| Markarian 817 | |
|---|---|
.jpg) Mrk 817 taken byHubble Space Telescope | |
| Observation data (J2000epoch) | |
| Constellation | Draco |
| Right ascension | 14h 36m 22.068s |
| Declination | +58d 47m 39.38s |
| Redshift | 0.031328 |
| Heliocentric radial velocity | 9,392km/s |
| Distance | 456Mly (140Mpc) |
| Apparent magnitude (V) | 14.6 |
| Characteristics | |
| Type | SBc, Sy1.5 |
| 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 abarred spiral galaxy located in the constellationDraco. It is located 456 millionlight-years fromEarth, which, given its apparentdimensions, means that Markarian 817 is about 80,000 light-years across.[1] It is aSeyfert galaxy.
The nucleus of Markarian 817 is found to beactive. It is classified as aSeyfert 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 ofdust along the galaxy's bar according to theHubble image.[5]
A study conducted in February 2011, shows that the active core is not fixed as it shows strong variabilities inX-rays andultraviolet rays (UV). The X-rayluminosity varies by a factor of ~40 over 20 years, while the UVcontinuum/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 UVabsorption lines, suggesting a dust-free, ionized obscurer that is located in the innerbroad-line region, partially covering the central source.[8] During the first 55 days,scientists observed there is ade-coupling of the UV continuum and the UV broad emission linevariability. 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 theaccretion 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 ofastronomers led by Edward M. Cackett from theWayne State University inDetroit, monitored the galaxy with theNeil Gehrels Swift Observatory for 15 months, during which they obtainedobservations 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 deepXMM Newton andNuSTAR observations, the spectra presents a complex X-ray wind which consists of neutral and ionized absorption zones. Threevelocity components are detected from the part of the structured ultra-fastoutflow 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 opticalbroad line region.[10]
The centralblack hole in Markarian 817 has an estimatedsolar mass of (4.9 +/- 0.8) E+7 according to Peterson et al. 2004.[11] Such winds tend to move at many millions ofkilometers per hour, thus cleaning upinterstellar gas from their region of space. This cuts off the rate of production of newstars being formed in Markarian 817, leaving very little matter to feed the accretion disk.[12] This suggests that the black hole is experiencing a "temper tantrum" and is responsible for shaping its host galaxy.[13]
In an article in which Markarian 817 and another Seyfert galaxyNGC 7469 is studied, it is revealed both AGNs displayed time lags in the broad emission line, including H, H, He~{\sc ii} and He~{\sc i} and also the Fe~{\sc ii} for Markarian 817 with respect to the varyingcontinuum at 5100~Å.[14] From the relationship ofline widths and time lags, both galaxies showed that the broad-line regions (BLR) dynamics are consistent with the viral predication. Data provided from Markarian 817 showed almost the same kinetic structures, in which the time lags in the red wing is larger compared to the time lags in the blue wing. This indicates the BLR of Keplerian motion seemly has outflowing components during the monitoring period.[14]