GRB 150317A

Daniele Malesani (DARK/NBI), Nial R. Tanvir (Univ. Leicester), Zach Cano 
(Univ. Iceland), Pall Jakobsson (Univ. Iceland), and Tapio Pursimo (NOT) 
report on behalf of a larger collaboration:

We observed the field of GRB 150317A (Siegel et al., GCN 17592
Loading...
 
 ) using 
the Nordic Optical Telescope (NOT) located in La Palma. The mean time of 
the observation was March 23.95 UT, 6.77 days after the GRB. A 30 min 
exposure was collected using the SDSS i filter.

Inside the XRT error circle (Evans & Goad, GCN 17594
Loading...
 
 ), we detect a 
single source with i = 22.75 +- 0.25 AB (calibrated against nearby SDSS 
stars). The large error is mostly due to the bright, variable background 
from a nearby star. At the same position, an object with a consistent 
magnitude is also marginally visible in the archival SDSS data. Assuming 
that this object is coincident with the one detected by RATIR (Butler et 
al., GCN 17595
Loading...
 
 ), we thus suggest that this is the host galaxy of GRB 
150317A. Its coordinates are (J2000):

RA = 09:15:56.31
Dec = +55:27:58.0

with an uncertainty of 0.5". Such a bright galaxy may allow spectroscopy 
from an 8-m class telescope.

M. M. Chester (PSU) and M. H. Siegel (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 150317A
126 s after the BAT trigger (Siegel et al., GCN Circ. 17592
Loading...
 
 ).
Due to the location of the counterpart (Evans and Goad GCN Circ. 17594
Loading...
 
 , 
Butler et al. GCN Circ. 17595
Loading...
 
 ) in the wings of the nearby bright star 
(V~11.2), we cannot report a certain detection.  We therefore provide 
preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures, as follows:

Filter   T_start(s)   T_stop(s)      Exp(s)    Mag    

u_FC       126          376          246      >19.6   
v          432         6158          334      >19.2   
b          381         6978          571      >20.4   
u          126         6773          739      >20.2   
w1         481         6568          335      >19.6   
m2         457         6363          255      >19.4   
w2         407         7037          384      >20.0   

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).

A.P. Beardmore (U. Leicester), A. Amaral-Rogers (U. Leicester), M. de
Pasquale (INAF-IASFPA), A. Maselli  (INAF-IASFPA), A. Melandri
(INAF-OAB), D.N. Burrows (PSU), J.A. Kennea (PSU), B. Sbarufatti
(INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf of the Swift-XRT
team:

We have analysed 15 ks of XRT data for GRB 150317A (Siegel et al. GCN
Circ. 17592
Loading...
 
 ), from 68 s to 42.4 ks after the  BAT trigger. The data
comprise 19 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. Using 5905 s of PC mode data and 7 UVOT images, we
find an enhanced XRT position (using the XRT-UVOT alignment and
matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =
138.98467, +55.46573 which is equivalent to:

RA (J2000): 09h 15m 56.32s
Dec(J2000): +55d 27' 56.6"

with an uncertainty of 1.8 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.90 (+0.06, -0.05).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.3 (+/-0.3). The
best-fitting absorption column is  2.9 (+0.6, -0.5) x 10^22 cm^-2, in
excess of the Galactic value of 3.0 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 5.9 x 10^-11 (2.0 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.9 (+0.6, -0.5) x 10^22 cm^-2
Galactic foreground: 3.0 x 10^20 cm^-2
Excess significance: 9.2 sigma
Photon index:	     2.3 (+/-0.3)

If the light curve continues to decay with a power-law decay index of
0.90, the count rate at T+24 hours will be 2.7 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.6 x
10^-13 (5.3 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00635148.

This circular is an official product of the Swift-XRT team.

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU),
M. H. Siegel (PSU), M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):

Using the data set from T-236 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 150317A (trigger #635148)
(Siegel, et al., GCN Circ. 17592
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 138.995, 55.477 deg which is
    RA(J2000)  =  09h 15m 58.8s
    Dec(J2000) = +55d 28' 38.7"
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 78%.

The mask-weighted light curve shows three separate peaks, each of duration ~5 
seconds, with maxima at T+0, T+12 and T+23 seconds. T90 (15-350 keV) is 23.29 +- 
0.85 sec (estimated error including systematics).

