Hintze Centre for Astrophysical Surveys

Abstract:

Abstract We present the first results of the H i intensity mapping power spectrum analysis with the MeerKAT International GigaHertz Tiered Extragalactic Exploration (MIGHTEE) survey. We use data covering ∼ 4 square degrees in the COSMOS field using a frequency range 962.5 MHz to 1008.42 MHz, equivalent to H i emission in 0.4 < z < 0.48. The data consists of 15 pointings with a total of 94.2 hours on-source. We verify the suitability of the MIGHTEE data for H i intensity mapping by testing for residual systematics across frequency, baselines and pointings. We also vary the window used for H i signal measurements and find no significant improvement using stringent Fourier mode cuts. We compute the H i power spectrum at scales 0.5 Mpc−1 ≲ k ≲ 10 Mpc−1 in auto-correlation as well as cross-correlation between observational scans using power spectrum domain averaging for pointings. We report consistent upper limits of 29.8  mK2Mpc3 from the 2σ cross-correlation measurements and 25.82 mK2Mpc3 from auto-correlation at k ∼2 Mpc−1.The low signal-to-noise in this data potentially limits our ability to identify residual systematics, which will be addressed in the future by incorporating more data in the analysis.

Abstract:

Recently, a class of long-period radio transients (LPTs) has been discovered, exhibiting emission thousands of times longer than radio pulsars1-5. These findings, enabled by advances in wide-field radio surveys, challenge existing models of rotationally powered pulsars. Proposed models include highly magnetized neutron stars6, white-dwarf pulsars7 and white-dwarf binary systems with low-mass companions8. Although some models predict X-ray emission6,9, no LPTs have been detected in X-rays despite extensive searches1-5,10. Here we report the discovery of an extremely bright LPT (10-20 Jy in radio), ASKAP J1832-0911, which has coincident radio and X-ray emission, both with a 44.2-minute period. Its correlated and highly variable X-ray and radio luminosities, combined with other observational properties, are unlike any known Galactic object. The source could be an old magnetar or an ultra-magnetized white dwarf; however, both interpretations present theoretical challenges. This X-ray detection from an LPT reveals that these objects are more energetic than previously thought and establishes a class of hour-scale periodic X-ray transients with a luminosity of about 1033 erg s-1 linked to exceptionally bright coherent radio emission.