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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"

45438 results found.

  1. Fermi GRB 250827A: Global MASTER-Net observations report
  2. EP250827a: confirmation of optical rebrightening with LCO
  3. EP250827a: GOTO observation of the optical afterglow
  4. GRB 250826A: SVOM/GRM observation
  5. GRB 250827A: Fermi GBM Final Real-time Localization
  6. EP250827A: An optical rebrightening was detected by LCO.
  7. EP250827a: Swift-XRT counterpart detection
  8. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  9. The EP-WXT trigger 01709200800 is likely a flaring star
  10. EP250827a: TRT optical observations
  11. EP250827a: BOOTES-7 early optical dectection
  12. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  13. EP250827a: Gemini-South redshift z = 1.613
  14. EP250827a: Global MASTER-Net observations report
  15. EP250827a: Las Cumbres independent detection of the optical counterpart
  16. EP250827a: Gemini-South optical counterpart detection
  17. EP250827a: Einstein Probe detection of an X-ray transient
  18. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  19. Fermi GRB 250826A: Global MASTER-Net observations report
  20. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  21. EP250821a: Gemini GMOS Redshift Confirmation
  22. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  23. Fermi trigger No 777883624: Global MASTER-Net observations report
  24. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  25. GRB 250826A: Fermi GBM Final Real-time Localization
  26. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  27. Fermi GRB 250824B: Global MASTER-Net observations report
  28. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  29. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  30. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  31. GRB 250823A: Swift-BAT refined analysis
  32. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  33. GRB 250821B: AstroSat CZTI detection
  34. GRB 250819A: AstroSat CZTI detection
  35. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  36. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  37. GRB 250821B: Insight-HXMT detection
  38. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  39. GRB 250823A: Swift-XRT refined Analysis
  40. EP250821a: MeerKAT radio counterpart
  41. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  42. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  43. GRB 250824B: Fermi GBM Final Real-time Localization
  44. The EP-WXT trigger 01709200707 is likely a flaring star
  45. GRB 250823A: COLIBRÍ optical observations
  46. The EP-WXT trigger 01709200706 is likely a flaring star
  47. GRB 250823A: SVOM/VT optical observation
  48. GRB 250824A: Fermi GBM Final Real-time Localization
  49. GRB 250823A: Swift/UVOT Detection
  50. GRB 250823A: NOT optical observations
  51. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  52. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  53. GRB 250823A: Fermi GBM Observation
  54. GRB 250818B: MeerKAT Detection
  55. GRB 250823A: Enhanced Swift-XRT position
  56. GRB 250823A: LCOGT Optical Detection
  57. GRB 250823A: BOOTES6/DPRT early optical detection
  58. GRB 250823A: Liverpool Telescope optical detection
  59. GRB 250823A: Swift detection of a burst
  60. GRB 250823A: Fermi GBM Final Real-time Localization
  61. Swift GRB250823.84: Global MASTER-Net observations report
  62. Konus-Wind detection of GRB 250821B
  63. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  64. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  65. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  66. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  67. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  68. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  69. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  70. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  71. GRB 250806A: Gemini observations of host galaxy candidate
  72. IPN triangulation of GRB 250821B (long/bright)
  73. GRB 250821A: Kilonova-Catcher optical upper limits
  74. EP250821a: Swift/XRT counterpart fading
  75. GRB 250812A: SVOM/ECLAIRs refined analysis
  76. GRB 250821A: Swift-BAT refined analysis
  77. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  78. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  79. EP250821a: Swift/UVOT further observations.
  80. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  81. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  82. GRB 250821A: VLT/FORS2 Optical Observation
  83. GRB 250821A: GECAM-B detection
  84. GRB 250821B: SVOM/GRM observation
  85. EP250821a: SVOM/VT optical observation
  86. Fermi GRB 250821B: Global MASTER-Net observations report
  87. GRB 250821A: NOT z-band upper limit
  88. GRB 250821C: Fermi GBM Final Real-time Localization
  89. GRB 250821A: KAIT optical upper limit
  90. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  91. GRB 250821A: Swift-XRT refined Analysis
  92. Swift GRB 250821A: Global MASTER-Net observations report
  93. GRB 250821B: Fermi GBM Detection
  94. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  95. GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
  96. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  97. GRB 250821B: Fermi GBM Final Localization of a Bright Burst
  98. GRB 250821A: Enhanced Swift-XRT position
  99. GRB 250821A: Swift/UVOT Upper Limits
  100. EP250821a: Rapidly fading optical source detected in Las Cumbres followup

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