J/A+A/704/A198 MAXI J1820+070 optical spectra and light curves (Baglio+, 2025)
Tracking optical variability and outflows across the accretion states of the
black hole transient MAXI J1820+070.
Baglio M.C., Alabarta K., Russell D.M., Masetti N., Messa M.M.,
Munoz-Darias T., Vincentelli F.M., Rout S.K., Saikia P., Gabuya A.,
Chavushyan V., Al Qaissieh T., Palado A.
<Astron. Astrophys. 704, A198 (2025)>
=2025A&A...704A.198B 2025A&A...704A.198B (SIMBAD/NED BibCode)
ADC_Keywords: Binaries, X-ray ; Black holes ; Photometry ; Optical ;
Spectra, optical ; Spectra, ultraviolet
Keywords: stars: black holes - stars: jets - stars: winds, outflows
Abstract:
We present a study of the evolution of the minute-timescale optical
variability and of the optical spectroscopic signatures of outflows
in the black hole X-ray binary MAXI J1820+070 during its main 2018
outburst and subsequent re-brightenings. Multi-filter, minute-cadence
optical light curves were obtained with the Las Cumbres Observatory
network and the Al Sadeem Observatory (UAE) over 2018-2020,
complemented by archival X-ray data from Swift/BAT and XRT and from
MAXI. We also acquired contemporaneous low-resolution optical spectra
with the 2.1 m OAN San Pedro Martir (Mexico), the 2.1m OAGH Cananea
(Mexico), and the "G.D. Cassini" 1.5m telescope at Loiano (Italy).
The optical fractional rms is highest in the hard state and is best
described by short time-scale flickering that is stronger at longer
wavelengths. This suggests that the minute-timescale optical
variability is driven by the jet in the hard state. In this scenario,
the variability could be due to variations in the inflow that inject
velocity fluctuations at the base of the jet (internal shock model).
The variability is then quenched in the soft state, with any residual
signal likely associated with variability in the accretion flow. This
is in agreement with the accretion-ejection coupling in black hole
binaries and confirms that the variability signature of the jet is
present at optical wavelengths in all hard states. In the dimmest hard
states, any residual optical variability may instead be linked to
cyclo-synchrotron emission from the hot flow.
The optical spectra reveal double-peaked emission lines and possible
signatures of cold winds during the hard state. Such winds were
previously reported in this source during the main 2018 outburst; here
we provide one of the first tentative detections of their presence
also during the subsequent re-brightenings. The absence of optical
wind signatures in the soft state likely reflects a higher level of
disc ionisation driven by the increased X-ray flux, which suppresses
the low-ionisation features detectable in the optical band.
Description:
Light curves:
Observations obtained with Las Cumbres Observatory (LCO) and
Al Sadeem Observatory.
Photometric system: SDSS g', r', and i' (AB system).
Time system: Modified Julian Date (MJD), mid-exposure, UTC.
Zero-points: AB magnitudes.
Uncertainties: 1-sigma magnitude errors from the respective pipelines.
Extinction: No Galactic extinction correction applied in these tables.
Spectra:
This collection includes 13 one-dimensional, wavelength-calibrated
optical spectra of the black hole transient MAXI J1820+070 obtained
during different epochs of its 2018-2019 outburst decay.
All spectra are stored in 3D FITS images following the IRAF
"multispec" format (WCSDIM=3, NAXIS3=4). Each file contains 4 planes:
Plane 1 : Extracted 1D flux-calibrated spectrum (erg/cm2/s/Å)
Plane 2 : Spectrum extracted without variance weighting
Plane 3 : Local background
Plane 4 : Sigma (per-pixel 1sigma uncertainty)
Fluxes are in physical units of erg/cm2/s/Å.
Please cite the following publication when using these data:
Baglio, M. C. et al. (2025), "Tracking optical variability and outflows
across the accretion states of the black hole transient MAXI J1820+070",
A&A, in press.
Wavelengths are in Angstroms, in the observed frame.
Spectra were reduced using standard IRAF and custom Python pipelines.
Wavelength calibration was derived from arc lamps; flux calibration from
spectrophotometric standard stars.
Usage notes:
- The FITS files can be read directly using astropy.io.fits or IRAF splot.
- Plane 1 contains the final reduced spectrum.
