We present the discovery of ASASSN-18jd (AT 2018bcb), a luminous optical/ultraviolet(UV)/X-ray transient located in the nucleus of the galaxy 2MASX J22434289–1659083 at z = 0.1192. Over the year ...after discovery, Swift UltraViolet and Optical Telescope (UVOT) photometry shows the UV spectral energy distribution of the transient to be well modelled by a slowly shrinking blackbody with temperature $T \sim 2.5 \times 10^{4} \, {\rm K}$, a maximum observed luminosity of $L_{\rm max} = 4.5^{+0.6}_{-0.3}\times 10^{44} \, {\rm erg \,s}^{-1}$, and a radiated energy of $E = 9.6^{+1.1}_{-0.6} \times 10^{51} \, {\rm erg}$. X-ray data from Swift X-Ray Telescope (XRT) and XMM–Newton show a transient, variable X-ray flux with blackbody and power-law components that fade by nearly an order of magnitude over the following year. Optical spectra show strong, roughly constant broad Balmer emission and transient features attributable to He ii, N iii–v, O iii, and coronal Fe. While ASASSN-18jd shares similarities with tidal disruption events (TDEs), it is also similar to the newly discovered nuclear transients seen in quiescent galaxies and faint active galactic nuclei (AGNs).
In this work, we present the ultraviolet (UV) spectroscopic evolution of a tidal disruption event (TDE) for the first time. After the discovery of the nearby TDE iPTF16fnl, we obtained a series of ...observations with the Space Telescope Imaging Spectrograph (STIS) onboard the HubbleSpaceTelescope (HST). The dominant emission features closely resemble those seen in the UV spectra of the TDE ASASSN-14li and are also similar to those of N-rich quasars. There is evolution in the shape and central wavelength of the dominant emission features over the course of our observations, such that at early times the lines tend to be broad and redshifted, while at later times they are narrower and peak near the wavelengths of their atomic transitions. Like ASASSN-14li, but unlike N-rich quasars, iPTF16fnl shows neither Mg II 2798 Å nor C III 1909 Å emission features. We also present optical photometry and spectroscopy, which suggest that the complex He II profiles observed in the optical spectra of many TDEs are in part due to the presence of N III and C III Wolf–Rayet features, which can potentially serve as probes of the far-UV when space-based observations are not possible. Finally, we use Swift X-ray Telescope and Ultraviolet/Optical Telescope (UVOT) observations to place strong limits on the X-ray emission and determine the characteristic temperature, radius and luminosity of the emitting material. Lastly, we find that iPTF16fnl is subluminous and evolves more rapidly than other optically discovered TDEs.
X-ray properties of TDEs Saxton, R; Komossa, S; Auchettl, K ...
arXiv.org,
03/2021
Paper, Journal Article
Odprti dostop
Observational astronomy of tidal disruption events (TDEs) began with the detection of X-ray flares from quiescent galaxies during the ROSAT all-sky survey of 1990-1991. The flares complied with ...theoretical expectations, having high peak luminosities (\(L_{\rm x}\) up to \(\ge4\times 10^{44}\) erg/s), a thermal spectrum with \(kT\sim\)few\(\times10^5\) K, and a decline on timescales of months to years, consistent with a diminishing return of stellar debris to a black hole of mass \(10^{6-8}\) solar masses. These measurements gave solid proof that the nuclei of quiescent galaxies are habitually populated by a super-massive black hole. Beginning in 2000, XMM-Newton, Chandra and Swift have discovered further TDEs which have been monitored closely at multiple wavelengths. A general picture has emerged of, initially near-Eddington accretion, powering outflows of highly-ionised material, giving way to a calmer sub-Eddington phase, where the flux decays monotonically, and finally a low accretion rate phase with a harder X-ray spectrum indicative of the formation of a disk corona. There are exceptions to this rule though which at the moment are not well understood. A few bright X-ray TDEs have been discovered in optical surveys but in general X-ray TDEs show little excess emission in the optical band, at least at times coincident with the X-ray flare. X-ray TDEs are powerful new probes of accretion physics down to the last stable orbit, revealing the conditions necessary for launching jets and winds. Finally we see that evidence is mounting for nuclear and non-nuclear intermediate mass black holes based on TDE flares which are relatively hot and/or fast.
