DISCOVERY OF A SECOND TRANSIENT LOW-MASS X-RAY BINARY IN THE GLOBULAR CLUSTER NGC 6440
Name
Heinke-2010-DISCOVERY OF A SECON.pdf
Size
1.09 MB
Format
Adobe PDF
Checksum (MD5)
b63361af5ca6099f23f6126205d8b596
Author(s)
Heinke, C. O.
Altamirano, D.
Cohn, H. N.
Lugger, P. M.
Budac, S. A.
Servillat, M.
Linares, Manuel Alegret
Strohmayer, T. E.
Markwardt, Craig B.
Wijnands, R.
Date Issued
May 2010
Journal
Astrophysical Journal
Publisher
Institute of Physics/American Astronomical Society
Citation
Heinke, C. O., D. Altamirano, H. N. Cohn, P. M. Lugger, S. A. Budac, M. Servillat, M. Linares, et al. “DISCOVERY OF A SECOND TRANSIENT LOW-MASS X-RAY BINARY IN THE GLOBULAR CLUSTER NGC 6440.” The Astrophysical Journal 714, no. 1 (April 15, 2010): 894–903. © 2010 American Astronomical Society.
Version
Final published version
Abstract
We have discovered a new transient low-mass X-ray binary, NGC 6440 X-2, with Chandra/ACIS, RXTE/PCA, and Swift/XRT observations of the globular cluster NGC 6440. The discovery outburst (2009 July 28-31) peaked at LX ~ 1.5 × 10[superscript 36] erg s[superscript –1] and lasted for <4 days above LX = 10[superscript 35] erg s[superscript –1]. Four other outbursts (2009 May 29-June 4, August 29-September 1, October 1-3, and October 28-31) have been observed with RXTE/PCA (identifying millisecond pulsations) and Swift/XRT (confirming a positional association with NGC 6440 X-2), with similar peak luminosities and decay times. Optical and infrared imaging did not detect a clear counterpart, with best limits of V>21, B>22 in quiescence from archival Hubble Space Telescope imaging, g'>22 during the August outburst from Gemini-South GMOS imaging, and J gsim 18.5 and K gsim 17 during the July outburst from CTIO 4 m ISPI imaging. Archival Chandra X-ray images of the core do not detect the quiescent counterpart (LX < (1-2) × 10[superscript 31] erg s[superscript –1]) and place a bolometric luminosity limit of L NS < 6 × 1031 erg s[superscript –1] (one of the lowest measured) for a hydrogen atmosphere neutron star. A short Chandra observation 10 days into quiescence found two photons at NGC 6440 X-2's position, suggesting enhanced quiescent emission at LX ~ 6 × 10[superscript 31] erg s[superscript –1]. NGC 6440 X-2 currently shows the shortest recurrence time (~31 days) of any known X-ray transient, although regular outbursts were not visible in the bulge scans before early 2009. Fast, low-luminosity transients like NGC 6440 X-2 may be easily missed by current X-ray monitoring.
MIT Department
MIT Kavli Institute for Astrophysics and Space Research
Terms of Use
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1088/0004-637x/714/1/894
