Markarian 817
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| Markarian 817 | |
|---|---|
.jpg) Mrk 817 taken by Hubble Space Telescope | |
| Observation data (J2000 epoch) | |
| Constellation | Draco |
| Right ascension | 14h 36m 22.068s |
| Declination | +58d 47m 39.38s |
| Redshift | 0.031328 |
| Heliocentric radial velocity | 9,392 km/s |
| Distance | 456 Mly (140 Mpc) |
| Apparent magnitude (V) | 14.6 |
| Characteristics | |
| Type | SBc, Sy 1.5[1] |
| Size | 28.69 kpc (93,500 ly) (diameter; D25 isophote)[1] |
| Apparent size (V) | 0.6' x 0.6' |
| Notable features | Seyfert galaxy |
| Other designations | |
| UGC 9412, SBS 1434+590, CGCG 296-015, IRAS 14349+5900, PGC 52202 | |
Markarian 817 is a barred spiral galaxy located in the constellation Draco. It is located 456 million light-years from Earth, which, given its apparent dimensions, means that Markarian 817 is about 94,000 light-years across.[1] It is a Seyfert galaxy.
The nucleus of Markarian 817 is found to be active. It is classified as a Seyfert 1.5[2] or Seyfert 1.2 galaxy by the recent work done, according to Koss et al. 2017.[3] The nucleus sits in a barred spiral galaxy, close to face-on and not typical for optically selected unobscured Seyferts.[4] There is evidence of dust along the galaxy's bar according to the Hubble image.[5]
A study conducted in February 2011, shows that the active core is not fixed as it shows strong variabilities in X-rays and ultraviolet rays (UV). The X-ray luminosity varies by a factor of ~40 over 20 years, while the UV continuum/emission lines vary at the most by a factor of ~2.3 over the past 30 years.[6][7]
A 2021 study shows that the X-ray spectrum in Markarian 817 is highly absorbed and there are new blueshifted, broad, and narrow UV absorption lines, suggesting a dust-free, ionized obscurer that is located in the inner broad-line region, partially covering the central source.[8] During the first 55 days, scientists observed there is a de-coupling of the UV continuum and the UV broad emission line variability. The next 42 days of the campaign showed the correlation recovering, as Markarian 817 entered the less obscured state. The short C IV and Lyα lags suggest that the accretion disk extends beyond the UV broad-line region.[8]
Markarian 817 has become a notable target of the AGN STORM 2 project, in which a group of astronomers led by Edward M. Cackett from the Wayne State University in Detroit, monitored the galaxy with the Neil Gehrels Swift Observatory for 15 months, during which they obtained observations in X-rays and six ultraviolet/optical filters to shed more light on Markarian 817.[9]
Further observations done in 2022 showed that the source flux in Markarian 817 has declined compared to that recorded at a prior point during the 19-year mission. From the deep XMM Newton and NuSTAR observations, the spectra presents a complex X-ray wind which consists of neutral and ionized absorption zones. Three velocity components are detected from the part of the structured ultra-fast outflow with v/c = 0.043 (+0.007,-0.003), v/c = 0.079 (+0.003,-0.0008), and v/c = 0.074 (+0.004,-0.005).[10] These suggest that the wind likely arises at radii that are smaller compared to the optical broad line region.[10]
