3A 1954+319
Also known as: 4U 1954+31
Coordinates
RA 19h 55m 42.32s, Dec +32° 05' 49.2"
RA 298.926333 , Dec 32.097000
l 068.3920 , b +01.9270
Binary System
Distance determined to be 1.7 kpc by [1]
Orbit
The orbital parameters of this system are not known.
Optical Companion
Name: U1200_13816030 (M06) Spectral Type: M4 III[1]
Available data
- INTEGRAL: many obs during the Cyg X-1 key programme, only partly published: [2], Marcu et al., 2011, ApJ, in prep.
- RXTE: ObsID 30143-04 (10ksec, Dec 1997) and 95427-01 (3ksec, Jul 2010), YU proposal accepted prnb=96314
- Chandra: 1ksec position determination (HRC-I, Jan 2006), 37.5ksec ObsID=12474 (ACIS-S, 2011)
- Swift: ObsID 00030392001 (Apr 2006, 2.6ksec XRT) and 00030392002 (Apr 2007, 4.2ksec XRT), but slightly different pointings
- BeppoSAX et al.: see [3], including BeppoSAX, ROSAT, RXTE, Swift, EXOSAT I, and EXOSAT II
- Suzaku: ObsID=406046010
Description
3A 1954+319 was first detected as a highly variable X-ray source in surveys by Uhuru and Ariel V ([4], [5]). [1] identified the companion star as a M-type giant making it a SyXB.
A ~5 h period was discovered in the Swift-BAT X-ray flux, which has been interpreted as the neutron star's pulse period, making it one of the slowest rotating neutron stars in an X-ray binary ([6]). Marcu et al., 2011, ApJ, in prep. found the pulse period to be ~5.3 h in recent Swift/BAT and INTEGRAL/ISGRI data.
Flares of the source occurred in 2008 November and 2010 June. The 20-100 keV flux during the 2008 flare had an average of ~60 mCrab and a peak value of ~190 mCrab (Marcu et al., 2011, ApJ, in prep.). The 2008 flare was analyzed by Marcu et al., 2011, ApJ, in prep. with INTEGRAL using science windows from satellite revolutions 739, 741-746, 756, 758. The 2010 flare was ~100 mCrab and was analyzed by Grieves et al. (2011, NASA-GSFC summer internship report) using science windows from INTEGRAL satellite revolution 938.
Flux
Luminosity 5x1034 erg s-1, assuming 1.7 kpc distance ([3]), but highly variable. During the 2008 flare 3A 1954+319 had an average flux of ~8.6x10-10 erg cm-2 s-1 between 20-100 keV (~60 mCrab) and a peak flux of more than 180 mCrab ([7]). For the 2010 flare the 20-80 keV flux was found to be 2.03x10-9 erg cm-2 s-1 from INTEGRAL revolution 938 using the convolution model cflux (Grieves et al., 2011, NASA-GSFC summer internship report).
Spectrum
[3] described the 0.2-150 keV spectrum in terms of a hot gas component plus thermal Comptonization modified by complex absorption. Marcu et al., 2011, ApJ, in prep. analyzed the 2008 flare of 3A 1954+319 and the spectrum was again best described by an absorbed thermal Comptonization model. Using INTEGRAL data the 2010 flare was compared to the 2008 flare with the compTT model. The 2010 flare showed the presence of a more optically thin plasma (Grieves et al., 2011, NASA-GSFC summer internship report).
INTEGRAL spectrum of satellite revolutions 742 and 938 fit with a phabs*compTT model. Colors correspond to lightblue=rev742jemx blue=rev742isgri orange=rev938jemx red=rev938isgri (Grieves et al., 2011, NASA-GSFC summer internship report).
Pulse Profile
Pulse profiles in the energy ranges of 20-40 keV and 40-100 keV obtained from the 2008 outburst data show a double peaked structure, in contrast to the single peaked pulse profile displayed by the prototype SyXB GX 1+4 (Marcu et al., 2011, ApJ, in prep.)
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