Abstract
Most tidal disruption events (TDEs) are currently found in time-domain optical and soft X-ray surveys, both of which are prone to significant obscuration. The infrared (IR), however, is a ...powerful probe of dust-enshrouded environments; hence, we recently performed a systematic search of NEOWISE mid-IR data for nearby, obscured TDEs within roughly 200 Mpc. We identified 18 TDE candidates in galactic nuclei, using difference imaging to uncover nuclear variability among significant host galaxy emission. These candidates were selected based on the following IR light-curve properties: (1)
L
W2
≳ 10
42
erg s
−1
at peak; (2) fast rise, followed by a slow, monotonic decline; (3) no significant prior variability; and (4) no evidence for active galactic nucleus (AGN) activity in Wide-field Infrared Survey Explorer (WISE) colors. The majority of these sources showed no variable optical counterpart, suggesting that optical surveys indeed miss numerous obscured TDEs. Using narrow-line ionization levels and variability arguments, we identified six sources as possible underlying AGN, yielding a total of 12 TDEs in our gold sample. This gold sample yields a lower limit on the IR-selected TDE rate of (2.0 ± 0.3) × 10
−5
galaxy
−1
yr
−1
((1.3 ± 0.2) × 10
−7
Mpc
−3
yr
−1
), which is comparable to optical and X-ray TDE rates. The IR-selected TDE host galaxies do not show a green valley overdensity nor as a preference for quiescent, Balmer strong galaxies, which are both overrepresented in optical and X-ray TDE samples. This IR-selected sample represents a new population of dusty TDEs that have historically been missed by optical and X-ray surveys and helps alleviate tensions between observed and theoretical TDE rates and the so-called missing energy problem.
ABSTRACT We report a multiwavelength (X-ray, ultraviolet/optical/infrared (UVOIR), radio) analysis of the relativistic tidal disruption event (TDE) candidate Sw J2058+05 from 3 months to 3 yr ...post-discovery in order to study its properties and compare its behavior with that of Sw J1644+57. Our main results are as follows: (1) The long-term X-ray light curve of Sw J2058+05 shows a remarkably similar trend to that of Sw J1644+57. After a prolonged power-law decay, the X-ray flux drops off rapidly by a factor of 160 within a span of Δt/ . Associating this sudden decline with the transition from super-Eddington to sub-Eddington accretion, we estimate the black hole mass to be in the range of 104-6 M . (2) We detect rapid ( 500 s) X-ray variability before the drop-off, suggesting that, even at late times, the X-rays originate from close to the black hole (ruling out a forward-shock origin). (3) We confirm using Hubble Space Telescope and Very Long Baseline Array astrometry that the location of the source coincides with the galaxy's center to within 400 pc (in projection). (4) We modeled Sw J2058+05's UVOIR spectral energy distribution with a single-temperature blackbody and find that while the radius remains more or less constant at a value of 63.4 4.5 AU ( cm) at all times during the outburst, the blackbody temperature drops significantly from ∼30,000 K at early times to a value of ∼15,000 K at late times (before the X-ray drop-off). Our results strengthen Sw J2058+05's interpretation as a TDE similar to Sw J1644+57.
We present SN2018kzr, the fastest declining supernova-like transient, second only to the kilonova, AT2017gfo. SN2018kzr is characterized by a peak magnitude of Mr = −17.98, a peak bolometric ...luminosity of ∼1.4 × 1043 erg s−1, and a rapid decline rate of 0.48 0.03 mag day−1 in the r band. The bolometric luminosity evolves too quickly to be explained by pure 56Ni heating, necessitating the inclusion of an alternative powering source. Incorporating the spin-down of a magnetized neutron star adequately describes the lightcurve and we estimate a small ejecta mass of Mej = 0.10 0.05 M . Our spectral modeling suggests the ejecta is composed of intermediate mass elements including O, Si, and Mg and trace amounts of Fe-peak elements, which disfavors a binary neutron star merger. We discuss three explosion scenarios for SN2018kzr, given the low ejecta mass, intermediate mass element composition, and high likelihood of additional powering-the core collapse of an ultra-stripped progenitor, the accretion induced collapse (AIC) of a white dwarf, and the merger of a white dwarf and neutron star. The requirement for an alternative input energy source favors either the AIC with magnetar powering or a white dwarf-neutron star merger with energy from disk wind shocks.
