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 between 2 × 1023 and 3 × 1025 W Hz-1,[4] and optically luminous,[5] 7C 1415+2556 is classified as a blazar,[6][7][8] a type of active galaxy shooting out an astrophysical jet towards the direction of Earth as observed by Fermi.[9] As a blazar, 7C 1415+2556 shows a higher electron energy (γ p ≲ 1.6 × 103) and a weak magnetic field with a high electron-to-magnetic energy ratio (U e/U B), making it quite unstable.[10] Its velocity gradient in its jet is noted to be a low kinetic power (~1042-1044.5 erg s-1), corresponding to Fanaroff-Riley (FR) I radio galaxies and other BL Lac objects.[11]

Through the Bayesian classification, 7C 1415+2556 is classified as a high synchrotron peak blazar with log(vp/Hz) > 14.9, with its γ-ray and optical emission having the closest relationship with radio emission. However, the weakest relationship is that with X-ray emission. It is also known to have a strong positive 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 stronger in the 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 known to radio-loud[14] and has local volume density above 1041 erg s-1 of 2.4 × 10-3 Mpc-3, about 10% of the total luminous local galaxy density above M* = - 19.75.[15]

Compared together with flat-spectrum radio quasars, 7C 1415+2556 is found separated by Γ =-0.127 log Lγ +8.18 in its γ-ray luminosity versus photon index plane with a success rate found to be 88.6% suggesting the accretion power is found larger compared to its radio jet.[16]

According to Swift-Burst Alert Telescope (BAT), the galaxy is also known to have a hot supermassive black hole of M bh ∼ 109 M ⊙ and a luminous accretion disk of L d ∼ 1046 erg s-1 but has a less powerful jet compared to blazars at high redshift (z > 2)[17] but still exhibits the same correlation between its kinetic power carried by accelerated particles and the gamma-ray luminosity, implying the energy dissipation in its jets produced in the black hole system of 7C 1415+2556, is similar over 10 orders of magnitude in jet power.[18]

Through new spectrophotometric observations, 7C 1415+2556 is found to be a medium-redshift quasar and associated with a nearby Seyfert galaxy, NGC 5548.[19]

Observations

According to IRAS in which 7C 1415+2556 and 161 other blazars were observed, the galaxy is found to be variable across the electromagnetic spectrum with range of variability in its spectral index and flux density increasing as the wavelength decreases. Moreover, researchers found that the spectra of 7C 1415+2556 steeping continuously between 109 and 1015 Hz, and its x-ray flux density closer to an extrapolation of the optical and ultraviolet continuum. According to them, the global energy budget of 7C 1415+2556 is dominated by the infrared emission from 1 to 100 microns, and its bolometric luminosity ranging from 109 to 1014 L_sun_.[20]

Researcher also studied 7C 1415+2556 further. From the results, the resolved component is fit by an exponential disk with scale length of 18 kpc and an absolute magnitude of roughly -24.2. They estimated the object to be at z = 0.237 from its stellar absorption features. No emission lines are found in the 3200-9000 A wavelength range of the galaxy. They estimated that the decomposition of the optical spectrum into a standard galaxy plus a power law yields a spectral index of 0.5 + or - 0.5, which is significantly flatter than an average BL Lac object. Its linear polarization of the nonstellar component is around 6 percent in the 4500-7000 A wavelength range. Researchers also noted the X-ray flux in the 0.3-3.5 keV band is 1.16 x 10 to the -11th ergs/sq cm/s, corresponding to a luminosity of 3.5 x 10 to the 45th ergs/s. The radio flux density however, is 85.6 mJy at 20 cm and 54.5 mJy at 6 cm.[21] As observed by ROSAT PSPC, 7C 1415+2556 contains a hardening spectrum during overall flux increase, though it varies randomly likely accounted by relative dominance between its synchrotron and inverse Compton emission in the soft X-ray band.[22]

Gamma source

The gamma source in 7C 1415+2556 is of extragalactic origin. As detected at high energy (VHE; E > 100 GeV), the source is found to distributed along underdense lines of sight at the 2.4σ level. Apart from it, a correlation between 10 and 500 GeV flux is found at 2.4σ and 2.6σ, calculated from Pearson correlation coefficients of r = 0.57 and 0.47. This suggests the attenuation of gamma-rays in 7C 1415+2556 decreases no more than 10 per cent.[23]

Host galaxy

Previously reported to either lie inside a spiral or disk galaxy, the host galaxy of 7C 1415+2556 is found to be elliptical galaxy[24][25] due to a researcher presenting a new optical CCD imagery of the galaxy, and an image-modeling analysis of the observed host galaxy. Using the model, the host galaxy shows a jetlike feature, that extends about 3" from the nucleus of the object suggesting there is optical jet emanating from the 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 with similar morphologies of a disk galaxy such as a rotating disk, 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 is an identical twin galaxy with a separation from 2.0 to 2.5 arcsecs from the other galaxy that is lying in a region 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, it is found have no evolution on the product of the absorption cross section and comoving spatial number density of damped Lyα absorption systems. However it is noted that cosmological mass density Ωg(z) of neutral gas associated with damped Lyα absorption systems decreasing significantly from z 3.5 to 0.008 observed in 7C 1415+2556. Apart from that, observed evolution of Ωg(z) also results from a steady decrease in the incidence of high column density absorption systems with decreasing redshift, suggesting the star population in 7C 1415+2556 is metal poor.[30]

Water megamaser emission

According to researchers who obtained new observations with the Green Bank and Effelsberg telescopes, the detection rate of water megamaser emission at 22 GHz is 15 ± 3% including 7C 1415+2556, but there are no signs of correlation between the water maser and X-ray luminosity. Although a powerful tool for astrophysical studies of active galactic nuclei (AGN), as it allows an accurate determination of the mass of the central black hole and of the accretion disc geometry and dynamics, only 200 of them show spectroscopic features of uncertain classification. The physical and geometrical conditions under which a maser is caused are still a mystery.[31]

References

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