Gamma-ray Burst 010921

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN/BACODINE POSITION NOTICE
  

  
  TITLE:          GCN/HETE BURST POSITION NOTICE
  NOTICE_DATE:    Fri 21 Sep 01 05:16:08 UT
  NOTICE_TYPE:    HETE S/C_Alert
  TRIGGER_NUM:    1761,   Seq_Num: 1
  GRB_DATE:       12173 TJD;   264 DOY;   01/09/21
  GRB_TIME:       18950.56 SOD {05:15:50.56} UT
  TRIGGER_SOURCE: Trigger on the 6-120 keV band.
  GAMMA_RATE:     376  [cnts/s]  on a 1.300 [sec] timescale
  SC_-Z_RA:       358 [deg]
  SC_-Z_DEC:        0 [deg]
  SUN_POSTN:      178.44d {+11h 53m 45s}   +0.68d {+00d 40' 39"}
  MOON_POSTN:     228.39d {+15h 13m 33s}  -14.42d {-14d 25' 08"}
  MOON_ILLUM:     19 [%]
  COMMENTS:       Probable GRB.
  

• GCN/BACODINE POSITION NOTICE
  

  TITLE:          GCN/HETE BURST POSITION NOTICE
  NOTICE_DATE:    Fri 21 Sep 01 05:19:57 UT
  NOTICE_TYPE:    HETE S/C_Last
  TRIGGER_NUM:    1761,   Seq_Num: 2
  GRB_DATE:       12173 TJD;   264 DOY;   01/09/21
  GRB_TIME:       18950.56 SOD {05:15:50.56} UT
  TRIGGER_SOURCE: Trigger on the 6-120 keV band.
  GAMMA_RATE:     376  [cnts/s]  on a 1.300 [sec] timescale
  SC_-Z_RA:       358 [deg]
  SC_-Z_DEC:        0 [deg]
  SUN_POSTN:      178.44d {+11h 53m 45s}   +0.68d {+00d 40' 39"}
  MOON_POSTN:     228.39d {+15h 13m 33s}  -14.42d {-14d 25' 08"}
  MOON_ILLUM:     19 [%]
  COMMENTS:       Probable GRB.
  COMMENTS:       There is no WXM or SXC position in this notice.
   
  

• GCN notice #1096
  H1761: A Bright GRB Detected by HETE
  G. Ricker, D. Lamb, and S. Woosley on behalf of the HETE Science Team;
  R. Vanderspek, G. Crew, J. Doty, G. Monnelly, J. Villasenor, N. Butler, T. Cline, J.G. Jernigan, A. Levine, F. Martel, E. Morgan, G. Prigozhin, J. Braga, R. Manchanda, and G. Pizzichini, on behalf of the HETE Operations and HETE Optical-SXC Teams;
  N. Kawai, M. Matsuoka, Y. Shirasaki, T. Tamagawa, K. Torii, T. Sakamoto, A. Yoshida, E. Fenimore, M. Galassi, T. Donaghy, and C. Graziani, on behalf of the HETE WXM Team;
  J-L Atteia, M. Boer, J-F Olive, J-P Dezalay, and K. Hurley on behalf of the HETE FREGATE Team; write:
  The HETE Fregate instrument has detected a bright (>40 sigma) GRB that has been reported in a GCN Notice as H1761. The burst occurred at 18950.56 SOD {05:15:50.56} UT on 21 September. The burst is seen in the WXM X detector and is therefore well-localized in the X direction; the burst was apparently outside the coded FOV of the WXM Y detector, which therefore gives limited information about the Y direction of the burst.
  The X-detector data gives a good (+/-10 arcmin) localization in the X direction and crude limits on Y, resulting in a localization that is a thin, long strip.
  Two points along one side of the strip are:

   
  R.A. = 22h52m36s.7, Dec. =  39o35'13"
  R.A. = 23h10m22s.8, Dec. =  48o57'43"
  

  Two points along the other side of the strip are:

  R.A. = 22h54m04s.0, Dec. =  39o34'23"
  R.A. = 23h11m52s.5, Dec. =  48o57'00"
  

