BlackCAT A Catalog of Stellar-Mass Black Holes in X-ray Binaries

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ID# 30

SAX J1819.3-2525

V4641 Sgr

(Samus1999)

RA     (ICRS)     DEC [hh:mm:ss.ss]          [dd:mm:ss.ss] 18:19:21.58  -25:24:25.10

ℓ                      b [deg]                            [deg] 006.7740023  -04.78873545

Year of discovery: 1999  
(intZand1999)

# of outbursts after discovery: 4

Basic data

Distance [kpc]	6.2±0.7	MacDonald2014
Distance to the plane (z) [kpc]	-0.52±0.06	MacDonald2014
Orbital period (Porb) [h]	67.6152±0.0002	Orosz2001
Peak X-ray flux [erg s-1 cm-2] [keV]	2.76E-07 [2-10]	Orosz2001
Outburst magnitude (AB)	V=8.8	Orosz2001
Quiescent magnitude (AB)	V=13.96±0.02	MacDonald2014Orosz2001
E(B-V) [mag]	0.32 – 0.38	MacDonald2014

Dynamically confirmed BH

NOTES

SAX J1819.3-2525 (V4641 Sgr) showed weak outbursts in 2002 ,2003 (Bailyn2003), 2010 (Yamaoka2010), 2014 (Tachibana2014) and 2018 (Negoro2018), and a complete outburst in 2015 (Yoshii2015) and 2020 (Shaw2020). A new outburst was reported on Sep 2024 (Negoro2024) Gandhi2019 obtained a distance of 6.24+2.04-1.30 kpc from Gaia DR2.

Dynamical parameters

Orbital period [h]	67.6152±0.0002	Orosz2001
Star's spectral type	B9III	Orosz2001
Star's radial velocity amplitude (K2) [km/s]	211±3	Orosz2001
Mass function 'f(M1)' [M☉]	2.7±0.1	Orosz2001
BH mass (M1) [M☉]	6.4±0.6	MacDonald2014
Mass ratio (q=M2/M1)	0.63 – 0.70	MacDonald2014
Inclination angle (i) [deg]	72±4	MacDonald2014
Rot. broadening (v sini) [km/s]	100.9±0.8	MacDonald2014

Optical/NIR magnitudes

Mag. Outburst (AB) Orosz2001
	V=8.8
Mag. Quiescent (AB) MacDonald2014Orosz2001
B∼13.91±0.04	V=13.96±0.02		R=13.73±0.02
	I=13.52±0.03
J=14.86±0.05	H=14.23±0.05	K=12.83±0.05

Aladin finding chart

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SAX J1819.3-2525 in Simbad

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Pan-STARRS1 finding chart

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Finding charts

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