Near-infrared brightening of MAXI J1820+070/ ASASSN18ey detected with Palomar Gattini-IR

ATel #13044; Matthew Hankins (Caltech), Kishalay De (Caltech), Mansi M. Kasliwal (Caltech), Ryan M. Lau (ISAS/JAXA), Roberto Soria (NAOC), Michael Coughlin (Caltech), Kevin Burdge (Caltech), Anna Moore (ANU), Jamie Soon (ANU), Michael Ashley (UNSW), Tony Travouillon (ANU) report on behalf of the Palomar Gattini-IR team
on 26 Aug 2019; 21:05 UT
Credential Certification: Kishalay De (kde@astro.caltech.edu)

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We report recent near-infrared brightening of the black hole X-ray binary MAXI J1820+070/ ASASSN18ey. Observations of the current outburst in this source have been reported at optical, X-ray, and radio wavelengths (ATels #13014, #13025, and #13041), and a prior outburst of this source was observed in 2018 (e.g., Tucker+ 2018).

Palomar Gattini-IR observed MAXI J1820+070 as a part of normal survey operations, which scans the entire visible northern sky every two nights to a median depth of ~16 AB mag in J-band (Moore & Kasliwal 2019). A transient source consistent with the position of MAXI J1820+070/ASASSN18ey was identified, saved with the internal name PGIR 19auj, in difference imaging produced as part of the real-time data reduction pipeline for Gattini-IR (De et al., in prep.). Forced photometry was run at the source location to examine all prior data collected at this position. A summary of detections is listed below. Prior to the outburst we detect a ~14.4 mag source at this position going back several months, which could be the quiescent source or is possibly unrelated (the median FWHM of Gattini-IR is about 16 arcsecs and can be easily confused in crowded regions). For reference, we include the first two photometry points before we begin to see a modest rise in the source. We encourage further observations of the source and will continue to monitor its evolution at J-band.

Date (JD) | J (Vega mag) | error
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2458699.772 14.35 0.38
2458703.754 14.12 0.31
2458706.762 13.71 0.24
2458709.749 13.42 0.20
2458712.735 13.01 0.11
2458716.717 12.33 0.06
2458720.723 12.35 0.07