GRB 150513A

D. Kocevski (NASA/GSFC/ORAU), J. A. Kennea (PSU),
A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester) and
J. L. Racusin (NASA/GSFC) report on behalf of the Swift Team:

At 20:31:19 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150513A (trigger=640584).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 49.058, -22.913 which is 
   RA(J2000) = 03h 16m 14s
   Dec(J2000) = -22d 54' 45"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 140 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~4 sec after the trigger. 

Due to a Sun observing constraint, Swift cannot slew to the BAT
position until 11:32 UT on 2015 May 28. There will thus be no XRT or
UVOT data for this trigger before this time. 

Burst Advocate for this burst is D. Kocevski (dankocevski AT gmail.com). 
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.)

GRB 150513A: Fermi-LAT detection

D. Kocevski (NASA/GSFC), G. Vianello (Stanford), and M. Arimoto (Tokyo Tech),
report on behalf of the Fermi-LAT team:

At 20:33:15.25 on May 05, 2015, Fermi-LAT detected high-energy emission from GRB 150513A, which was also detected by Fermi-GBM (trigger 453241998) and Swift-BAT (Kocevski et al. 2015, GCN 17810
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 ).

The best LAT on-ground location is found to be

RA, Dec 49.2, -23.2 (J2000)

with an error radius of 0.4 deg (90% containment, statistical error only). This position was 50 deg from the LAT boresight at the time of the trigger and consistent with the position found by Swift-BAT.

The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The highest-energy event is a 2.1 GeV event detected at T0 + 60 s. The GRB was observable from T0 to T0 + 385 s, before the spacecraft entered the South Atlantic Anomaly, where data gathering is disabled.

The Fermi-LAT point of contact for this burst is Makoto Arimoto (arimoto@hp.phys.titech.ac.jp<mailto:arimoto@hp.phys.titech.ac.jp>).

The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.

Younes G. (USRA at GWU) and Meegan C. (UAH) report on behalf of the Fermi GBM Team:

"At 20:33:15.25  UT, on 2015 May 13, the Fermi
Gamma-Ray Burst Monitor triggered and located GRB 150513A
(trigger 453241998 / 150513856) which was also detected
by Swift (Kocevski  et al. 2015, GCN 17810
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 ) and Fermi/LAT
(Kocevski et al. 2015, GCN 17812
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 ). The GBM on-ground location
is consistent with the Swift position. The angle from the
Fermi LAT boresight is about 45 degrees.

The GBM light curve shows two peaks separated by about 150 s
with a duration (T90) of 165 s (50-300 keV). The time-averaged
spectrum from T0-161.5 s to T0+4.3 s is well fit by a BAND function
with Epeak = 252 +/- 63 keV, alpha = -0.9 +/- 0.1, and
beta = -1.69 +/- 0.06.

The event fluence (10-1000 keV) in this time interval is
(1.36 +/- 0.04)E-05 erg/cm^2. The 1 second peak photon
flux measured starting from T0+0.2 s in the 10-1000 keV
band is 4.1 +/- 0.3 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

GRB 150513A: Swift-BAT refined analysis

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

Using the data set from T-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 150513A (trigger #640584) (Kocevski, et al.,
GCN Circ. 17810
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 ).  The BAT ground-calculated position is
RA, Dec = 49.044, -22.868 deg which is
    RA(J2000)  =  03h 16m 10.6s
    Dec(J2000) = -22d 52' 03.3"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 64%.

The mask-weighted light curve shows multiple peaks with a return to background
levels in between them.  T90 (15-350 keV) is 162 +- 5 sec (estimated error
including systematics).

The time-averaged spectrum from T-54.33 to T+129.36 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.40 +- 0.07.  The fluence in the 15-150 keV band is 5.4 +- 0.2 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T+115.41 sec in the 15-150 keV band
is 2.9 +- 0.3 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

R. Ruffini, C. L. Bianco, M. Enderli, M. Kovacevic, M. Muccino, G. B.
Pisani, J. A. Rueda, Y. Wang reports:

The observation of high-energy emission from GRB 150513A by Fermi-LAT
[1] clearly points to a binary-driven hypernova (BdHN) nature of the
source [2], in spite of the missing follow-up from Swift/XRT and UVOT
due to a Sun observing constraint which will last until the 28th of May
[3].

BdHNe have a standard behavior in the late X-ray luminosity [4,5,6],
thus we expect the X-ray emission of GRB 150513A to follow such a
behavior as well.

Assuming that the X-ray luminosity of GRB 150513A is comparable with
the BdHN prototypical one of GRB 090618 (GRB 130427A), a detection by
Swift/XRT of GRB 150513A on the 28th of May implies an upper limit for
its redshift z<0.8 (z<2).

Therefore, we strongly encourage observation by Swift/XRT of GRB
150513A from the 28th of May on. This would give a fundamental
information on the nature of this source, despite the absence of data
between May 13th and May 28th.

References:
[1] Kocevski et al. 2015, GCN 17812
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[2] Ruffini et al. 2015, ApJ, 798, 10R
[3] Kocevski et al. 2015, GCN 17810
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[4] Ruffini et al. 2014, A&A, 565, L10
[5] Pisani et al. 2013, A&A, 552, L5
[6] Ruffini et al. 2014, A&A, 569, A39

A. Maselli  (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo
(INAF-OAB), D.N. Burrows (PSU), J.A. Kennea (PSU), B. Sbarufatti
(INAF-OAB/PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester),
C. Pagani (U. Leicester) and A. Y. Lien (GSFC/UMBC) report on behalf of
the Swift-XRT team:

We have analysed  of XRT data for the Swift/BAT-detected burst GRB
150513A (Lien et al. GCN Circ. 17814
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 ), collecting 5.0 ks of Photon
Counting (PC) mode data between T0+1309.8 ks and T0+1322.8 ks. 

No X-ray sources have been detected inside or close to the Swift/BAT
error region. The 3-sigma upper limit at the Swift/BAT position is
0.001 ct s^-1, corresponding to a 0.3-10 keV observed flux of 5.8e-14
to  erg cm^-2 s^-1 (assuming a typical GRB spectrum).

The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
http://www.swift.ac.uk/ToO_GRBs/00640584.

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