PKS 0735+178
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| PKS 0735+178 | |
|---|---|
 The BL Lac object PKS 0735+178 | |
| Observation data (Epoch J2000) | |
| Constellation | Gemini |
| Right ascension | 07h 38m 07.394s[1] |
| Declination | +17° 42′ 19.00″[1] |
| Redshift | 0.424[2] |
| Distance | 7,380 Mly (2,263 Mpc)[3] |
| Type | BL Lac blazar |
| Apparent magnitude (V) | 16.22[2] |
| Notable features | Candidate neutrino source |
| Other designations | |
| QSO J0738+1742, LEDA 2825195[4] | |
| See also: Quasar, List of quasars | |
PKS 0735+178 is a classical BL Lac object in the northern constellation of Gemini. This is one of the brightest objects of its type in the night sky.[5] It has a redshift of z = 0.424, with a luminosity distance of 7,380 million light-years (2,263 Mpc). PKS 0735+178 is a nearly point-like source with an angular size of a milliarcsecond.[3]
This object was identified as a radio source during the third part of a radio survey at the Parkes Observatory,[6] and became catalogued as PKS 0735+178.[4] An optical counterpart was found in 1970 which showed a continuous optical spectrum. In contrast, the radio emission is variable at frequencies greater than 6 GHz. The radio spectrum appears mostly flat above 1 GHz and the properties are similar to BL Lacertae. That is, it is an extragalactic object that resembles a quasar but lacks optical emission lines.[7] It has a very complex light curve which shows indications of periodicity.[8]
Gamma-ray emission was detected from this source in 1999. X-ray and gamma-ray emission was found to be steady from this source, whereas it displayed extreme variability in radio and optical bands.[9] Radio images of this object produced via very long baseline interferometry show a compact core with a jet that extends toward the northeast. The latter displays features of superluminal motion. Higher resolution observations show a pair of bends in the jet.[3]
In 2021, this target was found to be a candidate source for multiple neutrino events. Neutrino event 211208A was detected by the IceCube observatory and a best fit location was found within 2.2° of PKS 0735+178.[10] This observation occurred while PKS 0735+178 was undergoing a particularly strong flare event that was detected in the optical, ultraviolet, X-ray, and gamma-ray bands.[5]