  Our estimate is that the strip is ~10 degrees in the long direction.
  The burst duration in the 8-85 keV band was ~12 s. A total of 5310 counts were detected during that interval, corresponding to a fluence of ~1 x 10-6 ergs cm-2. The peak flux was >3 x 10-7 ergs cm-2 s-1 (ie >8 x Crab flux).
  Further refinement of the X localization is in progress; a further attempt is also being made to improve the coarse Y localization.
• GCN notice #1097
  K. Hurley and T. Cline, on behalf of the Ulysses and HETE GRB teams;
  F. Frontera, E. Montanari, C. Guidorzi, and M. Feroci, on behalf of the BeppoSAX GRBM team;
  G. Ricker, D. Lamb, and S. Woosley on behalf of the HETE Science Team;
  R. Vanderspek, G. Crew, J. Doty, G. Monnelly, J. Villasenor, N. Butler, T. Cline, J.G. Jernigan, A. Levine, F. Martel, E. Morgan, G. Prigozhin, J. Braga, R. Manchanda, and G. Pizzichini, on behalf of the HETE Operations and HETE Optical-SXC Teams;
  N. Kawai, M. Matsuoka, Y. Shirasaki, T. Tamagawa, K. Torii, T. Sakamoto, A. Yoshida, E. Fenimore, M. Galassi, T. Donaghy, and C. Graziani, on behalf of the HETE WXM Team;
  J-L Atteia, M. Boer, J-F Olive, and J-P Dezalay, on behalf of the HETE FREGATE Team;
  report:
  Ulysses and BeppoSAX observed GRB010921 (=H1761, GCN 1096). Triangulation gives an annulus centered at RA(2000), Decl.(2000)= 232.299 deg., +67.605 deg., with radius 60.003 +/- 0.156 deg (3 sigma). This annulus intersects the HETE-II WXM error box (GCN 1096) at

  RA(2000)        Dec(2000)
  
  343.596         +40.669
  343.763         +41.069
  344.027         +40.816
  344.195         +41.215
  

  to form an error box whose area is approximately 250 sq. arcmin. Some improvement to this error box is possible.
• GCN notice #1098
  A. Mahabal, S. G. Djorgovski, and R. Brunner of the Caltech DPOSS group, with D. W. Fox and P. A. Price of the Caltech-NRAO-CARA GRB collaboration, report:
  "We have made Digital Palomar Observatory Sky Survey (DPOSS) images of the GRB 010921 error box (GCN #1097) publicly available through the React Group webpages at:

  
  http://www.srl.caltech.edu/~react/GRB010921.html
  

  The images may also be accessed directly as:

          http://www.srl.caltech.edu/~react/fits/GRB010921j.fits
          http://www.srl.caltech.edu/~react/fits/GRB010921f.fits
          http://www.srl.caltech.edu/~react/fits/GRB010921n.fits
  

