Twin radio relics in a near-by low-mass galaxy cluster Abell 168
  We report the discovery of twin radio relics in the outskirts of the low-mass
merging galaxy cluster Abell 168 (redshift=0.045). One of the relics is
elongated with a linear extent $\sim$ 800 kpc, a projected width of $\sim$ 80
kpc and is located $\sim$ 900 kpc toward the north of the cluster center,
oriented roughly perpendicular to the major axis of the X-ray emission. The
second relic is ring-shaped with a size $\sim$ 220 kpc and is located near the
inner edge of the elongated relic at a distance of $\sim$ 600 kpc from the
cluster center. These radio sources were imaged at 323 and 608 MHz with the
Giant Meterwave Radio Telescope and at 1520 MHz with the Karl G Jansky Very
Large Array (VLA). The elongated relic was detected at all the frequencies with
a radio power at 1.4 GHz of 1.38$\pm 0.14 \times 10^{23}$ W Hz$^{-1}$ having a
power law in the frequency range 70 - 1500 MHz (S$\propto \nu^{\alpha}, \alpha
= -1.1 \pm 0.04$). This radio power is in good agreement with that expected
from the known empirical relation between the radio powers of relics and the
host cluster masses. This is the lowest mass (M$_{500}$ = 1.24$\times$10$^{14}$
M$_{o}$) cluster in which relics due to merger shocks are detected. The
ring-shaped relic has a steeper spectral index ($\alpha$) of -1.74$\pm$0.29 in
the frequency range 100 - 600 MHz. We propose this relic to be an old plasma
revived due to adiabatic compression by the outgoing shock which produced the
elongated relic.
