AT2017fej

AT2017fej is classified as a superluminous supernova (SLSN). Proposed power sources include magnetar spin-down and ejecta–CSM interaction; which engine applies to this object is not established from the classification label alone.

The specific progenitor of AT2017fej has not been observed. Events of this spectroscopic class are generally associated with massive-star core collapse after successive nuclear burning stages (hydrogen → helium → carbon → neon → oxygen → silicon → iron). Typical lifetimes of such progenitors are tens of millions of years, but that is a class expectation—not a measured age or evolutionary track for this star. No pre-explosion imaging identification is cited in the available record for AT2017fej.

AT2017fej has a luminosity distance of approximately 126709.0 Million Light-Years (redshift z = 4.1974, d_L = 38849.2 Mpc). Under a flat ΛCDM cosmology (H₀≈70 km/s/Mpc, Ωₘ≈0.3), the corresponding lookback time is ≈12036 Myr — when the light set out 12036.0 million years ago in deep Precambrian time, well before multicellular animals dominated Earth. Luminosity distance is larger than the light-travel distance because cosmic expansion stretches the path; the two must not be equated.

AT2017fej exhibits a measured spectroscopic redshift of z = 4.1974. The cockpit reports a user-facing recession velocity of 278,388.6 km/s, computed as the redshift Doppler-equivalent v = c·((1+z)²−1)/((1+z)²+1). Cosmological redshift is not generally equivalent to special-relativistic motion through space; this number is a convenient velocity label for z, not a measured peculiar velocity and not supernova ejecta speed. Bare c·z (≈1,258,349 km/s) is a different low-z approximation and is not mixed here.

At peak brightness, AT2017fej achieved an apparent magnitude of 23.84 around 2017/06/20. Corrected for cosmic distance and foreground interstellar dust, its intrinsic absolute magnitude was -22.3174. At this peak, the exploding star radiated with the incandescent brilliance of approximately 72.3 billion Suns combined, briefly outshining the cumulative starlight of entire dwarf galaxies!

SLSN radiated energies can exceed ordinary supernovae by large factors, but the power source (magnetar, CSM interaction, or other) is model-dependent. No object-specific energy release is published for AT2017fej.

Spectroscopic line blueshifts imply an ejecta velocity of approximately 278,390 km/s (~92.9% of c) for AT2017fej. This is distinct from cosmological recession velocity inferred from redshift.

SLSN light curves may be powered by magnetar spin-down, CSM interaction, or (in some models) large ⁵⁶Ni masses. Which engine powers AT2017fej is not established here, and no object-specific nickel mass is published.

Events of AT2017fej's broad spectroscopic class are discussed in galactic chemical evolution as sources of oxygen-group and intermediate-mass elements (and, for some channels, iron-peak material). No measured elemental yields are published for AT2017fej.

A core-collapse explosion associated with AT2017fej's class forges an ultra-dense compact stellar remnant at the center of the detonation. If the progenitor had an initial mass under ~20 solar masses, it left behind a neutron star (pulsar)—packing the mass of our entire Sun into a city-sized sphere barely 20 kilometers wide, spinning dozens or hundreds of times per second. If the progenitor exceeded ~25–30 solar masses, gravity overcame neutron degeneracy pressure, creating a permanent stellar-mass black hole.

Supernova remnants in general evolve through free-expansion, Sedov–Taylor, and radiative phases over centuries to millennia, sometimes becoming bright X-ray shells and occasionally compressing nearby molecular clouds. These are standard remnant-evolution models, not forecasts measured for AT2017fej. Whether this site will trigger star formation, reach particular X-ray temperatures, or match Cassiopeia A depends on local density and magnetic field—none of which are constrained by the data shown here.

No host galaxy is identified for AT2017fej in this catalog record. A blank host field means the association is unresolved here—it does not establish that the host is uncataloged, resolved in imaging, or securely linked by astrometry. Possible states (unidentified, hostless candidate, imaging detection without a catalog name, or a securely matched cataloged galaxy) require separate evidence that is not present in this field.