  The images are 1801x1801 pixels, centered at (J2000) RA 22:55:34.86, Dec +40:56:32.1, and covering 30'x30'. The images are from the second Palomar Sky Survey and were digitized at STScI; they have subsequently been corrected for vignetting effects and have corrected astrometric coefficients in the image headers. Note that the image bandpasses are green (j), red (f), and near-infrared (n), corresponding, respectively, to the IIIa-J, IIIa-F, and IV-N emulsions used in the survey. Going forward, we hope to make DPOSS images of GRB fields in the northern hemisphere available on a regular basis.
  Please contact Ashish Mahabal or one of the other authors of the Circular if you have any questions."
• GCN notice #1099
  D. W. Fox, R. Burruss, E. Berger, J. S. Bloom, S. G. Djorgovski, and S. R. Kulkarni (Caltech), with M. Haynes (Cornell), report on behalf of the larger Caltech-NRAO-CARA GRB collaboration:
  "R. Burrus obtained Sloan r' images of the joint HETE/IPN localization for GRB010921 (HETE trigger #1761; GCNs #1096 and #1097) with the Hale 200-inch telescope at Palomar Observatory beginning 22 hours after the trigger (22 September 03:18 UT). The instrument used was the Large Format Camera (LFC) and the observations were 4 min in duration (3 pointings). Visual comparison with the Digital Palomar Observatory Sky Survey F plate reveals no obvious new source to the depth of the DPOSS image (R ~ 20.5 mag)."
• GCN notice #1100
  A. Henden (USRA/USNO) reports on behalf of the USNO GRB team:
  We have acquired UBVRcIc all-sky photometry for an 11x11 arcmin field that covers the center of the error box for GRB010921 (GCN 1096,1097) with the USNOFS 1.0-m telescope on one photometric night. Stars brighter than V=13.5 are saturated and should be used with care. We have placed the photometric data on our anonymous ftp site: ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb010921.dat The current photometry has a potential external zero-point error of about two percent. The astrometry in this file is based on linear plate solutions with respect to USNO-A2.0. The internal errors are less than 100mas. Further calibration of this field will be performed if an optical afterglow is identified.
• GCN notice #1101
  A. Henden (USRA/USNO) reports on behalf of the USNO GRB team:
  We have acquired single R-band images with the NOFS 1.0m telescope from 010922 0654-0807 UT, forming a mosaic that covers nearly all of the HETE/IPN error box (GCN 1097).
  Inspecting the DPOSS images posted by Fox, et al. (GCN 1098), this region shows a few galaxies, but also a fair amount of nebulosity and bright stars. It is located at galactic longitude 100.5 and latitude -16.8, so not very far out of the galactic plane. At the same time, the star colors (Henden GCN 1100) indicate that there is not a great deal of reddening in the field.
  In agreement with Fox, et al. (GCN 1099), we find no obvious afterglow candidate down to the DPOSS plate limit. There are several probable variable stars and a couple of faint high proper motion objects.
• GCN notice #1107
  P. A. Price, E. Berger, D. W. Fox, D. A. Frail, S. R. Kulkarni, J. S. Bloom, R. S. Burrus, S. G. Djorgovski, M. Haynes, and A. Mahabal report on behalf of the Caltech-NRAO-CARA GRB collaboration:
  Following our observations of 2001 Sep 22.14 UT (t_GRB + 22 hr; GCN #1099), we re-observed the error box of GRB 010921 (HETE trigger #1761) with the Large Format Camera (LFC) on the Palomar 200-inch telescope on 2001 Sep 27.35 UT. Both observations covered the entire 250 square arcminute error box (GCN ##1096, 1097) with three pointings in Sloan r'. In preliminary reduction of the images, we identified a number of variable sources, and so further observations were made of the error box on 2001 Oct 17.15 UT with LFC. We now identify one source within the error box that exhibited a power-law decay, with index alpha ~ 1.6, superposed on a bright (R ~ 21.7 mag) galaxy. The coordinates of this source are

