7C 1415+2556

7C 1415+2556
7C 1415+2556, as seen by DESI Legacy Surveys
Observation data (J2000.0 epoch)
ConstellationBoötes
Right ascension14h 17m 56.67s
Declination+25d 43m 26.22s
Redshift0.240000
Heliocentric radial velocity71,950 km/s
Distance3.249 Gly (996.1 Mpc)
Apparent magnitude (V)0.052
Apparent magnitude (B)0.069
Surface brightness16.0
Characteristics
TypeOpt.var. BLLAC
Notable featuresBL Lacertae object
Other designations
RX J1417.9+2543, PGC 1747267, 2E 1415+2557, RBS 1366, 2MASS J14175667+2543260, MG2 J141757+2543, 2FGL J1418.1+2539, EXO 1415.6+2557, SWIFT J1417.7+2539

7C 1415+2556 also known as 2E 1415+2557 and PGC 1747267, is a BL Lac object with an X-ray flux of >=4×10-13 ergs s-1 cm-2,[1] located in the constellation of Boötes. With a redshift of 0.24, the galaxy is located 3.2 billion light-years from Earth.[2] It was discovered in 1988 as part of a program of optical polarimetry of a complete sample of radio sources.[3]

Characteristics

A low-excitation radio galaxy with a 1.4 GHz luminosity range within values of 2 × 1023 and 3 × 1025 W Hz-1,[4] and highly luminous,[5] 7C 1415+2556 is categorized a blazar,[6][7][8] a type of active galaxy shooting out an astrophysical jet towards the direction of Earth when observed by Fermi.[9] As a blazar, 7C 1415+2556 contains a robust electron energy (γ p ≲ 1.6 × 103) with weaker magnetic field with a high electron-to-magnetic energy ratio (U e/U B), making it unstable.[10] Its velocity gradient in its jet is noted to be of lower kinetic power (~1042-1044.5 erg s-1), that matches with the power in Fanaroff-Riley (FR) I radio galaxies and other BL Lac objects.[11]

Through the Bayesian classification, 7C 1415+2556 is classified a high synchrotron peak blazar with log(vp/Hz) > 14.9, with its γ-ray and optical emission having a close bond with radio emission but a weak bond in X-ray emission. It is also known to have a strong connection between its curvature (1/∣P 1∣) and peak frequency of logvp.[12] Moreover, 7C 1415+2556 has a weak high ionization emission line but considerably powerful when observed in X-ray and radio bands compared to high redshift quasars between redshifts of z =2.7 and z=5.9.[13] The active galactic nucleus in 7C 1415+2556 is radio-loud[14] with local volume density found higher 1041 erg s-1 of 2.4 × 10-3 Mpc-3 making up 10% of the overall luminous local galaxy density above M* = - 19.75.[15]

Compared together with flat-spectrum radio quasars, 7C 1415+2556 has separation value of Γ =-0.127 log Lγ +8.18 within γ-ray luminosity versus photon index plane. The success rate is 88.6% suggesting the power of accretion is larger than the radio jet.[16]

According to Swift-Burst Alert Telescope (BAT), the galaxy contains a supermassive black hole of M bh ~ 109 M ⊙ with luminous accretion disk of L d ~ 1046 erg s-1 but a less intensive jet when compared to high redshift blazars at z > 2.[17] However, it still exhibits a similar correlation pattern between the kinetic power carried by accelerated particles and luminosity of gamma-rays, indicating the energy dissipation in the jets produced by the black hole system of 7C 1415+2556, is much the same over 10 orders of magnitude for jet power.[18]

Through new spectrophotometric observations, 7C 1415+2556 is also a quasar located at a moderate redshift but within the field of a nearby Seyfert galaxy, NGC 5548.[19]

Observations

According to IRAS in which 7C 1415+2556 and 161 other blazars were monitored, the galaxy is found fluctuating across the electromagnetic spectrum with its spectral index and flux density becoming greater when the wavelength decreases. Moreover, researchers found that the spectra of 7C 1415+2556 has steepened continuously between ranges of 109 and 1015 Hz, with an X-ray flux density, closest to extrapolation of the optical and ultraviolet continuum. According to them, the total energy emission of 7C 1415+2556 is influenced by the infrared emission reaching high as 1 to 100 microns, and bolometric luminosity with a radius of 109 to 1014 L_sun_.[20]

