Astronomicalcentre & INAF Atel 5941 Optical activity of HDE 245770: the counterpart of the X-ray

 

Title: Optical activity of HDE 245770: the counterpart of the X-ray
pulsar A0535+26
Author: INAF-Istituto di Astrofisica e Planetologia Spaziali
Queries: franco.giovannelli@iaps.inaf.it
Posted: 3 Mar 2014; 13:06 UT
Subjects:Optical, Request for Observations, Binary, Neutron Star,
Transient

Franco Giovannelli(1), Ivan Bruni(2), Giorgio Corfini(3), Fabio Martinelli(3),
Corinne Rossi(4)

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
observatory
with the 1.52 m Cassini telescope, and at the Montecatini Val di Cecina
Astronomical
Center 36 cm telescope around the periastron passage of the neutron star
A0535+26
(JD 2456710) following the ephemeris of Giovannelli et al.: 2013, A&A,
560, A1G
(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
same period
of the photometric measurements.
This is a strong indication that the X-ray pulsar is close to experience
an X-ray
outburst after about 8 days from the periastron passage.
Moreover the probable relative maximum in the optical emission on Feb 16,
2014 of
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
will
experience stronger emission in the harder X-ray bands.
Hard X-ray measurements are strongly required.

 

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