  	RA: 22:55:59.9, Dec: +40:55:53 (J2000)
  

  with an estimated error of 0.6 arcseconds.
  Radio observations made with the VLA on 2001 Oct 17.15 reveal a radio source at the location of the optical transient with a nu^1/3 spectrum between 4.86 and 22.5 GHz, as has been seen in previous GRB afterglows.
  At the above coordinates, we also find a source detected with the USNOFS 1.0-m telescope (GCN #1100), which when corrected for Galactic extinction has a ~ nu^-2.3 spectrum over BVRI, possibly indicating extinction in the source frame.
  While all properties of this transient source appear to be consistent with those of a GRB afterglow, we can not with this information completely exclude the possibility that this object is a low luminosity AGN. Nevertheless, we believe that this object is most likely the afterglow of GRB 010921, detected and localised by HETE.
  This message may be cited.
• GCN notice #1108
  GRB010921: Spectroscopy of the Host Galaxy
  S.G. Djorgovski, A. Mahabal, P.A. Price, J.S. Bloom, D.E. Reichart, E. Berger, D.W. Fox, S.R. Kulkarni, D.A. Frail, R. Sari, T. Galama, F. Harrison, and S. Yost report on behalf of the Caltech-NRAO-CARA GRB collaboration:
  "We obtained a spectrum of the host galaxy of the proposed afterglow of GRB010921 (Price et al., GCN 1107) using the Double Spectrograph at the Palomar 200-inch telescope, on 17 October 2001 UT. Preliminary reductions of the spectrum indicate a redshift of z = 0.450 +- 0.005, on the basis of 4 emission lines, [O II] 3727, H-beta, [O III] 5007, and H-alpha. The spectrum is typical for an actively star-forming galaxy, with no sign of an active nucleus. Further analysis is in progress.
  Assuming an H_0 = 65 km/s/Mpc, Omega_m = 0.3, Omega_lambda = 0.7 cosmology, we derive the luminosity distance of 8.30e+27 cm. Using the fluence of 1.0e-6 erg/cm2 (Ricker et al. GCN #1096), the total energy release in the restframe range 12-123 keV (redshifted bandpass of the HETE band at 8-85 keV) is 6.0e+50 erg. Though no spectral information was reported, we estimate that the isotropic equivalent energy release in the 20-2000 keV range (see Bloom et al. 2001, AJ, 121, 2879) was E_iso(gamma) = (2.65 +- 1.45)e+51 erg.
  To conform with the constant energy of E_gamma = 5e+50 erg (Frail et al. 2001, ApJ Letters, accepted; astro-ph/0102282), the time of the jet break would be t_jet ~ 130 days after the GRB. However, a possible supernova associated with this event may be detectable now."
  This note can be cited.
• GCN notice #1113
  S. Klose, B. Stecklum (Thueringer Landessternwarte Tautenburg), on behalf of a larger collaboration, report:
  The improved error box of GRB 010921 (Hurley et al., GCN #1097) was imaged in the I band using the Tautenburg Schmidt telescope on Sep. 22, 18:45 UT - 23:13 UT (38 frames, 2 min exposure time each; field of view about 35 x 35 arcmin).
  The source reported by Price et al. (GCN #1107) is clearly detected. Based on the standard stars provided by Henden (GCN #1100) we measure a magnitude of I=18.93 +/- 0.05.
  This message is quotable.
• GCN notice #1114
  H.S. Park, G. Williams, S. Barthelmy, D. Hartmann, K. Hurley report on behalf of the LOTIS collaboration:
  LOTIS observed the GRB 010921 optical afterglow area reported in GCNC #1107 on 09/21/2001 at 06:08:31 (52 min after the burst) during a routine sky patrol. LOTIS uses 4 11 cm aperture telephoto lenses to view an 8.8 x 8.8 deg field of view in the R, V and clear bands. We searched for an optical counterpart in the region of GRB 010921 and we found no source. The 10 sigma limits are:

