GMRT observations of a first sample of Extremely Inverted Spectrum
  Extragalactic Radio Sources (EISERS) candidates in the Northern sky
  We present an extension of our search for Extremely Inverted Spectrum
Extragalactic Radio Sources (EISERS) to the northern celestial hemisphere. With
an inverted radio spectrum of slope $\alpha$ > +2.5, these rare sources would
either require a non-standard particle acceleration mechanism (in the framework
of synchrotron self-absorption hypothesis), or a severe free-free absorption
which attenuates practically all of their synchrotron radiation at metre
wavelengths. By applying a sequence of selection filters, a list of 15 EISERS
candidates is extracted out by comparing two large-sky radio surveys, WENSS
(325 MHz) and TGSS-ADR1 (150 MHz), which overlap across 1.03$\pi$ steradian of
the sky. Here we report quasi-simultaneous GMRT observations of these 15 EISERS
candidates at 150 MHz and 325 MHz, in an attempt to accurately define their
spectra below the turnover frequency. Out of the 15 candidates observed, two
are confirmed as EISERS, since the slope of the inverted spectrum between these
two frequencies is found to be significantly larger than the critical value
$\alpha_c$ = +2.5: the theoretical limit for the standard case of synchrotron
self-absorption (SSA). For another 3 sources, the spectral slope is close to,
or just above the critical value $\alpha_c$. Nine of the sources have GPS type
radio spectra. The parsec-scale radio structural information available for the
sample is also summarised.
