ULTRASAT: A Wide-field Time-domain UV Space Telescope

Shvartzvald, Y.; Waxman, E.; Gal-Yam, A.; Ofek, E. O.; Ben-Ami, S.; Berge, D.; Kowalski, M.; Bühler, R.; Worm, S.; Rhoads, J. E.; Arcavi, I.; Maoz, D.; Polishook, D.; Stone, N.; Trakhtenbrot, B.; Ackermann, M.; Aharonson, O.; Birnholtz, O.; Chelouche, D.; Guetta, D.; Hallakoun, N.; Horesh, A.; Kushnir, D.; Mazeh, T.; Nordin, J.; Ofir, A.; Ohm, S.; Parsons, D.; Pe’er, A.; Perets, H. B.; Perdelwitz, V.; Poznanski, D.; Sadeh, I.; Sagiv, I.; Shahaf, S.; Soumagnac, M.; Tal-Or, L.; Santen, J. Van; Zackay, B.; Guttman, O.; Rekhi, P.; Townsend, A.; Weinstein, A.; Wold, I.

doi:10.3847/1538-4357/ad2704

Cited by 30 publications

(9 citation statements)

References 372 publications

(399 reference statements)

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“…The ultrastripped SNe candidates in the literature show an early luminosity excess that is powered by shock cooling. Future widefield UV surveys such as ULTRASAT (Sagiv et al 2014;Shvartzvald et al 2024), UVEX (Kulkarni et al 2021), and deep ground-based surveys such as LSST (Ivezić et al 2019) in synergy with high-cadenced surveys such as ZTF will provide an exciting opportunity to explore this phase space. (This table is available in its entirety in machine-readable form in the online article.…”

Section: Discussionmentioning

confidence: 99%

SN 2023zaw: An Ultrastripped, Nickel-poor Supernova from a Low-mass Progenitor

Das,

Fremling,

Kasliwal

et al. 2024

ApJL

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We present SN 2023zaw—a subluminous (M r = −16.7 mag) and rapidly evolving supernova (t 1/2,r = 4.9 days), with the lowest nickel mass (≈0.002 M ⊙) measured among all stripped-envelope supernovae discovered to date. The photospheric spectra are dominated by broad He i and Ca near-infrared emission lines with velocities of ∼10,000−12,000 km s−1. The late-time spectra show prominent narrow He i emission lines at ∼1000 km s−1, indicative of interaction with He-rich circumstellar material. SN 2023zaw is located in the spiral arm of a star-forming galaxy. We perform radiation-hydrodynamical and analytical modeling of the lightcurve by fitting with a combination of shock-cooling emission and nickel decay. The progenitor has a best-fit envelope mass of ≈0.2 M ☉ and an envelope radius of ≈50 R ⊙. The extremely low nickel mass and low ejecta mass (≈0.5 M ⊙) suggest an ultrastripped SN, which originates from a mass-losing low-mass He-star (zero-age main-sequence mass < 10 M ⊙) in a close binary system. This is a channel to form double neutron star systems, whose merger is detectable with LIGO. SN 2023zaw underscores the existence of a previously undiscovered population of extremely low nickel mass (<0.005 M ☉) stripped-envelope supernovae, which can be explored with deep and high-cadence transient surveys.

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Section: Discussionmentioning

confidence: 99%

SN 2023zaw: An Ultrastripped, Nickel-poor Supernova from a Low-mass Progenitor

Das,

Fremling,

Kasliwal

et al. 2024

ApJL

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“…The DART impact was also detected using Swift-UVOT (Gehrels et al 2004;Roming et al 2005) in the near-ultraviolet (NUV) band (Ofek et al 2024), peaking at about 16.4 mag. Such events in the NUV band can be potentially detected by ULTRASAT (Sagiv et al 2014;Shvartzvald et al 2024). Therefore, we also calculate the expected magnitude distribution in the NUV band and find that the fraction of collision events at Sun-observer-asteroid angles larger than 50°, and brighter than the limiting magnitude of ULTRASAT in 900 s, is about 10 −6 .…”