AT2019pev is a nuclear transient in a narrow-line Seyfert 1 galaxy at \(z=0.096\). The archival ultraviolet, optical and infrared data showed features of both tidal disruption events (TDEs) and ...active galactic nuclei (AGNs), and its nature is not fully understood. We present detailed X-ray observations of AT2019pev taken with Swift, Chandra and NICER over 173 days of its evolution since the first Swift XRT epoch. The X-ray luminosity increases by a factor of five in five days from the first Swift XRT epoch to the lightcurve peak. The lightcurve decays by a factor of ten over \(\sim\)75 days and then flattens with a weak re-brightening trend at late times. The X-ray spectra show a "harder-when-brighter" trend before peak and a "harder-when-fainter" trend after peak, which may indicate a transition of accretion states. The archival ground-based optical observations show similar time evolution as the X-ray lightcurves. Beyond the seasonal limit of the ground-based observations, the Gaia lightcurve is rising toward an equally bright or brighter peak 223 days after the optical discovery. Combining our X-ray analysis and archival multi-wavelength data, AT2019pev more closely resembles an AGN transient.
The number of binaries containing black holes or neutron stars depends critically on the fraction of binaries that survive supernova explosions. We searched for surviving star plus remnant binaries ...in a sample of 49 supernova remnants (SNR) containing 23 previously identified compact remnants and three high mass X-ray binaries (HMXB), finding no new interacting or non-interacting binaries. The upper limits on any main sequence stellar companion are typically <0.2Msun and are at worst <3Msun. This implies that f<0.1 of core collapse SNRs contain a non-interacting binary, and f=0.083 (0.032<f<0.17) contain an interacting binary at 90% confidence. We also find that the transverse velocities of HMXBs are low, with a median of only 12~km/s for field HMXBs, so surviving binaries will generally be found very close to the explosion center. We compare the results to a "standard" StarTrack binary population synthesis (BPS) model, finding reasonable agreement with the observations. In particular, the BPS models predict that 5% of SNe should leave a star plus remnant binary.
We present UV/optical/NIR observations and modeling of supernova (SN) 2024ggi, a type II supernova (SN II) located in NGC 3621 at 7.2 Mpc. Early-time ("flash") spectroscopy of SN 2024ggi within +0.8 ...days of discovery shows emission lines of H I, He I, C III, and N III with a narrow core and broad, symmetric wings (i.e., IIn-like) arising from the photoionized, optically-thick, unshocked circumstellar material (CSM) that surrounded the progenitor star at shock breakout. By the next spectral epoch at +1.5 days, SN 2024ggi showed a rise in ionization as emission lines of He II, C IV, N IV/V and O V became visible. This phenomenon is temporally consistent with a blueward shift in the UV/optical colors, both likely the result of shock breakout in an extended, dense CSM. The IIn-like features in SN 2024ggi persist on a timescale of \(t_{\rm IIn} = 3.8 \pm 1.6\) days at which time a reduction in CSM density allows the detection of Doppler broadened features from the fastest SN material. SN 2024ggi has peak UV/optical absolute magnitudes of \(M_{\rm w2} = -18.7\) mag and \(M_{\rm g} = -18.1\) mag that are consistent with the known population of CSM-interacting SNe II. Comparison of SN 2024ggi with a grid of radiation hydrodynamics and non-local thermodynamic equilibrium (nLTE) radiative-transfer simulations suggests a progenitor mass-loss rate of \(\dot{M} = 10^{-2}\)M\(_{\odot}\) yr\(^{-1}\) (\(v_w\) = 50 km/s), confined to a distance of \(r < 5\times 10^{14}\) cm. Assuming a wind velocity of \(v_w\) = 50 km/s, the progenitor star underwent an enhanced mass-loss episode in the last ~3 years before explosion.
We present LAISS (Lightcurve Anomaly Identification and Similarity Search), an automated pipeline to detect anomalous astrophysical transients in real-time data streams. We deploy our anomaly ...detection model on the nightly ZTF Alert Stream via the ANTARES broker, identifying a manageable \(\sim\)1-5 candidates per night for expert vetting and coordinating follow-up observations. Our method leverages statistical light-curve and contextual host-galaxy features within a random forest classifier, tagging transients of rare classes (spectroscopic anomalies), of uncommon host-galaxy environments (contextual anomalies), and of peculiar or interaction-powered phenomena (behavioral anomalies). Moreover, we demonstrate the power of a low-latency (\(\sim\)ms) approximate similarity search method to find transient analogs with similar light-curve evolution and host-galaxy environments. We use analogs for data-driven discovery, characterization, (re-)classification, and imputation in retrospective and real-time searches. To date we have identified \(\sim\)50 previously known and previously missed rare transients from real-time and retrospective searches, including but not limited to: SLSNe, TDEs, SNe IIn, SNe IIb, SNe Ia-CSM, SNe Ia-91bg-like, SNe Ib, SNe Ic, SNe Ic-BL, and M31 novae. Lastly, we report the discovery of 325 total transients, all observed between 2018-2021 and absent from public catalogs (\(\sim\)1% of all ZTF Astronomical Transient reports to the Transient Name Server through 2021). These methods enable a systematic approach to finding the "needle in the haystack" in large-volume data streams. Because of its integration with the ANTARES broker, LAISS is built to detect exciting transients in Rubin data.