In the celestial sphere, AT2017fej is located at Right Ascension 10:02:58.12 and Declination +02:13:04.1, situated in the constellation Sextans (The Sextant). Because its declination is +02:13:04.1, it is primarily placed in the Northern celestial hemisphere.

Along this line of sight, the catalog records a Milky Way foreground color excess of E(B−V) = 0.0163 mag (source: published extinction estimate), corresponding to roughly A_V ≈ 0.05 mag for R_V = 3.1. Band-specific corrections (e.g. A_r) differ from A_V and should be applied when available. Map-based values (IRSA / Schlafly & Finkbeiner 2011) must not be claimed unless that map was actually queried.

No calibrated photometry is published for AT2017fej. Without multi-epoch flux measurements, neither a light curve nor a peak magnitude can be established. Follow-up imaging from survey alert streams would be required to map its brightness evolution.

No spectrum has been published for AT2017fej. Without spectroscopy, its chemical composition, expansion velocity, and physical classification cannot be established. Classification spectra from follow-up observatories would be required to identify diagnostic absorption and emission lines.

AT2017fej was officially reported on 2017/04/26 by HSC collaboration. Discoveries are typically flagged by high-cadence robotic survey telescopes (such as ATLAS, ZTF, Pan-STARRS, ASAS-SN, or Gaia) and worldwide amateur astronomers scanning the night sky, followed by rapid spectroscopic classification by international observatories.

Data for AT2017fej are compiled from international astronomical notices, the IAU Transient Name Server (TNS), and peer-reviewed astrophysical journals.

Throughout global alert streams and survey databases, AT2017fej has also been designated as: HSC17dsid. These cross-matched identifiers allow astronomers to cross-reference observations across the Zwicky Transient Facility (ZTF), the Asteroid Terrestrial-impact Last Alert System (ATLAS), Pan-STARRS, Gaia Photometric Science Alerts, and the IAU Transient Name Server (TNS).

AT2017fej cannot currently be used for cosmological distance work because its classification is unresolved. The distance ladder relies on type-specific techniques: Type Ia supernovae use the Phillips relation between peak absolute magnitude and decline rate, while Type II events use the Expanding Photosphere Method or SCM-II. An unclassified transient fits neither, so no Hubble-constant constraint can be derived from it until a spectrum establishes its type.

No neutrino or gravitational-wave counterpart has been reported for AT2017fej, and none is expected to be identifiable without a classification. The multi-messenger signature differs sharply by type: core-collapse events emit a neutrino burst at shock breakout (detected once, for SN 1987A), while thermonuclear Type Ia events produce negligible neutrinos and gravitational waves. Searching for a counterpart before knowing which mechanism applies would be unfocused.

Compared to historical landmarks like SN 1987A in the Large Magellanic Cloud (168,000 light-years away, naked-eye peak m = 2.9) or the Crab Supernova of 1054 (6,500 light-years away), AT2017fej occurred at a distance of 126709.0 Million Light-Years. While historical naked-eye supernovae occurred within our Milky Way or its immediate satellites, modern discoveries like AT2017fej allow astrophysicists to probe diverse galactic environments, metallicities, and stellar populations across the broader universe.

Unknown — no measured brightness. AT2017fej was discovered 3489 days ago (2017/04/26), but no calibrated photometry is published for it, so its current apparent magnitude cannot be stated. Without a magnitude there is no basis for a telescope-aperture recommendation. Use the coordinates and airmass chart above to plan a follow-up observation and report what you measure.

No, Earth is in zero danger. Supernovae are violent events emitting powerful gamma rays, X-rays, and cosmic rays; however, the astrophysical 'lethal kill zone' for our planet's protective ozone layer is estimated at 50 to 100 light-years. At a distance of 126709.0 Million Light-Years, the inverse-square law dilutes the radiation by quintillions of times, making AT2017fej completely harmless to our biosphere and purely a fascinating spectacle for human exploration.