An Optically Discovered Outburst from XTE J1859+226 Bellm, Eric C.; Wang, Yuankun; van Roestel, Jan ...
Astrophysical journal/The Astrophysical journal,
10/2023, Letnik:
956, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
Using the Zwicky Transient Facility, in 2021 February we identified the first known outburst of the black hole X-ray transient XTE J1859+226 since its discovery in 1999. The outburst was ...visible at X-ray, UV, and optical wavelengths for less than 20 days, substantially shorter than its full outburst of 320 days in 1999, and the observed peak luminosity was 2 orders of magnitude lower. Its peak bolometric luminosity was only 2 × 10
35
erg s
−1
, implying an Eddington fraction of about 3 × 10
−4
. The source remained in the hard spectral state throughout the outburst. From optical spectroscopy measurements we estimate an outer disk radius of 10
11
cm. The low observed X-ray luminosity is not sufficient to irradiate the entire disk, but we observe a surprising exponential decline in the X-ray light curve. These observations highlight the potential of optical and infrared synoptic surveys to discover low-luminosity activity from X-ray transients.
Abstract
This study describes the nature of HD 345723, a variable star identified in TESS photometric data. Analyzing the light curve, we obtain a period of 19 hr and 17 minutes in phase domain. The ...star, a K6 spectral class, suggest that the variation is due to the presence of large stellar spots in a very close binary system, detected by GAIA spectrum. The double star, at coordinates R.A. (J2000) 20:06:51.33 and decl. (J2000) +22:39:51.7, has a distance of 719 pc, according to reliable GAIA parallax measurements.
Abstract
In this study we describe the reclassification of the variable star CzeV818, discovered in 2015 by Pavel Cagas (Skarka et al. 2017), which was cataloged as a delta Scuti variable. From the ...photometric study performed with the telescopes of the SSV-UAI-GRAV (Unione Astrofili Italiani, Variable Star Section), All-Sky Automated Survey for Supernovae (Kochanek et al. 2017) (ASAS-SN) and Zwicky Transient Facility (Masci et al. 2019) (ZTF) surveys and the G-spectrum obtained from Gaia DR3 (Gaia Collaboration et al. 2023) (Astrophysical parameters inference system, Apsis) data, it was possible to understand that the luminous variation was not due to pulsations but due to spots (as discussed in Roxburgh 1964), present in the photosphere with a cycle of 0.402533 day (9.66 hr). Analyzing the long-term data present in the ASAS-SN and ZTF surveys, it was possible to determine a cycle of 2900 days (7.95 yr), which is similar to the solar cycle.
Using the Zwicky Transient Facility, in 2021 February we identified the first known outburst of the Black Hole X-ray Transient XTE J1859+226 since its discovery in 1999. The outburst was visible at ...X-ray, UV, and optical wavelengths for less than 20 days, substantially shorter than its 320-day full outburst in 1999, and the observed peak luminosity was two orders of magnitude lower. Its peak bolometric luminosity was only \(2\times 10^{35}\) erg s\(^{-1}\), implying an Eddington fraction of about \(3\times10^{-4}\). The source remained in the hard spectral state throughout the outburst. From optical spectroscopy measurements we estimate an outer disk radius of 10\(^{11}\) cm. The low observed X-ray luminosity is not sufficient to irradiate the entire disk, but we observe a surprising exponential decline in the X-ray lightcurve. These observations highlight the potential of optical and infrared (O/IR) synoptic surveys to discover low-luminosity activity from X-ray transients.