Section: The Apparent Magnitude Distribution Of Collision Eventsmentioning

confidence: 91%

Asteroid Collisions: Expected Visibility and Rate

Ofek,

Polishook,

Kushnir

et al. 2024

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Asteroid collisions are one of the main processes responsible for the evolution of bodies in the main belt. Using observations of the Dimorphos impact by the DART spacecraft, we estimate how asteroid collisions in the main belt may look in the first hours after the impact. If the DART event is representative of asteroid collisions with a ∼1 m sized impactor, then the light curves of these collisions will rise on timescales of about ≳100 s and will remain bright for about 1 hr. Next, the light curve will decay on a few hours' timescale to an intermediate luminosity level in which it will remain for several weeks, before slowly returning to its baseline magnitude. This estimate suffers from several uncertainties due to, e.g., the diversity of asteroid composition, their material strength, and spread in collision velocities. We estimate that the rate of collisions in the main belt with energy similar to or larger than the DART impact is of the order of 7000 yr−1 (±1 dex). The large range is due to the uncertainty in the abundance of ∼1 m sized asteroids. We estimate the magnitude distribution of such events in the main belt, and we show that ∼6% of these events may peak at magnitudes brighter than 21. The detection of these events requires a survey with ≲1 hr cadence and may contribute to our understanding of the asteroids’ size distribution, collisional physics, and dust production. With an adequate survey strategy, new survey telescopes may regularly detect asteroid collisions.

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“…In addition, the model can be also discriminated by constraining the spectral shape of the emission. This can be done by simultaneously observing the flares with the ZTF, the Vera Rubin Observatory (Ivezić et al 2019), the Roman Space Telescope (Spergel et al 2015), and the Ultraviolet Transient Astronomy Satellite (ULTRASAT; Shvartzvald et al 2024; Figure 2) in the future.…”

Section: Shock Cooling Emissionmentioning

confidence: 99%

Shock Cooling and Breakout Emission for Optical Flares Associated with Gravitational-wave Events

Tagawa,

Kimura,

Haiman

et al. 2024

ApJ

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The astrophysical origin of stellar-mass black hole (BH) mergers discovered through gravitational waves (GWs) is widely debated. Mergers in the disks of active galactic nuclei (AGNs) represent promising environments for at least a fraction of these events, with possible observational clues in the GW data. An additional clue to unveil AGN merger environments is provided by possible electromagnetic emission from postmerger accreting BHs. Associated with BH mergers in AGN disks, emission from shocks emerging around jets launched by accreting merger remnants is expected. Here we compute the properties of the emission produced during breakout and the subsequent adiabatic expansion phase of the shocks, and we then apply this model to optical flares suggested to be possibly associated with GW events. We find that the majority of the reported flares can be explained by breakout and shock cooling emission. If the optical flares are produced by shock cooling emission, they would display moderate color evolution, possibly color variations among different events, and a positive correlation between delay time and flare duration and would be preceded by breakout emission in X-rays. If the breakout emission dominates the observed lightcurve, we predict the color to be distributed in a narrow range in the optical band and the delay time from GW to electromagnetic emission to be longer than ∼2 days. Hence, further explorations of delay time distributions, flare color evolution, and associated X-ray emission will be useful to test the proposed emission model for the observed flares.

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ULTRASAT: A Wide-field Time-domain UV Space Telescope

Cited by 30 publications

References 372 publications

SN 2023zaw: An Ultrastripped, Nickel-poor Supernova from a Low-mass Progenitor

SN 2023zaw: An Ultrastripped, Nickel-poor Supernova from a Low-mass Progenitor

Asteroid Collisions: Expected Visibility and Rate

Shock Cooling and Breakout Emission for Optical Flares Associated with Gravitational-wave Events

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