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 AGN activity over ...the past decade. With a redshift of \(z = 0.01107\) and a peak UV/optical luminosity of \((5.4\pm0.4)\times10^{42}\) erg s\(^{-1}\), ASASSN-23bd is the lowest-redshift and least-luminous TDE discovered to date. Spectroscopically, ASASSN-23bd shows H\(\alpha\) and He I emission throughout its spectral time series, 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\(^{+1}_{-1}\), \(\sim\)9 days before discovery, with a nearly linear rise in flux, peaking in the \(g\) band on MJD \(60000^{+3}_{-3}\). Scaling relations and TDE light curve modelling find a black hole mass of \(\sim\)10\(^6\) \(M_\odot\), which is on the lower end of supermassive black hole masses. ASASSN-23bd is a dim X-ray source, with an upper limit of \(L_{0.3-10\,\mathrm{keV}} < 1.0\times10^{40}\) erg s\(^{-1}\) from stacking all \emph{Swift} observations prior to MJD 60061, but with soft (\(\sim 0.1\) keV) thermal emission with a luminosity of \(L_{0.3-2 \,\mathrm{keV}}\sim4\times10^{39}\) erg s\(^{-1}\) in \emph{XMM-Newton} observations on MJD 60095. The rapid \((t < 15\) days) light curve rise, low UV/optical luminosity, and a luminosity decline over 40 days of \(\Delta L_{40}\approx-0.7\) make ASASSN-23bd one of the dimmest TDEs to date and a member of the growing ``Low Luminosity and Fast'' class of TDEs.
We report the discovery of a stripped giant + lower giant binary,
2M04123153+6738486 (2M0412), identified during a search for non-interacting
compact object-star binaries. 2M0412 is an evolved ...($T_{\rm eff,
giant}\simeq4000$ K), luminous ($L_{\rm giant}\simeq150~L_\odot$) red giant in
a circular $P=81.2$ day binary. 2M0412 is a known variable star previously
classified as a semi-regular variable. The cross-correlation functions of
follow-up Keck/HIRES and LBT/PEPSI spectra show an RV-variable second component
with implied mass ratio $q=M_{\rm giant}/M_{\rm comp}\simeq0.20\pm0.01$. The
ASAS-SN, ATLAS, TESS and ZTF light curves show that the giant is a Roche lobe
filling ellipsoidal variable with an inclination of
$49.4^\circ{}\pm{0.3^{\circ}}$, and a giant mass of $M_{\rm giant}=0.38\pm0.01~
M_\odot$ for a distance of $\simeq3.7$ kpc. The mass of the giant indicates
that its envelope has been stripped. The giant companion on the lower red giant
branch has a mass of $M_{\rm comp}=1.91\pm0.03~M_\odot$ with $T_{\rm eff,
comp}\simeq5000$ K, $L_{\rm comp}\simeq60~L_\odot$ and $R_{\rm
comp}\simeq11~R_\odot$. We also identify an orbital phase dependent, broad $\rm
H\alpha$ emission line which could indicate ongoing accretion from the stripped
red giant onto the companion.
We present the Keck Infrared Transient Survey (KITS), a NASA Key Strategic Mission Support program to obtain near-infrared (NIR) spectra of astrophysical transients of all types, and its first data ...release, consisting of 105 NIR spectra of 50 transients. Such a data set is essential as we enter a new era of IR astronomy with the James Webb Space Telescope (JWST) and the upcoming Nancy Grace Roman Space Telescope (Roman). NIR spectral templates will be essential to search JWST images for stellar explosions of the first stars and to plan an effective Roma} SN Ia cosmology survey, both key science objectives for mission success. Between 2022 February and 2023 July, we systematically obtained 274 NIR spectra of 146 astronomical transients, representing a significant increase in the number of available NIR spectra in the literature. The first data release includes data from the 2022A semester. We systematically observed three samples: a flux-limited sample that includes all transients \(<\)17 mag in a red optical band (usually ZTF r or ATLAS o bands); a volume-limited sample including all transients within redshift \(z < 0.01\) (\(D \approx 50\) Mpc); and an SN Ia sample targeting objects at phases and light-curve parameters that had scant existing NIR data in the literature. The flux-limited sample is 39% complete (60% excluding SNe Ia), while the volume-limited sample is 54% complete and is 79% complete to \(z = 0.005\). All completeness numbers will rise with the inclusion of data from other telescopes in future data releases. Transient classes observed include common Type Ia and core-collapse supernovae, tidal disruption events (TDEs), luminous red novae, and the newly categorized hydrogen-free/helium-poor interacting Type Icn supernovae. We describe our observing procedures and data reduction using Pypeit, which requires minimal human interaction to ensure reproducibility.
