Near-IR and Optical Observations of the Ongoing Outburst of SAX J1808.4-3658
ATel #1733; D. Maitra (Univ. of Amsterdam), M. Buxton, S. Tourtellotte (Yale), D. Altamirano, A. Patruno, P. Casella, M. Linares, V. Tudose, D. Russell, R. Wijnands, (Univ. of Amsterdam), C. Bailyn (Yale)
on 23 Sep 2008; 23:03 UT
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Credential Certification: Dipankar Maitra (firstname.lastname@example.org)
Subjects: Infra-Red, Optical, Binary, Neutron Star, Transient, Pulsar
Referred to by ATel #: 1748
Following the report of a new outburst of the accreting millisecond
pulsar SAX J1808.4-3658 by Markwardt and Swank (ATel #1728), the
source was observed using
the CTIO/SMARTS 1.3m telescope on MJD 54732.0998, in I- and H-bands.
We clearly detected the source at magnitudes significantly higher than
its quiescent level, confirming that the source is indeed in outburst.
The I-band magnitude of the source was estimated to be 16.93+/-0.05,
by comparing against the reference stars in Greenhill et al. (2006
MNRAS, 370, 1303).
This indicates that the source is already ~4.6 mag brighter than the
average quiescent I-band magnitude (~21.5) reported by Campana et al. (2004, ApJ, 614, L49)! This
increase in brightness is much larger than the expected variability in
the light curve due to orbital modulation (~0.1-0.2 mag;
Giles et al.
1999, MNRAS, 304, 47), and confirms the onset of a new outburst.
The H-band magnitude was estimated to be 16.1 +/- 0.5 using three
nearby stars from the 2MASS point source catalog as reference.