4 research outputs found
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
Discovery of an intermediate-luminosity red transient in M51 and its likely dust-obscured, infrared-variable progenitor
We present the discovery of an optical transient (OT) in Messier 51,
designated M51 OT2019-1 (also ZTF19aadyppr, AT 2019abn, ATLAS19bzl), by the
Zwicky Transient Facility (ZTF). The OT rose over 15 days to an observed
luminosity of (), in the
luminosity gap between novae and typical supernovae (SNe). Spectra during the
outburst show a red continuum, Balmer emission with a velocity width of
km s, Ca II and [Ca II] emission, and absorption features
characteristic of an F-type supergiant. The spectra and multiband light curves
are similar to the so-called "SN impostors" and intermediate-luminosity red
transients (ILRTs). We directly identify the likely progenitor in archival
Spitzer Space Telescope imaging with a m luminosity of
and a color redder than 0.74 mag, similar
to those of the prototype ILRTs SN 2008S and NGC 300 OT2008-1. Intensive
monitoring of M51 with Spitzer further reveals evidence for variability of the
progenitor candidate at [4.5] in the years before the OT. The progenitor is not
detected in pre-outburst Hubble Space Telescope optical and near-IR images. The
optical colors during outburst combined with spectroscopic temperature
constraints imply a higher reddening of mag and higher
intrinsic luminosity of
() near peak than seen in previous ILRT
candidates. Moreover, the extinction estimate is higher on the rise than on the
plateau, suggestive of an extended phase of circumstellar dust destruction.
These results, enabled by the early discovery of M51 OT2019-1 and extensive
pre-outburst archival coverage, offer new clues about the debated origins of
ILRTs and may challenge the hypothesis that they arise from the
electron-capture induced collapse of extreme asymptotic giant branch stars.Comment: 21 pages, 5 figures, published in ApJ
Discovery of an Intermediate-luminosity Red Transient in M51 and Its Likely Dust-obscured, Infrared-variable Progenitor
We present the discovery of an optical transient (OT) in Messier 51, designated M51 OT2019-1 (also ZTF 19aadyppr, AT 2019abn, ATLAS19bzl), by the Zwicky Transient Facility (ZTF). The OT rose over 15 days to an observed luminosity of M_r = −13 (νL ν = 9 × 10^6 L_⊙), in the luminosity gap between novae and typical supernovae (SNe). Spectra during the outburst show a red continuum, Balmer emission with a velocity width of ≈400 km s^(−1), Ca II and [Ca II] emission, and absorption features characteristic of an F-type supergiant. The spectra and multiband light curves are similar to the so-called "SN impostors" and intermediate-luminosity red transients (ILRTs). We directly identify the likely progenitor in archival Spitzer Space Telescope imaging with a 4.5 μm luminosity of M_([4.5]) ≈ −12.2 mag and a [3.6]–[4.5] color redder than 0.74 mag, similar to those of the prototype ILRTs SN 2008S and NGC 300 OT2008-1. Intensive monitoring of M51 with Spitzer further reveals evidence for variability of the progenitor candidate at [4.5] in the years before the OT. The progenitor is not detected in pre-outburst Hubble Space Telescope optical and near-IR images. The optical colors during outburst combined with spectroscopic temperature constraints imply a higher reddening of E(B − V) ≈ 0.7 mag and higher intrinsic luminosity of M_r ≈ −14.9 mag (νL_ν = 5.3 × 10^7 L⊙) near peak than seen in previous ILRT candidates. Moreover, the extinction estimate is higher on the rise than on the plateau, suggestive of an extended phase of circumstellar dust destruction. These results, enabled by the early discovery of M51 OT2019-1 and extensive pre-outburst archival coverage, offer new clues about the debated origins of ILRTs and may challenge the hypothesis that they arise from the electron-capture induced collapse of extreme asymptotic giant branch stars