BROADBAND SPECTRAL INVESTIGATIONS OF SGR J1550-5418 BURSTS

Journal Article · Sat Sep 01 04:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/756/1/54· OSTI ID:22092459

Lin, Lin; Goegues, Ersin; Kaneko, Yuki ^[1]; Baring, Matthew G. ^[2]; Granot, Jonathan ^[3]; Kouveliotou, Chryssa ^[4]; Van der Horst, Alexander; Watts, Anna L. ^[5]; Gruber, David; Von Kienlin, Andreas ^[6]; Younes, George ^[7]; Gehrels, Neil ^[8]

---

1. Faculty of Engineering and Natural Sciences, Sabanc Latin-Small-Letter-Dotless-I University, Orhanl Latin-Small-Letter-Dotless-I Tuzla, Istanbul 34956 (Turkey)
2. Department of Physics and Astronomy, Rice University, MS-108, P.O. Box 1892, Houston, TX 77251 (United States)
3. Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel)
4. Space Science Office, VP62, NASA/Marshall Space Flight Center, Huntsville, AL 35812 (United States)
5. Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Postbus 94249, 1090 GE Amsterdam (Netherlands)
6. Max-Planck-Institut fuer extraterrestrische Physik, Postfach 1312, D-85748 Garching bei Mnchen (Germany)
7. USRA, National Space Science and Technology Center, 320 Sparkman Drive, Huntsville, AL 35805 (United States)
8. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

We present the results of our broadband spectral analysis of 42 SGR J1550-5418 bursts simultaneously detected with the Swift/X-ray Telescope (XRT) and the Fermi/Gamma-ray Burst Monitor (GBM), during the 2009 January active episode of the source. The unique spectral and temporal capabilities of the XRT windowed timing mode have allowed us to extend the GBM spectral coverage for these events down to the X-ray domain (0.5-10 keV). Our earlier analysis of the GBM data found that the SGR J1550-5418 burst spectra were described equally well with either a Comptonized model or with two blackbody functions; the two models were statistically indistinguishable. Our new broadband (0.5-200 keV) spectral fits show that, on average, the burst spectra are better described with two blackbody functions than with the Comptonized model. Thus, our joint XRT-GBM analysis clearly shows for the first time that the SGR J1550-5418 burst spectra might naturally be expected to exhibit a more truly thermalized character, such as a two-blackbody or even a multi-blackbody signal. Using the Swift and RXTE timing ephemeris for SGR J1550-5418 we construct the distribution of the XRT burst counts with spin phase and find that it is not correlated with the persistent X-ray emission pulse phase from SGR J1550-5418. These results indicate that the burst emitting sites on the neutron star need not to be co-located with hot spots emitting the bulk of the persistent X-ray emission. Finally, we show that there is a significant pulse phase dependence of the XRT burst counts, likely demonstrating that the surface magnetic field of SGR J1550-5418 is not uniform over the emission zones, since it is anticipated that regions with stronger surface magnetic field could trigger bursts more efficiently.

• OSTI ID: 22092459
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 756; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ASTROPHYSICS
COSMIC GAMMA BURSTS
EMISSION SPECTRA
GAMMA ASTRONOMY
GAMMA DETECTION
HOT SPOTS
KEV RANGE
MAGNETIC FIELDS
NEUTRON STARS
PULSARS
SPIN
TELESCOPE COUNTERS
TELESCOPES
X RADIATION
X-RAY DETECTION