The time-averaged spectrum from T-0.44 to T+24.00 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.52 +- 0.16.  The fluence in the 15-150 keV band is 6.5 +- 0.6 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.15 sec in the 15-150 keV band
is 1.2 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/635148/BA/

Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William
H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB),
J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara
(ORAU/GSFC), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico
Ramirez-Ruiz (UCSC), Jos� A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes�s
Gonz�lez (UNAM), Carlos Rom�n-Z��iga (UNAM), Neil Gehrels (GSFC), and
Harvey Moseley (GSFC) report:

We observed the field of GRB 150317A (Siegel, et al., GCN 17592
Loading...
 
 ) with the
Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the
1.5m Harold Johnson Telescope at the Observatorio Astron�mico Nacional on
Sierra San Pedro M�rtir from 2015/03 17.18 to 2015/03 17.43 UTC (3 minutes
to 5.9 hours after the BAT trigger), obtaining a total of 3 hours exposure
in the r, i, and z bands.

We find an uncatalogued source within the Swift-XRT error circle (Evans et
al., GCN 17594
Loading...
 
 ).  In comparison with the SDSS DR9 and 2MASS, we obtain the
following detections and upper limit (3-sigma):

  r     20.5 +/- 0.1
  i     21.7 +/- 0.1
  z     > 20.8

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.  This photometry is preliminary and
can be expected to improve with a more detailed analysis due to the
proximity of a bright star (e.g., Xu, et al., GCN 17593
Loading...
 
 ).

We thank the staff of the Observatorio Astron�mico Nacional in San Pedro
M�rtir.

P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the
Swift-XRT team:

Using 2091 s of XRT Photon Counting mode data and 2 UVOT images, we find 
an astrometrically corrected X-ray position (using the XRT-UVOT 
alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, 
Dec = 138.98467, 55.46618 which is equivalent to:

RA  (J2000):  09h 15m 56.32s
Dec (J2000): +55d 27' 58.2"

with an uncertainty of 2.2 arcsec (radius, 90% confidence).

This position may be improved as more data are received.  The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).

This circular is an official product of the Swift-XRT team.

D. Xu (DARK/NBI), D. Malesani (DARK/NBI), P. Blay (IAC, NOT), P. 
Jakobsson (Univ. Iceland), report on behalf of a larger collaboration:

We observed the field of the Swift GRB 150317A (Siegel et al., GCN 
17592
Loading...
 
 ) with the NOT equipped with the AlFOSC camera. A single 300-s 
R-band exposure was secured, starting at 04:48 UT (25 min after the GRB).

No new sources are detected within the X-ray position reported by Siegel 
et al. (GCN 17592
Loading...
 
 ), but we remark that in our image the bright glare 
from the nearby R=11 USNO star 1454-0197654 covers part of the XRT error 
circle. The limiting magnitude of our image is R ~ 21.5, but it is 
considerably shallower in the regions contaminated by the star PSF.

It cannot be excluded at the present time that the X-ray source detected 
by XRT is due to the USNO star. Visual inspection of the BAT error 
circle also does not reveal any new object compared to archival DSS and 
SDSS images, down to R = 21.5.

M. H. Siegel (PSU), S. D. Barthelmy (GSFC), M. M. Chester (PSU),
N. Gehrels (NASA/GSFC), H. A. Krimm (CRESST/GSFC/USRA),
A. Y. Lien (GSFC/UMBC), D. Malesani (DARK/NBI),
C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL) and B. Sbarufatti (INAF-OAB/PSU) report on behalf
of the Swift Team:

At 04:22:42 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150317A (trigger=635148).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 138.935, +55.452, which is 
   RA(J2000)  =  09h 15m 45s
   Dec(J2000) = +55d 27' 08"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows three spikes 
spaced about 10 seconds apart, with a total duration of about 35 sec. 
The peak count rate was ~1700 counts/sec (15-350 keV), at ~0 sec 
after the trigger. 

The XRT began observing the field at 04:23:46.5 UT, 64.6 seconds after
the BAT trigger. 
In a 25 s SPER image XRT detects 10 photons at 
RA, DEC 138.9832, 55.4681 which is    
   RA(J2000)  =  09h 15m 55.98s
   Dec(J2000) = +55:28:05.23
with an uncertainty of 8.6 arcsec (radius, 90% containment). This position is 1.9 
arcmin away from the BAT onboard position, within the BAT error circle. 

We notice the presence of a bright star (R~11) at 11 arcseconds from the XRT 
position. At this time we cannot exclude that emission from the star 
may be affecting the XRT data. 

UVOT took a finding chart exposure of 250 seconds with the U filter
starting 126 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers none of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
XRT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.03. 

Burst Advocate for this burst is M. H. Siegel (siegel AT swift.psu.edu). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)