A subset of ultraluminous X-ray sources (those with luminosities of less than 10(40) erg s(-1); ref. 1) are thought to be powered by the accretion of gas onto black holes with masses of ∼5-20M cicled ...dot, probably by means of an accretion disk. The X-ray and radio emission are coupled in such Galactic sources; the radio emission originates in a relativistic jet thought to be launched from the innermost regions near the black hole, with the most powerful emission occurring when the rate of infalling matter approaches a theoretical maximum (the Eddington limit). Only four such maximal sources are known in the Milky Way, and the absorption of soft X-rays in the interstellar medium hinders the determination of the causal sequence of events that leads to the ejection of the jet. Here we report radio and X-ray observations of a bright new X-ray source in the nearby galaxy M 31, whose peak luminosity exceeded 10(39) erg s(-1). The radio luminosity is extremely high and shows variability on a timescale of tens of minutes, arguing that the source is highly compact and powered by accretion close to the Eddington limit onto a black hole of stellar mass. Continued radio and X-ray monitoring of such sources should reveal the causal relationship between the accretion flow and the powerful jet emission.
The particle-induced background of X-ray observatories is produced by galactic cosmic ray (GCR) primary protons, electrons, and He ions. Events due to direct interaction with the detector are usually ...removed by onboard processing. The interactions of these primary particles with the detector environment produce secondary particles that mimic X-ray events from celestial sources, and are much more difficult to identify. The filter-wheel closed data from the XMM-Newton EPIC-pn camera in small window mode (SWM) contains both the X-ray-like background events, and the events due to direct interactions with the primary particles. From this data, we demonstrate that X-ray-like background events are spatially correlated with the primary particle interaction. This result can be used to further characterize and reduce the non-X-ray background in silicon-based X-ray detectors in current and future missions. We also show that spectrum and pattern fractions of secondary particle events are different from those produced by cosmic X-rays.
We report the discovery by the Palomar Transient Factory (PTF) of the transient source PTF11agg, which is distinguished by three primary characteristics: (1) bright, rapidly fading, optical transient ...emission; (2) a faint, blue-quiescent optical counterpart; and (3) an associated year-long, scintillating radio transient. The observed properties are all consistent with the population of long-duration gamma-ray bursts (GRBs), marking the first time such an outburst has been discovered in the distant universe independent of a high-energy trigger. We searched for possible high-energy counterparts to PTF11agg, but found no evidence for associated prompt emission. We therefore consider three possible scenarios to account for a GRB-like afterglow without a high-energy counterpart: an "untriggered" GRB, an "orphan" afterglow. While not definitive, we nonetheless speculate that PTF11agg may represent a new, more common class of relativistic outbursts lacking associated high-energy emission. If so, such sources will be uncovered in large numbers by future wide-field optical and radio transient surveys.
The High Energy X-ray Probe (HEX-P) is a proposed NASA probe-class mission that combines the power of high angular resolution with abroad X-ray bandpass to provide the necessary leap in capabilities ...to address the important astrophysical questions of the next decade. HEX-P achieves breakthrough performance by combining technologies developed by experienced international partners. To meet the science goals, the payload consists of a suite of co-aligned X-ray telescopes designed to cover the0.2–80 keV bandpass. The High Energy Telescope (HET) has an effective bandpass of 2–80 keV, and the Low Energy Telescope (LET) has an effective bandpass of 0.2–20 keV. HEX-P will be launched into L1 to enable high observing efficiency, and the combination of bandpass and high observing efficiency delivers a powerful platform for broad science to serve a wide community. The baseline mission is 5 years, with 30% of the observing time dedicated to thePI-led program and 70% to a General Observer (GO) program. The GeneralObserver program will be executed along with the PI-led program
HEX-P
is a probe-class mission concept that will combine high spatial resolution X-ray imaging (
<
1
0
′
′
FWHM) and broad spectral coverage (0.2–80 keV) with an effective area superior to
NuSTAR
...above 10 keV to enable revolutionary new insights into a variety of astrophysical problems, especially those related to compact objects, accretion and outflows.
HEX-P
will launch at a time when the sky is being routinely scanned for transient gravitational wave, electromagnetic and neutrino phenomena that will require the capabilities of a sensitive, broadband X-ray telescope for follow up studies. These include the merger of compact objects such as neutron stars and black holes, stellar explosions, and the birth of new compact objects. A response time to target of opportunity observation requests of
<
24
hours and a field of regard of 3
π
steradians will allow
HEX-P
to probe the accretion and ejecta from these transient phenomena through the study of relativistic outflows and reprocessed emission, provide unique capabilities for understanding jet physics, and potentially revealing the nature of the central engine.
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