Kinder optical observations of the X-ray brightening blazar NVSS J004348+342626

ATel #16726; M.-H. Lee, A. Aryan, Y. J. Yang (all NCU), A. K. H. Kong (NTHU), T.-W. Chen, W.-J. Hou, C.-S. Lin, H.-Y. Hsiao, C.-C. Ngeow, A. Sankar. K, C.-H. Lai, Y.-C. Pan, H.-C. Lin, J.-K. Guo (all NCU), S. Yang (HNAS), S. J. Smartt (Oxford/QUB), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, J. Gillanders, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (IfA, University of Hawaii)
on 20 Jul 2024; 15:57 UT
Credential Certification: Amar Aryan (amararyan941@gmail.com)

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We observed the field of the EP-WXT detected point source (Jiang et al. ATel #16725) using the 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2024). The first SLT epoch of observations started at 18:46 UT on the 18th of July 2024 (MJD = 60509.782), 1.648 days after the EP trigger.

We utilized the astroalign (Beroiz et al. 2020) and astropy (Astropy Collaboration et al. 2022) packages to align and stack the individual frames. We did not detect any evidence of an uncatalogued source in the error box of 2.2 arcminutes around the reported position of the point source in the stacked frame. Further, we utilized the Python-based package AutoPhOT (Brennan & Fraser 2022) to perform the PSF photometry on our stacked frame.

In our stacked frame, we also measured the photometry of the X-ray brightening blazar NVSS J004348+342626, only 45" away from the reported position of the EP-WXT detected point source. Through our photometry, the current magnitude of this source is r (AB) = 18.38 +/- 0.05. By comparing our photometry with the publicly available ZTF (Bellm et al. 2019) r-band light curve recorded in the past few years, we find that the blazar is currently in its flaring stage. The long-term variation is also shown in the ATLAS (Smith et al. 2020) light curves for this blazar.

Moreover, the details of the observations and measured 3-sigma upper limit (in the AB system) at the reported position of the EP-WXT detected point source are as follows:

Telescope | Filter | MJD (start) | t-t0 | Exposure | Magnitude | avg. Seeing | med. Airmass

SLT | r | 60509.782 | 1.648 days | 300 sec * 12 | > 21.3 | 1".09 | 1.89

The presented magnitudes are calibrated using the field stars from the Pan-STARRS1 catalog and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.09 mag in the direction of the reported point source (Schlafly & Finkbeiner 2011).

We thank the Einstein Probe team for useful communication.

Reference:

[1] Chen & Yang et al. 2024, 2024arXiv240609270C

[2] Beroiz et al. 2020, A&C, 32, 100384

[3] Astropy Collaboration et al., 2022, ApJ, 935, 167

[5] Brennan & Fraser, 2022, A&A, 667, A62

[6] Bellm et al. 2019, PASP, 131, 018002

[7] Smith et al. 2020, PASP, 132, 085002

[8] Schlafly & Finkbeiner 2011, ApJ, 737, 103