The optical counterpart of the bright X-ray transient Swift J1745-26

Abstract

We present a 30-day monitoring campaign of the optical counterpart of the bright X-ray transient Swift J1745-26, starting only 19 minutes after the discovery of the source. We observe the system peaking at i' ~17.6 on day 6 (MJD 56192) to then decay at a rate of ~0.04 mag/day. We show that the optical peak occurs at least 3 days later than the hard X-ray (15-50 keV) flux peak. Our measurements result in an outburst amplitude greater than 4.3 magnitudes, which favours an orbital period < 21 h and a companion star with a spectral type later than ~ A0. Spectroscopic observations taken with the GTC-10.4 m telescope reveal a broad (FWHM ~ 1100 km/s), double-peaked H_alpha emission line from which we constrain the radial velocity semi-amplitude of the donor to be K_2 > 250 km/s. The breadth of the line and the observed optical and X-ray fluxes suggest that Swift J1745-26 is a new black hole candidate located closer than ~7 kpc.

5 pages, 4 figures, accepted for publication in MNRAS

References in corpus (12)

• X-ray Properties of Black-Hole Binaries
• The Black Hole Mass Distribution in the Galaxy
• Empirical Color Transformations Between SDSS Photometry and Other Photometric Systems
• Jets from black hole X-ray binaries: testing, refining and extending empirical models for the coupling to X-rays
• Global optical/infrared - X-ray correlations in X-ray binaries: quantifying disc and jet contributions
• On the masses and evolutionary status of the black hole binary GX 339-4. A twin system of XTE J1550-564?
• A Black Hole Nova Obscured by an Inner Disk Torus
• Evidence for a jet contribution to the optical/infrared light of neutron star X-ray binaries
• Multiwavelength Observations of EXO 0748--676 -- II. Emission Line Behavior
• Multiwavelength Observations of EXO 0748-676 - I. Reprocessing of X-ray Bursts
• The 2005 outburst of the halo black hole X-ray transient XTE J1118+480
• Echoes from the companion star in Sco X-1

Cited by in corpus (16)

• The Swift/BAT Hard X-ray Transient Monitor
• BlackCAT: A catalogue of stellar-mass black holes in X-ray transients
• WATCHDOG: A Comprehensive All-Sky Database of Galactic Black Hole X-ray Binaries
• The evolving polarised jet of black hole candidate Swift J1745-26
• Revealing the nature of the QPO and its harmonic in GX 339-4 using frequency-resolved spectroscopy
• The INTEGRAL view on Black Hole X-ray Binaries
• The long outburst of the black hole transient GRS 1716-249 observed in the X-ray and radio band
• Spectral and timing evolution of the bright failed outburst of the transient black hole Swift J174510.8-262411
• The Galactic LMXB Population and the Galactic Centre Region
• Sub-mm Jet Properties of the X-Ray Binary Swift J1745$-$26
• Orbital period dependent spatial scatter of Galactic Black Hole Transients
• Black holes: Timing and spectral properties and evolution
• Multiwavelength observations of the black hole transient Swift J1745-26 during the outburst decay
• Quiescent NIR and optical counterparts to candidate black hole X-ray binaries
• Optical nebular emission following the most luminous outburst of Aquila X-1
• Broad-band spectral energy distribution of the X-ray transient Swift J1745-26 from outburst to quiescence