On 2017-08-27-16:20:18 UTC (2017-08-27.68076389), we found a bright burst as part of the ongoing FRB search program (UTMOST), at the Molonglo telescope.
Molonglo is a 1.6 km long East-West array (see Bailes et al 2017) and was operating in drift-scan mode with pointing centred on the meridian at the time of detection. Source localisation is excellent in Right Ascension (5 arcsec at 1-sigma) but poor in Declination (~1.2 deg at 1-sigma) (see Caleb et al 2017 MNRAS 468, 3746).
FRB170827 was found during a blind FRB search programme in real-time using an automated GPU-accelerated/machine learning based pipeline and the raw voltages were recorded for offline processing. Using 300 ms of voltage data, we improved localisation of the FRB by repointing the array to different directions and maximising S/N.
The most likely position is RA = 00:49:18.66, DEC = -65:33:02.3, J2000. The optimal dispersion measure (DM) that maximizes the signal-to-noise ratio is: 176.4 pc cm^-3. The DM estimate of NE2001 model is ~37 pc cm^-3, and YMW16 model is ~27 pc cm^-3 at this position, resulting in an intergalactic excess of ~145 pc cm^-3, the lowest known. The upper limit on the DM-inferred redshift is thus ~0.15. An early estimate of the event’s fluence is ~ 20 Jy ms, width ~ 395 us, with a signal-to-noise ratio > 90.
The 95% confidence localisation arc is as follows:
00:50:09.05 -67:54:48.9
00:50:01.57 -67:35:35.5
00:49:54.31 -67:16:22.2
00:49:47.25 -66:57:08.7
00:49:40.40 -66:37:55.3
00:49:33.74 -66:18:41.9
00:49:27.27 -65:59:28.4
00:49:20.98 -65:40:14.9
00:49:14.85 -65:21:01.4
00:49:08.90 -65:01:47.8
00:49:03.09 -64:42:34.3
00:48:57.45 -64:23:20.7
00:48:51.95 -64:04:07.1
00:48:46.59 -63:44:53.5
00:48:41.36 -63:25:39.9
00:48:37.53 -63:11:14.7
A formula describing the localization arc is: DEC = -60.71088 -253.7786*(RA – 0.8) + 1480.220*(RA – 0.8)^2.
Where RA is in hours, Dec is in deg, and is valid in the RA range [0.84, 0.81].
Note that this localisation arc crosses through the SMC (Small Magellanic Cloud) if extended a further ~6 degrees, where we expect a beam attenuation of ~15 dB. We note that the measured DM of the FRB is similar to SMC pulsars.