- Wavelengths are in vacuum and uncorrected for heliocentric velocity.
- Flux units: erg/cm2/s/Å (absolute calibration approximate).
Objects:
---------------------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------------------
18 20 21.94 +07 11 07.2 MAXI J1820+070 = AT 2018amn
---------------------------------------------------------
Description of file: fits/*
----------------------------------------------------------------
FITS data structure (common to all files):
----------------------------------------------------------------
NAXIS1 = number of wavelength pixels
NAXIS2 = 1
NAXIS3 = 4
CRVAL1 = wavelength at first pixel [AA]
CD1_1 = wavelength increment per pixel [AA/pix]
CRPIX1 = reference pixel (usually 1)
BUNIT = 'erg/cm2/s/AA'
WCS = Linear dispersion solution, units in Angstrom
---------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
gband.dat 32 517 LCO g'-band (AB) photometry from the XB-NEWS pipeline
iband.dat 32 609 LCO i'-band (AB) photometry from the XB-NEWS pipeline
gbanda.dat 32 196 Al Sadeem Observatory Blue (g'-band, AB) photometry
rbanda.dat 32 977 Al Sadeem Observatory Red (R-band, Vega) photometry
vbanda.dat 32 1035 Al Sadeem Observatory Green (V-band, Vega) photometry
list.dat 149 13 List of fits spectra
fits/* . 13 Individual fits spectra
--------------------------------------------------------------------------------
See also:
J/ApJ/889/142 : MAXI J1820+070 Swift/XRT & NICER timing study (Stiele+, 220)
J/MNRAS/493/L81 : Radio astrometry of MAXI J1820+070 (Atri+, 2020)
J/MNRAS/496/L96 : Polarization of LMXB MAXI J1820+070 (Kosenkov+, 2020)
Byte-by-byte Description of file: [gi]band.dat [grv]banda.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 F15.9 d MJD Modified Julian Date, mid-exposure (UTC)
17- 23 F7.4 mag mag ? Magnitude in Band (1)
25- 30 F6.4 mag e_mag ? Magnitude uncertainty on Band
32 A1 --- Band [griRV] Observed band
--------------------------------------------------------------------------------
Note (1): gri magnitudes are in AB, RV magnitudes in Vega.
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Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh Simbad right ascension (J2000)
4- 5 I2 min RAm Simbad right ascension (J2000)
7- 11 F5.2 s RAs Simbad right ascension (J2000)
12 A1 --- DE- Simbad declination sign (J2000)
13- 14 I2 deg DEd Simbad declination (J2000)
16- 17 I2 arcmin DEm Simbad declination (J2000)
19- 22 F4.1 arcsec DEs Simbad declination (J2000)
24- 27 I4 --- Nx Number of pixels along X-axis
29 I1 --- Ny Number of pixels along Y-axis
31- 53 A23 "datime" Obs.date Observation date
55- 61 F7.2 0.1nm bLambda Lower value of wavelength interval
63- 69 F7.2 0.1nm BLambda Upper value of wavelength interval
71- 77 F7.5 0.1nm/pix dLambda Wavelength resolution
79- 80 I2 Kibyte size Size of FITS file
82-109 A28 --- FileName Name of FITS file, in subdirectory fits
111-123 A13 --- Tel Telescope (1)
125-138 A14 --- Inst Instrument
140-143 I4 s ExpTime Exposure time
145-149 F5.3 --- Airmass Airmass
--------------------------------------------------------------------------------
Note (1): Instruments as follows:
OAGH 2.1m = (Cananea, Mexico) Boller & Chivens spectrograph (April 2018)
OAN-SPM 2.12m = (San Pedro Martir, Mexico) Boller spectrograph (August 2018)
Loiano 1.52m = (Italy) BFOSC spectrograph (June 2018 - September 2019)
--------------------------------------------------------------------------------
Acknowledgements:
From Maria Baglio, Maria.baglio(at)inaf.it
If you use these data, please cite:
"Tracking optical variability and outflows across the accretion
states of the black hole transient MAXI J1820+070"
(M. C. Baglio et al., A&A, in press)
and acknowledge Las Cumbres Observatory and Al Sadeem Observatory.
(End) Patricia Vannier [CDS] 27-Oct-2025