Circumstantial evidence for a blue supergiant companion of IGR J16465-4507
ATel #338; D. M. Smith (Physics Department and Santa Cruz Institute for Particle Physics, U. C. Santa Cruz)
on 5 Oct 2004; 22:41 UT
Credential Certification: David M. Smith (firstname.lastname@example.org)
Subjects: Infra-Red, Optical, X-ray, Binary, Transient
Referred to by ATel #: 429
The 2MASS counterpart to IGR J16465-4507 (ATEL #329) identified by Heras and
Walter (ATEL #336) is also a bright star in the USNO B1.0 catalog,
0448-0520455, with the magnitudes shown in the table below. Its
short outburst and high duty cycle of quiescence suggest a similarity
with the systems XTE J1739-302 (ATEL #181,#182,#184,#186,#218) and IGR
J17544-2619/1RXS J175428.3-262035 (ATEL #190,#191,#192,#194,#252, IAUC
# 8202 ). The former is known from optical and infrared spectroscopy to
have a supergiant companion of spectral type O7.5Iaf or O8Iaf
(I. Negueruela et al., in preparation), and the latter
also has a blue supergiant companion (S. Chaty et al.,
in preparation). The photometry of all three sources
from USNO B1.0 and 2MASS also suggests they may all be similar. Taking
canonical values of R, B, and K for an O9I supergiant and the
relations between interstellar absorption in these bands from Cox
(Allen's Astrophysical Quantities, 4th Edition, AIP Press, 2000), I
find the following parameters for each system:
|Name|| USNO B1.0||USNO B1.0||2MASS||B Extinction||Distance||K Excess|
| B2|| R2 || K ||(Ab, mag.)|| (kpc) || (K mag.) |
| XTE J1739-302 || 17.0 || 12.9 || 7.43 || 11.1 || 3.3 || 0.5|
| IGR J17544-2619 || 13.9 || 11.9 || 8.02 || 6.0 || 8.5 || 1.5 || IGR J16465-4507 || 15.2 || 13.0 || 9.84 || 6.5 || 12.5 || 0.5
All three systems show an infrared excess beyond the expectation for
this spectral type, which may be related to the local material which
creates high x-ray absorption in XTE J1739-302 and IGR J17544-2619 at least.
The derived columns are somewhat sensitive to the exact spectral
class assumed and to differences between magnitudes from the first and
second epochs in the USNO B1.0 catalog (I have used the second epoch
throughout for consistency). More precise values will await
higher-quality photometry as well as detailed spectroscopy on all systems.
The large distance to IGR J16465-4507 and an early-type companion are
consistent with its small Galactic latitude (0.13 degrees).
It is interesting to note that two very bright, persistent binaries with blue
supergiant companions also show extremely fast outbursts lasting on the order
of hours: Cyg X-1, a black-hole binary with a companion of type O9.7Iab (Golenetskii et al.
2003, ApJ 596, 1113), and Vela X-1, an x-ray pulsar with a companion of type B0.5Iab
(Krivonos et al. 2003, ATEL #211). Fast transient
outbursts may be a hallmark of systems with blue supergiant secondaries,
perhaps due either to the short viscous timescale in small accretion disks
associated with wind accretion, or to some kind of brief ejection intrinsic
to the secondaries.
I am grateful to I. Negueruela and S. Chaty for permission to mention their
upcoming results on the other two systems.