uGMRT Monitoring of Swift J1727.8-1613 during the X-ray plateau of its decay phase
ATel #16378; Arka Chatterjee (University of Manitoba), Dusmanta Patra, Arghajit Jana, Narendra Nath Patra, Birendra Chhotaray, Sachindra Naik, Samar Safi-Harb
on 14 Dec 2023; 03:55 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Arka Chatterjee (arka.chatterjee@umanitoba.ca)
Subjects: Radio, Black Hole
Swift J1727.8-1613 is a newly discovered outbursting black hole candidate (ATel #16208). The source has been monitored in the X-ray (ATel #16205, #16206, #16217, #16219, #16235, #16237), optical (ATel #16209, #16216, #16245), and radio (ATel #16211, #16228, #16231, #16271, #16279, #16289) bands since its discovery. Upgraded Giant Metrewave Radio Telescope (uGMRT) first observed Swift J1727.8-1613 on October 1, 2023, in band 4 (550 to 900 MHz), when the measured flux density was 32.3 ± 0.03 mJy at 681 MHz (ATel #16295). Following these observations, we monitored Swift J1727.8-1613 three times on November 25, 27, and December 2, 2023, using the uGMRT facility in band 4. In the table below, we list the estimated flux densities, at 660 MHz with the 2-20 keV count rates and the hardness ratio of the source (ratio between the count rates in 4-20 keV and 2-4 keV bands) from the Monitor of All-sky X-ray Image on board the International Space Station.
| Date | MJD | Flux Density | RMS | MAXI count | X-ray HR |
| | | (mJy) | (mJy/beam) | (Crab) | (4-20/2-4) keV |
| 2023/10/01 | 60218 | 32.3 ± 0.03 | 0.80 | 7.03 ± 0.070 | 0.32 ± 0.001 |
| 2023/11/25 | 60273 | 8.88 ± 0.22 | 0.08 | 1.46 ± 0.018 | 0.21 ± 0.001 |
| 2023/11/27 | 60275 | 11.97 ± 0.78 | 0.10 | 1.31 ± 0.016 | 0.19 ± 0.0016 |
| 2023/12/02 | 60280 | 9.28 ± 0.08 | 0.04 | 1.31 ± 0.017 | 0.17 ± 0.0015 |
Compared to the initial uGMRT observation, the radio flux density and hardness ratio of Swift J1727.8-1613 have decreased. However, there is no change in the source coordinate observed by uGMRT during the four epochs of observations.
The GMRT is a national facility operated by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. We thank the Director's discretionary time allotment and the staff who made the observations possible.
