First MeerKAT radio non-detection of the neutron star X-ray binary SRGA J144459.2-604207 and Swift/XRT detection of a Type-I X-ray burst

ATel #16475; I. Mariani, S. Motta, M. C. Baglio, (INAF-OAB), R. Fender (Oxford University), J. van den Eijden (Warwick University) for the X-KAT collaboration, I. Mereminskiy, A. Lutovinov (IKI)
on 23 Feb 2024; 09:42 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Sara Elisa Motta (sara.motta@physics.ox.ac.uk)

Tweet

A new X-ray transient source SRGA J144459.2-604207 was first detected by the SRG / Mikhail Pavlinsky ART-XC telescope at RA, DEC (J2000) = 221.2467, -60.7020 (Atel #16464) on February 21, 2024. MAXI/GSC observations further confirmed this detection (Atel #16469). A 2MASS source (2MASS 14445957-6042066) has been proposed to be the NIR counterpart, within 10 arcsec from the X-ray detection, located at a distance of ~ 1.9 kpc (ATel #16470). The MAXI instrument on-board the ISS confirmed the X-ray detection (ATel #16469). Data from the XRT instrument onboard the Neil Gehrels Swift Observatory (Swift) allowed the the X-ray position of system to be refined to RA, DEC (J2000) = 221.248375, -60.697972 (ATel #16471). NICER data taken on February 21 evidenced the presence of a X-ray pulsations at approximately 447.8 Hz and of type-I X-ray bursts, establishing that SRGA J144459.2-604207 is a new accreting millisecond pulsar (ATel #16474).

Following the optical and X-ray detections, we initiated follow-up radio observations with the MeerKAT radio telescope as part of the X-KAT programme. SRGA J144459.2-604207 was observed for 15 minutes between 03:18:20.769 and 04:03:39.619 on 2024 Feb 22. Observations were carried out at a central frequency of 1.28 GHz (L-band), with a total bandwidth of 209 kHz. J1939-6342 was used for flux and bandpass calibration, J1424-4913 for complex gain calibration. On September 22 no source was detected at the X-ray location of SRGA J144459.2-604207, and we estimated a 3 sigma upper limit of ~ 170uJy.

As part of the SwiftKAT program we triggered observations with Swift. The target was observed on 2024 Feb 22 at 01:25:10.733 UT for a total of 1000s with the XRT (500s in Photon Counting Mode and 500s in Windowed Timing mode). The Windowed timing mode light curve shows a clear type-I X-ray burst. The burst lasted approximately 40s and showed a 10s plateau. The pre/post burst persistent emission is well fitted by an absorbed powerlaw spectrum (NH~2.5(+/-0.1)x10^22, Gamma ~ 2(+/-0.1)), and during the burst an additional thermal component with a temperature kT~3(+/-0.5) keV is observed. The pre-burst flux and the burst flux in the 0.5-10 keV band are ~ 2.4(+/-0.1) e-9 and 1.3(+-0.1)e-8 erg/cm^2/s, respectively.

We will continue monitoring SRGA J144459.2-604207 with the MeerKAT radio telescope and with Swift. Multi-wavelength observations are encouraged to study the rise of the outburst. Further radio monitoring is planned, as well as weekly Swift observations of the target.

X-KAT is a large MeerKAT open-time programme to observe X-ray binaries in the radio band, performing weekly monitoring of bright, active systems, with capacity for higher cadence observations, and in coordination with large X-ray and optical monitoring programmes. For further information on this programme contact Rob Fender. The Swift follow-up of X-ray binaries is largely performed as part of the SwiftKAT program, which provides quasi simultaneous X-ray coverage of the X-KAT targets.