaxy extinction) and shows an unusually red color (0.2 mag ≲
g
ZTF
−
r
ZTF
≲ 0.4 mag) due to strong line-blanketing blueward of ∼5000 Å. These properties resemble those of SN 2018byg, a peculiar SN Ia consistent with an He-shell double detonation (DDet) SN. Using detailed radiative transfer models, we show that the optical spectroscopic and photometric evolution of SN 2020jgb is broadly consistent with a ∼0.95–1.00
M
⊙
(C/O core + He-shell) progenitor ignited by a ≳0.1
M
⊙
He-shell. However, one-dimensional radiative transfer models without non-local-thermodynamic-equilibrium treatment cannot accurately characterize the line-blanketing features, making the actual shell mass uncertain. We detect a prominent absorption feature at ∼1
μ
m in the near-infrared (NIR) spectrum of SN 2020jgb, which might originate from unburnt helium in the outermost ejecta. While the sample size is limited, we find similar 1
μ
m features in all the peculiar He-shell DDet candidates with NIR spectra obtained to date. SN 2020jgb is also the first peculiar He-shell DDet SN discovered in a star-forming dwarf galaxy, indisputably showing that He-shell DDet SNe occur in both star-forming and passive galaxies, consistent with the normal SN Ia population.
Abstract
We report multiwavelength observations and characterization of the ultraluminous transient AT 2021lwx (ZTF20abrbeie; aka “Barbie”) identified in the alert stream of the Zwicky Transient ...Facility (ZTF) using a Recommender Engine For Intelligent Transient Tracking filter on the ANTARES alert broker. From a spectroscopically measured redshift of 0.995, we estimate a peak-observed pseudo-bolometric luminosity of log(
L
max
/
erg
s
−
1
) = 45.7 from slowly fading ztf-
g
and ztf-
r
light curves spanning over 1000 observer-frame days. The host galaxy is not detected in archival Pan-STARRS observations (
g
> 23.3 mag), implying a lower limit to the outburst amplitude of more than 5 mag relative to the quiescent host galaxy. Optical spectra exhibit strong emission lines with narrow cores from the H Balmer series and ultraviolet semi-forbidden lines of Si
iii
λ
1892, C
iii
λ
1909, and C
ii
λ
2325. Typical nebular lines in Active Galactic Nucleus (AGN) spectra from ions such as O
ii
and O
iii
are not detected. These spectral features, along with the smooth light curve that is unlike most AGN flaring activity and the luminosity that exceeds any observed or theorized supernova, lead us to conclude that AT 2021lwx is most likely an extreme tidal disruption event (TDE). Modeling of ZTF photometry with
MOSFiT
suggests that the TDE was between a ≈14
M
⊙
star and a supermassive black hole of mass
M
BH
∼ 10
8
M
⊙
. Continued monitoring of the still-evolving light curve along with deep imaging of the field once AT 2021lwx has faded can test this hypothesis and potentially detect the host galaxy.
Abstract
We present a comprehensive catalog of observations and stellar population properties for 23 highly secure host galaxies of fast radio bursts (FRBs). Our sample comprises 6 repeating FRBs and ...17 apparent nonrepeaters. We present 82 new photometric and 8 new spectroscopic observations of these hosts. Using stellar population synthesis modeling and employing nonparametric star formation histories (SFHs), we find that FRB hosts have a median stellar mass of ≈10
9.9
M
⊙
, mass-weighted age ≈5.1 Gyr, and ongoing star formation rate ≈1.3
M
⊙
yr
−1
but span wide ranges in all properties. Classifying the hosts by degree of star formation, we find that 87% (20 of 23 hosts) are star-forming, two are transitioning, and one is quiescent. The majority trace the star-forming main sequence of galaxies, but at least three FRBs in our sample originate in less-active environments (two nonrepeaters and one repeater). Across all modeled properties, we find no statistically significant distinction between the hosts of repeaters and nonrepeaters. However, the hosts of repeating FRBs generally extend to lower stellar masses, and the hosts of nonrepeaters arise in more optically luminous galaxies. While four of the galaxies with the clearest and most prolonged rises in their SFHs all host repeating FRBs, demonstrating heightened star formation activity in the last ≲100 Myr, one nonrepeating host shows this SFH as well. Our results support progenitor models with short delay channels (i.e., magnetars formed via core-collapse supernova) for most FRBs, but the presence of some FRBs in less-active environments suggests a fraction form through more delayed channels.
Abstract
We present observations of SN 2022joj, a peculiar Type Ia supernova discovered by the Zwicky Transient Facility. SN 2022joj exhibits an unusually red
g
ZTF
−
r
ZTF
color at early times and a ...rapid blueward evolution afterward. Around maximum brightness, SN 2022joj shows a high luminosity (
M
g
ZTF
,
max
≃
−
19.7
mag), a blue broadband color (
g
ZTF
−
r
ZTF
≃ −0.2 mag), and shallow Si
ii
absorption lines, consistent with those of overluminous, SN 1991T-like events. The maximum-light spectrum also shows prominent absorption around 4200 Å, which resembles the Ti
ii
features in subluminous, SN 1991bg-like events. Despite the blue optical-band colors, SN 2022joj exhibits extremely red ultraviolet minus optical colors at maximum luminosity (
u
−
v
≃ 0.6 mag and
uvw
1 −
v
≃ 2.5 mag), suggesting a suppression of flux at ∼2500–4000 Å. Strong C
ii
lines are also detected at peak. We show that these unusual spectroscopic properties are broadly consistent with the helium-shell double detonation of a sub-Chandrasekhar mass (
M
≃ 1
M
⊙
) carbon/oxygen white dwarf from a relatively massive helium shell (
M
s
≃ 0.04–0.1
M
⊙
), if observed along a line of sight roughly opposite to where the shell initially detonates. None of the existing models could quantitatively explain all the peculiarities observed in SN 2022joj. The low flux ratio of Ni
ii
λ
7378 to Fe
ii
λ
7155 emission in the late-time nebular spectra indicates a low yield of stable Ni isotopes, favoring a sub-Chandrasekhar mass progenitor. The significant blueshift measured in the Fe
ii
λ
7155 line is also consistent with an asymmetric chemical distribution in the ejecta, as is predicted in double-detonation models.
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