Researcher also studied 7C 1415+2556 further. From the results collected by them, the resolved component in 7C 1415+2556 is best fitted by an exponential disk measuring a scale length of 18 kpc and absolute magnitude of roughly -24.2. Looking at its stellar absorption features, the galaxy is estimated to be at z = 0.237. No traces of emission lines are found within 3200-9000 A wavelength range of the galaxy. However the decomposition of the optical spectrum estimated, together with the power law yields a spectral index of 7C 1415+2556 to be 0.5 + or - 0.5.This is flatter compared to a normal BL Lac object. Within the 4500-7000 A wavelength range, the linear polarization of the nonstellar component is 6 percent. Researchers also noted the X-ray flux in the 0.3-3.5 keV band is 1.16 x 10, comparable to -11th ergs/sq cm/s. These values is in agreement to a luminosity of 3.5 x 10 to 45th ergs/s. As for radio flux density, it measured at 85.6 mJy at 20 cm and 54.5 mJy at 6 cm.[21] When observed by ROSAT, 7C 1415+2556 contains a hard spectrum when observed for its increased flux, although it varies at different time periods by relative dominance between its synchrotron and inverse Compton emission observed in soft X-ray band.[22]

Gamma source

The gamma source in 7C 1415+2556 is of extragalactic origin. Detected at high energy values, VHE; E > 100 GeV, the source is scattered along the lines of sight at 2.4σ level. Apart from it, a correlation between 10 and 500 GeV flux is found at 2.4σ and 2.6σ, when calculated by a Pearson correlation coefficient technique of r = 0.57 and 0.47. This suggests the gamma-rays in 7C 1415+2556 declines as low to 10 percent.[23]

Host galaxy

Previously reported to either lie inside a spiral or disk galaxy, the host galaxy of 7C 1415+2556 is an elliptical galaxy[24][25] due to a researcher showing a new optical CCD image of the galaxy, and also the image-modeling analysis of host galaxy that was observed. Using the model, the host galaxy has a jetlike feature, with extension of about 3" from the nucleus of the object indicating an optical jet is emitted from the central region of a BL Lac object.[26]

This host galaxy has an absolute magnitude of MR= -23.5 (H0= 50 km s-1 kpc-1 and q0= 0).[27] but has the same morphology of a disk galaxy like rotating disk features, an extended emission-line region and detections of strong absorption in the H I 21 cm line, Na I λλ5891, 5897 and Ca II λλ3934, 3969 doublets.[28] In addition, 7C 1415+2556 makes up one of the two identical galaxies with a separation from 2.0 to 2.5 arcsecs of about 20 x 20 arcsecs.[29]

Lyα and Lyman- limit absorption system

7C 1415+2556 is known to have a Lyα and Lyman-limit absorption system. Based on the IUE Survey, there is no absorption cross section evolution and number density of damped Lyα absorption systems. However it is noted that cosmological mass density Ωg(z) of neutral gas connected with damped Lyα absorption systems goes down significantly from z = 3.5 to 0.008 when observed in 7C 1415+2556. Apart from that, observed evolution of Ωg(z) is also caused by a steady decrease in the incidence rate of high column density absorption systems with low redshifts, suggesting the metal poor star population in 7C 1415+2556.[30]

Water megamaser emission

Researchers who obtained recent observations from Green Bank and Effelsberg telescopes, found the rate of detection for water megamaser emission at 22 GHz, is estimated to be 15 ± 3% including 7C 1415+2556. However, there are no signs of any correlation between the water maser and X-ray luminosity for the galaxy. Although a useful tool to study active galactic nuclei (AGN), as it ensures an accurate determination of the mass of the central black hole and of the accretion disc geometry and dynamics, only 7C 1415+2556 and 199 other AGNs show uncertain classification of spectroscopic features. The physical and geometrical conditions caused by the master in 7C 1415+2556 still remains a mystery to this day.[31]

References

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