  	clear filter	15.3 +/- 0.15
  	V filter	14.2 +/- 0.15
  	R filter	shutter failed to open
  

  Further analys is in progress.
  This message may be cited.
• GCN notice #1117
  P.A. Price, S.R. Kulkarni, D.W. Fox, E. Berger, J.S. Bloom, S.G. Djorgovski, D.A. Frail, T.J. Galama, F.A. Harrison, A. Mahabal, D.E. Reichart, R. Sari and S.A. Yost of the Caltech-NRAO-CARA GRB collaboration report:
  We re-observed the optical transient associated with GRB 010921 (GCN ##1107,1108) with the Palomar 200-inch telescope in Sloan g'r'i'z' on 2001 Oct 19.1 UT. Magnitudes of the counterpart were measured relative to stars in the field calibrated with the Palomar 60-inch telescope and the USNOFS 1.0-metre telescope (GCN #1100). We find that, at this epoch, the counterpart has a spectral flux distribution that peaks between the r' and i' bands, and falls away on the red and blue sides as ~ nu^3.5 and ~ nu^-2.1 respectively.
  This spectral flux distribution finds a natural explanation in terms of a supernova underlying the GRB afterglow (Bloom et al. 1999; Reichart 1999; Galama et al. 2000). If this interpretation is correct, the source should continue to fade beyond R ~ 22 mag over a timescale of a few weeks.
  We strongly encourage further monitoring of this source, especially in the blue and near infrared.
  This message may be cited.
  References: Bloom, J.S. et al., 1999, Nature, 401, 453. Reichart, D.E., 1999, ApJ, 521, L111. Galama, T.J. et al., 2000, ApJ, 536, 185.
• GCN notice #1125
  D. Q. Lamb, B. C. Lee, D. L. Tucker, D. E. Vanden Berk, P. Newman, J. Krzesinski and A. N. Kleinman, on behalf of the SDSS GRB team, report:
  We observed the HETE error box for GRB 010921 (GCN 1096) using the SDSS 0.5-m "Photometic Telescope" at APO under partly cloudy conditions on 2001 September 22 beginning at UT 02:36 and on 2001 September 23 beginning at UT 05:23. Images of the entire improved HETE error box (GCN 1097) were acquired in the SDSS u, g , r, i, and z filters on both nights.
  The optical transient (OT) reported by Price et al. (GCN 1107; see also GCN 1108 and GCN 1113) was r'=19.6 +/-0.3 on September 22 and significantly fainter on September 23 (we place an upper limit on r' of roughly 20.0). The OT is marginally visible (at perhaps the 1 to 2 sigma level) in g and i on September 22 and in g and r on September 23. We place upper limits on u, g, i, and z of roughly 20.5, 18.5, 17.5, and 15.0 on September 22, with the completeness limit of the i and z filters heavily degraded by clouds, and 19.5, 20.0, 18.5, and 18.5 on September 23, again impacted by clouds. These upper limits are consistent with a ~ nu^{-2.3} spectrum over u, g, r, i, and z (GCN 1107). Images can be found at http://sdss.fnal.gov:8000/grb/.
  This message is quotable.
• GCN notice #1131
  H.S. Park, G. Williams, S. Barthelmy, T. Cline, D. Hartmann, K. Hurley, W. Pereira report on behalf of the LOTIS collaboration:
  Super-LOTIS observed the HETE/IPN error box of GRB 010921 (GCNC #1096, #1097) on 09/22/2001 starting at 03:05 UTC, 21.8 hr after the burst. Super-LOTIS is a 0.6 m telescope located at Kitt Peak. These observations were made with a clear filter and an effective integration time is 1000 s. We detect the afterglow reported by Price et al. (GCNC #1107) at 2 epochs. The magnitude of the afterglow is calibrated against R band secondary standards reported in GCNC #1100 by Henden.

