SUMMARY OF PROPOSAL 63012

PROFESSOR PHILIP ALLAN CHARLES
PAC@ASTRO.OX.AC.UK

UNIVERSITY OF OXFORD
NUCLEAR PHYICS LABORATORY, KEBLE ROAD
OXFORD
OXFORDSHIRE UK OX1 3RH
Tel: 44-1865 273374 Fax: 44-1865 273390
Medium: CD ROM
Subject: X-RAY BINARIES

GS1826-24: THE FIRST 2HR PERIOD LMXB?


ABSTRACT

GS1826-24 was first discovered by Ginga in 1988 and originally suggested to be a soft X-ray transient black-hole candidate. However, bursts have recently been detected in X-rays by SAX and in the optical counterpart by us, thereby confirming a neutron star primary. More importantly, our fast optical photometry reveals a 2hr modulation, plus irregular variability that is reminiscent of X1636-536 and X1735-444. If confirmed as the orbital period, this places GS1826-24 in a unique evolutionary position amongst LMXBs. We propose here to use ASCA to undertake the first detailed X-ray spectral study, in particular (a) to search for soft X-ray spectral features, (b) to undertake a spectral analysis of the bursts, (c) to investigate the structure of the short-term optical variations.

CO-INVESTIGATORS
CO-I NAME INSTITUTE COUNTRY
LEE HOMERUNIVERSITY OF OXFORDUK
ERIK KUULKERSUNIVERSITY OF OXFORDUK
DARRAGH O'DONOGHUESA ASTR. OBSERVATORYS AFRICA

TARGETS

TARGET NAMEPRIRADECTIMETCOFFGISSIS CNTOBS
1)GS1826-24
1
277.3675-23.7970 20 ksN
N
P
400.00000
1

TARGET 1

NOTE THAT WE SHALL ENDEAVOUR TO ARRANGE FOR SIMULTNEOUS OPTICAL OBSERVATIONS FROM SAAO ONCE THE ASCA SCHEDULING IS KNOWN.