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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').
Advanced Search

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.

Advanced Search Examples (click to copy):

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

24705 results found.

  1. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  2. GRB 250317B: SVOM detection of a burst / correction to GRB name of GCN 39752
  3. GRB 250317B: SVOM detection of a burst
  4. GRB 250316A: Fermi GBM Observation
  5. GRB 250316A: Swift-XRT observations
  6. GRB 250314A: SVOM/GRM analysis
  7. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  8. GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
  9. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  10. GRB 250314A: EP-FXT afterglow detection
  11. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  12. GRB 250314A: Swift/UVOT Upper Limits
  13. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
  14. GRB 250314A: Swift XRT Detection
  15. EP250315a: optical counterpart candidate detected by Gemini North
  16. GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
  17. EP250315a: Einstein Probe detection of an X-ray transient
  18. GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
  19. SVOM/MXT upper limit on GRB 250314A
  20. GRB 250314A: SVOM/VT upper limit
  21. GRB 250314A: NOT near-infrared candidate counterpart
  22. GRB 250313A: Fermi GBM Detection
  23. GRB 250312B: Fermi GBM Observation
  24. GRB 250313A: Swift-XRT observations
  25. GRB250314A: SVOM/VT lack of bright optical candidate from VHF data
  26. GRB 250314A: SVOM detection of a burst
  27. GRB 250313A: AstroSat CZTI detection of a bright long burst
  28. IceCube-250309A: MASTER detection of J140105.33-091631.6 blazar flare with Zhirkov effect
  29. GRB 250313A: Fermi-LAT detection
  30. EP250304a: Pan-STARRS r and i-band imaging and photometry
  31. GRB 250312B: Swift/BAT-GUANO localization skymap of a burst
  32. GRB 250309B: PRIME near-infrared upper limits in 2nd epoch
  33. GRB 250313A???: BALROG localization (Fermi Trigger / GRB 250313607)
  34. ATCA detection of the radio counterpart of GRB 250309B-AT2025dws
  35. GRB 250312A: Swift-XRT refined Analysis
  36. GRB 250312A: Enhanced Swift-XRT position
  37. LIGO/Virgo/KAGRA S250304cb: Upper limits from Swift/BAT-GUANO
  38. GRB 250226B: Fermi GBM Observation
  39. GRB 250302A: Fermi GBM Observation
  40. GRB 250309B/AT2025dws: Daochen/RC-10 optical counterpart observation
  41. GRB 250312A: Swift detection of a burst
  42. GRB 241213A: VIRT Optical Upper Limit
  43. GRB 241228A: VIRT Optical Upper Limit
  44. GRB 250311A/EP250311a: Optical upper limits with Kinder observations
  45. GRB 250311A: Swift-XRT observations
  46. GRB 230509B: 1.3m DFOT Optical observations
  47. IceCube-250309A: Upper limits from a search for additional neutrino events in IceCube
  48. GRB 250308A: Swift/BAT-GUANO localization skymap of a short burst
  49. GRB 250302A: Swift/BAT-GUANO localization skymap of a burst
  50. GRB 250228A: Swift/BAT-GUANO localization skymap of a likely short burst
  51. GRB 250226B: Swift/BAT-GUANO localization skymap of a likely long GRB
  52. GRB 250226A: Swift/BAT-GUANO localization skymap of a long GRB
  53. GRB 250223B: Swift/BAT-GUANO localization skymap of a short burst
  54. GRB 250309B: PRIME near-infrared detection
  55. GRB 250225B: Swift-BAT refined analysis
  56. GRB 250311A/EP250311a: TRT optical upper limit
  57. EP250311a/GRB 250311A: EP-WXT detection
  58. GRB 250311B: SVOM detection of a burst
  59. GRB 250311A/MAXI J1457-026: MAXI/GSC detection
  60. GRB 250309B / AT2025dws: further SAO RAS optical observations
  61. EP250308a: 1.6m Mephisto optical upper limits
  62. Konus-Wind detection of GRB 250309B
  63. IPN triangulation of GRB 250308A (short)
  64. IceCube-241224A: MASTER detection of PKS 1217+02 blazar flare with Zhirkov effect
  65. GRB 250309B/AT2025dws : COLIBRÍ Detection of the Optical Counterpart
  66. GRB 250309B: Swift-XRT refined Analysis
  67. GRB 250309B / IceCube-250309A: GECAM-B observations
  68. GRB 250309B / AT2025dws: SAO RAS optical observations
  69. AT 2025dws, likely optical counterpart of GRB 250309B: LCO confirmation of fast fading
  70. GRB 250309B: Fermi GBM Observation
  71. GRB250309B: One candidate counterpart from the Zwicky Transient Facility
  72. IceCube-250309A: No candidates from the Zwicky Transient Facility
  73. Fermi-LAT gamma-ray observations of IceCube-250309A
  74. IceCube-250309A - IceCube observation of a high-energy neutrino candidate track-like event
  75. GRB 250309B: BALROG localization (Fermi Trigger 763198715 / GRB 250309318)
  76. EP250308a: GSP optical upper limit
  77. EP250308a: Einstein Probe detection of an X-ray transient
  78. EP250308a: NOT optical upper limit
  79. GRB 250306A: EIRSAT-1 GMOD detection
  80. GRB 250306A: Swift-BAT refined analysis
  81. GRB 250306A: NuSTAR detection of the prompt emission
  82. EP250304a: MeerKAT detection of a possible radio counterpart
  83. IceCube-241016A: MASTER flaring blazar 5BZU J073038.29-320820.2 with Zhirkov effect
  84. GRB 250305A: AstroSat CZTI detection
  85. EP250302a:Xinglong optical observations
  86. LIGO/Virgo/KAGRA S250207bg: Update-5 NED Galaxies in the Localization Volume
  87. LIGO/Virgo/KAGRA S250207bg: Updated Sky localization
  88. GRB250101A: Radio upper limits from VLA observations
  89. GRB 250305A: SVOM/GRM observation of a burst
  90. The EP-WXT trigger 01709132323 is likely a flaring star
  91. EP250304A: Upper limits from Fermi-GBM Observations
  92. Fermi-LAT Gamma-ray Observations of IceCube-250302A
  93. EP250302a: Optical Observations at CrAO and SAO RAS
  94. GRB 250219A: SVOM/C-GFT optical upper limit at early phase
  95. EP 250304A: Optical counterpart detection by LCO
  96. EP250302A: 1.3m DFOT optical afterglow detection
  97. IceCube-250302A: Upper limits from a search for additional neutrino events in IceCube
  98. EP250304a: refined analysis of the EP-WXT and EP-FXT observations
  99. EP250304a: REM NIR upper limits
  100. EP250304a: Swift/UVOT detection of an optical counterpart with a rising light curve

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