Title: Optical activity of HDE 245770: the counterpart of the X-ray
Author: INAF-Istituto di Astrofisica e Planetologia Spaziali
Posted: 3 Mar 2014; 13:06 UT
Subjects:Optical, Request for Observations, Binary, Neutron Star,
Franco Giovannelli(1), Ivan Bruni(2), Giorgio Corfini(3), Fabio Martinelli(3),
1) INAF-Istituto di Astrofisica e Planetologia Spaziali
2) INAF-Osservatorio Astronomico di Loiano
3) Montecatini Val di Cecina Astronomical Center
4) Dept. of Physics, Sapienza University, Roma
Optical activity of HDE 245770: the counterpart of the X-ray pulsar A0535+26
We planned optical photometry and spectroscopy of HDE 245770 at the Loiano
with the 1.52 m Cassini telescope, and at the Montecatini Val di Cecina
Center 36 cm telescope around the periastron passage of the neutron star
(JD 2456710) following the ephemeris of Giovannelli et al.: 2013, A&A,
(JD_opt?outb = JD_0(2444944) +- n(111.0 +- 0.4) days).
This passage is just 106 orbital periods after the 811205-E.
The results of photometry are:
Date JD+2456700 V mag (+-0.01)
16 Feb 2014 05.43675 9.14
17 Feb 2014 06.30500 9.17
22 Feb 2014 11.25100 9.16
23 Feb 2014 12.25099 9.16
24 Feb 2014 13.25100 9.16
25 Feb 2014 14.25100 9.18
26 Feb 2014 15.25100 9.18
The H_gamma, usually in absorption, is filling the continuum during the
of the photometric measurements.
This is a strong indication that the X-ray pulsar is close to experience
outburst after about 8 days from the periastron passage.
Moreover the probable relative maximum in the optical emission on Feb 16,
0.02 mag is the other indicator of the incoming X-ray outburst.
Unfortunately photometric data are not available before Feb 16, 2014.
Tagagi et al. 2014, ATel #5931, announce a weak increase of X-ray emission
of about 20 mCrab in the 4-10 keV band on Feb 27 2014.
We predict that in the following days, after February 27, the X-ray pulsar
experience stronger emission in the harder X-ray bands.
Hard X-ray measurements are strongly required.