High resolution Halpha spectroscopy and R-band photometry of Swift J1357.2-0933

ATel #3206; Jorge Casares (IAC), Manuel A. P. Torres (SRON/CfA), Ignacio Negueruela and Carlos Gonzalez-Fernandez (Universidad de Alicante), Jesus M. Corral-Santana, Cristina Zurita and Sergio Rodriguez Llano (Instituto de Astrofisica de Canarias)
on 4 Mar 2011; 11:50 UT
Credential Certification: Manuel Torres (mtorres@cfa.harvard.edu)

Tweet

We report on high resolution Halpha spectroscopy and time-resolved photometry of the optical counterpart to the X-ray transient Swift J1357.2-0933 in outburst (Krimm et al. ATEL #3138).

SPECTROSCOPY: Six 30-33 min spectra were obtained on the nights of 2011 Feb 25-27 using the IDS Spectrograph on the 2.5m Isaac Newton Telescope (INT) at the Observatorio del Roque de Los Muchachos. The observations were performed with the H1800V grating and a slit width 1.6 arcsec to yield a spectral coverage of 6270-7000 Angs with a 30 km/s FWHM spectral resolution at Halpha..

The spectra show the presence of weak Halpha and HeI 6678 emission lines. Halpha has an equivalent width of 6-9 Angs, consistent with previous reports (Milisavljevic et al. ATEL #3146). The profile is double-peaked, an indication of emission from an accretion disc. The line is very broad with FWHM=3270 +/- 200 km/s and peak-to-peak separation of about 1800 km/s. These large velocities are characteristic of black hole transients both in outburst and quiescence, such as Swift J1753.5-0127 (Torres et al. ATEL #551, #566), XTE J1118+480 (Torres et al. 2002 ApJ 569 4239) and GRO J0422+32 (Casares et al. 1995 MNRAS 274 565). Swift J1357.2-0933 also shares with the above group of black hole transients its high Galactic latitude (b=50 deg), large outburst amplitude (~6.7 mags in g, Rau et al. ATEL #3140) and low-hard X-ray spectrum (Krimm et al. ATEL #3142).

PHOTOMETRY: Rau et al. (ATel #3140) report that the colours of the optical counterpart in quiescence are consistent with a M4V star at ~1.5 kpc. Assuming no disc contamination and that the donor star fills its Roche lobe, Paczynski's relation (Paczynski 1971 ARAA 9 183) combined with Kepler's Third Law would imply an orbital period P~2.0 hr. This is even shorter than the 2.4 hr period of the BH transient MAXI J1659-152 (Kuulkers et al. 2011 astro-ph/1102.2102).

To test this possibility, time-resolved R-band photometry of Swift J1357.2-0933 was obtained on 2011 March 2 with the IAC 80cm Telescope at the Observatorio del Teide, Tenerife. All exposures were 300s covering a total of 4 hours. The light curve is dominated by flickering with ~0.05 mags amplitude but no periodicity is detected. We measure an average magnitude R=16.57 +/- 0,05

More observations, in particular time-resolved optical photometry, are required to search for the orbital period or related (superhump) periodicities.

The INT is operated on the island of La Palma by the Isaac Newton Group (ING) in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias (IAC).The 0.82m IAC80 Telescope is operated on the island of Tenerife by the Instituto de Astrofisica de Canarias in the Spanish Observatorio del Teide.