PRIME discovery of a likely fading near-infrared counterpart to SRGA J144459.2-604207
ATel #16499; O. Guiffreda (UMD), K. De (MIT), J. Durbak (UMD), A. Kutyrev (NASA/GSFC), E. Troja (U Rome), S. B. Cenko (NASA/GSFC) report on behalf of the PRIME collaboration
on 3 Mar 2024; 16:10 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Kishalay De (kde1@mit.edu)
Subjects: Infra-Red, Optical, X-ray, Neutron Star, Transient, Variables, Pulsar
Referred to by ATel #: 16510
The SRG/Mikhail Pavlinsky ART-XC telescope reported the discovery of a new bright Galactic X-ray transient SRGA J144459.2-604207 on 21 February 2024 (ATel #16464). The outburst was subsequently confirmed with MAXI data (ATel #16469) and an improved localization was reported from follow-up Swift XRT observations (3.5 arcsec uncertainty; ATel #16471). The source has been identified as a new accreting millisecond X-ray pulsar with the detection of Type I X-ray bursts and pulsations in NICER, Swift and INTEGRAL data (ATel #16474, #16475 and #16485). No optical brightening has been detected in survey and follow-up imaging (ATel #16477, #16476 and #16489), possibly due to the high reddening towards the source as indicated by the X-ray column density (~ 3e22 cm^-2; ATel #16474).
On UT 2024-02-23 and UT 2024-02-27, we obtained follow-up observations of the localization region using the PRIME near-infrared telescope. We obtained J and H band observations amounting to a total exposure time of ~ 30 mins on each epoch. Comparing the images to archival VISTA images, we clearly detect a fading point source within the Swift XRT localization region in H band at J2000 coordinates
RA 14:44:59.34
Dec -60:41:52.04
The source is not visible in the J band images or previous optical sources reported in ATels #16487 and #16489. Performing aperture photometry at the source position to estimate preliminary magnitudes (the field is heavily crowded), we find the source to have faded from H = 15.1 +/- 0.1 mag to H > 16.2 mag between the epochs. The fading of the source is consistent with the decaying X-ray flux of the source, while the X-ray to infrared flux ratio (~1e3) is consistent with a low mass X-ray binary in outburst.
We encourage further follow-up observations in the infrared band to track the long term evolution. A finding chart showing the NIR detection and fading can be found at this link. PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa. We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations.
