HIRAX

The HIRAX will comprise of 1,024 six-meter parabolic dishes on a compact grid and will map most of the
southern sky over the course of four years. The primary goal of HIRAX is to use 21-cm intensity mapping to measure baryon acoustic oscillations (BAOs). These are remnant ripples in the distribution of galaxies that are imprinted by primordial sound waves that existed in the early universe. The characteristic BAO length scale can be used as a ‘ruler’ for charting the expansion history of the universe and for shedding light on the nature of dark energy.

• Observations from experiments that span a wide range of redshifts, like HIRAX, allow us to measure both geometry and growth, provide a probe of dynamical Dark Energy, constrain modified gravity models, measure the isotropy of the Universe, and improve limits on deviations from Gaussianity of the initial density perturbations.

• Observations of the southern sky provide access to the galactic plane, enabling a wide variety of transient measurements with HIRAX. A new window on the transient sky will be possible in the future from upcoming wide-field imagers like LSST and gravitational wave detections of coalescing compact objects from LIGO 29 and explosions. HIRAX will add radio transient monitoring to this suite of observations,which will open the discovery space for transient phenomena and contribute to multi-messenger science, for example following up nearby explosive events found by LIGO.

• Fast Radio Bursts (FRBs) are a source of enormous interest to the radio transient community because
of their high dispersion measures and isotropic spatial distributions, indicating possible cosmological
distances. Their origin is unknown and a subject of ongoing study. Projecting from current discovery
rates of FRBs, HIRAX will find dozens per day (with significant uncertainty in the estimated number
due to limited FRB statistics in the HIRAX band) and be able to measure properties associated with
their spectra, pulse arrival times, and spatial distribution.

• In addition to FRBs, HIRAX can be used as a pulsar discovery engine and an efficient pulsar monitoringtelescope. HIRAX pulsar searches have the potential to discover a few thousand new pulsars, while pulsar monitoring would provide important inputs to timing arrays used for the detection of long-wavelength gravitational waves, inaccessible to other probes.

• Finally, up-channelizing the data to a spectral resolution of ∼ 3 kHz (1.5 km/s in the center of the
band) will yield a spectral rms of ∼ 4.4 mJy/beam. This will provide a competitive 21-cm absorption
line survey in a redshift range 1.36 < z < 2.5 which will not be covered by any of the upcoming radio surveys.

QLA is hosting a 32-element array HIRAX outrigger telescope in Rwanda. This outrigger telescope can get very long baseline interferometry (VLBI) positions for HIRAX events. VLBI is a geometric technique; it measures the time difference between the arrival at two Earth-based antennas of a radio wave front emitted by a distant quasar. Using large numbers of time difference measurements from many quasars observed with a global network of antennas, VLBI determines the inertial reference frame defined by the quasars and simultaneously, the precise positions of the antennas. The outrigger is also designed to store baseband for 1-2 minutes, save or transmit when triggered. Researchers based at QLA and other partner institutions will be analyzing data from this experiment to help obtain a deeper understanding on the fate of our universe. It will also provide a huge source of Data for QLA research in Big Data and Analytics.