Diffuse Radio Emission in Abell 754
  We present a low frequency study of the diffuse radio emission in the galaxy
cluster A754. We present new 150 MHz image of the galaxy cluster A754 made with
the Giant Metrewave Radio Telescope (GMRT) and discuss the detection of 4
diffuse features. We compare the 150 MHz image with the images at 74, 330 and
1363 MHz; one new diffuse feature is detected. The flux density upperlimits at
330 and 1363 MHz imply a synchrotron spectral index, $\alpha > 2$, ($S\propto
\nu^{-\alpha}$) for the new feature. The 'west relic' detected at 74 MHz
(Kassim et al 2001) is not detected at 150 MHz and is thus consistent with its
non-detection at 1363 MHz (Bacchi et al 2003) and 330 MHz(Kassim et al 2001).
Integrated spectra of all the diffuse features are presented. The fourth
diffuse feature is located along the proposed merger axis (Zabludoff et al
1995) in A754 and 0.7 Mpc away from the peak of X-ray emission. We have made
use of the framework of adiabatic compression model (Ensslin & Gopal-Krishna
2001) to obtain spectra. We show that the spectrum of the fourth diffuse
feature is consistent with that of a cocoon of a radio galaxy lurking for about
$9\times10^{7}$ yr; no shock compression is required. The other three diffuse
emission have spectra steeper than 1.5 and could be cocoons lurking for longer
time. We discuss other possibilities such as shocks and turbulent
reacceleration being responsible for the diffuse emission in A754.