  	UTC		Ropen
  	9/22/01 03:05	19.4 +/- 0.2
  	9/22/01 06:25	19.9 +/- 0.2
  	9/23/01 03:05	> 21.2 +/- 0.3
  	9/23/01 06:27	> 21.2 +/- 0.3
  

  Further analysis is in progress.
  This message can be cited.
• GCN notice #1135
  GRB 010921: HST Detection of the Afterglow and Host Galaxy
  J. S. Bloom, S. R. Kulkarni, F. A. Harrison, T. J. Galama, P. A. Price, S. G. Djorgovski, D. W. Fox, E. Berger, and D. A. Frail report on behalf the larger Caltech-NRAO-CARA GRB Collaboration:
  "We observed the field of GRB 010921 (Ricker et al., GCN #1096; Hurley et al., GCN #1097; Price et al., GCN #1107) on 2001 October 26-27 UT using the WFPC F450W, F555W, F606W, F814W, F850LP filters on the Hubble Space Telescope for a total of 1200 s integration in each bandpass. The observations were conducted as part of the HST-GO Proposal #8867 (S. Kulkarni, P.I.).
  An astrometric comparison of the HST images with the Price et al. discovery image from Palomar reveals that the transient position is consistent (to better than 1 sigma) with a red compact source O.41 arcsec to the East of the center of a galaxy. The Palomar localization is inconsistent (at the 3-sigma level) with the center of the galaxy (note: no correction has yet been made to the Palomar transient position in the Palomar image for the contribution of the galaxy to the centroid position; correcting for this effect would tend to push the Palomar transient position further from the galaxy center). Given that the red color of the compact source is consistent with the Price et al. spectral slope and that the localization is consistent, we identify this source as the afterglow of GRB 010921 and the galaxy (z=0.45; Djorgovski et al. #1108) as the host."
  An image of the host and the optical transient may be found at:
  http://www.astro.caltech.edu/~jsb/GRB/grb010921-host-reg.ps
  The 1 and 3-sigma uncertainty contours of the OT position measured from the Palomar discovery images is shown.
  Links to false-color images of the WFPC field and close-up images of the OT-host system may be found at:
  http://www.astro.caltech.edu/~jsb/grb010921
  Analysis of the broadband afterglow spectra is underway and more HST observations are scheduled.
  This message may be cited.
• GCN notice #1162
  Julie McEnery on behalf of the Milagro collaboration reports:
  Milagro observed GRB010921 at GeV/TeV energies during the burst duration (12 s) reported by the HETE WXM (GCN 1096). No evidence for GeV/TeV emission was found. A preliminary analysis (assuming a differential photon spectral index of -2.4) gives an upper limit on the fluence at the 99% confidence level of:
  J(E > 2 TeV) < 2 * 10^(-7) erg cm^(-2)
  The spectrum of the host galaxy of the proposed afterglow of GRB010921 implies a redhift of 0.45 (GCN 1108). We expect that TeV photons will be attenuated by pair production with infrared photons in intergalactic space so we also calculate an upper limit on the fluence, assuming a spectrum truncated at 150 GeV. In this case we find an upper limit on the fluence at the 99% confidence level of:
  J(100-150 GeV) < 4 * 10^(-5) erg cm^(-2)
  These upper limits are preliminary and will be refined with further analysis. These limits do not incorporate systematic uncertainties which may be of order 50%.
• GCN notice #1259
  P.A. Price, B.P. Schmidt (RSAA, ANU) and S.R. Kulkarni (Caltech) report on behalf of the larger REACT GRB collaboration:
  As a part of our AO-9 HST GRB program, we observed the afterglow (Price et al GCN #1107) of GRB 010921 (Ricker et al. GCN #1096). We obtained WFPC2 observations through multiple filters, designed to detect or constrain underlying supernovae for low-redshift GRBs. The observations were obtained on 2001 Oct 26, Nov 6, Nov 25 and 2002 Jan 4. We have drizzled, registered and subtracted the images to obtain host-subtracted fluxes at each of the first three epochs, assuming the flux of the GRB in the final epoch image is negligible. The light-curve is available from
  http://www.mso.anu.edu.au/~pap/grb010921/
  We identify a break in the light-curve at approximately 35 days which may be due to collimation of the ejecta. If so, then we calculate a jet-corrected gamma-ray energy release of 6.7 x 10^51 erg, consistent with the clustering of gamma-ray energy releases found by Frail et al. (2001, ApJ, 562, L55).
  SN 1998bw at z = 0.451 should peak in the F702W and F814W bands, at approximately 4 uJy. No evidence for such a component in the light-curve is seen in the F555W, F702W, F814W and F850LP bands. These measurements rule out the existence of a SN with a luminosity greater than approximately 20% that of SN 1998bw underlying the GRB. We note, however, that we cannot rule out the existence of a more typical SN Ib/c, such as SN 1994I. We strongly recommend that observers planning a search for a SN underneath a GRB afterglow do not assume that the SN will be as luminous as SN 1998bw.
  A more detailed analysis of the data is in progress.
  This message may be cited.
• GRB 010921: Discovery of the First High Energy Transient Explorer Afterglow
  Price et al: ApJ 571 (2002), L121
  We report the discovery of the optical and radio afterglow of GRB 010921, the first gamma-ray burst afterglow to be found from a localization by the High Energy Transient Explorer satellite. We present optical spectroscopy of the host galaxy, which we find to be a dusty and apparently normal star-forming galaxy at z = 0.451. The unusually steep optical spectral slope of the afterglow can be explained by heavy extinction, AV > 0.5 mag, along the line of sight to the GRB. Dust with similar AV for the host galaxy as a whole appears to be required by the measurement of a Balmer decrement in the spectrum of the host galaxy.
• 1002.3849 from 23 Feb 10
  M. Arimoto et al.: Spectral Lag Relations in GRB Pulses Detected with HETE-2
  T. Tamagawa, Y. Shirasaki, S. Sugita, I. Takahashi, J.-L. Atteia, A. Pelangeon, R. Vanderspek, C. Graziani, G. Prigozhin, J. Villasenor, J. G. Jernigan, G. B. Crew, T. Sakamoto, G. R. Ricker, S. E. Woosley, N. Butler, A. Levine, J. P. Doty, T. Q. Donaghy, D. Q. Lamb, E. Fenimore, M. Galassi, M. Boer, J.-P. Dezalay, J.-F. Olive, J. Braga, R. Manchanda, G. Pizzichini Using a pulse-fit method, we investigate the spectral lags between the traditional gamma-ray band (50-400 keV) and the X-ray band (6-25 keV) for 8 GRBs with known redshifts (GRB 010921, GRB 020124, GRB 020127, GRB 021211, GRB 030528, GRB 040924, GRB 041006, GRB 050408) detected with the WXM and FREGATE instruments aboard the HETE-2 satellite. We find several relations for the individual GRB pulses between the spectral lag and other observables, such as the luminosity, pulse duration, and peak energy (Epeak). The obtained results are consistent with those for BATSE, indicating that the BATSE correlations are still valid at lower energies (6-25 keV). Furthermore, we find that the photon energy dependence for the spectral lags can reconcile the simple curvature effect model. We discuss the implication of these results from various points of view.