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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
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To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

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subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

7396 results found.

  1. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  2. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  3. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  4. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  5. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  6. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  7. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  8. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  9. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  10. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  11. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  12. GRB 250823A: Swift detection of a burst
  13. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  14. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  15. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  16. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  17. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  18. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  19. GRB 250806A: Gemini observations of host galaxy candidate
  20. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  21. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  22. GRB 250821A: KAIT optical upper limit
  23. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  24. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  25. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  26. GRB 250821A: Swift detection of a burst
  27. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  28. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  29. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  30. GRB 250818B: Kilonova-Catcher optical afterglow detection
  31. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  32. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  33. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  34. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  35. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  36. GRB 250818B: Keck redshift of the optical afterglow
  37. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  38. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  39. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  40. GRB 250818B: Swift-XRT afterglow detection
  41. GRB 250818B: GOTO optical counterpart candidate
  42. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  43. GRB 250818A: Swift detection of a burst
  44. sb25081602: Swift-XRT observations
  45. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  46. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  47. GRB 250814A: P200/WIRC observations of the afterglow candidate
  48. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  49. GRB 250814A: KAIT optical upper limit
  50. GRB 240814A: Fermi GBM Observation
  51. GRB 250814A: Possible afterglow candidate from P200/WIRC
  52. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  53. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  54. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  55. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  56. LIGO/Virgo/KAGRA S250813k: Updated Sky localization
  57. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  58. EP250812a: Liverpool Telescope upper limits
  59. IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event
  60. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  61. GRB 250812A: Swift ToO observations
  62. EP 250812a: GOTO optical upper limit
  63. GRB 250812A: Kilonova-Catcher optical afterglow detection
  64. EP250812a: Swift-XRT counterpart detection
  65. LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
  66. LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate
  67. GRB 250808A: VLT X-shooter candidate counterpart
  68. GRB 250809A: Swift detection of a gamma ray burst
  69. GRB 250808A: Swift-XRT candidate counterpart detection
  70. GRB 250806A: SVOM/MXT refined analysis
  71. GRB 250806A: SVOM/ECLAIRs refined analysis
  72. GRB 250806A: NOT z-band upper limit and host galaxy candidate
  73. EP 250807.979: GOTO optical upper limit
  74. GRB 250807B: Swift detection of a burst with an optical counterpart.
  75. GRB 250805A: Kilonova-Catcher optical upper limits
  76. EP250806a:SVOM/VT refined analysis
  77. EP250806a: Liverpool telescope optical upper limit
  78. GRB 250807A: Swift detection of a burst with an optical counterpart
  79. EP250806a: Earlier Detection of the VT Candidate by COLIBRÍ and LS
  80. EP250806a: SVOM /VT optical candidate
  81. GRB 250806A: KAIT optical upper limit
  82. GRB 250806A: SVOM/VT refined analysis
  83. IceCube-250804A - IceCube observation of a high-energy neutrino candidate track-like event
  84. GRB 250804B: Tiled Swift observations
  85. LIGO/Virgo/KAGRA S250802dn: Updated Sky localization
  86. LIGO/Virgo/KAGRA S250802dn: Identification of a GW compact binary merger candidate
  87. The EP-WXT trigger 01709198202 is likely a flaring star
  88. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  89. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  90. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  91. LIGO/Virgo/KAGRA S250727dc: DECam DESGW Epoch 1 Candidates
  92. LIGO/Virgo/KAGRA S250725j: DECam DESGW Epoch 1-2 Candidates
  93. LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
  94. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  95. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
  96. GRB 250727A: EP-FXT follow-up observation
  97. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  98. LIGO/Virgo/KAGRA S250727dc: Updated Sky localization
  99. GRB 250728A: Swift ToO observations
  100. LIGO/Virgo/KAGRA S250727cl: Updated Sky localization

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